Constitutive Description Of Mechanical Behavior Of SAC305 Under Thermo-mechanical Coupled Condition

With the increasingly prominent environmental problems,the trend of lead-free solder replacing lead-containing solder is obvious.Because solder plays a connecting role in packaging devices,the performance of solder determines the reliability of the whole packaging device.The structure and service environment of packaging devices determine that solder will bear complex mechanical and temperature cycling loads,at present,there are relatively few studies on mechanical properties of lead-free solders under cyclic stress/strain and cyclic temperature load in academia,therefore,it is necessary to conduct a comprehensive experimental study and constitutive description of the mechanical properties of solder under mechanical and temperature loads.SAC305 is chosen as the research object in this paper for it is currently recognized as the most likely material to replace lead-containing solder.A series of uniaxial tension experimental data under different temperatures and loading rates were used to quantitatively study the saturation characteristic and normalized characteristics of SAC305,and the constitutive model describing the mechanical properties of SAC305 under constant temperature conditions is established,then,the reason why the stress predicted by the constant temperature model is higher than the experimental in describing the thermo-mechanical coupling condition is analyzed,and the model is modified by introducing a temperature rate correlation term into the back stress evolution equation.Finally,the model is validated by stress relaxation test data,uniaxial ratcheting data under room temperature and uniaxial ratcheting data under thermomechanical coupling conditions.In this paper,a semi-implicit constitutive integral algorithm is derived to solve the constitutive model constructed previously,a user subroutines to define a material(UMAT)for ABAQUS is also developed.After embedding the subroutine into the finite element software,the rod specimen is modeled in ABAQUS,and the uniaxial ratchet data of the rod specimen under the thermo-mechanical coupling condition are calculated by the embedded user subroutine.The results are consistent with the experimental data.