SUMMARYThis study evaluated the stress distribution on an endodontically treated maxillary central incisor restored with different post-and-core systems by using a three-dimensional finite element analysis model. Seven three-dimensional finite element models were created. Each model contained cortical bone, cancelous bone, periodontal ligament, 3 mm apical root canal filling, post-andcore and all-ceramic crowns. Two different prefabricated zirconia ceramic post systems, a glass fiber-reinforced post system and a titanium post system were modeled. As a control, an all-ceramic crown on an endodontically treated maxillary central incisor without a post-and-core was modeled. Each model received a 45°oblique occlusal load at a constant intensity of 100 N. In each model, the ratio of Von Mises stress distribution was compared. The greatest stresses were observed in the coronal third of the roots on facial surfaces. The ratio of Von Mises stress distribution in dentin for the zirconia ceramic post According to FEA analysis, under a simulated occlusal load, the cervical area of endodontically treated and crowned maxillary central incisors was the most stress concentrated area. Zirconia ceramic posts create slightly less dentinal stress concentration than titanium and glass-fiber posts. 90Operative Dentistry stress concentrations in dentin created by two different zirconia ceramic post systems were nearly the same. The zirconia ceramic post systems created slightly less stress concentration in dentin than the glass fiber-reinforced and titanium posts.

The effects of the strip delamination width on the buckling loads of the simply supported carbon/epoxy woven laminated composite plates have been investigated. For this purpose, 3D finite elements models of the square carbon/epoxy laminated plates have been established. Each of these models possesses four layers and different delamination width between second and third layers. Firstly, the harmony between theoretical and finite element solutions results of the plate without delamination has been shown. Then, the buckling loads have been determined for each model and different fiber orientation angles. The results show that important decrease in the buckling loads occur after a certain value of the delamination width. The changing ratios of the results of the symmetric or antisymmetric cases are approximately the same for each angle. For the high values of orientation angles, the values and changing ratios of the buckling loads are also higher than those of the low angles.

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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.

In this study an elastic-plastic stress analysis is carried out in a woven steel fiber reinforced thermoplastic (LDFE, F.2.12) composite cantilever beam loaded uniformly at the upper surface. The intensity of the uniform force is chosen as a small value; therefore the normal stress component of ay is neglected during the elastic-plastic solution. An analytical solution is found, satisfying both equations of equilibrium and boundary conditions for a plane stress case. The orientation angle of the fibers is chosen as 00, 150, 300 and 45. The intensity of the residual stress component of ox is maximum at the upper or lower surfaces of the beam. Yielding begins earlier at the upper surface of the beam for 150 and 300 orientation angles. The intensity of the residual stress component of the shear stress is maximum on or around the longitudinal axis of the beam.