The Criterion For V-notched Brittle Fracture Under Mixed-modes

In marine equipment components and all kinds of engineering machinery, Vshaped incision is widespread, such as root, stepped shaft, gear steps and toolwithdrawal groove etc. As the notch tip stress concentration or singular, it is easy tocause fracture and cause the accident. At present, the problem of V notches of Ⅰinboth theory and experiment conducted the full research and established a fracturecriterion of mature. However, the study of composite V incision member brittle fracturecriterion is relatively less. Therefore, it is important for the theory significance andengineering value fracture criterion to establish a reasonable and practical composite Vincision component. The main works are as follows:First，the research status of V incision and the stress intensity factor are introduced.At present, the study of V incision is mainly divided into two categories, namely stresscriteria and energy criteria. The stress intensity factor criterion, the maximumcircumferential tensile stress criterion, the average circumferential stress criterion arestress criteria. The energy release rate criterion, strain energy density criterion areenergy criteria. The studies of these standards are introduced and explained. The stressintensity factor is mechanical constants, reflect the neighborhood near the crack tip or Vnotch tip singular force. In general, when the fracture safety analysis calculation, it is tocalculate the structure of the stress intensity factor K and associated with the magnitudeof load, load cracks or incision, geometry; on the other hand, need critical intensityfactor determination of material, when the critical intensity factorK1cdetermining material in the experiment, the strength factor of standard format is one must firstdetermine. So calculation of strength factor K of various kinds of component orspecimen expression is the primary task.Then, based on the singular stress field near the V-notch tip and two basicassumptions in this paper, twin-shear yield criterion and the volume strain energydensity factor criterion under mixed loading mode I and II and I-II mixed-mode isestablished and the numerical results of the crack angles and load critical stress arecalculated by these criterion.Firstly, in order to verity twin-shear yield criterion and the volume strain energydensity factor criterion,tension tests are carried out under mixed mode loading bytension testing machine using polymethyl methacrylate(PMMA). One hand, themechanical constants of organic glass were measured, such as organic glass elasticmodulus, Poisson’s ratio and fracture toughness. On the other hand, In order to verifythis criterion, V-notch specimens were made of brittle polymethyl methacrylate (PMMA)and tests of tension fracture were performed. These experimental critical loads andcracking angles are in good agreement with the predicted results, which suggests thattwin-shear yield criterion and the volume strain energy density factor criterion are validfor the V-notch brittle facture.