SEDL / STP / STP877-EB / STP32885S

Potential-Drop Monitoring of Cracks in Surface-Flawed Specimens

VanStone, RH
Engineer, Materials Life and Methods, and research and development specialist, General Electric Co., Aircraft Engine Business Group, Cincinnati, OH

Richardson, TL
Engineer, Materials Life and Methods, and research and development specialist, General Electric Co., Aircraft Engine Business Group, Cincinnati, OH

Pages: 19    Published: Jan 1985

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Abstract

A direct-current potential-drop crack monitoring technique has been modified for use with test specimens having rectangular cross sections and semicircular crack starting notches, with radii as small as 0.075 mm (0.003 in.). An experimental program was conducted to evaluate an analytical model which predicts the crack depth from the potential drop, crack aspect ratio, and potential probe spacing. The fatigue crack growth rates of Rene'95, an advanced nickel-base superalloy, were determined at room temperature for three levels of gross section stress. There was extremely close agreement between the crack depths determined experimentally through post-test fractography and those predicted by the analytical potential-drop model. The critical barrier for fully automated monitoring of surface flaw crack growth with potential drop is the development of relationships to predict the crack aspect ratios as a function of material and testing parameters.