Pehlivan, Levent; Baykasoğlu, Cengiz

The in-plane crushing behavior and energy absorption performance of carbon fiber reinforced polymer (CFRP) honeycombs with different core topologies were experimentally investigated under uniaxial loading conditions. Three types of CFRP honeycomb core topologies (i.e. circular, square and hexagonal) with different cell wall thicknesses and heights were considered in the designs. The honeycomb samples were fabricated by the molding and bonding process, which is widely used in the easy, fast and economical manufacturing of thin-walled honeycomb structures. A total of twenty-seven sample groups were experimentally tested for each loading condition, in which honeycomb samples with different core topologies were designed to have almost the same weights for a meaningful comparison. The experimental results revealed that all honeycomb designs have higher in-plane compression strength in the expansion direction, and hexagonal honeycombs showed the highest strength and energy absorption performance in both directions due to their stable load-carrying capacity and outstanding force efficiency. In particular, the experimental findings showed that the crushing strength and the specific energy absorption of CFRP honeycomb structures can be improved up to 6.1 and 4.2 times, respectively, by properly adjusting the cell wall thickness and height parameters. The results also revealed that the proposed lightweight CFRP honeycombs with the structural densities of 155–283 kg/m3 showed better in-plane crushing performance than many competing cellular topologies.

Ozyurt, E.

This study numerically investigates the elevated temperature resistance of collar plate and doubler plate reinforced Square Hollow Section (SHS) T-joints subjected to brace axial compressive load. The extensive numerical simulations were performed to examine the effects of the geometrical parameters of main members and reinforcing plate on the fire resistance of reinforced SHS T-joints after verification of the numerical models based on the available test results. The corresponding unreinforced joints were also analysed as reference resistance at five different temperature levels (20 °C, 400 °C, 500 °C, 600 °C, and 700 °C). Results indicate that the elevated temperature capacity of SHS T-joints can be significantly increased by using a collar plate or a doubler plate. Although the initial stiffness of the doubler plate reinforced joints was higher than the collar plate reinforced joints, their capacity was similar to each other. Also, the fire resistance of the reinforced joints mainly depended on the brace-to-chord width ratio and reinforcing plate thickness to chord wall thickness ratio. However, there was no beneficial effect on the fire resistance of reinforced joints when the thickness of the reinforcing plate was greater than 1.5 times the chord wall thickness. Moreover, there was an insignificant effect of half-width to thickness ratio of the chord, reinforcing length and reinforcing type as long as the required limit values of the reinforcing length and width were used based on the Eurocode 3 EN 1993-1-8. It is worth mentioning that modifying the steel yield strength in the ambient temperature design method to calculate the capacity of the reinforced SHS T-joints at elevated temperatures may be unsafe. A new design method was developed to predict the capacity of a collar plate and doubler plate reinforced SHS T-joints subjected to brace compressive load in fire.

Topal, U.; Uzman, Ü.

In this study, the applicability of the Modified Feasible Direction (MFD) method on the thermal buckling optimization of laminated plates subjected to uniformly distributed temperature load is investigated. The objective function is to maximize the critical temperature capacity of laminated plates and the fiber orientation is considered as design variable. The first-order shear deformation theory is used in the mathematical formulation. For this purpose, a program based on FORTRAN is used for the optimization of laminated plates. Finally, the effect of aspect ratio, antisymmetric lay-up, boundary condition, material anisotropy, ratio of coefficients of thermal expansion, and hybrid laminates on the results is investigated and the results are compared.