Patent ID: 6983660

Claim:
An apparatus for measuring the fatigue life of a structural member of known composition, said apparatus comprising: a. a flat test-coupon uniformly cast and composed of any material mountable on said structural member, b. said test-coupon having at least two cut-out portions of different area which define at least two parallel ligaments of different lengths, c. said cut-out portions defining said ligaments having a shape described by at least two centrally aligned adjoining rectangles of different surface area, said centrally aligned adjoining rectangles having rounded corners described by ninety degree arcs joining any two adjacent sides and positioned so that said centrally aligned adjoining rectangles become progressively smaller in surface area, and d. said ligaments having a shape so as to effect failure due to fatigue of said ligaments at lower percentages of fatigue life of said structural member and prior to failure of said structural member due to fatigue when said ligament and said structural member are subjected to substantially similar stress conditions and history.