Papers by Author: Yu Qi Liu

Abstract: A trimming algorithm is presented for trimming process of refined meshes in sheet metal forming simulation. Firstly, trimming line is pretreated to guarantee it smooth enough for trimming process. Secondly, the elements around the trimming line are found and refined to the highest adaptive level. Thirdly, the intersection points between trimming line segment and the element edge can be obtained using an Advancing Inciting and Adjustment method. Then new number is distributed to nodes of elements on one side of trimming line so that the meshes can be divided into several parts by the trimming line. Finally physical quantities of the remained elements are inherited from the original elements. At last the validity, practicability and speediness of the algorithm are verified with a numerical experiment. And the algorithm is integrated into a sheet metal forming simulation program, FASTAMP.

Abstract: Springback is one of the major problems of high strength steel.Based on the NUMISHEET’96 S_Rail standard examination questions,using the characteristics of the servo press 200T,the blank holder force,different pressure holding time and the holding times of advanced high strength steel DP280-440, DP340-590, DP400-780 are studied. By changing one of the three impact factors ,three group experiments are carried out.The experimental results show that the springback can change evidently with the increasing of the blank holder force and the holding times,but the holding time has little influence on the springback.What’s more,the springback angle of DP400-780 is the biggest ,proving the higher the yield stress,the bigger the springback angle.Therefore, in the stamping of advanced high strength steel, increasing the blank holder force and holding times are effective methods to solve the springback.

Abstract: The formation mechanism of skid lines in automobile panel forming process is investigated in this paper. Based on finite element dynamic explicit algorithm and area coordinate method, a numerical system for predicting skid line is proposed. By comparing with the experimental results, the prediction system is proved to be accurate and efficient.

Abstract: A selective reduced integration 8-node hexahedral element for coining simulation is developed in this paper. The element is free of volume locking by assumed strain method. The standard velocity gradient matrix is derived in which the shear items are ignored to avoid shear locking. Hourglass modes are successfully suppressed without user-input parameters. The element is successfully employed in the coining simulation package - COINFORM. Numerical tests and experiments of a typical coin are carried out to show the good performances of the element.

Abstract: A novel hybrid method is proposed in the paper, which is an assistant tool for product designers to estimate springback in sheet metal forming process at the preliminary design stage. In the hybrid method, the forming results are obtained firstly by an inverse finite element approach (IA) with a membrance element. The thickness strain and stress can be calculated according to the approximate curvature radius of the discrete meshes. Then, a rotation-free shell element is employed, with only three displacements at the corner nodes of the element, to calculate the springback. To verify the accuracy and efficiency of the hybrid method, the numerical results of the hybrid method on two benchmark tests are compared with experimental results.

Abstract: A special elasto-plastic dynamic finite element code named RingForm has been developed to analyze cold ring rolling process. Central difference method was introduced to solve the dynamic explicit finite element equations. Strain state was estimated by the value of yield function of the last and the present time step. To reduce the accumulative error caused by elasto-plastic constitutive relations, the radial return algorithm was employed. In comparison with the experimental results, the cold ring rolling process of a ring with rectangular section has been simulated to verify the accuracy and stability of the system solver.