Accession Number : ADA581422


Title :   Crack Initiation and Growth Behavior at Corrosion Pit in 7075-T6 High Strength Aluminum Alloy


Descriptive Note : Master's thesis


Corporate Author : AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING AND MANAGEMENT


Personal Author(s) : Hunt, Eric M


Full Text : http://www.dtic.mil/get-tr-doc/pdf?AD=ADA581422


Report Date : Jun 2013


Pagination or Media Count : 124


Abstract : Research on fatigue crack formation from two types corrosion pits tangent to a circular hole in a 7075-T6 aluminum alloy subjected to uni-axial loads (R = 0.5, lambda = 0) in both an air and saltwater environment provides a method for exploring crack initiation and initial growth rates. This work focuses on a fracture mechanics approach to explore the transition from corrosion pit to crack growth. Specimens with a cylinder shaped through-pit tangent to a circular hole have a closed form solution to predict this delta K that closely resembles the finite element solutions. Specimens with a semi-circular corner-pit tangent to hole lack a closed form solution and finite element modeling was used to determine delta K of these specimens. Optical and electron microscopy provided an accurate way to measure and observe the crack growth rate (da/dN) and the cycles until initiation of the fatigue cracks. This research shows that corner-pit specimens initially have a slower crack growth rate than through-pit specimens due to the propagation of a quarter-circular crack front through the thickness of the sample. After initial crack growth, both corner-pit and through-pit samples have the same growth rate as their machine notched counterparts exposed air and saltwater environments.


Descriptors :   *ALUMINUM ALLOYS , *CRACKING(FRACTURING) , *HIGH STRENGTH ALLOYS , CORROSION , CRACK PROPAGATION , FATIGUE(MECHANICS) , FINITE ELEMENT ANALYSIS , FRACTURE(MECHANICS) , PITTING


Subject Categories : Properties of Metals and Alloys
      Mechanics


Distribution Statement : APPROVED FOR PUBLIC RELEASE