Study On Crack Propagation Of Concrete Members Based On Extended Finite Element Method

The finite element model of crack propagation in limited-width center crack plate is established in ABAQUS finite element software,then according to the results of finite element post-processing,some necessary data are extracted by using python codes.By selecting different numbers of elements at the crack front and fitting the stress field and displacement field data pair(r _i,K_Ii)with three least square methods based on element stress extrapolation methods,I crack stress intensity factor at the crack tip of the central crack plate is obtained.By comparing with the theoretical solution,the results show conclusions below.Each method corresponds to an optimal element selection number,among three methods,the optimal element selection numbers which method two corresponds to are the smallest,method three corresponds to are in the middle,method one corresponds to are the biggest.When the element selection number of crack front is less than the optimal number,the numerical solution is smaller than the theoretical solution,and when the element selection number of crack front is larger than the optimal number,the numerical solution is larger than the theoretical solution.The accuracy of the stress intensity factor is related to the number of element selection at the crack front and the fitting method.The comparison and analysis of the three methods are of great guiding significance to the selection of the number of elements and the selection of the fitting method based on the element stress extrapolation method.The reinforced concrete beam based on the plastic damage constitutive model is gradually loaded by ABAQUS.The statistical analysis of the increment of the first principal stress of concrete and rebar during the approach to the ultimate bearing capacity is carried out.The statistical result shows that the distribution of the element first principal stress increment of the concrete is relatively divergent at the initial loading stage.With the increase of the load,the distribution becomes more and more concentrated,the proportion of negative increments increases,and the proportion of positive increments decreases.The final proportions of positive and negative increments are both about 0.5.There are only positive element first principal stress increments at the initial loading stage.With the increase of load,the proportion of negative increments becomes larger and larger,and the proportion of positive increments gets smaller and smaller.By rules above,the ultimate bearing capacity load can be acquired effectively.Under the condition of ultimate bearing capacity,the elements corresponding to the first principal stress increments in the vicinity of zero are basically cracking elements.Through a suitable stress interval,the cracking elements can be screened out so as to achieve the purpose of predicting the cracking region.The model is established according to the three-point bending experiment beam in the reference,and the load-displacement curve and load-CMOD curve are compared to prove the reliability and validity of the numerical simulation in this paper.The three-point bending beams with pre-set cracks in different inclination angles and different offset distances are studied,finally the influence laws of different inclination angles and different offset distances on the ultimate bearing capacity,cracking load and crack propagation of the beam members are given.Meanwhile,the study finds out that the hysteresis characteristic of the P-CMOD curves gets more and more obvious with the increase of the ratio of longitudinal reinforcement and the increase of the distance from the mid-span.The two-dimensional and three-dimensional random aggregate delivery programs are compiled by MATLAB,and the aggregate,interface and mortar are visualized in MATLAB.Then the data generated by MATLAB are imported into ABAQUS through the Python program compiled in this paper,finally XFEM crack is added to establish two-dimensional and three-dimensional random aggregate finite element models.According to the three-point bending beam size and material parameters in the reference,random aggregate model is established in ABAQUS.By comparison with the fracture parameters of the three-point bending experiment beam,the reliability and effectiveness of the numerical simulation are verified.Then,the aggregates with different area ratios and different gradations are delivered,and the law of the crack propagation in the aggregate,the interface and the mortar is studied from a mesoscopic level.