Case hardening definition

Fig. 1. (a) Schematic diagram showing definition of case hardening and of case depth where (—) is the diameter (b) residual stress across the radius of a... 

Thermochemical treatments, sometimes referred to as case hardening or cementation, are based on the modification of the chemical composition of the substrate material. These treatments can be succeeded by a change in the structure through heat treatment. The formal definition available in BS EN 10052 1994 reads as follows (British standard, 1994) ... 

Even this definition needs to be classified [7, 8]. To some researchers it is still too broad because it includes many materials that are not usually thought of as composites such as concrete, copolymers and blends, reinforced plastics, and carbon-black-filled rubber. On the other hand, some of the more recent composites are excluded from the category of composites if this definition is strictly applied. For example, many particulate-type composites such as dispersion-hardened alloys and cermets have composite structures that are microscopic rather than macroscopic [2,8]. In some cases, the composite structures are nano-scopic, with the physical constraint of several nanometers as the minimum size of the components [9-16]. The terms... 

The existing definitions used by various authors are influenced by diverging attitudes towards induction. Several expressions are used synonymously to describe hardening phenomena accommodation (McOsker and Beck 1967), chemical calluses (Klaschka 1985), adaptation phenomena (Klaschka 1985), local hypo-reactivity (Andersen et al. 1987) and immunological tolerance (Wilkinson and Rycroft 1986). These terms show that no real clear delimitation is available between an adaptation to substances with exclusively irritative potential and adaptation to allergens in the case of proven sensitization. 

Where a definitive identification of the contents of the munition is required, it will normally be necessary to breach the munition case and take and analyse a sample of the chemical fill. This is a difficult and hazardous task, and will normally be attempted only in the field, in exceptional circumstances. Techniques for safely penetrating a munition in the field have, however, been developed. One system, developed by the United Kingdom, is based on the use of a commercial nail gun to penetrate the case of thin walled munitions. A special rubber patch is first placed on the wall of the munition and the nail gun, fitted with a specially designed hardened steel pin, is clamped to the wall of the munition. The gun is set up so that it can be fired remotely, and when this is done the steel pin is driven through the rubber patch and penetrates the wall of the munition. The rubber patch reduces the risk of leakage due to any over-pressure present within the munition. Once the pin has been safely inserted, the munition is transferred to a sealed glovebox. The pin can then be carefully removed and a sample of the fill extracted via the resulting hole in the munition wall for chemical analysis. 

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