GB1579336A - Apparatus for computing elapsed fatique life of a component which is subjected to a fluctuating stress - Google Patents
Apparatus for computing elapsed fatique life of a component which is subjected to a fluctuating stress Download PDFInfo
- Publication number
- GB1579336A GB1579336A GB2778776A GB2778776A GB1579336A GB 1579336 A GB1579336 A GB 1579336A GB 2778776 A GB2778776 A GB 2778776A GB 2778776 A GB2778776 A GB 2778776A GB 1579336 A GB1579336 A GB 1579336A
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- values
- stored
- value
- minimum
- incremental
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-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M99/00—Subject matter not provided for in other groups of this subclass
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/32—Investigating strength properties of solid materials by application of mechanical stress by applying repeated or pulsating forces
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
- Testing Of Devices, Machine Parts, Or Other Structures Thereof (AREA)
Description
(54) APPARATUS FOR COMPUTING ELAPSED
FATIGUE LIFE OF A COMPONENT WHICH
IS SUBJECTED TO A FLUCTUATING
STRESS
(71) We, LUCAS INDUSTRIES
LIMITED, a British Company of Great King
Street, Birmingham, B19 2XF, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to apparatus for computing the elapsed fatigue life of a component which is subjected, in use, to a fluctuating stress.
In a particular embodiment the invention relates to an apparatus for computing the elapsed fatigue life of a movable component wherein the level of stress is a function of the component's speed. Examples of such a component are the compressor or tubine rotors of a gas turbine engine.
According to the invention an apparatus for providing an indication of the elapsed fatigue of a device which is, in use, subjected to a fluctuating stress comprises means for supplying an input signal whose value is dependent on the instantaneous magnitude of said fluctuating stress, and a computer which is responsive to said input signals and is programmed::
to respond to the last sequentiallyoccurring maximum value of said input signal, to determine an instantaneous reference minimum level,
to respond to the last sequentiallyoccurring minimum value of said input signal, to determine an instantaneous reference maximum level,
to reject any maximum value having a next-occurring minimum value which is above said reference minimum level, and to reject any minimum value having a nextoccurring maximum value which is below said reference maximum level,
to store sequentially any maximum and minimum values not so rejected,
to carry out a first discriminating routine for determining, from the last four values so stored, whether a later stored maximum
value is not less than an earlier stored
maximum value, and if so to calculate, and
to add to the contents of an incremental
store of the computer, a first incremental value corresponding to [(ab)/(lab)]P where
a=the earlier-stored maximum value
b=the earlier-stored minimum value and
a and P are given stress coefficients for
the component under stress,
in the event of a negative result of said first
discriminating routine, to carry out a second
discriminating routine for determining, from
said last four stored values, whether a latter
stored maximum value is less than an
earlier-stored maximum value. and
whether an earlier-stored minimum value is
greater than a later-stored minimum value,
and if so to calculate, and to add to the
contents of an incremental store of the
computer, a second incremental value
corresponding to [(c-b)/(l-ab)]P where
c=a later-stored maximum value
the value in said incremental store
representing the expired fatigue life of the
component during the time when said input
signals are supplied.
In a preferred embodiment said computer
is programmed:
to determine, from said last four stored
values, whether an earlier-stored maximum
value is greater than a later-stored
maximum value, and whether an earlier
stored minimum value is less than a later
stored minimum value, and if so, to add to said store the next-occurring significant maximum and minimum values,
and subsequently,
to carry out said first and second
discriminating routines, as appropriate, on the last four values so stored, and subsequently,
to calculate, and add to the contents of said incremental store, said first or said second incremental values for the last four values so stored.
In a further preferred embodiment said computer is programmed:
to discard any of said stored values which have been used in calculating said first or said second incremental values, and
to shift the remaining stored values into consecutive store locations, including locations from which values have previously been discarded.
In another preferred embodiment said computer is programmed to determine said instantaneous maximum values from the equation Vmax=[ss(1-αx)+x] where
x=the next preceding minimum value of
said input signal, and p=a given stress coefficient of the
component, and is programmed to
determine said instantaneous minimum
values from the equation Vm1n=[(-y2)/(a- 1)] 1/2 where
y=the next preceding maximum value of
said input signal.
In a particular embodiment of the invention, now described by way of example only and with reference to the accompanying drawing, the apparatus is intended for computing the elapsed fatigue life of a rotor disc 10 which forms part of an aircraft gas turbine engine.An electromagnetic probe 11 co-operates with prqjections on the disc 10 to provide on a line 12 a signal whose frequency is a function of the rotational speed of the disc 10.
A converter circuit 13 is responsive to the signals on line 12 to provide a digital input signal on a line 14 to a computer 15. The computer 15 is programmed in a manner to be described to provide an output to an indicator device 16, this output being an indication of the elapsed fatigue life of the rotor disc 10 during the time that the apparatus is in operation.
The stress in the rotor disc 10 is a function of the square of the speed of the disc 10. A reference speed of the disc 10, which results in a maximum acceptable working stress is known, or can be determined, from the structure and materials of the disc 10. The actual speed N of the disc is, for the purposes of the present invention, expressed as fraction of this reference speed.
The fatigue life of a component is the sum of a series of cycles in each of which the stress in the component fluctuates between local maxima and local minima, this fatigue life being expressed in the formula l(5H5L)/( IAS,)] (1) where
s,=a local maximum stress spa local minimum stress
a and P= given stress coefficients for the
component, and, since stress in the
rotor 10 is proportional to the square of
the speed,
Equation (1) becomes r[(NH2-NL2)/( I-aN,2)]P (2) where NH a local maximum speed N,= a local minimum speed
As indicated in Figure 2, during a single flight the disc 10 will experience a number of local maximum NHl, NH2 etc, and a number of local minima NL1, NL2, the first and last of these minima being zero.
There is, moreover, at any time a significant maximum speed (SIGMAX) which is a local maximum NH must exceed if the speed cycle of which it forms part is to effect the fatigue life. This value of
SIGMAX varies through the whole flight cycle and its instantaneous value is determined by SIGMAX=[l-ax2)+x2]112 (3) where
x=the next preceding minimum value N, p=a further stress coefficient for the rotor
There is also a significant minimum speed (SIGMIN) which a local mimimum N, must fall below if the speed cycle of which it forms part is to affect the fatigue life. This value of SIGMIN varies through the whole flight cycle and its instantaneous value is given by SIGMIN[(p~y2)/(X~1)]1/2 (4) where
y=the next preceding maximum value NH
Considering the flight cycle shown in
Figure 2, the computer 15 is programmed to operate as follows:
A first instantaneous significant maximum speed SIGMAX1 is calculated, using equation (3), it being understood that for this first calculation the value of x is zero.
The next-occurring maximum value NH1 is detected and placed in a store location N
MAX TEMP of the computer 15.
The value NH1 is substituted for y in equation (4) and a first instantaneous significant minimum speed SIGMIN1 is calculated.
The next-occurring minimum value NL2 is detected and compared with SIGMIN1. If NL2 is less than, or equal to SIGMIN1, NL2 is placed in a store location N MIN TEMP of the computer 15, NHT is shifted to a store location N DATA, to be used for subsequent calculation, and a new value
SIGMAX2 is calculated, using value NL2.
If, however, NL2 is greater than SIGMIN1, the value NH1 is discarded from the N MAX
TEMP store and is no longer available. The computer continues to examine the input signal to locate the next maximum value NH2.
If NH2 is equal to, or greater than,
SIGMAX2 the value NH2 is placed in the N
MAX TEMP store, NL2 is shifted to an N
DATA store for subsequent use in calculation, and a new significant minimum value SIGMIN2 is calculated.
If NH2 is less than SIGMAX2 the value N.2 is discarded and the computer continues to examine the input signal to locate the next minimum value N,3.
The above process continues until two NH and two N, signals are in the N DATA store.
These four values are examined. As shown in Figure 3, nine forms of cycle can occur.
In Figures 3(i) to 3(vi) a second value c of NH is greater than, or equal to, a first value a of N H In this case the values a and b are substituted for NH and N, respectively in equation (2) and the result added to contents of a further incremental store, the contents of this further store representing the expired fatigue life of the disc 10 during the time when the apparatus is in operation.
If, as shown in Figures 3(viii) and 3(ix), the value a is greater than the value c and the value b is greater than, or equal to, the value d, the values c and b are substituted for
NH and N, respectively in equation (2) and the results added to the contents of the aforesaid further incremental store.
The values a and b or the values c and b which have been used for calculation as above are discarded from the N DATA store, and the remaining values shifted to occupy consecutive store locations, including those from which data has been discarded, so that a minimum of store space is required by the N DATA store.
In the event that the values in the N
DATA store define a cycle as shown in
Figure 3(vii) no calculation and incrementation takes place. This condition
is indicated at NH3 to NLg in Figure 2. The
next-occurring maximum value NH5 is detected and, if significant in terms of the
next minimum signal NL6 and calculated
value of SIGMIN5, is entered in the N
DATA store with the existing values NH3 to NL5. The next-occurring minimum value N, is if significant, similarly entered in the N
DATA store.
The four values last inserted in the N
DATA store are again examined, as
explained above in connection with Figure
3, the appropriate calculations carried out,
unless condition 3(vii) is present, the
incremental store is updated and the
numbers used for calculation discarded
from the N DATA store.
The computer continues to operate to
detect maximum and minimum values of N,
to store these values, if significant with
reference to updated values of SIGMAX or
SIGMIN, to perform calculations, if
possible, on two of the last four values
entered in the N DATA store, and to
discard values on which these calculations -have been performed.
It will thus be seen that, except in the case
shown in Figure 3(vii), the N DATA store is
not required to hold more than four values.
The condition shown in Figure 3(vii) is
convergent, and experience has shown that,
for an aircraft gas turbine engine no more
than five pairs of converging maximum and
minimum values may be expected. It is thus
possible to provide an N DATA store of a
small maximum capacity, and at the same
time to be confident that this capacity will
not need to be exceeded. Moreover, in the
event that the values remain convergent
after five pairs of maxima and minima, the
difference between the next-occurring
maximum and minimum will be small, and
the result of the calculation of incremental
value will itself be small.
It will thus be seen that the store capacity
required is extremely small, and that the
computer may be carried as an airborne unit
with the associated engine. The invention also provides a running indication of the
elapsed fatigue life of a component without
the need for recording of stress levels over
the whole of an operating sequence, and the
subsequent processing of data so recorded.
It will be realised, however, that the
present invention could be used to process
pre-recorded data in a simple manner, and
to provide an indication of elapsed fatigue
life, this indication being concurrent with
the supply of pre-recorded data to the
computer.
In the example described the engine rotor
disc has been selected as the component for
which fatigue life is to be determined, since
this component is known to be subjected, in
use, to the severest stress conditions and
thereby provides an indication of the fatigue
life of the engine as a whole. It will be
apparent, however, that any other component can be selected, provided that stress thereon can be readily sampled.
It will also be apparent that the apparatus is equally applicable to any other component subjected, in use to a fluctuating stress, as for example a pressure vessel, in which case stress would be measured and the values used directly in determining SIGMAX, SIGMIN and the first or second incremental values.
WHAT WE CLAIM IS:
1. An apparatus for providing an indication of the elapsed fatigue life of a device which is, in use, subjected to a fluctuating stress, comprising means for supplying an input signal whose value is dependent on the instantaneous magnitude of said fluctuating stress, and a computer which is responsive to said input signals and is programmed::
to respond to the last sequentiallyoccurring maximum value of said input signal, to determine an instantaneous reference minimum level,
to respond to the last sequentiallyoccurring minimum value of said input signal, to determine an instantaneous reference maximum level,
to reject any maximum value having a next-occurring minimum value which is above said reference minimum level, and to reject any minimum value having a nextoccurring maximum value which is below said reference maximum level,
to store sequentially any maximum and minimum values not so rejected,
to carry out a first discriminating routine for determining, from the last four values so stored, whether a later stored maximum value is not less than earlier stored maximum value, and if so to calculate, and to add to the contents of an incremental store of the computer, a first incremental value corresponding to [(a-b)/( 1 -ab)] where
a=the earlier-stored maximum value
b=the earlier-stored minimum value and
a and P are given stress coefficients for
the components under stress, in the event of a negative result of said first discriminating routine, to carry out a second discriminating routine for determining, from said last four stored values, whether a latterstored maximum value is less than an earlier-stored maximum value, and whether an earlier-stored minimum value is greater than a later-stored minimum value, and if so to calculate, and to add to the contents of an incremental store of the computer, a second incremental value corresponding to [(cb)/( I -b)] P where
c=a later-stored maximum value, the value in said incremental store representing the expired fatigue life of the component during the time when said input signals are supplied.
2. An apparatus as claimed in Claim 1 in which said computer is programmed:
to determine, from said last four stored values, whether an earlier-stored maximum value is greater than a later-stored maximum value, and whether an earlierstored minimum value is less than a laterstored minimum value, and if so,
to add to said store the next-occurring significant maximum and minimum values, and subsequently,
to carry out said first and second discriminating routines, as appropriate, on the last four values so stored, and subsequently,
to calculate, and add to the contents of said incremental store, said first or said second incremental values for the last four values so stored.
3. An apparatus as claimed in Claim 1 or
Claim 2 in which said computer is programmed:
to discard any of said stored values which have been used in calculating said first or said second incremental values, and
to shift the remaining stored values into consecutive store location including locations from which values have previously been discarded.
4. An apparatus as claimed in any preceding claim in which said computer is programmed to determine said instantaneous maximum values from the equation Vmax=[p( 1-ax2)+x2] 1/2 where
x=the next preceding minimum value of
said input signal, and
p=a given stress coefficient of the
component, and is programmed to
determine said instantaneous
minimum values from the equation V =[(p~y2)/(X~ l )] 1/2 where
y=the next preceding maximum value
of said input signal.
5. An apparatus for providing an indication of the elapsed fatigue life of a
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (5)
1. An apparatus for providing an indication of the elapsed fatigue life of a device which is, in use, subjected to a fluctuating stress, comprising means for supplying an input signal whose value is dependent on the instantaneous magnitude of said fluctuating stress, and a computer which is responsive to said input signals and is programmed::
to respond to the last sequentiallyoccurring maximum value of said input signal, to determine an instantaneous reference minimum level,
to respond to the last sequentiallyoccurring minimum value of said input signal, to determine an instantaneous reference maximum level,
to reject any maximum value having a next-occurring minimum value which is above said reference minimum level, and to reject any minimum value having a nextoccurring maximum value which is below said reference maximum level,
to store sequentially any maximum and minimum values not so rejected,
to carry out a first discriminating routine for determining, from the last four values so stored, whether a later stored maximum value is not less than earlier stored maximum value, and if so to calculate, and to add to the contents of an incremental store of the computer, a first incremental value corresponding to [(a-b)/( 1 -ab)] where
a=the earlier-stored maximum value
b=the earlier-stored minimum value and
a and P are given stress coefficients for
the components under stress, in the event of a negative result of said first discriminating routine, to carry out a second discriminating routine for determining, from said last four stored values, whether a latterstored maximum value is less than an earlier-stored maximum value, and whether an earlier-stored minimum value is greater than a later-stored minimum value, and if so to calculate, and to add to the contents of an incremental store of the computer, a second incremental value corresponding to [(cb)/( I -b)] P where
c=a later-stored maximum value, the value in said incremental store representing the expired fatigue life of the component during the time when said input signals are supplied.
2. An apparatus as claimed in Claim 1 in which said computer is programmed:
to determine, from said last four stored values, whether an earlier-stored maximum value is greater than a later-stored maximum value, and whether an earlierstored minimum value is less than a laterstored minimum value, and if so,
to add to said store the next-occurring significant maximum and minimum values, and subsequently,
to carry out said first and second discriminating routines, as appropriate, on the last four values so stored, and subsequently,
to calculate, and add to the contents of said incremental store, said first or said second incremental values for the last four values so stored.
3. An apparatus as claimed in Claim 1 or
Claim 2 in which said computer is programmed:
to discard any of said stored values which have been used in calculating said first or said second incremental values, and
to shift the remaining stored values into consecutive store location including locations from which values have previously been discarded.
4. An apparatus as claimed in any preceding claim in which said computer is programmed to determine said instantaneous maximum values from the equation Vmax=[p( 1-ax2)+x2] 1/2 where
x=the next preceding minimum value of
said input signal, and
p=a given stress coefficient of the
component, and is programmed to
determine said instantaneous
minimum values from the equation V =[(p~y2)/(X~ l )] 1/2 where
y=the next preceding maximum value
of said input signal.
5. An apparatus for providing an indication of the elapsed fatigue life of a
device which is subjected, in use, to a fluctuating stress, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.
Priority Applications (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB2778776A GB1579336A (en) | 1976-07-03 | 1976-07-03 | Apparatus for computing elapsed fatique life of a component which is subjected to a fluctuating stress |
| IT2511877A IT1075728B (en) | 1976-07-03 | 1977-06-28 | DEVICE FOR CALCULATING THE PAST FATIGUE LIFE OF A COMPONENT WHICH IS SUBJECT TO AN OSCILLATING STRESS |
| DE19772729467 DE2729467A1 (en) | 1976-07-03 | 1977-06-30 | DEVICE FOR CALCULATING THE ELAPSED EMERGENCY TIME OF A COMPONENT SUBJECT TO CHARACTERISTICS |
| JP7729777A JPS536092A (en) | 1976-07-03 | 1977-06-30 | Indicator for repeated fatigue life |
| FR7720322A FR2399067A1 (en) | 1976-07-03 | 1977-07-01 | DEVICE FOR CALCULATING THE LENGTH OF PAST FATIGUE |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB2778776A GB1579336A (en) | 1976-07-03 | 1976-07-03 | Apparatus for computing elapsed fatique life of a component which is subjected to a fluctuating stress |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB1579336A true GB1579336A (en) | 1980-11-19 |
Family
ID=10265316
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB2778776A Expired GB1579336A (en) | 1976-07-03 | 1976-07-03 | Apparatus for computing elapsed fatique life of a component which is subjected to a fluctuating stress |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS536092A (en) |
| DE (1) | DE2729467A1 (en) |
| FR (1) | FR2399067A1 (en) |
| GB (1) | GB1579336A (en) |
| IT (1) | IT1075728B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2181250A (en) * | 1985-10-04 | 1987-04-15 | Semco Instr Inc | Comprehensive turbine engine monitor and recorder system |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3048964A1 (en) * | 1980-12-24 | 1982-07-08 | Mannesmann AG, 4000 Düsseldorf | METHOD AND DEVICE FOR DETERMINING THE LOAD OF A LIFTER |
| DE102007009085A1 (en) | 2007-02-24 | 2008-08-28 | Oerlikon Leybold Vacuum Gmbh | Method for determining the fatigue of a pump rotor of a turbo gas pump |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1958257C3 (en) * | 1969-11-20 | 1974-08-15 | Pietzsch, Ludwig, Dr.-Ing., 7500 Karlsruhe | Process for monitoring the service life of machines or components subject to constant alternation and the device for carrying out the process |
| FR2079502A5 (en) * | 1970-02-03 | 1971-11-12 | Kollsman Instr Corp | |
| US3777555A (en) * | 1972-05-03 | 1973-12-11 | Us Navy | Cumulative fatigue life indicator |
-
1976
- 1976-07-03 GB GB2778776A patent/GB1579336A/en not_active Expired
-
1977
- 1977-06-28 IT IT2511877A patent/IT1075728B/en active
- 1977-06-30 DE DE19772729467 patent/DE2729467A1/en not_active Withdrawn
- 1977-06-30 JP JP7729777A patent/JPS536092A/en active Pending
- 1977-07-01 FR FR7720322A patent/FR2399067A1/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2181250A (en) * | 1985-10-04 | 1987-04-15 | Semco Instr Inc | Comprehensive turbine engine monitor and recorder system |
| GB2181250B (en) * | 1985-10-04 | 1989-12-06 | Semco Instr Inc | Comprehensive engine monitor and recorder |
Also Published As
| Publication number | Publication date |
|---|---|
| IT1075728B (en) | 1985-04-22 |
| FR2399067A1 (en) | 1979-02-23 |
| JPS536092A (en) | 1978-01-20 |
| DE2729467A1 (en) | 1978-01-05 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PS | Patent sealed | ||
| PCNP | Patent ceased through non-payment of renewal fee |