JP2018072060A - Strength estimation method for bake-processed molded article - Google Patents
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Abstract
Description
本発明は、焼き付けにより硬化する鋼板を用いてプレス成形し焼き付け処理した部材（本明細書および特許請求の範囲において、「焼き付け処理成形品」という）について、耐衝突性能等の強度を推定する焼き付け処理成形品の強度推定方法に関する。 The present invention relates to a process for estimating the strength such as the impact resistance performance of a member that is press-formed and baked using a steel plate that is hardened by baking (referred to as “baked-processed molded product” in the present specification and claims). The present invention relates to a method for estimating the strength of a processed molded product.
自動車や自動車車体に用いられる自動車部品の耐衝突性能を解析する手法として、コンピュータシミュレーションを用いた衝突解析がある。自動車や自動車車体の衝突解析においては、自動車部品に使用される材料の特性を基にして行われる。 As a technique for analyzing the collision resistance performance of automobile parts used in automobiles and automobile bodies, there is a collision analysis using computer simulation. The collision analysis of an automobile or an automobile body is performed based on the characteristics of materials used for automobile parts.
自動車部品に用いられる材料のひとつに、焼き付けにより硬化する鋼板がある。自動車の製造に際してホワイトボデーは、各自動車部品のプレス成形、組み立て、電着塗装、焼き付け処理といった工程を経る。焼き付けにより硬化する鋼板は、上記工程中のプレス成形工程において与えられた加工ひずみの程度に応じて、焼き付け処理工程において焼き付け硬化して強度が上昇する特性を有する。したがって、焼き付けにより硬化する鋼板を使用して製造した自動車部品の強度をコンピュータシミュレーションによって予測するためには、予め与えられた加工ひずみ（予ひずみ）と焼き付け硬化による強度の上昇との関係を正確に把握し、この関係に基づく自動車部品の材料特性を得て、衝突解析等のコンピュータシミュレーションを行う必要がある。 One of the materials used for automobile parts is a steel sheet that hardens by baking. When manufacturing automobiles, white bodies go through processes such as press molding, assembling, electrodeposition coating, and baking treatment of each automobile part. The steel plate that is hardened by baking has a characteristic that the strength is increased by baking and hardening in the baking treatment step in accordance with the degree of processing strain given in the press forming step in the above step. Therefore, in order to predict by computer simulation the strength of automobile parts manufactured using steel plates that harden by baking, the relationship between the pre-strained processing strain (pre-strain) and the increase in strength by bake hardening is accurate. It is necessary to grasp and obtain material characteristics of automobile parts based on this relationship and perform computer simulation such as collision analysis.
プレス成形品の焼き付け硬化後の強度を予測する手法に関して、いくつかの従来技術が挙げられる。
特許文献１には、プレス成形後におけるプレス成形品のひずみ状態から相当塑性ひずみを算出し、該算出した相当塑性ひずみと焼き付けにより硬化する鋼板の硬化量を関連付けて前記プレス成形品の耐デント性を予測する手法が開示されている。
また、特許文献２には、予ひずみを与えた後に焼き付け処理して硬化させた鋼材の応力とひずみの関係を推定する方法が開示されている。
There are several conventional techniques for predicting the strength of a press-molded product after baking and curing.
In Patent Document 1, the equivalent plastic strain is calculated from the strain state of the press-formed product after press forming, and the calculated equivalent plastic strain and the amount of hardening of the steel plate hardened by baking are related to each other, and the dent resistance of the press-formed product is related. A method for predicting the above is disclosed.
Patent Document 2 discloses a method for estimating a relationship between stress and strain of a steel material that has been pre-strained and then hardened by baking.
一般的に、プレス成形品の強度を議論する際には、プレス成形中に鋼板に与えられた累積相当塑性ひずみや流動応力と関連付けてなされることが多い。そのため、焼き付け処理して硬化させた焼き付け処理成形品の強度を推定する場合においても、累積相当塑性ひずみや流動応力を用いることが考えられる。
しかし、プレス成形中にひずみ経路が大きく変化した部位、例えばハット断面部品を絞り成形する際に曲げ曲げ戻し変形を受ける縦壁部などに関しては、塑性ひずみをどのように見積もるべきかについてこれまで詳細な議論がなされていなかった。
In general, when discussing the strength of a press-formed product, the strength is often associated with cumulative equivalent plastic strain or flow stress applied to the steel sheet during press forming. For this reason, it is conceivable to use cumulative equivalent plastic strain or flow stress even when estimating the strength of a baking-processed molded product cured by baking.
However, details of how the plastic strain should be estimated for parts where the strain path has changed significantly during press molding, such as the vertical wall part that undergoes bending and bending back deformation when drawing a hat cross-section part, has been detailed. There was no debate.
特許文献１に開示されている方法によれば、プレス成形後の相当塑性ひずみの値に基づいて焼き付け硬化したプレス成形品の強度を予測することができるとされているが、プレス成形中におけるひずみ経路については考慮されておらず、例えば、引張から圧縮へ、または、圧縮から引張へと面内の反転負荷を受けてプレス成形後にひずみの値が0となるような部位について、前記相当塑性ひずみの値では焼き付け硬化後の焼き付け処理成形品の強度を正しく予測できないという問題があった。 According to the method disclosed in Patent Document 1, it is said that the strength of a press-molded product that has been baked and hardened can be predicted based on the value of equivalent plastic strain after press molding. The path is not taken into account, for example, the equivalent plastic strain at a site where the strain value becomes 0 after press molding due to in-plane reversal load from tension to compression or from compression to tension. With the value of 1, there was a problem that the strength of the baking-processed molded product after baking hardening could not be predicted correctly.
また、特許文献２に開示されている方法においても、焼き付け処理して硬化させた鋼材の応力を推定するために用いる相当塑性ひずみの定義が曖昧であり、成形中におけるひずみ経路については考慮されていない。 Also in the method disclosed in Patent Document 2, the definition of equivalent plastic strain used to estimate the stress of a steel material hardened by baking is ambiguous, and the strain path during forming is considered. Absent.
本発明は、上記のような課題を解決するためになされたものであり、例えば、焼き付けにより硬化する鋼板を用いて、引張から圧縮へ、圧縮から引張へとひずみ経路が変化する変形を受けてプレス成形されたプレス成形品について焼き付け処理後の焼き付け処理成形品における耐衝突性能等の強度を推定する焼き付け処理成形品の強度推定方法を提供することを目的とする。 The present invention has been made in order to solve the above-described problems. For example, a steel sheet that is hardened by baking is used to undergo deformation in which a strain path changes from tension to compression and from compression to tension. An object of the present invention is to provide a strength estimation method for a baking-processed molded product that estimates the strength such as the impact resistance performance of the press-molded press-molded product after the baking process.
（１）本発明に係る焼き付け処理成形品の強度推定方法は、焼き付けにより硬化する鋼板のプレス成形品を焼き付け処理した焼き付け処理成形品の強度を推定するものであって、予ひずみを付与して焼き付け処理した焼き付けにより硬化する鋼板の焼き付け硬化後の材料特性と前記予ひずみとの関係を取得する焼き付け硬化材料特性取得ステップと、前記焼き付けにより硬化する鋼板を前記プレス成形品にプレス成形するプレス成形解析を行い、プレス成形過程における単軸相当の塑性ひずみを算出するプレス成形解析ステップと、該算出した単軸相当の塑性ひずみのプレス成形過程のひずみ経路における最大値を求める単軸相当の塑性ひずみ最大値取得ステップと、前記焼き付け硬化材料特性取得ステップで取得した焼き付け硬化後の材料特性と予ひずみとの関係を用いて、前記単軸相当の塑性ひずみの最大値に対応する焼き付け硬化後の材料特性を前記プレス成形品の材料データとして設定する焼き付け硬化材料特性設定ステップと、該焼き付け硬化後の材料特性が設定された前記プレス成形品の強度解析を行い、前記焼き付け処理成形品の強度を推定する強度解析ステップを有することを特徴とするものである。 (1) The strength estimation method of a baking-processed molded product according to the present invention is to estimate the strength of a baking-processed molded product obtained by baking a press-formed product of a steel sheet that is hardened by baking, and applying pre-strain. A baking hardening material property acquisition step for acquiring a relationship between the pre-strain and a material property after baking hardening of a steel plate that is hardened by baking, and press forming that presses the steel plate that is hardened by baking to the press-formed product. Analyzing and calculating the plastic strain equivalent to the uniaxial in the press forming process, and calculating the maximum value in the strain path of the press forming process of the plastic strain equivalent to the calculated uniaxial plastic strain equivalent to the uniaxial The material after baking hardening acquired in the maximum value acquisition step and the baking hardening material property acquisition step. Bake hardening material property setting step for setting the material property after bake hardening corresponding to the maximum value of plastic strain equivalent to the single axis as the material data of the press-formed product, using the relationship between the property and the pre-strain; It has a strength analysis step of performing strength analysis of the press-molded product in which material characteristics after bake hardening are set, and estimating strength of the bake-processed molded product.
（２）上記（１）に記載のものにおいて、前記単軸相当の塑性ひずみ最大値取得ステップは、前記単軸相当の塑性ひずみの最大値を要素毎に取得し、前記焼き付け硬化材料特性設定ステップは、前記単軸相当の塑性ひずみの最大値が所定の範囲に含まれる要素群からなる領域に前記プレス成形品を分割し、該分割した領域毎に前記焼き付け硬化後の材料特性を設定することを特徴とするものである。 (2) In the above-mentioned (1), in the plastic strain maximum value obtaining step corresponding to the uniaxial axis, the maximum value of the plastic strain equivalent to the uniaxial shaft is obtained for each element, and the baking hardening material property setting step is performed. Dividing the press-molded product into regions composed of element groups in which the maximum value of plastic strain equivalent to the uniaxial axis is included in a predetermined range, and setting the material properties after the bake hardening for each of the divided regions It is characterized by.
本発明は、焼き付けにより硬化する鋼板のプレス成形品を焼き付け処理した焼き付け処理成形品の強度を推定するものであって、予ひずみを付与して焼き付け処理した焼き付けにより硬化する鋼板の焼き付け硬化後の材料特性と前記予ひずみとの関係を取得する焼き付け硬化材料特性取得ステップと、前記焼き付けにより硬化する鋼板を前記プレス成形品にプレス成形するプレス成形解析を行い、プレス成形過程における単軸相当の塑性ひずみを算出するプレス成形解析ステップと、該算出した単軸相当の塑性ひずみのプレス成形過程のひずみ経路における最大値を求める単軸相当の塑性ひずみ最大値取得ステップと、前記焼き付け硬化材料特性取得ステップで取得した焼き付け硬化後の材料特性と予ひずみとの関係を用いて、前記単軸相当の塑性ひずみの最大値に対応する焼き付け硬化後の材料特性を前記プレス成形品の材料データとして設定する焼き付け硬化材料特性設定ステップと、該焼き付け硬化後の材料特性が設定された前記プレス成形品の強度解析を行い、前記焼き付け処理成形品の強度を推定する強度解析ステップを有することにより、プレス成形過程においてひずみ経路が変化するような変形を受けてプレス成形された前記プレス成形品の焼き付け硬化後の材料特性を的確に設定することができ、前記焼き付け処理成形品の耐衝突性能等の強度を精度良く推定することができる。 The present invention estimates the strength of a baking-processed molded product obtained by baking a press-formed product of a steel plate that is hardened by baking, and after the baking and hardening of a steel plate that is hardened by baking after applying a pre-strain. Bake-hardened material property acquisition step for acquiring the relationship between material properties and the pre-strain, and press forming analysis for press-molding the steel plate hardened by the baking into the press-formed product, plasticity equivalent to a single axis in the press forming process A press forming analysis step for calculating strain, a single axis equivalent plastic strain maximum value obtaining step for obtaining a maximum value in a strain path in the press forming process of the calculated plastic strain equivalent to the single axis, and the bake hardened material property obtaining step Using the relationship between pre-strain and material properties after bake hardening obtained in step 1, Bake-hardened material property setting step for setting the material property after bake hardening corresponding to the maximum value of plastic strain as material data of the press-formed product, and the strength of the press-formed product in which the material property after bake-hardening is set By performing an analysis and having a strength analysis step for estimating the strength of the baking-processed molded product, the press-molded product after the baking and curing of the press-molded product that has been subjected to deformation such that the strain path changes in the press molding process. The material characteristics can be accurately set, and the strength such as the anti-collision performance of the baked product can be accurately estimated.
本発明の実施の形態に係る焼き付け処理成形品の強度推定方法の説明に先立ち、本発明で対象とする焼き付けにより硬化する鋼板と、焼き付け硬化後の強度とひずみの関係について説明する。 Prior to the description of the method for estimating the strength of the bake-processed molded article according to the embodiment of the present invention, the steel sheet that is hardened by baking, which is the subject of the present invention, and the relationship between strength and strain after bake hardening will be described.
焼き付けにより硬化する鋼板とは、プレス成形等によって与えられた加工ひずみ（予ひずみ）の量に応じて、焼き付け処理により硬化して強度が上昇する性質を持った鋼板である。この焼き付け処理時の強度上昇を、時効硬化、若しくは焼き付け硬化と呼ぶ。 The steel plate that is hardened by baking is a steel plate that has the property of being hardened by baking and having increased strength in accordance with the amount of processing strain (pre-strain) given by press forming or the like. This increase in strength during the baking process is referred to as age hardening or bake hardening.
焼き付けにより硬化する鋼板には、焼き付け処理により降伏強度が上昇するBH鋼板（Bake Hardened）、降伏強度に加えて引張強度も上昇するBHT（登録商標：Bake Hardenable steel with Tensile strength increase）鋼板がある。 Steel plates that harden by baking include BH steel plates (Bake Hardened) in which the yield strength increases by baking treatment, and BHT (registered trademark: Bake Hardenable steel with Tensile strength increase) steel plates in which tensile strength increases in addition to yield strength.
焼き付け硬化の基本的なメカニズムは、BH鋼板、BHT鋼板ともに共通であり、焼き付けにより硬化する鋼板にプレス成形等によって予ひずみが与えられたとき、鋼板内の転位密度が上昇し、鋼板中に転位が導入された状態で焼き付け塗装等により温度が上昇すると、鋼板中の結晶粒界に留まっていた炭素原子や窒素原子が動き、転位に吸着することによって鋼板が硬化する。したがって、焼き付け硬化量は、鋼板に導入された転位の量（転位密度）、すなわち予ひずみと相関性を有する。 The basic mechanism of bake hardening is the same for both BH and BHT steel sheets. When pre-strain is applied to the steel sheet that is hardened by baking, such as by press forming, the dislocation density in the steel sheet rises and dislocations occur in the steel sheet. When the temperature is increased by baking coating or the like with carbon introduced, the carbon atoms and nitrogen atoms staying at the crystal grain boundaries in the steel plate move, and the steel plate is hardened by adsorbing to the dislocations. Therefore, the bake hardening amount has a correlation with the amount of dislocations (dislocation density) introduced into the steel sheet, that is, pre-strain.
したがって、焼き付け硬化した焼き付け処理成形品の強度を推定するためには、プレス成形などにより与えられた予ひずみを正しく見積り、該予ひずみに基づいて焼き付け硬化した後の強度などの材料特性を把握することが重要である。 Therefore, in order to estimate the strength of the bake-cured molded product, correctly estimate the pre-strain given by press molding, etc., and grasp the material properties such as strength after bake-hardening based on the pre-strain. This is very important.
前述のとおり、従来、焼き付け硬化した後の焼き付け処理成形品の強度は、プレス成形により与えられた予ひずみとしてプレス成形中の累積相当塑性ひずみを用いて予測されていた。しかしながら、ひずみ経路が変化する変形を受けてプレス成形される場合、累積相当塑性ひずみはプレス成形過程で受けた圧縮、引張の各ひずみの絶対値の加算値であったため、焼き付け硬化後の強度を正しく予測できず、予ひずみをどのように見積るかが課題であった。 As described above, conventionally, the strength of the baking-processed molded article after baking and hardening has been predicted using the cumulative equivalent plastic strain during press molding as the pre-strain given by press molding. However, when press molding is performed with deformations that change the strain path, the cumulative equivalent plastic strain is the sum of the absolute values of the compression and tension strains received during the press molding process. The problem was how to estimate the pre-strain because it could not be predicted correctly.
そこで、発明者らは、種々の材料試験の結果を鋭意検討した結果、焼き付け処理成形品の焼き付け硬化後の強度は、プレス成形開始からプレス成形終了までの間のひずみ径路における単軸相当の塑性ひずみの最大値と強い相関があることを見出した。 Accordingly, the inventors have intensively studied the results of various material tests, and as a result, the strength after baking hardening of the baking-processed molded product is a plastic equivalent to a single axis in the strain path from the start of press forming to the end of press forming. It was found that there was a strong correlation with the maximum strain value.
ここで、本発明における単軸相当の塑性ひずみとは、プレス成形の一連のひずみ経路において、各塑性変形過程におけるそれぞれのひずみを意味する。
例えば、一軸方向のひずみ経路であれば、引張および／または圧縮の一連のひずみ経路において、各引張過程または各圧縮過程におけるそれぞれのひずみを意味する。すなわち、引張(１)、圧縮(１)、引張(２)の順となる一連のひずみ経路であれば、引張(１)のひずみ、圧縮(１)のひずみ、引張(２)のひずみをそれぞれ意味する。
Here, the plastic strain corresponding to a single axis in the present invention means each strain in each plastic deformation process in a series of strain paths of press forming.
For example, in the case of a uniaxial strain path, it means a strain in each tension process or each compression process in a series of strain paths of tension and / or compression. That is, if a series of strain paths are in the order of tension (1), compression (1), and tension (2), the strain of tension (1), the strain of compression (1), and the strain of tension (2), respectively. means.
また、二軸方向のひずみ経路であれば、二軸が交差する方向に引張−引張、引張−圧縮、圧縮−圧縮のいずれかのひずみが作用するので、これらの一連のひずみ経路において、これらをそれぞれ単軸相当のひずみに換算して求めた値を意味する。すなわち、［X軸方向ひずみ−Y軸方向ひずみ］として表すと、［引張−引張］(１)、［引張−圧縮］(１)、［圧縮−圧縮］(１)、［引張−引張］(２)の順となる一連のひずみ経路であれば、［引張−引張］(１)、［引張−圧縮］(１)、［圧縮−圧縮］(１)、［引張−引張］(２)の二軸方向ひずみをそれぞれ単軸相当に換算したそれぞれの値を意味する。そして、単軸相当の塑性ひずみの最大値とは、プレス成形中のひずみ経路における最大値である。 In addition, in the case of a biaxial strain path, any strain of tension-tensile, tension-compression, and compression-compression acts in the direction in which the two axes intersect. Each means a value obtained by converting to a strain equivalent to a single axis. That is, [Tension-Tension] (1), [Tension-Compression] (1), [Compression-Compression] (1), [Tension-Tension] ( If the strain path is in the order of 2), [Tension-Tension] (1), [Tension-Compression] (1), [Compression-Compression] (1), [Tension-Tension] (2) It means each value obtained by converting the biaxial strain to a single axis equivalent. The maximum value of plastic strain equivalent to a single axis is the maximum value in the strain path during press forming.
なお、ひずみ経路を持つ塑性変形の場合、一般に、相当塑性ひずみの最大値とは、ひずみ経路における単軸相当の塑性ひずみの絶対値を加算した累積値であるが、本発明に係る単軸相当の塑性ひずみは、上記の定義のとおり、ひずみ経路における累積値ではないため、本発明に係る単軸相当の塑性ひずみの最大値と前記相当塑性ひずみの最大値とは異なるものである。 In the case of plastic deformation having a strain path, the maximum value of equivalent plastic strain is generally a cumulative value obtained by adding absolute values of plastic strain equivalent to a single axis in the strain path, but is equivalent to a single axis according to the present invention. Since the plastic strain is not a cumulative value in the strain path as defined above, the maximum value of the plastic strain corresponding to the uniaxial axis according to the present invention is different from the maximum value of the equivalent plastic strain.
また、本発明において、単軸相当の塑性ひずみの最大値は、次のように求めることができる。
焼き付けにより硬化する鋼板に単軸荷重を付与した時の応力−ひずみの関係が、例えば、次式のSwiftの式に従うと仮定する。
σ＝K（ε0＋εp）n ・・・（１）
ここで、σは真応力、εpはひずみ、K、ε0、nは、定数である。
In the present invention, the maximum value of plastic strain corresponding to a single axis can be obtained as follows.
It is assumed that the stress-strain relationship when a uniaxial load is applied to a steel plate hardened by baking follows, for example, the following Swift equation.
σ = K (ε 0 + ε p ) n (1)
Here, σ is a true stress, ε p is a strain, K, ε 0 , and n are constants.
式（１）より、塑性ひずみεpは次のように表すことができる。
εp＝(σ)1／n／K−ε0＝f(σ)・・・（２）
From equation (1), the plastic strain ε p can be expressed as follows.
ε p = (σ) 1 / n / K−ε 0 = f (σ) (2)
そして、焼き付けにより硬化する鋼板のプレス成形品のプレス成形過程における単軸相当の塑性ひずみは、式（２）中の真応力σとしてプレス成形過程における相当応力を与えることにより表されるものとすると、相当応力に対応する塑性ひずみは応力−ひずみ曲線から一義的に求まるため、単軸相当の塑性ひずみの最大値は、プレス成形中における相当応力の最大値σmaxを用いてεeqmax＝f(σmax)と表される。 And the plastic strain equivalent to the uniaxial in the press forming process of the press-formed product of the steel sheet cured by baking is expressed by giving the equivalent stress in the press forming process as the true stress σ in the equation (2). Since the plastic strain corresponding to the equivalent stress is uniquely determined from the stress-strain curve, the maximum value of the plastic strain equivalent to the uniaxial axis is εeqmax = f (σmax) using the maximum value σmax of the equivalent stress during press forming It is expressed.
このように、プレス成形中に相当応力が最大値σmaxとなったときにおける塑性ひずみにより単軸相当の塑性ひずみの最大値εeqmaxを求めることができる。 As described above, the maximum value εeqmax of the plastic strain corresponding to the single axis can be obtained from the plastic strain when the equivalent stress reaches the maximum value σmax during the press forming.
なお、上記の例では、応力−ひずみの関係をSwiftの式で表したが、応力に対して塑性ひずみが一意に定まる関係で表現できれば、必ずしもSwiftの式を利用する必要はなく、例えば応力とひずみを点列データにより関連付けたものでも構わない。 In the above example, the stress-strain relationship is represented by the Swift equation. However, if the plastic strain can be expressed uniquely with respect to the stress, it is not always necessary to use the Swift equation. The strain may be associated with point sequence data.
上記の例を含めて求めた単軸相当の塑性ひずみの最大値が焼き付け硬化後の強度と関係するということは、単軸相当の塑性ひずみの最大値が転位密度と相関があることを示している。そこで、この関係を検証するため、単軸引張圧縮試験およびビッカース硬度測定試験を行ったので、以下、その結果を示す。 The fact that the maximum value of uniaxial equivalent plastic strain, including the above examples, is related to the strength after bake hardening indicates that the maximum value of uniaxial equivalent plastic strain is correlated with the dislocation density. Yes. Therefore, in order to verify this relationship, a uniaxial tensile compression test and a Vickers hardness measurement test were performed, and the results are shown below.
まず、440MPa級、板厚2.0mmのBH鋼板の試験片に対して、単軸引張荷重又は単軸圧縮荷重を作用させて予ひずみを付与した。予ひずみ付与後の試験片を焼き付け処理して焼き付け硬化させた試験片のビッカース硬度を測定し、焼き付け処理による硬度の上昇量を求めた。 First, a pre-strain was applied by applying a uniaxial tensile load or a uniaxial compressive load to a test piece of a 440 MPa class BH steel plate having a thickness of 2.0 mm. The Vickers hardness of the test piece after baking and hardening the test piece after applying the pre-strain was measured, and the amount of increase in hardness due to the baking process was determined.
ここで、試験片に付与した予ひずみから、引張荷重又は圧縮荷重を単軸で試験片に作用させ、該試験片に生じるひずみ経路の塑性ひずみ（上述の単軸相当の塑性ひずみ）の最大値(絶対値)を抽出した。
表１に、単軸引張荷重よび／又は単軸圧縮荷重を作用させて試験片に生じさせるひずみ経路と塑性ひずみの最大値を示す。
Here, from the pre-strain applied to the test piece, a tensile load or a compressive load is applied to the test piece with a single axis, and the maximum value of the plastic strain of the strain path (plastic strain equivalent to the above-mentioned single axis) generated in the test piece. (Absolute value) was extracted.
Table 1 shows the strain path and the maximum value of plastic strain generated in the test piece by applying a uniaxial tensile load and / or a uniaxial compressive load.
表１の各条件において試験片に作用させる引張荷重と圧縮荷重とを区別するため、引張荷重の場合の引張ひずみの値を正（+）、圧縮荷重の場合の圧縮ひずみを負（-）で表しているが、試験片に付与した予ひずみである単軸相当の塑性ひずみは、各ひずみの絶対値で表すことができる。 In order to distinguish the tensile load and the compressive load applied to the specimen under each condition in Table 1, the tensile strain value for the tensile load is positive (+), and the compressive strain for the compressive load is negative (-). Although it represents, the plastic strain equivalent to the uniaxial axis which is the prestrain given to the test piece can be expressed by the absolute value of each strain.
条件０は、試験片に圧縮ひずみおよび引張ひずみのいずれも付与せずに焼き付け処理したものであり、試験片に付与された予ひずみは0%である。 Condition 0 is a test piece that is baked without applying either compressive strain or tensile strain, and the pre-strain applied to the test piece is 0%.
条件１〜４は、単軸引張荷重を作用させて引張ひずみを与えて除荷した試験片に焼き付け処理したものである。条件１〜４において、試験片に付与された予ひずみは、各条件で試験片に与えられた引張ひずみの絶対値（＝1%、3%、5%および9%）である。 Conditions 1 to 4 are those in which a uniaxial tensile load is applied and subjected to a baking treatment on a test piece unloaded by applying a tensile strain. In conditions 1 to 4, the prestrain applied to the test piece is an absolute value (= 1%, 3%, 5%, and 9%) of the tensile strain applied to the test piece in each condition.
条件５〜７は、単軸圧縮荷重を作用させて圧縮ひずみを与えて除荷した試験片に焼き付け処理したものである。条件５〜７において、試験片に付与される予ひずみは、各条件で試験片に与えられた圧縮ひずみの絶対値である（＝1%、3%、5%）。 Conditions 5 to 7 are those in which a uniaxial compressive load is applied and subjected to a baking treatment on a test piece unloaded by applying a compressive strain. In conditions 5 to 7, the pre-strain applied to the test piece is an absolute value of the compressive strain applied to the test piece in each condition (= 1%, 3%, 5%).
条件８〜１２は、まず単軸引張荷重を作用させて引張ひずみを与え、その後、単軸圧縮荷重を作用させて圧縮ひずみを与えて除荷した試験片を焼き付け処理したものである。条件８〜１２において、試験片に付与される予ひずみは、引張荷重又は圧縮荷重を作用させて与えられたひずみの最大値（絶対値）である。 Conditions 8 to 12 are those in which a uniaxial tensile load is first applied to give tensile strain, and then the uniaxial compressive load is applied to apply compressive strain to unload the test piece. In conditions 8 to 12, the pre-strain applied to the test piece is the maximum value (absolute value) of the strain applied by applying a tensile load or a compressive load.
例えば、条件１１は、単軸引張荷重を作用させて+5%の引張ひずみを与えた状態から、単軸圧縮荷重を作用させて-3%の圧縮ひずみを与えて除荷するものであるので、条件１１において付与された塑性ひずみの最大値は5%である。
なお、比較となる累積相当塑性ひずみは、引張変形→圧縮変形の各過程で与えられるひずみ（絶対値）を累積した値であるため、例えば、条件１１における累積相当塑性ひずみは、5+3＝8%となる。
For example, condition 11 is to unload by applying a uniaxial compressive load and applying a −3% compressive strain from a state in which a uniaxial tensile load is applied and + 5% tensile strain is applied. The maximum value of plastic strain applied in condition 11 is 5%.
The cumulative equivalent plastic strain to be compared is a value obtained by accumulating strain (absolute value) given in each process of tensile deformation → compression deformation. For example, the cumulative equivalent plastic strain in condition 11 is 5 + 3 = 8%.
条件１３〜１７は、まず単軸引張荷重を作用させた後に単軸圧縮荷重を作用させ、さらに単軸引張荷重を作用させた試験片に焼き付け処理したものである。 Conditions 13 to 17 are those in which a uniaxial tensile load is applied first, then a uniaxial compressive load is applied, and a test piece subjected to a uniaxial tensile load is further baked.
例えば、条件１４は、単軸引張荷重を作用させて+5%の引張ひずみを与えた状態から、単軸圧縮荷重を作用させて-5%の圧縮ひずみを与え、さらに単軸引張荷重を作用させて+3%の引張ひずみを与えて除荷したものであり、条件１４において付与される塑性ひずみの最大値は5%である。
これに対し、条件１４における比較となる累積相当塑性ひずみは、引張変形→圧縮変形→引張変形の各過程で与えられるひずみ（絶対値）を累積した値であり、5+5+3＝13%となる。
For example, in condition 14, a uniaxial tensile load is applied to give + 5% tensile strain, a uniaxial compressive load is applied to give -5% compressive strain, and a uniaxial tensile load is applied. The tensile strain of + 3% was applied and the unloading was performed, and the maximum value of the plastic strain applied under the condition 14 is 5%.
On the other hand, the cumulative equivalent plastic strain to be compared in condition 14 is a value obtained by accumulating strain (absolute value) given in each process of tensile deformation → compression deformation → tensile deformation, and 5 + 5 + 3 = 13% It becomes.
図２に、各条件において試験片に付与した塑性ひずみの最大値と焼き付け硬化させた試験片の強度の指標となるビッカース硬度の上昇量（ΔHv）の結果を示す。また、比較として、図３に、各条件において試験片に付与したひずみの累積値（累積相当塑性ひずみ）と焼き付け硬化させた試験片のビッカース硬度の上昇量（ΔHv）の結果を、図４に、各条件において試験片に生じた流動応力と焼き付け硬化させた試験片のビッカース硬度の上昇量（ΔHv）の結果を示す。 FIG. 2 shows the results of the increase in the Vickers hardness (ΔHv), which is an index of the maximum value of the plastic strain applied to the test piece under each condition and the strength of the bake-cured test piece. For comparison, FIG. 3 shows the results of the cumulative value of strain applied to the test piece under each condition (cumulative equivalent plastic strain) and the increase in the Vickers hardness (ΔHv) of the bake hardened test piece. The results of the flow stress generated in the test piece under each condition and the amount of increase in the Vickers hardness (ΔHv) of the bake hardened test piece are shown.
図２〜４より、焼き付け処理による試験片のビッカース硬度の上昇量は、引張荷重及び圧縮荷重を作用させた際の塑性ひずみの最大値に強く相関するのに対し、比較とした累積相当塑性ひずみや流動応力との相関は弱かった。 2-4, the amount of increase in the Vickers hardness of the test piece due to the baking treatment strongly correlates with the maximum value of the plastic strain when a tensile load and a compressive load are applied, whereas the cumulative equivalent plastic strain as a comparison. The correlation with flow stress was weak.
この結果は、圧縮から引張のようにひずみ経路が変化する変形を受けてプレス成形された焼き付け処理成形品の強度を推定するにあたり、焼き付け硬化後の強度と相関がある予ひずみとして該ひずみ経路における塑性ひずみの最大値を用いて焼き付け処理成形品の材料特性を見積ることが可能であることを示している。 This result shows that in estimating the strength of a press-molded product that has been press-molded under deformation where the strain path changes, such as compression to tension, the pre-strain in the strain path is correlated with the strength after bake hardening. This shows that it is possible to estimate the material characteristics of the baked molded article using the maximum value of the plastic strain.
本発明に係る焼き付け処理成形品の強度推定方法は、これらの検証結果に基づいてなされたものである。以下、本発明の実施の形態に係る焼き付け処理成形品の強度推定方法について詳細に説明する。 The strength estimation method of the baking-processed molded product according to the present invention is based on these verification results. Hereinafter, the strength estimation method of the baking-processed molded article which concerns on embodiment of this invention is demonstrated in detail.
本実施の形態に係る焼き付け処理成形品の強度推定方法は、図５に一例として示す焼き付けにより硬化する鋼板のプレス成形品１を焼き付け処理した焼き付け処理成形品の強度を推定するものであって、図１に示すように、焼き付け硬化材料特性取得ステップＳ１と、プレス成形解析ステップＳ３と、単軸相当の塑性ひずみ最大値取得ステップＳ５と、焼き付け硬化材料特性設定ステップＳ７と、強度解析ステップＳ９を有する。
以下、上記の各ステップについて詳細に説明する。
The strength estimation method of the baking-processed molded product according to the present embodiment is to estimate the strength of the baking-processed molded product obtained by baking the press-formed product 1 of the steel sheet that is hardened by baking as shown in FIG. As shown in FIG. 1, a bake hardened material property acquisition step S1, a press forming analysis step S3, a plastic strain maximum value acquisition step S5 corresponding to a single axis, a bake hardened material property setting step S7, and a strength analysis step S9 are performed. Have.
Hereinafter, each of the above steps will be described in detail.
＜焼き付け硬化材料特性取得ステップ＞
焼き付け硬化材料特性取得ステップＳ１は、予ひずみを付与して焼き付け処理した焼き付けにより硬化する鋼板の焼き付け硬化後の材料特性と予ひずみの関係を取得するものである。
<Bake hardened material characteristics acquisition step>
The bake hardened material property acquisition step S1 is a step of acquiring the relationship between the material property after bake hardening of the steel sheet to be hardened by baking after applying the pre-strain and baking, and the pre-strain.
本実施の形態で取得する焼き付け硬化後の材料特性としては、焼き付け硬化させた後の応力とひずみの関係（応力−ひずみ曲線）があり、応力−ひずみ曲線は、例えば、単軸引張試験などにより得ることができる。 As a material characteristic after bake hardening acquired in this embodiment, there is a relation between stress and strain (stress-strain curve) after bake hardening, and the stress-strain curve is obtained by, for example, a uniaxial tensile test. Can be obtained.
予ひずみを付与して焼き付け処理した後の材料特性の一例として、図６に、0%、1%、5%、10%および15%の予ひずみを付与して焼き付け処理した後の応力−ひずみ曲線のグラフを示す。 As an example of material characteristics after baking with pre-strain, Fig. 6 shows stress-strain after baking with 0%, 1%, 5%, 10% and 15% pre-strain. A curve graph is shown.
なお、以下のステップは、コンピュータが行うものであり、プレス成形解析ステップＳ３および強度解析ステップＳ９については、例えば市販の構造解析ソフトウェアを用いてもよい。 The following steps are performed by a computer, and commercially available structural analysis software may be used for the press forming analysis step S3 and the strength analysis step S9, for example.
＜プレス成形解析ステップ＞
プレス成形解析ステップＳ３は、焼き付けにより硬化する鋼板を目標形状のプレス成形品１にプレス成形するプレス成形解析を行い、成形過程における単軸相当の塑性ひずみを算出するものである。
<Press forming analysis step>
In the press forming analysis step S3, press forming analysis for press forming a steel plate hardened by baking into a press-formed product 1 having a target shape is performed, and a plastic strain corresponding to a single axis in the forming process is calculated.
本実施の形態において、プレス成形解析ステップＳ３は、要素毎に単軸相当の塑性ひずみを算出するものであるが、節点毎に単軸相当の塑性ひずみを算出しても良い。 In the present embodiment, the press forming analysis step S3 calculates a plastic strain equivalent to a single axis for each element, but may calculate a plastic strain equivalent to a single axis for each node.
＜単軸相当の塑性ひずみ最大値取得ステップ＞
単軸相当の塑性ひずみ最大値取得ステップＳ５は、プレス成形解析ステップＳ３において算出した単軸相当の塑性ひずみのプレス成形過程（ひずみ経路）における最大値を求めて取得するものである。単軸相当の塑性ひずみの最大値は、後述する強度解析ステップＳ９での強度解析において、プレス成形品１の材料データとして焼き付け硬化後の材料特性を設定するために用いる。
<Maximum plastic strain equivalent to single axis acquisition step>
In the single-axis equivalent plastic strain maximum value acquisition step S5, the maximum value in the press-forming process (strain path) of the single-axis equivalent plastic strain calculated in the press-forming analysis step S3 is obtained and acquired. The maximum value of plastic strain equivalent to a single axis is used to set material characteristics after baking and hardening as material data of the press-formed product 1 in strength analysis in strength analysis step S9 described later.
例えば、焼き付けにより硬化する鋼板を用いて図５に示すような断面ハット形状のプレス成形品１を絞り成形する場合、縦壁部３は成形中に曲げ曲げ戻し変形を受けるためにひずみ経路が大きく変化する部位である。そこで、ひずみ経路の変化を考慮して、プレス成形過程における単軸相当の塑性ひずみの最大値を求める。 For example, when a press-formed product 1 having a cross-sectional hat shape as shown in FIG. 5 is drawn using a steel plate that is hardened by baking, the vertical wall portion 3 is subjected to bending and bending back deformation during forming, so that the strain path is large. It is a site that changes. Therefore, the maximum value of the plastic strain corresponding to a single axis in the press forming process is obtained in consideration of the change of the strain path.
本実施の形態において、単軸相当の塑性ひずみ最大値取得ステップＳ５は、要素毎に算出した単軸相当の塑性ひずみの最大値を求めるが、プレス成形解析ステップＳ３において節点毎に単軸相当の塑性ひずみを算出した場合においては、節点毎に単軸相当の塑性ひずみの最大値を求めるものであっても良い。 In the present embodiment, the plastic strain maximum value obtaining step S5 corresponding to a single axis obtains the maximum value of the plastic strain corresponding to a single axis calculated for each element, but the single axis equivalent plastic strain maximum value is obtained for each node in the press forming analysis step S3. When the plastic strain is calculated, the maximum value of the plastic strain corresponding to a single axis may be obtained for each node.
＜焼き付け硬化材料特性設定ステップ＞
焼き付け硬化材料特性設定ステップＳ７は、焼き付け硬化材料特性取得ステップＳ１で取得した応力−ひずみ曲線と予ひずみの関係（図６参照）を用いて、単軸相当の塑性ひずみ最大値取得ステップＳ５で取得した単軸相当の塑性ひずみの最大値に対応する焼き付け硬化後の材料特性をプレス成形品１の材料データとして設定するものである。
<Bake hardened material property setting step>
The bake hardened material property setting step S7 is obtained in the plastic strain maximum value obtaining step S5 corresponding to a single axis using the relationship between the stress-strain curve obtained in the bake hardened material property obtaining step S1 and the pre-strain (see FIG. 6). The material characteristic after baking hardening corresponding to the maximum value of the plastic strain equivalent to the single axis is set as the material data of the press-formed product 1.
本実施の形態に係る焼き付け硬化材料特性設定ステップＳ７においては、単軸相当の塑性ひずみ最大値取得ステップＳ５で取得した単軸相当の塑性ひずみの最大値が所定の範囲に含まれる要素群からなる領域にプレス成形品１を分割し、該分割した領域毎に焼き付け硬化後の材料特性（応力−ひずみ曲線）を設定してもよい。 In the bake hardened material property setting step S7 according to the present embodiment, the uniaxial equivalent plastic strain maximum value obtaining step S5 is composed of an element group in which the uniaxial equivalent plastic strain maximum value is included in a predetermined range. The press-formed product 1 may be divided into regions, and the material characteristics (stress-strain curve) after baking and hardening may be set for each of the divided regions.
領域分割における単軸相当の塑性ひずみの最大値の所定の範囲と、該単軸相当の塑性ひずみの最大値に対応する焼き付け硬化後の材料特性は、例えば以下のように設定することができる。 For example, the predetermined range of the maximum value of plastic strain corresponding to a single axis in the region division and the material characteristics after bake hardening corresponding to the maximum value of plastic strain corresponding to the single axis can be set as follows.
単軸相当の塑性ひずみ最大値取得ステップＳ５で取得した単軸相当の塑性ひずみの最大値が0%以上1%未満の範囲に含まれる要素群からなる領域に対しては、予ひずみ0%、すなわち、予ひずみを与えずに焼き付け処理した応力−ひずみ曲線を前記領域の材料特性として設定する。 For a region consisting of element groups in which the maximum value of plastic strain equivalent to single axis acquired in step S5 of single axis is within the range of 0% or more and less than 1%, 0% pre-strain, That is, a stress-strain curve obtained by baking without prestraining is set as the material property of the region.
同様に単軸相当の塑性ひずみ最大値取得ステップＳ５で取得した単軸相当の塑性ひずみの最大値が1%以上5%未満に含まれる要素群からなる領域に対しては、予ひずみ1%を付与して焼き付け処理した応力−ひずみ曲線を前記領域の材料特性として設定する。 Similarly, 1% of the pre-strain is applied to the region composed of the element group in which the maximum value of the plastic strain corresponding to the single axis acquired in the single-axis equivalent plastic strain maximum acquisition step S5 is 1% or more and less than 5%. A stress-strain curve applied and baked is set as the material property of the region.
さらに、単軸相当の塑性ひずみの最大値が5%以上10%未満および10%以上15%未満の範囲に含まれる要素群から領域に対しては、それぞれ予ひずみ5%および10%を付与して焼き付け処理した応力−ひずみ曲線を前記領域の材料特性としてそれぞれ設定する。 In addition, prestrain 5% and 10% are applied to the elements from the group of elements whose maximum plastic strain equivalent to a single axis is within the range of 5% to less than 10% and 10% to less than 15%, respectively. The stress-strain curve obtained by baking is set as the material property of the region.
上記の例では、単軸相当の塑性ひずみの最大値の所定範囲として0%以上1%未満、1%以上5%未満、5%以上10%未満および10%以上15%未満を設定し、各所定範囲に対応させてプレス成形品１を領域分割したものであるが、単軸相当の塑性ひずみの最大値の所定の範囲毎に材料特性（応力−ひずみ曲線）が取得されていれば、領域分割に用いる単軸相当の塑性ひずみの最大値の所定の範囲は任意に設定することができる。 In the above example, 0% or more and less than 1%, 1% or more and less than 5%, 5% or more and less than 10%, and 10% or more and less than 15% are set as the predetermined range of the maximum plastic strain equivalent to a single axis. The press-formed product 1 is divided into regions corresponding to a predetermined range. If material characteristics (stress-strain curve) are acquired for each predetermined range of the maximum value of plastic strain corresponding to a single axis, the region is obtained. The predetermined range of the maximum value of the plastic strain corresponding to the single axis used for the division can be arbitrarily set.
＜強度解析ステップ＞
強度解析ステップＳ９は、焼き付け硬化材料特性設定ステップＳ７において焼き付け硬化後の材料特性を設定したプレス成形品１の強度解析を行い、プレス成形品１を焼き付け処理した焼き付け処理成形品の強度を推定するものである。
<Strength analysis step>
In the strength analysis step S9, the strength analysis of the press-molded product 1 in which the material properties after bake-hardening are set in the bake-cured material property setting step S7 is performed, and the strength of the bake-processed molded product obtained by baking the press-molded product 1 is estimated. Is.
強度解析ステップＳ９における強度解析は、例えば、図７に示すように、プレス成形品１の下部の２点を拘束した状態でプレス成形品１の上面に強制変位を与えることにより行うことができ、この場合、前記下部の２点における反力をプレス成形品１の強度として求める。 The strength analysis in the strength analysis step S9 can be performed, for example, by applying a forced displacement to the upper surface of the press-formed product 1 in a state where the two lower points of the press-formed product 1 are constrained as shown in FIG. In this case, the reaction force at the two lower points is determined as the strength of the press-formed product 1.
以上、本実施の形態に係る焼き付け処理成形品の強度推定方法によれば、プレス成形中における単軸相当の塑性ひずみの最大値を用いて、焼き付け処理によって焼き付け硬化した材料特性をプレス成形品の材料データとして設定し、該材料データが設定されたプレス成形品について強度解析を行うことにより、焼き付け処理された焼き付け処理成形品の強度を精度良く推定することができる。 As described above, according to the strength estimation method of the baking-processed molded product according to the present embodiment, the material characteristics obtained by baking and hardening by the baking process using the maximum value of the plastic strain corresponding to the single axis during the press-molding are obtained. By setting the material data and performing strength analysis on the press-molded product for which the material data is set, the strength of the baking-processed molded product that has been subjected to the baking process can be accurately estimated.
本発明の作用効果について確認するための検証を行ったので、これについて以下に説明する。
本実施例では、図５に示すような焼き付けにより硬化する鋼板のプレス成形品１を焼き付け処理した焼き付け処理成形品の強度を本発明に係る部材強度推定方法により推定し、その妥当性を検証した。
Since verification for confirming the function and effect of the present invention was performed, this will be described below.
In this example, the strength of the baking-processed molded product obtained by baking the press-formed product 1 of the steel sheet cured by baking as shown in FIG. 5 was estimated by the member strength estimation method according to the present invention, and its validity was verified. .
まず、引張強度440MPa級、板厚2.0mmの焼き付けにより硬化する鋼板（BHT鋼板）に1%、5%、10%および15%の予ひずみを付与して焼き付け処理した後に単軸引張試験を行い、焼き付け硬化した後の材料特性である応力−ひずみ曲線と焼き付け硬化前の予ひずみとの関係を取得した（図６参照）。 First, a uniaxial tensile test was performed after applying pre-strain of 1%, 5%, 10% and 15% to a steel plate (BHT steel plate) that hardens by baking with a tensile strength of 440MPa and a thickness of 2.0mm. The relationship between the stress-strain curve, which is a material characteristic after bake-hardening, and the pre-strain before bake-hardening was obtained (see FIG. 6).
次に、前記焼き付けにより硬化する鋼板をプレス成形品１に絞り成形するプレス成形解析を行い、成形過程におけるプレス成形品１の単軸相当の塑性ひずみを要素毎に算出した。ここで、プレス成形解析には、FEMシミュレーションの汎用ソルバーであるLS-DYNA（登録商標：Livermore Software Technology Corporation）を使用し、動的陽解法を適用した。
そして、プレス成形過程における単軸相当の塑性ひずみの最大値を要素毎に取得した。
Next, press forming analysis was performed in which the steel sheet that was hardened by baking was drawn into the press-formed product 1, and a plastic strain corresponding to a single axis of the press-formed product 1 in the forming process was calculated for each element. Here, a dynamic explicit method was applied to press forming analysis using LS-DYNA (registered trademark: Livermore Software Technology Corporation), which is a general-purpose solver for FEM simulation.
And the maximum value of the plastic strain equivalent to a uniaxial in the press molding process was acquired for every element.
プレス成形解析結果に基づいて取得した単軸相当の塑性ひずみの最大値に応じて、焼き付け硬化前の各予ひずみ（0%、1%、5%、10%および15%）における焼き付け硬化後の材料特性である応力−ひずみ曲線（図６参照）をプレス成形品１の材料データとして設定した。 Depending on the maximum value of plastic strain equivalent to a single axis obtained based on the press forming analysis results, after pre-bake hardening at each pre-strain (0%, 1%, 5%, 10% and 15%) before bake hardening A stress-strain curve (see FIG. 6), which is a material characteristic, was set as the material data of the press-formed product 1.
ここで、焼き付け硬化後の材料特性である応力−ひずみ曲線の設定においては、要素毎に取得した単軸相当の塑性ひずみの最大値が所定の範囲に含まれる要素群からなる領域にプレス成形品１を分割し、該分割した領域毎に焼き付け硬化後の応力−ひずみ曲線を設定した。 Here, in the setting of the stress-strain curve, which is a material characteristic after bake hardening, a press-molded product is formed in an area consisting of element groups in which the maximum value of plastic strain equivalent to a single axis obtained for each element is included in a predetermined range. 1 was divided, and a stress-strain curve after baking and hardening was set for each of the divided areas.
単軸相当の塑性ひずみの最大値の所定範囲と焼き付け硬化後の材料特性について、本実施例では、図６に示す応力−ひずみ曲線を用いた。すなわち、取得した単軸相当の塑性ひずみの最大値が1%未満の要素群からなる領域には予ひずみ0%の応力−ひずみ曲線を、単軸相当の塑性ひずみの最大値が1%以上5%未満の要素群からなる領域には予ひずみ1%の応力−ひずみ曲線を、単軸相当の塑性ひずみの最大値が5%以上10%未満の要素群からなる領域には予ひずみ5%の応力−ひずみ曲線を、単軸相当の塑性ひずみの最大値が10%以上15%未満の要素群からなる領域には予ひずみ10%の応力−ひずみ曲線を、単軸相当の塑性ひずみの最大値が15%以上の要素群からなる領域には予ひずみ15%の応力−ひずみ曲線を、各領域における材料データとして設定した。 In this example, the stress-strain curve shown in FIG. 6 was used for the predetermined range of the maximum value of plastic strain corresponding to a single axis and the material characteristics after baking hardening. That is, a stress-strain curve with a pre-strain of 0% is applied to the region consisting of element groups with a maximum value of plastic strain equivalent to less than 1%, and the maximum value of plastic strain equivalent to more than 1% A stress-strain curve with a pre-strain of 1% is applied to the region consisting of element groups of less than 5%, and a pre-strain of 5% is applied to the region consisting of element groups where the maximum plastic strain equivalent to a single axis is 5% or more and less than 10%. The stress-strain curve shows the stress-strain curve with a pre-strain of 10% and the maximum value of plastic strain equivalent to a uniaxial in the region consisting of elements with a maximum plastic strain equivalent to 10% or less but less than 15%. A stress-strain curve with a pre-strain of 15% was set as material data in each region in a region composed of element groups with 15% or more.
そして、上記のように焼き付け硬化後の材料特性を設定したプレス成形品１の強度解析を行い、プレス成形品１の強度を算出した。強度解析では、図４に示すように、プレス成形品１の下部の２点を拘束して上面に強制変位を与えたときの前記２点における反力の履歴を計測し、該反力の最大値をプレス成形品１の強度とした。 And the strength analysis of the press molded product 1 which set the material characteristic after baking hardening as mentioned above was performed, and the strength of the press molded product 1 was computed. In the strength analysis, as shown in FIG. 4, the reaction force history at the two points when the two lower points of the press-formed product 1 are constrained and the upper surface is forcedly displaced is measured, and the maximum of the reaction force is measured. The value was the strength of the press-formed product 1.
本実施例では、プレス成形品１を焼き付け処理した焼き付け処理成形品の強度を上記手順により推定したものを発明例とした。さらに、比較対象として、従来利用されてきた指標である成形直後の単軸相当の塑性ひずみの値（比較例１）、および、成形中の累積相当塑性ひずみ（比較例２）を用いて焼き付け硬化後の材料特性をプレス成形品１の材料データとして設定し、その強度解析を行った。 In the present embodiment, an example of the invention was obtained by estimating the strength of the baking-processed molded product obtained by baking the press-formed product 1 by the above procedure. Further, as a comparison object, baking hardening is performed by using a value of plastic strain equivalent to uniaxial immediately after molding (Comparative Example 1) and a cumulative equivalent plastic strain during molding (Comparative Example 2), which are indexes conventionally used. The later material characteristics were set as the material data of the press-formed product 1, and the strength analysis was performed.
これらの成形直後の単軸相当の塑性ひずみや累積相当塑性ひずみを用いた焼き付け硬化後の材料特性の設定に関しては、上述の発明例と同様、成形直後の単軸相当の塑性ひずみ又は累積相当塑性ひずみをプレス成形品１に付与された予ひずみとし、当該予ひずみに対応する応力−ひずみ曲線をプレス成形品１の材料データとして設定した。 Regarding the setting of material properties after baking hardening using plastic strain equivalent to uniaxial or cumulative equivalent plastic strain immediately after molding, as in the above-described invention example, plastic strain equivalent to uniaxial immediately after molding or cumulative equivalent plasticity. The strain was set as the prestrain applied to the press-formed product 1, and the stress-strain curve corresponding to the pre-strain was set as the material data of the press-formed product 1.
さらに、発明例、比較例１および比較例２におけるプレス成形品１の強度の解析値を、実際に焼き付けにより硬化する鋼板を用いてプレス成形および焼き付け処理した焼き付け処理成形品の強度を測定した実験値と比較した。 Furthermore, the analysis value of the strength of the press-formed product 1 in the invention example, the comparative example 1 and the comparative example 2 was measured using the steel sheet that was actually hardened by baking, and the strength of the baking-processed molded product was measured. Compared with value.
図８に、プレス成形品１の強度解析の結果を示す。図８において縦軸は、焼き付け処理成形品の強度の実験値と強度解析により算出した解析値との比である。図８より、比較例１および比較例２に比べると発明例における強度の解析値は、実験値と最も良く一致していることがわかる。 FIG. 8 shows the result of strength analysis of the press-formed product 1. In FIG. 8, the vertical axis represents the ratio between the experimental value of the strength of the baking-processed molded product and the analytical value calculated by the strength analysis. From FIG. 8, it can be seen that compared to Comparative Example 1 and Comparative Example 2, the analytical value of the strength in the inventive example is the best match with the experimental value.
以上、本発明に係る強度推定方法によれば、焼き付けにより硬化する鋼板のプレス成形品を焼き付け処理した焼き付け処理品における焼き付け硬化後の材料特性を正確に設定することができ、焼き付け処理品の強度を良好に推定できることが実証された。 As described above, according to the strength estimation method according to the present invention, it is possible to accurately set the material properties after baking hardening in the baking processed product obtained by baking the press-formed product of the steel sheet that is hardened by baking, and the strength of the baking processed product. It was proved that can be estimated well.
１ プレス成形品
３ 縦壁部
1 Press-molded product 3 Vertical wall
Claims (2)
予ひずみを付与して焼き付け処理した焼き付けにより硬化する鋼板の焼き付け硬化後の材料特性と前記予ひずみとの関係を取得する焼き付け硬化材料特性取得ステップと、
前記焼き付けにより硬化する鋼板を前記プレス成形品にプレス成形するプレス成形解析を行い、プレス成形過程における単軸相当の塑性ひずみを算出するプレス成形解析ステップと、
該算出した単軸相当の塑性ひずみのプレス成形過程のひずみ経路における最大値を求める単軸相当の塑性ひずみ最大値取得ステップと、
前記焼き付け硬化材料特性取得ステップで取得した焼き付け硬化後の材料特性と予ひずみとの関係を用いて、前記単軸相当の塑性ひずみの最大値に対応する焼き付け硬化後の材料特性を前記プレス成形品の材料データとして設定する焼き付け硬化材料特性設定ステップと、
該焼き付け硬化後の材料特性が設定された前記プレス成形品の強度解析を行い、前記焼き付け処理成形品の強度を推定する強度解析ステップを有することを特徴とする焼き付け処理成形品の強度推定方法。 A method for estimating the strength of a baking-processed molded product for estimating the strength of a baking-processed molded product obtained by baking a press-formed product of a steel sheet that is hardened by baking,
A bake hardened material property acquisition step for acquiring a relationship between the pre-strain and material properties of the steel sheet that is hardened by baking that has been subjected to baking treatment with pre-strain, and
A press forming analysis step for performing press forming analysis for press forming the steel sheet to be hardened by the baking into the press formed product, and calculating a plastic strain corresponding to a single axis in the press forming process;
A uniaxial equivalent plastic strain maximum value obtaining step for obtaining a maximum value in a strain path of the press molding process of the calculated uniaxial equivalent plastic strain;
Using the relationship between the pre-strain and the material property after bake hardening acquired in the bake hardened material property acquisition step, the material property after bake hardening corresponding to the maximum value of the plastic strain equivalent to the uniaxial is the press-formed product. Bake hardened material characteristic setting step to set as material data,
A strength estimation method for a baking-processed molded product, comprising: a strength analysis step of performing strength analysis of the press-molded product in which material characteristics after the baking and curing are set, and estimating the strength of the baking-processed molded product.
前記焼き付け硬化材料特性設定ステップは、前記単軸相当の塑性ひずみの最大値が所定の範囲に含まれる要素群からなる領域に前記プレス成形品を分割し、該分割した領域毎に前記焼き付け硬化後の材料特性を設定することを特徴とする請求項１記載の焼き付け処理成形品の強度推定方法。 The single axis equivalent plastic strain maximum value obtaining step obtains the maximum value of the plastic strain equivalent to the single axis for each element,
The bake-hardened material property setting step divides the press-formed product into regions composed of element groups in which the maximum value of plastic strain corresponding to the single axis is included in a predetermined range, and after the bake-hardening for each divided region. The method for estimating the strength of a baked molded article according to claim 1, wherein the material characteristics are set.
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| KR102143835B1 (en) | 2020-08-12 |
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| CN109891209B (en) | 2021-06-22 |
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