Local Viscoelastic Properties of a Thermoplastic/Carbon Laminate as an Indicator of Fatigue Damage

The paper is aimed at an assessment of influence of damage accumulation in a thermoplastic/carbon laminate during a tensile cycling loading on durability, Young modulus and both instant and time-dependent local mechanical characteristics of a thermoplastic matrix, analysed by means of instrumented microindentation. Standard mechanical data from three-point bending are compared with results of the local microindentation testing.

Experimental Studies of Elastic Properties of Dental Enamel and Photopolymer Used for early Caries Treatment

The paper is concerned with the study of the elastic properties of dental enamel and its destruction by a microindentation technique. A series of experiments were performed to find differences in the mechanical properties of healthy and diseased dental enamel. It has been found that the times of dental enamel destruction in healthy and carious areas under a constant force are different. The effect of an infiltrated photopolymer on the hardness and elastic modulus of dental enamel was investigated by microindentation testing. A comparative analysis of the features of healthy, damaged by caries and treated by photopolymer enamel was carried out.

Surface Cracking and Degradation of Dense Hydroxyapatite through Vickers Microindentation Testing

Surface degradation and cracking of dense hydroxyapatite were evaluated through Vickers micro indentation using indentation loads ranged from 25 gf to 2000 gf. Crack lengths, imprint diameters and the number of lateral cracks and chips were measured using SEM. The crack length-indentation load data were analyzed with regard to the specific relations of Palmqvist and fully developed radial cracks. Crack type transition load from Palmqvist to median crack was experimentally assessed through serial sectioning technique. The analytical estimated transition load, based on the theoretical relation of the indentation load and crack lengths showed a good agreement with one obtained from experimental itinerary. Palmqvist and median cracks were identified in low and medium indentation loads, respectively. High indentation load could also lead to the formation of lateral cracks and chips. The tendency for lateral cracking was evaluated taking into account the number of lateral cracks and chips. The chips were found to be appeared just after test in higher indentation load, whereas in medium loads they could be detectable only after several weeks.

Hardness and deformation microstructures of nano-polycrystalline diamonds synthesized from various carbons under high pressure and high temperature

Mechanical properties of high-purity nano-polycrystalline diamonds synthesized by direct conversion from graphite and various non-graphitic carbons under static high pressures and high temperatures were investigated by microindentation testing with a Knoop indenter and observation of microstructures around the indentations. Results of indentation hardness tests using a superhard synthetic diamond Knoop indenter showed that the polycrystalline diamond synthesized from graphite at ⩾15 GPa and 2300–2500 °C (consisting of fine grains 10–30 nm in size and layered crystals) has very high Knoop hardness (Hk ⩾ 110 GPa), whereas the hardness of polycrystalline diamonds synthesized from non-graphitic carbons at ⩾15 GPa and below 2000 °C (consisting only of single-nano grains 5–10 nm in size) are significantly lower (Hk = 70 to 90 GPa). Microstructure observations beneath the indentations of these nano-polycrystalline diamonds suggest that the existence of a lamellar structure and the bonding strength of the grain boundary play important roles in controlling the hardness of the polycrystalline diamond.

Microindentation Testing of Rat Brain Tissue Slices

In addition to traditional testing methods, which generally involve complex sample preparation, indentation exists as an alternative, non-destructive testing technique for measuring the mechanical properties of materials. Indentation is increasingly being used in the mechanical assessment of soft hydrated materials, e.g., biological tissues, because of its non-destructive nature, small sample capacity, and ability to hone in on localized regions of interest.