Fractography

About: Fractography is a research topic. Over the lifetime, 5043 publications have been published within this topic receiving 86068 citations.

Development and property evaluation of aluminum alloy reinforced with nano-ZrO2 metal matrix composites (NMMCs)

Abstract: In the present research, nano-ZrO2 particulates were dispersed in aluminum alloy (LM 13) by melt deposition technique followed by hot extrusion. The size of the particles dispersed varies from 50 to 80 nm and amount of addition varies from 3 to 15 wt.% in steps of 3%. Microstructural studies of the nano-composite developed indicate that there is uniform distribution of the reinforcement in the matrix alloy with significant grain refinement and retention of residual porosity. Mechanical properties reveal that the presence of nano-ZrO2 particulates has improved significantly the strength and hardness with slight reduction in ductility as compared against the matrix alloy. Fractography of the specimens showed that the fracture behavior of matrix alloy has changed from ductile intergranular mode to cleavage mode of fracture. Results of the thermal and electrical tests on the composite developed indicate that, thermal conductivity and electrical resistance both decreased with increase in reinforcement content.

Methanol-Induced crack healing in poly(methyl methacrylate)†

Abstract: Crack healing in poly(methyl methacrylate) (PMMA) by methanol treatment at 40°C–60°C has been investigated. It is found that the methanol treatment reduces the glass transition temperature in PMMA. Crack healing only occurs at an operating temperature higher than the effective glass transition temperature. There are two distinctive stages for crack healing based on the recovery of mechanical strength. The first stage corresponds to the progressive healing due to wetting, which has a constant crack closure rate at a given temperature. Immediately following the first stage, the second stage corresponding to diffusion enhances the quality of healing behavior. The surface morphologies obtained during healing and after fracture tests confirm these two stages. By comparing the fracture stress with the fractography, the fracture surface for stage I of crack healing is coplanar to the original crack surface. On the other hand, the original crack surface is destroyed in stage II of crack healing. It occurs in the region incorporating the original healed surface and appears to be like the Virgin fracture surface. It is also found that the tensile fracture stress of PMMA treated by methanol can recover to that of the virgin material. In addition, it is interesting to find that after sustained methanol treatment, the “snake bone” phenomenon on the fracture surface emerges.

Effect of microstructure on the mechanical properties and fracture of commercial hypoeutectic Al-Si alloy modified with Na, Sb and Sr

Abstract: The microstructure, hardness, tensile properties and fracture have been studied for the non-modified and modified aluminium (Al) silicon (Si) commercial hypoeutectic alloy. Three modifiers were used being sodium (Na), antimony (Sb) and strontium (Sr). The Sb-modified structure revealed small plate-like Si morphology. The Na and Sr-modified structures exhibited fibrous Si. A slight increase in the hardness values (HV) due to modification was observed. A general increase in the tensile properties was observed due to modification. The tensile properties of the sand mould Sr-modified alloy were significantly higher than those of the Na-modified alloy by 12.7% in proof stress, 16.3% in ductility and 33.3% in toughness. For the metal mould ingots the increase in tensile properties of Sr-modified alloy were respectively: 16.7%, 32.5% and 41.7% compared to a Na-modified alloy. Optical fractography on longitudinal sections near the fracture surfaces of the modified alloys revealed that the crack propagates in the eutectic thus, circumventing the Al-dendrites. The dimple and smooth ripple patterns observed by scanning electron microscope (SEM) on the fracture surface of the Na and Sr-modified alloys suggest a transgranular type of fracture across the grains of the eutectic matrix.