Tensile strength prediction method for resistance spot welding with initial gap

Abstract

The invention relates to a tensile strength prediction method for resistance spot welding with initial gaps, and the method comprises the steps: inputting real stress-strain curves of three gaps of an automobile sheet into a refined finite element model, and obtaining peak loads of different initial gaps of the automobile sheet; performing quasi-static tensile test on the three physical resistance spot welding test samples with the initial gaps corresponding to the automobile sheet selection gaps to obtain three test peak loads respectively; comparing and analyzing the peak load with a corresponding test peak load to obtain a quantitative relation between the initial gap and the peak load when the plate thickness is 1mm; based on an automobile thin plate with the plate thickness being 1.5 mm, the steps are repeatedly executed, and the quantitative relation between the initial gap and the peak load when the plate thickness is 1.5 mm is obtained; analyzing and integrating the two quantitative relationships to obtain a tensile strength prediction model; and inputting a to-be-predicted automobile sheet into the tensile strength prediction model, and outputting a predicted peak load.

Description

Technical Field

[0001] The present application relates to the technical field of tensile strength prediction of resistance spot welding, and in particular to a method for predicting the tensile strength of resistance spot welding with an initial gap. Background Art

[0002] At present, resistance spot welding has become the dominant sheet metal connection process in the automotive industry due to its low cost and high efficiency. The fatigue limit of spot welded joints is estimated by establishing the relationship between the tensile load difference, tensile load and fatigue limit. This method has good adaptability to the rapid and effective prediction of the fatigue limit of spot welded joints of automotive thin plates. Another method is to obtain the stress-strain curve of each area of ​​the weld through a press-in test, and then establish a coupled damage finite element model to obtain the mechanical performance indicators of each area of ​​the weld, thereby accurately predicting the mechanical properties of the weld joint.

[0003] However, both of the above methods are based on experiments to study the fatigue limit of resistance spot welding and the mechanical properties of weld joints, and do not consider the effect of initial gap on resistance spot welding. Thin plate gap is a common abnormal welding condition in the manufacture of automobile body structures, which may cause assembly changes and affect welding quality; in addition, errors such as stamping deviation and process clamping error of thin plate structural parts accumulate during the body assembly process, forming a comprehensive deviation in body manufacturing, which will also produce initial gaps before plate welding. It can be seen that the initial gap between plates is an inevitable problem in thin plate RSW processing. Therefore, it is necessary to study the effect of initial gap on the mechanical properties and destructive behavior of resistance spot welding materials. Summary of the invention

[0004] Based on this, it is necessary to provide a method for predicting the tensile strength of resistance spot welding with an initial gap, the method comprising:

[0005] S1: Establish a refined finite element model of resistance spot welding with an initial gap. The thickness of the automobile sheet is 1 mm, and a gap is selected every 1 mm in the initial gap of the automobile sheet. The true stress-strain curves of the three gaps of the automobile sheet are input into the refined finite element model to obtain the peak loads of the automobile sheet with different initial gaps.

[0006] S2: Perform quasi-static tensile tests on three physical resistance spot welding test specimens corresponding to the initial gap and the selected gap of the automobile sheet, and obtain three test peak loads respectively;

[0007] S3: Comparing and analyzing the peak load with the corresponding test peak load, obtaining a quantitative relationship between the initial gap and the peak load when the plate thickness is 1 mm;

[0008] S4: Based on the automobile sheet with a thickness of 1.5 mm, S1-S3 were repeated to obtain the quantitative relationship between the initial gap and the peak load when the sheet thickness was 1.5 mm;

[0009] S5: Analyze and integrate the two quantitative relationships to obtain a tensile strength prediction model;

[0010] S6: Input the automobile sheet to be predicted into the tensile strength prediction model, and output the predicted peak load.

[0011] Preferably, the initial gap of the automobile sheet is 0 mm-5 mm.

[0012] Preferably, the quantitative relationship between the initial gap and the peak load when the plate thickness is 1 mm is expressed as:

[0013]

[0014] in, It represents the peak load of the automobile sheet metal with a thickness of 1 mm; δ represents the initial gap.

[0015] Preferably, the quantitative relationship between the initial gap and the peak load when the plate thickness is 1.5 mm is expressed as:

[0016]

[0017] in, It represents the peak load when the thickness of the automobile sheet is 1.5 mm; δ represents the initial gap.

[0018] Preferably, the expression of the tensile strength prediction model is:

[0019]

[0020] f(T)=kT n ;

[0021] F peak =F δ＝0 -0.07913T 2 δ;

[0022] F peak =F Idea -0.1176T 2 δ;

[0023] Among them, F peak represents the predicted peak load; F δ＝0 represents the peak load of resistance spot welding with an initial gap of 0 mm; f(T) represents the influencing factor; T represents the thickness of the automobile sheet; k represents the constant coefficient; n is the power index; δ represents the initial gap; F Idea Represents the peak load of an ideal solder joint.

[0024] Preferably, the method further comprises applying the tensile strength prediction model to a fine finite element model with an initial gap of 6 mm-10 mm to verify the tensile strength prediction model.

[0025] Beneficial effects: This method can accurately predict the tensile strength of resistance spot welding with initial gap, thereby reducing time and experimental costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 The flowchart of the tensile strength prediction method of resistance spot welding with initial gap according to an embodiment of the present application. DETAILED DESCRIPTION

[0028] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.

[0029] like Figure 1 As shown, this embodiment provides a method for predicting the tensile strength of resistance spot welding with an initial gap, the method comprising:

[0030] S1: Establish a refined finite element model of resistance spot welding with an initial gap (the refined finite element model is constructed by a refined numerical simulation method of a warpage defect weld disclosed in announcement number CN117574739B, wherein the equivalent displacement is consistent with the initial gap size), the thickness of the automobile sheet is 1 mm, and a gap is selected every 1 mm in the initial gap of the automobile sheet; the true stress-strain curves of the three gaps of the automobile sheet are input into the refined finite element model to obtain the force and displacement curves, from which the peak loads and failure deformation modes of the automobile sheet with different initial gaps can be known, and the failure deformation modes of welds with different initial gap types are all pull-out failures.

[0031] In this embodiment, the initial gap of the automobile sheet is 0 mm-5 mm; the automobile sheet is taken as an example of commonly used low-carbon steel.

[0032] S2: Quasi-static tensile tests were performed on three physical resistance spot welding test specimens with initial gaps corresponding to the selected gaps of automobile thin plates to obtain three test peak loads and observe their failure fracture modes.

[0033] S3: Compare and analyze the peak load with the corresponding test peak load to obtain a quantitative relationship between the initial gap and the peak load when the plate thickness is 1 mm.

[0034] The quantitative relationship between the initial gap and the peak load when the plate thickness is 1 mm is expressed as:

[0035]

[0036] in, It represents the peak load of the automobile sheet metal with a thickness of 1 mm; δ represents the initial gap.

[0037] S4: Based on an automotive sheet with a thickness of 1.5 mm, S1-S3 were repeated to obtain the quantitative relationship between the initial gap and the peak load when the sheet thickness was 1.5 mm.

[0038] The quantitative relationship between the initial gap and the peak load when the plate thickness is 1.5 mm is expressed as:

[0039]

[0040] in, It represents the peak load when the thickness of the automobile sheet is 1.5 mm; δ represents the initial gap.

[0041] S5: Analyze and integrate the two quantitative relationships to obtain a tensile strength prediction model.

[0042] The expression of the tensile strength prediction model is:

[0043]

[0044] f(T)=kT n ;

[0045] F peak =F δ＝0 -0.07913T 2 δ;

[0046] F peak =F Idea -0.1176T 2 δ;

[0047] Among them, F peak represents the predicted peak load; F δ＝0represents the peak load of resistance spot welding with an initial gap of 0 mm; f(T) represents the influencing factor; T represents the thickness of the automobile sheet; k represents the constant coefficient; n is the power index; δ represents the initial gap; F Idea represents the peak load of an ideal solder joint (F Idea =F δ＝0 ).

[0048] S6: Input the automobile sheet to be predicted into the tensile strength prediction model, and output the predicted peak load.

[0049] In this embodiment, the tensile strength prediction model is also applied to a fine finite element model with an initial gap of 6mm-10mm, the difference between the peak load in the fine finite element model with an initial gap of 6mm-10mm and the peak load predicted by the tensile strength prediction model is analyzed, and the tensile strength prediction model is verified.

[0050] It is worth noting that the 1mm and 1.5mm thick automobile thin plates selected in this embodiment are the thickness types commonly used in car body structures; due to the "2mm project", that is, the comprehensive error index of car body manufacturing = 2.0mm, the initial gap of this embodiment is selected as 0mm-5mm, so as to further reflect the accuracy of the tensile strength prediction model, and an initial gap of 6mm-10mm is used for verification.

[0051] The tensile strength prediction method of the resistance spot welding with initial gap provided in this embodiment has the following beneficial effects:

[0052] 1. Reveal the influence of initial gap on the mechanical properties and mechanical response behavior of resistance spot welding under tensile shear load.

[0053] 2. The tensile strength of resistance spot welds with initial gaps can be accurately predicted, thus reducing time and experimental costs.

[0054] 3. The corresponding mechanical behavior of resistance spot welding with initial gap under tensile shear load can be predicted more quickly and accurately.

[0055] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0056] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A method for predicting the tensile strength of resistance spot welding with an initial gap, characterized in that: include: S1: Establish a refined finite element model of resistance spot welding with an initial gap. The thickness of the automobile sheet is 1 mm, and a gap is selected every 1 mm in the initial gap of the automobile sheet. The true stress-strain curves of the three gaps of the automobile sheet are input into the refined finite element model to obtain the peak loads of the automobile sheet with different initial gaps. S2: Perform quasi-static tensile tests on three physical resistance spot welding test specimens corresponding to the initial gap and the selected gap of the automobile sheet, and obtain three test peak loads respectively; S3: Comparing and analyzing the peak load with the corresponding test peak load, obtaining a quantitative relationship between the initial gap and the peak load when the plate thickness is 1 mm; S4: Based on the automobile sheet with a thickness of 1.5 mm, S1-S3 were repeated to obtain the quantitative relationship between the initial gap and the peak load when the sheet thickness was 1.5 mm; S5: Analyze and integrate the two quantitative relationships to obtain a tensile strength prediction model; S6: Input the automobile sheet to be predicted into the tensile strength prediction model, and output the predicted peak load.

2. The method for predicting the tensile strength of resistance spot welding with an initial gap according to claim 1, characterized in that: The initial gap of automotive sheet metal is 0mm-5mm.

3. The method for predicting the tensile strength of resistance spot welding with an initial gap according to claim 1, characterized in that: The quantitative relationship between the initial gap and the peak load when the plate thickness is 1 mm is expressed as: in, It represents the peak load of the automobile sheet metal with a thickness of 1 mm; δ represents the initial gap.

4. The method for predicting the tensile strength of resistance spot welding with an initial gap according to claim 3, characterized in that: The quantitative relationship between the initial gap and the peak load when the plate thickness is 1.5 mm is expressed as: in, It represents the peak load when the thickness of the automobile sheet is 1.5 mm; δ represents the initial gap.

5. The method for predicting the tensile strength of resistance spot welding with an initial gap according to claim 4, characterized in that: The expression of the tensile strength prediction model is: f(T)=kT n ; F peak =F δ＝0 -0.07913T 2 d; F peak =F Idea -0.1176T 2 d; Among them, F peak represents the predicted peak load; F δ＝0 represents the peak load of resistance spot welding with an initial gap of 0 mm; f(T) represents the influencing factor; T represents the thickness of the automobile sheet; k represents the constant coefficient; n is the power index; δ represents the initial gap; F Idea Represents the peak load of an ideal solder joint.

6. The method for predicting the tensile strength of resistance spot welding with an initial gap according to claim 1, characterized in that: The method also includes applying the tensile strength prediction model to a fine finite element model with an initial gap of 6 mm to 10 mm to verify the tensile strength prediction model.

Images