Investigation On The Fracture Energy Of Cement-based Materials Based On The Analysis Of Energy Dissipation

Fracture energy is the energy consumed per unit area of fracture propagation.This parameter represents the ability of material to prevent fracture propagation and is a key factor to control the possibility of structural failure.Meanwhile,it is also an indispensable input parameter in fracture model used for fracture performance analysis.However,there are some influencing factors in the study of fracture energy of cement-based materials,which lead to the failure of accurate and stable results as a material parameter.These influencing factors are mainly reflected in three aspects: first,kinetic energy dissipation caused by loading speed;Second,the influence of fracture mode;Thirdly,the elastic and plastic deformation energy dissipation outside the fracture surface.In view of the existing problems in the study of the fracture energy of cement-based materials,this study adopts the digital image correlation method(DIC)to study the fracture energy of cement-based materials.The method can achieve: based on the image results at different deformation moments,the kinetic energy at the corresponding loading speed can be analyzed;the angle between main strain direction and fracture propagation was calculated based on strain cloud image,and then the fracture mode can be analyzed;the deformation energy dissipation outside the fracture surface during loading can be calculated based on strain results.An accurate and stable fracture energy research method could be established with consideration of these influencing factors.The main work and findings of this study are as follows:(1)The fracture energy research method based on energy dissipation analysis is established.The kinetic energy of the sample,the fracture mode and the analysis of deformation energy are put forward.At the same time,through the analysis of the test results of different influence factors,prove that the selection of the rationality of the loading speed,and determine the fracture model,finally,the deformation is calculated by the proposed calculating idea of deformation energy.After considering these factors influencing fracture can get more accurate fracture energy result.(2)Based on the analysis of energy dissipation,the cement-based material under different loading modes of fracture energy research is carried out.Through the analysis of fracture model prove that the three-point bending test and four-point bending test of this study are open fracture type.Energy dissipation can be analyzed based on the assumption that open fracture is a plane problem.The results show that the energy dissipation is different under different loading modes,which affects the consistency of fracture energy.(3)Based on the energy dissipation analysis,fracture energy of cement-based materials with different sizes was studied.The results showed that the deformation energy dissipation of the inner region of samples with different sizes was different after fracture.The larger the size was,the greater the influence of deformation energy was.After considering the deformation energy,the fracture energy of samples with different sizes is basically the same,and the influence of size effect on the fracture energy result is small.(4)Based on the analysis of energy dissipation,the fracture energy of different notch height ratio of cement-based materials is investigated.The length of the fracture ligament is related to the deformability of sample.The notch height ratio of samples is different,the deformation capacity is also different,resulting in different deformation energy dissipation after fracture.After considering the deformation energy,the difference of fracture energy results with different height ratios decreases,and the fracture energy results are basically consistent along the ligament of the sample.(5)The fracture energy research of the cement-based materials(fiber concrete and rubber concrete)with the deformation ability enhanced.The results show that the fiber or rubber will enhance the toughness and deformation capability of cement-based materials,leading to the deformation energy dissipation increases,if the deformation energy is not considered,fracture energy result will be 18%-30% overvalued,affecting the analysis of fracture properties of structures.