It Meng Low

Vickers contact damage of micro-layered Ti3SiC2

Abstract The nature, evolution, and degree of deformation microfracture damage around and beneath Vickers contacts in monophase Ti 3 SiC 2 (312) are studied. The 312 material exhibits a pronounced shear deformation during indentation, indicating microscale plasticity which can be associated with infragrain multiple basal-plane slip between microlamellae, intergrain sliding, lamellae or grain pushout, and microfailures at the ends of the constrained shear-slips. No contact-induced cracks are observed and the micro-damage is widely distributed within the shear-compression zone around and below the contacts. The damage process is stochastic which results from a complex interplay of statistical variation in both relative size and crystallographic orientation of individual grains. The ability of 312 to absorb energy from the loading system and to distribute damage is somewhat akin to that of ceramics with either coarse-grained or heterogeneous microstructures, and perhaps geological structures.

Effect of water absorption on the mechanical properties of cotton fabric-reinforced geopolymer composites

Abstract Cotton fabric (CF) reinforced geopolymer composites are fabricated with fibre loadings of 4.5, 6.2 and 8.3 wt%. Results show that flexural strength, flexural modulus, impact strength, hardness and fracture toughness are increased as the fibre content increased. The ultimate mechanical properties were achieved with a fibre content of 8.3 wt%. The effect of water absorption on mechanical and physical properties of CF reinforced geopolymer composites is also investigated. The magnitude of maximum water uptake and diffusion coefficient is increased with an increase in fibre content. Flexural strength, modulus, impact strength, hardness and fracture toughness values are decreased as a result of water absorption. Scanning electron microscopy (SEM) is used to characterise the microstructure and failure mechanisms of dry and wet cotton fibre reinforced geopolymer composites.

Fabrication and Properties of Recycled Cellulose Fibre-Reinforced Epoxy Composites

Epoxy matrix composites reinforced with recycled cellulose fibre (RCF) were fabricated and characterized with respect to their flexural and impact properties. Reinforcement of the epoxy by RCF resulted in a significant increase in the strain at failure, fracture toughness and impact toughness but only a moderate increase in flexural strength and flexural modulus. The effect of accelerated exposure to seawater on the flexural and impact properties was also investigated. The salient toughening mechanisms and crack-tip failure processes were identified and discussed in light of observed microstructures, in particular the orientation of RCF sheets to the applied load.

Synthesis and characterization of mechanical properties in cotton fiber-reinforced geopolymer composites

Abstract Geopolymers are inorganic aluminosilicate materials that possess relatively good mechanical properties and desirable thermal stability but they exhibit failure behavior similar to brittle solids. This limitation may be remedied by fiber reinforcement to improve their strength and toughness. This paper describes the synthesis of cotton fiber-reinforced geopolymer composites and the characterization of their mechanical properties. The effects of cotton fiber content (0–1.0 wt.%) and fiber dispersion on the mechanical characteristics of geopolymer composites have been investigated in terms of hardness, impact strength and compressive strength. A fiber content of 0.5 wt.% was observed for achieving optimum mechanical properties in these composites.

Infiltration-processed, functionally graded aluminium titanate/zirconia–alumina compositePart I Microstructural characterization and physical properties

A novel route for processing aluminium titanate (AT)/(alumina–zirconia (AZ)) with graded microstructure and properties is described. This process offers a simple means of tailoring the composition and microstructure of ceramic materials. The processing involves infiltrating porous AZ preforms with a solution of TiCl4, followed by sintering at 1550°C for 3 h. The resultant material has a homogeneous core encased with a graded and heterogeneous layer of AT/AZ. Analyses by X-ray diffraction and energy-dispersive spectrometry have revealed the existence of concentration gradients, the AT content decreasing with increasing sample depth. The presence of both AT and zirconia inhibits the growth of alumina grains through a pinning mechanism. The existence of microcracking in AT and zirconia grains has been revealed by scanning electron microscopy. The graded material displays gradual changes in thermal expansion values due to the presence of AT which gradually reduces in amount from the surface to the core. The inclusion of zirconia has a favourable effect on the thermal stability of AT against phase decomposition.

Indentation responses of viscoelastic materials

Vickers indentation is arguably one of the most widely used techniques for characterizing the mechanical properties of materials because it is easy, inexpensive, and nondestructive. However, its popularity has so far been limited to ceramics and metals, and very little literature information is available on the Vickers indentation properties of high or rigid polymers. In this article, the Vickers indentation responses of an epoxy and acrylic polymer have been studied. The hardness of these materials is found to be time-dependent as a result of viscoelastic flow and relaxation processes. Unlike ductile metals, the microhardness is not dependent on the indentation load. The elastic recovery in the Vickers impression takes place only along the side faces but not along the diagonals. Thus, the use of Vickers indentation as a convenient tool for evaluating the hardness and viscoelastic responses of rigid polymers is justified.

Effect of particle size, filler loadings and x-ray tube voltage on the transmitted x-ray transmission in tungsten oxide—epoxy composites

The effect of particle size, filler loadings and x-ray tube voltage on the x-ray transmission in WO(3)-epoxy composites has been investigated using the mammography unit and a general radiography unit. Results indicate that nano-sized WO(3) has a better ability to attenuate the x-ray beam generated by lower tube voltages (25-35 kV) when compared to micro-sized WO(3) of the same filler loading. However, the effect of particle size on x-ray transmission was negligible at the higher x-ray tube voltages (40-120 kV).

Effect of nano-clay on mechanical and thermal properties of geopolymer

Abstract The effect of nano-clay platelets (Cloisite 30B) on the mechanical and thermal properties of fly ash geopolymer has been investigated in this paper. The nano-clay platelets are added to reinforce the geopolymer at loadings of 1.0%, 2.0%, and 3.0% by weight. The phase composition and microstructure of geopolymer nano-composites are also investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) techniques. Results show that the mechanical properties of geopolymer nano-composites are improved due to addition of nano-clay. It is found that the addition of 2.0 wt% nano-clay decreases the porosity and increases the nano-composites resistance to water absorption significantly. The optimum 2.0 wt% nano-clay addition exhibited the highest flexural and compressive strengths, flexural modulus and hardness. The microstructural analysis results indicate that the nano-clay behaves not only as a filler to improve the microstructure, but also as an activator to facilitate the geopolymeric reaction. The geopolymer nano-composite also exhibited better thermal stability than its counterpart pure geopolymer.

Characteristics of a layered and graded alumina/calcium-hexaluminate composite

Abstract A novel route to simple processing of a layered and graded material (LGM) based on alumina/calcium-hexaluminate (CA 6 ) is described. The processing involves partial infiltration of a porous alumina preform with hydrolysed calcium acetate to yield a homogeneous layer of alumina and a heterogeneous graded layer of CA 6 /alumina. Analysis by X-ray diffraction (XRD) has revealed the existence of concentration gradients, the CA 6 content decreasing with increasing sample depth. In-situ high temperature neutron diffraction (HTND) shows that the formation temperatures of CA, CA 2 , and CA 6 are respectively 1000°, 1200° and 1350°C. The presence of CA 6 appears to hinder the shrinkage and thus densification during sintering, as well as causing a reduction of hardness and flexural modulus. Scanning electron microscopy (SEM) has revealed the presence of plate-like morphology of CA 6 grains and the graded microstructure within the LGM.

Processing of an in-situ Layered and Graded Alumina/Calcium-Hexaluminate composite: Physical Characteristics

Abstract A novel route to simple processing of an in-situ layered and graded alumina/calcium-hexaluminate (CA 6 ) composite is described. The processing involves partial infiltration of a porous alumina preform with hydrolysed calcium acetate to yield a homogeneous layer of alumina and a heterogeneous graded layer of CA 6 /alumina. The homogeneous layer is designed to provide strength, hardness, and wear resistance, while the graded layer is tailored to impart toughness and damage tolerance. The effect of CA 6 on the physical and graded characteristics is discussed.