Research On Anti-buckling Device Of SAPH440 Thin Plate In Tension-compression Fatigue

As an important raw material,thin sheet is widely used in the automotive industry to produce various important structural parts and stamping parts.Under the working conditions,the vehicle driving requires not only excellent static mechanical properties and stamping forming properties,but also good fatigue properties.In the context of lightweight vehicles,SAPH440,as a high-strength steel,can replace ordinary strength steel.The low-cycle fatigue performance test of automobile steel plates is an important design index in automobile research and development.According to the national standard,the thin metal plate with a thickness of less than 2.5mm needs to use an anti-buckling device during the strain controlled fatigue test to prevent the sample from buckling instability.How to ensure the buckling device conform to the requirements of the standard,to ensure the sheet tension and compression fatigue performance test process smoothly and accuracy of test results is the research hot spot.In this paper,the critical buckling load of thin plate was calculated and analyzed based on the differential equation of deflection curve.The critical buckling load of SAPH440 thin plate specimens with the same length and different thickness and the same thickness and different length was calculated,and the variation law was analyzed.Before the test,the test material and size could be used to determine whether the anti-buckling device was needed during the test.A novel anti-buckling device of TC4 titanium alloy with adjustable clamping force was designed.By measuring the friction force between the sample and the modified PTFE film,calculating the deformation in the thickness direction of the sample,and measuring the deformation of the anti-buckling device,the stability of the fatigue life data of the sample was analyzed,and the applicability of the anti-buckling device in the tensile and compressive strain control fatigue test of the thin plate was studied.The main conclusions drawn by this subject are:for the sample with a thickness of 1,5mm,a length of 76mm and a width of 10mm parallel section,the critical stress and the critical strain are 253MPa and 0.13%respectively.When the strain amplitude exceeds 0.13%in the test,the sample will buckling instability,and anti-buckling devices shall be used.The relationship between the axial force of bolt fastening and the torque level measured in the test is as follows:F=0.4139W+.3025.The axial force of bolt fastening can be adjusted by adjusting the torque level,so as to adjust the friction between anti-buckling material and sample.The friction can be reduced and the creep resistance and lubrication property of the modified PTFE friction reducer can be enhanced.The test results show that the newly designed lightweight high strength TC4 titanium alloy anti-buckling device can reduce the dead weight and provide sufficient rigid support for the sample.The design of the U-shaped slot effectively solves the problem of uneven force on the rubber rope when the extensometer is clamped.One side of the sample flush with one side of the anti-buckling device and reserve 1mm on the other side for convenient mounting of the extenometer,the alignment between the anti-buckling device and the sample can be realized in the installation process.Using the anti-buckling device,the modified PTFE is used to reduce the friction value generated by the contact between the friction plate and the sample dose not exceed 2%of the test force value.The amount of deformation caused by the pressure of the anti-buckling device and the deformation of the anti-buckling device in the thickness direction of the sample are small,when the torque is 2.5N·m,the strain in the thickness direction of the sample is 0.0030%,which have no obvious effect on the test results.Under the same test condition,the overall fatigue life test data of the sample had less fluctuation and high stability.