Habib Pouriayevali

Quasi-Static and Low-Velocity Impact Response of Fully Backed or Simply Supported Sandwich Beams

The present paper describes analysis of low-velocity transverse impact on sandwich beam, with composite faces from Eglass/epoxy and cores from Polyurethane or PVC. Boundary conditions are fully backed rigid or simply supported. This research is based on a step by step study to generate more reliable impact results. Indentation of laminated beam, indentation of sandwich beams, and three-point loading have been analyzed with existing theories and modeled with the FE code ABAQUS, also their results are compared with experimental results. In quasi-static three-point bending, energy is consumed through three mechanisms: indentation of laminated beam, indentation of sandwich beam, and bending of sandwich beam. Impact on fully backed specimen is modeled in two cases of impactor energies using mass spring model of SDOF (single-degree-of-freedom) and indentation stiffness, lower energy of impactor for elastic indentation of sandwich beams, and higher energy for indentation in plastic area. TDOF (two-degree-of-freedom) with flexural and contact stiffnesses are used for impact on simply supported beams. Impacts are simulated by ABAQUS, as well. Results can describe response of beam and impactor displacements in terms of core and faces thicknesses, core material, and impactor energies for static and impact results. The experimental results are in good agreement with the analytical and FE analyses.

A study of gradient strengthening based on a finite-deformation gradient crystal-plasticity model

A comprehensive study on a finite-deformation gradient crystal-plasticity model which has been derived based on Gurtin’s framework (Int J Plast 24:702–725, 2008) is carried out here. This systematic investigation on the different roles of governing components of the model represents the strength of this framework in the prediction of a wide range of hardening behaviors as well as rate-dependent and scale-variation responses in a single crystal. The model is represented in the reference configuration for the purpose of numerical implementation and then implemented in the FEM software ABAQUS via a user-defined subroutine (UEL). Furthermore, a function of accumulation rates of dislocations is employed and viewed as a measure of formation of short-range interactions. Our simulation results reveal that the dissipative gradient strengthening can be identified as a source of isotropic-hardening behavior, which may represent the effect of irrecoverable work introduced by Gurtin and Ohno (J Mech Phys Solids 59:320–343, 2011). Here, the variation of size dependency at different magnitude of a rate-sensitivity parameter is also discussed. Moreover, an observation of effect of a distinctive feature in the model which explains the effect of distortion of crystal lattice in the reference configuration is reported in this study for the first time. In addition, plastic flows in predefined slip systems and expansion of accumulation of GNDs are distinctly observed in varying scales and under different loading conditions.

Computer-Integrated Engineering and Design

Virtual product development aims at the use of information modeling techniques and computer-aided (CAx-) tools during the product development process, to represent the real product digitally as an integrated product model (Anderl and Trippner 2000). Thereby, data related to the product as well as product properties are generated and stored as result of the product development process (e.g., product planning, conceptual design) (Pahl et al. 2007; VDI 2221 1993). Within virtual product development CAx process chains have been established. They comprise the concatenating of the applied tools and technologies within the steps of the virtual product development process enabling the consistent use of product data (Anderl and Trippner 2000). The computer-aided design (CAD) technology aims at the integration of computer systems to support engineers during the design process such as design conceptualization, design, and documentation. It provides the geometry of the design and its properties (e.g., mass properties, tolerances) which is abstracted to be used in computer-aided engineering (CAE) systems (e.g., finite element method (FEM)) for design analysis, evaluation, and optimization. The computer-aided process planning (CAPP) technology provides tools to support process planning, Numerical Control (NC) programming, and quality control (Hehenberger 2011; Lee 1998; Vajna 2009). The advantages are continuous processing and refinement of the product model, minimizing the modeling efforts regarding time as well as costs and avoiding error sources. In addition, all relevant data and information related to the product can be provided for subsequent processing (Anderl and Trippner 2000). CAx technologies have been widely established within the product development processes in industry. They have been further developed in the last years; however efforts to integrate and to automate them are still a topic of research. Especially, with the introduction of innovative manufacturing technologies such as linear flow and bend splitting require new methods and tools for the virtual product development process. These technologies enable the production of a new range of sheet metal products with characteristic properties (e.g., Y-profile geometry, material properties) that are not addressed in state-of-the-art methods and tools.