Research On Fatigue Load Spectrum Parameter Effect On The Fatigue Life Of Polymer Laminate

Due to the wide use of polymer composite materials,the ability to control the material physical and mechanical characteristics,including the fatigue resistance characteristics,is of great importance.The thesis is devoted to the fatigue life evaluation of samples from carbon fiber reinforced polymer.Fatigue life prediction is based on the fatigue stress spectrum program.It is known that modern programs of full-scale fatigue testing have a rather complex structure.These programs contain 5-10 types of flights,5-10 loading levels at each stage of the flight,a large number and random alternation of loading cycles.The relevance of this work in scientific terms is determined by the need to optimize the structures of such programs.The main purpose of the study is to assess the relative damage to various loading levels based on a quasi-random program simulating flight loading.In this work,one of the types of complex loading is considered: a repeating block of loads,which is a multi-stage cyclic loading with different stress amplitudes at each loading stage.The block is an air stage of the well-known standardized quasi-random program "Transport Wing Standard Test"(TWIST),which is the program simulating the flight loading of elements of a longitudinal assembly of a composite wing structure of a transport category aircraft.Such a block was used,in particular,in fatigue testing of samples with a free hole made of carbon-fiber loaded by the "TWIST" program.To achieve the purpose,the following tasks were carried out:1.Calculation of the fatigue load spectrum and then prediction of fatigue life of carbon fiber reinforced polymer laminate.2.Design on an estimation method for fatigue durability of samples.3.Analysis on dominate parameter influences of the studied loading program on the fatigue life of carbon fiber reinforced samples with polymer laminate.4.Optimization of load parameters for the studied program.On the basis of the obtained results,conclusions were drawn about the main parameters influence of the investigated loading program on the fatigue life of samples.The main innovative work among the thesis is the optimization method of program loading,were the structure(the number of levels and loading cycles)is optimized to achieve the necessary damage to the "TWIST" program when testing the composite wing of a transport category aircraft.This optimization allows reducing the number of load cycles required for testing by more than 6 times while maintaining the necessary damage.The proposed optimization will significantly reduce the amount of experimental research in the future,which makes it possible to reduce the testing cost,material consuming,but most importantly to shorten the testing duration.