Strength And Progressive Damage Analysis Of Fiber Reinforced Composite Laminates

Because of its excellent properties,high specific strength,high specific stiffness,fatigue resistance and corrosion resistance,carbon fiber reinforced composite materials are more and more widely used in aerospace,sports and leisure products manufacturing,energy,automobile and other industrial sectors.The structural static strength failure and fatigue failure of composite materials are of great concern to designers.Therefore,the mechanism of the damage and failure process needs to be studied in detail.In order to develop the advantages of carbon fiber composite structure as far as possible and to accurately grasp and predict their mechanical behaviors under static and fatigue loads,this paper explores and analyzes this process.?1?Analyzing the application of phenomenological and physics-based failure criteria and numerical simulation methods of carbon fiber composite structure in the research of static strength failure;the development of test and numerical simulation in the process from constant amplitude/random fatigue damage to failure.?2?Using the floating node method,a numerical simulation method,combined with the in-situ strength effect theory,modified the Pinho criterion,and establishing the progressive damage model of carbon fiber reinforced laminates under static tensile load.?3?According to the static failure characteristics of carbon fiber reinforced composites,using Hashin failure criterion based on physical mechanism and combining with residual strength model and residual stiffness model,a prediction model of progressive damage process and fatigue life of composite structures under constant amplitude loading was established.?4?To solve the problem that the mechanical behavior of carbon fiber composite structure under random load is complex and its life is difficult to predict,the evolution law of residual strength and failure probability prediction of life of the method combining time and frequency domain are deduced.The life prediction model of the composite structure under random load is established.The main work and research results are as follows:?1?The floating node method allocates additional nodes?additional degrees of freedom?on element boundaries or nodes based on the original finite element method.In this way,the crack can be shown explicit and the singularity caused by the integral at the damage point can be prevented.In-situ strength calculation method based on fracture mechanics hypothesis is introduced and deduced,and Pinho criterion is modified to improve the accuracy of failure strength prediction.Tensile tests of two kinds of open-hole composite laminates were carried out.Experimental results show that different layering sequences([45₃/90₃/-45₃/0₃]_s and[45/0/-45/90]_3s)have different failure strength and failure process.The reliability of the model is verified by comparing the experimental results with the simulation results.The comparison results show that the model can realize explicit crack propagation and predict crack failure strength accurately.In addition,the simulation model can also represent the failure modes such as fiber fracture,matrix damage and layering observed from experimental phenomena.Compared with the improved failure criterion,the prediction accuracy of failure strength is significantly improved.?2?Seven fatigue failure criteria were written by referring to the Hashin criterion of the static failure of carbon fiber composite laminates and combining with the residual strength and residual stiffness model.By referring to various kinds of constant amplitude fatigue data of unidirectional plates with laminates'Angle of 0^?,45^?and 90^?,the normalized residual strength and residual modulus evolution rules are obtained.According to the constant life graph,the fatigue life of 0^?,45^?and 90^?laminating Angle unidirectional plys under arbitrary stress ratio and stress state is obtained by means of linear interpolation.At last,a finite element model for damage evolution and life prediction of composite structures based on stiffness and strength degradation rules and improved Hashin criterion is established.Simulation prediction of unidirectional laminates and bolted carbon fiber composite laminates(layering sequence are[45₃/90₃/-45₃/0₃]_s and[45/0/-45/90]_3s)is carried out,which verifies the reliability of the model.?3?The fatigue characteristics of fiber reinforced composite structures under random loads are complex.The fatigue properties of materials are studied theoretically in this paper.Using the method of time domain theory and frequency domain theory,the life prediction model of composite structure under random load is established.In the frequency domain,the model uses power spectral density?PSD?to obtain root mean square?RMS?and probability distribution function?PDF?curves.In the time domain,the residual strength evolution over time is better than the linear accumulation method.Taking residual strength as damage factor and using residual strength test data under constant amplitude load,the damage evolution curve under random load was calculated.The advantage of this method is that there is no need to consider the loading order.Finally,the fatigue process of bolts is simulated?the lamination sequence is[45₃/90₃/-45₃/0₃]_s?.Simulation and experimental results show that the model is successful.