Papers by Keyword: Shear Fracture

Abstract: Recently, advanced high strength steels (AHSSs) have been widely applied to the structural parts of vehicles thanks to their good combination of strength and ductility. When one makes parts with AHSSs, however, fractures in sharp corners of the parts are frequently observed below forming limit, which is normally defined by strain based FLC(Forming Limit Curve). This phenomenon is well-known as “Shear Fracture”. Recent researches point out that additional numerical techniques should be considered in order to predict it accurately. Kim et al. [1] suggested that shear fracture can be predictable with continuum-based finite elements rather than conventional shell elements, and more constitutive informations for large strain thermo-mechanical simulation are needed to improve accuracy. Luo and Wierzbicki [2] showed that shear fracutre in stretch-bending test can be fully characterized by proposed MMC(Modified Mohr-Coulomb). This paper shows that solid-shell approach based on hyper-elastoplastic material model enables one to properly predict shear fracture pheonomenon without any special failure criteria. Furthermore, the effects of non-associated flow rule on shear fracture will be also discussed with several numerical examples.

Abstract: The press bonding experiments of Ti-17 alloy were conducted at the bonding temperatures ranging from 730°C to 880°C, a bonding pressure of 20 MPa and a bonding time of 15 min. The results show that the plastic deformation is a main bonding mechanism in the press bonding of Ti-17 alloy. With an increase in bonding temperature, the plastic deformation enhances and voids in the bonding interface disappear gradually. The grain boundary migration and grain growth spanning the bonding interface start to activate, which is of benefit to obtaining a sound bond. The failure mode of bonding interface changes from a brittle fracture to a ductile fracture. However, a higher bonding temperature will induce grain coarsening which result in strength decreasing. The SEM of lap shear fracture surfaces indicates that a bond with superior strength can be obtained at a bonding temperature of 860°C.

Abstract: Adiabatic shear band (ASB) is a typical response of materials under high strain rate loading. Based on the instability analysis of the thermo-viscoplastic constitutive model, a new rate-dependent failure criteria is proposed, which links dynamical evolution of ASB with macro mechanical critical conditions, and is successfully applied to account for the shear fracture mode of cylindrical structures subjected to explosive loading. Using finite element method, the transient failure procedure and shearing fragments induced by ASB is simulated, and the calculated fracture profile shows a good agreement with the experimental results. The failure analysis indicates that the rate-dependent failure criteria, as well as impulsive loading, govern the shear damage mode of the structures.

Abstract: Based on fundamental ideas in tribology and basic concept of stress state in solid mechanics, the existence of frictional force on shear plane is discussed under uniaxial compression of brittle materials. On account of macroscopic fracture forms and mesoscopic fracture mechanisms, the key factors influencing shear fracture angle are analyzed. The results show that, when brittle materials are compressed and shear fracture occurs, shear fracture surface at the crack initiation point is consistent with the maximum shear stress. But the reason of shear fracture angle examined in experiment greater than 45º lies in that, the existence of frictional force between endface of specimen and pressure head of testing machine, and additional tensile stress produced in the materials when harder crystalline grain wedge in softer medium have changed original uniaxial compression stress state and the direction of maximum shear stress on next fracture path.

Abstract: In this paper, experimental and numerical analysis is used to investigate the failure modes of dual phase steels under different loading paths. Numerical models are established for uniaxial tensile tests and stretch flanging tests. Special attention has been paid to the behavior of DP780 in stretch flanging tests with small die radius. The occurrence of shear fracture is identified by comparing numerical simulation results with test data. The study suggests that traditional theory of localized necking is feasible for DP780 under uniaxial tensile condition but invalid when it is undergoing stretch flanging tests with small radius.

Abstract: The fractographs of Mg-9Gd-4Y-0.6Zr alloy specimens which were tensioned at different temperatures were investigated by optical and scanning electron microscopy, respectively. The results showed that different slip systems were activated at different temperatures, which were responsible for varied deformation mechanisms and fracture mechanisms. At 25 °C, the enabled slip systems were few and only the slip systems on basal plane were able to be activated, so cleavage fracture was observed. At −196°C
the number of enabled slip systems increased, prismatic or pyramidal slip maybe occurred, so that an obvious low-temperature plasticity was observed, while fracture mechanisms were mainly microvoid coalescence fracture with cleavage fracture in local areas. At 250 °C, 300 °C and 350 °C, the multisystem slips on the basal planes, the prismatic planes and the pyramidal planes were able to be activated, while fracture mechanisms were also microviod coalescence fracture. At 400 °C, recrystallization happened, grain-boundary sliding in new fine recrystallized grains made the plastic deformation easy, showing coarse-grain superplasticity phenomenon, and an intergranular shear fracture took place.

Abstract: Using the double-edge notched geometry proposed by Xu and Reinhardt recently, the dimension of 200 mm×200 mm×100mm concrete cube specimens, of which the crack length are 10 mm, 20 mm, 30mm, 40mm, 50mm respectively, are designed to experimentally measure mode II fracture toughness KIIC of concrete. For almost all specimens, typical shear fracture features i.e. approximately 0º initial cracking angle as well the following crack forwards propagation along the direction of ligament is phenomenally observed. This fact strongly confirms that this double-edge notched geometry is validly and capable of being utilized as a mode II fracture geometry to evaluate mode II fracture behavior. Then, from the discontinuity point of the measured load-displacement plot, the critical shear fracture load Pc is determined and the corresponding mode II fracture toughness KIIC is also calculated using the formula developed by Xu and Reinhardt. The computed results show that KIIC has no dependency on initial crack length, about 3.36MPa·m1/2 for the tested specimens.