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

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\ua0(NCF) reinforced composite materials. Compared to Uni-Directional\ua0(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

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

In this paper, a set of failure criteria for transverse failure in non-crimp fabric-reinforced composites is presented. The proposed failure criteria are physically based and take into account the orthotropic character of non-crimp fabric composites addressing the observed lack of transverse isotropy. Experimental data for transverse loading out-of-plane in combination with in-plane loads are scarce. Therefore, to validate the developed criteria, experimental data are complemented with numerical data from a representative volume element model using a meso-micromechanical approach. The representative volume element model also provides a deeper understanding of how failure occurs in non-crimp fabric composites. Strength predictions from the developed set of failure criteria show good agreement with the experimental and numerical data

Verification of hot-spot in complex composite structures using detailed FEA

Motivation Current shell-element based design tools used in the automotive industry do not allow for failure prediction in complex composite structures. An automated method to identify and analyse structural hot-spots for all potential failure modes is therefore needed

Failure prediction of orthotropic Non-Crimp Fabric reinforced composite materials

The automotive industry needs to reduce the energy consumption to decrease the impact on the environment. One part of this is to reduce the weight of cars, thereby reducing the fuel consumption. A promising way to be successful with this is to introduce carbon fibre composites in the structural parts. This as carbon fibre composites have outstanding properties. However, design of cars are made in a virtual environment while composite designs are today made using guidelines that require large amounts of testing.The automotive industry needs an efficient design methodology for carbon fibre composite structures that can be used in the virtual development. In addition to this, the automotive industry needs new material systems and production methods to be able to produce in large scale at a profitable cost.In this thesis, the basis for a design methodology for composite structures within the automotive industry is given. A methodology that uses numerical models at multiple scales is proposed. Assessing failure on full scale models cannot be done as analysis of composite structures needs to be done with more detailed models due to the different failure mechanisms. An approach with global models for screening for critical locations and local higher fidelity models for verification is outlined.The first step in the methodology is to find accurate failure modes for the intended material systems. A strong candidate material for the automotive industry is Non Crimp-Fabric (NCF) reinforced composites. Compared to Uni-Directional (UD) reinforced composite materials, NCFs have been found not to be transversely isotropic but orthotropic. This is valid for both stiffness and strength. Current state-of-the-art failure criteria are based on the assumption of transverse isotropy. In this thesis and the appended papers a set of criteria for assessing failure initiation of NCF reinforced composites are proposed. The proposed failure criteria are compared and verified against data from literature and numerical models. It have also been implemented into a commercial finite element code and verified against physical testing.Keywords: Design methodology; Carbon fibre composite; Non crimp-fabric; Failure initiation; Orthotropi

Implementation of failure criteria for transverse failure of orthotropic Non-Crimp Fabric composite materials

In this paper a set of failure criteria for Non-Crimp Fabric (NCF) reinforced composites is implemented in a Finite Element (FE) software. The criteria, implemented at the ply level, predict transverse failure of NCF reinforced composites, in particular accounting for their inherent orthotropic properties. Numerical simulations are compared with tests on specimens with a generic design feature found in automotive structures. The current implementation enables correct prediction of failure mode and location

Framework for durability analysis of composite structures in the automotive industry

High performance composite materials possess properties that make them great candidates for reducing the weight of cars. However, analysis of large structures or assemblies with complex geometries made from fibre reinforced composite materials is a difficult task. Modern state of the art set of failure initiation criteria are based on the full stress state while efficient standard shell models cannot provide this. This either requires high fidelity models or the risk that potentially critical failure modes may be neglected due to assumptions made in the numerical models.In this paper, a framework for computationally efficient durability analysis of composite structures in automotive industry is presented

Implementation of failure criteria for orthotropic non crimp fabric composite structures

In this paper a set of failure criteria for Non-Crimp Fabric (NCF) reinforced composites are implemented in a Finite Element (FE) software. The criteria are valid for transverse failure of NCF reinforced composites with their inherent orthotropic properties and are used at ply level. Validation of the failure criteria is performed on coupons with features typically found in automotive structures

Verification of hot-spot in complex composite structures using detailed FEA

Analysis of large complex composite structures with state of the art failure initiation criteria is difficult and simplifications are therefore needed. This is often done using shell models as these are computationally efficient. However, by this approach, potential failure modes are disregarded as out-of-plane stresses cannot be accounted for.In this paper, a methodology for verification of large models accounting for full 3D stress states is presented. This is done by identification of critical hot spots in global Finite Element (FE) models. The identified hot spots are further resolved and analysed with detailed FE models. To make this efficient, the different steps needed are combined into a chain of standardized processes

Efficient screening of composite structures using the extended 2D FEM approach in Meta together with a state of the art failure initiation criterion

In order to assess complex composite structures, the full 3D stress tensor is needed to ensure that all possible failure modes can be captured. Conventional shell elements only give accurate results for the in-plane stress components, while the out-of-plane components are neglected. The implementation of the Extended 2D FEM approach [1] into Metapost [2] makes it possible to get the full 3D stress tensor from second order shell elements. With the full stress tensor, state of the art set of failure initiation criteria can be used to evaluate the component. Two different cases are used to show the applicability of the procedure. The first example is a simply supported plate from the literature [3] is in particular used to demonstrate the visualisation capabilities in Metapost. The second example is a set-up used to measure\ua0 the out-of-plane strength of composite materials [4], it is here analysed using both the Extended 2D FEM approach and a state of the art set of failure initiation criteria, LaRC05 [5]

Industrial framework for identification and verification of hot-spots in automotive composite structures

In this article, a framework for efficient strength analysis of large and complex automotive composite structures is presented. This article focuses on processes and methods that are compliant with common practice in the automotive industry. The proposed framework uses efficient shell models for identification of hot spots, automated remodelling and analysis of found hot spots with high-fidelity models and finally an automated way of post-processing the detailed models. The process is developed to allow verification of a large number of load cases in large models and still consider all potential failure modes. The process is focused on laminated composite primary structures. This article highlights the challenges and tools for setting up this framework