Analysis Of Influencing Factors On Fatigue Performance Of Spot Welded Joints And Life Evaluation

The focus of research in the field of welded structure reliability includes the fatigueresistant design of welded structures and the theoretical methods of life evaluation.The antifatigue design of the welded structure needs to consider the influence of related factors on the fatigue performance of the welded structure.Information entropy reflects the amount of information carried by the influencing factor,that is,the importance of the factor.The concept of information entropy is used to study the influence of the fatigue life of the welded joint.Factors,which can realize quantitative analysis of various influencing factors from a statistical perspective;for the research on welding fatigue life assessment theory,traditional methods have disadvantages such as time-consuming,labor-intensive,and expensive.Because thermodynamic entropy can reflect the integrity of the system,explaining the physical mechanism of the fatigue damage process has unique advantages and has attracted more and more scientific researchers’ attention.In this paper,based on the fatigue research of stainless steel and carbon steel spot welded joints,combined with basic concepts such as information entropy and thermodynamic entropy,the analysis of influencing factors of welding fatigue performance and welding fatigue life evaluation methods are studied.Changes in influencing factors will lead to different fatigue properties of welded joints.This article firstly affects the plate thickness,plate width,lap length,electrode diameter,electrode pressure,welding time,welding current,welding heat input,etc.in the spot welding process.Factors are regarded as the carrier of information,and then the fatigue data obtained under different processes are used to draw the F-N curve with different magnification standard deviations,and the fatigue performance is divided into four levels.Finally,based on the concept related to information entropy,the information of each parameter is calculated Entropy,information gain and information gain rate are analyzed to study their influence on welding fatigue performance.The results show that the information entropy and information entropy of the plate thickness and the welding time account for the largest proportion,the uncertainty is the highest,and the electrode diameter is just the opposite of the electrode force.The information gain rate of electrode diameter and electrode pressure is 59.34%,which has the greatest impact on fatigue performance;the information gain rate of plate width is 38.89%,which has the least impact on fatigue performance.To judge the fatigue damage degree of components based on the fatigue damage entropy model,it is necessary to measure the components under different loads.In order to quickly obtain the fatigue damage of the components under any load,this paper proposes a fatigue damage entropy prediction model,which combines the fatigue damage entropy,Load and cycle times are integrated together,only need to determine the value of any variable,you can get the relationship between the other two variables.And in order to verify the model,four sets of spot welded joint specimens with different welding processes are taken in the article,and the predicted fatigue damage entropy of these four sets of specimens is compared with the true value.The results show that the predicted value of fatigue damage entropy is compared with the true value.It is very close,and the established prediction model can better reflect the relationship between damage entropy and cycle times.The fatigue damage entropy at fracture is a constant,which represents the characteristics of the structure itself.Substituting this constant into the fatigue damage entropy prediction model,an expression reflecting the relationship between load and fatigue life can be obtained.And this expression is the FN curve,which reflects the relationship between load and fatigue life when the structure is broken.In order to verify the accuracy of the F-N curve based on the fatigue damage entropy,this paper compares it with the three-parameter power function F-N curve,and compares the overlap and fatigue limit of the F-N curve obtained by two different methods.The comparison results show that the overlap of the F-N curves obtained by the two different methods is very high,and the error of the fatigue limit is 15.4% at the highest and 1.6%at the lowest.The article finally analyzes the influence of the number of loads referred to when the fatigue damage entropy prediction model is established on the accuracy of the F-N curve based on the fatigue damage entropy.The results show that the more the number of reference loads,the obtained F-N curve and the three-parameter power function formula the higher the degree of coincidence of the FN curve.