Fracturing of a defective plate under cyclic loading

Abstract

In 1994 the authors of the present paper, with the assistance of the staff of the Laboratory of Strength Mechanics in Vilnius Gediminas Technical University initiated investigation into defective construction elements. Cyclic fracturing processes were investigated in such construction elements that are subject to geometric uniformity disturbance, i.e. in heavily loaded defective elements. The limit value of the stress intensity factor was determined using the CT specimens. This value defines the threshold for stress intensity below that a crack does not propagate. The accuracy of these results was tested for a compact specimen with a rounded notch. A cyclic loading program was selected and tests were conducted to determine conditions favouring crack appearance in a defective plate. A cast iron plate with natural defects was loaded cyclically and studied until its breakdown. Experimental investigations prove that conditions for crack formation in defective construction elements are only satisfactorily defined by the fracture mechanics criterion Δ K th (stress intensity factor threshold) and the endurance limit of a plane-surface specimen. The stress and strain state in a defective area having an influence on crack appearance was analysed, and the effect of defects and loading conditions on the processes of crack formation and propagation was evaluated. Programmed computations of geometrical parameters qualify the experimental results