Search

Modified ring (MR) specimen was suggested for investigating the mixed-mode (I/II) fracture behavior of brittle materials by rotating the crack orientation with respect to the loading direction. Crack tip fracture parameters (KI, KII, and Tstress) of MR were calculated for different geometric dimensions. To verify the numerical modeling procedure, two sets of comparisons were drawn between the results of prior studies on MR Mode Ifracture behavior and those of this study, showing good agreement between the results. Through some graphs, the effects of geometric parameters on YI, YII, and T*(dimensionless crack tip parameters) and also on βII(pure Mode IIcrack angle) were studied. In addition, the biaxiality ratio (B), as an influential factor in the generalized maximum tangential stress (GMTS) criterion, was calculated for the whole range of mode mixity in the MR specimens. Next, fracture behavior of the specimen was discussed by means of the GMTS criterion in terms of the results obtained for the biaxiality ratio (B). At the end, as an appendix, the entire results obtained for YI, YII, T*, and βIIwere presented.

Summary: The pattern of sperm retention and migration in the vagino-cervical region of rabbit was studied by means of scanning electron microscopy. The following phenomena were observed: 1) Spermatozoa located in the vagina and at the orifice of the ectocervix are usually distributed diffusely. They appear to be resting on the epithelial surface; many are structurally abnormal or decapitated. 2) The great majority of spermatozoa, however, seems to be anchored or retained in narrow epithelial channels with their heads in close file formations. This phenomenon was observed particularly in the fornix vaginae as late as 24 h post coitum. 3) A great number of spermatozoa invading the cervix evidently migrates in groups along the mucosal surface. Their heads are oriented toward the uterus and contact the epithelial cells. Spermatozoa that migrate beyond the cervico-uterine junction are distributed in the same manner. 4) Spermatozoa colonizing the cervical crypts appear to be attached via the anterior margins of their heads to the epithelial cells or to the tips of kinocilia. Their tails project into the crypt lumen. It is suggested that mainly three factors may be responsible for these phenomena: (i) the fact that only motile spermatozoa overcome the vagino-cervical barrier; (ii) the tendency of spermatozoa to move along the mucosa in close vicinity to the epithelial cells; and (iii) the inability to recognize mechanical barriers on the migration route (e.g., cervical crypts) and to overcome them quickly. This may be one of many possible causes leading to sperm retention in the vagino-cervical region.