Abstract
New specimen geometries with various stress states are designed and applied for dynamic loading tests. Oscillation-free force is measured during multiaxial loading tests in the strain range of 10-4 – 103 s-1. The deformation and local strain fields of specimens have been measured using high-speed camera and evaluated by digital image correlation (DIC) techniques. It is found that the strain rate effects on fracture strain are stressstate dependent. To model the material plasticity and ductile fracture behaviour during dynamic tests, an extended damage mechanics model (eMBW model) is used. In this work, the model is enhanced and implemented into LS-DYNA. To cover the strain rate effects on plasticity at a large strain rate range, a modified Johnson–Cook-type rate-dependency and exponential temperature-dependency are used. In addition, the influences of both stress state and strain rate on fracture locus are considered. The enhanced damage mechanics model successfully predicts the deformation and fracture behaviour of the investigated steel under dynamic multiaxial loading.
Highlights
Lightweight construction plays an important role in automotive development and environment protection
Accurate characterization of material deformation and fracture behaviour under various stress states, strain rates, and temperatures is necessary to improve the predictive capability of crash simulation
The ductile damage initiation and fracture strain are defined by Eq (3) and Eq (4), respectively
Summary
Lightweight construction plays an important role in automotive development and environment protection. Large multiaxial deformation and fracture might occur in the strain rate range of quasi-static (QS) to 103 s-1 in vehicle crash event. Accurate characterization of material deformation and fracture behaviour under various stress states, strain rates, and temperatures is necessary to improve the predictive capability of crash simulation. A servo-hydraulic machine is often applied to determine material dynamic properties at strain rates lower than 103 s-1. The accurate measurement of the force signal on the servo-hydraulic machine under high-speed loading is always problematic due to the system ringing effects [1,2,3]. A new specimen geometry and a corresponding high-speed testing approach have been developed for oscillation-free force measurement during tensile tests in the strain range of 10-4 – 103 s-1 in previous studies [4,5]
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