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The Forming Limit Stress Diagram (FLSD) can accurately describe the forming process of high-strength steel. However, obtaining FLSD is relatively difficult. In order to predict fracture in advanced high-strength dual-phase (DP) steels, limit maximum and limit minimum principal strains of sheet were obtained through multiple sets of test and simulation. Two material parameters, strength coefficient K and hardening exponent n are introduced into the FLSD function which is established by the strain-stress transformation function. The function shows that the k-value determines the value of the maximum principal stress, while the n-value affects the curvature of the curve. Verification of correctness by testing and simulation to within 10% accuracy. This paper explores a new approach to FLSD research based on material properties, which can expand the application scope of FLSD. [ABSTRACT FROM AUTHOR]

The article focuses on Europe's changing perceptions of the world amid the COVID-19 pandemic and the Ukraine crisis, emphasizing the importance of Sino-Europe relations in shaping the future regional and world order and the need for collaboration to establish a new type of international relations.

Sheet-metal forming is one of the most important manufacturing processes in the automotive industry. This study proposes a multiobjective optimisation scheme that controls both sheet-metal formability and springback. First, the mechanical properties of DP590 steel were characterised to obtain the mechanical parameters and forming limit diagram (FLD) of DP590. Then, the FLD, thinning rate, and average springback were selected as forming quality evaluation indices. Response surface tests were then conducted for different process parameters for the A-pillar side-stiffener drawing process to analyse the DP590 steel's formability and springback. The optimal process parameters for the drawing process were obtained using a multiobjective optimisation algorithm based on an improved particle swarm method. Finally, a springback compensation scheme was proposed based on the results of the multiprocess simulation. The scheme was applied experimentally to the A-pillar side-stiffener drawing process, and the formability and springback compensation performances verified that the scheme successfully and efficiently eliminated springback and rupture in formed DP590 steel. [ABSTRACT FROM AUTHOR]

Under warm forming, the damage parameters of extended GTN model are easily affected by temperature, and the failure of materials under warm forming is less studied by using this model. In this paper, based on the extended GTN model, the damage parameters of DP590 at different temperatures are determined by experiment and numerical simulation, studying the trend of damage parameters changing with temperature. Through the analysis of shear specimens at different angles and temperatures, we studied the changes in shear damage and void damage under different conditions, discussing the influence of shear damage and void damage on competitive fracture failure under warm forming. We modify the damage by using a function based on stress triaxiality, and present a competitive failure equation considering temperature and stress triaxiality. It is found that the extended GTN model can be applied to the failure study of DP590 steel under warm forming. [ABSTRACT FROM AUTHOR]

The article discusses the background, characteristics and prospects of structural changes in China's relations with the European Union (EU). Topics discussed include factors propelling these structural changes, including a major change in relative economic strength of the two sides, changes in policy orientation and priorities of China and the EU, and Brexit. Also mentioned is the impact of U.S. President Donald Trump's election on the China-EU relations.