JP3756798B2

JP3756798B2 - Metal pipe workability evaluation apparatus and evaluation method

Info

Publication number: JP3756798B2
Application number: JP2001321521A
Authority: JP
Inventors: 美昭伊丹
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2001-02-22
Filing date: 2001-10-19
Publication date: 2006-03-15
Anticipated expiration: 2021-10-19
Also published as: JP2002323419A

Description

【０００１】
【発明の属する技術分野】
本発明は鋼管，チタン管等の金属管の２次加工性を評価するための装置及び方法に関する。特に管の塑性異方性ｒ値や加工硬化指数ｎ値や肉厚ｔ、肉厚管径比鋼管寸法ｔ／Ｄなどの違いによる金属管の円周方向の加工性を一律に評価することができる。特に近年自動車用の構造部材のハイドロフォームを用いた成形を行う鋼管の製造時の加工性評価に適している。
【０００２】
【従来の技術】
一般に鋼管の材料の機械的な特性を評価する方法はＪＩＳ１１号の管の引張試験やＪＩＳ１２号による鋼管から弧状引張試験を行う方法が用いられている。
【０００３】
【発明が解決しようとする課題】
前記の材料試験法は鋼管の軸方向の単軸引っ張りの応力状態での応力−ひずみの関係しか評価できないという問題がある。
本発明は、金属管の種々の加工での変形に近い状態での材料の加工性を評価する装置及び評価方法を提供することを目的とする。
【０００４】
【課題を解決するための手段】
係る課題を解決するため、本発明の要旨とするところは、
（１）金属管１の両端を掴む支持部２と、金属管内へ流体圧を負荷する内圧負荷増圧装置３と，金属管に軸方向に応力を負荷する軸方向荷重制御装置４と、金属管の軸方向歪測定装置５と，金属管の円周方向径測定装置６と、前記軸方向歪測定装置５により測定した金属管軸方向歪と前記円周方向径測定装置６により測定した金属管円周方向径に基づいて金属管の軸方向に働く応力σ_φと金属管の円周方向に働く応力σ_θの応力比σ_φ／σ_θを制御する応力比制御手段７を有することを特徴とする金属管の加工性評価装置，
（２）金属管の両端を支持し、金属管内の軸方向に加える流体圧と金属管の軸方向に加える応力を制御しながら金属管の２次加工性を評価する方法において、金属管の軸方向歪と円周方向径を測定し、前記軸方向歪と前記円周方向径に基づいて金属管の軸方向に働く応力σ_φと金属管の円周方向に働く応力σ_θの応力比σ_φ／σ_θを求め、金属管が破断するまで前記応力比が一定となるように金属管に加える流体圧に応じて金属管の軸方向に加える応力を制御することを特徴とする金属管の加工性評価方法，にある。
【０００５】
【発明の実施の形態】
本発明を詳細に説明する。
図１（ａ）〜（ｃ）に本発明の実施例の評価装置を示す。
鋼管１をシールし、かつ軸方向の荷重の負荷により鋼管がすべらないように支持部２で左右を支持し、軸方向に応力を付与するシリンダーを鋼管両端に配置する。内圧負荷増圧装置３は金属管内に水，エマルジョン系の潤滑材やソリブル油等の水溶性潤滑材を添加した水等の流体に圧力を加える際に、油圧ポンプにより発生した１次圧の面積比を小さくさせて、増圧させる。
油圧等の１次圧の圧力を電磁減圧比例弁やサーボ弁を用いて１次圧を制御し、２次側の液体の圧力を増加させるものである。増圧装置としては、単動型、複動型があるが、どちらを用いてもよい。
【０００６】
軸方向の荷重制御装置４はサーボバルブを用いてシリンダーのロッドとヘッド側の圧力と受圧面積からデジタルシグナルプロセッサー（ＤＳＰ）を用いたデジタル制御を行う。鋼管の着脱等の位置決めを行う場合の位置制御はシリンダーに内蔵したデジタル変位計を用いた精密な位置のフィードバック制御により行う。
【０００７】
まず鋼管１と支持部２を位置あわせし、鋼管１を固定する、その後、内圧の上昇に伴い、軸方向の荷重制御をシリンダーのロッド受圧面積とロッド負荷圧力の積と、ヘッド受圧面積とヘッドの負荷圧力との積の差分から計算できる荷重により鋼管へ力を負荷するシリンダーの軸荷重制御を行う。荷重はロードセルなどで直接測定するか、圧力検出から軸荷重を求めて制御してもよい。
【０００８】
また、軸方向、円周方向の曲率により応力状態は変化するので、管中央部に間隔をＬ_０とする２本の罫書線（マーカー）を描き（図１（ｂ）参照）、軸方向歪み測定装置５としてリニアＣＣＤを用いた画像処理により罫書線の間隔の変化量から軸方向の歪を測定し，後述する（１３）式により軸方向の歪を求め，円周方向径測定装置６としてリニアCCDセンサーを内蔵したカメラを管軸方向に３箇所設置し，半径方向変位を非接触のレーザで３箇所測定し、軸方向の曲率半径Ｒ_Ｚ［ｍｍ］を求めた
軸方向の曲率Ｒ_Ｚは管軸方向の３点の測定点より３点を通る円の計算より，求められる。測定位置を(x₁,y₁),(x₂,y₂),(x₃,y₃)とすると
B=（(x₁−x₃)(x₁ ²−x₂ ²＋y₁ ²−y₂ ²)−（ｘ₁−ｘ₂）(x₁ ²−x₃ ²＋y₁ ²−y₃ ²) ）
/{(−2(y₁−y₂)(x₁−x₃)＋2(y₁−y₃)(x₁−x₂)) （１）
A=(−2B（ｙ₁−ｙ₂）＋ｘ₁ ²−ｘ₂ ²＋ｙ₁ ²−ｙ₂ ²）/(2(x₁−x₂)) （２）
R_z=SQR（（ｘ₂−A）²＋(y₂−B)²）（３）
中央部のセンサーの半径方向位置から求めた周方向の曲率半径Ｒ_Ｂ［ｍｍ］は以下のように求められる。
周方向の曲率半径Ｒ_Ｂは初期の鋼管径Ｄ［ｍｍ］と加圧により貼り出した量ΔＲ_Ｂ［ｍｍ］により，
Ｒ_Ｂ＝Ｄ／２+ΔＲ_Ｂにより求められる。
応力比制御手段７では、前記軸方向歪測定装置５により測定した金属管軸方向歪と前記円周方向径測定装置６により測定した金属管円周方向径に基づいて，後述するように金属管の軸方向に働く応力σ_φと金属管の円周方向に働く応力σ_θの応力比σ_φ/σ_θを算出し、金属管が破断するまで前記応力比が一定となるように金属管に加える流体圧に応じて金属管の軸方向に加える応力を制御する。
【０００９】
円周方向径測定装置６の測定結果に基づいて算出した曲率を用いて応力計算を行い（計算式は後述）、内圧負荷時に発生する鋼管端面受圧部に発生する荷重に加え、前述の応力状態によって規定されるシリンダー軸に与える荷重（計算式は後述）にてシリンダー軸荷重を制御する。また、内圧により周方向に鋼管が変形すると、管外径が変化し、カメラ５と罫書線までの距離が変化するので，円周方向径測定の結果を用いて補正する。
後述の（１２）式により鋼管の初期の鋼管までの距離をＨ₀として、鋼管の貼り出し量ΔＲ_Ｂだけ近づく分の距離変化が補正できる。
また、鋼管の変形により、肉厚も変化するので管円周方向および管軸方向の２軸ひずみから体積一定の条件より肉厚ひずみを算出して（計算式は後述）、肉厚を求めて上述の応力の釣り合い計算を行い（計算式は後述）、軸荷重を決定することを時事刻々繰り返し制御を行う。
【００１０】
以下に計算方法を詳細に説明する。
鋼管の肉厚中央の主曲率半径を鋼管の子午線方向曲率半径Ｒ_φ［ｍｍ］、円周方向曲率半径Ｒ_θ［ｍｍ］とする。
金属管の軸方向に働く応力σ_φ［ＭＰa］，金属管の円周方向に働く応力σ_θ［MPa］とする。
内圧ｐ［MPa］、軸方向荷重W［N］が作用すると、力の釣り合い条件から子午線方向の釣り合いは

となり、管の厚みをｔ［ｍｍ］とすれば、内圧との釣り合いは

となる。
ここで応力比α＝σ_φ/σ_θとすると、内圧によって変化する軸方向荷重を示すＷ_ｐ［ＭＰa］は

となる。内圧ｐが作用したときに、鋼管軸方向に対して圧力のかかる冶具端面荷重Ｗ_Ａは（４）式で表せるので、（５）式に示すように冶具端面荷重Ｗ_Ａ［Ｎ］と形状変化と応力比により規定される荷重Ｗ_ｐ［Ｎ］にて制御を行う。

Ｒ_Ｚ：3点の軸方向に配置したセンサーによる半径方向位置より求めた子午線方向外面半径［ｍｍ］

Ｒ_Ｂ：中央部のセンサーの半径方向位置から求めた周方向外面半径［ｍｍ］
管子午線方向の長さＬ［ｍｍ］は

となる。ここで、観測点からの距離変化（カメラから被測定物との距離）を考慮して，カメラからの距離をＨ₀［ｍｍ］，鋼管中央部の変位ΔＲ_Ｂ［ｍｍ］_、Ｌ₀は素管の罫書き長さＬ_Ｎ［ｍｍ］とすれば、

となる。内圧ｐに応じて応力比α＝σ_φ/σ_θを決め、軸方向の荷重を変形した管中央部の子午線、周方向曲率に応じて制御することで、一定の応力状態を保つことが可能となる。
α＝σ_φ/σ_θを応力比として管軸方向の罫書き線の長さ変化より、子午線方向ひずみε_φ、周方向ひずみε_θ、板厚方向ひずみε_ｔはそれぞれ下記（１3）〜（１5）式のようになる。

変形中の鋼管の肉厚は周方向の応力負荷のみであれば
α＝０（16）
となり、子午線と周方向の応力比が１：２であればα＝０．５で平面ひずみ状態となる。
本発明では管中央部分の子午線の長さ変化と周方向の径（曲率）、子午線方向の曲率の変化を考慮し管中央部の応力状態を制御して子午線・周方向のひずみも求めることができる。
よって、ハイドロフォーム加工時にいろいろ方向に応力が作用するが、本発明のように応力比を一定にして制御することにより、応力比の違いによる鋼管のハイドロフォーム加工性が評価できる。これにより、軸方向と円周方向の主曲率で管中央部の円周方向の応力σ_θと子午線方向応力σ_φの応力比を変えて試験を行うことで、鋼管の各応力比での応力歪線図と破断限界線が得られる。
このように応力状態を一定にして、鋼管を変形させ、破断までの挙動を捉えることにより、板材と同様な加工限界を求めることができる。
【００１１】
【実施例】
第２図に本発明の装置により、φ６０．５ｍｍ肉厚ｔ＝１．６ｍｍの冷延板を成形した長さ３００ｍｍの鋼管を用いてσ_φ/σ_θ＝０の場合と平面歪の状態σ_φ/σ_θ＝０．５の場合に加工硬化係数ｎ値を変えた場合（鋼管成形のひずみが大きい場合と小さい場合）のひずみ履歴を示す。
同一板材を鋼管に成形・溶接した溶接管を製造した場合、加工硬化係数が高い方が、加工限界が高く、加工性に優れることがわかる。
このように応力状態を一定にして、鋼管を変形させ、破断までの挙動を捉えることにより、板材と同様な加工限界を求めることができる。
円周方向単軸状態でのひずみから、管円周方向の塑性異方性を表すｒ_θ値を測定することが可能となる（第３図）。ｒ_θは単軸応力状態（管軸方向の応力がゼロのとき）で円周方向に膨くらむ際、軸方向と肉厚方向の歪増分（18式）より計算できる。
ｒ_θ値は各歪の変化量から計算でき、ε_φ，ε_θは計測により求まり、ある時間ごとの歪の変化量（増分）は体積一定の条件より（14）式で表せる。
ｄε_φ+ｄε_θ+ｄε_ｔ＝0 （17）の関係式から
肉厚方向の歪増分ｄε_ｔがもとめられ円周方向の異方性を示すｒ_θ値
ｒ_θ＝ｄε_φ/ｄε_ｔ（18）
を用いて算出できる。
ほぼ板材と同等な板材の円周方向の塑性異方性ｒ_θ値を得られていることが確認できている。
これにより従来の評価が困難であった、鋼管の塑性異方性を求めることが可能であり、かつ軸方向および円周方向の応力−ひずみ関係も求めることができた。
上述の計算により求められた軸方向は縦軸σ_φと、横軸ε_φを、円周方向は縦軸σ_θ、横軸にε_θをプロットすればよい。
【００１２】
【発明の効果】
以上詳述したように、従来技術では鋼管においては管引張りや切り出しによる引張り試験では軸（子午線）方向の応力−ひずみ関係しか捉えることができなかったが、本発明により、円周方向塑性異方性：ｒ_θ値を単軸応力場で測定することや、材料異方性により歪履歴が変化する挙動も捕らえることが可能である等優れた効果を有する。
【図面の簡単な説明】
【図１】本発明例の試験装置を示す全体概要図で、図１（ａ）は、初期状態を示す全体概要平面図、図１（ｂ）は、初期状態を示す全体概要立面図、図１（ｃ）は、試験時を示す全体概要図平面図。
【図２】本発明の制御に用いる鋼管の変形を示す説明図。
【図３】本発明例の評価装置を用いて、加工ｎ値を変えた場合の破断限界線を求めた説明図。
【符号の説明】
１金属管（鋼管）
２支持部
３内圧負荷増圧装置
４軸方向荷重制御装置（シリンダーのデジタルサーボ制御）
５軸方向歪測定装置
６円周方向径測定装置
７応力比制御手段[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus and method for evaluating secondary workability of a metal pipe such as a steel pipe or a titanium pipe. In particular, it is possible to uniformly evaluate the workability in the circumferential direction of a metal pipe due to differences in the plastic anisotropy r value, work hardening index n value, wall thickness t, wall thickness ratio steel pipe dimension t / D, etc. it can. In particular, in recent years, it is suitable for evaluation of workability at the time of manufacturing a steel pipe that is molded using a hydroform of a structural member for automobiles.
[0002]
[Prior art]
In general, as a method for evaluating the mechanical characteristics of the material of the steel pipe, there are used a JIS No. 11 pipe tensile test or a JIS No. 12 steel pipe arc tensile test.
[0003]
[Problems to be solved by the invention]
The material test method has a problem that only the stress-strain relationship in the uniaxial tensile stress state in the axial direction of the steel pipe can be evaluated.
An object of this invention is to provide the apparatus and evaluation method which evaluate the workability of the material in the state close | similar to the deformation | transformation in the various process of a metal pipe.
[0004]
[Means for Solving the Problems]
In order to solve the problem, the gist of the present invention is as follows:
(1) A support portion 2 that grips both ends of the metal tube 1, an internal pressure load intensifier 3 that applies fluid pressure into the metal tube, an axial load control device 4 that applies stress in the axial direction to the metal tube, and a metal Pipe axial strain measuring device 5, metal tube circumferential diameter measuring device 6, metal tube axial strain measured by axial strain measuring device 5 and metal measured by circumferential diameter measuring device 6 It has stress ratio control means 7 for controlling the stress ratio σ _φ / σ _θ between the stress σ _φ acting in the axial direction of the metal tube and the stress σ _θ acting in the circumferential direction of the metal tube based on the pipe circumferential direction diameter. A characteristic metal pipe workability evaluation device,
(2) A method for evaluating the secondary workability of a metal tube while supporting both ends of the metal tube and controlling the fluid pressure applied in the axial direction in the metal tube and the stress applied in the axial direction of the metal tube. Measure the direction strain and the circumferential diameter, and based on the axial strain and the circumferential diameter, the stress ratio σ of the stress σ _φ acting in the axial direction of the metal tube and the stress σ _θ acting in the circumferential direction of the metal tube seeking _phi / sigma _theta, of the metal tube, characterized in that to control the stress applied to the axial direction of the metal tube in accordance with the fluid pressure applied to the metal tube such that the stress ratio is kept constant until the metal tube is broken It is in the processability evaluation method.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail.
1A to 1C show an evaluation apparatus according to an embodiment of the present invention.
The steel pipe 1 is sealed, and left and right are supported by the support portion 2 so that the steel pipe does not slip due to an axial load, and cylinders that apply stress in the axial direction are disposed at both ends of the steel pipe. The internal pressure load intensifier 3 is an area of the primary pressure generated by the hydraulic pump when pressure is applied to a fluid such as water, water-based lubricants such as emulsion-based lubricants and solubilized oils added in metal pipes. Increase the pressure by decreasing the ratio.
The primary pressure such as hydraulic pressure is controlled by using an electromagnetic pressure reducing proportional valve or a servo valve to increase the secondary liquid pressure. As the pressure booster, there are a single-acting type and a double-acting type, either of which may be used.
[0006]
The axial load control device 4 uses a servo valve to perform digital control using a digital signal processor (DSP) from the cylinder rod and head side pressure and pressure receiving area. The position control when positioning such as attaching and detaching the steel pipe is performed by precise position feedback control using a digital displacement meter built in the cylinder.
[0007]
First, the steel pipe 1 and the support portion 2 are aligned, and the steel pipe 1 is fixed. Then, as the internal pressure increases, the axial load control is performed by multiplying the product of the rod pressure receiving area of the cylinder and the rod load pressure, the head pressure receiving area and the head. The axial load control of the cylinder that applies force to the steel pipe is performed by the load that can be calculated from the difference between the product and the load pressure. The load may be directly measured with a load cell or the like, or may be controlled by obtaining the axial load from pressure detection.
[0008]
In addition, since the stress state changes depending on the curvature in the axial direction and the circumferential direction, two ruled lines (markers) with an interval L ₀ are drawn at the center of the tube (see FIG. 1B), and the axial distortion As the measuring device 5, the axial distortion is measured from the amount of change in the interval between the ruled lines by image processing using a linear CCD, and the axial distortion is obtained by the following equation (13). the camera with a built-in linear CCD sensor placed three in the tube axis direction, the radial displacement is measured three laser non-contact, the curvature of the axial radius R _Z curvature in the axial direction obtained a _[mm] R _Z Is obtained by calculating a circle passing through three points from three measurement points in the tube axis direction. If the measurement position is (x ₁ , y ₁ ), (x ₂ , y ₂ ), (x ₃ , y ₃ )
B = ((x ₁ −x ₃ ) (x ₁ ² −x ₂ ² + y ₁ ² −y ₂ ² ) − (x ₁ −x ₂ ) (x ₁ ² −x ₃ ² + y ₁ ² −y ₃ ² ) )
/ {(− 2 (y ₁ −y ₂ ) (x ₁ −x ₃ ) +2 (y ₁ −y ₃ ) (x ₁ −x ₂ )) (1)
A = (− 2B (y ₁ −y ₂ ) + x ₁ ² −x ₂ ² + y ₁ ² −y ₂ ² ) / (2 (x ₁ −x ₂ )) (2)
R _z = SQR ((x ₂ −A) ² + (y ₂ −B) ² ) (3)
The radius of curvature R _B [mm] in the circumferential direction obtained from the radial position of the sensor in the center is obtained as follows.
The amount ΔR _B [mm] was put up by the circumferential direction of the radius of curvature _{R B} Initial steel pipe diameter D [mm] and a pressure,
R _B = D / 2 + ΔR _B
In the stress ratio control means 7, as will be described later, the metal tube axial strain measured by the axial strain measuring device 5 and the metal tube circumferential diameter measured by the circumferential diameter measuring device 6 are used. The stress ratio σ _φ / σ _θ between the stress σ _φ acting in the axial direction of the metal and the stress σ _θ acting in the circumferential direction of the metal tube is calculated, and the stress ratio is kept constant until the metal tube breaks. The stress applied in the axial direction of the metal tube is controlled according to the applied fluid pressure.
[0009]
Stress calculation is performed using the curvature calculated based on the measurement result of the circumferential diameter measuring device 6 (the calculation formula will be described later), and in addition to the load generated in the steel pipe end face pressure receiving portion generated at the time of internal pressure load, the stress state described above The cylinder shaft load is controlled by the load applied to the cylinder shaft defined by (the calculation formula will be described later). Further, when the steel pipe is deformed in the circumferential direction due to the internal pressure, the outer diameter of the pipe is changed and the distance between the camera 5 and the ruled line is changed. Therefore, the correction is made using the result of the circumferential diameter measurement.
The distance to the initial steel of the steel pipe by later-described equation (12) as H _0, minute distance varies toward amount [Delta] R _B out adhesion of the steel pipe can be corrected.
Also, since the wall thickness changes due to the deformation of the steel pipe, the wall thickness strain is calculated from the biaxial strain in the tube circumferential direction and the tube axis direction under the condition of constant volume (the calculation formula will be described later), and the wall thickness is obtained. The balance calculation of the stress described above is performed (the calculation formula will be described later), and the axial load is determined and controlled repeatedly over time.
[0010]
The calculation method will be described in detail below.
The main curvature radius at the thickness center of the steel pipe is defined as a meridian direction curvature radius R _φ [mm] and a circumferential curvature radius R _θ [mm] of the steel pipe.
The stress σ _φ [MPa] acting in the axial direction of the metal tube and the stress σ _θ [MPa] acting in the circumferential direction of the metal tube are assumed.
When internal pressure p [MPa] and axial load W [N] are applied, the balance in the meridian direction is

If the thickness of the tube is t [mm], the balance with the internal pressure is

It becomes.
Here, if the stress ratio α = σ _φ / σ _θ , W _p [MPa] indicating the axial load that changes depending on the internal pressure is

It becomes. When the internal pressure p is applied, since the jig end surface load W _A-consuming pressure to the steel pipe axis direction expressed by equation (4), (5) a jig end surface load W _{A [N]} as shown in equation shape change And the load W _p [N] defined by the stress ratio.

R _Z : meridian direction outer surface radius [mm] obtained from radial position by sensors arranged in three axial directions

R _B : Radius in the circumferential direction obtained from the radial position of the sensor in the center part [mm]
The length L [mm] in the meridian direction is

It becomes. Here, taking into account the change in distance from the observation point (distance from the camera to the object to be measured), the distance from the camera is H ₀ [mm], the displacement ΔR _B [mm] _and L ₀ of the steel pipe center is prime. If the ruled length L _N [mm] of the tube is

It becomes. It is possible to maintain a constant stress state by determining the stress ratio α = σ _φ / σ _θ according to the internal pressure p and controlling the axial load according to the meridian and circumferential curvature of the deformed tube center. It becomes.
From the change in the length of the scribe line in the tube axis direction with α = σ _φ / σ _θ as the stress ratio, the meridian direction strain ε _φ , the circumferential direction strain ε _θ , and the plate thickness direction strain ε _t are the following (13) to ( 15) It becomes like a formula.

If the thickness of the steel pipe being deformed is only the stress load in the circumferential direction, α = 0 (16)
If the stress ratio between the meridian and the circumferential direction is 1: 2, a plane strain state is obtained when α = 0.5.
In the present invention, the meridian / circumferential strain can be obtained by controlling the stress state in the central part of the pipe in consideration of the length change of the meridian at the central part of the pipe, the circumferential diameter (curvature), and the change of the meridian direction of curvature. it can.
Therefore, stress acts in various directions during hydroforming, but by controlling the stress ratio to be constant as in the present invention, the hydroforming workability of the steel pipe due to the difference in stress ratio can be evaluated. As a result, the stress at each stress ratio of the steel pipe is tested by changing the stress ratio between the circumferential stress σ _θ and the meridian stress σ _{φ at} the center of the pipe with the principal curvature in the axial direction and the circumferential direction. Strain diagram and break limit line are obtained.
In this way, by making the stress state constant, deforming the steel pipe, and capturing the behavior up to the fracture, the processing limit similar to that of the plate material can be obtained.
[0011]
【Example】
FIG. 2 shows the case of σ _φ / σ _θ = 0 and the state of plane strain σ using a 300 mm long steel pipe formed by cold-rolled sheet of φ60.5 mm wall thickness t = 1.6 mm by the apparatus of the present invention. _This shows the strain history when the work hardening coefficient n value is changed when _φ / σ _θ = 0.5 (when the steel pipe forming strain is large and small).
When a welded pipe is manufactured by welding and molding the same plate material to a steel pipe, it can be seen that a higher work hardening coefficient has a higher processing limit and excellent workability.
In this way, by making the stress state constant, deforming the steel pipe, and capturing the behavior up to the fracture, the processing limit similar to that of the plate material can be obtained.
From the strain in the uniaxial state in the circumferential direction, it is possible to measure the _rθ value representing the plastic anisotropy in the circumferential direction of the tube (FIG. 3). r _theta can be calculated from the single-axis stress state when (tube axis direction of the stress at zero) dazzling Rise circumferentially, strain increments of axial and thickness direction (18 type).
The _rθ value can be calculated from the amount of change in each strain, ε _φ and ε _θ can be obtained by measurement, and the amount of change (increment) in strain per time can be expressed by equation (14) from the condition of constant volume.
_{_{_{dε φ + dε θ + dε t}}} = 0 (17) r θ value indicating anisotropy in the circumferential direction is determined distortion increment d? _t in the thickness direction from the relation of _{_{_{r θ = dε φ / dε t}}} (18 )
Can be used to calculate.
It has been confirmed that the plastic anisotropy _rθ value in the circumferential direction of the plate material substantially equivalent to the plate material is obtained.
As a result, it was possible to determine the plastic anisotropy of the steel pipe, which was difficult to evaluate conventionally, and to determine the stress-strain relationship in the axial direction and the circumferential direction.
The axis direction obtained by the above calculation may be plotted with the vertical axis σ _φ and the horizontal axis ε _φ , the circumferential direction with the vertical axis σ _θ , and the horizontal axis with ε _θ .
[0012]
【The invention's effect】
As described in detail above, in the conventional technology, in the steel pipe, only the stress-strain relationship in the axial (meridian) direction can be grasped in the tensile test by pipe pulling and cutting, but according to the present invention, the circumferential plastic anisotropic sex: and measuring the r _theta value in uniaxial stress field, having equal excellent effect strain history can be captured even behavior varies depending on the material anisotropy.
[Brief description of the drawings]
FIG. 1 is an overall schematic diagram showing a test apparatus of an example of the present invention, FIG. 1 (a) is an overall schematic plan view showing an initial state, and FIG. 1 (b) is an overall schematic elevation view showing an initial state; FIG.1 (c) is a general | schematic schematic top view which shows the time of a test.
FIG. 2 is an explanatory diagram showing deformation of a steel pipe used for control according to the present invention.
FIG. 3 is an explanatory diagram for determining a fracture limit line when the machining n value is changed using the evaluation apparatus of the present invention example.
[Explanation of symbols]
1 Metal pipe (steel pipe)
2 Support section 3 Internal pressure load booster 4 Axial load controller (digital servo control of cylinder)
5 Axial strain measuring device 6 Circumferential diameter measuring device 7 Stress ratio control means

Claims

A support part (2) that grips both ends of the metal pipe (1), an internal pressure load intensifier (3) that applies fluid pressure into the metal pipe, and an axial load control device that applies axial stress to the metal pipe ( 4), the axial strain measuring device (5) of the metal tube, the circumferential diameter measuring device (6) of the metal tube, the axial strain of the metal tube measured by the axial strain measuring device (5), and the Stress ratio σ _φ / σ of stress σ _φ acting in the axial direction of the metal tube and stress σ _θ acting in the circumferential direction of the metal tube based on the circumferential diameter of the metal tube measured by the circumferential diameter measuring device (6) An apparatus for evaluating the workability of a metal tube, comprising stress ratio control means (7) for controlling _θ .

In a method for evaluating the secondary workability of a metal tube while supporting both ends of the metal tube and controlling the fluid pressure applied in the axial direction in the metal tube and the stress applied in the axial direction of the metal tube, The circumferential diameter is measured, and the stress ratio σ _φ / σ of the stress σ _φ acting in the axial direction of the metal tube and the stress σ _θ acting in the circumferential direction of the metal tube based on the axial strain and the diameter in the circumferential direction _θ is obtained, and the processability evaluation of the metal tube is characterized by controlling the stress applied in the axial direction of the metal tube according to the fluid pressure applied to the metal tube so that the stress ratio is constant until the metal tube breaks Method.