Research On Wave Propagation And Crack Propagation Based On The Theory Of Near-field Dynamics

There is an interaction between wave propagation and crack growth.Stress wave theory and fracture mechanics theory play an important role in the study of the relationship between wave propagation and crack growth.As a kind of brittle material which is resistant to pressure and non-tension,the transmission of wave in concrete will have a significant influence on its fracture failure and crack propagation.Concrete material,as a basic material for infrastructure construction,is widely used in engineering field and its mechanical properties and reliability of material structure play a vital role in national property and human life safety.So concrete materials are the focus of this paper.Peridynamic theory(PD)is the latest theoretical system for studying material fracture and crack propagation in the early 21 st century.It has attracted the attention of many scholars in the field of solid mechanics and fracture mechanics.This theoretical system abandons the previous partial differential mechanical theory based on continuity assumption and establishes the integral equation of motion of material points,which makes it have more obvious advantages in fracture research,especially in computational fracture mechanics.It avoids the problems of mesh reconstruction and solution singularity of traditional finite element method for fracture analysis.In this paper,the bondbased pridynamic theory is used to analyze the relationship between wave propagation and crack growth.The main contents and important achievements of the research are as follows:(1)In theoretical research: Based on the bond-based peridynamic theory,the construction process and characteristics of PMB material constitutive function are introduced firstly.Then based on the theory of PMB material constitutive function and the non-linear mechanical characteristics of concrete after loading,the bond damage variable function is introduced to construct the bond-type constitutive equation suitable for concrete material,and the bond fracture criterion in the process of tension and compression is redefined.Finally,the physical parameters which can reflect the crack growth state of concrete under impact load are derived,such as the micro-potential energy function of bond and material point,the deformation energy density function of bond and material point,the damage release energy function of bond and material point,and the energy release rate.In this chapter,the case that the micro-modulus of the bonds is constant in nonlinear stretching and compression is corrected by proposing the micro-modulus function.(2)In numerical methods research: By introducing CCI cubic lattice method and combining the theoretical algorithm proposed in this paper,a three-dimensional simulation software PDSimulator V1.1 for analysis of impact fracture and wave characteristics of concrete is developed by using C language and MATLAB programming language.In this part,we build the core algorithm of the software through C language,and construct a concise and humanized software interface and data visualization post-processing with MATLAB.According to the numerical calculation method,a boundary loading method,step loading method,is proposed for the analysis of non-constant load(impact load)fracture problem,which focuses on the analysis of concrete fracture under impact load.(3)In numerical simulation analysis research: Through the developed three-dimensional simulation software,the fracture of concrete material model under static load and impact load is simulated and analyzed,and the damage of the model is compared with the relevant experimental results to verify the rationality of the software and the constitutive equation.Then,the interaction between wave propagation and crack propagation is analyzed through two concrete impact examples: one is the analysis of wave characteristics of concrete slabs with prefabricated defects,the other is the analysis of influencing factors of impact spallation of concrete rods.In the analysis of wave characteristics of concrete slabs with prefabricated defects,the peridynamic force wave have obvious wave reflection,diffraction and superposition phenomena which is related with the crack propagation.It is also found that the near-field force wave velocity is in good agreement with the P-wave velocity obtained in traditional mechanics.After that,the most obvious spallation phenomena in the study of the relationship between wave transfer and impact fracture are simulated and analyzed.It is found that the form of impulse load,the acting time of impulse load and the geometric size of the model all affect the spallation occurrence time,the thickness of spallation and the number of spallation.The purpose of this paper is to explore the relationship between crack growth and wave propagation under impact loading.It not only takes advantage of the peridynamic theory in the fracture problem,but also combines the study of the mechanism of crack growth by wave propagation in stress wave theory.It can provide a new reference for the study of crack formation mechanism and the analysis of peridynamic force transfer fluctuation characteristics in the peridynamic theory in the process of material impact failure.