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R. J. Asaro - One of the best experts on this subject based on the ideXlab platform.

  • Skin wrinkling of sandwich Polymer Matrix Composite panels subjected to fire exposure
    Thin-walled Structures, 2012
    Co-Authors: Pei Gu, R. J. Asaro
    Abstract:

    Abstract This paper presents an analytical solution of skin wrinkling for sandwich Polymer Matrix Composite panels in a combined thermal–mechanical condition. The thermal gradient in the transverse direction is induced by one-sided fire exposure, and the mechanical load is the in-plane compression. Due to low thermal conductivities of Polymer Matrix Composites, the thermal gradient exists for a long period of time. The material properties of Polymer Matrix Composites are degraded as temperature rises. These behaviors induce mechanical properties' gradients along the transverse direction. The general solution for the wrinkling load in the thermal–mechanical loading condition is investigated. The solution is characterized in terms of two non-dimensional parameters that represent material properties and dimensional lengths of the skin and the core. The wrinkling load is presented for fairly complete ranges of the two non-dimensional parameters. The wrinkling load is also derived from Winkler model for non-homogeneous materials. An example of thermal-mechanical simulation to design the wrinkling load-bearing capacity of a panel exposed to fire is given.

  • influence of material nonlinearity on thermal distortion of Polymer Matrix Composite panels
    Composites Part B-engineering, 2010
    Co-Authors: Pei Gu, R. J. Asaro
    Abstract:

    Abstract This paper discusses the influence of material nonlinearity on thermal distortion of Polymer Matrix Composite panels. The load is transverse temperature gradient introduced by one-sided heat exposure, e.g., fire. For such low thermal conductivity materials, when there are no external mechanical loads, the transverse thermal gradient induces non-uniform thermal expansion along the thickness that results in transverse deformation field, known as thermal distortion. The power form stress–strain relation and the Ramberg–Osgood form stress–strain relation are discussed to include the temperature dependent behavior of Polymer Matrix Composites. The degradation of Polymer Matrix Composites at elevated temperature, thermal softening, is discussed. The variations of the reference stress and the reference strain with temperature are specified to describe the temperature dependent constitutive relationships. Semi-analytical simulation and finite element simulation are carried out for panels with roller end support condition. Results suggest that, while the material nonlinearity has insignificant influence on the transverse displacement of the panel, it has strong influence on local stress and strain. The stress and strain can go beyond the yield stress and the yield strain into plastic stage in certain circumstances.

  • Structural stability of Polymer Matrix Composite panels in fire
    Marine Structures, 2009
    Co-Authors: Pei Gu, R. J. Asaro
    Abstract:

    Abstract Development in advanced Composite fabrication technology offers the clear prospect of cost effective application of Polymer Matrix Composites for large load-bearing structures. However, Polymer Matrix Composites can be severely degradated under the thermal condition caused by fire. This paper addresses the compressive load-bearing capacity for Polymer Matrix Composite panels in naval structures and civil infrastructures under the combined thermal–mechanical condition. The failure modes arising from structural instability for single skin and sandwich panels in such combined thermal–mechanical condition are the focus in this study. The thermal field under fire heating and the degradation of mechanical properties with elevated temperature are discussed. Analytical solutions for these mechanical failure modes are presented for design considerations. The approach to the development of a quantitative methodology for fire protection design is discussed in the context of the analyses and the experiments. Design diagrams are constructed to design mechanical loads for given fire protection time, and on the opposite, to design fire protection time for given mechanical loads.

  • designing sandwich Polymer Matrix Composite panels for structural integrity in fire
    Composite Structures, 2009
    Co-Authors: Pei Gu, R. J. Asaro
    Abstract:

    This is the continuation of our published paper [Gu P, Asaro RJ. Designing Polymer Matrix Composite panels for structural integrity in fire. Compos Struct 2008;84:300–9]. This paper addresses the compressive mechanical load bearing capacity of sandwich Polymer Matrix Composite panels under transverse thermal gradients caused by fire. An example of such combined loading condition is that of panels in ship and vessel structures under transverse thermal gradients caused by fire. Specifically, we discuss the mechanical design considerations, failure modes that lead the panels to fail in the combined thermal–mechanical condition. An approach to assess critical load among the failure modes is discussed for design purpose. A computer program is developed based on the approach to evaluate sandwich panel’s load bearing capacity in fire. Examples are presented to design the panel for given thermal and mechanical requirements. Due to the core’s low bending stiffness, there is a large decrease of the panel’s load bearing capacity when the fire-exposed skin is degradated.

  • designing Polymer Matrix Composite panels for structural integrity in fire
    Composite Structures, 2008
    Co-Authors: Pei Gu, R. J. Asaro
    Abstract:

    This paper discusses the compressive load bearing capability of Polymer Matrix Composite panels in fire, a combined thermal and mechanical loading condition. An example of such combined loading condition is that of panels in ship structures under transverse thermal gradients caused by fire. Investigation is focused on failure modes under transverse thermal gradients and compressive mechanical loads, i.e. buckling, deflection induced by the shift of the neutral axis, thermal distortion without mechanical loads. Thermal field and mechanical fields for these failure modes are presented and discussed in details for the purposes of design considerations. Design diagrams are constructed to design mechanical loads for given fire protection time, and on the opposite, to design fire protection time for given mechanical loads. Unlike panels made by the conventional ship building material steel, the design diagrams for the temperature dependent materials with transverse thermal gradients consist of multiple failure mechanisms.

Pei Gu - One of the best experts on this subject based on the ideXlab platform.

  • Structural integrity of Polymer Matrix Composite panels in fire
    Failure Mechanisms in Polymer Matrix Composites, 2020
    Co-Authors: Pei Gu
    Abstract:

    Abstract: Developments in advanced Composite technology offer cost-effective application of Polymer Matrix Composites for large load-bearing structures. However, Polymer Matrix Composites can be severely damaged under thermal conditions caused by fire. This chapter addresses failures of Polymer Matrix Composite panels under combined thermal-mechanical conditions. Specifically, the thermal load is fire exposure which can occur in accidental events, and the mechanical load is in-plane compression which is the common loading condition for panels in naval structures and civil infrastructure. The failure modes under such thermal-mechanical conditions for single-skin and sandwich panels are the focus in this chapter. The thermal field under fire heating and the degradation of mechanical properties with respect to temperature rise are discussed. Modeling methodology for these failure modes is presented. The development of a quantitative approach to assess structural fire integrity is discussed in the context of analysis and experimental observation.

  • 4 – Structural integrity of Polymer Matrix Composite panels in fire
    Failure Mechanisms in Polymer Matrix Composites, 2020
    Co-Authors: Pei Gu
    Abstract:

    : Developments in advanced Composite technology offer cost-effective application of Polymer Matrix Composites for large load-bearing structures. However, Polymer Matrix Composites can be severely damaged under thermal conditions caused by fire. This chapter addresses failures of Polymer Matrix Composite panels under combined thermal-mechanical conditions. Specifically, the thermal load is fire exposure which can occur in accidental events, and the mechanical load is in-plane compression which is the common loading condition for panels in naval structures and civil infrastructure. The failure modes under such thermal-mechanical conditions for single-skin and sandwich panels are the focus in this chapter. The thermal field under fire heating and the degradation of mechanical properties with respect to temperature rise are discussed. Modeling methodology for these failure modes is presented. The development of a quantitative approach to assess structural fire integrity is discussed in the context of analysis and experimental observation.

  • Skin wrinkling of sandwich Polymer Matrix Composite panels subjected to fire exposure
    Thin-walled Structures, 2012
    Co-Authors: Pei Gu, R. J. Asaro
    Abstract:

    Abstract This paper presents an analytical solution of skin wrinkling for sandwich Polymer Matrix Composite panels in a combined thermal–mechanical condition. The thermal gradient in the transverse direction is induced by one-sided fire exposure, and the mechanical load is the in-plane compression. Due to low thermal conductivities of Polymer Matrix Composites, the thermal gradient exists for a long period of time. The material properties of Polymer Matrix Composites are degraded as temperature rises. These behaviors induce mechanical properties' gradients along the transverse direction. The general solution for the wrinkling load in the thermal–mechanical loading condition is investigated. The solution is characterized in terms of two non-dimensional parameters that represent material properties and dimensional lengths of the skin and the core. The wrinkling load is presented for fairly complete ranges of the two non-dimensional parameters. The wrinkling load is also derived from Winkler model for non-homogeneous materials. An example of thermal-mechanical simulation to design the wrinkling load-bearing capacity of a panel exposed to fire is given.

  • influence of material nonlinearity on thermal distortion of Polymer Matrix Composite panels
    Composites Part B-engineering, 2010
    Co-Authors: Pei Gu, R. J. Asaro
    Abstract:

    Abstract This paper discusses the influence of material nonlinearity on thermal distortion of Polymer Matrix Composite panels. The load is transverse temperature gradient introduced by one-sided heat exposure, e.g., fire. For such low thermal conductivity materials, when there are no external mechanical loads, the transverse thermal gradient induces non-uniform thermal expansion along the thickness that results in transverse deformation field, known as thermal distortion. The power form stress–strain relation and the Ramberg–Osgood form stress–strain relation are discussed to include the temperature dependent behavior of Polymer Matrix Composites. The degradation of Polymer Matrix Composites at elevated temperature, thermal softening, is discussed. The variations of the reference stress and the reference strain with temperature are specified to describe the temperature dependent constitutive relationships. Semi-analytical simulation and finite element simulation are carried out for panels with roller end support condition. Results suggest that, while the material nonlinearity has insignificant influence on the transverse displacement of the panel, it has strong influence on local stress and strain. The stress and strain can go beyond the yield stress and the yield strain into plastic stage in certain circumstances.

  • Structural stability of Polymer Matrix Composite panels in fire
    Marine Structures, 2009
    Co-Authors: Pei Gu, R. J. Asaro
    Abstract:

    Abstract Development in advanced Composite fabrication technology offers the clear prospect of cost effective application of Polymer Matrix Composites for large load-bearing structures. However, Polymer Matrix Composites can be severely degradated under the thermal condition caused by fire. This paper addresses the compressive load-bearing capacity for Polymer Matrix Composite panels in naval structures and civil infrastructures under the combined thermal–mechanical condition. The failure modes arising from structural instability for single skin and sandwich panels in such combined thermal–mechanical condition are the focus in this study. The thermal field under fire heating and the degradation of mechanical properties with elevated temperature are discussed. Analytical solutions for these mechanical failure modes are presented for design considerations. The approach to the development of a quantitative methodology for fire protection design is discussed in the context of the analyses and the experiments. Design diagrams are constructed to design mechanical loads for given fire protection time, and on the opposite, to design fire protection time for given mechanical loads.

D. D. L. Chung - One of the best experts on this subject based on the ideXlab platform.

  • Effect of fiber lay-up configuration on the electromagnetic interference shielding effectiveness of continuous carbon fiber Polymer-Matrix Composite
    Carbon, 2019
    Co-Authors: D. D. L. Chung, Asma A. Eddib
    Abstract:

    Continuous carbon fiber Polymer-Matrix multifunctional structural Composites capable of electromagnetic interference (EMI) shielding are needed for electronics and radiation sources. The laminate's fiber lay-up configuration affects the shielding effectiveness, as shown in this work for unmodified conventional carbon fiber Polymer-Matrix Composite laminates with high-strength PAN-based carbon fiber and a polyamide thermoplastic Matrix. The radiation is normal-incidence unpolarized plane wave, as commonly used. The shielding is dominated by absorption rather than reflection – more so for crossply Composites than unidirectional Composites. Due to the electrical conductivity longitudinal-to-transverse ratio of 930 for a lamina, the absorption-loss/thickness longitudinal-to-transverse ratio is 30 at 1.0 GHz. This factor of 30 means that the contribution of the fibers transverse to the electric field to absorption is negligible compared to that of the fibers parallel to the electric field. The ratio of absorption-loss/thickness for the crossply Composite to that for the unidirectional Composite with the same number of laminae is ∼4, and the ratio of the reflection loss for the crossply Composite to that for the unidirectional Composite is ∼2. The values of these ratios are consistent with electromagnetic theory for unpolarized radiation. This work strengthens the science base for the design of continuous fiber Composites for shielding.

  • first report of capacitance based self sensing and in plane electric permittivity of carbon fiber Polymer Matrix Composite
    Carbon, 2018
    Co-Authors: Asma A. Eddib, D. D. L. Chung
    Abstract:

    Abstract Capacitance-based damage self-sensing and the in-plane electric permittivity of continuous carbon fiber Polymer-Matrix Composite are unprecedentedly reported. Capacitance-based self-sensing is advantageous over previously reported electrical-resistance-based self-sensing in not needing intimate electrical contacts and that two (rather than four) contacts suffice. Using a 220 × 220-mm2 unidirectional one-lamina polyamide-6-Matrix Composite, the capacitance (2 kHz) is measured in the through-thickness and in-plane directions using 25 × 25-mm2 aluminum-foil electrodes that are sandwiching and coplanar, respectively. Due to the Composite's conductivity and the LCR meter's limitation, a dielectric film (adhesive tape) is positioned between electrode and specimen. In practice, this film can be the paint on the Composite. Judiciously positioned artificial damage (1.1-mm diameter through-holes) causes the through-thickness capacitance to increase monotonically and the in-plane capacitance to decrease monotonically with increasing damage, due to the effect of the damage on the fringing electric field. The relative permittivity is 2160 ± 510 and 1640 ± 330 for the longitudinal and transverse directions, respectively, with anisotropy 1.3. The DC resistivity is 0.0072 ± 0.0004 and 10.9 ± 0.9 Ω cm in the longitudinal and transverse directions, respectively, with anisotropy 1500. The conductivity controls the current spreading, while the high permittivity provides the capacitance effect. The resistivity anisotropy causes the dependence of the capacitance-based sensing on the fiber orientation.

  • self sensing of flexural strain and damage in carbon fiber Polymer Matrix Composite by electrical resistance measurement
    Carbon, 2006
    Co-Authors: Shoukai Wang, D. D. L. Chung
    Abstract:

    The self-sensing of flexural strain and damage has been demonstrated in carbon fiber Polymer-Matrix Composite by measuring the DC electrical resistance. Upon strain in the elastic regime, the compression surface resistance decreases reversibly (due to increase in the current penetration), while the tension surface resistance increases reversibly (due to decrease in the current penetration), and the oblique resistance increases reversibly. Upon minor damage, (i) the oblique resistance after unloading decreases, (ii) the oblique resistance decreases during load increase near the start of loading, and (iii) the curve of the oblique resistance or the resistance of the tension or compression surface vs. deflection becomes nonlinear. Upon major damage, all resistances abruptly and irreversibly increase, such that the onset occurs earlier for the compression surface resistance and the oblique resistance than the tension surface resistance. The surface resistances are superior indicators of strain, whereas the oblique resistance is a superior indicator of damage.

  • comparative evaluation of the electrical configurations for the two dimensional electric potential method of damage monitoring in carbon fiber Polymer Matrix Composite
    Smart Materials and Structures, 2006
    Co-Authors: Daojun Wang, D. D. L. Chung
    Abstract:

    The effectiveness of the two-dimensional electric potential method of damage sensing in a quasi-isotropic carbon fiber Polymer–Matrix Composite depends on the electrical configuration, i.e., the current direction relative to the surface fibers and the electrical contact scheme. Oblique current application in any direction provides effective damage sensing, as shown by using electrical contacts on the opposite in-plane surfaces. In-plane current application through the cross section in any direction also provides effective damage sensing, as shown by using electrical contacts that are either on the edge surfaces or in holes through the Composite. In-plane surface current application is effective when the current is perpendicular to the surface fibers (due to the low resistivity in the direction of the fibers) and is ineffective when the current is parallel to the surface fibers (due to the high resistivity in the direction perpendicular to the fibers). The oblique configuration is recommended for practical implementation. In general, the potential method is reliable when (i) the resistance between the electric current line and the nearly parallel electric potential gradient line is sufficiently low, as attained when these lines are sufficiently close, and (ii) the resistance between the current line and the damage location is sufficiently low, as attained when the distance of separation is sufficiently small.

  • piezoresistivity in continuous carbon fiber Polymer Matrix Composite
    Polymer Composites, 2000
    Co-Authors: Shoukai Wang, D. D. L. Chung
    Abstract:

    Piezoresistivity involving the volume resistivity of a continuous unidirectional carbon fiber epoxy-Matrix Composite in the fiber direction decreasing reversibly upon tension in the fiber direction was observed by the four-probe method, due to an increase in the degree of fiber alignment. Use of the two-probe method resulted in measurement of the contact resistance rather than the volume resistance. The contact resistance increased reversibly upon tension.

Pablo D Zavattieri - One of the best experts on this subject based on the ideXlab platform.

  • competing failure mechanisms in mixed mode fracture of an adhesively bonded Polymer Matrix Composite
    International Journal of Adhesion and Adhesives, 2006
    Co-Authors: Suyi Li, M D Thouless, Anthony M Waas, Jessica A Schroeder, Pablo D Zavattieri
    Abstract:

    In this paper, the use of cohesive-zone models to analyze crack-path selection in adhesive joints made from a Polymer-Matrix Composite is demonstrated. Cohesive-zone parameters for the adhesive and Composite obtained in a previous work were used without any modifications to make the predictions presented in this study. The results of numerical simulations of two mixed-mode geometries, single-lap shear and asymmetrical double-cantilever beam specimens, are compared to experimental observations. It is shown that the numerical simulations provided reasonably good predictions for the strength and failure mechanisms of the joints, allowing the nature of the competition between failure of the Composite and failure of the interface to be determined.

  • mixed mode cohesive zone models for fracture of an adhesively bonded Polymer Matrix Composite
    Engineering Fracture Mechanics, 2006
    Co-Authors: Suyi Li, M D Thouless, Anthony M Waas, Jessica A Schroeder, Pablo D Zavattieri
    Abstract:

    Abstract As a direct extension of previous mode-I work on the adhesion of Composite joints, this paper uses a cohesive-zone approach to model the mixed-mode fracture of adhesive joints made from a Polymer–Matrix Composite. Mode-II cohesive-zone parameters were obtained using sandwich end-notch flexure specimens. These parameters were used directly with the previously determined mode-I parameters to predict the fracture and deformation of mixed-mode geometries. It was shown that numerical simulations provided quantitative predictions for these geometries, including predictions for both the strengths of the joints and for the failure mechanisms. In conjunction with the earlier work, these results demonstrate the use of cohesive-zone approaches for the design of adhesively bonded Composite joints, and indicate approaches for determining the relevant material properties to describe mixed-mode fracture.

  • use of a cohesive zone model to analyze the fracture of a fiber reinforced Polymer Matrix Composite
    Composites Science and Technology, 2005
    Co-Authors: Suyi Li, M D Thouless, Anthony M Waas, J A Schroeder, Pablo D Zavattieri
    Abstract:

    Abstract A cohesive-zone model for a fiber-reinforced Polymer–Matrix Composite is presented. A two-parameter model with a characteristic toughness and a characteristic strength can be used to predict the fracture of notched or cracked specimens. The two parameters can be determined by comparing numerical predictions to experimental observations of a fracture test. It is shown that the engineering behavior, in terms of strength, deformation and energy dissipation is well-described by such a two-parameter model, but when the characteristic dimensions of the Composite structure (e.g., the initial crack length or ligament length) are very small, extra details about the cohesive law such as the Matrix-cracking strength may be required. Finally, it is shown that a cohesive-zone model provides excellent predictions of transitions between stable and catastrophic crack growth in the Composite, and, hence, permits an understanding of the energy dissipation during fracture that occurs in these different regimes.

  • use of mode i cohesive zone models to describe the fracture of an adhesively bonded Polymer Matrix Composite
    Composites Science and Technology, 2005
    Co-Authors: Suyi Li, M D Thouless, Anthony M Waas, J A Schroeder, Pablo D Zavattieri
    Abstract:

    In this paper, the use of a cohesive-zone approach to model the mode-I fracture of adhesive joints made from a Polymer-Matrix Composite is demonstrated. Cohesive-zone parameters were obtained by matching numerical results to experimental observations. It is shown that there is a distinction between the characteristic strength of the interface associated with the toughness, and the intrinsic cohesive strength of the interface. While the characteristic strength and toughness are often sufficient to describe fracture in the presence of a crack, the intrinsic cohesive strength is also required to analyze some geometries that have very small characteristic dimensions or crack lengths. It is shown that cohesive-zone models accurately predict the behavior of the joints studied. In particular, not only are the strengths and deformations accurately described, but the transition between failure of the Composite and failure of the interface can also be predicted. This mode-I transition cannot be predicted by conventional fracture mechanics as it depends on both the energy-based and strength-based failure parameters associated with cohesive-zone models.

Suyi Li - One of the best experts on this subject based on the ideXlab platform.

  • competing failure mechanisms in mixed mode fracture of an adhesively bonded Polymer Matrix Composite
    International Journal of Adhesion and Adhesives, 2006
    Co-Authors: Suyi Li, M D Thouless, Anthony M Waas, Jessica A Schroeder, Pablo D Zavattieri
    Abstract:

    In this paper, the use of cohesive-zone models to analyze crack-path selection in adhesive joints made from a Polymer-Matrix Composite is demonstrated. Cohesive-zone parameters for the adhesive and Composite obtained in a previous work were used without any modifications to make the predictions presented in this study. The results of numerical simulations of two mixed-mode geometries, single-lap shear and asymmetrical double-cantilever beam specimens, are compared to experimental observations. It is shown that the numerical simulations provided reasonably good predictions for the strength and failure mechanisms of the joints, allowing the nature of the competition between failure of the Composite and failure of the interface to be determined.

  • mixed mode cohesive zone models for fracture of an adhesively bonded Polymer Matrix Composite
    Engineering Fracture Mechanics, 2006
    Co-Authors: Suyi Li, M D Thouless, Anthony M Waas, Jessica A Schroeder, Pablo D Zavattieri
    Abstract:

    Abstract As a direct extension of previous mode-I work on the adhesion of Composite joints, this paper uses a cohesive-zone approach to model the mixed-mode fracture of adhesive joints made from a Polymer–Matrix Composite. Mode-II cohesive-zone parameters were obtained using sandwich end-notch flexure specimens. These parameters were used directly with the previously determined mode-I parameters to predict the fracture and deformation of mixed-mode geometries. It was shown that numerical simulations provided quantitative predictions for these geometries, including predictions for both the strengths of the joints and for the failure mechanisms. In conjunction with the earlier work, these results demonstrate the use of cohesive-zone approaches for the design of adhesively bonded Composite joints, and indicate approaches for determining the relevant material properties to describe mixed-mode fracture.

  • use of a cohesive zone model to analyze the fracture of a fiber reinforced Polymer Matrix Composite
    Composites Science and Technology, 2005
    Co-Authors: Suyi Li, M D Thouless, Anthony M Waas, J A Schroeder, Pablo D Zavattieri
    Abstract:

    Abstract A cohesive-zone model for a fiber-reinforced Polymer–Matrix Composite is presented. A two-parameter model with a characteristic toughness and a characteristic strength can be used to predict the fracture of notched or cracked specimens. The two parameters can be determined by comparing numerical predictions to experimental observations of a fracture test. It is shown that the engineering behavior, in terms of strength, deformation and energy dissipation is well-described by such a two-parameter model, but when the characteristic dimensions of the Composite structure (e.g., the initial crack length or ligament length) are very small, extra details about the cohesive law such as the Matrix-cracking strength may be required. Finally, it is shown that a cohesive-zone model provides excellent predictions of transitions between stable and catastrophic crack growth in the Composite, and, hence, permits an understanding of the energy dissipation during fracture that occurs in these different regimes.

  • use of mode i cohesive zone models to describe the fracture of an adhesively bonded Polymer Matrix Composite
    Composites Science and Technology, 2005
    Co-Authors: Suyi Li, M D Thouless, Anthony M Waas, J A Schroeder, Pablo D Zavattieri
    Abstract:

    In this paper, the use of a cohesive-zone approach to model the mode-I fracture of adhesive joints made from a Polymer-Matrix Composite is demonstrated. Cohesive-zone parameters were obtained by matching numerical results to experimental observations. It is shown that there is a distinction between the characteristic strength of the interface associated with the toughness, and the intrinsic cohesive strength of the interface. While the characteristic strength and toughness are often sufficient to describe fracture in the presence of a crack, the intrinsic cohesive strength is also required to analyze some geometries that have very small characteristic dimensions or crack lengths. It is shown that cohesive-zone models accurately predict the behavior of the joints studied. In particular, not only are the strengths and deformations accurately described, but the transition between failure of the Composite and failure of the interface can also be predicted. This mode-I transition cannot be predicted by conventional fracture mechanics as it depends on both the energy-based and strength-based failure parameters associated with cohesive-zone models.