Effect of Wall Thickness on Thermal-Induced /Flow-Induced Residual Stresses of Injection Molded Polycarbonate Parts Based on Numerical Simulation

Based on the linear viscoelastic model and compressible viscoelastic constitutive model, the finite differ- ence method and finite volume method were used as the discrete methods of the governing equations to calculate the flow-induced residual stresses and thermal-induced residual stresses of injection molded products, respectively. Numeri- cal simulation of the flow-induced residual stresses and thermal-induced residual stresses of 3 mm, 7 mm and 11 mm in- jection molded polycarbonate sheets were realized. Combined with the injection molding tests, the difference in the dis- tribution of flow- induced residual stresses, thermal- induced residual stresses and total residual stresses of thin- walled/ thick-walled parts were analyzed. The calculation results show that the thermal-induced residual stress area is mainly dis- tributed around the edge of the plate, and the thermal-induced stresses in the central area are significantly lower than in the edge. As the wall thickness increases, the thermal- induced stresses gradually increase, and the distribution area of high residual stresses is increased significantly. When the wall thickness is increased from 3 mm to 11 mm, the distribu- tion area has more than doubled at least. Flow-induced stresses decrease along the melt flow direction. As the wall thick- ness increases, the residual flow-induced stresses is decreased significantly. When the wall thickness is increased from 3 mm to 11 mm, the maximum flow-induced stresses drop from 15 MPa to 1.5 MPa, and the decrease rate reaches 90%. As the wall thickness increases, the contribution of the flow-induced stresses to the total residual stresses of the plates gradually decreases, while that of the thermal-induced stresses gradually increases. For 3 mm thin-walled part, the flow- induced stresses are absolutely dominant. When the thickness of the plate is increased to 7 mm, the flow-induced stress- es in the area near the gate are dominated, and the thermal-induced stresses in the area far away from the gate are domi- nated. For 11 mm thick-walled parts, the thermal residual stresses are absolutely dominant. The numerical simulation re- sults of the residual stress distribution of the plates with different thicknesses are in good agreement with the experimen- tal results, indicating that the numerical simulation method in this paper can effectively predict the residual stresses. © 2022, Editorial Board of Polymer Materials Science & Engineering. All right reserved.