Çıbıkçı, Kübra Çağla

Sandwich beams are widely used in many engineering applications such as aerospace, automotive, marine, and defense industries due to their high stiffness-to-weight ratios and superior mechanical performance. However, cutouts in the beam due to connection elements, weight reduction requirements, maintenance procedures, or damage during service can significantly affect dynamic behavior. In this study, the effects of cutout geometry, cutout position, number of cutouts, and cutout depth on the free vibration behavior of sandwich beams with clamped-free boundary conditions were parametrically investigated using the finite element method. These parameters, which have been addressed together in a limited number of studies in the literature, have been systematically evaluated within the same parametric framework in this study. Three different cutout geometries (circular, square, and triangular) were evaluated in the analysis; the cutout position was modeled at distances of 25, 75, and 125 mm from the clamped end, respectively, and the number of cutouts was modeled as one, two, and three. Furthermore, the effects of shallow and full-depth cutouts on natural frequencies were compared. The developed finite element model was validated against a reference study in the literature, and it was determined that the deviation between the obtained natural frequencies was less than 5%. The results showed that the cutout geometry particularly affects the natural frequencies in higher modes, that the natural frequencies increase with increasing distance of the cutouts from the clamped end to the free end, and that an increase in the number of cutouts leads to a decrease in the natural frequencies. Furthermore, it was determined that the effect of cutout depth varies depending on the cutout position, and that full-depth cutouts in regions close to the free end can increase the natural frequency. These findings comprehensively reveal the effects of cutout parameters on the dynamic behavior of sandwich beams, contributing to the development of sandwich structures designed with vibration performance in mind.

Küçükgöze, Osman Mert; Çam, Salim; Özel, Adnan; Deveci, Hamza Arda

This study aims to investigate face sheet asymmetry caused by the thickness difference between the top and bottom facings on the three-point bending performance of honeycomb composite plates. Aluminum alloys 5754-H22 and 3005-H19 were chosen for the surface plates and honeycomb core respectively. Two different types of adhesives were used: polyurethane and epoxy-based. The experiments were designed using generalized subset designs, and the results were analyzed in depth using analysis of variance tests. Initially, panel strength was evaluated independent of weight and cost where the optimal configuration is achieved by utilizing the maximum values of all parameters. Subsequently, panel strength, weight, and cost are considered concurrently, with four distinct optimization approaches employed: panel strength priority, weight priority, cost priority, and equal priority for all responses. When panel strength is prioritized, the optimal configuration is 20 mm thick core, 2 mm thick top plate, 1 mm thick bottom plate and 15 g of polyurethane adhesive. This weighs 166.6 g, costs $1.56 and achieves a maximum load capacity of 4.01 kN. The minimization of the bottom plate thickness suggests an inherent structural imbalance between the plates regarding the load-bearing capacity. Compared to the initial stage, where all parameters were maxed, the load capacity decreased by 13.9%; however, the weight and cost also decreased by 25.5% and 28.8%, respectively. In applications where weight and cost are as important as load-bearing capacity, this structural asymmetry can be used to reduce weight and cost with only a slight decrease in performance.

Çam, Salim

In interference fits, the difference in length between the shaft and hub leads to stress concentrations on the shaft at the locations corresponding to the ends of the hub. This creates a numerical singularity in finite element analysis and makes it hard to determine the true maximum stress. Hence, the accuracy of the stress concentration factor computed using the finite element method is uncertain. One of the primary objectives of this paper is to introduce a novel methodology to tackle numerical singularity, by adopting a concept from fracture mechanics. Subsequently, the proposed method was employed to assess the influence of geometric variables and the specific material utilized on the stress concentration factor. The parameters are the ratio of shaft outer diameter to hub outer diameter ((Formula presented.)), the ratio of hub length to shaft outer diameter ((Formula presented.)), the ratio of shaft inner diameter to outer diameter ((Formula presented.)) and the type of hub material. Then, analysis of variance tests were employed for a comprehensive understanding. The results demonstrated the efficacy of the method in addressing the numerical singularity problem through their consistency, which is a significant finding given the importance of precise determination of the stress concentration factor in predicting joint behavior and its direct implications for practical applications. Furthermore, the rigidity of the material selected for the hub, in conjunction with the utilization of hollow or solid shafts, was identified as the primary parameters influencing the stress concentration factor. When supplemented by other variables, the stress concentration factor can be manipulated on a wide scale.