Published: Jan 1993
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A unified cumulative damage picture of spectrum load notch fatigue is presented, covering all its three stages: crack initiation, short crack growth, and long crack growth. The analysis uses rainflow cycle count, low-cycle fatigue, and crack growth constants as inputs. While cumulative damage in crack initiation is handled using conventional methods, recent observations of a substantial difference between notch root crack closure and crack opening stress serve as the inputs for modeling sequence sensitive damage accumulation in short and long crack growth. Range/damage-exceedance (RDE) diagrams showing contribution of individual load cycles to spectrum load cumulative damage are presented for an Al-Cu alloy (2014-T6511) subject to FALSTAFF and TWIST load spectra. These diagrams include information on load sequence sensitivity of damage in crack initiation and growth. RDE diagrams can be used to assess effects of load sequence reconstitution from rainflow cycle count and of load spectrum editing on cumulative damage.
cumulative fatigue damage, range/damage-exceedance (RDE) diagram, exceedance curve, crack initiation, short and long crack growth, crack opening and closure, upper and lower bound damage
National Aeronautical Laboratory, Bangalore,