Study On Fracture Characteristics Of Walnut Under Dynamic And Static Load

Walnut,as one of the four major nut crops in the world,walnut output in China is the world’s first,so the walnut output of Cinderella to promote the development of walnut processing industry and improve the economic income of fruit farmers,has important practical significance.The primary processing of walnuts is an important way to realize the transformation from picked walnuts to walnut kernels.In the process of primary processing,walnuts are affected by extrusion,impact and other loads,and fracture occurs,which significantly affects the processing quality and seriously restricts the development of cracking work.Therefore,effective control of walnut fracture is an important problem to be solved in the research of walnut primary processing,and the key lies in the revelation of walnut fracture mechanism and clear fracture characteristics.The further study of walnut fracture mechanism and fracture characteristics can not only provide theoretical knowledge for solving the problem of walnut fracture in the initial processing.The further study of walnut fracture mechanism and fracture characteristics can not only provide theoretical knowledge for solving the problem of walnut fracture in the initial processing.It can also enrich the basic theories and methods of nut fracture research.In order to clarify the determination conditions of walnut fracture under dynamic and static loads and reveal the characteristics of walnut fracture,the influence of physical parameters on walnut fracture was discussed on this basis.Firstly,the stress distribution of walnut under quasi-static compression was analyzed,and the critical strength factor and the critical crack length were calculated.Then,the influence of related physical parameters on walnut size and crack location was discussed,and the mathematical model of critical strength factor,walnut size and crack location was established.Secondly,the walnut fracture probability model was established by combining Hertz theory and Weibull distribution model,and the characteristic parameters in the model were defined as the criterion of walnut fracture resistance under impact load and whether fracture occurred.Furthermore,the relationship between characteristic parameters and material properties was explored.The relationship between impact energy and crack length was further observed.Finally,the damage evolution process of walnut was analyzed,the walnut fracture model was established,and the characteristic parameters were defined as the ability to resist damage.The effects of walnut size and impact energy on the characteristic parameters were also discussed.Furthermore,the cracks were photographed,and the roughness of cracks was quantified by fractal dimension,and a mathematical model was established by fractal dimension and characteristic parameters.The specific research conclusions are as follows:(1)To clarify the principle of compression fracture.The curve beam theory and thin shell theory can describe the stress distribution of walnut under compression,and the critical stress intensity factor and the critical crack length can be used to judge the fracture of walnut under compression or to measure the ability to resist fracture.(2)The position of both ends of walnut and the size of walnut significantly affect the stress intensity factor.Further calculated to the critical crack length.The critical length of walnut was significantly affected by different positions.It lays the foundation for revealing the mechanism of extrusion fracture and clarifying the fracture characteristics of walnut.(3)Reveal the fracture mechanism and fracture characteristics of walnut under single impact load.With the increase of size,the resistance of walnut to impact fracture decreases and the minimum threshold of walnut fracture increases.The prefabricated initial crack location significantly affected the cracking resistance of walnut.The length of crack after fracture is determined by impact energy.The results provide reference for the determination of fracture and support for the theoretical study of crack propagation.(4)The damage evolution process of walnut under cyclic impact load was revealed.Walnut size had a linear relationship with the damage accumulation coefficient,and impact energy had a polynomial relationship with the damage accumulation coefficient.The fractal dimension of crack is also linear with the damage accumulation coefficient.The study of crack roughness can provide support for the study of crack propagation in walnut.The results of this study can provide support for the further study of walnut fracture characteristics,and provide a new method for the study of nut materials.