Download or read book Experimental Study of Fatigue Crack Propagation and Retardation Using Polymethylmethacrylate written by Francis J. Pitoniak and published by . This book was released on 1972 with total page 88 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fatigue cracks were grown in compact tension specimens of polymethylmethacrylate, a transparent polymer which was used as a model for metals. Various peak overloads applied to the constant DeltaK baselines used produced changes in the baseline load crack growth rates. A study of the monochromatic light interference fringe patterns emanating from the fatigue cracks at zero load indicated that the crack surface were closed along the saw cut edge and on the free surface of the specimens. The crack surfaces were displaced in the interior of the specimen at zero load. Measurement of the crack opening displacements from the fringe patterns indicated that the crack surfaces opened on the free surface at approximately half the baseline load level for a stress ratio of approximately zero. This is in agreement with the Elber crack closure concept.