Mechanical Properties of

Physical, mechanical, and performance characteristics are material-process related properties which collectively give the fastener its service capability. Physical properties are inherent in the raw material and remain unchanged, or with only slight alteration, in the fastener following its manufacture. Such physicalproperties as density, coefficient of thermal expansion, electrical resistance, thermal conductivity, and magnetic susceptibility all have importance and frequently dictate fastener material selection. Mechanical properties identify the reaction of a fastener to applied loads. Rarely are the mechanical properties of the fastener equal to those of the raw material from which it is made. Properties such as tensile strength, yield strength, hardness, and ductility are all subject to dramatic changes depending on the choice of manufacturing methods and metallurgical treatments. Selection of the raw material establishes a basic plateau of properties while the fmal combination of mechanical properties of the fastener itself are obtained during the manufacture and post-treatment processes. Performance properties are functional design features built into the fastener in order to satisfy criteria of the service application. Properties such as locking ability, prevailing torque, sealing, and driving torque are generally gained through the manufactur-

ing control of dimensional features. Choice of the material and its metallurgical treatment influence the magnitude rather than the existence of a particular performance property.