Research On Fatigue Crack Propagation And Dynamics Of Taper Leaf Spring Of Light Commercial Vehicle

The leaf springs are used to connect the axle and frame of a commercial vehicle,and have both vibration damping and guiding effects.The nucleation period of fatigue cracks of taper leaf spring(ie,the formation time of fatigue sources)is long,and the micro cracks are polymerized into macroscopic cracks until the failure of the taper leaf spring breaks,which occurs in a short time,and It seriously affects the driving safety of automobiles.The dynamic characteristics of the taper leaf spring have a great influence on the ride comfort and manipulation stability of the vehicle.Therefore,it is of great significance to study the propagation of fatigue crack and dynamics of taper leaf springs,which is mounted on a light commercial vehicle.Firstly,a finite element model of taper leaf spring is established,and the stress distribution of the main reed is calculated.According to the installation method of the taper leaf spring on the real vehicle,the fatigue test bench of taper leaf spring is built.A few strain gauges are attached to the leaf spring and the displacement sensor is installed.In order to obtain the stress of different distances from the central bolt hole of the main reed,loading test is carried out on the leaf spring sample and relevant data is collected and stored.It is found that the finite element analysis of taper leaf spring is in good agreement with the bench test result.The maximum stress value appears at the root of the leaf spring,and the stress value in the middle of the whole reed is larger.Data is processed by using finite width central crack specimen model and linear elasticity method,it is found that the maximum fatigue crack growth rate coincides with the position where such leaf springs are prone to fatigue failure.In addition,it is found that there is no propagation of fatigue crack at the front and lifting ear of the taper leaf spring.Secondly,the unevenness of random road surface is modeled as input excitation signal,and the two-degree-of-freedom dynamics model of taper leaf spring of quarter car is established.The displacement of the center bolt hole of the leaf spring relative to the frame of a vehicle running on different grade road surface is simulated and analyzed,which provides a reference for the displacement data collected in the actual vehicle test.Finally,stress acquisition equipment and displacement sensor are adopted to achieve the real time acquisition of spring stress and relative frame displacement of central bolt hole.The position,where the stress and fatigue crack growth rate of the leaf spring is maximum,is obtained by the impact test of the deceleration belt.The stress of the leaf spring is collected in real time with the strain gauges pasted at the above position and the position 16 mm away from the center bolt hole.At the same time,a displacement sensor is adopted to achieve the real time acquisition of the displacement of center bolt hole,which is relative to the frame.And the data is analyzed based on the method of stress field and stress intensity factor of crack tip nearby.The road test under seven working conditions is completed in the end.The results show that the fatigue crack growth rate of 116 mm from the center bolt hole is larger,which is consistent with the position of such leaf springs which are prone to fatigue failure.through theoretical analysis and experimental verification,this method can be applied to the growth rate prediction of leaf spring crack.By comparing the test results of real road and bench test,the method of improving bench test is found,so that the bench test can also more accurately predict the fatigue crack growth rate.