Papers by Author: A.R. Othman

Abstract: This research work was concerned with the evaluation of mechanical properties; flexural strength and impact strength of coconut coir textile composites. The coir fabric reinforcement was in a form of woven and cross ply structure. The two types of laminates orientations for cross-ply structures were 0/90 degrees and 45/-45 degrees. Composites with fibre weight fraction of 30% were prepared by hand lay-up and vacuum bagging technique. Mechanisms of composites failure were examined using scanning electron microscopy (SEM). Results have shown that the woven coir reinforced composites exhibited higher impact resistance and flexural strength (warp woven) compare to cross-ply composites. Moreover, 0/90 degrees orientations demonstrated better strength performance compare to 45/-45 degrees. However, damage propagation on woven composites was found to be larger than cross-ply composites. Normality test of data distribution were evaluated using Minitab software and it was proven that all samples were in a very stable behaviour (p > 0.05). Experimental results were also validated using one way analysis of variance technique (one way-ANOVA) and it revealed there was statistically significant difference (p < 0.05) between all different fabric structures of coir fabric as reinforcement in composite.

Abstract: Fiber reinforced composite structures are widely used in the aerospace, aircraft, civil and automotive applications due to their high strength-to-weight and stiffness-to-weight ratios and these applications require joining composite either to composite or to metal. There are three main methods for joining composite structures namely, bonding, mechanically fastened or a combination of the two. Bolted joint are preferred in structures where the disassembly is required for the purpose of maintenance and repair. Due to the stress concentration around the holes, bolted joints often represents the weakest part in the structure, and therefore it is important to design them safely. A review on the study of bolted joints in fiber reinforced composite structure is presented. It was found that the behavior of bolted joints in composite structure is affected by many factors, such as geometry, joint material, clamping–load provided by the bolts, ply orientations, etc. Accordingly, various researches have been conducted on the analyses of stress distribution, failure prediction, and strength properties of bolted joint both experimentally and numerically. Accurate prediction of stresses in bolted joints is essential for reliable design of the whole structure; if it is not optimally designed, premature and unexpected failures may be occurred.

Abstract: This paper presented the effect of constituent materials on impact damage and strength reduction of sandwich structure, composed of laminated woven E-glass facesheets and polypropylene thermoplastic honeycomb core. Effect of low-velocity impact was the main interest in a variety of layered configurations. Compression after impact (CAI) has been carried out to determine the residual strength of impacted sandwich structures. Three different thicknesses of core of 20, 40 and 60mm subjected to three different levels of impact energy of 15, 30 and 45J were investigated. Impact response of the panel was recorded and analyzed in terms of peak load, indentation, energy absorbed and time. A profile analysis using optical 3D surfaces profiler was carried out to attain the indentation depth and damage area of the samples. The tested samples were then sectioned into halves to capture the failure mode or damaged sequence of the polypropylene thermoplastic honeycomb core. The dominant failure modes of the core indicated that polypropylene thermoplastic honeycomb core is a high strength material which can absorb higher impact energy and retain a higher degree of structural integrity.

Abstract: Past and on-going research works on adhesive bonding in composite and sandwich were reviewed. Discussion was emphasized on critical failure mechanisms (e.g. mechanism of peel fracture) to enhance the performance of the bonding. This paper also focused on the application of good adhesive bonding in the application of sandwich structures. Debonding between skin and core is one of the failure mechanisms that should be given more attention in fabrication of sandwich structures. Incorporating fillet in composite bonding is one of the alternative ways to reduce the stress concentration at the edges of overlap length and to produce high peel strength for bonding. Basic understanding of the designs, theories and manufacturing of adhesive bonding were also presented. Several important parameters in the design such as the strain energy release rate (SERR) and formation of fillet also discussed. The analysis of SERR using virtual crack closure technique (VCCT) has also been highlighted to achieve high strength of adhesive bonding, providing the key element for optimization of the delamination resistance in maximizing energy absorption during fracture. Significant challenges or limitations in improving and optimizing the design were also highlighted.