Shot peening, cold working of holes, and adhesive bonding of metallic or composite doublers are often used singly or in combination in order to increase the fatigue life of critical aerospace components. A doubler, applied to a highly loaded area, provides an alternate load path and can reduce the propensity for fatigue Cracking. Adhesive bonding of a doubler requires a number of steps involving heat and pressure cycles where the temperature of the part might exceed the maximum temperature to which shot peened aluminium alloys should be subjected to, because of the possibility of thermal stress relaxation. The maximum exposure temperature ranges from 90°C to 121°C for aluminium alloys, depending on the shot peening specification used. [1] Slow relaxation of shot peening Stresses in the 7075-T6 aluminium alloy heated to 225°F (107°C) has been reported. [2].
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