CN103624479A - Method for repairing steel structure fatigue crack - Google Patents

Abstract

The invention discloses a method for repairing a steel structure fatigue crack. The method is suitable for the relative initial phase of the fatigue crack, can be used for repairing the fatigue crack at a low cost, and can prolong the fatigue life of a steel structure by means of stopping or delaying the development of the fatigue crack. The method includes the steps that in the hammering process nearby the fatigue crack, at least one side of the two sides of the fatigue crack in a steel plate is hammered so as to enable the surface of the steel plate to generate plastic deformation, and therefore a crack contact surface can be formed for preventing continuous cracking of the crack. Serving as a follow-up process of the hammering process nearby the fatigue crack, the method further includes the step of increasing the contact surface or the contact pressure of the contact surface of the crack by rapid cracking of the steel plate right above the fatigue crack so as to greatly prolong the fatigue life.

Description

The method of repaired steel-structure fatigue crack

Technical field

The present invention relates to a kind of restorative procedure of fatigue crack, relate in particular to a kind of restorative procedure of fatigue of steel structures crackle.

Background technology

If a steel construction, take steel structure bridge as example, be subject to the effect of cyclic load, due to metal fatigue, on its surface, can crack, if it is let go unchecked, fatigue crack will further develop, and makes steel structure bridge can not meet the requirement of ultimate bearing capacity.Therefore, in the maintenance and management of steel structure bridge, the method for reply fatigue crack, as the prevention of fatigue crack, earlier detection, the measures such as repairing and reinforcing are very important.

In China, since the eighties in 20th century, along with rapid development of economy, roadnet development rapidly, during this period, has been built many steel structure bridges.These bridges complete for use and have pass by more than 30 year, and various aging phenomena are very serious, and in addition, along with increasing the weight of and the increase of frequency of utilization of traffic in recent years load, some steel structure bridge has occurred fatigue crack at weld seam position.

What Figure 16 represented is a fatigue crack at exterior surface angle weld seam, and what it showed is the generation situation at toe of weld position, weld metal zone fatigue crack.In the drawings, 5 is angle welding, in figure gusset 6 by vertical welding on steel plate 14.The stress that the accumulation of the stretching residual stress causing due to when welding heating and weld seam 2 cause in the shape sudden change of 7 place's toe of weld ends is concentrated, thus fatigue crack more easily in the drawings 3 positions produce.

Figure 16 (a) is the situation of fatigue crack 3 while not occurring, and the situation that Figure 16 (b) starts to occur at the toe of weld end of shape sudden change place 7 for fatigue crack 3 is (hereinafter referred to as N _toe), Figure 16 (c) is that fatigue crack 3 continues development, starts separated (hereinafter referred to as N from weld seam toe zone _b), Figure 16 (d) is (hereinafter referred to as N ₁₀) be that fatigue crack 3 continues development in 7 toe zones, place, and separated from weld seam toe zone, the situation of extending about 10mm on steel plate 14.From N ₁₀in we are not difficult to find that the development in crack 3 is very rapidly.

When can judging such crackle, we can continue at short notice development, and according to the significance level of the state of development of crackle and steel structure bridge, know the words of its danger close, as the repairing and reinforcement to it, we can arrange a splice plate in crackle generation area, use high-strength bolt to connect, this is a lasting measure that crackle is repaired and reinforced.

When we judge fatigue crack, can not develop into the stage of danger close, we can bore an aperture in the end of fatigue crack development, discharge concentrated stress herein, and this measure can temporarily stop the development of fatigue crack.

The fatigue crack prevention method of describing in patent documentation 1 (JP, 2008-520443, A) is equally applicable to the prevention of weld seam toe zone fatigue crack.As shown in Figure 17 (a), we carry out hammering by the toe zone of ultrasonic impact device 15 butt welded seams 2, make this region produce plastic deformation as shown in Figure 17 (b), produce ultrasonic wave treatment surface 16.

In welding process, the heat the producing residual stress accumulation that can make to stretch in steel member, formation along with ultrasonic wave treatment surface 16, stretching residual stress is discharged, and near ultrasonic wave treatment surface 16, produce compressive residual stress, meanwhile, toe of weld position and near shape become round and smooth, and the concentrated impact of stress is weakened.By these, process, fatigue strength is strengthened, and fatigue crack is just not easy to produce.

The above-mentioned conventional method of carrying out crackle reparation and reinforcing of mentioning,, by arranging splice plate, use high-strength bolt to connect, to expend a large amount of manpower and materials on the one hand, cost a lot of money, and in real work process, need to suspend traffic, be not suitable for being applied in whole bridges that produces fatigue crack.

By bore the method for removing hole at Near A Crack Tip, it is a method that the little fatigue crack of effective prevention further develops.Although repairing effect is fine, because suitable fatigue analysis method is not set up, so in actual conditions, be used usually used as emergency treatment.

Although the thickness of steel plate is depended in the aperture of aperture, generally, can not be less than 20mm, so in some cases, as the fatigue crack of weld seam toe zone, do not have enough borehole space to hole.Because this reason, can only wait until that crack growth arrives disengaging toe zone, while extending at dull and stereotyped position, re-uses the method.That is to say, this method shall not be applied to the starting stage of crack growth.

The fatigue crack prevention method of describing in patent documentation 1 is applicable to the stage that fatigue crack not have generation, even if it is used in the starting stage of crack growth, be in general do not have resultful.

Therefore, provide a kind of method of the repaired steel-structure fatigue crack that can address the above problem to become urgent problem in the industry.

Summary of the invention

For the deficiencies in the prior art, the object of the invention is to: a kind of method of repaired steel-structure fatigue crack is provided, and the present invention is applicable too in the starting stage of crack growth, so can the reparation fatigue crack of cheap and simple or the development of prevention fatigue crack.Fatigue crack restorative procedure provided by the invention can delay fatigue crackle development, extended the fatigue life of steel construction.

The position that the fatigue crack of steel surface generally produces from it, is transversely half elliptic development with depth direction, and will soon arrives the bottom surface of steel.Although the boring method of mentioning above-mentioned has stoped crackle toward crosswise development, can not stop it to depth direction, to develop.Based on this point, the present invention will stop crackle toward horizontal and depth direction development simultaneously, so just stop and tear surperficial expansion.

According to the present invention, a kind of method of repaired steel-structure fatigue crack is provided, wherein, on the surface of steel construction of opening that is formed with fatigue crack, the direction of extending along fatigue crack by least one side at fatigue crack applies hammer peening to the surface of steel construction, thereby make the surface of steel construction produce plastic deformation, to form crackle contact-making surface along fatigue crack, makes fatigue crack closed at the lip-deep opening of steel construction.

Preferably, the direction that can extend along fatigue crack in the both sides of fatigue crack respectively applies hammer peening to the surface of steel construction.

Preferably, may further include the direction of extending along fatigue crack directly over fatigue crack the surface of steel construction is applied to hammer peening.

Preferably, may further include the track that adopts guiding device to make hammer peening when the surface of steel construction is applied to hammer peening and be equidistantly close to fatigue crack along the direction of fatigue crack extension.

Preferably, hammer peening can be set as making forming the residual stress producing on the surface of fatigue crack and be greater than the tensile stress of design.

Preferably, hammer peening can be set as making forming the residual stress producing on the surface of fatigue crack and be greater than the yield stress of steel structure material.

Next by describing the solution of each the problems referred to above, operating effect is described if desired.

The fatigue crack producing on fatigue of steel structures method for repairing crack handle reparation flat board of the present invention and curved slab Steel material is as main target, in the method, there is a near process of carrying out hammering fatigue crack, in this process, by on crackle both sides, (at least on one side) carries out hammering along crackle parallel direction, in steel material surface, produce plastic deformation, make the opening of fatigue crack closed, and produce a crackle contact-making surface.

If apply external force on the Steel material that produces fatigue crack, fatigue crack surrounding just has tension and produces, and this tension can make the inner surface of fatigue crack separated to both sides, and crack width will be expanded, and crackle will develop towards depth direction.Discussion before according to the present invention, by method for repairing crack of the present invention, fatigue crack opening is closed, and can form crackle contact-making surface at crackle inner surface, at crackle contact-making surface, can produce very large residual compressive stress.Therefore, residual compressive stress can be offset the tension that external force produces, and fatigue crack is just not easy cracking like this, stops or postponed the development of fatigue crack, has extended the fatigue life of steel construction.

If just implement hammering directly over fatigue crack, owing to being difficult to produce plastic deformation in the direction fatigue crack inner surface is closed, crackle contact-making surface is just difficult to effectively form.In this patent, owing to having implemented near hammering process fatigue crack, in the direction that fatigue crack inner surface is closed, produce plastic deformation, crackle contact-making surface effectively forms.

Because the present invention is just by carry out the method for hammering at steel structure surface, and be well suited for the primary stage at crack growth, also need not consider that fatigue crack produces the steel construction state of development in region.So, simple inexpensive the carrying out of the present invention fatigue crack reparation.

The fatigue crack producing on fatigue of steel structures method for repairing crack handle reparation flat board of the present invention and curved slab Steel material is as main target, if necessary, as beating the subsequent treatment of process near above-mentioned fatigue crack, by beat fatigue crack directly over, in steel material surface, produce plastic deformation, so just can increase contact area or the contact of fatigue crack.

By beating process near fatigue crack, form crackle contact-making surface, by beating process directly over fatigue crack, the contact area of crackle contact-making surface and contact increase.Near fatigue crack, produce so very large compressive residual stress, the effect of opposing tension will be better.

Conventionally we can suppose, through the process of beating directly over crackle, the contact area of crackle contact-making surface and contact all can increase, but we also should be taken into account, only have contact to increase, contact area is constant, or only has contact area to increase, contact is constant, or contact area reduces with releasing pressure portion.

Because the effect of opposing tension is determined by the product of contact area and contact, so as near the subsequent process of hammering fatigue crack, directly over fatigue crack, hammering must have certain effect.

When fatigue of steel structures method for repairing crack of the present invention using the fatigue crack of Steel material weld seam toe zone when repairing object, near having a fatigue crack, beat process, with this, in steel material surface, produce plastic deformation, close the opening of fatigue crack, form crackle contact-making surface, this process of beating should be carried out along crack parallel direction in the one side that is different from weld metal face.

When fatigue of steel structures method for repairing crack of the present invention using the fatigue crack of Steel material weld seam toe zone when repairing object, when it is repaired before fatigue crack is separated from weld seam toe zone, should use the fatigue crack restorative procedure of the above-mentioned weld seam of the present invention toe zone of mentioning.

When fatigue of steel structures method for repairing crack of the present invention using the fatigue crack of Steel material weld seam toe zone when repairing object, at fatigue crack, develop into from weld seam toe zone and separate, and while extending on steel plate, the crackle of butt welded seam toe zone should be used the fatigue crack restorative procedure of the above-mentioned weld seam of the present invention toe zone of mentioning, and to extending to the crack of steel plate part, should use the above-mentioned restorative procedure that occurs in the fatigue crack on steel plate of mentioning.

Before fatigue crack is separated from weld seam toe zone, we use N _toerepresent the situation that crackle has just produced, N _brepresent crack progress one little can youngster, N ₁₀represent that crackle is further made progress, and from the situation of weld seam toe zone separation.

If the present invention is used to repair the fatigue crack of weld seam toe zone, by hammering simply, just can obtain the repairing effect of cheap and simple, improve the durability of fillet welding contact, stop or postpone further developing of fatigue crack, extend the fatigue life of steel construction.About tired restorative procedure of the present invention, because fatigue crack is from N _bdevelop into N ₁₀very rapidly, so we can wait until N ₁₀time carry out again crackle reparation.

In fatigue of steel structures method for repairing crack of the present invention, we preferably utilize guiding device along the parallel direction hammering of fatigue crack when implementing hammering.

If hammering is along guiding device, even just in case fatigue crack is turned, we also can guarantee that hammering is that track along crackle carries out.The plastic deformation of the steel structure surface obtaining by hammering like this, will be very accurate.

In fatigue of steel structures method for repairing crack of the present invention, act on the residual compressive stress of above-mentioned crackle contact-making surface more preferably greater than design tension.

If act on the residual compressive stress of above-mentioned crackle contact-making surface, be greater than design tension, under the effect of design tension, fatigue crack just can not ftracture so.Like this, just can effectively stop or postpone further developing of fatigue crack, extend the fatigue life of steel construction.

If acting on the residual compressive stress of above-mentioned crackle contact-making surface, to be greater than the yield stress of Steel material just better.

According to the regulation of allowable stress method, allowable tensile stress accounts for 1/1.7 of yield stress, and the tension of practical function on material accounts for the 1/2 more of allowable tensile stress.Therefore,, if the compressive residual stress producing is greater than yield stress, just can stop reliably the development of fatigue crack.

Steel construction is designed certain life-span conventionally, and we should safeguard the resistance to overturning of steel construction.So we there is no need certain a part of repair solid especially, the solid life-span that has surpassed total to this part.What we will do is exactly, and when carrying out the reparation of fatigue crack, can effectively stop the development of fatigue crack, makes the residual life that its development speed can commensurate structure.From this point, the present invention can regard as with perforate reparation above with to be fixed plate restorative procedure the same, is a kind of permanent fatigue crack restorative procedure.

Accompanying drawing explanation

Below in conjunction with accompanying drawing, the present invention is further described.

Fig. 1 directviewing description fatigue crack restorative procedure of the present invention, (a) generation of steel plate top fatigue crack has been described, (b) shown the first embodiment in the present invention, it is near the situation of hammering process fatigue crack, (c) the second embodiment in the present invention, the i.e. situation of hammering process directly over fatigue crack have been shown.

Fig. 2 directviewing description fatigue crack restorative procedure of the present invention, (a) generation of angle welding toe zone fatigue crack has been described, (b) shown the 3rd embodiment in the present invention, it is near the situation of hammering process fatigue crack, (c) the 4th embodiment in the present invention, the i.e. situation of hammering process directly over fatigue crack have been shown.

Fig. 3 is one group of cross-sectional view, pictute the effect that in this patent, fatigue crack restorative procedure produces, (a) generation of steel plate top fatigue crack has been described, (b) represent when the two ends of External Force Acting at (a) light plate, at surface of steel plate, produce the situation of tensile stress, (c) represent after the method for repairing crack in the present invention, produced crackle contact-making surface, thereby closed the fatigue crack of Steel material in (a), in this process, compressive residual stress produces, (d) show be in (c) steel under the External Force Acting of two ends, the situation that compressive residual stress reduces.

The curve map of Fig. 4 has been described after fatigue crack restorative procedure of the present invention, the effect that extends fatigue life.

Fig. 5 has shown the 5th embodiment in the present invention, has described exterior surface angle weld fatigue method for repairing crack, front fillet weld toe zone.

Fig. 6 is the stress-strain diagram of common iron.

Fig. 7 describes and adopts fatigue crack restorative procedure of the present invention to repair, and forms first example of crackle contact-making surface, and this figure shows is the finite element analysis model that only carries out hammering process directly over crackle.

Fig. 8 is the stress envelope of analytical model in Fig. 7.

Fig. 9 describes and adopts fatigue crack restorative procedure of the present invention to repair, and forms second example of crackle contact-making surface, and this figure shows is near the finite element analysis model that fatigue crack, hammering process is carried out hammering process directly over crackle again after completing.

Figure 10 is the stress envelope of analytical model in Fig. 9.(a) being near the situation of hammering process first step crackle after completing, is (b) near the situation of hammering process second step crackle after completing, and is (c) situation of hammering process directly over crackle after completing.

Figure 11 is the side view of flat plate fatigue bending machine.

Figure 12 is the plate test specimen structure chart in example 1 of the present invention.

Figure 13 is S-N curve, describes the prolongation effect of fatigue life in example 1 of the present invention.

Figure 14 is example 2 outer surface angle welding test specimen structure charts of the present invention.

Figure 15 is S-N curve, describes the prolongation effect of fatigue life in example 2 of the present invention.

Figure 16 has described the situation that fatigue crack of the prior art produces and develops in exterior surface angle weld seam toe zone, (a) situation while not occurring for fatigue crack, (b) for fatigue crack starts situation about occurring at the welding toe of front fillet weld, (c) for fatigue crack continues development, beginning is opened separation from weld seam toe zone, (d) be that fatigue crack continues development in toe zone, separated from weld seam toe zone, the situation of extending about 10mm on steel plate.

Figure 17 illustrates the pretreatment technology that prevention angle welding of the prior art toe zone fatigue crack produces, (a), for angle welding toe zone is carried out to punching press with ultrasonic impact device, (b) be the plastic deformation producing in steel material surface after ultrasonic punching press is processed.

Description of reference numerals

L1, L2, L3--hammering

1--steel plate 2--angle welding metal

3--fatigue crack 3a--crackle contact-making surface

4--hammering device 4a--tup

5--angle welding 6 gussets

7--front fillet weld 8,8a--guiding device

9--guide fixture 10--flat plate fatigue bending machine

10a--vibrator 11--plate test specimen

11a--weld seam 11b--recess

12--foil gauge 13--angle welding tested object

14--steel structure assembly 15--ultrasonic impact device

16--ultrasonic wave treatment surface

The specific embodiment

Next with reference to accompanying drawing, specifically describe fatigue of steel structures method for repairing crack of the present invention.

< the first example >

Fig. 1 (a) and Fig. 1 (b) have described the sketch of fatigue crack restorative procedure in this example.Wherein Fig. 1 (a) produces at upper surface of steel plate for fatigue crack, and Fig. 1 (b) is near the hammering process fatigue crack of implementing in this example.

The track that guarantees hammering does not overlap on crackle.As shown in Fig. 1 (a), if fatigue crack 3 occurs on steel plate 1, we can repair to stop the continuation development of fatigue crack.Fig. 1 (b) has shown repairing condition, in the both sides of fatigue crack, along the hammering of fatigue crack parallel direction, goes out two track L1 and L2.Here, L1 and L2 equate apart from the interval of fatigue crack, and will guarantee that two hammerings do not overlap on fatigue crack.

Next, along with the appearance of hammering L1 and L2, on the surface of steel plate 1, can produce plastic deformation, the opening of fatigue crack 3 can be closed, and crackle contact-making surface 3a forms.This process is called as near the hammering process of fatigue crack.Crackle contact-making surface 3a only forms contact-making surface on crackle top, bottom not too can touch.

Tup 4a ins succession in the end of fullering tool 4.Under the help of Pneumatic pressure power compressor (not shown), tup 4a vibration at high speed, fullering tool 4 becomes the pneumatic hammer of a vibration at high speed.

The planar rectangular that is shaped as a 4mm * 5mm of tup 4a, the right angle of surrounding is cut into rounding.Although this shape is considered to the most easily produce plastic deformation on the surface of steel plate 1, optimal hammer-shaped is along with the service condition of air pressure and fullering tool can be different.

Operability consideration although bead also can complete hammering operation from various execution conditions, pneumatic hammer is most suitable.

According to this example, the opening of fatigue crack 3 is closed, and fatigue crack contact-making surface 3a forms, and at fatigue crack contact-making surface, has produced a large amount of compressive residual stresses.Therefore, residual compressive stress can be offset the tension that external force produces, and fatigue crack is just not easy cracking like this, stops or postponed the development of fatigue crack, has extended the fatigue life of steel construction.

If just implement hammering directly over fatigue crack, owing to being difficult to produce plastic deformation in the direction fatigue crack inner surface is closed, crackle contact-making surface is just difficult to effectively form.In written or printed documents example, owing to having implemented near hammering process fatigue crack, in the direction that fatigue crack inner surface is closed, produce plastic deformation, crackle contact-making surface effectively forms.

Owing to just carrying out hammering by fullering tool 4 at steel structure surface in this example, and be well suited in the primary stage of fatigue crack 3 development, also need not consider that fatigue crack 3 produces the steel construction state of development in region.So, simple inexpensive the carrying out of the present invention fatigue crack reparation, and just on the surface of steel plate 1, process.

In this example, this fatigue crack restorative procedure is 3 inapplicable while developing into a certain degree in crack.When fatigue crack further develops, when crack width becomes very large, even form crackle contact-making surface 3a by apply plastic deformation at surface of steel plate, consider that now plastic deformation is very large, the cross section performance of steel plate is had to adverse effect.

In example below, we adopt fullering tool 4 and the tup 4a same with this example.

< the second example >

In this example, as shown in Fig. 1 (c), there is hammering process directly over a fatigue crack.Near fatigue crack in implementing the first example after hammering process (as shown in Fig. 1 (b)), directly over fatigue crack, implement the hammering of hammering L3, L3 can make contact area and contact increase, and the hammering process of hammering L3 is called as hammering process directly over fatigue crack.

Therefore,, after hammering process directly over fatigue crack, the fatigue crack contact-making surface 3a having formed can not ftracture again.Here will emphasize a bit, the width of the tup 4a of fullering tool 4 does not depend on the width in crack 3 in Fig. 1 (a).

Along with the increase of contact area and contact, at crackle contact-making surface 3a place, produce very high compressive residual stress, the effect of opposing tension also becomes better.

< the 3rd example >

Fig. 2 (a) and Fig. 2 (b) have described the sketch of fatigue crack restorative procedure in this example.Wherein Fig. 2 (a) is that fatigue crack produces in angle welding toe zone, and Fig. 2 (b) is near the hammering process fatigue crack of implementing in this example.

As Fig. 2 (a), fatigue crack 3 produces on the steel plate 1 of angle welding toe zone, in order to stop the development of fatigue crack 3, it is repaired.Fig. 2 (b) has shown reparation situation, first in a side (side of non-angle welding metal 2) of fatigue crack 3, carries out the hammering of hammering L1.In hammering, the contact-making surface of tup 4a and steel plate should guarantee that hammering L1 can not drop on the top of crackle 3.

Next, along hammering L1, carry out hammering, on the surface of steel plate 1, produce plastic deformation, the opening of fatigue crack 3 is closed, and fatigue crack contact-making surface 3a forms.This process is called as near the hammering process of fatigue crack.The implementation result of this example is the same with first example.

< the 4th example >

As shown in Fig. 2 (c), demonstration be hammering process directly over crackle in this example.After near the hammering hammering process fatigue crack shown in Fig. 2 (b) in the 3rd example, crack contact-making surface 3a forms, along hammering L2 (fatigue crack 3 directly over), carry out hammering again, the contact area of crack contact surface 3a and contact increase.The process of carrying out hammering along hammering L2 is called as hammering process directly over fatigue crack.The implementation result of this example is the same with the 2nd example.

In 1-4 example of foregoing description, when producing compressive residual stress in crackle contact-making surface 3a, can negative function tensile stress herein, so just can stop or postpone the cracking of fatigue crack 3, will increase the fatigue life of steel construction.

What Fig. 3 showed is the sectional view of this method implementation result, and Fig. 3 (a) represents that crackle produces on steel plate 1.Fig. 3 (b) represents when external force is if tension and Moment are at Fig. 3 (a) light plate 1 two ends, fatigue crack 3 development, and steel plate 1 surface produces tension.Fig. 3 (c) represents is on Fig. 3 (a) light plate 1, to implement crackle near hammering process directly over hammering process and crackle, and in this process, contact surface 3a in crack forms, residual compressive stress generation.What Fig. 3 (d) represented is the performance of compressed residual compression opposing external force, and along with the effect of external force, residual compressive stress reduces.

In Fig. 3 (b), if fatigue crack do not repair, if very large action of pulling stress at surface of steel plate, pulling force can be towards the directive effect that increases crack width, if cyclic reversed loading, crackle will develop.

On the other hand, if fatigue crack is repaired shown in picture Fig. 3 (c), crackle opening is closed, and crackle contact-making surface 3a forms, and compressive residual stress produces in 3a.In this state, if there is very large tensile stress to act on the surface of steel plate 1, tension can be towards the directive effect that crackle is strengthened.As shown in Fig. 3 (d), if the compressive residual stress producing at contact-making surface 3a place is greater than tension, compressive residual stress can be offset tension, and fatigue crack 3 just can not ftracture.So when cyclic load, will stop or postpone the cracking of fatigue crack 3.

The stopping or postponing the process that can regard following as of fatigue crack 3.

In the crack progressing model of application fatigue mechanics, stress intensity factor width Δ K becomes a parameter of fatigue crack growth rate.Fatigue crack growth rate da/dN (mm/cycle) is as shown in equation 1.

Da/dN=C (Δ Km-Δ Kthm) .... formula 1

In above formula, a represents the length of crack progressing direction, and N represents the quantity of stress repetition period, and c and m are material constant, and m is one and approaches 3 value in Steel material.Δ Kth is the critical value of a crack growth rate, and in Steel material, its value is 2.5 (MPa * m ^1/2).Stress intensity factor width Δ K is represented by equation 2.

$\mathrm{\&Delta;K}=F\&CenterDot;\mathrm{\&Delta;\&sigma;}\&CenterDot;\sqrt{\left(\mathrm{\&pi;a}\right)}$ .... formula 2

In above formula, stress amplitude Δ σ and F are coefficient, along with kit form or crack form change.

By equation 2 substitution equations 1, by solving differential equation of motion, can try to achieve Crack Growth Fatigue Life Np (making crack reach the crack cycle-index N of fracture length a).This is the method for general fracture mechanics analysis Crack Growth Fatigue Life.If Δ K diminishes, fatigue crack growth rate diminishes, and Crack Growth Fatigue Life Np increases.

Crack Growth Fatigue Life N in Fig. 3 (a) and Fig. 3 (c) _pjust with equation above, compare.

Fatigue crack 3 in Fig. 3 (a) is that a limit is split, we can crack length regard as surface from steel plate 1 to crack 3 the darkest places.On the other hand, if the fatigue crack 3 in picture Fig. 3 (c) is underbead cracks, in the time of external force action, crack contact-making surface 3a does not ftracture, and we can regard crack length as to the innermost distance of crackle crackle contact-making surface 3a.We can case of internal crack length be original half.Therefore,, when comparing PROPAGATION OF FATIGUE CRACK life-span Np, fracture length is decided to be to a/2.

In Fig. 3 (c), the stress spreading coefficient width Δ K of fatigue crack 3 is represented by equation 3.

$\mathrm{\&Delta;K}=F\&CenterDot;\mathrm{\&Delta;\&sigma;}\&CenterDot;\sqrt{\left(\mathrm{\&pi;a}\right)/2}\&ap;0.7F\&CenterDot;\mathrm{\&Delta;\&sigma;}\&CenterDot;\sqrt{\left(\mathrm{\&pi;a}\right)}$ .... formula 3

From above formula, we are not difficult to find, in Fig. 3 (c), the stress diffusion coefficient width Δ K of fatigue crack 3 is 0.7 times of stress intensity factor width Δ K of fatigue crack 3 in Fig. 3 (a).According to above-mentioned formula, if Δ K diminishes, fatigue crack growth rate da/dN will diminish, if Δ K becomes original 0.7 times, propagation life of fatigue Np is approximately original 1/ (0.7 ³)=3 times

Fig. 4 is the comparison diagram of fatigue crack life-span Np in Fig. 3 (a) and Fig. 3 (c).The situation of solid line for not carrying out fatigue crack reparation in figure.If crack length reaches a ₁in time, does not repair it, and cyclic load is when proceeding to Np0 time, and crack length reaches a ₂.

In Fig. 4, chain line is to have carried out the situation that fatigue crack is repaired, and has two kinds of situations, i.e. Δ K > Δ K _thtime and Δ K≤Δ K _thtime, Δ K≤Δ K _thtime be supposed situation.

When fatigue crack length reaches a ₁, it is beaten to reparation, now Δ K > Δ K _th, cyclic load is to N _pptime, crack length reaches a ₂.Now, N _pp/ N _p0=3, that is to say, the fatigue crack life-span is original 3 times.As Δ K≤Δ K _thtime, fatigue crack length maintains a ₁, no longer development.

As mentioned above, after implementing fatigue crack restorative procedure of the present invention, can effectively stop or postpone the development of fatigue crack, extend the fatigue of steel structures life-span.

< the 5th example >

Figure 5 shows that the 5th kind of example, the fatigue crack restorative procedure being about in 1-4 kind example is above applied on angle welding fatigue crack.Fig. 5 (a) represents that fatigue crack 3 produces at the welding toe at 7 places, front fillet weld district, departs from angle welding metal 2 situation (N before _b), Fig. 5 (b) represents the situation that fatigue crack 3 departs from angle welding metal 2 and partly extends 10mm at steel plate.

When carrying out hammering, guiding device should be installed along the direction of parallel fatigue crack with reference to the form of fatigue crack 3.If hammering carries out along guiding device, even if fatigue crack 3 occurs to turn, also can guarantee that hammering is accurate, especially in the position in front fillet weld district 7.Therefore can guarantee the accuracy of the plastic deformation that hammering produces in steel material surface.

As shown in Fig. 5 (a), aluminium sheet is made to U-shaped thin plate along the shape of the fatigue crack 3 at 7 places, front fillet weld district, so just form guiding device 8.For example, by fixture 9 (clamp) guiding device 8 is fixed on gusset 6.So just make this solution have very strong operability.

If clamp does not have local fixing, use magnet instead.As shown in Fig. 5 (b), 8a is that we can carry out with wooden unit for repairing the guiding device of the fatigue crack of steel plate 1 dull and stereotyped position generation.It is fixed on flat board along direction of check.If due to the relation in space, fixture does not have sufficient space to install, and we can make wooden unit into magnet.

The method is simply inexpensive, just by simple hammering, with regard to the fatigue crack of energy commissure, diagonal angle, repairs, and can effectively stop or postpone the development of fatigue crack, extends fatigue life.In this example, because fatigue crack is from N _pto N ₁₀very fast, so we can wait until N ₁₀stage repairs it again.

The compressive residual stress that acts on crackle contact-making surface 3a here, is more preferably greater than design tension.If act on the residual compressive stress of above-mentioned crackle contact-making surface, be greater than design tension, under the effect of design tension, fatigue crack just can not ftracture so.Like this, just can effectively stop or postpone further developing of fatigue crack, extend the fatigue life of steel construction.

If it is just better that compressive residual stress is greater than yield stress.According to the regulation of allowable stress method, allowable tensile stress accounts for 1/1.7 of yield stress, and the tension of practical function on material accounts for the 1/2 more of allowable tensile stress.Therefore,, if the compressive residual stress producing is greater than yield stress, just can stop reliably the development of fatigue crack.

Like this, in order to make crack contact-making surface produce very large compressive residual stress, we need to produce larger plastic deformation at surface of steel plate in hammering, make the contact of crackle contact-making surface 3a larger.

When action of compressive stress is on material, steel can shrink along action direction, and extend to rapidly the rectangular orientation of load direction.Therefore, if by after near hammering process fatigue crack, Steel material will compress in hammering direction, and extends to the rectangular orientation of load direction.That is to say the Direction distortion of meeting 3 closures along crack.If distortion 3 reaches plastic deformation region while closing in crack, crack contact surface 3a will form and maintain, and then produces compressive residual stress.

What Fig. 6 showed is the stress-strain diagram of ordinary steel material.Although this stress-strain diagram is the tensile properties of the Steel material that obtained by pulling test, because tensile properties is similar with compression property, also can be used as compression property curve.In figure, describe steel material surface and produced the situation of plastic strain.

In Fig. 6, p ₁be called proportional limit, p ₂be called elastic limit, p ₃be called upper yield point, p ₄be called lower yield point, p ₆be called ultimate strength, p ₇be called breakaway poing, 0-p in figure ₁ess-strain is linearly proportional, if be only loaded into ε, is lower yield point p ₄time, after unloading, ε can become 0 again, and plastic deformation does not occur, if be loaded into ε, surpasses p ₅, will on Steel material, produce plastic deformation, and produce residual stress.

For example, when the compression stress on acting on Steel material increases gradually, the p in will soon arrival curve _apoint.If now unloading, ε will be from p _ato p _b, be equivalent to 0-p _boverstrain will accumulate.

If the impact load of hammering is repeated is added to steel material surface, steel will be in the direction compression of Impact Load, and extends to the rectangular orientation of load direction.Yet, after forming crack contact-making surface 3a, even if stop hammering, the plastic deformation that steel material surface produces is held, and fatigue crack contact-making surface 3a is also held, so along with the effect of impact load, because load action in-plane is suppressed, Steel material shrinks.

Below very detailed discussion fatigue of steel structures of the present invention crack restorative procedure and select the reparation of carrying out fatigue crack that the method can be simply inexpensive why.

Certainly, the present invention is not confined to the example of above-mentioned proposition.Only otherwise depart from main thought of the present invention, can use.

The 3a that Fig. 1 and Fig. 2 show only forms on the top of crackle 3 inner surfaces, and the not contact in crackle 3 inner surface bottoms.But fatigue crack contact-making surface 3a also likely forms in whole region, from top to bosom.

Since the product that is contact and contact area determines the situation that affects of fatigue life, so there is no need the non-contact-making surface that forms in the top.Yet, if we consider that maximum tensile stress usually occurs in surface of steel plate, so the formation position of contact-making surface 3a normally approaches the top of fatigue crack 3.Like this, when contact area and contact are constant, the effect that extends fatigue life can be very high.

Near hammering process fatigue crack in Fig. 1 and Fig. 2, is to have a hammering in one side although we show, under special circumstances, is simultaneously having two or more hammerings to be also fine.

In the fatigue crack both sides hammering process shown in Fig. 1, although on crackle both sides, along crackle parallel direction, formed two hammerings, as long as can guarantee the formation of contact-making surface 3a, Yi Bian be also fine only forming a hammering.

Although the point of hammering drill bit is made into planar rectangular, neither strictly be limited, also have uneven situation.Being not only rectangle, is likely also circular.Directly over fatigue crack edge hammering process and fatigue crack, in hammering process, hammering drill bit 4a miscellaneous is likely used to.

In fatigue crack edge hammering process, although hammering drill bit 4a is rectangular with steel plate 1 substantially, hammering is also likely carried out from the side.

Although what Fig. 2 showed is the fatigue crack reparation of angle welding, is not limited to angle welding, can be also other forms of weld seam, as butt weld.

If by this method for repairing and mending, the development in crack 3 is postponed, extend the fatigue life of steel construction, so just can be used as a kind of lasting fatigue crack method for repairing and mending, but after maintenance, fatigue crack still further develops, we can proceed this restorative procedure, can certainly carry out conventional restorative procedure.

According in fatigue crack hammering process in this case, compressive residual stress is not only that the region producing at fatigue crack produces, and also has residual stress produce at its periphery.Therefore, if the adopted words of the method for this patent, it equally can be in the situation that not producing fatigue crack, be used as a kind of method of fatigue of steel structures strength increase, in present case, the expection line of fatigue crack development can be judged, after the expection line of fatigue crack development is definite with hammering interval, we carry out hammering along fatigue crack development expection line is parallel with it, residual stress can generate expection line and periphery generation thereof at fatigue crack, and fatigue crack will be prevented from.

(analysis example)

Because directly over fatigue crack, before hammering, we have carried out the process of fatigue crack edge hammering carrying out, so fatigue crack contact-making surface 3a can more effective formation, the compressive residual stress of generation is also just more.Finite element analysis has proved the effect of this operation qualitatively.

(comparative analysis example)

Fig. 7 for only carrying out the finite element analysis model of hammering above crack.The steel plate 1 of supposing generation fatigue crack 3 is the steel rolling of Q235 type Welding Structure.Q235 type Welding Structure is 400MPa by steel rolling hot strength, and yield strength is 235MPa, although here hypothesis be Q235, common Q345 is also often used as steel structure assembly.

Analysis condition is as follows, analyzes grid and is divided into 0.125mm, but be left in the basket in diagram.

Material constant: elastic modulus E=200GPa, Poisson's ratio mu=0.3, yield stress ${\mathrm{\&sigma;}}_{a_{\mathrm{\&gamma;}}}=235\mathrm{MPa}$

Material behavior: direction hardening rule, for example linear elasticity-perfect plasticity (fullering tool is linear elasticity)

Yield condition: equivalent stress

Contact condition: system converts compression stress to, does not consider frictional force

Analysis software: Msc Marc2005r3

Hammering size: 10mm is wide, 0.5mm is thick

As shown in Figure 7, the width of steel plate 1 is 50mm, thickness is 12mm, and the width of fatigue crack 3 is 0.01mm, and the degree of depth is 4mm, occur in the surperficial center of steel plate 1, the lower surface hinge support of steel plate 1, lower surface is except center position X, outside Y-direction is all fixed, all the other positions are all that directions X is free, and Y-direction is fixed.

The width of tup 4a is 10mm, and chamfer radius is 1.25mm, for when tup 4a hammering directly over fatigue crack, after producing the displacement of 0.5mm, just can stop hammering, as shown in Fig. 7 dotted line.This distortion is defined as hammering total amount.

Surface of steel plate shown in dotted lines in Figure 7 distortion (being hammering total amount) is the summation of strain and plastic deformation, if we are when steel plate 1 is removed tup 4a, load will unload, and strain part will be recovered.

Fig. 8 represents is the stress envelope of hammering after completing in present case, and Fig. 8 has shown the peripheral part of fatigue crack 3 simultaneously, although the fracture width of 0.01mm is very little, we can not determine whether crack contact-making surface forms under this contraction scale.Therefore, we determine the position in a fatigue analysis crack 3.

That is to say, topmost at fatigue crack 3 does not form crack contact-making surface, as shown in Figure 8, near fatigue crack 3 the tops, produced tensile stress (white portion in figure), yield stress reaches the compressive residual stress that 210MPa is even larger (black part in figure) and only at the two ends of surface of steel plate distortion, produces, and 70MPa or more compressive residual stress produce in the bosom of fatigue crack 3.

In design, allowable tensile stress accounts for 1/1.7 left and right of yield stress, and the tension of practical function is approximately 1/2 of allowable tensile stress, and this mentions above.Therefore, in Q235, allowable tensile stress σ _a=140MPa, the tensile stress sigma of practical function _a=70MPa.

Since produced stretching residual stress near the top of fatigue crack 3, and in the bosom of fatigue crack 3, there is no to produce larger compressive residual stress, we can infer, as a σ _athe action of pulling stress of=70MPa is when steel plate 1 surperficial, and fatigue crack 3 can not be resisted this tension, continues to become large.

(analysis of cases)

Fig. 9 is the finite element analysis model of above-mentioned the second situation of mentioning, the size of tup 4a is the same with the first situation, analysis condition, near the hammering (L1 and L2) of two tracks track directly over hammering crackle (L3) first carries out crackle before, all the other and the first situation are too.

In Fig. 9, the width of tup 4a is 10mm, and chamfer radius is 1.25mm.As near the first step (hammering L1) of hammering process fatigue crack, fatigue crack 3 left side 2.5mm of usining carry out hammering as tup 4a center, when hammering is when from surface of steel plate 0.5mm depths, stop hammering, and remove fullering tool.

As near the second step (hammering L2) of hammering process fatigue crack, the fatigue crack 3 the right 2.5mm of usining carry out hammering as tup 4a center, when hammering is when from surface of steel plate 0.5mm depths, stop hammering, and remove fullering tool.

Finally, as hammering process directly over fatigue crack (hammering L3), using fatigue crack 3 directly over as tup 4a center, carry out hammering, when hammering is when from surface of steel plate 0.5mm depths, stop hammering, and remove fullering tool.

By the hammering process (hammering L1, L2, L3) in above-mentioned 3 stages, the areal deformation of steel plate 1 is to the dotted portion in Fig. 9, and this distortion is defined as hammering total amount, and this hammering total amount equals in fact the hammering total amount in comparative analysis example.

Figure 10 shows that the stress envelope after hammering completes.Figure 10 (a) is the situation after near the hammering process first step (hammering L1) of crackle completes, Figure 10 (b) is near the situation of hammering process second step (hammering L2) crackle after completing, and Figure 10 (c) is the situation of hammering process (hammering L3) directly over crackle after completing.

Through near the hammering process first step (hammering L1) crackle, crackle contact-making surface forms in the topmost portion of fatigue crack 3, size be 140MPa or more compressive residual stress on the one side of implementing hammering, near the place of fatigue crack 3 the tops, produce.

(from the place near fatigue crack 3 the tops to fatigue crack bosom) generation in whole region through near hammering process second step (hammering L2) 70MPa crackle or more compressive residual stress.In the analysis of this example, we can think, the contact area that stops fatigue crack 3 to continue cracking is enough (even if only having carried out near the hammering process of crackle) with crackle contact surface contact.

After hammering process directly over crackle (hammering L3) completes, near the topmost of fatigue crack 3, (also have therein sub-fraction stretching residual stress to produce) and the darker place of fatigue crack 3 has produced the even larger compressive residual stress of 210Mp.So the effect that resisting fatigue crackle 3 is subject to external force to continue cracking is very high.

By relatively we find, carry out before hammering process, carrying out directly over fatigue crack near hammering process fatigue crack than simple only carry out fatigue crack directly over hammering can more effectively crack contact-making surface and contact, although the hammering amount of the two generation equates.

(example)

As mentioned before, this method is the development in delay fatigue crack effectively, extends fatigue life, stops fatigue crack cracking, and about this point, we can describe by the method for arithmetic according to fracture mechanics.Here, we have made actual sample, come relatively through repairing different with fatigue life without two kinds of situations of reparation.

(example 1)

This case verification the effect that extends fatigue life in the second example of mentioning in experiment above.Plate fatigue bending machine 10 in Figure 11 is used to do this experiment.Plate fatigue bending machine 10 is fixed one end fixed-use bolt of plate test specimen 11, at test specimen other end loaded cycle load.

Figure 12 has described a structure chart of plate test specimen 11 in this example.The wide 300mm of plate test specimen 11, long 700mm, thick 12mm, steel material is Q235, and weld seam 11a is along test specimen longitudinal direction center line, and width is about 10mm, and for the center at weld seam 11a causes fatigue crack, we have cut a recess that 8mm is wide at this.

Plate test specimen 11 is positioned on plate fatigue bending machine 10, and the stress amplitude of the cyclic load loading in fatigue test is 150Mp.The length that plate test specimen 11 is fixed on plate fatigue bending machine 10 is 240mm, and the cyclic load position of loading is the place apart from end points 115mm at the other end of test specimen.

At the horizontal center line of distance, along load, applying locality 12mm, a stress section 12 is respectively pasted in the both sides of vertical center line 75mm, is used for the stress of detection effect on test specimen 11.

S-N curve description in Figure 13 the effect that extends fatigue life in this example.The abscissa of S-N curve represents the cycle-index N of cyclic load, ordinate represents STRESS VARIATION amplitude, ao σ, in figure, drawn out breakaway poing, the dotted line in S-N curve represents 8 grades, and Steel Construction In China association has assessed the fatigue fracture durability of steel structure node.CSCS-E in figure (80) represents, if apply the cyclic load 2,000,000 times of Δ σ=80Mp, can cause fatigue fracture.

Black round dot in Figure 13 represents, in the situation of fatigue crack 3 not being repaired, produces the result of fatigue fracture.In this test, through 2,100, after 000 cyclic load, test specimen generation fatigue fracture.That is to say, we can think that the durability of test specimen fatigue fracture is equivalent to CSCS-E grade in the situation that not carrying out fatigue crack reparation.

White round dot in Figure 13 represents to carry out the fatigue test results after fatigue crack reparation, and wherein the white round dot on the left side represents through after the cyclic load of 300,000 times, and the wide fatigue crack 3 of 10mm starts to produce in indent.Although now there is not fatigue fracture, in order to contrast, we also by its mark in the drawings.Now fatigue crack is repaired, first the weld seam 11a at 15mm place before and after fatigue crack is shaved off, and then carry out hammering.After this hammering process, after having carried out 10,000,000 cyclic load, there is not yet fatigue fracture.That is to say, we can think that plate test specimen 11 is after the reparation of fatigue crack 3, and the durability of test specimen fatigue fracture at least reaches CSCS-B grade.

Like this, we repaired fatigue crack in the suitable time, will stop or postpone further developing of crackle, and the durability of fatigue fracture can obviously improve.And then, extended fatigue crack life-span of steel construction.

This case verification the effect that extends fatigue life in the 5th example of mentioning in experiment above.With example 1, the plate fatigue bending machine 10 in Figure 11 is used to carry out this experiment.

Figure 14 has described a structure chart of this example outer surface angle welding specimen joints 13.In exterior surface angle weld seam specimen joints 13, gusset 6 (high 100mm, long 340mm, thick 12mm) is vertically welded in to the upper surface of steel plate 1 (wide 300mm, long 700mm, thick 12mm), steel material is Q235.

Exterior surface angle weld seam specimen joints 13 is positioned in above flat plate fatigue bending machine 10, while carrying out fatigue test, STRESS VARIATION amplitude is controlled to 80Mp.The installation site of exterior surface angle weld seam specimen joints 13 and cyclic load position are the same with the situation in example 1.

Apart from steel plate 1 cross central line, along load, applying locality 12mm, longitudinal centre line and respectively paste a stress section 12 (three places altogether) apart from the both sides of longitudinal centre line 75mm, is used for the stress of detection effect on test specimen 13.

S-N curve description in Figure 15 the effect that extends fatigue life in this example.Black round dot represents, in the situation of fatigue crack 3 not being repaired, produces the result of fatigue fracture.In this test, after 800,000 cyclic loads, test specimen generation fatigue fracture.That is to say, we can think that exterior surface angle weld seam specimen joints 13 is not in the situation that carrying out fatigue crack reparation, and the durability of test specimen fatigue fracture is equivalent to CSCS-F grade.

White round dot and white side's point represent, at N _bstage, the fatigue experiment result producing when fatigue crack 3 starts from the separation of angle welding toe zone, white triangles point represents, at N ₁₀in the stage, fatigue crack 3 is separated from angle welding toe zone, and the fatigue test results producing when steel plate partly develops into 10mm.

N _band N ₁₀in the stage, approximately through 700,000 to 1,000, produce fatigue crack 3 000 time.Although now there is not fatigue fracture, in order to contrast, we also by its mark in the drawings.From figure, we can find, test specimen light plate portion crackle almost produces with angle welding toe zone crackle simultaneously.

Our interrupt experiments now, angle welding toe zone fatigue crack is carried out near the hammering fatigue crack shown in Fig. 2 (b), to developing into the fatigue crack 3 of steel plate 1 flat part, carry out near the fatigue crack shown in Fig. 1 (c) hammering directly over hammering and fatigue crack.

After this hammering process, after having carried out 10,000,000 cyclic load, there is not fatigue fracture in test specimen yet.That is to say, we can think that exterior surface angle weld seam specimen joints 13 is after the reparation of fatigue crack 3, and the durability of test specimen fatigue fracture at least reaches CSCS-D grade.

Like this, we repaired angle welding toe zone fatigue crack in the suitable time, will stop or postpone further developing of crackle, and the durability of fatigue fracture can obviously improve.And then, extended fatigue crack life-span of steel construction.

Although described the preferred embodiment of the present invention in detail at this, but should be understood that the present invention is not limited to the concrete structure of describing in detail and illustrating here, in the situation that not departing from the spirit and scope of the invention, can be realized by those skilled in the art other modification and variant.

Claims (6)

1. the method for a repaired steel-structure fatigue crack, it is characterized in that, on the surface of steel construction of opening that is formed with fatigue crack, the direction of extending along fatigue crack by least one side at described fatigue crack applies hammer peening to the surface of described steel construction, thereby make the surface of described steel construction produce plastic deformation, to form crackle contact-making surface along described fatigue crack, makes described fatigue crack closed at the lip-deep described opening of described steel construction.

2. the method for repaired steel-structure fatigue crack as claimed in claim 1, is characterized in that, the direction of extending along fatigue crack in the both sides of described fatigue crack respectively applies hammer peening to the surface of described steel construction.

3. the method for repaired steel-structure fatigue crack as claimed in claim 1 or 2, is characterized in that, be further included in described fatigue crack directly over the direction of extending along fatigue crack the surface of described steel construction is applied to hammer peening.

4. the method for repaired steel-structure fatigue crack as claimed in claim 1 or 2, it is characterized in that, be further included in when the surface of described steel construction is applied to hammer peening and adopt guiding device to make the direction that the track of hammer peening extends along fatigue crack equidistantly be close to described fatigue crack.

5. the method for repaired steel-structure fatigue crack as claimed in claim 1 or 2, is characterized in that, hammer peening is set as making forming the residual stress producing on the surface of fatigue crack and be greater than the tensile stress of design.

6. the method for repaired steel-structure fatigue crack as claimed in claim 1 or 2, is characterized in that, hammer peening is set as making forming the residual stress producing on the surface of fatigue crack and be greater than the yield stress of steel structure material.

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