Papers by Author: Mei Rong Zhao

Abstract: Using elastoplastic finite element method study the interface stress distribution of Sn3.5Ag0.75Cu lead-free solder at different temperatures and different strain rate. Numerical analysis results show that: when strain-rate is identical, as the temperature rises, the interface stress increased rapidly of Sn3.5Ag0.75Cu lead-free solder and the substrate binding sites, from 11 °C when 2.6MPa rose to 90 °C in 49.7MPa, so the temperature is very large have effects of the interface stress of the lead-free solder and the substrate binding sites; when the temperature is constant, as the strain rate increases, Sn3.5Ag0.75Cu lead-free solder and the substrate binding sites of the interface stress showed a slight increase, from 0.005% / S when the 49.47MPa rose to 0.005% / S when the 50.08MPa, so strain rate on lead-free solder and the substrate binding sites of the interface stress effect is very small, indicating Sn3 .5Ag0.75Cu lead-free solder has strong rate-independent nature.

Abstract: The effect of recessing on the stresses distributed along the mid-bondline in both standard single lap joints and co-axial ones were analyzed using elasto-plastic finite element method (FEM). The results obtained show that the values of the peak stresses of all the stresses distributed in the mid-bondline were changed greatly as the preformed angle in over lap zone was about 10 0 when the high elastic modulus adhesive is used. The effect of the elastic modulus level on the stress distribution (especially the peak stresses) is small in the middle part of the lap zone. When taken the stress distributed in the middle part of the lap zone into account, there is nearly no significant difference between the peel stress distributed in the standard joint and co-axial single lap joint when the adhesives with lower elastic modulus was used. It is recommended that a co-axial joint is suitable for the recessing joint made by aluminum alloy and a higher elastic modulus adhesive.

Abstract: The influence of fillets with different geometry shape on the stress distribution in aluminum alloy weld-bonded single lap joint was investigated using elasto-plastic finite element method (FEM). The results show that it is advantageous of reducing stress concentration in adhesive layer near the ends of the lap zone in single lap weld-bonded aluminum joints and part of the stress transferring from adhesive layer to the nugget when the joints with a couple of right triangle fillets over other shapes. The load-bearing capacity of the whole weld-bonded joints may be improved. The full-triangular fillet is recommended that it be more advantageous of decreasing the stress peak value and making the stress distribution in overlap zone more uniform.

Abstract: The stress distributed in the mid-bondline of the joints made of aluminium alloy and an epoxy adhesive was determined with the ANSYS software. The results from the FEA showed that the values of the peak stresses of the all the stress components (including the longitudinal stress Sx, the peel stress Sy, the shear stress Sxy, the 1st principal stress S1 and the von Mises equivalent stress Seqv) distributed in the mid-bondline are changed a little as the notch distance L was increased while the notch depth d was not great than 0.6mm. But the evidently changes occurred when the notch depth d was great than 0.9 mm for the stress Sx, Sy and S1 distributed in both the mid-bondline and the interface of the lap zone. When taken the stress distributed in the middle part of the lap zone into account, the peak stress at the point in the mid-bondline corresponding to the edge of the notch decreased firstly and then increased again as the notch distance L was increased from 0 mm to 8 mm. The proper geometry of the notch in the specimen was chosen by finite element analysis.

Abstract: The 3-D elasto-plastic finite element method (FEM) was used to analyze the thermal stress in the laminated composite (SiC/6061Al) under the condition of a temperature cycling of 200 0C-30 0C- 200 0C-30 0C. The results from the FEM analysis showed that the hysteretic peak value of the von Mises equivalent stress in the substrate 6061Al was increased significantly as the temperature loading cycles processed on but it was nearly the same after the first cycle in the interface layer SiC of the laminated composite. The elastic strain in the substrate 6061Al varied within the range of -0.15% to 0.15% and the maximum plastic deformation was equal to about 0.26 %. The results also showed that the maximum normal stress Sx was increased from 32.8 MPa to 87.9 MPa after ten cycles and the work-hardening of the substrate 6061Al occurred during the stress and strain hysteresis loop.