Modelling composite crushing initiation using a cohesive element formulation

SAE Int. J. Mater. Manf.

2016

The development of the latest generation of wide-body carbon-fibre composite passenger aircraft has heralded a new era in the utilisation of these materials. The premise of superior specific strength and stiffness, corrosion and fatigue resistance, is tempered by high development costs, slow production rates and lengthy and expensive certification programmes. Substantial effort is currently being directed towards the development of new modelling and simulation tools, at all levels of the development cycle, to mitigate these shortcomings. One of the primary challenges is to reduce the extent of physical testing, in the certification process, by adopting a 'certification by simulation' approach. In essence, this aspirational objective requires the ability to reliably predict the evolution and progression of damage in composites. The aerospace industry has been at the forefront of developing advanced composites modelling tools. As the automotive industry transitions towards the increased use of composites in mass-produced vehicles, similar challenges in the modelling of composites will need to be addressed, particularly in the reliable prediction of crashworthiness. While thermoset composites have dominated the aerospace industry, thermoplastics composites are likely to emerge as the preferred solution for meeting the high-volume production demands of passenger road vehicles. This keynote paper outlines recent progress and current challenges in the development of finite-element-based predictive modelling tools for capturing impact damage, residual strength and energy absorption capacity of thermoset and thermoplastic composites for crashworthiness assessments.

Section: Falzon Et Al / Sae Int J Mater Manf / Volume 9 Issue 3 mentioning

confidence: 99%

Section: Implementation Of Intralaminar Damage Modelmentioning

confidence: 99%

Predicting Impact Damage, Residual Strength and Crashworthiness of Composite Structures

SAE Int. J. Mater. Manf.

2016

“…Mesh objectivity of the model was achieved by employing the crack-band model of Bažant and Oh [53], where a characteristic length of the finite element (equivalent to a RVE), g = Γ / * . * and the corresponding fracture toughness Γ were used.…”

Section: Damage Evolutionmentioning

confidence: 99%

Modelling the nonlinear behaviour and fracture process of AS4/PEKK thermoplastic composite under shear loading

Composites Science and Technology

2016

The accurate determination of non-linear shear behaviour and fracture toughness of continuous carbonfibre/polymer composites remains a considerable challenge. These measurements are often necessary to generate material parameters for advanced computational damage models. In particular, there is a dearth of detailed shear fracture toughness characterisation for thermoplastic composites which are increasingly generating renewed interest within the aerospace and automotive sectors. In this work, carbon fibre (AS4)/ thermoplastic Polyetherketoneketone (PEKK) composite V-notched cross-ply specimens were manufactured to investigate their non-linear response under pure shear loading. Both monotonic and cyclic loading were applied to study the shear modulus degradation and progressive failure. For the first time in the reported literature, we use the essential work of fracture approach to measure the shear fracture toughness of continuous fibre reinforced composite laminates.Excellent geometric similarity in the load-displacement curves was observed for ligament-scaled specimens. The laminate fracture toughness was determined by linear regression, of the specific work of fracture values, to zero ligament thickness, and verified with computational models. The matrix intralaminar fracture toughness (ply level fracture toughness), associated with shear loading was determined by the area method. This paper also details the numerical implementation of a new three-dimensional phenomenological model for carbon fibre thermoplastic composites using the measured values, which is able to accurately represent the full non-linear mechanical 2 response and fracture process. The constitutive model includes a new non-linear shear profile, shear modulus degradation and load reversal. It is combined with a smeared crack model for representing ply-level damage initiation and propagation. The model is shown to accurately predict the constitutive response in terms of permanent plastic strain, degraded modulus as well as load reversal. Predictions are also shown to compare favourably with the evolution of damage leading to final fracture.

“…Mesh objectivity of the model was achieved by employing the crack-band model of Bažant and Oh [13].The characteristic length associated with the longitudinal direction is determined by = ⁄ , where is the element volume and is calculated using an approach proposed in [18].…”

Section: Damage Evolutionmentioning

confidence: 99%

“…Pinho et al [11], Palanivelu et al [12] and Fleming [13] proposed various numerical models for the crushing simulation of fibre-reinforced composite materials. Sokolinsky et al [14] investigated a corrugated carbon-epoxy fabric composite plate subjected to quasi-static crushing, where intralaminar failure was simulated using an in-plane constitutive model and delamination was modelled by cohesive surface contact.…”

Section: Introductionmentioning

confidence: 99%

Modelling the crush behaviour of thermoplastic composites

Composites Science and Technology

2016

Thermoplastic composites are likely to emerge as the preferred solution for meeting the high-volume production demands of passenger road vehicles. Substantial effort is currently being directed towards the development of new modelling techniques to reduce the extent of costly and time consuming physical testing. Developing a high-fidelity numerical model to predict the crush behaviour of composite laminates is dependent on the accurate measurement of material properties as well as a thorough understanding of damage mechanisms associated with crush events. This paper details the manufacture, testing and modelling of self-supporting corrugated-shaped thermoplastic composite specimens for crashworthiness assessment. These specimens demonstrated a 57.3% higher specific energy absorption compared to identical specimen made from thermoset composites. The corresponding damage mechanisms were investigated in-situ using digital microscopy and post analysed using Scanning Electron Microscopy (SEM). Splaying and fragmentation modes were the 2 primary failure modes involving fibre breakage, matrix cracking and delamination. A mesoscale composite damage model, with new non-linear shear constitutive laws, which combines a range of novel techniques to accurately capture the material response under crushing, is presented. The force-displacement curves, damage parameter maps and dissipated energy, obtained from the numerical analysis, are shown to be in a good qualitative and quantitative agreement with experimental results. The proposed approach could significantly reduce the extent of physical testing required in the development of crashworthy structures.