Tamer Sinmazçelik

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.

Influence of Annealing on the Performance of Short Glass Fiber-reinforced Polyphenylene Sulfide (PPS) Composites:

The influence of annealing on the morphology and the performance of randomly oriented short glass fiber-reinforced polyphenylene sulfide (PPS) composites have been investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMTA), impact tests, and scanning electron microscopy (SEM). Endotherms belonging to secondary crystals are seen 10–20 C above the annealing temperatures. DMTA results showed that the annealed samples had higher glass transition temperatures and elastic moduli values when compared with the quenched samples. The effect of microstructure on elastic deformation, crack formation, and crack propagation are studied with instrumented impact tester.

Erosive Wear Studies of Glass fiber- and Carbon Fiber-reinforced Polyetheretherketone Composites at Low Particle Speed

In this study, solid particle erosive wear behavior of randomly oriented short glass fiber and carbon fiber-reinforced polyetheretherketone (PEEK) composites was investigated. The solid particle erosion experiments were carried out at six different contact angles (15—90°) and at low particle speed using brown fused aluminum oxide (Al2O3) particles (500—710 µm) as an erodent. The PEEK composites showed semi-ductile erosion behavior, with a maximum wear amount at a contact angle of 45°. The fiber type and the contact angle had a significant influence on erosion behavior. Glass fiber-reinforced PEEK composites showed better erosive wear resistance than carbon fibre-reinforced composites. Scanning electron microscopy studies were conducted to understand the wear mechanisms involved during the erosive wear.

Fracture characteristics of high impact polystyrene under impact fatigue loadings

This study analyses the impact properties of high impact polystyrene (HIPS). HIPS is one of the well-known toughened polymers. The high toughness is given by the rubbery phase. The impact fatigue behavior of HIPS was studied with a Ceast pendulum type tester (Resil 25). The fracture mechanisms were examined with a scanning electron microscopy. The nature of crack initiation and propagation was investigated for small impact angles and three different spans. The impact angles of charpy hammer were chosen as 5°, 10°, 15°, 20°, and 25°. The fracture characteristics varied with the impact angle, the number of impacts, and the distance between supports. The rate of crack propagation was high at higher impact angles with lower endurance, and low at lower impact angles with higher endurance.

Effects of Geometric Parameters on the Pin-bearing Strength of Glass/Polyphenylenesulphide Composites

In this experimental study, under conditions of static loading, load-bearing performance of pin connected multilayered (angle-ply) glass fiber-reinforced polyphenylenesulphide matrix composites with [(0°/90° )]4s and [(0°/90°)/ (+/—45 °)]2s stacking sequence was analyzed. The experiments were carried out according to the ASTM D953. The ratio of the distance between pin center and sample end, to pin diameter E/D; and the ratio of sample width to pin diameter W/D, were changed systematically during the experiments. From the results of the experiment, maximum bearing failure loads were obtained for [(0°/90°)/(+/—45°)] 2s lay-up with geometric parameters of D = 10 mm and W/D = 2. Macro images belonging to failure modes, which occurred as results of the tests were examined. In addition to this, from the fractographic examinations carried out with scanning electron microscope, it was concluded that the geometric parameters intimately affect fracture morphology.

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.

BIOMECHANICAL COMPARISON OF MEDIAL VERSUS LATERAL SIDED PLATING IN FEMORAL FRACTURES

ABSTRACT Objective: The aim of the present study was to determine whether the side of application of the plate itself affects the mechanical stability of the fixation. The specific question addressed is whether or not a lateral or medial plate application is biomechanically better, for the treatment of distal diaphysis fractures of the femur. Methods: Stability and stiffness of medial sided plating relative to the conventional lateral sided plating in distal diaphysis of the femur were measured by analyzing axial loading forces leading to implant failure. Sixty synthetic femurs were tested in physiological bending, to calculate the yield and ultimate load to displacement following fixation of distal diaphysis fractures of the femur by either medial or lateral sided plating. Axial loading was applied to samples using a uniaxial testing machine. Results: There was more implant deformation in the lateral sided plating group – a difference with statistical significance. Conclusion: Medial sided plating was found to be as stiff as lateral plating. Medial plating may be a reasonable treatment option that can be used safely in selected cases. Level of Evidence I, Therapeutic Studies Investigating the Results of Treatment