Research On Dynamic Characteristics Of Cracked Crankshaft

With the continuous development of social construction,people's requirements for internal combustion engines in terms of power and reliability are also increasing.As a common failure in the mechanical field,crankshaft cracks are the most prominent safety hazards during equipment operation.If they cannot be found and handled in time,the micro cracks will rapidly expand into macro cracks as the equipment operates,which will then cause the crankshaft to break and cause Serious safety accidents that endanger personal and property safety.The crankshaft is constantly subjected to repeated impact loads during the working process,and it is easy to produce fatigue cracks at the maximum stress.Research on the dynamic characteristics of cracked crankshafts helps to identify whether there are cracks in the structure.First,the Timoshenko beam transfer matrix method is used to construct the space transfer matrix of the straight beam element,the torsion spring is introduced to represent the crack defect,and the dynamic model of the cracked crankshaft is constructed through the force balance condition and the displacement coordination condition.Bring the real excitation of the crankshaft system(cylinder pressure curve)into the forced vibration equation,and use the Newmark-? method to solve the dynamic response of the cracked crankshaft.The finite element model of the cracked crankshaft is established,and its modal analysis and response calculation are carried out.The influence of different crack parameters on the modal and response is discussed.The finite element results are compared with the theoretical calculation results to verify the correctness of the theoretical method.Secondly,the finite element method is used to perform a transient calculation on the finite element model of the crankshaft,and the overall stress distribution law of the crankshaft is obtained.Establish a sub-model containing crack faults,impose displacement constraints on the boundary position of the sub-model,calculate the steady-state response and use the displacement method to solve the crack tip stress intensity factor,adjust the crack size,and calculate the crack tip stress intensity factor at different crack depths.Finally,a test bench was built,reciprocating excitation was applied to simulate the bending load on the crankshaft,which caused fatigue cracks in the crankshaft,and the effect of cracks on the dynamic characteristics of the crankshaft system was analyzed.The results show that the acceleration signal has obvious fluctuations in the time domain and frequency domain.Therefore,the system acceleration signal can be monitored for a long time to determine whether there are cracks in the system,so as to achieve the purpose of guiding crack detection.