Effect of Transport/Bomber Loads Spectrum on Crack Growth
Abstract
This program investigated analytically and experimentally the effect of transport/bomber loads spectrum variations on crack growth. The spectrum represented a STOL transport (C-15) wing lower surface loading. 116 spectrum variations were generated, grouped in the following categories: (1) baseline spectra, (2) mission mix, (3) sequence of missions, (4) individual flight length, (5) flight segments, (6) exceedances spectra, (7) design stress level, (8) valley/peak coupling, (9) low load truncation, (10) high infrequent loads, (11) clipping of large loads, (12) miscellaneous variations, and (13) combined variations. Spectra were generated as random cycle-by-cycle, flight-by-flight sequences. Analyses and tests were performed on 7475-T7651 aluminum, t=0.25 inches, starting with an initial through-the-thickness 0.03-inch crack out of a 1/4-inch diameter hole. Crack growth analysis predictions were made for all 116 spectra using the linear model. Crack growth tests were performed with 33 of these spectra. Good correlation was obtained between analysis and test results in all cases except with spectra dealing with increased frequency and magnitude of high infrequent loads and spectra which were drastically changed from a wing- type to a vertical tail-type spectrum. Largest effects on crack growth life, as measured in flight hours, was due to flight length, mission, mission mix, and design stress level variations. Based on the results of this program, fleetwide crack growth variations by a factor of 100 and 10 could be experienced, depending on whether it was short-term or long-term variation.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 1978
- Accession Number
- ADA069287
Entities
People
- P. R. Abelkis
Organizations
- Douglas