Industrial framework for hot-spot identification and verification in automotive composite structures
Doctoral thesis, 2019
In this thesis, a design methodology for composite structures within the automotive industry is proposed. A methodology that combines numerical models at multiple scales to first find potential hot-spots in global models and then assess only these using high fidelity models. The important part is to ensure that all potential failure modes can be captured both in the global model as well as in the local models.
The first step in the methodology is to find accurate failure modes for material systems that are likely to be used within automotive industry. A possible material system for the automotive industry is Non Crimp-Fabric (NCF) reinforced composite materials. Compared to Uni-Directional (UD) reinforced composite materials, NCF composite materials have been found not to be transversely isotropic but orthotropic. This is valid for both stiffness and strength. Current state-of-the-art set of failure initiation criteria are based on the assumption of transverse isotropy. In this thesis, a set of criteria for assessing failure initiation of NCF reinforced composite materials are proposed. The failure criteria are compared and verified against data from literature and numerical models. The set of criteria have also been implemented into a commercial finite element code and verified against physical experiments.
Global - local
Carbon fibre composite
Chalmers, Industrial and Materials Science
Orthotropic criteria for transverse failure of non-crimp fabric-reinforced composites
Journal of Composite Materials,; Vol. 50(2016)p. 2445-2458
Implementation of failure criteria for transverse failure of orthotropic Non-Crimp Fabric composite materials
Composites Part A: Applied Science and Manufacturing,; Vol. 92(2017)p. 158-166
Hot spot Analysis in complex composite material structures
Composite Structures,; Vol. 207(2019)p. 776-786
Molker, H., Gutkin, R. & Asp, L. E., Industrial framework for identification and verification of hot-spots in automotive composite structures
Verification of hot-spot in complex composite structures using detailed FEA
ECCM 2018 - 18th European Conference on Composite Materials,; (2019)
Paper in proceedings
However, predicting failure in composite materials is not as easy as in isotropic materials like metals. Failure depends on the loading conditions, material orientation, and how they are stacked. To accurately predict initiation of failure, models with a resolution that is about 10 to 100 times finer than used for metals are needed. They are however too computationally demanding and to use them within current design loops is not feasible, thus more efficient tools are needed.
One part of this thesis covers how an efficient analysis framework can be set up, which allows the automotive industry to use tools and models that are familiar. The framework screens complete car models and presents potential critical hot-spots. These are then remodelled in higher detail for verification.
Composite reinforcements exist in a number of different forms, uni-directional tapes, woven textiles or oriented mats that are stitched together. These are then made with a variety of production methods. Due to their use within the aerospace industry, the most explored material for simulation is uni-directional tape-based pre-impregnated composite materials. Since the automotive industry needs cheaper materials and higher production rates, other material systems are of interest. One such system is Non-Crimp Fabric reinforcement composites.
In this work, understanding of how failure initiates in Non-Crimp Fabric reinforcements, given their orthotropic properties, is also studied. A set of criteria is proposed to predict all failure modes in these materials. The criteria are validated with physical experiments and implemented into commercial software.
Composite Science and Engineering
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4545
Chalmers University of Technology
VDL, Chalmers Tvärgata 4C
Opponent: Prof. Raimund Rolfes, Leibniz Universität Hannover, Tyskland