Material characterisation for crash modelling of composites
Doktorsavhandling, 2018

The transport industry must find solutions to reduce its impact on climate change. A promising way to reduce the weight of vehicles and therefore to reduce the CO2 emissions is to introduce components made of lightweight composite materials, in particular carbon fibre reinforced plastics (CFRPs). Aside from the new design possibilities for lighter vehicle structures, CFRPs can also potentially offer improvements in terms of crash performance in comparison to traditional metallic structures.

During crushing of composite structures, energy is absorbed through the stable progressive failure of the structure. The crushing process is a complex phenomenon involving the interaction of different competing failure mechanisms and frictional interactions taking place at different scales in the material. Today there is no reliable numerical tool to predict the behaviour of composite structures in crash scenarios, which is a hindrance to the introduction of composite materials in mass-produced vehicles. Joint research efforts from both numerical and experimental perspectives are needed to fill this gap.

In this doctoral thesis experiments are carried out to extract relevant material properties for crash modelling, and to assist in the development and the validation of numerical models as a first step of a building block approach with increasing structural complexity. The material selected for the study is a carbon fibre/epoxy uni-weave non-crimp fabric (NCF) composite. The first step in the material characterisation is to extract the different strengths and stiffnesses of the material, which requires dedicated tests because of the orthotropic nature of NCFs. Because several compressive failure mechanisms are driven by the shearing of the matrix polymer, a methodology is presented to extract the damage evolution laws from Iosipescu shear tests and indirect shear tests (uniaxial and biaxial compression tests). A quasi-static test method that uses crush coupons of simple geometry is proposed to measure the crush stress of composite plies for different fibre orientations and to characterise the associated crushing mechanisms. The experimental results of the crush coupons are then compared to blind predictions from finite element simulations to assess the predictive capabilities of a ply-based material model coupling damage and friction in a continuum damage approach. This material model is currently being developed in parallel to this thesis. Its aim is to pre-emptively simulate structural tests in order to optimise the design of crashworthy structures and to limit the number of physical tests.

carbon fibre composite

non-crimp fabric (NCF)

damage mechanics

mechanical testing

finite element analysis (FEA)


VDL, Tvärgata 4C, Chalmers
Opponent: Prof. Ivana Partridge, University of Bristol, UK


Thomas Bru

Chalmers, Industri- och materialvetenskap, Material- och beräkningsmekanik

Use of the Iosipescu test for the identification of shear damage evolution laws of an orthotropic composite

Composite Structures,; Vol. 174(2017)p. 319-328

Artikel i vetenskaplig tidskrift

Development of a test method for evaluating the crushing behaviour of unidirectional laminates

Journal of Composite Materials,; (2017)p. 4041-4051

Artikel i vetenskaplig tidskrift

S Costa, T Bru, R Olsson and A Portugal. Improvement and validation of a physically based model for the shear and transverse crushing of orthotropic composites (Accepted for publication in Journal of Composite Materials).


Hållbar utveckling


Teknisk mekanik

Kompositmaterial och -teknik





Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4486


Chalmers tekniska högskola

VDL, Tvärgata 4C, Chalmers

Opponent: Prof. Ivana Partridge, University of Bristol, UK

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