Onur Çoban

Effect of Fiber Orientation on Scratch Resistance in Unidirectional Carbon-Fiber-Reinforced Polymer Matrix Composites

Polymer composites have been widely used in industrial applications because of their high-specific strength and modulus. During their maintenance and service life small scratches can be formed on the surface of the composite material. These small scratches can result in crack initiation causing material failure and also some esthetic defects. When we consider that polymer composites may have various fiber orientations, it is possible to develop a remarkable increase in their scratch resistance. For this reason it is necessary to investigate the effect of fiber orientation on scratch resistance for polymer composites. In this study, scratch resistance of continuous carbon-fiber-reinforced polyetherimide composites were investigated as a function of fiber orientations by means of CSM microscratch tester machine. During the experiments the relation between the scratch resistance and operational parameters are determined as a function of scratch hardness, penetration depth, and coefficient of friction.

Thermal, viscoelastic and mechanical properties' optimization of polyphenylene sulfide via optimal processing parameters using the Taguchi method

ABSTRACT Thermal, viscoelastic and mechanical properties of polyphenylene sulfide (PPS) were optimized as a function of extrusion and injection molding parameters. For this purpose, design of experiments approach utilizing Taguchis L27 (37) orthogonal arrays was used. Effect of the parameters on desired properties was determined using the analysis of variance. Differential scanning calorimeter (DSC) tests were performed for the analysis of thermal properties such as melting temperature (Tm) and melting enthalpy (ΔHM). Dynamic mechanical analysis (DMA) tests were performed for the analysis of viscoelastic properties such as damping factor (tan δ) and glass transition temperature (Tg). Tensile tests were performed for the analysis of mechanical properties such as tensile strength and modulus. With optimized process parameters, verification DSC, DMA and tensile tests were performed for thermal, viscoelastic and mechanical properties, respectively. The Taguchi method showed that ‘barrel temperature’ and its level of ‘340°C’ were seen to be the most effective parameter and its level; respectively. It was suggested that PPS can be reinforced for further improvement after optimized thermal, viscoelastic and mechanical properties.

Detecting Impact Damages in an Aramid/Glass Fiber Reinforced Hybrid Composite with Micro Tomography

This paper utilizes the micro computerized tomography (micro-CT) as the NDI technique to characterize the initial matrix delaminations locations and sizes in an aramid/glass fiber reinforced hybrid composite test specimen after a low velocity impact tests. Further, to visualize the localized low velocity impact damage volumes; based on the specimens micro-CT results; image analysis, geometric modeling and meshing softwares CtAn and CtVox were used. Finally, interpretation of damage mechanisms occurred in aramid/glass fiber reinforced hybrid composite after low velocity impact loading presented with accurate 3-D rendered models obtained from a series of micro-CT slices. 3-D rendered models gained from impacted specimens help to quantify the internal microscopic damage modes of complex material system such as aramid/glass fiber reinforced hybrid composite. It is very important to predict or determine composite materials response to an impact loading since impacts occur during manufacture, normal operations, maintenance, etc. After low velocity impact loading tests, investigation of damage zone will provide a better composite manufacturing process. For example, it is acknowledged that up to 80% of the cost of manufacture of a composite is xed once the preliminary conguration had been nalised. Further detail changes afterwards can only make a small impact on the nal cost of the manufacturing process.