CN110907082B - Residual stress detection method - Google Patents
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- CN110907082B CN110907082B CN201911259001.7A CN201911259001A CN110907082B CN 110907082 B CN110907082 B CN 110907082B CN 201911259001 A CN201911259001 A CN 201911259001A CN 110907082 B CN110907082 B CN 110907082B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
- G01L5/0047—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes measuring forces due to residual stresses
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/20—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
- G01L1/22—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress using resistance strain gauges
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
Abstract
According to the residual stress detection method provided by the invention, the metal sample with a special structure is selected, and the metal sample can concentrate the residual stress generated in the heat treatment process to the middle position of the thin section, so that the position where the maximum concentrated stress appears is controllable, the size of the residual stress is improved, and the detection and quantification work of the residual stress is simpler and more accurate; in addition, a sectional quenching method is adopted, so that a larger temperature gradient can be generated, and the residual stress in the middle of the thin section of the connecting rod is further increased. The concentration and amplification of the residual stress can weaken the influence of errors in the detection process and ensure the accuracy of single sample measurement, and because the residual stress is amplified and the influence of the errors is weakened, the difference between the residual stresses of samples with the same size is increased and more obvious after the samples undergo different heat treatment processes, thereby facilitating the comparison of the residual stress values in the heat treatment optimization process and ensuring the accuracy of the result.
Description
Technical Field
The invention relates to the field of residual stress detection, in particular to a method for detecting residual stress after concentrating the residual stress to a specified position and amplifying the residual stress.
Background
After the metal member is prepared, in order to improve the performance of the metal member, the metal member is often required to be subjected to heat treatment, the heat treatment process is accompanied by complex phase change and temperature gradient, the phase change and the temperature gradient can form heat treatment stress and remain in the metal member, and finally form residual stress, and the residual stress can have very obvious negative effects on the subsequent processing and the final quality of the member and the reliability in the using process. Because the shape of the metal component is often more complicated, the distribution of the residual stress is uneven, the position where the maximum value of the residual stress appears is uncontrollable, and the residual stress value is small after the heat treatment is finished, so that the residual stress value is easily influenced by error factors in the detection process. Therefore, how to accurately position and detect the maximum residual stress, so that the optimal heat treatment process is determined by comparing the magnitude of the residual stress is an urgent problem to be solved.
Disclosure of Invention
The invention aims to provide a residual stress detection method, which is characterized in that a metal sample with a special structure can concentrate and amplify residual stress to enable the maximum value of the residual stress to appear at a specified position, and a step quenching mode is adopted to form a larger temperature gradient and amplify the residual stress to the maximum extent, so that the maximum residual stress generated by different heat treatment processes is compared through detecting the residual stress at the specified position, and the heat treatment process is further optimized.
The invention provides a residual stress detection method, which comprises the following steps:
s1. preparation of metal sample
The metal sample comprises a sample base body, two ends above the sample base body are respectively provided with a protruding part, the two protruding parts and the upper surface of the sample base body form a groove together, the two protruding parts are connected through a connecting rod, and a gap is formed between the lower surface of the connecting rod and the upper surface of the sample base body; the connecting rod is symmetrical along a horizontal shaft and comprises thick sections at two ends and a thin section in the middle, the thick sections at the two ends are connected with the two convex parts, the thin section in the middle is respectively connected with the thick sections at the two ends through two transition sections with gradually changed widths, and the upper surface and the lower surface of the thick section, the upper surface and the lower surface of the thin section and the upper surface and the lower surface of the sample substrate are mutually parallel; the metal sample is integrally formed, and the shape of the metal sample is symmetrical along a vertical axis; smelting, refining, casting and surface processing are sequentially adopted to obtain metal samples with corresponding sizes;
s2, heat treatment of metal sample
Carrying out solution quenching treatment on a metal sample; the quenching adopts layered quenching, namely the connecting rod is not quenched and the sample matrix is quenched;
s3, strain detection
After the metal sample is completely cooled, polishing the middle position of the lower surface of the thin section to ensure flatness, cleaning, attaching a resistance strain gauge to the middle position of the lower surface of the thin section by using a binder, sawing off the part of one end of the connecting rod connected with the transition section, releasing stress, and measuring strain data;
s4, calculating residual stress
According to the formula: the stress is the elastic modulus strain and the residual stress is calculated.
The residual stress detection method can ensure that the maximum residual stress is concentrated and limited to appear at the middle point of the thin section of the connecting rod through a special structural design, further increases the temperature gradient through a stepped quenching method, improves the residual stress level, realizes the maximization of the residual stress and the fixation of the maximum position of the residual stress, can detect the residual stress value through a known residual stress detection method, and can determine the heat treatment process generating the minimum residual stress by combining the comparison of the residual stress detection results under different heat treatment regimes.
As an improved technical solution, step S2 further includes an aging treatment after the solution quenching. The aging process is usually accompanied after the solution quenching, and the residual stress detection is carried out after the aging process, thereby being more beneficial to
As a specific dimensioning scheme, the dimensions of the metal sample substrate are as follows: the length is 100-: the length is 15-30mm, the width is 15-20mm, the thickness is 5-15mm, and the size of the thick section is as follows: the length is 15-25mm, the width is 10-15mm, the thickness is 5-15mm, and the size of the thin section is as follows: the length is 20-30mm, the width is 4-10mm, and the thickness is 5-15 mm. The thickness of the thin section is preferably 6-10mm, and the width is preferably 5-8 mm. The thin section is used as a stress concentration area, the proper size is beneficial to the measurement of the final result, the small width and thickness have fracture risks, the width or thickness is too large, the stress concentration degree is reduced, and the miniaturization of the size of the sample is also not beneficial, experiments prove that the thickness of 6-10mm and the width of 5-8mm have the best stress concentration effect, the proper length of the thin section is important for the convenience of the measurement of the final result and the miniaturization of the size of the sample, and the length of the thin section is 20-30 mm.
As an improved technical scheme, the layered quenching specifically comprises the following steps:
1) preparing a container filled with a quenching medium;
2) inserting a metal sheet into a gap between the connecting rod and the sample base;
3) and immersing the sample substrate into a quenching medium for quenching, wherein the two ends of the metal sheet are lapped on the edge of the container, and the upper surface of the metal sheet is in supporting contact with the lower surfaces of the two thick sections, so that the thick sections and the thin sections are not quenched.
The technical scheme has the advantages that the accuracy is high in the quenching process, the process is simple, the lower part of the metal sample can be effectively guaranteed to be quenched, the upper part of the metal sample is not quenched, accordingly, a large temperature gradient is generated, and the concentration and the amplification of residual stress are formed.
As a modified solution, in step S3, cleaning is performed by using acetone, and the adhesive is selected from 502 glue, 101 glue, or 302 glue.
As an improved technical scheme, the sections of the thick section and the thin section of the connecting rod are both rectangular; the structure design ensures the consistency of the sample, so that the experimental result is more accurate and the processing is facilitated. In the production process, the sections of the thick section and the thin section are selected to be rectangular, batch production can be carried out, namely, a metal sample with larger thickness is cast firstly, then the metal sample is cut piece by adopting mechanical processing, and finally the metal sample meeting the technical scheme is obtained. Of course, it is also permissible and acceptable to produce a metal specimen alone that satisfies this improvement.
As an improved technical scheme, the width of the narrowest part of the gap between the lower surface of the connecting rod and the upper surface of the sample substrate is 2-8mm, preferably 4-6 mm; the width of the widest part is 4-12mm, preferably 6-10 mm; the size of the gap is selected by considering the situation of concentrated amplification of residual stress on one hand, and considering the overall size layout of the sample according to the requirement of miniaturization on the other hand; meanwhile, enough gap at the widest position is required to be ensured, and the resistance stress sheet is convenient to polish, clean and adhere.
As an improved technical scheme, the material of the metal sample is aluminum or aluminum alloy, copper or copper alloy, magnesium or magnesium alloy, titanium or titanium alloy, cast iron and steel.
As an improved technical scheme, the whole metal sample is of the same thickness; the structure design ensures the consistency of the sample, so that the experimental result is more accurate and the processing is facilitated. In the production process, the metal sample with the whole equal thickness is selected, and batch production can be carried out, namely, the metal sample with the larger thickness is cast firstly, then the metal sample is sliced piece by adopting mechanical processing, and finally the metal sample meeting the technical scheme is obtained. Of course, it is also permissible and acceptable to produce a metal specimen alone that satisfies this improvement.
Further, water or oil is used as a quenching medium for quenching.
It should be noted that the description of the structural dimensions of the metal sample in the present invention is made based on the lower surface of the sample substrate being placed on a horizontal surface, and the terms "length", "width" and "thickness" in the present invention refer to: when the lower surface of the sample substrate is placed on a horizontal surface, the horizontal direction is the length, the vertical direction is the width, and the direction vertical to the horizontal direction and the vertical direction is the thickness; the rectangle of the cross section comprises a common rectangle with unequal adjacent edges and a special rectangle with equal adjacent edges, namely a square.
According to the residual stress detection method provided by the invention, the metal sample with a special structure is selected, and the metal sample can concentrate the residual stress generated in the heat treatment process to the middle position of the thin section, so that the position where the maximum concentrated stress appears is controllable, the size of the residual stress is improved, and the detection and quantification work of the residual stress is simpler and more accurate; in addition, a sectional quenching method is adopted, so that a larger temperature gradient can be generated, and the residual stress in the middle of the thin section of the connecting rod is further increased. The concentration and amplification of the residual stress can weaken the influence of errors in the detection process and ensure the accuracy of single sample measurement, and because the residual stress is amplified and the influence of the errors is weakened, the difference between the residual stresses of samples with the same size is increased and more obvious after the samples undergo different heat treatment processes, thereby facilitating the comparison of the residual stress values in the heat treatment optimization process and ensuring the accuracy of the result.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a schematic diagram of a metal sample constructed in simulation example 1;
FIG. 2 is an equivalent stress cloud of simulation example 1;
FIG. 3 is a pictorial representation of a metal coupon from example 1 prior to residual stress testing;
FIG. 4 is a schematic sectional front view showing a quenching process of a metal sample according to example 1;
FIG. 5 is a schematic top view of a quenching process of the technical sample of example 1;
fig. 6 is a pictorial representation of a metal coupon of example 1 after residual stress testing.
Detailed Description
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
Simulation example
In order to determine the sample size structure with better residual stress concentration and amplification degree, a metal sample is firstly constructed for analog simulation, and the position of the maximum stress concentration is determined.
Simulation conditions are as follows: simulation was performed using ANSYS software.
After the solution treatment is finished at the temperature of 495 ℃, the sample is taken out of the furnace (the temperature in the furnace is 510-530 ℃ in an actual test, but a temperature drop exists after the actual sample is taken out, but the problem does not exist in simulation, so that the temperature of 495 ℃ is considered as the heat treatment temperature in simulation), then the part below the coarse section (without the coarse section) is immersed into a cooling medium at the temperature of 22 ℃, the sample is subjected to sharp temperature drop, the positions above the coarse section of the sample and the air perform convective heat exchange, and the temperature and stress change of the sample after the quenching process is started and is quenched for 200s are calculated. This process is a non-steady state process and therefore requires consideration of initial conditions and boundary conditions.
Initial conditions:
(1) the temperature of the whole sample is 495 ℃; (2) the cooling medium temperature was 22 ℃.
Boundary conditions:
(1) the part below the thick section of the sample (without the thick section) and a cooling medium (water or oil, and no difference exists in the simulation) carry out convective heat transfer, and the convective heat transfer coefficient is 4000W/(m)2DEG C), the temperature of a cooling medium is 22 ℃; (2) the thick section and the above part of the sample generate heat convection with air, and the heat convection coefficient is 12W/(m)2DEG C.), the temperature of the cooling medium (air) is 22 ℃.
Since the sample is symmetrical along the vertical axis, the stress distribution obtained by the final simulation calculation is necessarily symmetrical along the vertical axis, and therefore, in order to reduce the calculation amount of the simulation, half of the structure of the sample is selected for simulation.
Simulation example 1
As shown in fig. 1, the simulation example provides a metal sample, which is made of an aluminum alloy and includes a sample substrate, wherein the sample substrate is 110mm long and 22mm wide, two ends above the sample substrate are respectively provided with a protruding portion, the protruding portion is 15mm long and 18mm wide, the two protruding portions and the upper surface of the sample substrate jointly form a groove, the two protruding portions are connected through a connecting rod, a gap is formed between the lower surface of the connecting rod and the upper surface of the sample substrate, and the width of the narrowest part of the gap is 4 mm;
the shape of the connecting rod is symmetrical along a horizontal shaft, the connecting rod comprises thick sections at two ends and a thin section in the middle, the thick sections at the two ends are connected with the two convex parts, and the thin section in the middle is respectively connected with the thick sections at the two ends through two transition sections with gradually changed widths; the length of the thick section is 19mm, the width is 14mm, and the length of the thin section is 24mm, and the width is 6 mm; the section of the thick section is rectangular, and the section of the thin section is square;
the upper surface and the lower surface of the thick section, the upper surface and the lower surface of the thin section and the upper surface and the lower surface of the sample substrate are mutually parallel;
the metal test piece is integrally formed and has an equal thickness of 6mm, and the shape of the metal test piece is symmetrical along a vertical axis.
Simulating according to the simulation conditions to obtain an equivalent stress distribution cloud chart shown in figure 2, wherein the maximum residual stress of the sample is distributed in the middle of the lower surface of the thin section; it can be seen that the structural dimensions of the sample of simulation example 1 have excellent residual stress concentration characteristics, with the lower surface of the segment having the highest degree of residual stress concentration.
The following examples, taking the aluminum alloy samples in the production simulation example 1 as example 1 and comparative example 1, comparative example 2 was produced, comparative example 2 having the same dimensions as example 1 except that the tie rod had no thin section and transition section, being an equally sized thick section, i.e., the tie rod had dimensions of 80mm (length) x 14mm (width) x 6mm (thickness), and an aluminum alloy block of 110mm (length) x 40mm (width) x 6mm (thickness) was produced as comparative example 3. Selecting ZL109 aluminum alloy, manufacturing 150mm (length) x 60mm (width) x 80mm (thickness) aluminum alloy blocks by adopting a conventional smelting + refining + sand mold casting method, then performing surface processing, removing surface scale, and then performing slicing cutting by using wire cutting to manufacture samples of example 1 and comparative examples 1-3, manufacturing two groups of samples for each example or comparative example, performing corresponding heat treatment on each group of two samples, performing residual stress test after the heat treatment, and displaying the measured values of the residual stress in Table 1.
Example 1
S1, preparation of aluminum alloy sample
Performing line cutting on the aluminum alloy block subjected to surface processing and oxide skin removal to obtain an aluminum alloy sheet body; machining an aluminum alloy sheet, and preparing an actual aluminum alloy sample according to the sample size of simulation example 1, wherein the actual aluminum alloy sample is shown in figure 3;
s2, heat treatment of aluminum alloy sample
The following two heat treatments were performed on the aluminum alloy specimens: 1) solid solution at 520 ℃ for 6h, 2) solid solution at 520 ℃ for 6h, aging at 160 ℃ for 16h and air cooling; the quenching adopts layered quenching, namely the connecting rod is not quenched and the sample matrix is quenched; the process schematic diagram is shown in fig. 4 and 5, and the aluminum alloy sample 1 is subjected to layered quenching, and the method comprises the following specific steps:
1) preparing a container 3 filled with a quenching medium 2, wherein the quenching medium 2 is selected to be water with the temperature of 22 ℃;
2) inserting a stainless steel sheet 4 with the thickness of 3mm into a gap between the connecting rod and the aluminum alloy sample substrate;
3) immersing an aluminum alloy sample substrate into water for quenching, wherein at the moment, two ends of a stainless steel sheet 4 are lapped on the edge of the container 3, and the upper surface of the stainless steel sheet 4 is in supporting contact with the lower surfaces of the two thick sections, so that the thick sections and the thin sections are not quenched;
s3, strain detection
After the aluminum alloy sample is completely cooled, polishing the middle position of the lower surface of the thin section to ensure flatness, cleaning with acetone, attaching a resistance strain gauge to the middle position of the lower surface of the thin section by using 502 glue, converting the deformation of an engineering structural member into resistance change by using the strain effect of a resistance material, converting the resistance change into a voltage or current change signal through a measuring circuit, outputting the voltage or current change signal, sawing off the part, connected with the transition section, of one end of a connecting rod by adopting a quarter-bridge connection method, performing stress release, and measuring strain data, wherein a sample real image after residual stress test is shown in fig. 6;
s4, calculating residual stress
According to the formula: calculating the stress as elastic modulus strain to obtain residual stress; the modulus of elasticity of the material was measured according to a known method, and in this test, the modulus of elasticity of ZL109 was found experimentally to be 71.849 GPa.
Comparative example 1
S1, preparation of aluminum alloy sample
Performing line cutting on the aluminum alloy block subjected to surface processing and oxide skin removal to obtain an aluminum alloy sheet body; machining an aluminum alloy sheet, and preparing an actual aluminum alloy sample according to the sample size of the simulation example 1;
s2, heat treatment of aluminum alloy sample
The following two heat treatments were performed on the aluminum alloy specimens: 1) solid solution at 520 ℃ for 6h, 2) solid solution at 520 ℃ for 6h, aging at 160 ℃ for 16h and air cooling; the quenching adopts integral quenching, and the sample is wholly immersed into water with the temperature of 22 ℃ for quenching;
s3, strain detection
After the aluminum alloy sample is completely cooled, polishing the middle position of the lower surface of the thin section to ensure flatness, cleaning with acetone, attaching a resistance strain gauge to the middle position of the lower surface of the thin section by using 502 glue, converting the deformation of an engineering structural part into resistance change by using the strain effect of a resistance material, converting the change of the resistance into a voltage or current change signal through a measuring circuit, outputting the voltage or current change signal, sawing off the part, connected with the transition section, of one end of a connecting rod by adopting a bridge connection method of a quarter bridge, releasing stress, and measuring strain data;
s4, calculating residual stress
According to the formula: calculating the stress as elastic modulus strain to obtain residual stress; the modulus of elasticity of the material was measured according to a known method, and in this test, the modulus of elasticity of ZL109 was found experimentally to be 71.849 GPa.
Comparative example 2
S1, preparation of aluminum alloy sample
Performing line cutting on the aluminum alloy block subjected to surface machining and scale removal to obtain an aluminum alloy sheet, and then machining to prepare a sample, wherein the length of a sample base body is 110mm, the width of the sample base body is 22mm, and the thickness of the sample base body is 6mm, the length of the protruding parts at two ends above the sample base body is 15mm, the width of the protruding parts is 18mm, and the thickness of the protruding parts is 6mm, the two protruding parts are connected through a connecting rod, the size of the connecting rod is 80mm (length) × 14mm (width) × 6mm (thickness), and a gap is formed between the lower surface of the connecting rod and the upper surface of the sample base body and;
s2, heat treatment of aluminum alloy sample
The following two heat treatments were performed on the aluminum alloy specimens: 1) solid solution at 520 ℃ for 6h, 2) solid solution at 520 ℃ for 6h, aging at 160 ℃ for 16h and air cooling; the quenching adopts layered quenching, namely the connecting rod is not quenched and the sample matrix is quenched; carrying out layered quenching on an aluminum alloy sample, comprising the following specific steps:
1) preparing a container filled with a quenching medium, wherein the quenching medium is selected to be water with the temperature of 22 ℃;
2) inserting a stainless steel sheet with the thickness of 3mm into a gap between the connecting rod and the aluminum alloy sample substrate;
3) immersing an aluminum alloy sample substrate into water for quenching, wherein two ends of a stainless steel sheet are lapped on the edge of the container, and the upper surface of the stainless steel sheet is connected with the edge of the container; the lower surfaces of the connecting rods are in supporting contact, so that the connecting rods are not quenched;
s3, strain detection
After the aluminum alloy sample is completely cooled, polishing the middle position of the lower surface of the connecting rod to ensure flatness, cleaning with acetone, attaching a resistance strain gauge to the middle position of the lower surface of the connecting rod by using 502 glue, converting the deformation of an engineering structural part into resistance change by using the strain effect of a resistance material, converting the change of the resistance into a voltage or current change signal through a measuring circuit, outputting the voltage or current change signal, sawing off the part, connected with the transition section, of one end of the connecting rod by adopting a bridge connection method of a quarter bridge, releasing stress, and measuring strain data;
s4, calculating residual stress
According to the formula: calculating the stress as elastic modulus strain to obtain residual stress; the modulus of elasticity of the material was measured according to a known method, and in this test, the modulus of elasticity of ZL109 was found experimentally to be 71.849 GPa.
Comparative example 3
Performing line cutting on the aluminum alloy block subjected to surface processing and oxide skin removal to obtain an aluminum alloy sheet body; then, an aluminum alloy sample of 110mm (length) × 40mm (width) × 6mm (thickness) was prepared by machining.
The residual stress test method of comparative example 3 is as follows: two heat treatments were first performed: 1)520 ℃ for 6h solid solution, 2)520 ℃ for 6h solid solution, 160 ℃ for 16h aging and air cooling, quenching after solid solution adopts layered quenching, a clamp is used for clamping the aluminum alloy plate of comparative example 3 for layered quenching, the aluminum alloy plate is quenched below 22mm in width, and the part above 22mm is not quenched; the maximum residual stress of the test piece will occur at the uppermost surface of the non-quenched portion of the test piece due to the temperature gradient, and therefore, the center position of the surface is tested for the residual stress. Since the test sample can not be subjected to the patch test after cutting, the test of the residual stress of the test sample in the comparative example 3 adopts an X-ray method, and the test is carried out according to a side-tipping method (section 5.4 of national standard) in GB/T7704 and 2017 nondestructive testing X-ray stress determination method, and CuK alpha rays and Ni filters are selected.
The results of the residual stress test of example 1 and comparative examples 1 to 3 are shown in table 1.
TABLE 1
As can be seen from the above comparison, the residual stress of the sample of example 1 is greatly improved compared with that of the ordinary sample of comparative example 3; the samples of comparative examples 1 and 2 have a structure of one connecting rod, so that stress can be concentrated on the lower surface of the connecting rod to a certain degree, and compared with a common sample, the sample has a certain promotion effect and can also obtain a better effect; however, the comparative example 1 adopts integral quenching, so that the temperature gradient is not generated, the concentration and amplification of stress are not facilitated, and the residual stress improvement effect is far inferior to that of the sample of the example 1; comparative example 2, which employs a connecting rod of equal size, is not favorable for concentration and amplification of residual stress, but due to the layered quenching, the concentration and amplification effects of residual stress are still satisfactory, but there is a certain difference from example 1.
The sample of embodiment 1, because special structural design and layering quenching, causes the residual stress to be concentrated and enlarged, and the influence of measurement error in the testing process is correspondingly reduced to make the authenticity and comparability of result strengthen, in addition, the position that its maximum residual stress appears is controllable, in the actual test work, can directly confirm the position of setting resistance foil gage, has simplified test work.
For metallic materials other than the aluminum alloy claimed in the present application, due to the particularity of the sample structure of the present application, the temperature gradient distribution during the heat treatment is the same as that of the previous embodiment, so that those skilled in the art can reasonably expect that the stress concentration point is necessarily located on the lower surface of the thin section, and further, although other materials are not exhausted in the embodiments, those skilled in the art can know that the sample structure of the present application is equally applicable to any metallic material such as aluminum, copper or copper alloy, magnesium or magnesium alloy, titanium or titanium alloy, cast iron, steel, etc. according to the general knowledge of the art.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. A residual stress detection method is characterized by comprising the following steps:
s1. preparation of metal sample
The metal sample comprises a sample base body, two ends above the sample base body are respectively provided with a protruding part, the two protruding parts and the upper surface of the sample base body form a groove together, the two protruding parts are connected through a connecting rod, and a gap is formed between the lower surface of the connecting rod and the upper surface of the sample base body; the connecting rod is symmetrical along a horizontal shaft and comprises thick sections at two ends and a thin section in the middle, the thick sections at the two ends are connected with the two convex parts, the thin section in the middle is respectively connected with the thick sections at the two ends through two transition sections with gradually changed widths, and the upper surface and the lower surface of the thick section, the upper surface and the lower surface of the thin section and the upper surface and the lower surface of the sample substrate are mutually parallel; the metal sample is integrally formed, and the shape of the metal sample is symmetrical along a vertical axis; smelting, refining, casting and surface processing are sequentially adopted to obtain metal samples with corresponding sizes;
s2, heat treatment of metal sample
Carrying out solution quenching treatment on a metal sample; the quenching adopts layered quenching, namely the connecting rod is not quenched and the sample matrix is quenched;
s3, strain detection
After the metal sample is completely cooled, polishing the middle position of the lower surface of the thin section to ensure flatness, then cleaning, attaching a resistance strain gauge to the middle position of the lower surface of the thin section by using a binder, sawing off the part of the middle thin section of the connecting rod, which is connected with the transition section, releasing stress, and measuring strain data;
s4, calculating residual stress
According to the formula: stress = elastic modulus strain, the residual stress is calculated.
2. The residual stress detection method according to claim 1, wherein step S2 further comprises an aging treatment after solution quenching.
3. The residual stress detection method according to claim 1, wherein the dimensions of the metal specimen substrate are: the length is 100-: the length is 15-30mm, the width is 15-20mm, the thickness is 5-15mm, and the size of the thick section is as follows: the length is 15-25mm, the width is 10-15mm, the thickness is 5-15mm, and the size of the thin section is as follows: the length is 20-30mm, the width is 4-10mm, and the thickness is 5-15 mm.
4. The residual stress detection method according to claim 1, wherein the layered quenching specifically comprises:
1) preparing a container filled with a quenching medium;
2) inserting a metal sheet into a gap between the connecting rod and the sample base;
3) and immersing the sample substrate into a quenching medium for quenching, wherein the two ends of the metal sheet are lapped on the edge of the container, and the upper surface of the metal sheet is in supporting contact with the lower surfaces of the two thick sections, so that the thick sections and the thin sections are not quenched.
5. The residual stress detection method of claim 1, wherein in step S3, cleaning treatment is performed by using acetone, and the adhesive is selected from 502 glue, 101 glue or 302 glue.
6. The residual stress detection method according to claim 1, wherein the sections of the thick section and the thin section of the connecting rod are both rectangular.
7. The residual stress detection method according to any one of claims 1 to 6, wherein the width of the narrowest part of the gap between the lower surface of the tie bar and the upper surface of the sample base body is 2 to 8 mm; the width of the widest part is 4-12 mm.
8. The residual stress detection method according to any one of claims 1 to 6, wherein the material of the metal specimen is aluminum or an aluminum alloy, copper or a copper alloy, magnesium or a magnesium alloy, titanium or a titanium alloy, cast iron, or steel.
9. The residual stress detection method according to any one of claims 1 to 6, wherein the entire metal sample is of a uniform thickness.
10. The residual stress detection method according to any one of claims 1 to 6, wherein the quenching employs water or oil as a quenching medium.
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