Abstract
The purpose of this research is to predict fracture loci and fracture forming limit diagrams (FFLDs) considering strain rate for aluminum alloy 7050-T7451. A fracture model coupled Johnson-Cook plasticity model was proposed to investigate its strain rate effect. Furthermore, a hybrid experimental-numerical method was carried out to verify the strain rate-dependent fracture model by using fracture points of uniaxial tension, notched tension, flat-grooved tension, and pure shear specimens. The results show that the fracture points are in accordance with the fracture loci and FFLDs under different strain rates. The increasing strain rate decreases the FFLDs of aluminum alloy 7050-T7451. The difference of force-displacement responses under different strain rates is larger for notched tension and pure shear conditions.
Highlights
Forming limit diagrams (FLD) have been widely used to predict the formability in the sheet metal forming processes, and it can be constructed by experiments such as Marciniak cup tests [1].Fracture forming limit diagrams (FFLDs) present forming limits in the space of (ε1, ε2 ) from the uniaxial compression to the balanced biaxial tension [2]
Dong et al [19] found failure strain decreases with an increase in the strain rate of U-5.5Nb alloy. These results indicate the effect of strain rate on FLD is sensitive to materials
The specimen geometries used in the analysis is to present strain evolution under various strain paths in the fracture loci or FFLDs
Summary
Forming limit diagrams (FLD) have been widely used to predict the formability in the sheet metal forming processes, and it can be constructed by experiments such as Marciniak cup tests [1].Fracture forming limit diagrams (FFLDs) present forming limits in the space of (ε1 , ε2 ) from the uniaxial compression to the balanced biaxial tension [2]. To fully investigate and understand the FFLDs of structural part under various strain rates, the research of mechanical behavior of materials under various loading paths becomes significant. Some experimental studies have revealed that the mechanical behaviors of materials, including initial yield stress, plastic deformation evolution, and even the final fracture strain, present apparent difference under various strain rates [3,4,5]. Xiao et al [13] studied the fracture behavior of the ZK60 alloy by using modified J-C model by considering the effects of strain, stress state, and strain rate. A cryomilled nanostructured 5083 aluminum alloy exhibits the higher ductility at lower strain rates because of a diffusion-mediated stress relaxation mechanism [14]
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