Environmental issues enforce transportation sectors to limit their carbon dioxide emissions in various ways. Automotive manufacturers attempt to reduce carbon dioxide emissions by seeking various strategies, e.g., increasing aerodynamic efficiency, using more fuel-efficient engines, reducing friction and wear of transmission systems, and, most importantly, by using lightweight materials and structures. This dissertation is a contribution toward a lightweight design of structures by proposing numerical models suitable for damage prediction of thermoplastic composite materials.
In this dissertation, predictive damage models for two different length scales, namely micromechanics, and mesomechanics, were proposed. Micromechanics is used to predict the nonlinear damage behavior of elementary thermoplastic composite ply, while the mesomechanics is used to predict the failure behavior of thermoplastic composite laminates (test coupon or plate scale).
For the micromechanics, a representative volume element (RVE) of such materials was rigorously determined using a geometrical two-point probability function and the eigenvalue stabilization of homogenized elastic tensor obtained by Hill-Mandel kinematic homogenization. We proposed a viscoelastic viscoplastic model for the polypropylene matrix to extend the capability of the micromechanics model in predicting the damage behavior of the composite ply at various loading cases and strain rates.
At the mesoscale, we improved the classical mesomechanics damage modeling in the off-axis direction by introducing the confinement effect. The pragmatic approach consists of separating the progressive damage into two parts, namely "diffuse damage regime" and "transverse-cracking regime", were described by two distinct damage parameters. We also enriched the mesomechanics model by proposing a viscoelastic and viscoplastic model to account for the rate-dependent behavior of the thermoplastic composites. We showed that the predictions given by the proposed micromechanics and mesomechanics models were in excellent agreement with the experimental results in terms of the global stress-strain curves, including the linear and nonlinear portion of the response and also the failure point, making it useful virtual testing tools for the design of thermoplastic composites.
Ditho obtained his B. Eng. from Bandung Institute of Technology, Indonesia (2010), and M.Sc. from Korea Advanced Institute of Science and Technology (KAIST), South Korea (2012). He joined KAUST in 2013 as a Ph.D. student in Computational Solid Mechanics Laboratory (CSML). In 2014, He started to work on the KAUST-SABIC thermoplastic project under the supervision of Prof. Gilles Lubineau (COHMAS Laboratory) to develop predictive micro- and meso-mechanics models for thermoplastic composites, which led him to his Ph.D. dissertation.