CN108181190B - Method for rapidly predicting fatigue limit of spot-welded joint made of dissimilar materials - Google Patents
Method for rapidly predicting fatigue limit of spot-welded joint made of dissimilar materials Download PDFInfo
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Abstract
The invention discloses a method for rapidly predicting fatigue limit of spot-welded joints made of dissimilar materials, and relates to the technical field of fatigue reliability evaluation of welded structures. The method comprises the following steps: determining the fatigue temperature rise slope corresponding to each load level in the third stage; dividing a plurality of fatigue temperature rise slopes according to a specified rule to obtain two groups of fatigue temperature rise slope data; the method can realize the rapid prediction of the fatigue limit of the spot-welded joint made of dissimilar materials, and the result has authenticity and reliability.
Description
Technical Field
The invention relates to the technical field of fatigue reliability assessment of welding structures, in particular to a method for quickly predicting fatigue limit of spot-welded joints made of dissimilar materials.
Background
High speed, heavy load, energy saving, safety and comfort are the main characteristics of modern railway transportation, and the light structure is an effective way to achieve the above aims. The SUS301L austenitic stainless steel train is widely applied by virtue of the advantages of light dead weight, good corrosion resistance, high tensile strength, attractive appearance, safety and the like; the Q235 low-carbon steel has good weldability and hardenability, and the hardness of a welded joint and a heat affected zone of most low-carbon steels is higher than that of a base metal. A part of automobile body parts adopt a connection method of spot welding of stainless steel and carbon steel dissimilar materials, so that the advantages of the stainless steel and the carbon steel can be comprehensively utilized, and the problem of joint strength reduction caused by large welding deformation of the traditional thin plate arc welding can be solved. However, the overload mechanical property, the fatigue property and the fracture mechanism of the two materials are completely different, so that the reliable prediction of the fatigue limit of the two spot-welded joints is an extremely important link in the structural design process.
In recent years, the infrared thermography is gradually favored by domestic and foreign scholars by virtue of the advantages of full field, real time, non-contact, non-destruction and the like, and is applied to the research of fatigue limit. The existing fatigue prediction method based on the infrared thermal imaging technology is mainly based on a Risitano single-line method and a Luong double-line method, Risitano and the like, and through fifteen years of intensive research, the temperature value and the load size in the temperature stabilization stage in the material fatigue failure process have approximate linear relation under the action of a load higher than the fatigue limit; and under the action of the load lower than the fatigue limit, the temperature change of the material is small, and the fatigue limit of the material can be determined by drawing a linear relation between the temperature rise value and the load in the temperature stabilization stage under different load levels. Luong et al found that although fatigue failure does not occur when the applied load is below the fatigue limit, non-plastic effects (such as viscous effects) also cause temperature changes, and that by linearly fitting the two sets of temperature data above and below the fatigue limit, the intersection of the two lines is the fatigue limit of the material.
However, spot welded joints, particularly spot welded joints of dissimilar materials, are susceptible to nugget migration on the one hand; on the other hand, as the action point of the cyclic load is positioned in the center of the nugget, the temperature evolution phenomenon of the nugget surface in the fatigue process is difficult to monitor. Due to the factors, the fatigue temperature rise evolution law of the spot-welded joint made of dissimilar materials is different from that of a typical metal material and a butt joint. Firstly, the fatigue temperature rise value in the whole fatigue process is not large, which is determined by the structural characteristics of a spot welding joint and the geometric size of a sample, the spot welding joint bears the action point of cyclic shearing and stretching, namely a heat source point is positioned in the center of a nugget, and the heat is transferred to the surface of the sample in the plate thickness direction, so that the heat dissipation is more, the temperature rise value of several degrees or even a few zero degrees can be monitored, but the integral trend of fatigue temperature evolution and the intensive research developed by the temperature rise value are not influenced; thirdly, the peak value formed by the rapid temperature rise in the first stage is far lower than the peak value corresponding to the final fracture, because the spot-welded joint has low bearing capacity, small applied load and less mechanical energy input from the outside compared with a pure metal or butt joint sample; in addition, a stage with no stable temperature appears, for a third stage occupying most of the whole fatigue process, the temperature is a stable increasing process, the fatigue temperature increasing slope of the whole third stage is a stable value, and a second stage of a typical metal material 'three stages' does not appear, so that the Risitano single-line method and the Luong double-line method cannot be applied to rapid prediction of the fatigue limit of the spot-welded joint made of dissimilar materials.
Disclosure of Invention
The embodiment of the invention provides a method for quickly predicting the fatigue limit of a spot-welded joint made of dissimilar materials, which is used for solving the problem that the Risitano single-line method and the Luong bilinear method in the prior art cannot be suitable for quickly predicting the fatigue limit of the spot-welded joint made of dissimilar materials.
The embodiment of the invention provides a method for rapidly predicting the fatigue limit of spot-welded joints made of dissimilar materials, which comprises the following steps:
s1, spraying a layer of uniform black matte paint on the surface of the fatigue test sample, wherein the radiance of the black matte paint is 0.9; the fatigue test sample is prepared from spot-welded joints made of dissimilar materials;
s2, monitoring the temperatures of a stainless steel side nugget of the spot-welded joint of the dissimilar material and a local hot spot on the surface of the plastic ring in real time by using a thermal infrared imager;
s3, determining the original relation between fatigue temperature rise and cycle times under different load levels; the fatigue temperature rise is the difference between the highest temperature of a stainless steel side nugget of the spot-welded joint made of dissimilar materials and a local hot spot on the surface of the plastic ring and the highest temperature of the environment;
s4, filtering the original relation between the fatigue temperature rises and the cycle frequency to obtain the evolution trend of the fatigue temperature rises and the cycle frequency under different load levels; the fatigue temperature rise and cycle evolution trend comprises four stages, wherein the first stage is a temperature rapid rise stage, the second stage is a temperature decrease stage, the third stage is a temperature stable rise stage, and the fourth stage is a cooling stage;
s5, determining the fatigue temperature rise slope corresponding to each load level in the third stage; wherein the fatigue temperature rise slope is the fatigue temperature rise change of millions of cycles of the cycle;
s6, dividing the multiple fatigue temperature rise slopes according to a specified rule to obtain two groups of fatigue temperature rise slope data;
dividing the multiple fatigue temperature rise slopes according to a specified rule to obtain two groups of temperature rise slope data, wherein the two groups of temperature rise slope data comprise:
dividing the temperature rise slope smaller than or equal to a specified threshold into a group;
dividing the temperature rise slope larger than a specified threshold into a group;
s7, respectively carrying out linear fitting on the two sets of fatigue temperature rise slope data to obtain two linear equations, and taking the load level value corresponding to the intersection point of the two linear equations as the fatigue limit predicted value of the spot-welded joint made of dissimilar materials;
the two groups of fatigue temperature rise slope data are respectively subjected to linear fitting to obtain two linear equations which are respectively:
θ1＝0.000278567F+0.12346
θ2＝1.12259F-6.12676
wherein F is the load level, θ1Is a first temperature rise slope, theta2Is the second temperature rise slope.
Preferably, the step S7 is followed by:
s8, predicting the spot-welded joints of dissimilar materials by using a step method to obtain a fatigue limit test value;
and S9, comparing the fatigue limit predicted value with the fatigue limit test value to obtain an error value.
Preferably, the dissimilar materials are composed of SUS301L stainless steel and Q235B mild steel each having a thickness of 4 mm.
Preferably, the sensitivity of the thermal infrared imager is less than 0.03 ℃, the temperature range is-20 ℃ to 1200 ℃, and the image capturing frequency is 9 Hz.
In the embodiment of the invention, the fatigue temperature rise slope corresponding to each load level in the third stage is determined; dividing a plurality of fatigue temperature rise slopes according to a specified rule to obtain two groups of fatigue temperature rise slope data; the method comprises the steps of respectively carrying out linear fitting on two groups of fatigue temperature rise slope data to obtain two straight lines, taking a load level value corresponding to an intersection point of the two straight lines as a predicted value of the fatigue limit of the dissimilar material spot welding joint, namely, taking the load size corresponding to the turning of the temperature rise slope as a critical point of the change of a fatigue damage mechanism, and predicting the fatigue limit of the dissimilar material spot welding joint according to the predicted value and a test value, wherein the error obtained by comparing the predicted value with the test value is 5.21%, and the predicted value has high consistency, so that the method can realize the rapid prediction of the fatigue limit of the dissimilar material spot welding joint, and the result has authenticity and reliability.
Drawings
FIG. 1 is a sample size of a spot weld joint of dissimilar materials provided by an embodiment of the present invention;
FIG. 2 is a temperature measurement system for a fatigue test of a method for rapidly predicting the fatigue limit of a spot-welded joint made of dissimilar materials according to an embodiment of the present invention;
fig. 3 is a schematic flowchart of a method for rapidly predicting fatigue limit of a spot-welded joint made of dissimilar materials according to an embodiment of the present invention;
FIG. 4 is a graph of fatigue temperature rise versus cycle number for a fatigue test specimen provided by an embodiment of the invention at a load level of 7.0 KN;
FIG. 5 is a graph showing the relationship between fatigue temperature rise and cycle frequency of a fatigue test specimen under different load levels according to an embodiment of the present invention;
FIG. 6 is a graph illustrating fatigue limit prediction for a spot-welded joint made of dissimilar materials according to an embodiment of the present invention;
fig. 7 is a graph showing the test results of predicting spot-welded joints made of dissimilar materials by using a stepped method according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Test materials and apparatus of embodiments of the invention
SUS301L stainless steel and Q235B low-carbon steel with the thickness of 4mm are selected for the test, overlapping double-sided single-spot welding of dissimilar materials is carried out, and the nominal chemical components and the main mechanical properties are shown in tables 1 and 2. In order to ensure the quality of a welded joint, the surface of a welded part needs to be cleaned before welding to remove dirt and an oxide film on the surface, so that small, uniform and consistent contact resistance is obtained, which is a main premise for avoiding electrode adhesion and splashing and ensuring the spot welding quality and the test stability. The spot welding test is carried out on a suspension type spot welding machine, the electrode material is CrZrCu, the diameter of the electrode is 22mm, the spherical radius of the end of the electrode is 100mm, and the stroke of the electrode is 30 mm. After spot welding, appearance test, smoothness test and cross-section test were carried out in accordance with JIS Z3140-2000 and JIS Z3139-2000.
TABLE 1 nominal chemical composition of the test materials
TABLE 2 Main mechanical Properties of the test materials
In the embodiment of the invention, a spot-welded joint made of SUS301L-Q235B dissimilar materials is selected as a fatigue sample, a fatigue temperature evolution test of the fatigue sample is carried out on a PLG-200D high-frequency fatigue testing machine, the size of the fatigue sample is shown in figure 1 (unit: mm) according to the ISO14234-2003 standard, the longitudinal direction of the sample is the plate rolling direction, the edge of a plate-shaped test piece needs to be properly trimmed, and the test piece is required to be symmetrical and have sufficient precision.
Specifically, in order to improve the emissivity of the metal surface, a layer of uniform black matte paint with the emissivity of 0.9 is sprayed on the surface of the fatigue test sample. Stress ratio R in the fatigue test was 0.1, and the test was carried out in a sine wave manner, and the specified life was 2 × 106Next, the process is carried out.
Fig. 2 is a temperature measurement system for a fatigue test of a method for rapidly predicting the fatigue limit of a spot-welded joint made of dissimilar materials according to an embodiment of the present invention, the system records the temperature changes of a stainless steel side nugget and a local hot spot of a plastic ring of the spot-welded joint by using a Ti450 thermal infrared imager manufactured by Fluke corporation in usa, the sensitivity of the thermal infrared imager is not more than 0.03 ℃, the temperature range is-20 to 1200 ℃, the image capturing frequency is 9Hz, and the thermal infrared imager is placed at a position 30cm away from a sample and shot perpendicular to the surface of the sample.
And (3) mechanical property testing, in order to obtain tensile property parameters of the spot-welded joint made of the dissimilar materials of US301L-Q235B so as to determine the level of an initial load applied in a fatigue test, three groups of samples are respectively taken to carry out a static load tensile test, and the measured tensile strength is shown in Table 3. It can be seen that under the technological parameters selected by the test, the tensile strength of the spot-welded joint is lower than that of the base material due to the eccentric shearing and stretching effect caused by the characteristics of the spot-welded lap joint.
TABLE 3 static load tensile Properties of spot-welded joints made of US301L-Q235B dissimilar materials
Fig. 3 is a schematic flow chart of a method for rapidly predicting fatigue limit of a spot-welded joint made of dissimilar materials according to an embodiment of the present invention. As shown in fig. 3, the method includes:
s1, spraying a layer of uniform black matte paint on the surface of the fatigue test sample, wherein the radiance of the black matte paint is 0.9; the fatigue test sample is prepared from spot-welded joints made of dissimilar materials.
And S2, monitoring the temperatures of the stainless steel side nuggets of the spot-welded joints made of the dissimilar materials and the local hot spots on the surfaces of the plastic rings in real time by using a thermal infrared imager.
In the examples, high frequency pull-pull load fatigue tests were carried out on fatigue specimens of spot welded joints of dissimilar materials SUS301L-Q235B at different load levels, and seven load levels of 5.0KN, 5.5KN, 6.0KN, 6.5KN, 7.0KN, 7.5KN, and 8.0KN were selected. And during the test, a high-performance thermal infrared imager is used for monitoring local hot spots on the surfaces of a stainless steel side nugget and a plastic ring of the spot welding head SUS301L, and the temperature evolution data of the spot welding head in the whole fatigue test process is recorded.
S3, determining the original relation between fatigue temperature rise and cycle times under different load levels; the fatigue temperature rise is the difference between the highest temperature of a stainless steel side nugget and a local hot spot on the surface of the plastic ring of the spot-welded joint made of the dissimilar materials and the highest temperature of the environment.
S4, filtering a plurality of original relations between the fatigue temperature rise and the cycle frequency to obtain the evolution trends of the fatigue temperature rise and the cycle frequency under different load levels; the fatigue temperature rise and cycle evolution trend comprises four stages, wherein the first stage is a temperature rapid rise stage, the second stage is a temperature decrease stage, the third stage is a temperature stable rise stage, and the fourth stage is a cooling stage.
In order to perform unified analysis and comparison, the difference value between the highest temperature of the local hot spot on the stainless steel side nugget and the plastic ring surface of the spot-welded joint sample SUS301L at each moment and the highest temperature of the environment is used as fatigue temperature rise delta T, the cycle number N is used as an abscissa, and the fatigue temperature rise delta T is used as an ordinate, so that an original temperature evolution curve of the dissimilar spot-welded joint in the fatigue process is established. The sample was taken as an example at a load level of 7.0 KN. Due to the existence of the elastic effect, the original temperature of the dissimilar material spot welding joint in the fatigue process is a continuous oscillation process, and the original temperature needs to be filtered by Matlab software so as to eliminate the elastic effect and obtain the integral trend of the temperature evolution of the spot welding joint in the fatigue process. The overall temperature evolution trend obtained after Matlab filtering is shown in fig. 4, wherein (a) is a photograph of a spot-welded joint sample made of dissimilar materials taken under visible light, and (b) to (f) are infrared thermographs corresponding to key points. It can be seen that the temperature change of the nugget and the local hot spot on the surface of the plastic ring under the cyclic load of the spot-welded joint made of the dissimilar materials of SUS301L-Q235B is divided into four stages, namely, a rapid temperature rise stage from (b) to (c), a temperature fall stage from (c) to (d), a stable temperature rise stage from (d) to (f) and a subsequent natural cooling stage, which is obviously different from the typical characteristics reported about the pure metal material "three stages" and the butt joint "five stages". Firstly, the fatigue temperature rise value in the whole fatigue process is not large, which is determined by the structural characteristics of a spot welding joint and the geometric size of a sample, the spot welding joint bears the action point of cyclic shearing and stretching, namely a heat source point is positioned in the center of a nugget and transfers heat to the surface of the sample through the thickness of 4mm, the heat dissipation is more, and the temperature rise value of a few degrees or even a few degrees at zero can be monitored, but the integral trend of fatigue temperature evolution and the intensive research developed by the temperature rise value are not influenced; thirdly, the peak value at the position (c) formed by the rapid temperature rise in the first stage is far lower than the peak value at the position (f) corresponding to the final fracture, because the spot welding joint has low bearing capacity, small applied load and less mechanical energy input from the outside compared with a pure metal or butt joint sample; in addition, the stage without stable temperature appears, for the third stage occupying most of the whole fatigue process, the temperature is a stable rising process, and the fatigue temperature rising slope of the whole third stage is a stable value.
In order to deeply study the internal relationship between the fatigue temperature rise and the fatigue limit, the fatigue temperature rise and cycle times of seven spot-welded joint samples are established under the same coordinate system, as shown in fig. 5. It can be seen that the peak value of the fatigue temperature rise gradually increases with the increase in the load level, and the temperature change rate, i.e., the temperature rise per unit week, is larger. Wherein, the samples with the load levels of 5.0KN and 6.5KN do not break when the cycle frequency reaches the preset frequency of 200 ten thousand, the fatigue temperature rise is a vibration platform, and the temperature change amount is small; and the specimens which have fatigue fracture all show significant temperature changes. Therefore, the load magnitude corresponding to the turning of the temperature rising slope is used as the critical point of the change of the fatigue damage mechanism, and the fatigue limit of the spot-welded joint made of dissimilar materials is predicted according to the critical point.
S5, determining the fatigue temperature rise slope corresponding to each load level in the third stage; wherein, the fatigue temperature rise slope is the fatigue temperature rise change of millions of cycles of the cycle.
And S6, dividing the multiple fatigue temperature rise slopes according to a specified rule to obtain two groups of fatigue temperature rise slope data.
Wherein, dividing a plurality of fatigue temperature rise slopes according to a specified rule to obtain two groups of temperature rise slope data comprises:
and dividing the temperature rise slope which is less than or equal to a specified threshold into one group.
And dividing the temperature rise slope larger than a specified threshold into a group.
The specified threshold is an empirical value, and in the embodiment of the present invention, the threshold may be set to 0.5.
And S7, respectively carrying out linear fitting on the two groups of fatigue temperature rise slope data to obtain two linear equations, and taking the load level value corresponding to the intersection point of the two linear equations as the predicted fatigue limit value of the spot-welded joint made of the dissimilar materials.
Wherein a third stage temperature rise slope versus load level is established as shown in fig. 6. As can be seen from the graph, the temperature rise slopes corresponding to the load levels of 5.0KN, 5.5KN and 6.5KN are very small and less than the specified threshold of 0.5, and the temperature rise slopes of the other four load levels are changed significantly. In order to determine the load corresponding to the turning of the temperature rise slope, and using the load as a predicted fatigue limit value, two groups of fatigue temperature rise slope data are respectively subjected to linear fitting, and two linear equations are obtained:
θ1＝0.000278567F+0.12346 (1)
θ2＝1.12259F-6.12676 (2)
and (3) combining the formula (1) with the formula (2), wherein the abscissa corresponding to the intersection point of the two straight lines is 5.569 KN. Therefore, the predicted fatigue limit of the spot-welded joint of dissimilar materials was 5.569 KN.
In addition, in order to verify the authenticity and reliability of the fatigue limit prediction method of the present invention, a step method fatigue test was subsequently performed.
And S8, predicting the spot-welded joint of the dissimilar materials by using a step method to obtain a fatigue limit test value.
And S9, comparing the fatigue limit predicted value with the fatigue limit test value to obtain an error value.
Fatigue test by step method
According to the GB/T15111-94 shear-tensile-fatigue test method for spot-welded joints, fatigue tests are carried out by adopting 2X106 times as a discrimination standard, and when the sample exceeds the preset cycle, 2X106Without significant macrocracks, considered as "pass" or "fail" otherwise. Determining the initial load of a fatigue test according to experience and the tensile strength obtained by a static load tensile test of the spot-welded joint, wherein the fatigue load applied in the fatigue test is started from 7KN, and if a test piece in the previous test does not pass, the load is reduced by 0.5KN in the next test; otherwise, 0.5KN is increased. According to the rule, under the same loading frequency and stress ratioThe fatigue test is repeatedly carried out, according to GB/T24178-2009 statistical scheme and analytical method of fatigue test data of metal materials, at least 8 samples are selected for explanation test, two samples are tested at each load level under 4 load levels with equal intervals, and the test result is shown in FIG. 7.
Statistical analysis is carried out on the test data, and the dissimilar material spot-welded joint can be obtained at 2X106The fatigue limit corresponding to the cycle times is as follows:
the fatigue limit predicted value obtained by the method of the invention is compared with a fatigue limit test value obtained by a step method, and the error is calculated as follows:
therefore, the delta is the error between the predicted value of the fatigue limit and the experimental value of the fatigue limit, is 5.21 percent, has higher consistency, can realize the rapid prediction of the fatigue limit of the spot-welded joint of the dissimilar materials, and is expected to provide theoretical guidance and technical support for the research of the service behavior of the heterogeneous welding structure of the dissimilar materials with different thicknesses.
According to the embodiment of the invention, the temperature change of the nugget and the local hot spot on the surface of the plastic ring of the spot-welded joint made of the SUS301L-Q235B dissimilar materials under the action of cyclic load is divided into four stages, the peak value of fatigue temperature rise gradually rises along with the rise of the load level, and the temperature change rate, namely the temperature rise in unit cycle, is larger. And the fatigue temperature rise slope of the whole third stage is a stable value. Therefore, the fatigue temperature rise slope corresponding to each load level in the third stage is determined; dividing a plurality of fatigue temperature rise slopes according to a specified rule to obtain two groups of fatigue temperature rise slope data; respectively carrying out linear fitting on the two groups of fatigue temperature rise slope data to obtain two straight lines, taking a load level value corresponding to an intersection point of the two straight lines as a predicted value of the fatigue limit of the dissimilar material spot welding joint, namely, taking the load size corresponding to the turning of the temperature rise slope as a critical point of the change of a fatigue damage mechanism, predicting the fatigue limit of the dissimilar material spot welding joint according to the predicted value, obtaining the predicted value of the fatigue limit of the spot welding joint as 5.569KN, carrying out a step method fatigue verification test, obtaining the fatigue limit of the dissimilar material spot welding joint corresponding to 2X106 cycle times as 5.875KN, and obtaining the error between the predicted value and the test value as 5.21%, wherein the error has high consistency.
The above disclosure is only a few specific embodiments of the present invention, and those skilled in the art can make various modifications and variations of the present invention without departing from the spirit and scope of the present invention, and it is intended that the present invention encompass these modifications and variations as well as others within the scope of the appended claims and their equivalents.
Claims (4)
1. A dissimilar material spot welding joint fatigue limit rapid prediction method is characterized by comprising the following steps:
s1, spraying a layer of uniform black matte paint on the surface of the fatigue test sample, wherein the radiance of the black matte paint is 0.9; the fatigue test sample is prepared from spot-welded joints made of dissimilar materials;
s2, monitoring the temperatures of a stainless steel side nugget of the spot-welded joint of the dissimilar material and a local hot spot on the surface of the plastic ring in real time by using a thermal infrared imager;
s3, determining the original relation between fatigue temperature rise and cycle times under different load levels; the fatigue temperature rise is the difference between the highest temperature of a stainless steel side nugget of the spot-welded joint made of dissimilar materials and a local hot spot on the surface of the plastic ring and the highest temperature of the environment;
s4, filtering the original relation between the fatigue temperature rises and the cycle frequency to obtain the evolution trend of the fatigue temperature rises and the cycle frequency under different load levels; the fatigue temperature rise and cycle evolution trend comprises four stages, wherein the first stage is a temperature rapid rise stage, the second stage is a temperature decrease stage, the third stage is a temperature stable rise stage, and the fourth stage is a cooling stage;
s5, determining the fatigue temperature rise slope corresponding to each load level in the third stage; wherein the fatigue temperature rise slope is the fatigue temperature rise change of millions of cycles of the cycle;
s6, dividing the multiple fatigue temperature rise slopes according to a specified rule to obtain two groups of fatigue temperature rise slope data;
the method for dividing the fatigue temperature rise slopes according to the designated rule to obtain two groups of temperature rise slope data comprises the following steps:
dividing fatigue temperature rise slopes with the temperature rise slope less than or equal to a specified threshold into a group;
dividing fatigue temperature rise slopes with temperature rise slopes larger than a specified threshold into a group;
s7, respectively carrying out linear fitting on the two sets of fatigue temperature rise slope data to obtain two linear equations, and taking a load level value corresponding to the intersection point of the two linear equations as a fatigue limit predicted value of the spot-welded joint made of the dissimilar materials;
and respectively carrying out linear fitting on the two groups of fatigue temperature rise slope data to obtain two linear equations, wherein the two linear equations are respectively:
θ1＝0.000278567F+0.12346
θ2＝1.12259F-6.12676
wherein F is the load level, θ1Is a first temperature rise slope, theta2Is the second temperature rise slope.
2. The dissimilar material spot weld joint fatigue limit rapid prediction method according to claim 1, further comprising, after the step S7:
s8, predicting the spot-welded joints of dissimilar materials by using a step method to obtain a fatigue limit test value;
and S9, comparing the fatigue limit predicted value with the fatigue limit test value to obtain an error value.
3. A spot-welded joint fatigue limit rapid prediction method of dissimilar materials according to claim 1, characterized in that said dissimilar materials are composed of SUS301L stainless steel and Q235B low carbon steel each having a thickness of 4 mm.
4. The dissimilar material spot-welded joint fatigue limit rapid prediction method according to claim 1, wherein the thermal infrared imager has a sensitivity of less than 0.03 ℃, a temperature range of-20 ℃ to 1200 ℃, and an image capturing frequency of 9 Hz.
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| CN109596425A (en) * | 2019-01-09 | 2019-04-09 | 江西江铃集团新能源汽车有限公司 | A kind of lap joint Evaluation Method of Mechanical Property |
| CN111198140A (en) * | 2020-02-10 | 2020-05-26 | 大连交通大学 | Method for rapidly predicting fatigue limit of welding joint based on fatigue damage entropy production rate |
| CN112284942B (en) * | 2020-10-23 | 2024-03-26 | 哈尔滨工业大学 | Thermal boundary condition control method for fatigue limit assessment of welded joint |
| CN112924307B (en) * | 2021-01-29 | 2023-01-20 | 有研工程技术研究院有限公司 | Fatigue limit rapid prediction method based on infrared thermal imaging |
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