Memduh Kara

Dynamic Response of Laminated Composites Subjected to Low-velocity Impact

The dynamic response of E-glass/epoxy composite laminates under low velocity impact was experimentally investigated. Uni-directionally reinforced E-glass/epoxy laminates with the stacking sequence of [0°/-45°/45°/0°/ 90°/0°/45°/-45°/0°] s were studied with the aim of an impact test. The impact tests performed at impactor mass (30 kg) for three different impact velocities (2.0, 2.5, and 3.0 m/s) were conducted with a specially developed vertical drop weight testing machine. The radius of the impactor with a semispherical nose was 12 mm. Sample plate specimens that had dimensions of 180 × 50, 180 × 100, and 180 × 150 mm were clamped from two opposite sides while the other two sides were free. The center of each plate was exposed to impact loading. The differences in the impact responses of specimens with varying width are characterized. Moreover, it was shown that the peak force increased with the increase of the width of the specimen.

Impact resistance of gypsum board subjected to low velocity impact

Original scientific paper The aim of this study was to investigate the impact resistance and damage behaviour of gypsum and composite gypsum boards subjected to low velocity impact. Low velocity impact tests were performed on four different board materials which can be listed as gypsum boards, gypsum+75 gr/m2 mesh boards, gypsum+wallpaper boards and gypsum+75 gr/m2 mesh+wallpaper boards. Indenter used in the impact tests was 24 mm in diameter and has semi spherical tip geometry. Gypsum and composite gypsum boards were bonded in 500×400 mm sizes and simply supported at four sides. Various energy levels, i.e. 2, 4, 6, 8, 10 and 12 J were applied to the centre of each board. As a result of low speed impact tests, impact force-time and force-displacement variations were obtained and the damaged regions of the samples were examined. Penetration thresholds and perforation thresholds of gypsum and composite gypsum board samples were determined by using Energy Profile Method (EPM). The effect of adding mesh and wallpaper into the gypsum board on stab and puncture limits was evaluated. Around 62.40 % increase occurred on gypsum+mesh+wallpaper board comparing to gypsum board in perforation thresholds.

Experimental study of the impact behavior of laminated composites stricken by sharp impactors

Abstract In this study, the influence of the impactor shape on the dynamic response of E-glass/epoxy laminates was investigated. Composite samples were impacted using steel 90° and 120° conical, 24 mm and 12 mm in diameter hemispherical, pyramidal impactors via a specially developed drop weight test machine. The impact tests were performed at impactor mass (20 kg) for impact velocity (2.5 m/s). Plate specimens consisting of 18 plies for tests (180×50 mm) with a nominal thickness (7 mm) were used. Contact force-time and contact force-deflection data obtained from the experiments were interpreted. It was found that the contact force was smaller in the 90° conical impactor while it was bigger in the 24 mm hemispherical one. Absorbed energies were also investigated. The absorbed energy obtained for pyramidal impactor was greater than that of the others. Furthermore, overall damage areas caused by the impactor were evaluated.