Laurent Adam

Non-local Damage-Enhanced MFH for Multiscale Simulations of Composites

In this work, a gradient-enhanced mean-field homogenization (MFH) procedure is proposed for fiber reinforced materials. In this approach, the fibers are assumed to remain linear elastic while the matrix material obeys an elasto-plastic behavior enhanced by a damage model. As classical finite element simulations face the problems of losing uniqueness and strain localization when strain softening of materials is involved, we develop the mean-field homogenization in a non-local way. Toward this end we use the so-called non-local implicit approach, reformulated in an anisotropic way to describe the damage in the matrix. As a result we have a multi-scale model that can be used to study the damage process at the meso-scale, and in particular the damaging of plies in a composite stack, in an efficient computational way. As a demonstration a stack with a hole is studied and it is shown that the model predicts the damaging process in bands oriented with the fibers directions.

Compression Molding of Discontinuous Fiber Composites, a Thermodynamics Approach to the Compaction Problem

Discontinuous Fiber Composites (DFCs) constitute a new class of highperformance molding compounds that enable the use of compression molding as the manufacturing process of complex components with high volume fraction of fibers. However, the use of DFCs is still limited, one reason being the lack of theoretical modeling and numerical analysis methodologies enabling their use at full potential. During compression molding, the polymeric resin is brought above its melting temperature and thus the material system consists in the cohabitation of a fluid and solid component. In this paper we adopted a macroscopic point of view that consists in depicting the material system as an open thermodynamic system through which the fluid can flow thus yielding a macroscopically compressible system for which a specific state, referred to as the compaction point, exists. The compaction point denotes the state at which no relative motion of fluid can occur with respect to the solid one and thus the thermodynamics system becomes incompressible. A stabilized mixed finite element method is presented that allows for the direct solution of the compaction problem in which all variables are treated as primary ones. This method yields a generalized saddlepoint problem that is known to be stable only for specific coupling of interpolation orders between the primary variables. Circumventing the latter is achieved via a stabilization procedure based on the use of the Algebraic Sub-Grid Stabilization (ASGS) method that yields a fully stable Galerkin weak mixed formulation for equalorder interpolation between all primary fields. This method proves beneficial to highlight the physical phenomena occurring in compression molding of fiber-reinforced media.

Virtual Coupon Testing of Carbon Fiber Composites for Application in Structural Analysis

In the steady quest for lightweighting solutions, continuous carbon fiber composites are becoming more approachable for design, now not only used in the aerospace but also the automotive industries. Carbon Fiber Reinforced Plastics (CFRP) are now being integrated into car body structures, used for their high stiffness and strength and low weight. The material properties of continuous carbon fiber composites are much more complex than metal, especially with respect to failure; this is further complicated by the fact that a single part is typically made from stacks of several unidirectional plies, each with a different fiber orientation. Hence failure occurs because of various mechanisms taking place at the ply level (matrix cracking, fiber breakage, fiber-matrix debonding) or between the plies (delamination). These mechanisms remain not fully understood and are investigated through experimental and virtual testing.

A coupled formulation for Thermo-Viscoplasticity at Finite Strains: Application to Hot Metal Forming

Our goal in this paper is to present a complete thermo-viscoplastic formulation at finite strains and its implementation in a finite element code. The formulation is derived from the classical J2-plasticity with a flow criterion expressed in the current configuration in terms of the Cauchy stresses and the temperature distribution.

A coupled thermo-viscoplastic formulation at finite strains for the numerical simulation of superplastic forming

This paper is concerned with the numerical simulation of hot metal forming, especially superplastic forming. A complete thermo-viscoplastic formulation at finite strains is derived and a unified stress update algorithms for thermo-elastoplastic and thermo-elastoviscoplastic constitutive equations is obtained. The resulting unified implicit algorithm is both efficient and very inexpensive. Finally, numerical simulations of superplastic forming are exposed.