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Three-dimensional finite element modeling of the contact between a rigid spherical indenter and a rough surface is presented when considering both the loading and unloading phases. The relationships among the indentation load, displacement, contact area, and mean contact pressure for both loading and unloading are established through a curve fitting using sigmoid logistic and power law functions. The contact load is proportional to the contact area, and the mean contact pressure is related to the characteristic stress, which is dependent on the material properties. The residual displacement is proportional to the maximum indentation displacement. A proportional relationship also exists for plastically dissipated energy and work conducted during loading. The surface roughness results in an effective elastic modulus calculated from an initial unloading stiffness several times larger than the true value of elastic modulus. Nonetheless, the calculated modulus under a shallow spherical indentation can still be applied for a relative comparison. [ABSTRACT FROM AUTHOR]

Radius and area function of a spherical indenter are calibrated by performing spherical nanoindentation tests on fused silica with known properties. The spherical indenter is made of ruby with a relatively large radius of 200 μm in nominal value. Hertzian relation was found to be successful in characterizing radius of spherical indenter under purely elastic deformation condition. Oliver and Pharr's method is dependent on the measurement accuracy of residual displacement, which cannot be measured within acceptable precision under very little plastic deformation with values of residual displacement being only several nanometers. Area function calibrated with Oliver and Pharr's method on a brittle material like fused silica was found to be smaller than true value, leading to measured elastic modulus larger than true value. A softer material that can produce sufficient plastic deformation with large residual displacement is recommended as the standard material for area function calibration. [ABSTRACT FROM AUTHOR]

Cu-free resin-based brake material filled with waste foundry resin-bonded sand (waste sand) was prepared using the hot-pressing method. The changes in the physical and chemical properties of Cu and waste sand during braking were investigated, and their role in resin-based composites was discussed. The effects of the content of waste sand on the hardness, impact strength, indentation hardness, elastic modulus, friction coefficient, wear rate, micro-scratch friction coefficient, scratch depth, residual depth, and wear mechanism of resin-based brake material were investigated. Cu-contained composites generate Cu 2 O when braking at high temperatures, which adversely affects the friction and wear properties. Compared to Cu, waste sand was found to be more favorable for the overall friction and wear properties of resin-based composites. This suggests that waste sand can be used as a substitute for Cu in brake material. Waste sand is beneficial for improving the friction coefficient and stability of brake material through the formation of a friction layer. This layer can significantly impact the wear mechanism of brake material, particularly at high temperature (250–350 ℃). The brake material with 10–15% waste sand indicates excellent heat-fade resistance. • Waste foundry sand have been successfully replaced copper in brake material. • The role of waste foundry sand and copper in brake material were comparatively studied. • The effects of waste sand on mechanical and tribological properties of brake material were investigated. • The brake material containing 10–15% waste foundry sand show excellent heat-fade resistance. [ABSTRACT FROM AUTHOR]

• Pop-in or serrations cannot be detected at large loading rates. • Indentation hardness decreases with a constant elastic modulus under small loads. • Fracture toughness can be obtained from the total indentation energy. • Area of shear band scales with contact and residual areas. • Scaling relationships among indentation variables of Zr-based BMG were quantified. Berkovich nanoindentation experiments were conducted on Zr 55 Cu 30 Al 10 Ni 5 bulk metallic glass under a constant loading rate. Indentation hardness decreased linearly with contact depth, which defied the direct application of conventional indentation size effect model for crystalline material. Elastic modulus remained invariant under small loads, but decreased linearly under large loads. The scaling relationships between indentation variables such as contact depth, permanent depth, the maximum indentation displacement, plastic energy, the total work of indentation and their ratios were investigated. The area of shear band circle, the projected contact area at the maximum load, and the residual projected area were all found to be proportional to one another. A new methodology to determine fracture toughness was proposed based on the total work of indentation, provided that the critical indentation displacement at the onset of fracture corresponds to zero value of elastic modulus extrapolated from curve fitting. [ABSTRACT FROM AUTHOR]