Fracture Mechanics
Mixed Mode Cracks in Single Phase Materials
Six fracture criteria are compared to predict the fracture resistance and kinking angle of cement mortar and asphalt binder subjected to mixed mode loads. Cement concrete and asphalt mixture are two representative particle reinforced composites that are widely used for civil infrastructures. Cement mortar and asphalt binder are their matrices of those composite materials governing the strength and fracture resistance. The six fracture criteria employed in this study include three traditional criteria based on energy release rate (G), maximum tangential stress (MTS), and maximum tangential strain (MTSN) and the expanded versions of those considering the first nonsingular stress/strain term usually called T-term. The stress and strain field parameters around crack tip are obtained from finite element simulations, and the effects of each parameter on stress and strain distribution are studied.
For asphalt binder, a set of fracture tests are conducted at low temperature, and the crack kinking angles and fracture resistances under pure mode I, pure mode II, and mixed mode I/II conditions are measured. In case of cement mortar, previously published experimental data are used for validating the accuracy of the fracture criteria. The comparisons of the six criteria to the experimental data show that the three traditional criteria only considering the singular stress/strain terms have limitation in predicting mixed mode fracture. On the other hand, modified stress based criterion (GMTS) and extended strain based criterion (EMTSN) provide significantly improved predictions by taking into account the first nonsingular stress/strain term. However, strain energy density criterion (SED), which is an energy based criterion considering the effect of the nonsingular term, does not provide sufficient improvement in the fracture predictions. Comparison of GMTS and EMTSN reveals that the extended strain based criterion provides better predictions than the modified stress based criterion in mode II dominant conditions.
The similar results are obtained in case of cement mortar: the GMTS and EMTSN predict the mixed mode fracture resistance and crack propagation angle with high accuracy while the other traditional criteria are not. The results for both materials indicate that the first nonsingular term, T-stress/strain, plays an important role in the crack propagation of the binders of concrete and asphalt mixture. Since the mixed mode and pure mode II brittle fracture of the construction materials are rarely investigated so far, the results of this study will help researchers to understand the mechanism of crack propagation in civil infrastructures.
For asphalt binder, a set of fracture tests are conducted at low temperature, and the crack kinking angles and fracture resistances under pure mode I, pure mode II, and mixed mode I/II conditions are measured. In case of cement mortar, previously published experimental data are used for validating the accuracy of the fracture criteria. The comparisons of the six criteria to the experimental data show that the three traditional criteria only considering the singular stress/strain terms have limitation in predicting mixed mode fracture. On the other hand, modified stress based criterion (GMTS) and extended strain based criterion (EMTSN) provide significantly improved predictions by taking into account the first nonsingular stress/strain term. However, strain energy density criterion (SED), which is an energy based criterion considering the effect of the nonsingular term, does not provide sufficient improvement in the fracture predictions. Comparison of GMTS and EMTSN reveals that the extended strain based criterion provides better predictions than the modified stress based criterion in mode II dominant conditions.
The similar results are obtained in case of cement mortar: the GMTS and EMTSN predict the mixed mode fracture resistance and crack propagation angle with high accuracy while the other traditional criteria are not. The results for both materials indicate that the first nonsingular term, T-stress/strain, plays an important role in the crack propagation of the binders of concrete and asphalt mixture. Since the mixed mode and pure mode II brittle fracture of the construction materials are rarely investigated so far, the results of this study will help researchers to understand the mechanism of crack propagation in civil infrastructures.
Mixed Mode Cracks in Bi-Material Interfaces
Under construction