The evaluation of crack initiation toughness in an elastic-plastic situation is based on a blunting line approach suggested for J initiation toughness [1]. However, a similar approach may be used for CTOD (8) initiation toughness as well though not specified by BS 5762 [2]. The ASTM standard for J evaluation [ 1] leads to the following blunting line equation for CTOD.where Aa=~. h is the length (or width) of the stretched zone. Conventionally, the deformed crack tip is considered to be of a semi-circular type leading to a blunting angle of 45 degrees. However, viewpoints contrary to this have been expressed [3][4][5]. In the present work, the blunting angle (0) has been evaluated by measurement of the stretched zone width (SZW) and the stretched zone depth (SZD) in the Mo and C"r-Mo steels and a method for CTOD initiation toughness is proposed.The standard SEN bending specimens of Mo steel and Cr-Mo steel as well as their weldments were tested using standard methods [1,2] in a temperature range of 30-400°C. The details of testing are reported elsewhere [6]. For studying the profile of the stretched zone (SZ), the specimens were sectioned at the mid-thickness (as shown in Fig. 1), mounted on the back surface and viewed under a scanning electron microscope (SEM) so that the mid-thickness plane came under the SEM beam. By varying the back tilt between 10-30 degrees, the profile became clear and the SZW as well as the SZD could be measured. Table 1 presents the values of SZW and SZD along with the blunting angle i.e. tan-'(SZD/SZW).It may be noted that the SZD values are invariably smaller than the corresponding SZW values and thus the blunting angle is less than 45 degrees in all cases. It is our contention that the 2 SZD (at crack initiation) is a more appropriate measure of crack initiation CTOD. However, it does not include the elastic component of CTOD. Therefore, the actual crack initiation CTOD would be given byInt Journ of Fracture 47 (1991)
Electrical analogy is used to study the influence of contact areas on the hydraulic flow through rock fractures. The investigation has shown that in the case of radial flow the location of contact zones, as well as the total contact area, influences the flow rate. It is also demonstrated that when injection tests are conducted in boreholes, where the fracture close to the borehole is partially plugged by loose particles or other debris, the flow rate may be substantially underestimated.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.