Importance of load cell sensitivity in determination of the load dependence of hardness in recording microhardness tests

The behaviour of microhardness under varying load was investigated with an apparatus which measured both load and diamond pyramid motion simultaneously. There have been several experiments with this type of apparatus, which are designed to measure the hardness under load of a material. This type of measurement eliminates the effect of elastic recovery after the diamond is removed from the sample. Two types of load-independent hardness have been proposed on the basis of studies performed on this type of apparatus. The first follows the theory of Tate stating that elastic recovery is responsible for the load dependence of hardness. The second, proposed by Froelichet al. states that the load dependence of hardness is due to surface forces. This investigation used an apparatus similar to that of Froehlichet al. The results indicated that the load-independent hardness of Froehlichet al. was an experimental artifice caused by late detection of the surface, leading to underestimation of the penetration and overestimation of the hardness. Hardness measured under load using the apparatus in the present project was found to be load dependent.