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Thesis (M.A.)--Antioch University. / Includes bibliographical references (p. 38-44).

Thesis (M.A.)--Antioch University. / Includes bibliographical references (p. 38-44).

Yes / Nowadays Fiber Reinforced Polymers (FRPs) represent a well-established technique for rehabilitation of Reinforced Concrete (RC) and masonry structures. However, the severe degradation of mechanical properties of FRP under high temperature and fire as well as poor sustainability represents major weak points of organic-based systems. The use of eco-friendly inorganic geopolymeric matrices, alternative to the polymeric resins, would be highly desirable to overcome these issues. The present work aims to investigate the bond characteristic of a novel Steel Reinforced Geopolymeric Matrix (SRGM) strengthening system externally bonded to a concrete substrate having low mechanical properties. SRGM composite material consists of stainless steel cords embedded into a fireproof geopolymeric matrix. Single-lap shear tests by varying the bonded length were carried out. The main failure mode observed of SRGM-concrete joints was debonding at the fiber-matrix interface. Test results also suggest the effective bond length. On the basis of the experimental results, a cohesive bond-slip law was proposed. / Part of the analyses were developed within the activities of Rete dei Laboratori Universitari di Ingegneria Sismica (ReLUIS) for the research program funded by the Dipartimento di Protezione Civile (DPC), Progetto DPC/ReLUIS 2016–AQ DPC/ReLUIS 2014–2016.

<p dir="ltr">Defects in composite manufacturing often lead to compromised structural integrity and reduced performance of the final product. A robust constitutive modeling framework is needed to efficiently and accurately predict the deformation responses of dry fabrics and pre-impregnated fibers, paving the way for defect simulation. This thesis presents a comprehensive study on the development and application of a novel constitutive model of fabric preforms and pre-impregnated fibers during composite manufacturing processes.</p><p dir="ltr">This work proposes an integrated constitutive study for textile fabrics in the aspects of mesoscale tow and macroscale fabric behavior. First, a textile architecture-based discrete modeling approach was developed to predict and visualize fiber tow and fabric deformation. The fabrics consist of interlacing virtual fiber tows which are represented by Timoshenko beams joined by translational and rotational springs and rotary dashpots, which are used to capture the energy dissipation during in-plane shear deformation. Second, an anisotropic hyper-viscoelastic model was developed using the strain energy density function of a homogenized unit cell to predict the fabric deformation as a continuous field. A Maxwell model consisting of one Maxwell element and an additional spring is used to consider the nonequilibrium stresses generated during in-plane shear, transverse shear, and through-thickness compaction deformations. Both approaches were experimentally characterized and applied to a hemisphere draping model in the commercial Finite Element Analysis (FEA) software, Abaqus, to demonstrate the predictive capabilities.</p><p dir="ltr">Then, the robust hyper-viscoelastic model is extended to predict prepreg compaction and bending behavior. In the compaction aspect, a coupling term of energy that captures the effect of squeezing flow and a highly nonlinear transverse compression energy are proposed to predict the compaction response of prepreg with liquid and rubbery resin. The viscoelastic parameters were characterized by a Computational Fluid Dynamics (CFD) model for liquid resin and a discrete micromechanics model for rubbery resin. The method was applied to stepwise compaction simulation at different temperatures in Abaqus and compared to experiments for validation. In the bending aspect, the effective shear modulus is expressed as a function of the second-order gradient of deformation. Modeling parameters were characterized by an analytical model that captures the underlying fiber and matrix deformation mechanism. Parametric study was conducted to illustrate the influence of each parameter and the capability to enhance the accuracy of bending prediction.</p>

Drape simulation of textiles is a field of research, which is known in the clothing sector for a long time. The ongoing development of high-performance composites made of textile reinforcements and matrix materials focus the interests on a serial production in many industrial sectors, such as aviation and automotive industries. Challenges occur mainly in the serial production technologies and in supplying concepts for the preform architecture and shape. Research aims on the acceleration of preform manufacturing and the reduction of expensive pretests. Numerical simulation models can help to improve the composite development chain with structure and process simulation. A special challenge in drape modeling is the bending behavior of textiles. This study introduces a novel approach for modeling single textile layers as laminates to gain a correct mechanical behavior, where all deformation mechanisms are uncoupled. The implementation in the finite element software LS-DYNA® is described. An algorithm is introduced which provides the membrane stiffness for each layer of a laminate to fit the measured cantilever bending stiffness of textiles in every bending direction and bending side. The calculated parameters for the laminate formulation result in the requested bending stiffness for the textile layer. The cantilever bending stiffness can be used directly for dimensioning the model.