胶合木梁变幅疲劳寿命估算试验研究

Experimental study on estimation of variable amplitude fatigue life of plywood beams

【目的】疲劳破坏具有突发性的特点,且其破坏荷载低于极限荷载,是大多数结构物的破坏形式。当结构发生疲劳破坏时,是相当危险的。和其他结构构件一样,胶合木梁在承受循环荷载时也会发生疲劳破坏。因此,本研究旨更准确地预测胶合木梁的疲劳寿命,可为胶合木在工程中运用提供依据。【方法】基于前人等幅疲劳试验结果,开展了胶合木梁二级变幅疲劳试验。通过对3根胶合木梁的二级变幅疲劳试验,测试了其应变和挠度变化规律,观察了其变幅疲劳破坏形态和裂缝发展规律,并同时得到胶合木梁在不同幅值下的疲劳寿命。结合试验结果,运用疲劳累积损伤理论,估算胶合木梁的寿命。【结果】根据变幅疲劳试验结果,结合几种疲劳累积损伤理论,利用修正Miner理论计算公式反算得到公式中的参数a=0.54,同时利用Corten-Dolan理论计算公式反算得到公式中参数d=5.70。并分别运用Miner理论、修正Miner理论和Corten-Dolan理论对变幅疲劳试验下胶合木梁进行了寿命估算,得到在不同疲劳累积损伤理论下,3根变幅疲劳试验梁的估算寿命。并分别比较各种理论下的寿命估算值和试验值。【结论】利用Miner理论的估算寿命和试验结果相比,两者相差较大,Miner理论寿命估算精度较低,而修正Miner理论和Corten-Dolan理论计算结果和试验结果吻合较好且精确度较高。为今后工程应用中运用修正Miner理论或Corten-Dolan理论对胶合木梁的疲劳寿命进行设计计算提供了依据。建议在工程实践中,应用修正Miner理论或者Corten-Dolan理论对胶合木梁寿命进行估算。

【Objective】Fatigue failure has the characteristics of sudden,and its failure load is lower than the limit load,which is the failure form of most structures.It is very dangerous when the structure is damaged by fatigue.As other structural members,glued wood beams will also suffer fatigue failure when they are subjected to cyclic load.Predict the fatigue life of glued wood beam more accurately,and provide the basis for the application of glued wood in engineering.【Method】Based on the results of previous equal amplitude fatigue tests,this paper carried out two-stage variable amplitude fatigue tests of glued wood beams.Through the secondary variable amplitude fatigue test of three glued wood beams,the strain and deflection change laws of the beams were tested,the failure patterns and crack development laws of the beams were observed,and the fatigue life of the glued wood beams under different amplitude was obtained.Combined with the test results,the fatigue cumulative damage theory is used to estimate the life of glued wood beams.【Result】According to the results of variable amplitude fatigue test,combine with several fatigue cumulative damage theories,the parameter a=0.54 in the formula is obtained by using the modified Miner theory calculation formula,and the parameter d=5.70 in the formula is obtained by using the Corten Dolan theory calculation formula.The life of glued wood beams under variable amplitude fatigue test is estimated by Miner theory,modified Miner theory and Corten Dolan theory.The estimated life of three beams under different cumulative fatigue damage theory is obtained.The life estimates and test values under various theories are compared.【Conclusion】Compared with the test results,the life estimation accuracy of Miner theory is lower,and the calculated results of modified Miner theory and Corten Dolan theory are in good agreement with the test results.It provides a basis for the design and calculation of the fatigue life of glued wood beams by using the modified Miner theory or Corten Dolan theory in future engineering applications.It is suggested that the modified Miner theory or Corten Dolan theory should be applied to estimate the life of glued wood beams in engineering practice.