Development of In-Situ Type Biaxial Bending Testing Machine and Crack Growth Behavior Observation under Mixed-Mode on Glass

摘要

An attempt was made to investigate the crack growth behavior in soda-lime glass under mixed mode loading. Mixed mode crack growth tests under monotonic increasing biaxial loading were carried out by using the newly developed in-situ observation type biaxial bending testing machine. Biaxial stresses were applied by "saddle shape bending" for square plate. Crack extension from the residual stress free indentation-induced precrack were observed by a scanning laser microscope. The mode I and mode II stress intensity factors were calculated by Yoda's method. The major results of this study are summarized as follows Kinked cracks were initiated from indentation-induced precrack. With a crack growth, crack growth direction gradually approached to the direction perpendicular to the maximum principal stress. When crack growth rate was arranged by mode I stress intensity factor K_I, the threshold stress intensity K_(Ith) under mixed mode tends to decrease with decreasing in the stress mixing ratio R. The criteria in which the crack starts to grow under mixed mode condition was expressed by similar equation for the brittle fracture criteria. The stress intensity factor K_(eq), which is obtained by combining K_I and K_(II), is useful to discuss a crack growth behavior under mixed mode condition.