CFRP prepreg kompozitlerin ergimiş durumdaki konfigurasyonlarının eğilme davranışlarının modellenmesi ve testi

The goal of this thesis is to develop a material model for prepreg materials, which is a combination of viscoelastic and elastic properties. For validation of developed model, quasi-static tensile test of Celstran®CFR-TP PA6 CF60-01 thermoplastic prepreg has been investigated. This test is developed at Institute for Carbon Composites (LCC), Technical University of Munich, in a separate study parallel to current thesis. As a first step, outputs of tensile test which are deformation, force, stress and strain have been considered to determine viscoelastic parameters. In literature, viscoelastic materials are defined by a Prony series expansion of the dimensionless relaxation modulus [4, 22]. In this definition, Prony series coefficients are determined by fitting series to stress-strain curve of tensile, creep or relaxation tests. This curve is considered as proportion of stresses to strains with respect to time. In order to make this proportion dimensionless, it is divided by its initial value (i.e. time = 0). After determination of viscoelastic model, elastic properties of final model (modulus of elasticity and Poisson's ratio) have been adapted from other experimental tests done at LCC. Final material model of this thesis is created as a combination of elastic and viscoelastic material properties. Afterwards, developed model has been used to simulate quasi-static tensile test with commercial finite element software, ABAQUS. In this simulation, virtual specimen in same dimensions as real one has been modeled and its upper part has been defined as cantilever boundary condition and lower part has been exposed to tensile force as real sample. This simulation procedure is carried out with consideration and comparison of effects and influences of different parameters such as element type, displacement or force ramp, etc. Eventually stress-strain diagrams for both cases have been drawn and a comparison between experimental and simulation outputs is obtained, and their correlation has been discussed.