Papers by Keyword: Mechanical Behaviour

Abstract: This paper presents a representative volume element (RVE)-based modelling method to capture the mechanical behaviour of aluminum foams under compressive loadings. Octadecahedron is selected as a geometric basis shape to form closed cells of the aluminum foams in the microstructured RVE model to simulate the mechanical behaviour under compressive loadings. The stress-strain relationship obtained from the numerical modelling is compared to that from experimental study and agreements between these results demonstrate the validity of the proposed RVE model. Through observing the deformation evolution of cells during a compressive loading process, the failure modes of aluminum foams are identified and analysed using the proposed RVE model. Further the influence of strain rate on the mechanical behaviour of aluminum foams under compressive loadings is numerically studied via a parametric study.

Abstract: 2205 duplex (austenitic-ferritic) stainless steel has a good weldability and an excellent corrosion resistance. The good weldability is achieved when in close to 50-50 ferrite-austenite ratio. In this study, the welding process and properties were investigated by pulsed Nd:YAG laser welding. Tensile test, surface microhardness test, surface topography and microstructures of 2205 duplex stainless steel welds were performed under different welding speeds, input currents, pulse widths, frequencies and defocus distance. The relationship among them was revealed and the optimal welding parameters were obtained. The results showed in the condition of I = 160 A, T = 5 ms, f = 25 Hz, V = 500 mm/min and Z =-1 mm, the amount of ferrite and austenite in welds was roughly same, overlap rate of solder joints was above 78% and the weldability was good.

Abstract: Toughening is a concept frequently used in brittle materials in order to prevent premature failure. For concrete, toughening is almost exclusively achieved by pre-stressing, i.e. by creating residual stresses that force cracks to close. However, this can only be accomplished with certain element geometries and is particularly unsuitable for thin specimens.An alternative method of toughening is to deflect the crack or to absorb the crack tip by means of a suitable material, in particular viscoelastic polymers. In the present study, the concrete samples are transformed into hybrid inorganic/organic composites, in which the organic phase exerts the crack-stopping properties. To do so, the pore system is filled with a mixture of methyl methacrylate and 2-hydroxyethyl methacrylate, which is then polymerised to form a functional copolymer. Witha 1:1 ratio of the two monomers, a 4.5-fold increase in flexural strength and 2.3-fold increase in bending modulus was observed compared to the reference concrete. It is assumed that the additional increase compared to concrete impregnated with polymers not containing 2-hydroxyethyl methacrylate is the direct consequence of the interfacial interaction provided by the presence of pendant hydroxyethyl groups in the polymer.

Abstract: The Al-Zn-Mg system is a familiar age-hardenable 7xxx series of aluminium alloy. Aluminium alloys are gaining wide popularity in aeronautical, automotive, and transportation industries. Scandium (Sc) has the ability to refine grain size of cast aluminium structure. It has been possible to achieve an ideal combination of strength, density, and thermal stability because of the unique age-hardening characteristics of Sc. Moreover, low solid solubility of Sc in aluminium is responsible for the improvement of the microstructure and mechanical properties when added in small amounts (≤0.6 wt.%). Further, inoculation is an effective means of grain refinement in liquid state of as-castaluminium alloys. So, density of GP zones formation and early stage of ageing effects assessment main priority in the present work. However, coherent precipitates like ScAl₃are finely dispersed to provide thermal stability by increasing recrystallization temperature. Hence, the improvement in the high temperature stability of aluminium alloys (7xxx series) may be attributed to the grain boundary pinning (e.g. Zenerdrag mechanism) by the fine precipitates.In this paper, the relationship between the mechanical behavior and microstructure characteristics of Al-Zn-Mg-Sc based alloys are investigated to understand the thermal stability mechanism of grain refinement and dispersive precipitation.

Abstract: Deformation and damage at the meso-scale level in representative volumes (RVE) of light ultrafine grained (UFG) alloys with distribution of grain size were simulated in wide loading conditions. The computational models of RVE were developed using the data of structure researches aluminum and magnesium UFG alloys on meso-, micro -, and nanoscale levels. The critical fracture stress on meso-scale level depends not only probabilistic of grain size distribution in RVE but relative volumes of coarse grains. Microcracks nucleation is associated with strain localization in UFG partial volumes in alloys with bimodal grain size distribution. Microcracks branch in the vicinity of coarse and ultrafine grains boundaries. It is revealed that the occurrence of bimodal grain size distributions causes the increasing of UFG alloys ductility, but decreasing of the tensile strength. The distribution the shear stress and the local particle velocity takes place at mesoscale level under dynamic loading of UFG alloys with bimodal grain size. The increasing of fine precipitations concentration not only causes the hardening but increasing of ductility of UFG alloys with bimodal grain size distribution.

Abstract: In recent years, metal foams are becoming more and more popular due to their high energy absorption ability and low density, which are being widely used in automotive engineering and aerospace engineering. As a design guide, foams can be characterised by several main geometric parameters, such as pore size, pore shape, spatial distribution and arrangement and so on. Considering most foam materials have random distributions of cell size and cell shape, the digital material representation and modelling of such materials become more complex. Cell size and shape effects on mechanical behaviours of metal foams have been found and investigated numerically and experimentally in authors' previous studies in which the authors have developed a digital framework for the representation, modelling and evaluation of multi-phase materials including metal foams. In this study, 2-/3-D finite element models are both developed to represent metal foams with random cell distributions and then a series of digital testing are simulated to investigate the mechanical behaviours of such foams. For validation and verification purpose, the results obtained from 2-/3-D models have been compared and good agreement has been found which demonstrated the effectiveness of the digital framework developed for metal forms.

Abstract: For decades, carbon black is the most preferred reinforcing filler in rubber industry especially in tyre manufacturing. Carbon black which originated from crude oil is a non renewable source that may diminish over time. Therefore, an alternative from natural source is needed to replace carbon black as the reinforcing agent in rubber industries without so much affecting the physical and mechanical properties of the final products. Since bamboo is an abundant natural source in Malaysia and proved to be one of the strongest natural fibres comparable to other building materials like steel, concrete, and timber that have been subjected to lot of studies, bamboo seems to be the best alternative to replace carbon black in reinforcing rubber. Bamboo chips were first treated using alkalinisation method and dried before ground to 180-250μm to improve the interfacial adhesion with the rubber matrix. The bamboo fibres were then incorporated into rubber through compounding process at different loading. The cure characteristics of the composites were determined at 150oC using rheometer. The curing times were then used to vulcanise the rubber compounds using a hot press. The mechanical behaviour of the bamboo fibre filled natural rubber composite like tensile strength, elongation at break, and hardness are then evaluated by taking the optimum loading of carbon black as the comparison. The strength of the composite were decreased and become harder as the fibre loading were increased. The weak adhesion of fibres to rubber matrix and uneven particle size distribution of fibres contribute to the fracture of the composites. These can be observed through the surface morphological analysis of the composite by using scanning electron microscopy (SEM).