Failure And Damage Analysis Of Carbon Fiber Reinforced Composites Using Extended Finite Element Method(XFEM)

A generalized technique for determining and analyzing progressive damage in carbon fiber reinforced composites subjected to various loading conditions has been developed and experimentally validated using extended finite element XFEM method.The progressive damage theory operates for tensile,inplane and transverse failure criteria and post failure behavior.Delamination is also analysed for using different methods and the relative advantages of these approaches are studied.To accurately understand the response from the the composites,they need to investigate carefully.An improvement on the understanding of the response of the composites can lead to greater enhancements of composite materials.The main focus of this dissertation is to apply the extended finite element method(XFEM)to model fiber reinforced composites and develop the framework for precise and accurate investigation of properties.Damage modelling alongwith crack behaviour carbon fiber reinforced composites under tensile loading and different under conditions are simulated in ABAQUS and extensive experimentation has been performed for carbon fiber composites by grouping them into numerous categories of layup and orientations.1.In this work,an improved extended cohesive damage model(ECDM)for modeling the propagation of cracks in fiber reinforced composites is presented.By integrating the cohesive zone model(CZM)into the extended finite element method(XFEM)and without increasing the degree of freedom(Do F),ECDM implicitly determines the path of the connected crack in the goverming equations.The Equilibrium allows local enrichment of approximation spaces without additional Do F.To account for the evolution of the cohesion to crack propagation,the ECDM developed contains a new equivalent magnitude of damage relative to the strain field to avoid the appearance of enriched Do F and to replace the classical characteristic in the approximation of the displacement jump.By eliminating enrichment by using a condensation process,ECDM offered a significant computational efficiency advantage when modeling the propagation of cracks in materials.2.The experimentation is done in all the groups with different dimensions and parameters to figure out the values of strength and the prediction of the damage to the structure.The study has been carried out for both transversal damage and the phenomenon of delamination in composites with the multiple modes and categories A,B and C.The carbon fiber composite for all the categories and groups are compared and evaluated for the XFEM fracture simulation and the results are found to be promising for the cases,wherein the failure strength renders 0.9% of difference compared with the experimental results(16.7%,7.5% and 17.62)for the groups respectively.The specimen dimensions and the loading conditions are evaluated in the mentioned categories for the transversal damage as one of the objectives of the study.The composite model for single layer and multilayer are modelled in extended finite element method module in ABAQUS software previously alongwith interaction subroutines for the mentioned models and examined the study for experimental behaviour and response.The experimentation and numerical response of the interfacial debonding is in a good agreement for the mechanical properties of strength and stiffness,hence conforms the proposed technique as a simplified and efficient tool having an error value less than 2 %,hence validates the model.The comparative study has also been carried out and the results lie in reasonable convergence.The same method has been applied and validated for shear properties.3.The numerical and simulations outputs with experimental results for XFEM as framework for the initiation and propagation of a crack along an arbitrary,meshindependent,solution-dependent path are validated and found in a great agreement.The key parameters and critical aspects of convergence of the results while carrying out damage and fracture analysis when using numerical simulation in comparison with the experimentation setup required precise and accurate grip of deep understanding towards modelling.A novel and flexible framework has been developed for extended finite element method(XFEM)to simulate twodimensional and three-dimensional microcrack initiation and propagation through versatile material models for structures.In addition,mixed-mode cohesive zone is investigated and estimated for delamination,matrix cracking and fiber breakage in composite laminate models.The validation of Multiscale modeling for the fiber uniformity during the tensile behavior,prediction of crack and properties of composite material analyzed by XFEM modeling for the damage modes and comparison with the experimental work.The dimensions of the specimens and the effects are also studied regarding lengths,thickness and width in multiple categories.The proposed micro-mechanical model for three point bending test has also validated and compared with experimental and analytical framework accordingly.Finally,the study has been applied to different hybrid systems to evaluate the integrity of the model and application to multiple systems and conditions.4.The thesis research is concerned with development of a Extended Finite Element(XFEM)framework for Damage modelling alongwith crack behaviour carbon fiber reinforced composites(CFRCs)that can be successfully applied in various scenarios of damage modeling.The thesis addresses the following major barriers and solutions in XFEM Modelling of fiber reinforced composites:(i)crack behaviour and effective and improved XFEM techniques for carbon fiber reinforced composites under tensile,three point bending and in-plane shear loading,simulated for different variables and cases,(ii The extensive experimentation to provide a better convergence and validation for carbon fiber composites of categorized layups and orientations,(iii)To attain a novel and flexible framework for extended finite element method(XFEM)to simulate two-dimensional and three-dimensional microcrack initiation and propagation,(iv)The study simplifies the application of extended FEM for the prediction of multiple cracks applied to CFRCs,hence provides a better framework for extended cohesive damage modelling(ECDM),and finally(v)The framwork is investigated for the effect of the composite shell and laminated notched plate as an application problem.The model has been applied and proved to be in a good agreement.This work contributes and provides an novel exposure for the scientific knowledge and technology for equilibrium ECDM equations based on XFEM which are theoretically derived and validataed.The designed ECDM provides a very effective tool for the prediction and detailed analysis for progressive damage in various structures.The numerical simulations and a wide range of experimentation provides a significant agreement for the results as explained.