CN114509339A - A Biaxial Residual Stress Press-In Calibration Device - Google Patents

Abstract

The invention relates to a biaxial residual stress indentation calibration device, comprising a cross-shaped sample and a force applying mechanism, the force applying mechanisms are respectively arranged on the outer sides of the four axial ends of the cross-shaped sample, and are respectively connected with the cross-shaped sample. The shaft ends are detachably connected, and the force application mechanism is used to apply tensile stress or compressive stress to the cross-shaped sample in the axial direction to simulate residual stress; it also includes an upper cover plate and a universal support, and the cross-shaped sample is composed of The upper cover plate is pressed against the universal support, and a central test hole for pressing-in test is provided in the middle of the upper cover plate. The present invention solves the technical problem that the existing stress calibration device can only apply uniaxial or equi-biaxial residual stress, so that the complex state of other types of residual stress cannot be fully simulated and tested. In addition, the present invention is suitable for the detection of samples of various sizes, which greatly improves the versatility.

Description

A Biaxial Residual Stress Press-In Calibration Device

technical field

The invention relates to the technical field of experimental mechanics testing devices, in particular to a biaxial residual stress indentation calibration device.

Background technique

Residual stress widely exists in welds, 3D printing and other structures, and the existence of residual stress has a non-negligible impact on the stress corrosion resistance, fatigue performance and ultimate bearing capacity of components. Therefore, the accurate determination of residual stress is of great significance to ensure the safe service of structures containing residual stress. Compared with traditional residual stress detection methods such as drilling method, indentation method, as a nearly non-destructive and convenient detection method, has a good application prospect in residual stress assessment.

The key to the residual stress measurement by the indentation method is to calibrate the indentation response under different stress states for the material with the same work hardening behavior as the measured material. Considering the complexity of the residual stress state in the actual structure, the calibration should include uniaxial tension, uniaxial compression, equi-biaxial tension, equi-biaxial compression, non-equi-biaxial tension, and non-equi-biaxial compression as much as possible. And a variety of residual stress combinations such as unequal biaxial tension and compression. However, traditional residual stress calibration devices can only apply uniaxial or equi-biaxial residual stress, and have disadvantages such as large sample size requirements, poor matching with indentation testing, and inability to easily install optical measurement modules.

In addition, most of the existing biaxial residual stress calibration devices use bending method (in the vertical direction of the sample) to apply stress, and realize residual stress simulation after bending moment conversion, which is not only cumbersome in terms of specific operation and data processing, but also through bending method. It is also difficult to apply stress to ensure uniform force on both sides, which can easily cause the sample to lift or roll over, resulting in offline displacement in digital image acquisition and eventually virtual strain, which affects the subsequent indentation test.

SUMMARY OF THE INVENTION

In view of the deficiencies of the prior art, the present invention provides a biaxial residual stress indentation calibration device, which solves the problem that the existing stress calibration device can only apply uniaxial or equal biaxial residual stress, resulting in the inability to fully simulate and test other types of residual stress. Status of technical issues.

The technical scheme adopted in the present invention is as follows:

A biaxial residual stress indentation calibration device, comprising a cross-shaped sample and a force application mechanism, the force application mechanisms are respectively arranged on the outer sides of the four axial ends of the cross-shaped sample, and are respectively connected with the axial ends. Removably connected, the force application mechanism is used for applying tensile stress or compressive stress to the cross-shaped sample in the axial direction to simulate residual stress; it also includes an upper cover plate and a universal support, and the cross-shaped sample is supported by the upper The cover plate is pressed on the universal support, and the middle of the upper cover plate is provided with a central test hole for press-in testing.

Further technical solutions are:

The force-applying mechanism is connected to the base through fasteners, and is symmetrically distributed around the sample; each force-applying mechanism includes a motor, a reducer, a force-applying pin and a load sensor, and one end of the force-applying pin is connected to the decelerator. The output of the device is connected, and the other end is connected with the shaft end.

When in use, the two groups of force applying mechanisms in opposite positions have opposite directions of force to ensure that the center of the cross-shaped sample remains unchanged after applying residual stress.

The upper cover plate is detachably connected to the base, the center of the center test hole is coaxial with the center of the cross-shaped sample, and the outer ring of the upper cover plate located in the center test hole is provided with a force-applying bolt for installation hole, the force bolt is used to press the cross-shaped sample from the upper surface.

The universal support is detachably connected to the base, the height of the universal support is adjustable, the upper surface of the universal support is a support surface, the support surface is coaxial with the cross-shaped sample, and is used for The middle position of the bottom surface of the glyph sample is in contact.

The universal support is connected to the base through a stud, an upper nut and a lower nut are arranged on the stud, the upper nut is used to adjust the height of the universal support, and the lower nut is used to adjust the height of the universal support. The column is fastened to the base.

通过下式计算：When in use, by rotating the upper nut to complete the tightening of the cross-shaped sample and the compensation of the displacement from the surface, the rotation angle of the nut needs to be adjusted.

Calculated by the following formula:

为试样厚度变化，E，v分别为试样材料的杨氏模量和泊松比，H为试样的厚度，σ₁和σ₂为对试样的施加的残余应力，拉应力为正，压应力为负；π为圆周率，P为万向支撑所用螺柱的螺距。In the formula,

is the thickness change of the sample, E and v are the Young's modulus and Poisson's ratio of the sample material, respectively, H is the thickness of the sample, σ ₁ and σ ₂ are the residual stress applied to the sample, and the tensile stress is positive, The compressive stress is negative; π is the pi, and P is the pitch of the stud used for the universal support.

The supporting surface is a circle, and the diameter of the circle is 1-3 times the width of the middle shaft section of the cross-shaped sample.

The base is used to install the indentation detector and the optical measurement module.

The base is provided with a ferromagnetic connection seat, the structure of the optical measurement module includes an optical measurement device, a height-adjustable support structure, and a magnetic force meter seat is arranged at the bottom of the support structure, and the magnetic force meter seat is used for connecting with the iron. Magnetic connection seat mating connection.

The beneficial effects of the present invention are as follows:

The present invention can apply any combination of biaxial stress to simulate residual stress, and can ensure that the center of the pressed-in sample remains in place after the stress is applied. Through the force-applying device, various kinds of stretching, including uniaxial stretching, uniaxial compression, equibiaxial stretching, equibiaxial compression, unequal biaxial stretching, unequal biaxial compression, and unequal biaxial tension and compression, can be realized. The combination of residual stress in the axial direction can simulate and test various complex residual stress states.

Compared with the existing device for applying residual stress by bending, the residual stress applied by the present invention is uniformly distributed along the thickness direction, and there is no limit to the thickness of the test sample, and the sample will not warp. Any combination of biaxial stresses can be applied to simulate residual stress and ensure that the center of the indented specimen remains in place after stress is applied. There is no need to go through the calculation of bending moment conversion, and the high degree of automation, positioning and testing accuracy have been effectively improved.

The invention provides center positioning for the sample through the universal support, and ensures the fastening of the sample after stress is applied. The off-plane displacement is compensated by the height adjustment of the universal support, which ensures the accuracy of digital image acquisition and avoids the problems of virtual focus and virtual strain.

The application forms a detachable combined structure through the base, the optical test module and the press-in tester, which supports the convenient replacement of the press-in detector and the optical measurement module, and can ensure that the indenter of the instrument press-in detector is pressed in the central area of the cross-shaped indentation sample. It not only provides convenience for digital image acquisition but also improves the matching degree of optical measurement and indentation test results.

The present application overcomes the fact that the existing calibration device can only apply uniaxial or equal biaxial residual stress, is suitable for various sample sizes, and has good versatility.

Description of drawings

Figure 1 is a top view of the device of the present invention.

Figure 2 is a cross-sectional view of the device of the present invention.

FIG. 3 is a schematic structural diagram of the upper cover plate of the device of the present invention.

4 is a cross-sectional view of an optical measurement module of the device of the present invention.

In the figure: 1. Base; 2. Force-applying mechanism; 3. Cross-shaped sample; 4. Ferromagnetic connection seat; 5. Upper cover plate; 6. Universal support; 6-1, Upper nut; 6-2, Lower nut; 7. Center test hole; 8. Force bolt; 9. Stud; 10. Inner ring threaded hole; 11. Outer ring threaded hole; 12. Spirit level; 13. Industrial camera; 14. Fastening knob; 15 , light source; 16, optical lens; 17, slide rail; 18, magnetic table seat.

Detailed ways

The specific embodiments of the present invention will be described below with reference to the accompanying drawings.

A biaxial residual stress indentation calibration device in this embodiment, as shown in FIG. 1 , includes a cross-shaped sample 3 and a force-applying mechanism 2 , and the force-applying mechanisms 2 are respectively arranged on the four axial ends of the cross-shaped sample 3 . The outer side is detachably connected to the shaft end through the connecting piece respectively. The force application mechanism 2 is used to apply tensile (stretching) stress or compressive (compressive) stress to the cross-shaped sample 3 in the axial direction to simulate residual stress; as shown in Figure 2 As shown, it also includes an upper cover plate 5 and a universal support 6. When in use, the cross-shaped sample 3 is pressed on the universal support 6 by the upper cover plate 5. Center test hole 7.

The biaxial residual stress of this embodiment is pressed into the calibration device, and the tensile and compressive stresses can be directly applied in the plane through the force applying mechanism 2 along the axial direction of the four shaft segments constituting the cross-shaped sample. The direction of the force is shown in Figure 1. shown in the direction of the arrow.

By controlling the magnitude and direction of the force applied by the force applying mechanism 2, it can be applied including uniaxial stretching, uniaxial compression, equibiaxial stretching, equibiaxial compression, unequal biaxial stretching, equibiaxial compression and Various residual stress combinations, including unequal biaxial tension and compression, do not need to apply force in the vertical direction and then obtain residual stress simulation through bending moment conversion. And it is suitable for samples of various sizes.

There are four force-applying mechanisms 2 in this embodiment, which are respectively connected to the base 1 through fasteners such as fastening bolts, and are symmetrically distributed with the sample as the center; each force-applying mechanism includes a motor, a reducer, and a force-applying pin And the load sensor, one end of the force application pin is connected with the output of the reducer, and the other end is connected with the shaft end.

In this embodiment, the upper cover 5 is detachably connected to the base 1 . As shown in FIG. 3 , the middle of the upper cover 5 is provided with a center test for indentation testing and digital image acquisition of the surface of the indented sample. Hole 7, the center of the test hole 7 is coaxial with the center of the cross-shaped sample.

Specifically, the outer ring of the upper cover plate 5 located in the central test hole 7 is provided with mounting holes for the force-applying bolts 8 , which are named as inner ring threaded holes 10 as shown in FIG. 3 , and there are four in total. As shown in FIG. 2 , four force-applying bolts 8 pass through threaded holes 10 in the inner ring to press the cross-shaped sample 3 from the upper surface.

Specifically, the upper cover plate 5 is provided with outer ring threaded holes 11 at the four corners of the outer ring of the central test hole 7. As shown in FIG. 2, the upper cover plate 5 passes through the outer ring threaded holes 11 through four studs 9 and The base 1 is tightly connected.

As shown in FIG. 2 , the bottom of the universal support 6 in this embodiment is also detachably connected to the base 1 through studs. The studs are provided with an upper nut 6-1 and a lower nut 6-2, and the upper nut 6-1 is used for In order to adjust the height of the universal support 6 , the lower nut 6-2 is used to fasten the connection between the stud and the base 1 .

Specifically, the upper surface of the universal support 6 is a support surface, and the support surface is coaxially disposed with the cross-shaped sample 3 and is used for contacting the middle position of the bottom surface of the cross-shaped sample 3 .

Specifically, the supporting surface is a circle, and the diameter of the circle is 1 to 3 times the width of the middle shaft section of the cross-shaped sample.

Specifically, the diameter of the stud at the bottom of the universal support 6 should not be less than the width of the middle shaft section of the cross-shaped sample.

Specifically, the universal support 6 is made of cemented carbide.

When in use, the two sets of motors in opposite positions can be controlled by the same encoder, and are set to have the same displacement and opposite direction of force to ensure that the center of the cross-shaped sample remains unchanged after applying residual stress.

After stress is applied, the change in thickness of the specimen, ΔH, is calculated by the following formula:

In the formula, E and v are the Young's modulus and Poisson's ratio of the sample material, respectively, H is the thickness of the sample, σ ₁ and σ ₂ are the residual stress applied to the sample, the tensile stress is positive, and the compressive stress is burden.

通过下式计算：By rotating the upper nut 6-1 to complete the tightening of the cross-shaped specimen and the compensation of the out-of-plane displacement, the nut rotation angle needs to be adjusted

Calculated by the following formula:

In the formula, π is the circle ratio, ΔH is the thickness change of the sample, and P is the pitch of the stud used for the universal support.

As shown in FIG. 1 , a ferromagnetic connection seat 4 is installed on the base 1 of this embodiment, which is used for installing a press-fit detector, an optical measurement module, and the like.

The biaxial residual stress indentation calibration device of this embodiment can be used in conjunction with an optical measuring device and an indentation tester.

As shown in Figure 4, the structure of the optical measurement module includes:

Optical measuring device: an industrial camera 13, an optical lens 16 connected to the industrial camera 13, and a light source 15;

Height-adjustable support structure: beams, fastening knobs 14 and slide rails 17;

and a magnetic watch seat 18 arranged at the bottom of the support structure.

The magnetic meter seat 18 is used for mating connection with the ferromagnetic connecting seat 4 . By adjusting the switch of the magnetic meter base 18 , the optical measurement module can be quickly connected and separated from the base 1 . Two slide rails 17 are arranged parallel to each other and installed vertically with the base. Both ends of the beam are respectively installed on the slide rail 17 through the above-mentioned tightening knobs 14 at the position where the slide rail 17 can be positioned on the slide rail 17 to adjust the height.

Specifically, the beam includes two concentric circular holes, and the diameter of the hole connected to the upper surface of the beam (ie, the hole away from the base) is larger than the diameter of the hole connected to the lower surface of the beam (ie, the hole close to the base). The light source is fixed on the lower surface of the beam through magnets, the industrial camera 13 is installed in the circular hole connected to the upper surface of the beam, and the optical lens 16 connected to the industrial camera passes through the circular hole connected to the lower surface of the beam. A spirit level 12 is installed on the upper surface of the beam to determine the levelness of the beam.

Specifically, the base itself is made of light alloy, and the ferromagnetic connection seat on the base facilitates the rapid positioning, installation and disassembly of the press-in detector and the optical measurement module with the magnetic meter base.

For cruciform specimens, the residual stress distribution can be estimated from the load cell readings, or the strain distribution of the cruciform pressed into the central area of the specimen after stress is applied can be determined by optical measurements (eg, digital image correlation techniques). After the residual stress measurement is completed, the optical measurement module is quickly disassembled, and the indentation detector is replaced. The ferromagnetic connection seat on the base can ensure that the indenter of the instrument indentation detector is pressed in the central area of the cross-shaped indentation sample. After the indentation test is completed, the magnetic force meter seat of the indentation detector is separated from the ferromagnetic connection seat, and the optical measurement module is replaced again to collect images of the residual contour and strain distribution on the surface of the indentation sample.

The residual stress indentation calibration device provided in this application adopts a modular design. The four sets of force applying mechanisms with symmetrical distribution can apply any combination of biaxial stress to the indented sample according to the test requirements to simulate the residual stress, and can ensure that the center of the indented sample remains in place after the stress is applied. The ferromagnetic connection seat on the base facilitates the quick positioning, installation and removal of the press-in detector and the optical measurement module installed with the magnetic meter seat, which can ensure that (1) the application is determined by an optical measurement method (such as digital image correlation technology). (2) Quickly disassemble the optical measurement module, replace the indentation detector, and ensure that the indenter of the instrument is indented in the central area of the cruciform indentation sample (3) After the indentation test is completed, the indentation detector is quickly disassembled, and the optical measurement module is replaced, and the image acquisition of the residual contour and strain distribution on the surface of the indentation sample is carried out. By rotating the upper nut, the tightening of the pressed specimen and the compensation of the displacement from the surface can be completed, which ensures the accuracy of digital image acquisition.

Those of ordinary skill in the art can understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, it is still The technical solutions described in the foregoing embodiments may be modified, or some technical features thereof may be equivalently replaced. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. A biaxial residual stress is pressed into the calibration device, comprising a cross-shaped sample and a force-applying mechanism, wherein the force-applying mechanism is respectively arranged on the outside of the four axial ends of the cross-shaped sample, and respectively. Removably connected with the shaft end, the force applying mechanism is used for applying tensile stress or compressive stress to the cross-shaped sample in the axial direction to simulate residual stress; it also includes an upper cover plate and a universal support, a cross-shaped sample The sample is pressed on the universal support by the upper cover plate, and a central test hole for pressing-in test is provided in the middle of the upper cover plate. 2 . The biaxial residual stress indentation calibration device according to claim 1 , wherein the force applying mechanism is connected to the base through fasteners, and is symmetrically distributed with the sample as the center; The mechanism includes a motor, a reducer, a force application pin and a load sensor, one end of the force application pin is connected with the output of the reducer, and the other end is connected with the shaft end. 3. The biaxial residual stress press-fit calibration device according to claim 2, characterized in that, when in use, the two groups of force applying mechanisms in opposite positions have opposite force directions, ensuring that the cross-shaped sample after applying residual stress The center remains the same. 4 . The biaxial residual stress indentation calibration device according to claim 1 , wherein the upper cover plate and the base are detachably connected, and the center of the center test hole is the center of the cross-shaped sample. 5 . Coaxially arranged, the outer ring of the upper cover plate located in the central test hole is provided with a mounting hole for a force-applying bolt, and the force-applying bolt is used to press the cross-shaped sample from the upper surface. 5. The biaxial residual stress press-fit calibration device according to claim 1, wherein the universal support is detachably connected to the base, the height of the universal support is adjustable, and the upper surface of the universal support is detachable. It is a supporting surface, the supporting surface is coaxially arranged with the cross-shaped sample, and is used for contacting the middle position of the bottom surface of the cross-shaped sample. 6. The biaxial residual stress press-fit calibration device according to claim 1 or 5, wherein the universal support is connected to the base through a stud, and an upper nut and a lower nut are provided on the stud , the upper nut is used to adjust the height of the universal support, and the lower nut is used to fasten the connection between the stud and the base. 7. The biaxial residual stress indentation calibration device according to claim 6, characterized in that, when in use, by rotating the upper nut to complete the tightening of the cross-shaped specimen and the compensation of the off-plane displacement, wherein the required Adjusted nut rotation angle

Calculated by the following formula:

In the formula,

is the thickness change of the sample, E and v are the Young's modulus and Poisson's ratio of the sample material, respectively, H is the thickness of the sample, σ ₁ and σ ₂ are the residual stress applied to the sample, and the tensile stress is positive, The compressive stress is negative; π is the pi, and P is the pitch of the stud used for the universal support. 8 . The biaxial residual stress indentation calibration device according to claim 5 , wherein the supporting surface is a circle, and the diameter of the circle is 1 to 3 of the width of the middle shaft section of the cross-shaped sample. 9 . times. 9 . The biaxial residual stress indentation calibration device according to claim 1 , wherein the base is used to install an indentation detector and an optical measurement module. 10 . 10 . The biaxial residual stress indentation calibration device according to claim 9 , wherein a ferromagnetic connection seat is provided on the base, and the structure of the optical measurement module comprises an optical measurement device, a height-adjustable support The bottom of the structure and the supporting structure is provided with a magnetic force meter seat, and the magnetic force meter seat is used for mating connection with the ferromagnetic connection seat.

Images