Industrial framework for hot-spot identification and verification in automotive composite structures
Doktorsavhandling, 2019

The automotive industry needs to reduce energy consumption to decrease environmental impact. This can be achieved by reducing the weight of cars, which would consequently reduce the energy consumption and emission of greenhouse gases. A promising way to lose weight of automotive primary structures is to introduce carbon fibre composites, as they show outstanding specific properties. However, design of cars are made in virtual environments while composite designs today rely on methods and guidelines that require large amounts of testing. To be able to introduce composite materials in primary structures, the industry needs an efficient design methodology that can be used in virtual development processes. In addition to this, the automotive industry needs new material systems, and production methods to be able to produce composite structures in high volume at a profitable cost.

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

Failure initiation

Analysis framework

Carbon fibre composite

Non crimp-fabric

Orthotropic material


VDL, Chalmers Tvärgata 4C
Opponent: Prof. Raimund Rolfes, Leibniz Universität Hannover, Tyskland


Henrik Molker

Chalmers, Industri- och materialvetenskap

Orthotropic criteria for transverse failure of non-crimp fabric-reinforced composites

Journal of Composite Materials,; Vol. 50(2015)p. 2445-2458

Artikel i vetenskaplig tidskrift

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

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Hot spot Analysis in complex composite material structures

Composite Structures,; Vol. 207(2019)p. 776-786

Artikel i vetenskaplig tidskrift

Molker, H., Gutkin, R. & Asp, L. E., Industrial framework for identification and verification of hot-spots in automotive composite structures

Car transportation is responsible for 12% of the total CO2-emissions in Europe. With the legislation that is already in place for 2030, the emissions must decrease to about half of the levels of 2015. A promising way to contribute to reaching this goal is to reduce the weight of cars. The introduction of composite materials, in particular carbon fibre reinforced materials, is a promising way to decrease the weight, due to their superior properties. Cars made from Carbon Fibre Reinforced Polymer (CFRP) materials are considered to be 50% lighter compared to steel alternatives and 30% lighter compared to aluminium alternatives with similar performance.

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.



Teknisk mekanik


Kompositmaterial och -teknik



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4545


Chalmers tekniska högskola

VDL, Chalmers Tvärgata 4C

Opponent: Prof. Raimund Rolfes, Leibniz Universität Hannover, Tyskland

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