Experimental Study On Crack Formation And Propagation Of Pecan Under Impact Force

In order to solve the problem of broken kernels and unseparated shells in the process of pecan shell breaking,and increase the rate of mass.Based on the crack formation law,the thesis carried out the research on the crack propagation mechanism,established the mathematical model of the pre-crack system and carried on the theoretical analysis of the crack propagation..The specific research content is as follows:(1)Based on the knowledge of crack theory,the physical characteristics of pecan shell cracks were analyzed based on the literature,and the formation and propagation mechanism of shell cracks were theoretically analyzed by using the drop hammer shell crack test rig.With reference to the crack distribution law of"hand-peeled pecans",an exploration experiment of pre-crack treatment methods was launched.Combined with ANSYS simulation,the process of pre-cracking of the two punching-point pre-cracking treatment methods of X-type and Y-type is analyzed in detail,and the results show that the X-type pre-cracking method is better.(2)A baking test bench for heating pecans is designed.The main functions include temperature adjustment and PID control of the heating furnace,real-time monitoring of temperature and pecan quality,and storage of test data.Combining simulation analysis and baking test,the three pre-crack patterns of O,X,and Y were evaluated,and the analysis showed that the cracking effect of X-shaped pre-crack after heating was better.(3)Based on the X-shaped pre-cracked pecans,the crack propagation treatment is carried out.After 3 hours of immersion treatment,the moisture content reached 42.73%.Through the Abaqus thermo-solid coupling simulation,the thermal stress analysis of the hickory model treated with the X-punched pre-crack is carried out.The simulation results show that the outer edge of the pre-crack is easier to crack during the heating process,and the inner edge of the pre-crack It is more difficult to initiate cracks,and when the temperature is greater than 150°C,new cracks will initiate and crack propagation will occur in some areas of the unpre-cracked area.(4)Through orthogonal test,the optimal processing parameter of heating is A₃ B₄ C₄,that is,the heating treatment is carried out on the baking test bench,the heating temperature is 175?,and the heating time is 2min.Under this heating parameter,the test index change values(35)N_L,(35)N_S,(35)C₁ and(35)C₂ are 4,28,7 and 6 respectively.The vibration test makes the cracks further expand and improves the separation effect of the shell and kernel.The test results show that the direct crack index that affects the shell breaking effect is C₂(separation zone),and the vibration frequency is greater than 40Hz and when the vibration time is greater than 90s,the shell breaking effect is better.