Advanced multiscale modeling of layered andsandwich composites using coupledmicromechanical, zigzag, and isogeometric methods

Fiber-reinforced composites (FRC) are widely favored over conventional metallicmaterials for their superior mechanical characteristics and the ability to provide directionalproperties. However, predicting their structural performance is complexand requires development of robust and efficient numerical approaches. The parametrichigh fidelity generalized method of cells (PHFGMC) is a micromechanicalapproach that can be used to understand behavior of composite materials. In thismethod, a repeating unit cell (RUC) is determined based on the microstructure andanalyzed for obtaining the effective composite behavior at the macro level. On theother hand, refined zigzag theory (RZT) provides a robust, efficient, and reliabletechnique for modeling thin and thick layered composite structures. In this framework,a laminate is modeled as a single layer regardless of the stacking sequenceand number of plies. Furthermore, isogeometric analysis (IGA) provides a numericalapproach highly capable of modeling complex geometries with lower numberof elements by employing non-uniform rational B-splines (NURBS). In the currentdissertation, a novel modeling framework is developed for advanced multiscale linearand nonlinear analysis of composite materials. For this purpose, establishedcapabilities of the PHFGMC, RZT, and IGA frameworks are leveraged.The final main objective of the thesis is to be reached through following severalfundamental method development steps. First, a multiscale analysis technique is proposed by using the PHFGMC micromechanical approach and the RZT basedIGA plate formulation in a common framework. In this step, material constants fora composite layer are computed based on the constituent properties by employingthe PHFGMC method. Then, macroscale analyses are performed on thick sandwichstructures by employing the RZT based IGA formulation. In the next step, dimensionalconsistency is provided in the proposed multiscale framework by developing anovel higher order RZT{3,2} based IGA plate formulation. This improvement facilitatesdirect exchange of data between the micro and macro levels without additionalrequirements and thus provides ease of implementation. In the meantime, outcomesof the proposed linear and higher order multiscale techniques are validated usingexperimental studies in this step. In the final stage, the framework is extended tosupport progressive damage modeling of composite materials and soft-core sandwiches.This is enabled by incorporating the Ramberg Osgood (RO) model andHashin criteria for plasticity and failure assessments, respectively. Furthermore, amultipatch formulation is presented to apply the method on stiffened plates.As an additional contribution to the field, a macroscale damage modeling techniqueis developed in the scope of this thesis by integrating the continuum damage mechanics(CDM) into the IGA-RZT{3,2} plate formulation. This step provides anefficient and easy-to-implement phenomenological approach for failure analysis ofcomposite materials. In this context, the concept of mesh dependency is addressedby using the crack band theory. Finally, the method is validated through predictingfinal failure loads of notched tensile