RESIDUAL STRESS RELAXATION IN NICKEL BASE ALLOYS SUBJECTED TO LOW CYCLE FATIGUE

摘要

Aircraft turbine engine disks operate at high cyclic loads. Thermal strain and mechanical strain are applied. Compressive residual stresses are introduced to the surface by shot peening. Applied stresses, when they accumulate cycles above yield will gradually cause the surface compressive residual stress to be reduced until the surface becomes residually stressed to zero or in tension. The FMA database of disk residual stress measurements versus cycles accumulated by PROTO-FMA on turbine disks has shown a general linear trend. The slope of the linear fit depends on the severity of the cumulative service conditions. The S/N curves obtained from rotating beam testing showed extended lifetime on shot peened specimens at lower applied loads and no benefit at higher loads because of the surface condition.