Further evaluation of the Ascor test for stress corrosion testing of aluminium alloys

Further evaluation of the Ascor test for stress corrosion testing of aluminium alloys

Schra, L.
Wanhill, R.J.H.

National Aerospace Laboratory NLR

1997-08-25

In 1991 a simple automated stress corrosion testing method called the ASCOR (Automated Stress corrosion Ring) test was developed to test aluminium alloys according to ASTM specification G49. The present investigation concentrated on evaluating two aspects of the test method: The SCC initiation criterion (2 % load decrease). The possibility of defining a threshold stress for micro SCC growth in addition to that for macro SCC growth. It was found that substantial SCC growth had occurred at 2 % load decrease. We therefore propose reducing the load decrease criterion to 1 % as an improved compromise between determining the SCC initiation life in a well-defined way and limiting the contribution of SCC growth to this life. Fracture strength ratios (fracture strength of loaded exposed specimens divided by fracture strength of unloaded exposed specimens) less than 100 % were found at exposure stresses below the threshold stress for macro SCC growth. Fractographic investigation showed SCC on the fracture surfaces of specimens tested at these exposure stresses. A threshold stress for micro SCC growth was determined and is defined as the exposure stress at and below which the fracture strength ratio is 100 %.

stress corrosion, accelerated testing, constant load, threshold stress, alternate immersion, aluminium alloys

http://resolver.tudelft.nl/uuid:b22b65aa-53f9-4a7d-a7d7-17b34acd9918

Nationaal Lucht- en Ruimtevaartlaboratorium

Campus only

NLR Technical Publication TP 97425 L

Aerospace Engineering Reports

report

(c)1997 National Aerospace Laboratory NLR