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Bascharage, Luxembourg

Doghri I.,Catholic University of Louvain | Adam L.,E Xstream Engineering SA | Bilger N.,e Xstream Engineering L
International Journal of Plasticity

We propose a general formulation - which we believe to be new - for the mean-field homogenization of inclusion-reinforced elasto-viscoplastic composites assuming small strains. Our proposal is based on an interplay between constitutive equations and numerical algorithms, and the key ideas behind it are the following. The evolution equations for inelastic strain and internal variables at the beginning of each time interval are linearized around the ending time of the same interval. The linearized equations are then numerically integrated using a fully implicit backward Euler scheme. The obtained algebraic equations lead to an incrementally affine stress-strain relation which involves two important terms. The first one is the algorithmic tangent operator, obtained by consistent linearization of the time discretized constitutive equations. The second term is a new one and called an affine strain increment. The proposal leads to thermoelastic-like relations directly in the time domain, and not in the Laplace-Carson (L-C) one. There is no need for viscoelastic-type integral rewriting of the evolution equations, for L-C transforms, or for numerical inversion back from L-C to time domains. The proposed method can be readily applied to sophisticated elasto-viscoplastic models with an arbitrary set of scalar or tensor internal variables, and is valid for multi-axial, non-monotonic and non-proportional loading histories. The theory is applied in detail to a well-known constitutive model, and verified against finite element simulations of representative volume elements or unit cells, for a number of composite materials. © 2009 Elsevier Ltd. All rights reserved. Source

Seyfarth J.,e Xstream Engineering L | Assaker R.,e Xstream Engineering L | Melchior M.,e Xstream Engineering L
SPE Automotive and Composites Divisions - 12th Annual Automotive Composites Conference and Exhibition 2012, ACCE 2012: Unleashing the Power of Design

Following the request to build more and more lightweight structures, plastic composite materials are entering realms of application where exclusively metals have been used in the past. Especially for the automotive industry this means that a broad range of different performances have to be tested on parts which exhibit highly complex material properties. Covering performances of plastic parts means to describe properly the stiffness and failure of composites in static and dynamic load cases. A new topic which meets increasing demand is the prediction of fatigue properties to be able to go for the live time prediction of plastic parts. All this is challenging due to the influence of the fibers which reinforce the composite and cause anisotropic and locally different material behavior depending on the processing conditions. Moreover, the material response will be nonlinear, temperature and strain rate dependent. This is to be true for short, long and continuous type of fiber reinforcement. Each of these types of composites exhibits its own challenge and needs individual treatment to describe the material behavior. This paper will give an overview over recent micromechanical approaches to tackle stiffness, failure and fatigue for all three types of materials. The goal is to provide material models in an efficient way such that they can be used in an industrial simulation environment. Source

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