M. Evren Toygar

AN INVESTIGATION OF SQUARE DELAMINATION EFFECTS ON THE BUCKLING BEHAVIOR OF LAMINATED COMPOSITE PLATES WITH A SQUARE HOLE BY USING THREE-DIMENSIONAL FEM ANALYSIS

In the present study, the effects of the square delamination, around a square hole, on the buckling loads of the simply supported and clamped woven steel-reinforced thermoplastic (LDPE, F.2.12) laminated composite plates have been investigated. Three-dimensional finite element models of laminated plates with four layers have been established. The square delaminations exist between second/third layers. The stacking sequences are chosen as [0]4, [15 / 15]s, [15 / 15]2, [30 / 30]s, [30 / 30]2, [45]4. Firstly the harmony between theoretical and finite element solution results of the plate without hole and delamination has been shown. Then, the buckling loads have been determined for each of the models having different square delamination dimensions. Significant decreases in the buckling loads occur after a certain value of delamination dimension. It is seen, for clamped plates that the changing ratios of the results of the symmetric or antisymmetric cases are approximately the same and there is a linear relationship between the values of the fiber angles and buckling loads.

Effect of interface crack on lateral buckling behavior and free vibration response of a sandwich composite beam

The aim of this study is investigation of the effect of interface crack on lateral buckling load and free vibration response of a sandwich composite beam using experimental methods and finite element solutions. The lateral buckling load and natural frequencies in a thin sandwich composite cantilever beam with crack were considered. The crack was opened between the face sheets and foam core. The length of the crack was selected, such as 100, 150, 200, and 250 mm. Lateral buckling and vibration tests were applied on these samples and then the critical lateral buckling load and natural frequencies were found using experimental and finite element method. In the experimental studies, in-house test mechanisms were used. For the numerical analysis, ANSYS finite element software was used. Close results were obtained between both two methods.

An Investigation of Fracture Toughness of Carbon/Epoxy Composites

Fracture toughness of material has a great importance in the determination of the resistance of the material to crack propagation. The starting point in fracture mechanics analysis is to consider a crack of a certain size located in a component or specimen. The pure tensile specimen e.g., SENT (single edge notch tension), have the lowest constraint, while specimens dominated by bending have the highest constraint. In this paper, the woven carbon/epoxy composite material with eight lamina was produced which has a volume fraction of carbon fiber of approximately 60% mechanical properties of this woven composite have been calculated. The fracture toughness value was measured by using the crack mouth opening displacement (CMOD) method experimentally. An experimental investigation has been carried out on the fracture toughness of woven carbon/epoxy composite at room temperature using SENT specimens. The finite element study was carried out by using a 2-D model to obtain the fracture toughness value of woven carbon/epoxy composite numerically with the ABAQUS finite element software package. The result obtained via the CMOD method has been compared with the finite element method (FEM) results. Comparison showed good agreement.

Measurement of human walking on sagittal plane for exoskeleton walking pattern generation

Researchers have been worked on exoskeletons and active orthoses since 1960s. There are many competitions on these searches area. One of them is Human Exoskeleton Assistance System Prototype (HEASP) that is developed at Dokuz Eylül University. HEASPs goal is to assist one leg extremity persons. In this paper, the capturing of human walking parameters on sagittal plane is introduced. These parameters used for walking pattern generation and making pattern decision control strategies on HEASP.