Use this URL to cite or link to this record in EThOS:
Title: Damage and failure modelling of carbon/epoxy Non Crimp Fabric composites
Author: Greve, Lars
Awarding Body: Cranfield University
Current Institution: Cranfield University
Date of Award: 2005
Availability of Full Text:
Access from EThOS:
Access from Institution:
Advanced material models for the intra- and inter-laminar damage and failure prediction of biaxial carbon/epoxy Non Crimp Fabric (NCF) composites are presented, which enable application to large scale practical composite structures for the automotive industry. The model established for intra-laminar failure combines the elasto-plastic continuum damage constitutive model first proposed by Ladevèze, with the matrix failure model of Puck, and improves the shear damage representation by using an exponential damage evolution law. An extensive test program has been conducted using biaxial NCF composites with differing degrees of fabric pre-shear. The presheared biaxial NCF are considered to take into account potential changes of the damage and failure properties occurring due to the draping process in real structures. The database established is used to identify parameters for the proposed Ladevèze-Puck matrix damage and failure model, allowing prediction of the main matrix failure modes of unsheared and presheared biaxial NCF composites. Furthermore, the failure prediction within zones of stress concentrations is addressed utilising flat NCF laminates with different holes and lay-ups. For numerical elastic failure prediction of these tests a simple fibre criterion is presented which is related to a characteristic element size. The Puck failure model is adopted to represent the inter-laminar (delamination) crack initiation strength of the investigated NCF. This stress based model for delamination crack initiation operates in conjunction with existing methods for the simulation of delamination crack propagation, which are related to the critical strain energy release rate. All material models that have been combined and further developed during the course of this work have been implemented in a research version of a commercial crashworthiness Finite Element code. The intra-laminar failure model is validated against a test series of transversely loaded circular- composite discs having differing degrees of fabric pre-shear. The final validation example for intra-laminar failure has considered a complex composite door structure subjected to lateral punch intrusion. The enhanced delamination failure model is validated using a composite beam structure, exhibiting delamination failure under local transverse tension loading. For all validation tests a good agreement between simulations and experiments has been demonstrated. It is believed by the author that the new contributions presented in this thesis significantly raise the level of numerical prediction of deformation, damage, and failure for Continuous Carbon Fibre Reinforced Composites. Special emphasis is placed on the fact that all material model parameters have been obtained from simple specimen tests, and have been used without adjustment for the simulation of subsequent Validation tests utilising Composite structures of high complexity. This continuous approach is in contrast to the majority of similar investigations found in the literature, in which the adjustment of material model parameters appeared to be necessary in order to achieve a good agreement between simulations and experiments of complex structures.
Supervisor: Pickett, A. K. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available