LIU Yongning
,
ZHU Jinhua
,
ZHOU Huijiu Xi'an Jiaotong University
,
Xi'an
,
China A.Kildegaard
,
J.A.Kristensen Department of Mechanical Engineering
,
Aalborg University
,
Denmark Dept.of Materials Science and Engineering Xi'an Jiaotong University
,
Xi'an 710049
,
China
金属学报(英文版)
The dynamic fracture toughness of a mild steel has been studied at different loading rates and temperatures.The material exhibits a transition from tough to brittle fracture with the chang- ing loading rate alone.Analysis of the fracture process by the theory of thermal activation suggests that the fracture activation energy approximates to the bond energy of the{100}of a unit cell.The toughness can be resolved into two parts,J-(fd)=J_a+J_l,where J_a is the athermal part,being independent on temperature and loading rate,while J_l=(K/K_o)~(1/n)exp(Q_f/nkT),which controls the fracture process is temperature and load- ing rate dependent.The transition of fracture mechanism caused by both temperature and loading rate is associated with the thermal movement of atoms.
关键词:
mild steel
,
null
,
null
,
null
International Journal of Materials & Product Technology
In this paper, the production of stainless steel hemi-toroidal parts has been investigated using three different processes: the conventional stamping, the standard sheet hydroforming and the hydroforming adopting a movable die (MD) which can have a vertical stroke and whose shape completes the female die cavity. Tests adopting the MD were performed at Aalborg University using a specific experimental equipment; numerical simulations were performed using ABAQUS\Explicit and were aimed at investigating the effect of the friction condition of the MD tool on the blank deformation. The friction coefficient was varied on both the whole surface of the MD tool and locally (in the region of the MD corner radius). The role of the MD in the hydrofonning process was thus studied by comparing results in terms of thickness and strain distributions on the final part obtained adopting the same geometry of tools, but different forming techniques. Simulations put in evidence that a moderate increase of the friction can be successfully used for reducing thinning if the MD is adopted; in addition, the friction in the region of the MD corner radius shows to play a key role in forming sound parts.
关键词:
sheet hydroforming;movable tool;hemi-toroidal shape;finite element;method;deep-drawing process;welded blanks;sheet;technology;simulation;parts
