The process of subcritical crack growth under a monotonically increasing load in an elastic-plastic material comprises three stages — crack tip blunting, subcritical crack initiation and crack propagation . Determination the moment of initial subcritical crack in components (or specimens) under loading is problematic. A lot of attention has been devoted to predicting the critical value of fracture toughness in elastic-plastic materials in fracture mechanics tasks. A some of methods have been developed and standardized in relevant specifications, with the most popular being based on the critical value of J-integral — JIC, or on the critical value of crack tip opening, δTC . These quantities define the fracture toughness of a material at a chosen point when the average value of subcritical crack growth is 0.2 mm. The fracture toughness at subcritical crack initiation can be determined by measuring the geometry of the blunted crack tip, as proposed by Shih  (Fig. 1). The blunting of a primary sharp crack tip proceeds until subcritical crack initiation, and the radius of the blunted crack is dependent on the strength and plastic properties of the material. The assumptions of Shih’s model can be used for calculation of the crack tip opening displacement at crack initiation by measuring the stretch zone width (SZW), ΔaSZWi: dTi = 2∙ΔaSZWi (1) The blunting crack tip at moment according to start subcrack are shown in Figure 1. The view presented the situation in a axis plane of single edge notched bend specimen (SENB) which loading was stopped at subcritical crack initiation moment. The photography was made by scanning electron microscope (SEM). Shih proposed the relationship for calculating the J-integral value from the CTOD according to formula : J = (σY/dn)∙δT (2) where: dn - function dependent on the strength properties of the material and on the stress state ahea[...]
Wyniki 1-1 spośród 1 dla zapytania: authorDesc:"Piotr Furmańczyk"