Material Scatter in Crack Growth Rates of 7075-T7351 under Spectrum Loading

Abstract:

The probabilistic distribution of crack lengths at a critical location is a key input for risk assessment of structural failure of airframes due to fracture. This distribution depends on the initial surface condition of the structural component, the crack growth behaviour of the material, and the applied load history. MIL-STD-1530C suggests the use of a single master crack growth curve to derive the subsequent crack length distributions from the initial crack length distribution, without taking into consideration the well-recognized scatter in crack growth rates due to uncertainties in material properties. In this paper, we report the results of a study that aims to quantify the scatter in crack growth rates of 7075-T7351 aluminium alloy subjected to spectrum loading, and to assess its effect on risk assessment. About 80 middle-tension specimens were planned to be tested under nominally identical conditions, with the crack lengths recorded using crack cameras and direct current differential potential method. Based on the test data and the analyses, crack length distributions are developed for different times. These are then compared to the distributions derived from the master curve approach. This investigation attempts to quantitatively demonstrate the reasonableness, or otherwise, of using a single crack growth curve to derive the distributions of crack lengths for risk analyses, and the conditions under which the observations apply. The results reported here and those from other researchers show that this scatter in crack growth rates cause by variation in material properties cannot be appropriately addressed by the master crack growth curve approach for the purpose of risk analysis.

• Periodical: Advanced Materials Research (Volumes 891-892)
• Pages: 1197-1202
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.891-892.1197
• Online since: March 2014
• Authors: Wei Ping Hu*, Beau Krieg, Ribelito F. Torregosa
• Keywords: Distribution of Crack Size, Risk Analysis, Scatter in Crack Growth Rates

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