Barkawi Sahari

Effect of hybridisation on crushing behaviour of carbon/glass fibre/epoxy circular-cylindrical shells

Abstract This study concentrates on the effect of hybridisation on the crushing behaviour, energy absorption and failure mechanism and mode for composite cylinders. The static crushing behaviour of filament wound laminated (FWL) circular–cylindrical composite shell under uniform axial load has been investigated experimentally. Five different hybrids and non-hybrid FWL circular–cylindrical composite shell containing carbon and glass fibres were fabricated. Five types of composites were tested, namely, carbon fibre/epoxy, glass fibre/epoxy, carbon–glass–glass/epoxy, glass–carbon–glass/epoxy and glass–glass–carbon/epoxy. Failure modes were examined using the photographs taken during the different crushing stages for each specimen. Failure modes were highly dominated by the effect of hybridisation. The results also showed that the structure with material sequence of glass–carbon–glass/epoxy exhibited good energy absorption capability.

Finite element analysis of corrugated web beams under bending

Abstract The effect of web corrugation on the beam’s strength is presented in this paper. Beams with plane web, vertically and horizontally corrugated webs were investigated using LUSAS finite element package. For the horizontally corrugated case, one arc and two arcs were studied, while half-circular wave corrugation was used for the vertical type. Half of circle corrugations of 22.41 mm mean radius and 3.44 mm thickness were used throughout this study. Non-linear elastic–plastic behaviour has been considered. Three different corrugation radii were taken for each type of the beam to investigate its effect on the beam’s strength. Ordinary I-beams, with plane web, were also tested experimentally. The comparison between the results obtained from both methods, for the plane web type, shows 3.1% to 7.1% differences. On the other hand, it is also found that beams with vertically corrugated web stands 38.8% to 54.4% higher moments than the horizontal type. The vertically corrugated web provides a stronger support against the flange buckling, compared to the plane and horizontally corrugated web types. It is found to be the same for the three radii taken. Moreover, corrugated web beams with larger corrugation radius could sustain higher bending moment and it is true for the sizes used throughout this investigation.

An experimental investigation into crushing behaviour of filament-wound laminated cone-cone intersection composite shell

Abstract This paper presents the effect of cone vertex angle on the crushing behaviour, energy absorption, failure mechanism and failure mode of filament-wound laminated (FWL) cone–cone intersection composite shell. The static crushing behaviour of FWL cone–cone intersection composite shell under uniform axial load is investigated experimentally. Two types of composites were tested, namely, carbon fibre/epoxy and glass fibre/epoxy. The cones vertex angles tested are 10°, 15°, 20° and 25°. Failure modes were examined using the photographs taken during crushing the specimens. The results showed that the initial failure was dominated by interfacial and shear failure, while the delamination and eventually fibre fracture dominated the failure mechanism after the initial first failure. The results also showed that the structure with vertex angles 20° and 25° exhibited good energy absorption capability. The volume reduction is obtained and found to be significant for these sets of angles.

Quasi-static axial crushing of segmented and non-segmented composite tubes

Abstract This paper examines the effect of segmentation on the crushing behaviour, energy absorption and failure mechanism of composite tubes. Quasi-static axial crushing behaviour of segmented and non-segmented composite tubes is investigated experimentally. The segmented composite tube consists of three different material regions, each with its own specific functions. Load–displacement curves and deformation histories of typical specimens are presented and discussed.The results showed that non-segmented composite tubes were found to be very brittle (i.e. the tissue mat glass fibre/epoxy tubes), or have low energy absorption capability (i.e. cotton fabric fibre/epoxy). On the other hand, segmented composite tubes including the tissue mat glass fibres were found to suffer from low energy absorption and the catastrophic failure mechanism initiated at the part made of tissue mat glass fibre/epoxy. Segmented composite tubes from carbon fabric fibre and cotton fabric fibres exhibited good energy absorption capability as well as stable load-carrying capacity.

On the Stress Analysis of Functionally Graded Gear Wheels with Variable Thickness

This paper presents the elastic solutions of the gear wheels made of functionally graded material (FGM) with variable thickness subjected to rotating loads. The material properties and wheel thickness profile are assumed to be represented by two power law distributions. Solid and hollow wheels are considered and the solutions for the stresses and displacements are given under appropriate boundary conditions. The solutions for FGM are compared with that of non-FGM, and for variable thickness and for uniform thickness. The effects of the material grading index, n, and the geometry of the wheel on the stress and displacement are investigated. It is found that a functionally graded wheel with parabolic and hyperbolic convergent thickness profile has smaller stresses and displacements compared with that with uniform thickness. The maximum radial stress for the solid functionally graded wheel with parabolic thickness profile was not at the center, whereas for solid wheel with uniform thickness, the maximum was at the center. The results obtained suggest that an FGM gear wheel with hyperbolic convergent and parabolic concave thickness profile is more suitable compared with that of uniform thickness.

On the Collapse of Cotton/Epoxy Tubes under Axial Static Loading

Experimental quasi-static crushing tests and finite element analysis have been carried out for unidirectional filament wound laminated cotton/epoxy tubes. The work focuses on three main factors, which considerably affect the axial collapse load of unidirectional natural composite tubes. These factors are structural geometry, fibre diameter and fibre orientation. Cotton/epoxy tubes with different diameters (50, 70, 90, 110 and 130 mm) were examined and tested. The fibre orientation angles were 80 and 90°. The initial geometric imperfections are measured using the computerised Mistral coordinate measuring machine. The numerical prediction was obtained using commercially available finite element software. A limited agreement between the experimental and computational results was obtained. For all structures considered classical axial collapse eigenvalues were computed. The initial failure crush load computed from the finite element simulation model has been compared with the experiments.

Influences of Air Exchange Effectiveness and its Rate on Thermal Comfort: Naturally Ventilated Office

This article presents the effects of air exchange rate (ACH) and air exchange effectiveness (AEE) on thermal comfort level of a naturally ventilated office room. The study was conducted in an office at UPM, Malaysia. Influence of ACH and AEE on thermal comfort has not been investigated and is, therefore, not well understood. The main objective of this research is to investigate and assess these influences through the variable windows-door opening arrangements. To determine the windows-door opening performance in terms of ventilation air flow rate, 14 opening configurations have been considered. Thermal comfort variables were measured at the same time when ACH and AEE were evaluated. Through these data, the thermal comfort Fangers indices (Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD)), ACH and AEE were calculated. These results showed that for a naturally ventilated office room three linear regression equations of PMV versus ACH and three linear regression equations of PMV versus AEE can be derived.

Effect of Material and Geometry on Crushing Behaviour of Laminated Conical Composite Shells

This paper examines the effects of the material and structural geometry on the crushing behaviour, energy absorption, failure mechanism and failure mode of circular conical composite shell. The static crushing behaviour of circular conical composite shell under uniform axial compressive load has been investigated experimentally. The cone vertex angles used were 0, 6, 12 and 18 degrees. The cone vertical length and bottom outer diameter were kept for all the cases as 100 and 110 mm, respectively. Failure modes were examined using several photographs taken during the crushing stages for each specimen. Results obtained from this investigation showed that the initial failure was dominated by the interfacial and shear failure, while the delamination and eventually fibre fracture were dominated the failure mechanism after the initial failure. It has also found that the static crushing behaviour of the circular conical shell is very sensitive to the change in the vertex angle. Reinforcement type greatly affects the energy absorption of the circular conical and cylindrical shells.

Thermal comfort of an air-conditioned office through different windows-door opening arrangements

This paper investigates the thermal comfort level of an office room through various windows-door opening arrangements in hot and humid climate. To determine the windows-door opening performance, 14 opening configurations have been considered and the combination of opening arrangements was carried out in an air-conditioned office at UPM, Malaysia. After conducting objective measurement for each condition, Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD) were calculated. The concentrations of carbon dioxide (CO2) were also monitored. Subjective survey involved questions on the thermal environmental perception and indoor air quality for office occupants for this study. Objective data analysis showed that in most of conditions office had thermal conditions falling within the comfort zone of ASHRAE standard 55, and in all of conditions neutral temperatures are higher than ASHRAE standard requirements. Subjective results revealed that staff has higher thermal comfort level as compared to what PMV has predicted. Practical application: It is believed that the results in this paper will contribute to knowledge that international standards are not applicable in hot and humid climate. Fanger equations would give the results for European conditions, people in hot- humid climate have some cultural preferences that are different from the Europeans hence modifying these equations and standards for this climate are necessary. In terms of the use of climatic control to modify the indoor environment it is found that when the occupants have the freedom to modify the environment, and make necessary adjustment, they always use windows-door opening arrangements to compensate for the less comfortable thermal condition and increase air movement.

Effect of residual stresses in a filament wound laminated conical shell

Abstract This paper examines the effect of residual fabrication stresses on the crushing behaviour, energy absorption, failure mechanism and failure mode of a filament wound laminated conical composite shell. The static crushing behaviour of the conical composite shell under uniform axial compressive load is investigated experimentally. The cone vertex angles were 0°, 6°, 12° and 18°. The numerical result shows that residual stresses developed have been concentrated at the small ends of cones. Experimental results obtained from this investigation show that the initial failure was dominated by interfacial and shear failure, while the delamination and eventually fibre fracture were dominated by the failure mechanism after the initial failure. It is also found that the static crushing behaviour of the conical shell is highly sensitive to the change in cone vertex angle, which strongly dominates the residual fabrication stress development. It can be deduced that as the axial residual stress increases, the initial failure load decreases.