Papers by Keyword: Length Scale

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Authors: Giang Dinh Nguyen
Abstract: We develop a novel constitutive modeling approach for the analysis of fracture propagation in quasi-brittle materials using the Material Point Method. The kinematics of constitutive models is enriched with an additional mode of localized deformation to take into account the strain discontinuity once cracking has occurred. The crack details therefore can be stored at material point level and there is no need to enrich the kinematics of finite elements to capture the localization caused by fracturing processes. This enhancement also removes the drawback of classical smeared crack approach in producing unphysical snapping back constitutive responses when the spatial resolution is not fine enough. All these facilitate the implementation of the new approach in the Material Point Method for analysis of large scale problems. Numerical examples of fracture propagation are used to demonstrate the effectiveness and potentials of the new approach.
Authors: Roman Gröger, Turab Lookman
Abstract: We develop a phase field model that describes the elastic distortion of a ferroelastic material with cubic anisotropy due to an arbitrary dislocation network and a uniform external load. The dislocation network is characterized using the Nye tensor and enters the formulation via a set of incompatibility constraints for the internal strain field. The long-range elastic response of the material is obtained by minimization of the free energy that accounts for higher order terms of the order parameters and symmetry-adapted strain gradients. To demonstrate the performance of the model, a minimal version of continuum dislocation dynamics is used to investigate the simultaneous evolution of the network of geometrically necessary dislocations and the internal strain field.
Authors: G.P. Zhang, Cynthia A. Volkert, Ruth Schwaiger, Oliver Kraft
Abstract: Fatigue damage behaviour in micron and sub-micron thick Cu films has been investigated using focused ion beam (FIB) microscopy and transmission electron microscopy (TEM). The observations show that cyclic strain localization in the fatigued thin films is affected by the physical dimensions of the material, as evidenced by changes in the extrusion dimensions and by changes in the dislocation structures. The significant decrease in extrusion dimensions and the suppression of the development of bulk-like dislocation structures with decreasing film thickness and grain size is attributed to the strong inhibition of dislocation mobility and activity at small length scales.
Authors: S.C.V. Lim, Anthony D. Rollett
Abstract: The extraordinary strength values of composites with nano-scale layers or phases have inspired much investigation into the strengthening mechanisms of laminated composites such as Cu-Nb. The annealed microstructure and texture of any material govern its mechanical properties in composites just as much as in single-phase materials yet studies on the development of annealing textures of such deformed layered composites are still very limited as compared to studies of strengthening mechanisms. Recrystallization textures of monolithic pure Cu and alloyed Cu - C19210 as well as when they are reinforced with Nb using roll-bonding are investigated. The rollbonded samples of different layered length scales were deformed to reductions of 70-90% and annealed at 300oC and 800oC for 0.5 hours. We found that the Cube and R-orientation {124}<211> were the dominant components in the recrystallized texture of monolithic pure Cu and alloyed Cu respectively. However, retained rolling texture was obtained for the sub-micron Cu layers of the composites. X-ray analysis and EBSD was used to study the recrystallization evolution of the Cu in the composites. EBSD in particular was also used to observe recrystallization for the sub-micron Cu layers. In this paper we also discuss the effect of the length scale of the Cu layer thickness on the recrystallized texture especially in the sub-micron range.
Authors: G.P. Zhang, Y.P. Li, X.F. Zhu
Abstract: Deformation and fracture behaviors of Cu/Au and Cu/Cr multilayered composites with different length scales were investigated by using instrumented-indentation and three-point-bending methods. It is found that with decreasing the length scale (layer thickness and grain size), both multilayers tend to produce plastic instability via localized shear banding under indentation load in spite of high hardness they have, while quasi-brittle fracture under relatively low fracture stress prevails at three-point-bending test. Especially, the compressive flow stress and the tensile fracture stress exhibit inverse trend of variation with the length scales, which implies different mechanisms. Such length scale dependent deformation and plasticity were analyzed concerning size and interface effects under different stress state.
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