Multi-scale modeling of failure of continuous carbon fiber composites application to coupon tests

In the steady quest for lightweighting solutions, continuous carbon fiber composites come down to the ground, serving now not only the aerospace but also the automotive industries. This category of Carbon Fiber Reinforced Plastics (CFRP) has recently taken a step in car body structures for its high stiffness and strength. Continuous carbon fiber composites are much more complex than metal, with respect to failure in particular. If they are so-called unidirectional, they involve stacks of several plies, each ply characterized by a single fiber orientation. Hence they fail 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. To predict composite failure, we have developed advanced simulation strategies combining finite element analysis (FEA) and nonlinear micromechanical material modeling. In particular, we implemented progressive failure models such as Matzenmiller-Lubliner-Taylor to prevent the analysis to become unrealistic after the first elements have failed. In addition, we enriched these models with inputs computed at the micro scale. Indeed multi-scale modeling decomposes the macroscopic mechanical state between fibers and resin, enables the definition of per-phase failure criteria and provides access to macroscopic or microscopic stiffness degradation. In this paper, we will cover the application of micro-mechanically-based progressive failure models to simple demonstrator structures such as coupons. Introduction The automotive industry has recently increased its use of continuous carbon fiber composites. These carbon fiber reinforced plastics (CFRP) are replacing traditional materials such as extruded metals for structural parts and thermoplastic composites for body parts. CFRP are traditionally used in the aerospace industry due to their light weight, high strength and stiffness properties. The recent shift in the CFRP use by the automotive industry is due to the high demands for reduction of C02 emissions, fuel efficiency and high performance vehicles. The new BMW i3 and i8 models have achieved a 25% reduction in weight compared to conventional thermoplastic car designs through the use of CFRP composite materials [1]. CFRP provide substantial weight reduction and increased performance in automotive designs but also increased complexity. A crucial step for implementing CFRP into production parts is the ability to accurately predict and characterize the failure mechanisms of the material: it actually constitutes the bottleneck. In particular, the microstructure of laminates creates very