Study of strength properties of cattle bone material using indentation method

Abstract

A study has been made of strength properties of cattle bone materials using the indentation method. This work consists of three main parts. In the first part, the preparation and characterization of cattle bone material is found to be a single - phase hydroxyapatite when cattle bone powders are sintered in the temperature range 1100 to 1345' c. Their grain sizes are found to increase as the sintering temperature or / and time increases. The minimum grain size of 0.6 µm is obtained at sintering temperature of 1250 C and the maximum grain size of 6.0 µm is obtained at sintering temperature of 1345 C. At the beginning of applying a constant temperature, their densities increase as a function of time and tend to approach a constant value for prolonged heating. In contrast, their porosities decrease with increasing temperature or / and time. In the second part, the damage pattern produced on cattle bone material surfaces by a Vickers indenter is studied. It is found to consist of square deformation zone accompanying by two crack systems, the median / radial crack and the lateral crack. The median / radial crack is more penetrative than the lateral crack and is thus more likely source of premature breakdown in the indented cattle bone material. In addition, it is found that the cattle bone material is highly susceptible to moisture enhanced slow crack growth. This is manifest in the observation of tremendous Vickers - produced crack extension after the indentation event. In the last part, strengths of two sets of cattle bone materials with 0.6 µm grain size and with 6.0 µm grain size have been determined as a function of indentation load. On progressively diminishing the indentation load, the strengths of both sets of specimens first show a steady increase but subsequently tend to a plateau as the contact size begins to approach the dimension of grain size. This transition from indentation - controlled behavior (high indentation load) to microstructure .controlled behavior (low indentation load) is more pronounced in cattle bone materials with 6.0 µm grain size than those of 0.6 µm grain size. The threshold indentation load p* in which the microstructural effects start to influence the strengths are found to be 2 N and 8 N for cattle bone materials with 0.6 yum and with 6.0 µm grain size, respestively. Therefore, the indentation - controlled strength data accumulated in this study demonstrate that the microstructural influence on strength of cattle bone material does increase as the grain size increases. The strength data in the indentation - controlled region via the indentation fracture mechanics theory give the macroscopic toughness K∞C for 0.6 and 6.0 µm grain cattle bone materials as 0.20 and 0.18 MPa ½respectively. These quantities K∞C and P*obtained from the indentation - controlled strength data are sufficient to specify strengths of cattle bone materials with 0.6 µm and 6.0 µm grain sizes completely under a given stress-bearing application.