Study On Fatigue Extension Test And Numerical Simulation Of 6063-T651 Aluminum Alloy

Energy saving,emission reduction and light weight are the development trends for rail trains,and more and more aluminium alloys are being used to manufacture train bodies and components.6063-T651 aluminium alloy has superior corrosion resistance,extrudability and welding properties,and is widely used in train roof panels,side walls and end wall panels,and is one of the main materials used to achieve light weight in trains.High-speed trains must also ensure the reliability of their components while achieving light weight.As train structures are subjected to cyclically varying loads for long periods of time,the static strength design is no longer adequate and fatigue strength must also be considered.It is therefore necessary to carry out research into the fatigue crack expansion of materials for fracture and fatigue resistant design.The study of Mode I fatigue crack expansion is the basis for evaluating the fatigue resistance of materials.The alternating stresses in engineering vary greatly,so the fatigue crack expansion law under different stress ratios of mode I cracks needs to be studied clearly.At the same time,the components are often in a complex service environment with multiple loads,and fatigue cracks are mostly of mixed-mode.The compound fatigue test is difficult to study,and as the stress intensity factor of the compound fatigue crack during expansion cannot be calculated by experimental and theoretical methods,an accurate and reliable numerical calculation method is needed to solve this problem.The literature on 6063-T651 aluminium alloys in the field of fatigue is scarce.Therefore,in order to address the above issues,the following studies have been carried out on 6063-T651 plates:（1）Uniaxial tensile experiments.The basic mechanical properties of the material were tested according to the requirements of GB/T 228.1-2021 to provide reliable data for the subsequent finite element simulation of fatigue crack extension.（2）Mode I-loading tests with stress ratios R=0.1,0.2,0.3 and 0.5 were carried out on 6063-T651 aluminium alloy.（3）Mixed-mode I-II loading was carried out on 6063-T651 aluminium alloy material to obtain compound fatigue crack expansion test data.The MTS fatigue testing machine with CCD high-speed camera and its computer system was used to test the fatigue crack expansion of the aluminium alloy under different loading angles（0°,30°,45°,60°,75°）,and the test data were processed by the seven-point incremental polynomial method.（4）Finite element simulations of I-II composite loading were carried out to obtain data such as the stress intensity factor components K_I,K_II and the amplitude of the equivalent force intensity factorΔK*,which were not obtained in the tests.A reliable and effective crack expansion model was established with the aid of ABAQUS finite element analysis software and its fatigue sub-software FRANC3D.The changes in K_I and K_II under different loading angles,the stress-strain changes at the crack tip and the changes in the crack expansion path were obtained.（5）PlotΔK^*-Δa、da/d N-ΔK^*、da/d N-Δa curves and plot double logarithmic curves and calculate the material constants in the Paris formula.