Strain Aging. Failure in a die due to stress induced by sustained use, which continues to propagate while the die is at rest. The phenomenon often occurred over a weekend and was noticed that the failure rate of dies early in the work week were greater than later in the week. Dies change in hardness, tensile strength and ductility (due to atomic diffusion through the metal's crystalline structure) after two days of nonuse. The problem of strain aging is easily cured by stress relieving immediately after a long use and before being placed in storage.