Experimental investigation and FE simulation of spherical indentation on nano-alumina reinforced copper-matrix composite produced by three different techniques

Experimental and Numerical Investigation on Indentation of Orthotropic Microplates with Finite Thickness

This article presents comparative experimental and numerical studies to investigate the deformation and contact force of orthotropic microplates under indentation test. A simple model is developed to obtain the 3D homogenized elastic properties of orthotropic materials. In the FE simulation, the microplate is assumed to be a fully elastic orthotropic composite, and the indenter is a rigid body. Experimental indentation test is performed to obtain load-displacement curve, indentation profile, and maximum indentation depth. The numerical studies are performed to investigate the effect of indenter radius, material orthotropy, and microplate thickness on deformation of microplate under indentation load and contact pressure. The numerical model is applied to simulate two different load conditions: microplate rested on a fully supported rigid fixture, and microplate rested on a hollow support rigid fixture with circular cut-out. Numerical and experimental studies achieve excellent agreement and good correlation proving the validity of the proposed homogenization model. These parametric studies proved that the indentation behavior of orthotropic laminated structures is material independent and it depends greatly on the plate thickness.

Investigation of the Microstructure and Mechanical Properties of Copper-Graphite Composites Reinforced with Single-Crystal α-Al₂O₃ Fibres by Hot Isostatic Pressing

Single-crystal α-Al₂O₃ fibres can be utilized as a novel reinforcement in high-temperature composites owing to their high elastic modulus, chemical and thermal stability. Unlike non-oxide fibres and polycrystalline alumina fibres, high-temperature oxidation and polycrystalline particles boundary growth will not occur for single-crystal α-Al₂O₃ fibres. In this work, single-crystal α-Al₂O₃ whiskers and Al₂O₃ particles synergistic reinforced copper-graphite composites were fabricated by mechanical alloying and hot isostatic pressing techniques. The phase compositions, microstructures, and fracture morphologies of the composites were investigated using X-ray diffraction, a scanning electron microscope equipped with an X-ray energy-dispersive spectrometer (EDS), an electron probe microscopic analysis equipped with wavelength-dispersive spectrometer, and a transmission electron microscope equipped with EDS. The mechanical properties have been measured by a micro-hardness tester and electronic universal testing machine. The results show that the reinforcements were unevenly distributed in the matrix with the increase of their content and there were some micro-cracks located at the interface between the reinforcement and the matrix. With the increase of the Al₂O₃ whisker content, the compressive strength of the composites first increased and then decreased, while the hardness decreased. The fracture and strengthening mechanisms of the composite materials were explored on the basis of the structure and composition of the composites through the formation and function of the interface. The main strengthening mechanism in the composites was fine grain strengthening and solid solution strengthening. The fracture type of the composites was brittle fracture.