Investigation of strain rate sensitivity of polymer matrix composites

An investigation into high strain rate behaviour of polymer composites was performed by developing a finite element model for a fibre reinforced polymer (FRP) plates impacted at varying strain rates. The work was divided into three facets, firstly to characterize the FRP material at varying strain rates, to develop a constitutive model to elucidate the relationship between strain rate and ultimate stress and lastly to use the experimental data to develop a finite element model. Experimental work performed in support of this model includes material characterization of unidirectional carbon and glass fibre reinforced epoxy at varying impact strain rates. The data is then used to develop a suite of constitutive equations that relate the strain rate, ultimate stress and material loading type. The model is of a linear and non-linear viscoelastic type, depending on the type of loading and is applicable to a FRP plate undergoing out-of-plane stresses. This model incorporates techniques for approximating the quasi-static and dynamic response to general time-varying loads. The model also accounts for the effects of damage, the linear and non-linear viscoelastic constitutive laws reporting failure by instantaneously reducing the relevant elastic modulus to zero. An explicit solver is therefore utilised in order to ensure stability of the numerical procedure. Glass fibre reinforced plastics (GFRP) was found to be more strain rate sensitive in all directions when compared to carbon fibre reinforced plastics (CFRP). The validation process therefore involves plate impact experimental testing on GFRP plates. The data from these experiments compare to within 8% of the finite element model that incorporates both damage and the developed strain rate sensitivity constitutive equations. For the first time a model that includes progressive damage with built-in strain rate sensitivity is developed for these particular FRP systems. Furthermore, the ultimate stress has been related to strain rate using an empirical technique. This technique allows for the prediction of dynamic ultimate stresses given the quasi-static ultimate stresses, again for this particular material systems.

Grantor dc:publisher.institution

Centre for Materials Engineering

Year dc:date.issued

2004

Author dc:creator

• Ochola, Robert O

Advisors dc:contributor.advisor

• Marcus, Kashif
• Nurick, Gerald N

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/6740

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/6740