Undue Hardness/Modulus Ratio Claims instead of Physical Penetration Resistance and Applications with Mollusk Shells: A Recent Study

A precise method for revealing mechanical properties is nanoindentation. However, such elucidation calls for physically based loading curve interpretation, which is largely still not done. The most significant phase-transitions under load, which happen often, cannot be detected by using indentation hardness H and indentation modulus Er. The assertion that H vs E plots always correspond linearly is neither experimentally supported nor properly inferred. It is most hazardous and misleading because it produces incorrect material properties. It is incorrect to employ H/E, commonly known as the "elasticity index," in complex calculations for the brittle parameter, yield strength, toughness, and so-called "real hardness." Without taking into account phase-transitions under load, which necessitate the correct exponent 3/2 on h for the loading curves, the usage of H/E cannot show the true attributes of materials (instead of disproved 2). The physical data of various mollusk shells that go through phase transitions, a novel bionics model, and various contributions for their strengthening serve as examples of this. The information is contrasted with that of aragonite, calcite, and vaterite.