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Experimental and Numerical Approaches To Evaluate the Crushing Behavior of Combined Geometry Core Sandwich Structures Against Blast
(Izmir Institute of Technology, 2015) Kara, Ali; Taşdemirci, Alper; Güden, Mustafa
In this study, novel sandwich structures containing combined geometry structures as core materials were designed and developed for blast protection applications. The proposed combined geometries consist of a hemispherical geometry attached seamlessly to a cylindrical segment. Deep drawing method was used to obtain four different types of combined geometries having two different radii from blanks with two different initial thicknesses. The mechanical properties of the blank material were obtained by conducting tensile experiments at quasi-static and high strain rate regimes. Thereafter, crushing and energy absorption behavior of core units were determined by tests at quasi-static and low velocity regimes, experimentally. Before crushing simulations, manufacturing method was simulated to have realistic residual stress/strain and thickness variations of numerical specimens. Having accurate deformation history, crushing experiments were simulated and a good agreement was reached proving the realistic modeling of the manufacturing effects. The effect of heat treatment on the crushing behavior of combined geometry shells was also investigated both experimentally and numerically and there was a good agreement noted. After, cross-shaped sandwich structures of one type of combined geometry were prepared. Static, low velocity and high velocity crushing behavior of sandwiches were investigated. Study on sandwich structures also included confined experiments in order to account for the interaction between the core units and between the core units and surrounding environment; such a case might be a bigger sandwich in which adjacent cores could exert forces to each other. Numerical study was validated by comparing experimental and numerical results of three different loading regimes for sandwiches. Having well-verified numerical models, numerical study was extended to investigate strain rate and inertial effects on sandwich structures by simulations at high crushing velocities. With complete knowledge on crushing and energy absorption of single geometries and sandwiches, behavior of sandwiches under blast was investigated by using ConWep function. Various types were proposed for arrangements of sandwiches to have higher energy absorption and lower transmitted forces to the protected structures.
Development and Mechanical Characterization of Anti-Blast Sandwich Composites for Explosive Effect
(Izmir Institute of Technology, 2011) Baştürk, Suat Bahar; Tanoğlu, Metin
Composite sandwich structures have high potential to be used in anti-blast armour systems due to their lightweight and resistance to explosive effects. This study focuses on the production and mechanical characterization of sandwich structures with aluminium (Al) foams of various thicknesses in conjunction with skins composed of Al/GFPP fibre/metal laminates. The bonding between the components of the sandwich was achieved by various surface modification techniques such as silane surface treatment, polypropylene (PP) adhesive film addition and their combination. The Al sheet/Al foam sandwiches were also prepared to investigate the effect of GFPP addition on the performance of sandwich structures. The energy absorption capacities together with compressive and flexural behaviour of both Al foams and FML/Al foam sandwiches were evaluated by flatwise compression and three point bending tests. The samples with higher elastic modulus usually exhibited higher collapse strength for each thickness set of foam and foam based sandwiches. Also, the core thickness increase led to the increase of overall flexural collapse load and GFPP presence promoted the strength of the sandwiches and dissipated energy values. In order to investigate the blast response of the sandwich panels, the quasi-static sandwich panel analysis was related to dynamic blast loadings. For this purpose, the sandwich composites were subjected to compression loading with a specially designed loading fixture and the corresponding test method is called as “simulated blast test”. The sandwiches were assumed as single degree of freedom mass-spring systems to include the dynamic effect. The peak deflections and survivability of the panels under blast loading were predicted based on the formulations reported in the literature. To evaluate the blast response of the monolithic materials, composites and sandwich panels, blast testing was performed using specially designed blast test frame system and 0.5 to 6 kg TNT explosives. Test results revealed that composites such as GFPP exhibited successful results against blast explosions.

Phd Degree / Doktora

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