A. Aboutorabi

Quasi-static and dynamic compressive properties of ceramic microballoon filled syntactic foam

The compressive behaviour of epoxy based syntactic foams filled by ceramic microballoons is experimentally investigated in this study. Nine different types of syntactic foams are fabricated with three different microballoon sizes and three different microballoon fractions. All of the syntactic foam specimens are tested at various strain rates from quasi-static to high strain rates. Analysis of the results is carried out on the effect of the volume fraction, microballoon size and strain rate on the compressive behaviour of syntactic foams. Also, scanning electron microscopy is used to understand the fracture mechanisms of tested specimens. The results show that as the microballoon volume fraction increases the compressive strength, compressive modulus, failure strain and plateau stress decreases for all types of syntactic foams at all strain rates. Although, this decrease is slight for 20% and 40% volume fraction, it is considerable for 60% microballoon volume fraction syntactic foam. The results indicate that reducing the microballoon size or increasing the strain rate of testing would enhance the compressive strength.

Compressive Properties of Nanoclay-Reinforced Syntactic Foams at Quasi-Static and High Strain Rate Loading

The compressive behaviors of nanoclay-reinforced syntactic foams filled by ceramic microballoons are investigated. Eighteen different types of nano syntactic foams are fabricated with three different microballoons volume fraction, each containing six different weight fraction of nanoclay in their matrix. Quasi-static tests are carried out using an Instron 5500 machine test and Split Hopkinson Pressure Bar (SHPB) apparatus is used to perform the high strain rate tests. Also, scanning electron microscopy (SEM) is used to understand the fracture mechanisms and the microstructure of the tested specimens.

Analytical investigation of high-velocity impact on hybrid unidirectional/woven composite panels

In addition to fiber properties, the fabric structure plays an important role in determining ballistic performance of composite body armor textile. Textile structures used in ballistic protection are woven fabrics, unidirectional (UD) fabric structures, and nonwoven fabrics. In this article, an analytical model based on wave propagation and energy balance between the projectile and the target is developed to analyze hybrid fabric panels for ballistic protection. The hybrid panel consists of two types of structure: woven fabrics as the front layers and UD material as the rear layers. The model considers different cross sections of surface of the target in the woven and UD fabric of the hybrid panel. Also the model takes into account possible shear failure by using shear strength together with maximum tensile strain as the failure criteria. Reflections of deformation waves at interface between the layers and also the crimp of the yarn are modeled in the woven part of the hybrid panel. The results show greater efficiency of woven fibers in front layers (more shear resistance) and UD yarns in the rear layers (more tensile resistance), leading to better ballistic performance. Also modeling the yarn crimp results in more trauma at the backface of the panel producing data closer to the experimental results. It was found that there is an optimum ratio of woven to UD materials in the hybrid ballistic panel.

Experimental and numerical analysis of penetration into Kevlar fabric impregnated with shear thickening fluid

This study presents the high-velocity impact performance of a composite material composed of woven Kevlar fabric impregnated with a colloidal shear thickening fluids (STFs). Although the precise role of the STF in the high-velocity defeat, process is not exactly known but it is suspected to be due to the increased frictional interaction between yarns in impregnated fabrics. In order to explore the mechanism of this enhanced energy absorption, high-velocity impact test was conducted on neat, impregnated fabric and also on pure STF without fabric. A finite element model has been carried out to consider the effect of STF impregnation on the ballistic performance. For this purpose, fabric was modeled using LS-DYNA by employing the experimental results of yarn pull-out tests to characterize the frictional behavior of the STF impregnated fabric. The simulation result is a proof that the increased performance for STF impregnated Kevlar fabric is due to the increased friction.

The response of natural fibre composites to impact damage: a case study

Abstract: This chapter describes an investigation into hybrid laminate lay-up in multi-delaminated and single lap joint composite beams where the Charpy impact test was chosen to measure the energy absorbing capability of the beam. It was shown that beams that are stitched through the thickness are able to arrest crack propagation and consequently absorb more energy in comparison with non-stitched beams. It was also shown that composite beams that were bonded by stitching were able to absorb more energy in comparison with adhesively bonded composite joints in the hybrid composite beams.

Optimum configuration of compound parabolic concentrator (CPC) solar water heater types for dwellings situated in the northern maritime climate

SYNOPSIS For northern maritime climates with a high diffuse component of solar radiation, non-imaging CPC solar collectors with concentration ratios of up to 2 can be used to concentrate direct as well as diffuse incident solar radiation without tracking. Due to the concentrated solar flux incident on the absorber, these systems can produce temperatures in excess of those produced by conventional solar water heaters, thus reducing the auxiliary energy requirement. Additionally, a smaller absorber area is required, reducing the cost of the solar collector and making these systems more economically attractive. Two CPC solar collectors with an identical cavity profile were fabricated, one utilising a heat-pipe absorber and the other a simple direct flow absorber. Both collectors were tested under steady state operating conditions at inlet temperatures of 20°C, 30°C 40°C and 50°C, to simulate the conditions experienced by a typical domestic solar water heater. It was found that the direct flow CPC performed better at higher solar intensities and lower inlet temperatures, as the heat-pipe CPC had a much higher absorber plate temperature. Thus, for domestic applications, simple direct flow CPC systems would be preferred due to their higher efficiency and lower cost.

Investigation of Energy Absorption of a GFRP Composite Crash Box

Interlaminar fracture toughness of composite materials plays a key role on the specific energy absorption (SEA) of the crushing of composite materials. In this regard, an optimum composite crash box design is sought by studying the effect of fiber orientation and stacking sequence on the increase of interlaminar fracture toughness. In order to achieve this, various glass fiber/epoxy orientations were studied experimentally. Double cantilever beam and axial crush box specimens were produced and tested in a quasi-static condition to determine the interlaminar fracture toughness and SEA values for each set of fiber orientation and stacking sequence. The effect of stacking sequence on fracture toughness and the SEA of the GFRP composite crash box was quantified and optimum results were obtained.