Textile composites have a wide variety of applications in the aerospace, sports, automobile, marine and medical industries. Due to the availability of a variety of textile architectures and numerous parameters associated with each, optimal design through extensive experimental testing is not practical. Predictive tools are needed to perform virtual experiments of various options. The focus of this research is to develop a better understanding of linear elastic response, plasticity and material damage induced nonlinear behavior and mechanics of load flow in textile composites. Textile composites exhibit multiple scales of complexity. The various textile behaviors are analyzed using a two-scale finite element modeling. A framework to allow use of a wide variety of damage initiation and growth models is proposed. Plasticity induced non-linear behavior of 2x2 braided composites is investigated using a modeling approach based on Hill’s yield function for orthotropic materials. The mechanics of load flow in textile composites is demonstrated using special non-standard postprocessing techniques that not only highlight the important details, but also transform the extensive amount of output data into comprehensible modes of behavior. The investigations show that the damage models differ from each other in terms of amount of degradation as well as the properties to be degraded under a particular failure mode. When compared with experimental data, predictions of some models match well for glass/epoxy composite whereas other’s match well for carbon/epoxy composites. However, all the models predicted very similar response when damage factors were made similar, which shows that the magnitude of damage factors are very important. Full 3D as well as equivalent tape laminate predictions lie within the range of the experimental data for a wide variety of braided composites with different material systems, which validated the plasticity analysis. Conclusions about the effect of fiber type on the degree of plasticity induced non-linearity in a ±25° braid depend on the measure of non-linearity. Investigations about the mechanics of load flow in textile composites bring new insights about the textile behavior. For example, the reasons for existence of transverse shear stress under uni-axial loading and occurrence of stress concentrations at certain locations were explained.

The hot-workability of Titanium (Ti) alloys is of current interest to the aerospace industry due to its widespread application in the design of strong and light-weight aircraft structural components and engine parts. Motivated by the need for accurate simulation of large scale plastic deformation in metals that exhibit macroscopic plastic anisotropy, such as Ti, a constitutive model is developed for anisotropic materials undergoing plastic deformation coupled with ductile damage in the form of internal cavitation. The model is developed from a rigorous micromechanical basis, following well-known previous works in the field. The model incorporates the porosity and void aspect ratio as internal damage variables, and seeks to provide a more accurate prediction of damage growth compared to previous existing models. A closed form expression for the macroscopic yield locus is derived using a Hill-Mandel homogenization and limit analysis of a porous representative volume element. Analytical expressions are also developed for the evolution of the internal variables, porosity and void shape. The developed yield criterion is validated by comparison to numerically determined yield loci for specific anisotropic materials, using a numerical limit analysis technique developed herein. The evolution laws for the internal variables are validated by comparison with direct finite element simulations of porous unit cells. Comparison with previously published results in the literature indicates that the new model yields better agreement with the numerically determined yield loci for a wide range of loading paths. Use of the new model in continuum finite element simulations of ductile fracture may be expected to lead to improved predictions for damage evolution and fracture modes in plastically anisotropic materials.

A finite element model based on the layer-wise theory and the von Kármán type nonlinear strains is used to analyze damage in laminated composite beams. In the formulation, the Heaviside step function is employed to express the discontinuous interlaminar displacement field at the delaminated interfaces. Two types of the most common damage modes in composite laminates are investigated for cross-ply laminated beams using a numerical approach. First, a multi-scale analysis approach to determine the influence of transverse cracks on a laminate is proposed. In the meso-scale model, the finite element model based on the classical laminate theory provides the material stiffness reduction in terms of the crack density by computing homogenized material properties of the cracked ply. The multiplication of transverse cracks is predicted in a macro-scale beam model under bending loads. In particular, a damage analysis based on nonlinear strain fields in contrast to the linear case is carried out for a moderately large deformation. Secondly, the effect of delamination in a cross-ply laminated beam under bending loads is studied for various boundary conditions with various cross-ply laminate lay-ups. The crack growth of delamination is predicted through investigating the strain energy release rate. Finally, the interactions of a transverse crack and delamination are considered for beams of different configurations. The relationships between the two different damage modes are described through the density of intralaminar cracks and the length of the interlaminar crack. It is found that geometric nonlinearity plays an important role in progression of interlaminar cracks whereas growth of intralaminar cracks is not significantly influenced. This study also shows that the mixture of fracture mode I and II should be considered for analysis of delamination under bending loads and the fracture mode leading delamination changes as the damage develops. The growth of delamination originated from the tip of the transverse crack is found to strongly depend on the thickness of 90- degree layers as well as the transverse crack density. Further, the effect of interfacial crack growth on the transverse cracking can be quatitatively determined by the delamination length, the thickness of 90-degree layers and the transverse crack density.

Quercetin (Q), a water-soluble flavonoid that is ubiquitous to foods of plant origin is postulated to protect against colon cancer due to its antioxidant activity. In contrast, we have shown that a dietary combination of fish oil (FO; n-3 fatty acids) and pectin may protect against colon cancer by decreasing endogenous antioxidant enzyme activities leading to increased reactive oxygen species (ROS), an inducer of apoptosis. We hypothesized that adding an antioxidant to a FO diet may negate the beneficial effects of FO by counteracting FO effects on colonocyte redox status. To test this, we provided 40 rats with FO or CO (fiber = pectin) diets with Q being 0 or 0.45% of the diet for 10 wk. All rats were injected with azoxymethane (AOM) on d 21 and 28. Measurements included: aberrant crypt (AC) enumeration (colon cancer marker); apoptosis (TUNEL assay); catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) activities; reduced and oxidized glutathione concentrations (GSH/GSSG); and oxidative DNA damage (8-OHdG adducts). AC numbers were lower in FO vs CO rats (p<0.0001), but tended to increase for FO diets containing Q (P<0.098). The apoptotic index was higher (p<0.0001) when Q was added to the FO and CO diets. Total SOD (lipid main effect, p=0.0136) and GPX activity (p=0.0025) was elevated in CO rats. CAT activity was higher (p=0.0204) in FO rats, however Q diminished this effect. GSH was not affected by diet; yet, GSSG accumulated (p=0.0554) in CO rats with Q as compared to CO rats without Q. The GSH/GSSG ratio was lower (p=0.0314) in CO rats than in FO rats. There was no difference in 8-OHdG adduct levels in FO vs CO rats, however, Q decreased 8-OHdG adducts in CO rats (p=0.0428). Despite increasing apoptosis, Q did not significantly lower AC formation. These data suggest that the distinct effects of the CO/Q and FO/Q combinations are functioning through different mechanisms to induce apoptosis. The long-term consequences of adding antioxidants such as Q to a diet thought to exert its anticancer effect through a pro-oxidant mechanism are unknown and deserve further study.

In the coming decades, the world will require additional supplies of natural gas to meet the demand for energy. Tight gas reservoirs can be defined as reservoirs where the formation permeability is so low (< 0.1 md) that advanced stimulation technologies, such as large volume fracture treatments, are required before a reasonable profit can be made. Hydraulic fracturing is one of the best methods to stimulate a tight gas well. Most fracture treatments result in 3-6 fold increases in the productivity index. However, if one computes the effective fracture length of most wells, we usually find that the effective length is less than the designed propped fracture length. The “propped length” is the distance down the fracture from the wellbore where proppants have been placed at a high enough concentration to “prop open” the fracture. The “effective length” is the portion of the propped fracture that cleans up and allows gas flow from the reservoir into the fracture then down the fracture to the wellbore. Whenever the effective length is much shorter than the designed propped length, several reasons must be evaluated to determine what might have occurred. For example, the difference could be caused by one or more of the following issues: insufficient fracture fluid cleanup, proppant settling, proppant embedment, proppant crushing, or poor reservoir continuity. Although all these causes are possible, we believe that fracture fluid cleanup issues may be the most common reason the industry fails to achieve the designed propped fracture length in most cases. In this research, we have investigated fracture fluid cleanup problems and developed a better understanding of the issues involved which hopefully will lead to ways to improve cleanup. Fracture fluid cleanup is a complex problem, that can be influenced by many parameters such as the fluid system used, treatment design, flowback procedures, production strategy, and reservoir conditions. Residual polymer in the fracture can reduce the effective fracture permeability and porosity, reduce the effective fracture half-length, and limit the well productivity. Our ability to mathematically model the fundamental physical processes governing fluid recovery in hydraulic fractures in the past has been limited. In this research, fracture fluid damage mechanisms have been investigated, and mathematical models and computer codes have been developed to better characterize the cleanup process. The codes have been linked to a 3D, 3-phase simulator to model and quantify the fracture fluid cleanup process and its effect on long-term gas production performances. Then, a comprehensive systematic simulation study has been carried out by varying formation permeability, reservoir pressure, fracture length, fracture conductivity, yield stress, and pressure drawdown. On the basis of simulation results and analyses, new ways to improve fracture fluid cleanup have been provided. This new progress help engineers better understand fracture fluid cleanup, improve fracture treatment design, and increase gas recovery from tight sand reservoirs, which can be extremely important as more tight gas reservoirs are developed around the world.

Flooding inundation during hurricanes has been very costly and dangerous. However, the impact of climate change on hurricane flooding is not well understood at present. As sea surface temperatures increase, it is expected that hurricane intensity will increase and sea levels will rise. It is further hypothesized that climate change will increase hurricane flooding inundation, which would increase property damages and adversely affect a greater number of people. This thesis presents a case study of Corpus Christi, Texas, which analyzes the impact of climate change on hurricane flooding. Sea level rise projections and intensification of historical hurricanes were considered in this study. Storm surges were determined with the ADCIRC numerical model, while GIS was used to estimate area flooded, property damages, and population affected. Flooding inundation, property damages, and number of people affected by flooding increases as the intensity of the hurricane increases. As hurricane intensity increases and sea levels rise, the depth of flooding also increases dramatically. Based on two historical hurricanes and one shifted historical hurricane, on average the inundated area increases about 11 km2 per degree Celsius of sea surface temperature rise, the property damages increase by about $110 million per degree Celsius of sea surface temperature rise, and the number of people affected by flooding inundation increases by about 4,900 per degree Celsius of sea surface temperature rise. These results indicate that it may become necessary to consider the effects of climate change when building future coastal communities and adapting the protection of existing communities.

Based on continuum damage mechanics (CDM), an isotropic and anisotropic damage model coupled with a novel plasticity model for plain concrete is proposed in this research. Two different damage evolution laws for both tension and compression are formulated for a more accurate prediction of the plain concrete behavior. In order to derive the constitutive equations, the strain equivalence hypothesis is adopted. The proposed constitutive model has been shown to satisfy the thermodynamics requirements, and detailed numerical algorithms are developed for the Finite Element implementation of the proposed model. Moreover, the numerical algorithm is coded using the user subroutine UMAT and then implemented in the commercial finite element analysis program Abaqus, and the overall performance of the proposed model is verified by comparing the model predictions to various experimental data on macroscopic level. Using the proposed coupled plasticity-damage constitutive model, the effect of the micromechanical properties of concrete, such as aggregate shape, distribution, and volume fraction, the ITZ thickness, and the strength of the ITZ and mortar matrix on the tensile behavior of concrete is investigated on 2-D and 3-D meso-scale. As a result of simulation, the tensile strength and thickness of the ITZ is the most important factor that control the global strength and behavior of concrete, and the aggregate shape and volume fraction has somewhat effect on the tensile behavior of concrete while the effect of the aggregate distribution is negligible. Furthermore, using the proposed constitutive model, the pull-out analysis of the single straight and curved CNT embedded in cement matrix is carried out. In consequence of the analysis, the interfacial fracture energy is the key parameter governing the CNT pull-out strength and ductility at bonding stage, and the Young's modulus of the CNT has also great effect on the pull-out behavior of the straight CNT. In case of the single curved CNT, while the ultimate pull-out force of the curved CNT at sliding stage is governed by the initial sliding force when preexisting normal force is relatively high, the ultimate pull-out force, when the preexisting normal force is not significant, is increased linearly proportional to the curvature and the Young's modulus of the CNT due to the additionally induced normal force by the bending stiffness of the curved CNT.

The hydraulic fracturing treatment is an essential tight sand gas reservoir stimulation that employs viscous fluid to break the formation rock to create a fracture and transport the propping agent to support the fracture from naturally healing. Despite proven economic benefit, the hydraulic fracture fluid damages the producing formation and the propped fracture. To analyze the gel damage effect quantitatively, the filter cake thickness is used as a parameter that has not been measured before. This project was divided into two stages. The first stage built up a filter cake and measured the filter cake thickness by a laser profilometer. A correlation between leakoff volume and filter cake thickness was produced. The second stage eroded the filter cake by flowing original fracturing fluid through the core sample to study the fracturing fluid shear clean up effect on filter cake thickness. The filter cake was built up in the lab and the thickness was measured with different methods. The profilometer has been tested as an effective tool to measure the filter cake thickness. A correlation for crosslinked guar fracture fluid filter cake thickness was produced. An experiment setup used to shear erode the filter cake was built and tested. The results showed the filter cake was not eroded at 200 s-1 shear rate.

Coupling beams are structural elements used to connect two or more shear walls. The most common material used in the construction of coupling beam is reinforced concrete. The use of coupling beams along with shear walls require them to resist large shear forces, while possessing sufficient ductility to dissipate the energy produced due to the lateral loads. This study has been undertaken to produce a computational model to replicate the behavior of conventionally reinforced coupling beams subjected to cyclic loading. The model is developed in the finite element analysis software ABAQUS. The concrete damaged plasticity model was used to simulate the behavior of concrete. A calibration model using a cantilever beam was produced to generate key parameters in the model that are later adapted into modeling of two coupling beams with aspect ratios: 1.5 and 3.6. The geometrical, material, and loading values are adapted from experimental specimens reported in the literature, and the experimental results are then used to validate the computational models. The results like evolution of damage parameter and crack propagation from this study are intended to provide guidance on finite element modeling of conventionally reinforced concrete coupling beams under cyclic lateral loading.

This paper describes a method by means of FE code DEFORMTM-2D to simulate the formation of central bursting defects in extrusion processes; the effect of various extrusion parameters such as half die angle, reduction in area, friction factor, and strain hardening exponent on the maximum damage value is examined. The differences between various ductile fracture criteria are compared and critical damage value(CDV) of the material AA6061 is found. In addition, we get the strength coefficient(K), strain hardening exponent(n), CDV and friction factor(m) by material tests, such as uniform tensile test, notched tensile test, compression test, and ring compression test. Finally, the cold multistage extrusion experiment was conducted to verify the accuracy of the finite element simulations. From the continuous three pass extrusion experimental data, no fracture in the center of the extruded product was found. From the analytical data, it was known that the maximum damage value 1.0479 for third pass extrusion was small than critical damage value 1.068, thus, central bursting defects didn¡¦t occur in extrusion processes.