A discrete constitutive model for transverse and shear damage of symmetric laminates with arbitrary stacking sequence

A damage constitutive model in conjunction with a 2-D finite element discretization is presented for predicting onset and evolution of matrix cracking and subsequent stiffness reduction of symmetric composite laminates with arbitrary stacking sequence subjected to membrane loads. The formulation uses laminae crack densities as the only state variables, with crack growth driven by both mechanical stress and residual stress due to thermal expansion. The formulation is based on fracture mechanics in terms of basic materials properties, lamina moduli, and critical strain energy release rates GIC and GIIC, only. No additional adjustable parameters are needed to predict the damage evolution. Spurious strain localization and mesh size dependence are intrinsically absent in this formulation. Thus, there is no need to define a characteristic length. Comparison of model results to experimental data is presented for various laminate stacking sequences. Prediction of crack initiation, evolution, and stiffness degradation compare very well to experimental data

Evaluation of finite-element calculations in a part-circular crack by coherent optics techniques

Two techniques, speckle photography and holographic interferometry, were used to test three-dimensional finite-element calculations in an internally pressurized cylinder with an external part-circular crack. Opening displacements along the crack line were measured by speckle photography. Radial displacements were obtained from holographic fringe patterns. Good agreement between experimental and numerical data is obtained. Stress-intensity factor variations along the crack front are calculated from numerical results

Testing of full-scale confined inflatable for the protection of tunnels

There are approximately 337 highway tunnels and 211 rail transit tunnels in the United States; many of these tunnels are beneath bodies of water.1 Every day, more than 11.3 million passengers in 35 metropolitan areas and 22 states use some form of rail transit, either commuter, heavy, or light rail.2 It is well known that man-made or natural disasters can significantly disrupt the functionality of critical transportation infrastructure. Some examples in the United States include the 1992 Chicago freight tunnel flood;3 the 2003 flooding of the Midtown Tunnel in Virginia caused by Hurricane Isabel;4 and the 2012 flooding of New York City, when Hurricane Sandy caused seven subway tunnels under the East River to flood and remain inoperable for several days.5 Tunnel safety and integrity is a subject of special concern, not only because tunnels are of difficult and limited accessibility, but also because most of the potential threats (e.g. fires, flooding, or noxious substances) compromise the integrity of entire connecting system as the threat can spread along it.6Conventional emergency sealing systems are not always installed or operational during the occurrence of extraordinary events, prompting the evaluation of alternative solutions, such as inflatable plugs.7-10 An inflatable plug can seal off and protect an underground system by stopping hazards, such as smoke or flooding. Unlike floodgates, an inflatable plug is fast-deploying, relatively inexpensive, and can be quickly installed in a small space in an existing tunnel or conduit. The concept was demonstrated in 2008 in the Washington D.C. Metro system with promising results.7, 9 This work describes additional full scale testing performed between late 2011 and 2012 for the development of confined inflatable structures for the protection of tunnels completed at West Virginia University

On Micro-Buckling of Unidirectional Fiber-Reinforced Composites by Means of Computational Micromechanics

Micro-buckling of unidirectional fiber-reinforced composites is investigated in this paper by means of an explicit representation of a geometrically imperfect fiber within the context of kinematical and material non-linear behavior. Two types of fiber imperfections are considered: a helicoidal shape, identified as 3D imperfection; and a sinusoidal plane shape (2D imperfection). Both imperfection models are characterized by a maximum misalignment angle of the fiber with respect to the ideal or perfect configuration, as is usually considered in this field. A total of 816 cases were computed in terms of imperfection type (either 2D or 3D), fiber volume fraction, fiber arrangement (square or hexagonal array), orientation for 2D models, matrix yield stress, and misalignment angle. Two load cases, with constrained and unconstrained transverse strain, were considered. Assuming periodic boundary conditions, homogenization was carried out to obtain macroscopic stresses. Numerical results are compared with an analytical model available in the literature. The results show a high imperfection-sensitivity for small misalignment angles; on the other hand, the type of imperfection and the fiber arrangement do not have a large influence on the results. In addition, it was found that this problem is governed by fiber volume fraction and matrix yield stress only for small imperfections, whereas for large misalignment angles, a change in fiber volume fraction produces small changes in micro-buckling stress

Micro/macro Approach for Prediction of Matrix Cracking Evolution in Laminated Composites

A computational constitutive model is presented to predict matrix cracking evolution in laminates under in-plane loading. Transverse cracks are treated as separate discontinuities in the micro-model that provides damage parameters for the macro-model. Both micro- and macro-models are implemented using finite element analysis, specifically, ANSYS, to avoid limitation of analytical micro-modeling. The computational cost of the micro-model is limited to constructing a database of micro-model predictions a priori. The macro-model is simply a finite element analysis discretization of the structure using plane stress or shell elements in ANSYS. The macro-model queries the database, which effectively becomes a constitutive model. The damage surfaces in the database are obtained from the results of large number of finite element micro-scale (unit-cell) analyses. The proposed procedure is implemented in ANSYS as a usermaterial subroutine for transverse crack initiation and propagation in symmetric cross-ply and [0r/(θ/-θ)s/0n]s laminates under in-plane loads. This method is also examined to study matrix crack evolution in tensile specimen with open hole, and the results found to be in good agreement with available experimental data

Diseño y evaluación de tapones inflables para contención de inundaciones en túneles

La protección de túneles ferroviarios y viales usados por sistemas de transporte masivo de pasajeros es de suma importancia para departamentos de transporte y autoridades de tránsito. La ocurrencia de desastres naturales o eventos provocados por el hombre pueden afectar significativamente la funcionalidad de dicha infraestructura subterránea. Eventos naturales como el paso del huracán Sandy en 2012, que produjo la inundación de siete túneles de metro y tres túneles vehiculares en la ciudad de Nueva York, han demostrado la necesidad de desarrollar métodos alternativos para mitigar las vulnerabilidades o, al menos, reducir al mínimo las consecuencias de esos eventos. Este artículo presenta parte del trabajo realizado por la Universidad de Virginia Occidental para el desarrollo de tapones inflables capaces de contener la propagación de inundaciones en túneles típicos de sistemas ferroviarios urbanos. En particular, se presenta el trabajo experimental realizado para simular a escala real el despliegue, inflado, presurización de un prototipo instalado en un simulador de inundación de túneles. El grado de adaptabilidad, o conformidad, del inflable a una sección de túnel típica, así como la estabilidad axial y el caudal de agua filtrada durante la simulación de inundación se midieron y se utilizaron como indicadores de desempeño. Los resultados experimentales demostraron la factibilidad de instalación y posterior despliegue de un tapón inflable, así como la capacidad del mismo para sellar una sección de túnel manteniendo la estabilidad axial con un nivel relativamente bajo filtración de agua que es típicamente manejable con equipos de drenaje convencional

Matrix cracking evolution in open-hole laminates subjected to thermo-mechanical loads

In this work, a constitutive model is developed and used to predict matrix cracking and fiber damage evolution in all the plies of symmetric laminates when both mechanic and thermal loads are applied. A model previously developed is modified to take into account the thermal stresses that appear in each ply when the temperature is reduced below the Stress Free Temperature. Data of matrix damage initiation and evolution due to thermomechanical loads for four materials and six laminate lay-ups taken from the scientific literature are used to validate the model. A good correlation between the predictions and the experimental results is found. The model is used to analyze the thermomechanical damage in laminates containing a centered hole subjected to in-plane tensile loads. It is observed that the thermal load alone does not produce a stress concentration around the hole but the thermal residual stress accelerates damage accumulation during mechanical load. (C) 2017 Elsevier Ltd. All rights reserved.The authors are indebted for the financial support of this work to the Ministry of Economy and Finance of Spain (project DPI2013-42240-R)

Influence of ply cluster thickness and location on matrix cracking evolution in open-hole composite laminates

The influence of cluster thickness and its position on the damage evolution of open-hole composite laminates, subjected to uniaxial in-plane tensile loads, is studied in this work. The Discrete Damage Mechanics model of Barbero-Cortes augmented by a fiber damage criterion is employed. Several stacking sequences with clusters in different positions and thicknesses inside the laminate are analyzed. The influence of cluster thickness and its location on: the crack-density evolution, applied load, longitudinal stress and its contour plots is studied for all the stacking sequences selected.The authors are indebted for the financial support of this work to the Ministry of Economy and Competitiveness (grant number DPI2013 42240 R)

Friction and leakage characteristics of confined, reduced-scale inflatable structures

This work is focused on the evaluation of the performance of a small-scale inflatable, or plug, placed in a confined space provided by a circular rigid pipe as a way to contain the propagation of floods. The rigid pipe is a simplified and scaled approximation of an actual tunnel section. The evaluations were conducted using an inflatable plug made of a single layer of coated Vectran® fabric. Friction coefficients of the system were calculated for three different materials lining the pipe so a comparison could be made. These friction coefficients were also compared to laboratory friction machine testing of the same lining materials. This comparison showed that the friction coefficients of the pipe-plug system were lower than the laboratory friction machine tests. Rates of water leakage around the plug were also studied. The leakage rates were recorded for several different plug pressures while varying the tunnel pressure accordingly. It was observed that as pressure differential decreased between the plug and pipe, the leakage rate increased. Results showed also that the plug was able to withstand a pressure differential with manageable water leakage rates