1. Body hardness: historical development of concepts and testing methods

The notion of a body's hardness corresponds to its resistance to local penetration by a pointed object. This concept was intuitively perceived very early on, but it was difficult to define a simple test method that could be associated with a measurable quantity, despite the interest shown by many scientists. Only the simplest experiments have given rise to standardized test methods, but each of the most significant attempts retains all its interest for the study of the mechanical behavior of materials. Their field of application therefore remains the laboratory for the time being, with the eventual prospect of moving into the industrial domain thanks to the development of experimental techniques; the relatively recent commercialization of devices for scratching, then microraying coated materials, and devices for nanoindentation, nanoraying and ultramicrohardness has clearly demonstrated...