Process Parameter Optimization And Fracture Characteristics Analysis On Particle Reinforced Weld-bonded Joint Of DP780 Dual Phase Steel

The existence of the second phase of the particles can effectively improve the performance of the adhesive,but the impact of the particles on the mechanical properties of the weld-bonded joints,and the changes in the particle mass fraction,size and other factors have little research on the influence of the mechanical properties of the joints.Therefore the research of particle reinforced weld-bonded connection test was carried out for DP780 dual-phase steel by the response surface method,and the welding parameters were optimized.Meanwhile,the finite element model of particle adhesive structure mechanics was established,which was used to analyze the fracture failure characteristics.The research content and conclusions include:Firstly,the orthogonal test of the alumina particle reinforced adhesive joint was carried out.The effect of alumina particle size,mass fraction and adhesive thickness on the joint strength was analyzed through range and variance analysis,and the optimal process parameters of adhesive structure were determined.The results show that the thickness of the adhesive has the most significant effect on the failure load and energy absorption value.The optimal process parameters of alumina particles reinforce the adhesive joint are: particle size 80 mesh,mass fraction 10%,adhesive thickness 0.4 mm,which is the parameter of the adhesive in the weld-bonded joint.Secondly,based on the Box-Behnken Design response surface test design method,a mathematical regression model of particles reinforce the weld-bonded joint was established,which was between the test factors and the mechanical properties of the joint.The fracture of particle reinforced weld-bonded joints was analyzed with the SEM.The results show that the welding current has the most significant effect on the failure load,energy absorption and weld nugget diameter of the joint,and the optimal process parameters of the alumina particle reinforced weld-bonded joints are: welding current 8.5 k A,welding time 125 ms,electrode pressure 0.5 MPa.The maximum failure load of the joint is 20669.438 N in the process test,and the error calculated from the regression equation is within 3.4%.The crack of interface failure for weld-bonded joints was produced at the edge of the weld nugget,and the crack of pull-out failure is easy to expand in the thickness direction and the nugget ring direction.A finite element model of structural mechanics for particle-reinforced adhesive joints was established,and the effect mechanism of particles on joint failure was analyzed.The results show that the stress concentration appears at the interface between the particles and the adhesive firstly with the existence of the particles second phase,and the initial cracks of the adhesive are generated around the particles and extend along the particles.Hence,the length of the crack for adhesive failure was extended.And the fracture energy of the adhesive increases with the length of the crack,which leads to an increase of the mechanical properties for the weld-bonded joint.