Statistical Energy and Failure Analysis of CFRP Compression Behavior Using a Uniaxial Microbuckling Model

Abstract

Compression failure followed by fragmentation is a pre-eminent energy absorption mechanism in fiber-reinforced composites and, therefore, it is often used in crash absorption devices. Fragmentation is the last stage of degradation leading to total failure of a carbon fiber reinforced plastic (CFRP) laminate in compression. Micromechanical studies have shown that this phenomenon is initiated mainly by a microbuckling mechanism which depends on microstructural imperfections (fiber misalignment and matrix plasticity). As far as energy absorption and dedicated modeling strategies are concerned, the question is whether the failure scenario is dependent on these imperfections in terms of dissipated energy. In this context, we used a one-dimensional microscale approach to model plastic microbuckling and evaluate the corresponding dissipated energy for a realistic range of microstructural parameters (with statistical treatment). Contrary to our expectations and to the well-known sensitivity of the peak loads, these energies seem unaffected by microscopic parameters. In conclusion, we propose some ideas on how to include the main aspects of fragmentation, which can occur in composite materials under in-plane compression loading, on the mesoscale.

Micro-mechanical prediction of UD laminates behavior under combined compression up to failure: influence of matrix degradation

“…Although a severe dependence of their kinking experiments on interface softening is observed in Ref., 22 the kinking theory has been traditionally used with positive hardening (or perfectly plastic) elastic–plastic material models. However, simulations using the model previously described and an elastic–plastic behavior without damage for the matrix, as in Guimard et al 30 display extreme local hardening. This can be shown, for instance for a carbon–epoxy composite under compression without shear and a fiber waviness of 0.5°, by performing a simulation of the kink-band creation process.…”

“…From a statistical point of view, the latter question has been investigated in Guimard et al, 30 where the authors used a numerical model based on Budiansky and Fleck. 7 Thanks to the observation of fiber waviness statistics from Paluch, 31 they were able to draw distributions of critical stresses, dissipated energies, and kink-band sizes.…”

“…Considering the above hypotheses and formulation, the problem can be discretized in one dimension with the Finite Element Method, as described in Guimard et al 30 In addition, because of the antisymmetry of the problem, only half of the unidimensional structure is actually simulated. Hermitian beam elements are used (element size ≃ 3 fiber diameters), and since sharp snap-backs are expected, an arc-length control method 34 is implemented.…”

Integration of a Composite Crash Absorber in Aircraft Fuselage Vertical Struts

“…The matrix material is supposed to support the fibres against microbuckling, but as soon as its yield strength is reached, fibre bending increases sharply and stiffness drops with kink bands appearing that finally lead to catastrophic failure. An understanding of the energy dissipated in this process and influencing parameters was gained in [36] using a microscale modelling approach. To cover this energy absorption mechanism and also the fragmentation/delamination interaction in a meso-or macromodel for explicit finite element (FE) calculations typically used in industry today is still challenging and currently under investigations.…”

Composite crash absorber for aircraft fuselage applications

“…An understanding of the energy dissipated in this process and influencing parameters was gained in [22] using a microscale modelling approach. To cover this energy absorption mechanism and also the fragmentation/delamination interaction in a meso-or macromodel for explicit finite element (FE) calculations typically used in industry today is still challenging and currently under investigations.…”