Study On The Fracture Behaviors Of Concrete Central Cracked Brazilian Disk Specimens

Concrete,which is a kind of multiphase composite materials with a wide application and a large amount of use,plays an irreplaceable role in national life.Although the concrete is widely used,there is still some inadequate understanding of the concrete,for example,the use of assessment about concrete foundation,high-rise buildings,bridges,dams and other military protection facilities with cracks;the assessment of concrete structures suffering from loading such as variation of temperature between day and night,strong pressure,strong winds,collision,explosion,earthquake and so on.Therefore,it is very important to study the fracture failure of concrete for engineering construction and maintenance.The stress intensity factors(SIF)and T-stress play an important role in fracture mechanics.This paper's aim is to introduces how to use the weight function method,the finite element method and the interaction integral method to solve SIFs and T-stress of the cracked body.The interaction integral method based on the XFEM is elaborated with a detailed description in this paper.Because of the generality and high accuracy,the interaction integral method can be used to calculate the SIFs and T-stress for homogeneous materials,functional gradient materials and discontinuous material with a material interface under complex boundary conditions.Moreover,the modified maximum tangential stress criterion,which takes into account the effects of non-singular stress terms(i.e.the T-stress,A3 and B3 from the expansion of Williams series and the higher order terms are ignored)in addition to the singular stress terms around the crack tip,is described in detail in this paper.The study on fracture initiation angles and the fracture resistances for a group of concrete central cracked Brazilian disk(CCBD)specimens(mortar specimens,small aggregate concrete specimens,large aggregates concrete specimens with low strength,large aggregate concrete specimens with high strength)with four types of different proportions and crackmodes(pure mode I,pure mode II and I-II mixed mode)are carried out experimentally and theoretically by using the MTS,GMTS and MMTS criterion.And the three kinds of criterions applied to concrete are compared and analyzed.It is found that the results from MMTS criterion are more reliable compared to those from traditional MTS criterion or GMTS criterion when used for predicting the fracture initiation angles and the fracture resistances on concrete,particularly for mode II dominant loading condition.The weighted function method and the interaction integral method are employed to investigate the effects of confining pressure on SIFs and T-stress for CCBD specimens.The numerical results show that the results from interaction integral method with high accuracy are in very good agreement with those from weight function method.Confining pressure has a significant effect on the SIFs of model I and T-stress,but has no effect on the SIFs of mode II.A larger confining pressure may keep the crack close.When relative crack length and loading angle are certain values,the dimensionless SIFs of mode I is decreasing and T-stress is increasing with increasing of the confining pressure.The critical loading angle for pure mode II crack depends on the magnitude of the confining pressure,the critical loading angle decreases to 0 as the confining pressure coefficient increases to 1.