Aysun Baltaci

Buckling Analysis of Laminated Composite Circular Plates with Holes

In this study, buckling analysis of laminated composite circular plates having circular holes and subjected to uniform radial load is investigated by using the finite element method. The effects of hole sizes, location of the holes, thickness variations and boundary conditions on the critical buckling load, and the buckling mode shapes of the composite plates are determined. Eight node isoparametric shell elements with 24 degrees of freedom are used during the investigation.

Effect of storage solutions on microhardness of crown enamel and dentin

Objective: The aim of this study was to determine alterations in microhardness of crown dentin and enamel, after 2 and 12-month storage in de-ionized water, 0.2% glutaraldehyde, Hanks′ Balanced Salt Solution (HBSS), 0.1% sodium hypochlorite (NaOCl) or 0.1% thymol. Materials and Methods: Freshly extracted, nonsterile 60 intact human premolars were distributed to five groups. Six teeth from each group were evaluated after two, and other six teeth were evaluated after 12 months storage. After grinding and polishing of teeth, Vickers hardness was evaluated with making indentations on enamel and dentin, using a pyramid diamond indenter tip exerting 100 g load for 15 s. Results: After 2 months storage in solutions, range of the hardness values (HV) of enamel and dentin were in between 315-357 and 64-67, respectively. However, 12 months storage of the teeth resulted in a statistically significant decrease in microhardness when compared to microhardness of teeth stored for 2 months (P = 0.001). Although the differences were not significant regarding solutions, all solutions decreased the microhardness both in enamel and dentin (P > 0.05). However, decrease in microhardness was relatively less in de-ionized water and thymol solutions while glutaraldehyde decreased microhardness the most: 63% for enamel and 53% for dentin. Conclusions: Microhardness of enamel and dentin was in an acceptable range when teeth were stored for 2 months in de-ionized water, glutaraldehyde, HBSS, NaOCl or in thymol; thus, teeth kept up to 2 months in these solutions can be used for mechanical in vitro tests. However, 12 months storage significantly decreased the microhardness of enamel and dentin.

Determination of the effects of axial load on the natural frequency of a composite beam with the finite element method

The effects of axial load on the natural frequency in simply supported thick composite beams are determined using the finite element method. The material properties of the elements are calculated with two different average value methods (arithmetic and weighted average) and the effects of axial load on the natural frequency of the beam are examined. A computer program is developed to analyze the effect of axial load on the natural frequency. The finite element method is used to determine the axial load effects on the natural frequency of a fiber reinforced composite beam. The results are obtained and compared with the analytical solutions by taking different element numbers in the thickness direction. With the help of these two methods, eight-node brick elements are used in multilayer finite element analyses. It has been observed that the results obtained by the arithmetic average method are quite close to the analytic results.