Effects of constraint on crack growth under aircraft spectrum loading

Technical Report · Tue Sep 01 04:00:00 EDT 1992

OSTI ID:7000075

Newman, Jr, J C

The objective is to study the effects of constraint on fatigue crack growth under aircraft spectrum loading. A plasticity-induced crack-closure model that accounts for constraint variations during the transition from flat-to-slant crack growth was used to correlate crack-growth rate data under constant-amplitude loading and to calculate crack growth under simulated aircraft spectrum loading. The model was applied to several thin-sheet aluminum alloy materials. Under laboratory air conditions, the transition was shown to be related to the size of the cyclic plastic zone based on the effective stress-intensity factor range for several sheet materials and thicknesses. Results from three-dimensional, elastic-plastic, finite-element analyses of a flat, straight-through crack in a thin-sheet aluminum alloy specimen showed a constraint loss similar to that assumed in the model. Using test data and the closure model, the location of the constraint-loss regime in terms of growth rate and the value of the constraint factor at these rates were determined by trial and error. The model was then used to calculate crack growth under the TWIST spectrum. The calculated results agreed reasonably well with test data. In general, the model predicted shorter crack-growth lives than tests under the TWIST spectrum by about 40 percent. For the TWIST spectrum clipped at Level 3, the calculated lives were within about 20 percent. The results demonstrated that constraint variations, especially for thin-sheet alloys, should be accounted for to predict crack growth under typical aircraft spectra.

• Research Organization: National Aeronautics and Space Administration, Hampton, VA (United States). Langley Research Center
• OSTI ID: 7000075
• Report Number(s): N-92-34178; NASA-TM--107677; NAS--1.15:107677; CNN: RTOP 538-02-10-01
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360103* -- Metals & Alloys-- Mechanical Properties
AIRCRAFT
ALLOYS
ALUMINIUM ALLOYS
CALCULATION METHODS
CRACK PROPAGATION
CRACKS
FATIGUE
FINITE ELEMENT METHOD
MATHEMATICAL MODELS
MECHANICAL PROPERTIES
NUMERICAL SOLUTION
SHEETS
STRESS ANALYSIS
STRESS INTENSITY FACTORS