Fatigue Crack Growth in 7050T7451 Aluminium Alloy Thick Section ...

DSTO-TR-1477127mm Radius (5’)230mm65mm15mm6.35mmFigure 5A drawing of the specimens used in this testing programThe specimens were machined from a 5.5 inch thick 7050-T7451 aluminium alloy plate with theDSTO, AVD designation of ‘KS’ (produced by Ravenswood Aluminium Corporation,Ravenswood, West Virginia 3 ). The long axis of the specimen aligned with the rolling direction andthe width of the specimen in the rolling plane as shown, in Figure 6. This gave the coupons a grainorientation that was more resistant to fatigue crack growth than would have been the case hadthey been cut with the long axis across the plate width. The cracking in these specimens will be inthe Short/Transverse plane. The structural detail that was the subject of the previous testinggenerates cracking consistent with ‘across the plate’ specimens – cracking in theShort/Longitudinal plane, therefore the specimens tested here are not strictly representative of themould line flange of the F/A-18 bulkheads.Rolling directionT (Transverse)S (Short Transverse)L (Logitudinal)Figure 6A schematic showing the orientation of the specimens as they were cut from the plate3.3 Specimen Material PropertiesThe KS plate was certified by Ravenswood to conform to the requirements of the specificationAMS 4050E which is very similar to the McDonnell Douglas Process specification 1420. Thechemical composition specification requirements are shown in Table 1 along with the results ofanalysis of the KS plate. Table 2 shows the mechanical properties and conductivity requirementsof 7050T7451. The supplied mechanical properties and conductivity measurements are shown inTable 3 along with the measured conductivity and hardness values.3 now – Century Aluminium Company6