JP2002323419A - Device and method for evaluating workability of metallic pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device and method for evaluating workability of metallic pipe by which the workability of a steel pipe in the circumferential direction can be evaluated by evaluating the material characteristics of the pipe in the circumferential direction required for expanding the pipe by hydroforming, etc., and so on. SOLUTION: The device for evaluating workability of metallic pipe is provided with supporting sections 2 which seize both ends of the metallic pipe 1, an internal pressure applying and increasing device 3 which applies a fluid pressure into the pipe 1, and an axial load controller 4 which applies an axial stress to the pipe 1. The device is also provided with an axial strain measuring instrument 5 which measures the axial strain of the pipe 1, a circumferential diameter measuring instrument 6 which measures the circumferential diameter of the pipe 1, and a stress ratio control means 7 which controls the ratio σϕ /σθ of the stress σϕworking in the axial direction of the pipe 1 to the stress σθ working in the circumferential direction of the pipe 1 based on the axial strain measured by means of the instrument 5 and the circumferential diameter of the pipe 1 measured by means of the instrument 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an apparatus and a method for evaluating the secondary workability of a metal pipe such as a steel pipe and 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 pipe plastic anisotropy r value, work hardening index n value, wall thickness t, wall thickness ratio steel pipe size t / D, etc. it can.
Particularly, in recent years, it is suitable for workability evaluation at the time of manufacturing a steel pipe in which a structural member for an automobile is formed using a hydroform.

[0002]

2. Description of the Related Art Generally, as a method for evaluating the mechanical properties of a steel pipe material, a method of performing a JIS No. 11 pipe tensile test or a method of performing an JIS No. 12 arc-shaped tensile test on a steel pipe is used.

[0003]

However, the above-mentioned material testing method has a problem that only a stress-strain relationship in a state of uniaxial tensile stress in a steel pipe in an axial direction can be evaluated. The present invention
It is an object of the present invention to provide an apparatus and an evaluation method for evaluating workability of a material in a state close to deformation in various processes of a metal tube.

[0004]

[MEANS FOR SOLVING THE PROBLEMS]
Therefore, the gist of the present invention is as follows.
The support part 2 that grips the end and the internal pressure that applies fluid pressure into the metal tube
Load booster 3 and shaft for applying stress to metal tube in the axial direction
Directional load control device 4 and metal tube axial strain measuring device 5
A metal pipe circumferential diameter measuring device 6 and the axial strain measurement
Metal tube axial strain measured by the measuring device 5 and the circumferential direction
Based on the diameter in the circumferential direction of the metal tube measured by the diameter measuring device 6
Σ acting in the axial direction of the metal pipe_φAnd in the circumferential direction of the metal tube
Working stress σ_θStress ratio σ_φ/ Σ_θStress ratio control to control
Metal pipe workability evaluation apparatus characterized by having means 7
(2) Support both ends of the metal tube, and
Do not control the applied fluid pressure and the stress applied in the axial direction of the metal tube.
In the method for evaluating the secondary workability of a metal tube,
The axial strain and circumferential diameter of the tube are measured and the axial strain and
Stress σ acting in the axial direction of the metal pipe based on the circumferential diameter_φ
Σ acting in the circumferential direction of the pipe and metal tube_θStress ratio σ _φ/ Σ_θ
And the stress ratio is constant until the metal tube breaks
In the axial direction of the metal tube according to the fluid pressure applied to the metal tube
Workability of metal tube characterized by controlling applied stress
Evaluation method.

[0005]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail. FIG.
(A) to (c) show an evaluation device according to an embodiment of the present invention. The steel pipe 1 is sealed, and the left and right sides are supported by the support portion 2 so that the steel pipe does not slip due to the load in the axial direction, and cylinders that apply stress in the axial direction are arranged at both ends of the steel pipe. The internal pressure load intensifier 3 is an area of a primary pressure generated by a hydraulic pump when a pressure is applied to a fluid such as water or a water to which a water-soluble lubricant such as an emulsion-based lubricant or solble oil is added in a metal pipe. Reduce ratio and increase pressure. The primary pressure, such as oil pressure, is controlled using an electromagnetic pressure reducing proportional valve or a servo valve to increase the pressure of the liquid on the secondary side. There are a single-acting type and a double-acting type as a pressure intensifier, and either may be used.

The load control device 4 in the axial direction performs digital control using a digital signal processor (DSP) based on the pressure on the rod and head side of the cylinder and the pressure receiving area using a servo valve. Position control for positioning such as attachment and detachment of a steel pipe is performed by precise position feedback control using a digital displacement meter built in a cylinder.

First, the steel pipe 1 and the supporting part 2 are aligned and the steel pipe 1 is fixed. Then, as the internal pressure increases, the load control in the axial direction is performed by multiplying the product of the rod pressure receiving area of the cylinder by the rod load pressure and the head pressure. Axial load control of a cylinder that applies a force to a steel pipe with a load that can be calculated from the difference between the product of the area and the load pressure of the head is performed. The load may be measured directly by a load cell or the like, or may be controlled by obtaining a shaft load from pressure detection.

Further, the axial direction, since the stress state by the curvature of the circumferential direction changes, draw two scribed lines the distance between L ₀ in the pipe central part (Marker) (see FIG. 1 (b)), The axial distortion is measured from the amount of change in the interval between the scribe lines by image processing using a linear CCD as the axial distortion measuring device 5,
The axial strain is obtained by the following equation (13), and cameras having a built-in linear CCD sensor as circumferential diameter measuring devices 6 are installed at three places in the tube axis direction, and radial displacement is measured at three places by a non-contact laser. Measure the radius of curvature R _Z [mm] in the axial direction
Curvature R _Z axial sought than calculation of a circle passing through three points from the measurement point of the three points the tube axis direction can be calculated. Set the measurement position to (x ₁ , y ₁ ), (x
₂ , y ₂ ) and (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) of curvature of the circumferential direction determined from the radial position of the central portion of the sensor radius _R B [mm] is determined 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 +} Δ
It is determined by R _B. The stress ratio control means 7 uses the metal pipe axial strain measured by the axial strain measuring device 5 and the metal pipe circumferential diameter measured by the circumferential diameter measuring device 6 as described later, based on the metal pipe axial strain. Ratio of stress σ _φ acting in the axial direction of σ to stress σ _θ acting in the circumferential direction of the metal pipe σ _φ /
σ _θ is calculated, and the stress applied in the axial direction of the metal tube is controlled in accordance with the fluid pressure applied to the metal tube so that the stress ratio becomes constant until the metal tube breaks.

A stress is calculated by using the curvature calculated based on the measurement result of the circumferential diameter measuring device 6 (the calculation formula will be described later). The cylinder shaft load is controlled by the load (calculation formula will be described later) applied to the cylinder shaft specified by the stress state. Further, when the steel pipe is deformed in the circumferential direction by the internal pressure, the outer diameter of the pipe changes, and the distance between the camera 5 and the scribe line changes. Therefore, the correction is made using the result of the diameter measurement in the circumferential direction. 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. In addition, since the wall thickness changes due to the deformation of the steel pipe, the wall thickness distortion is calculated from the biaxial strain in the pipe circumferential direction and the pipe axis direction under a condition of constant volume (calculation formula is described later), and the wall thickness is obtained. The above-mentioned stress balance calculation is performed (the calculation formula will be described later), and the control of repeatedly determining the shaft load is performed every moment.

Hereinafter, the calculation method will be described in detail. The main radius of curvature at the center of the wall thickness of the steel pipe is defined as the radius of curvature R _{φ in} the meridian direction of the steel pipe.
[Mm] and the radius of curvature in the circumferential direction R _θ [mm]. Stress σ _φ [MPa] acting in the axial direction of the metal tube and stress σ _θ [MPa] acting in the circumferential direction of the metal tube. When the internal pressure p [MPa] and the axial load W [N] are applied, the balance in the meridian direction is And if the thickness of the tube is t [mm], the balance with the internal pressure is Becomes Here, assuming that the stress ratio α = σ _φ / σ _θ , W _p [MPa] indicating the axial load that changes with the internal pressure is 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 a load _Wp [N] specified by the stress ratio. R _Z : outer radius in the meridian direction [mm] obtained from radial positions obtained by three sensors arranged in the axial direction R _B : the circumferential outer surface radius [mm] obtained from the radial position of the sensor at the center, and the length L [mm] in the meridian direction are Becomes Here, taking into account the distance change from the observation point (the distance from the camera to the object to be measured), the distance from the camera to H ₀
[Mm], the displacement [Delta] R _B of the steel tube central portion _[mm], L ₀ is if ruling of blank tube write length _L N [mm], Becomes Decide stress ratio _α = σ φ _/ σ θ in response to internal pressure p,
By controlling the load in the axial direction according to the meridian and the curvature in the circumferential direction at the center of the deformed pipe, a constant stress state can be maintained. From the change in the length of the scored line in the tube axis direction with α = σ _φ / σ _θ as the stress ratio, the meridional strain ε _φ , circumferential strain ε _θ , and thickness strain ε _t are given below (1
Equations 3) to (15) are obtained. The wall thickness of the steel pipe during deformation becomes α = 0 (16) if only the stress in the circumferential direction is applied. If the stress ratio between the meridian and the circumferential direction is 1: 2, α =
At 0.5, a plane strain state occurs. In the present invention, it is possible to determine the meridian / circumferential strain by controlling the stress state of the pipe central portion in consideration of the change in the length of the meridian in the central portion of the pipe, the diameter in the circumferential direction (curvature), and the change in the curvature in the meridian direction. 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 the stress ratio can be evaluated. By changing the stress ratio between the circumferential stress σ _θ and the meridional stress σ _{φ at} the center of the pipe at the principal curvatures in the axial direction and the circumferential direction, the stress at each stress ratio of the steel pipe is obtained. A strain diagram and a breaking limit line are obtained. In this way, by keeping the stress state constant, deforming the steel pipe and capturing the behavior up to the fracture, it is possible to obtain the same processing limit as that of the sheet material.

[0011]

FIG. 2 shows an apparatus according to the present invention.
m: 300 m length formed from cold rolled sheet with thickness t = 1.6 mm
using a steel pipe of m_φ/ σ_θ= 0 and plane strain
σ _φ/ σ_θThe work hardening coefficient n value was changed when = 0.5
(In case of large and small strain of steel pipe forming)
Shows the strain history. The same plate material is formed and welded on a steel pipe.
When a pipe is manufactured, the higher the work hardening coefficient
It shows that the field is high and the workability is excellent. Like this
Deformation of steel pipe with constant force state, behavior until fracture
To obtain the same processing limit as the sheet material.
Can be. From the strain in the uniaxial state in the circumferential direction,
R representing plastic anisotropy in the direction_θValue can be measured
(Fig. 3). r_θIs the uniaxial stress state (the stress in the pipe axis direction)
(When is zero), when expanding in the circumferential direction, the axial direction and wall thickness
It can be calculated from the directional strain increment (Equation 18). r_θThe value is
Can be calculated from the amount of change, ε_φ, Ε_θIs determined by measurement,
The amount of change (increment) in strain for a certain time depends on the condition of constant volume.
(14) dε_φ+ dε_θ+ dε_t= 0 meat from the relational expression of (17)
Strain increment dε in the thickness direction_tCircumferential anisotropy
R_θValue r_θ= Dε_φ/ dε_tIt can be calculated using (18). Circumferential direction of plate material almost equivalent to plate material
Plastic anisotropy r_θThat the value has been obtained.
You. As a result, the plasticity of steel pipes was difficult to evaluate in the past.
Anisotropy can be determined, and axial and circular
The circumferential stress-strain relationship could also be determined. Above
The axis direction obtained by the calculation of_φAnd the horizontal axis ε_φ
And the circumferential direction is the vertical axis σ_θ, The horizontal axis is ε_θIf you plot
Good.

[0012]

As described above in detail, in the prior art, in a steel pipe, only a stress-strain relationship in the axial (meridian) direction can be grasped in a tensile test by pipe pulling or cutting, but according to the present invention, the circular pipe is used. Circumferential plastic anisotropy: r
It has excellent effects such as the ability to measure the _θ value in a uniaxial stress field and the ability to capture the behavior in which the strain history changes due to material anisotropy.

[Brief description of the drawings]

FIG. 1 is an overall schematic diagram showing a test apparatus according to an example of the present invention.
FIG. 1A is an overall schematic plan view showing an initial state, and FIG.
1 is an overall schematic elevation view showing an initial state, and FIG. 1C is an overall schematic plan view showing a test time.

FIG. 2 is an explanatory diagram showing deformation of a steel pipe used for control of the present invention.

FIG. 3 is an explanatory view showing the use of the evaluation apparatus of the present invention to determine a breaking limit line when the processing n value is changed.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Metal pipe (steel pipe) 2 Support part 3 Internal pressure load booster 4 Axial load control device (digital servo control of a cylinder) 5 Axial strain measurement device 6 Circumferential diameter measurement device 7 Stress ratio control means

Claims (2)

[Claims] 1. A support (2) for gripping both ends of a metal tube (1).
An internal pressure load intensifier (3) for applying a fluid pressure into the metal tube, an axial load controller (4) for applying an axial stress to the metal tube, and an axial strain measuring device (5) for the metal tube. )
A metal pipe circumferential diameter measuring device (6); a metal tube axial strain measured by the axial strain measuring device (5); and a metal tube circle measured by the circumferential diameter measuring device (6). that it has a stress stress ratio control means for controlling the stress ratio sigma _phi / sigma _theta stress sigma _theta acting in the circumferential direction of the sigma _phi and the metal tube (7) which acts in the axial direction of the metal tube based on the circumferential diameter 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 inside the metal tube and the stress applied in the axial direction of the metal tube. Is measured in the axial direction and the diameter in the circumferential direction, and the stress σ acting in the axial direction of the metal pipe is determined based on the axial strain and the diameter in the circumferential direction.
Stress ratio between _φ and stress σ _θ acting in the circumferential direction of the metal tube σ _φ / σ
_{Obtain θ} , and control 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.