Prediction On Crack Growth For V-notched Beams By Mode Frequency

Beam as a basic component is widely used in the field of aerospace and mechanical engineering,and so on.Due to the need of manufacture and assemblage,the surfaces of beam need make some notches frequently.This makes the notch as the importance site of stress concentration.Especially,the sites of notches are the critical position of crack initiation,crack growth,and even fracture when the beam is subject to vibration force.Thus,the study of prediction method of crack growth for notched beam is meaningful to improve the safe reliability of dynamic mechanical structure.In this article,a V-shape notched cantilever beam is used,and the prediction method of crack growth by mode frequencies on the experimental results of vibration mode and crack growth.The main works of this article include:Firstly,a test system for mode frequencies and crack growth of cantilever beam was set up.Subsequently,several V shape notched beam were designed.Using V notched beam with different parameters as objects,hammer method was used to do mode frequency.In addition,the experiments of fatigue crack propagation were done.The change law of mode frequencies with crack propagation parameters of notched beam was analyzed by Fourier transform.Thereafter,the inner interaction between the crack growth and the first three mode frequencies was studied.The relation between the stress on the surface of notch site with the crack growth,and the relation between mode frequencies with vibration cycles were discussed.The vibration fatigue crack growth curve of the V notched beam was set up in the end.Take the tested V shape notched beam as simulation object.The dynamic finite element model of cantilever beam was modeled by ABAQUS.The reasonable of the dynamic model was verified by experimental results.Based on the effective finite element model,the stress amplitude on the surface of the notch position and the stress amplitude on the tip of crack were calculated.The harmonic response of the cantilever beam was analyzed.Meanwhile,the results from finite element calculation and that from test was compared.All the conclusions can provide reference for the prediction of crack growth.Finally,take the length of crack growth to define accumulated damage,and take the decrease ratio of the first mode frequency as the indicator of damage,a three polynomial equation was fitted through using the decrease ratio of frequency as the self-varying quantity and using the damage as the varied quantities.The unknown parameters were fitted through the defined damage and the tested life based on the proposed exponential model of damage fatigue life.Through combing the exponential with the damage model and the fitted damage expression,a life prediction model for cantilever beam was proposed.The reasonable of the damage prediction model was verified by experimental results.