Journal of Material Sciences & Engineering

Dilemma between Physics and ISO Elastic Indentation Modulus

Abstract

Kaupp G

This paper challenges the ISO standard 14577 that determines the elastic indentation modulus by violating the first energy law, violating the physically deduced dimensional law, and omitting easily detected phase change onsets as well as initial surface effects under load. The double iteration for incorrect fitting indentation modulus to Hook's law Young's modulus of a standard with up to 11 free parameters must be cancelled and discontinued. The iterative evaluation of the elastic modulus E_r-ISO can by far not be reproduced by iteration-free direct calculation of E_r, when using the underlying formulas for S, hc, A_hc, and ε. For cubic aluminium the divergence amounts to a factor of 3.5 or 3.1, respectively (both smaller for the non-iterated calculations). Every interpretation of indentation moduli as single unidirectional "Young's moduli" is false. They are mixtures from all directions and include shear moduli. The three different packing diagrams of body centered cubic α-iron exemplify the mixture of three independent Young's moduli (and thus also three shear moduli) even in this simple but already anisotropic case. More linear moduli ensue in lower symmetry crystals as exemplified with α-quartz. The first physical indentation modulus is deduced by removal of the physical errors of E_r-ISO, or after indenter compliance correction E_ISO. E_phys does no longer violate the energy law. Five face-dependent elastic indentation moduli of α-quartz at the obsolete E_r-ISO level and two tensional Hook-law Young's moduli are compared with all of its six resonance ultrasound spectroscopy (RUS) evaluated Young's moduli, and with the bulk modulus. The dilemma between ISO and physics is particularly detrimental, as E_ISO is used for the calculation of very frequently applied mechanical parameters. These propagate the errors into failure risks of falsely calculated materials with severe violation of the basic energy law and other physical laws for daily life. Difficulties with the urgent settlement by new ISO standards are discussed. First suggestions for the use of E_phys, or S_phys, or eventually measured bulk modulus K are made. This should be urgently evaluated and discussed.