Fatigue Life Prediction And Failure Analysis Of Stranded-Wire Helical Springs

Stranded-wire helical springs is a kind of cylindrical springs coiling by steel cable.The coiling styles includes coreless and coiled coils.Due to the special structure and superior performance,it has replaced ordinary cylindrical coil springs in various fields such as aerospace,defense,and civilian installations to improve equipment reliability and performance properties.However,fatigue failure studies of stranded-wire helical springs are still immature.And fatigue failure of stranded-wire helical springs influences the reliability of aircraft engines and automatic weapons.Therefore,it is necessary to carry out fatigue life prediction and failure research to ensure the reliability of corresponding equipment.Therefore,the fatigue life prediction and failure research of the multi-strand spring must be conducted to provide a reference for the design calculation of the multistrand spring,thereby promoting the application of the multi-strand spring.This article used the stranded-wire helical springs in practical engineering to carry out the fatigue life failure research of stranded-wire helical springs.In the present work,the following research is performed on the fatigue failure of stranded-wire helical springs:(1)A parametric modeling method for stranded-wire helical springs was proposed to realize the rapid establishment of three-dimensional models of stranded-wire helical springs.Based on the three-dimensional model,a finite element model of stranded-wire helical springs was established,and finite element simulation of the compression process was performed to solve the stress-strain and dynamic response curve.Then,the result of the finite element was verified by stranded-wire helical springs dynamic response experiments.Based on this,the influence of the main geometric parameters of the stranded-wire helical springs on the dynamic response curve is studied.Finally,the submodel technology was used to calculate the stress and strain of the key areas of the stranded-wire helical springs,which achieved a more accurate result and reduced the time of finite element calculation.It provides a basis for stress and strain calculation in fatigue life prediction;(2)A method for predicting the fatigue life of stranded-wire helical springs was proposed.First,the stress-strain history of stranded-wire helical springs was calculated by finite element simulation and the accurate calculation of stress and strain was performed by sub-model technology.Then,the steel wire material test was performed.Combined with the universal slope method,the fatigue performance parameters of the stranded-wire helical springs material were derived.Finally,the fatigue life of the stranded-wire helical springs was predicted by combining the stress-strain history of the stranded-wire helical springs and the multi-axial fatigue life prediction model,and the experimental verification was performed.This method greatly reduces the high cost of fatigue testing of stranded-wire helical springs,shortens the test cycle,and provides a theoretical basis for the sensitivity analysis of the factors affecting the fatigue life of stranded-wire helical springs;(3)Aiming at the sensitivity of the influence of the geometric parameters of the stranded-wire helical springs on the fatigue life,based on the fatigue life prediction method,the life prediction of the stranded-wire helical springs under different geometric parameters was performed.Sensitivity of the structural parameters toward the fatigue life,including spring winding ratio,spring helix angle,wire rope twist angle,is analyzed.And a method for improving the fatigue life of stranded-wire helical springs is proposed in combination with the actual situation;(4)To find the causes of fatigue failure of stranded-wire helical springs,the physical and chemical tests were firstly performed on the multi-stranded helical springs that suffered fatigue failure in the fatigue test.The test includes macro-microscopic topography analysis of steel wire fractures,chemical composition analysis of steel wire materials,Vickers hardness test,and gold phase structure analysis.Then,combined with the analysis results and the processing technology of the stranded-wire helical springs,measures to improve the fatigue life of the stranded-wire helical springs are proposed.