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Ballistic impact mitigation requires the development of protective armor applications from composite material systems with good energy absorption and penetration resistance against threats, e.g., metallic projectiles. In this aim, high-strength and high-stiffness soft fibrous composite materials (such as ultra-high molecular weight polyethylene—UHMWPE) are often used. The high specific strength feature is one of the main reasons for using these soft composite systems in ballistic impact applications. In the present investigation, experimental and computational finite element (FE) studies were carried out to investigate the ballistic behaviors of these soft layered composite targets. To this end, a new FE multi-scale analysis framework for ballistic simulations is offered. The proposed analysis presents a new meso-scale sublaminate material model, which is applied to Dyneema® cross-ply laminate in order to predict its behavior under ballistic impact. The sublaminate model is implemented within an explicit dynamic FE code to simulate the continuum response in each element. The sublaminate model assumes a through-thickness periodic stacking of repeated cross-ply configuration. In addition, a cohesive layer is introduced in the sublaminate model in order to simulate the delamination effect leading to the subsequent degradation and deletion of the elements. This new approach eliminates the widely used costly computational approach of using explicit cohesive elements installed at pre-specified potential delamination paths between the layers. Furthermore, in-plane damage modes (such as fiber tensile, and out-of-plane shearing) are also accounted for by employing failure criteria and strain-softening. The obtained quantitative results of ballistic impact simulations show good correlation when compared to a relatively wide range of experiments. Moreover, the simulations include evidence of capturing the main energy absorption mechanisms under high-velocity impact. The proposed modeling approach can be used as a useful armor design tool. [ABSTRACT FROM AUTHOR]

A nonlinear formulation of the high fidelity generalized method of cells (HFGMC) is offered for the micromechanical analysis of two and three-dimensional (3D) multiphase periodic composites with evolving matrix damage. To that end, the microplane constitutive modeling theory is integrated within the HFGMC to represent the nonlinear and strain softening of the matrix subcells. The nonlinear micromechanical formulation of both the HFGMC and the microplane theories are both developed and integrated in a nested fashion. The formulation of the parametric HFGMC, with independent geometrical mapping, is expanded and shown to be well suited for efficient nonlinear computational micromechanics. A new average virtual work integral form is proposed for the HFGMC method which allows for the definition of a generalized internal resisting force vector along with its corresponding symmetric stiffness matrix. Unlike the nodal displacement-based finite element (FE), the proposed HFGMC and its weak form are cast in terms of the work-conjugate average displacement and traction vectors, defined on the surfaces (faces) of the subcells. This allows direct interface continuity relations between the hexahedral subcells. The microplane theory is formulated kinematically using its transformed strain with a double split, namely the volumetric (V) and a deviatoric-tangential (DT) splits. The microplane model is implemented with simple 1D continuum damage laws and strain softening, which are used in the two split parts. The stress–strain behavior in the volumetric part has independent nonlinear behaviors in tension and compression. Several applications for doubly and triply periodic 3D composites with evolving matrix damage are presented with refined micromechanical analysis. The use of the microplane theory is shown to be an effective approach for damage analysis in the constituents of the composite unit-cell. The HFGMC micromechanics is well suited for integrating the microplane response and predicting the fiber-matrix spatial local fields including damage effects. The proposed integrated microplane and micromechanics frameworks can be extended to other heterogeneous composites with different mechanical behaviors, such as visco-elasticity, visco-plasticity, among others. [ABSTRACT FROM AUTHOR]

This paper introduces a new fully coupled micro thermal–electrical–mechanical (TEM) formulation for periodic multi-phase thermoelectric (TE) material systems and devices. The high fidelity generalized method of cells (HFGMC) micromechanical method is extended to account for the fully (three-way) coupled TEM effects including Seebeck, Peltier, and Joule heat. A special attention is directed towards the induced mechanical field which has often neglected in the literature. The three-dimensional HFGMC formulation is performed by analyzing an isolated periodic volume or a repeated unit-cell (RUC) and by subdividing it into sub-volumes (subcells). Interfacial continuity between adjacent subcells along with periodicity conditions are expressed in terms of average TEM fields and fluxes. The three TEM conservation laws are also expressed in a volume average over the subcell. A three-way coupled set of constitutive equations are used to express the thermoelectric, thermomechanical and electro–mechanical relations for each subcell. Applications are presented for the steady state solutions of the TEM field distributions in two cases. The first for a TE generator device that consists of an array of repeating RUC. The second is for multi-layered laminated composite with a repeating stack of layers including two layers reinforced with p-type and n-type inclusions. The steady-state stress distribution is shown to be a nonlinear solution to the system of coupled TEM governing equations. The new HFGMC-TEM micromodel is effective in establishing the overall (average) TEM constitutive laws for the equivalent homogenized medium along with the spatial distributions of different local fields within the RUC. [ABSTRACT FROM AUTHOR]

A novel collagen-based bio-composite was constructed from micro-crimped long collagen fiber bundles extracted from a soft coral embedded in alginate hydrogel matrix. The mechanical features of this bio-composite were studied for different fiber fractions and in longitudinal and transverse loading modes. The tensile modulus of the alginate hydrogel was 0.60±0.35MPa and in longitudinal collagen-reinforced construct it increased up to 9.71±2.80 for 50% fiber fraction. Ultimate tensile strength was elevated from 0.08±0.04MPa in matrix up to 1.21±0.29 for fiber fraction of 30%. The bio-composite demonstrated hyperelastic behavior similar to human native tissues. Additionally, a dedicated constitutive material model was developed to enable the prediction of the longitudinal mechanical behavior of the bio-composite. These findings will allow tailor-designed mechanical properties with a quantitatively controlled amount of fibers and their designed spatial arrangement. This unique bio-composite has the potential to be used for a wide range of engineered soft tissues. [ABSTRACT FROM AUTHOR]

Abstract: The recent two-dimensional (2D) parametric formulation of the high fidelity generalized method of cells (HFGMC) reported by the authors is generalized for the micromechanical analysis of three-dimensional (3D) multiphase composites with periodic microstructure. Arbitrary hexahedral subcell geometry is developed to discretize a triply periodic repeating unit-cell (RUC). Linear parametric-geometric mapping is employed to transform the arbitrary hexahedral subcell shapes from the physical space to an auxiliary orthogonal shape, where a complete quadratic displacement expansion is performed. Previously in the 2D case, additional three equations are needed in the form of average moments of equilibrium as a result of the inclusion of the bilinear terms. However, the present 3D parametric HFGMC formulation eliminates the need for such additional equations. This is achieved by expressing the coefficients of the full quadratic polynomial expansion of the subcell in terms of the side or face average-displacement vectors. The 2D parametric and orthogonal HFGMC are special cases of the present 3D formulation. The continuity of displacements and tractions, as well as the equilibrium equations, are imposed in the average (integral) sense as in the original HFGMC formulation. Each of the six sides (faces) of a subcell has an independent average displacement micro-variable vector which forms an energy-conjugate pair with the transformed average-traction vector. This allows generating symmetric stiffness matrices along with internal resisting vectors for the subcells which enhances the computational efficiency. The established new parametric 3D HFGMC equations are formulated and solution implementations are addressed. Several applications for triply periodic 3D composites are presented to demonstrate the general capability and varsity of the present parametric HFGMC method for refined micromechanical analysis by generating the spatial distributions of local stress fields. These applications include triply periodic composites with inclusions in the form of a cavity, spherical inclusion, ellipsoidal inclusion, and discontinuous aligned short fiber. A 3D repeating unit-cell for foam material composite is simulated. [Copyright &y& Elsevier]

Abstract: The high fidelity generalized method of cells (HFGMC) has been originally developed by as a micromechanical method for periodic multi-phase composite media. A computational implementation of the HFGMC equations has been proposed by to enhance numerical efficiency, still with direct reference to the HFGMC formulation. Later, the same computational implementation is recast as a new method called “finite volume direct averaging micromechanics” (FVDAM), starting by . The current discussion paper has two aims. The first is to show that the FVDAM is not a new method and that it has the same assumptions and identical governing equations as those originally derived by the HFGMC. The only difference is in the solution procedure where intermediate dependent variables, in the form of average displacements at the interfaces, are used instead of directly solving for the unknown micro-variables; the coefficients of the displacement polynomials. Thus, renaming the HFGMC micromodel to FVDAM has not been justified. In fact, () have shown that the same reduction of variables can be achieved by a simple static condensation carried out at the global system of equations instead of introducing intermediate variables. The second aim of this paper is to address misrepresentations in a recent discussion paper by the FVDAM authors claiming, in part, that the HFGMC method using parametric geometry of the subcells should follow their formulation (termed parametric FVDAM). We show that the latter is limited to an incomplete quadratic expansion of the displacement and an approximation in the form of a priori constant Jacobian of the parametric mapping. However, the HFGMC with arbitrary cell geometry, (), has been formulated in a direct and general manner, i.e. retaining the full quadratic expansion of the displacement together with the complete Jacobian. Thus, the parametric FVDAM is a special case of the parametric HFGMC, i.e. when the Jacobian is sampled and evaluated only at one point, namely the origin of the parametric coordinate system. The intended new contribution of to refined micromechanics and progressive damage has been completely ignored by the FVDAM-discussion paper. Therefore, in order to maintain scientific clarity, it is strongly advocated to preserve the original name of the HFGMC method, regardless of the different computational implementations used for solving the governing equations for both orthogonal and parametric geometries of the subcells. [Copyright &y& Elsevier]

Abstract: A new parametric formulation for high-fidelity generalized method of cells (HFGMC) is presented for the micromechanical analysis of multiphase periodic composites. To this end, a linear parametric and geometric mapping is employed to transform arbitrary quadrilateral cell shapes from the physical space to an auxiliary uniform square shapes. A complete quadratic displacement expansion is performed in the mapped space. Thus, a new bilinear term is added to the quadratic displacement expansion; unlike the original HFGMC for regular array of rectangular cells where this term in not required. The continuity of displacements, tractions, together with the periodicity and equilibrium conditions are imposed in the average sense, similar to the original HFGMC formulation, using both the physical and mapping variables. However, the addition of bilinear terms requires the introduction of the first averaged moments of the equilibrium equations. In order to demonstrate the ability the new HFGMC formulation, spatial stress fields are compared with analytical and numerical solutions of circular and elliptical fibers in an infinite medium. Furthermore, two progressive damage methodologies are coupled with the new HFGMC formulation in order to predict the strain softening and elastic degrading behaviors. The first methodology employs a cell extinction approach, while the second uses cohesive interfaces between the cells. Due to the strain softening, both damage methodologies require an iterative solution approach of the governing system nonlinear equations. Damage applications are presented for the transverse loading of composites with square and hexagonal repeating unit-cells (RUC). [ABSTRACT FROM AUTHOR]

A new cohesive micromechanical modeling framework is presented for the progressive damage analysis of laminated composite materials and structures. The cohesive micromechanics (CM) modeling approach is based on simplified 3D unit cell with incremental and damage formulations. The unidirectional CM model formulated in this paper is implemented in a local-global nonlinear damage modeling framework that recognizes the fiber and matrix constituents along with the cohesive interface/interphase subcells at the lower level. The cohesive elements are embedded between the fiber-fiber, fiber-matrix, and matrix-matrix subcells. Separate tension and compression traction-separation constitutive relations are used for the cohesive subcells in order to degrade the traction and internal resisting force across the plane between the two adjacent constituents. As a result, progressive damage modeling in the structural level can be achieved at the micromechanical level while maintaining the full advantage of using concurrent nonlinear micromechanical modeling prior and during damage progression spanning the entire structure. The proposed CM damage framework allows nonlinear anisotropic response, including strain softening, and damaged elastic loading/unloading behavior. Robust and efficient numerical stress correction algorithms have been also developed in order to satisfy the local traction continuity and strain compatibility of the micromechanical model. The effectiveness of the proposed modeling approach is demonstrated by predicting the response of composite plates with an open hole under tension and compression loading using available test results from the literature. [ABSTRACT FROM AUTHOR]

Abstract: The recent High Fidelity Generalized Method of Cells (HFGMC) micromechnical modeling framework of multiphase composites is formulated in a new form which facilitates its computational efficiency that allows an effective multiscale material–structural analysis. Towards this goal, incremental and total formulations of the governing equations are derived. A new stress update computational method is established to solve for the nonlinear material constituents along with the micromechanical equations. The method is well-suited for multiaxial finite increments of applied average stress or strain fields. Explicit matrix form of the HFGMC model is presented which allows an immediate and convenient computer implementation of the offered method. In particular, the offered derivations provide for the residual field vector (error) in its incremental and total forms along with an explicit expression for the Jacobian matrix. This enables the efficient iterative computational implementation of the HFGMC as a stand alone. Furthermore, the new formulation of the HFGMC is used to generate a nested local-global nonlinear finite element analysis of composite materials and structures. Applications are presented to demonstrate the efficiency of the proposed approach. These include the behavior of multiphase composites with nonlinearly elastic, elastoplastic and viscoplastic constituents. [Copyright &y& Elsevier]

Abstract: Two quantitative thermoelastic strain analysis (TSA) experimental methods are proposed to determine the surface strain fields in mechanically loaded orthotropic materials using the spatial distribution of temperature gradient measured from the surface. Cyclic loadings are applied to orthotropic composite specimens to achieve adiabatic conditions. The small change in surface temperatures that resulted from the change in the elastic strain energy is measured using a high sensitivity infrared (IR) camera that is synchronized with the applied loading. The first method is applied for layered orthotropic composites with a coat layer made of isotropic or in-plane transversely isotropic material. In this case, one material parameter (pre-calibrated from the surface) is required to map the strain invariant to the temperature gradients. The proposed method can be used together with Lekhnitskii’s elasticity solution to quantify the full strain field and determine mixed-mode stress intensity factors (SIFs) for crack tips in composite plates subjected to off-axis loading. The second method is formulated for orthotropic layers without a coat and it requires thermo-mechanical calibrations for two material parameters aligned with the material axes. The virtual crack closure technique (VCCT), Lekhnitskii’s and Savin’s elasticity solutions, and finite element (FE) analyses are used for demonstrations and validations of the second experimental method. The SIFs from the TSA methods are very sensitive to the uncertainty in the location of the crack tip and the unknown inelastic or damage zone size around the crack tip. The two experimental methods are effective in generating the strain fields around notched and other FRP composites. [Copyright &y& Elsevier]

Abstract: An effective integration of a three-dimensional (3D) micromechanical and finite element (FE) modeling framework is proposed for the analysis of thick-section fiber reinforced plastic (FRP) composite materials and structures. The proposed modeling framework is applied to a pultruded composite system. It consists of two alternating layers with unidirectional fiber (roving) and continuous filaments mat (CFM) reinforcements. Nonlinear 3D micromechanical models representing the different composite layers are used to generate through-thickness composite’s effective responses. Approximate traction continuity and strain compatibility relations in the micromechanical models are expressed in terms of the average stresses and strains of the sub-cells that recognize the fiber and matrix responses. The nonlinear elastic behavior is attributed only to the matrix sub-cells. The nested nonlinear micromechanical models are implemented at each integration (Gaussian) point in the FE structural analyses. A linearized structural response will produce a trial strain increment for each Gaussian integration point and an iterative solution is performed until a structural-level convergence criterion is met. At every iteration, the micromechanical models are called to provide effective material responses. An efficient numerical implementation of the micromodels is required in order to achieve accurate solutions and accelerate the structural-level convergence. Thus, stress correction algorithm is performed in each level of the nested micromodels. Axial tension and compression tests on off-axis E-glass/vinylester coupons and notched specimens are used to calibrate the in situ material properties of the fiber and matrix and verify the prediction ability of the nested micromodels. The nonlinear calibration of the matrix is done by using the overall axial shear stress–strain response generated from Iosipescu (V-notched) specimens. Good agreement is shown for all off-axis angles when comparing the experimental stress–strain curves with those predicted by the analyses with the proposed micromodels. [Copyright &y& Elsevier]

This paper presents an integrated micromechanical–structural framework for local–global nonlinear and time-dependent analysis of fiber reinforced polymer composite materials and structures. The proposed modeling approach involves nested multiscale micromodels for unidirectional and continuous filament mat (CFM) layers. In addition, a sublaminate model is used to provide a three-dimensional (3D) effective anisotropic and continuum response to represent the nonlinear viscoelastic behavior of a through-thickness periodical multilayered material system. The 3D multiscale material framework is integrated with a displacement-based finite-element code to perform structural analyses. The time-dependent responses in the unidirectional and CFM layers are exclusively attributed to their matrix constituents. The Schapery nonlinear viscoelastic model is used with a newly developed recursive–iterative integration method applied for the polymeric matrix. The fiber medium is linear and transversely isotropic. The in situ long-term response of the matrix constituents is calibrated and verified using long-term creep coupon tests. Good prediction ability is shown by the proposed framework for the overall viscoelastic behavior of the layered material. Material and geometric nonlinearities of I-shape thick composite columns, having vinylester resin reinforced with E-glass unidirectional (roving) and CFM layers, are studied to illustrate the capability of the multiscale material-structural framework. Nonlinear elastic behavior and creep collapse analyses of the I-shape column are performed. The recursive–iterative and stress correction algorithms, which are implemented and executed simultaneously at each material scale, enhance equilibrium and avoid misleading convergent states. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a combined method for modeling the mode-I and II crack growth behavior in thick-section fiber reinforced polymeric composites having a nonlinear material response. The experimental part of this study includes crack growth tests of a thick composite material system manufactured using the pultrusion process. It consists of alternating layers of E-glass unidirectional roving and continuous filament mats in a polymeric matrix. Integrated micromechanical and cohesive finite element (FE) models are used to simulate the crack growth response in eccentrically loaded single-edge-notch, (tension), ESE(T) and notched butterfly specimens. Micromechanical constitutive models for the mat and the roving layers are used to generate the effective nonlinear material behavior from the in situ fiber and matrix responses. The validity of the numerical modeling approach before the onset of crack growth is investigated using an infrared thermal method. Cohesive FE models are calibrated and used to simulate the complete crack growth behavior for different crack configurations. The proposed integrated framework of multi-scale material models with cohesive fracture models is shown to be an effective method for predicting the structural and material responses including failure load and crack growth in thick-section fiber reinforced polymeric composites. [Copyright &y& Elsevier]

A multiscale modeling framework for the long-term behavior of fiber-reinforced-polymeric (FRP) laminated composite materials and structures is presented. Each unidirectional layer is idealized as a doubly periodic array of rectangular fibers. The authors' previously developed unit cell with four fiber and matrix subcells is used. The constitutive models for the elastic linear fiber and nonlinear viscoelastic matrix constituents are performed at the lowest level of the micromodel. This nonlinear micromodel is integrated with both three-dimensional and shellbased finite elements. A plane-stress constraint is added to the three-dimensional micromodel in the case where shell elements are used. Long-term experimental creep data from the literature for graphite/epoxy are used in order to characterize the material properties. The effect of material nonlinearity on the long-term behavior of FRP composites is also investigated. Applications are presented for long-term creep responses of a notched composite panel under surface pressure and a single lap joint under tensile load. This modeling approach is general and can include temperature, moisture, and physical aging effects. [ABSTRACT FROM AUTHOR]

The present study introduces analytical and numerical formulations in order to derive the effective nonlinear viscoelastic response of pultruded composite materials and structures. The studied pultruded composite system consists of two alternating layers reinforced with E-glass roving and continuous filament mat (CFM). Two 3D micromechanical models are used for the layers with roving and CFM, each having a unit-cell with four fiber and matrix subcells. A sublaminate model is also used to generate a nonlinear equivalent continuum of the layered medium. A new recursive-iterative procedure is introduced to integrate the Schapery nonlinear viscoelastic model used for the isotropic matrix subcells of the micromodels. An iterative numerical algorithm with predictor–corrector type steps is formulated for the sublaminate model and is used to interface with a nonlinear finite-element (FE). Off-axis creep compression and tension tests, with and without a circular hole, are performed for E-glass/vinylester and polyester pultruded plates to calibrate and predict the nonlinear viscoelastic response. The multiscale modeling approach shows good linear and nonlinear viscoelastic prediction compared with the experimental results. [Copyright &y& Elsevier]

A modified Arcan fixture with butterfly specimen geometry is designed to measure the in-plane shear response of thick-section pultruded FRP composites. The objective of the proposed testing method is to determine both the material shear stiffness and its non-linear stress–strain response up to ultimate stress. The tested pultruded specimens include two alternating layers in the form of a unidirectional glass roving and continuous filament mat layers. Finite element models for the butterfly specimen are generated to examine the effects of the notch radius and material orthotropy on the uniformity and distribution of stresses in the gage area. Butterfly geometry with a blunted notch and roving orientation parallel to the applied load is found to have a uniform shear stress in the gage section. The axial-shear response is measured under different biaxial stress states by varying the angle of the applied load. The tested non-linear shear stress–strain responses compare favorably to results previously obtained from off-axis compression tests used to calibrate a multi-axial constitutive model for this material. Results from strain gage and Infrared thermography measurements provide confirmation for the effectiveness of the fixture and the specimen geometry. [Copyright &y& Elsevier]

This paper presents an integrated micromechanical and structural framework for the nonlinear viscoelastic analysis of laminated composite materials and structures. Each unidirectional lamina is idealized using the Aboudi four-cell micromodel with incremental formulation in terms of the average strain and stress in the subcells. The fiber medium is considered as transversely isotropic and linear elastic. The Schapery nonlinear viscoelastic model is used to describe the isotropic viscoelastic behavior of the matrix subcells. A previously developed recursive–iterative method is employed for the numerical integration of the Schapery model. The subcells'' constitutive models are nested through a numerical stress-update algorithm. The latter is based on a predictor–corrector scheme that satisfies the fiber and matrix viscoelastic constitutive relations along with the micromechanical equations in the form of traction continuity and strain compatibility between the subcells. The effect of physical aging on creep is also examined. Several experimental creep tests on off-axis specimen, available in the literature, are used to validate the formulation. The proposed material and structural framework is general and can easily incorporate temperature, moisture, and physical aging effects. The micromechanical model is numerically implemented within a shell-based nonlinear finite element (FE) by imposing a plane stress constraint on its 3D formulation. Examples for nonlinear viscoelastic structural analyses are demonstrated for a laminated panel and a composite ring. [Copyright &y& Elsevier]

Coupon tests are investigated and used to calibrate three-dimensional (3D) micromechanical models and to verify their prediction for the nonlinear elastic behavior of pultruded fiber reinforced plastic composites. The tested composite material system is made from E-glass/vinylester pultruded composite plate with both glass roving and continuous filament mat (CFM) layers. Tension, compression, and shear tests were performed, using off-axis coupons cut with different roving reinforcement orientations. The overall linear elastic properties are identified along with the nonlinear stress–strain behavior under in-plane multi-axial tension and compression loading. The tests were carried out for coupons with off-axis angles: 0, 15, 30,45, 60, and 90°, where each test was repeated three to five times. Finite element analyses are used to simulate the off-axis tests and examine the effects of coupon geometry, end-clamping condition, and off-axis orientation, on the spatial distribution of the axial strains at the center of the coupons. Lower initial elastic modulus and a softer nonlinear stress–strain responses were consistently observed in the tension tests compared to those in compression, for all off-axis (roving) orientations. The nonlinear behavior can be attributed to the relatively low overall fiber volume fractions (FVFs) in pultruded composites and the existence of manufacturing defects, such as voids and microcracks. It is also shown that the end-clamping effects for the tested geometry are relatively small at the center and allow extracting the nonlinear stress–strain response of the anisotropic material. The analytical part of this study includes two (3D) micromechanical models for the roving and CFM layers. Shear tests are used to calibrate the in situ nonlinear elastic properties of the matrix. Good prediction ability is shown by the proposed micromodels in capturing the stress–strain behavior in the off-axis tests. [Copyright &y& Elsevier]

A new coupled micromechanical-damage formulation is presented by directly integrating the phase-field (PF) modeling approach for fracture and damage with the Parametric High-Fidelity-Generalized-Method-of-Cells (PHFGMC) micromechanical model. The combined PHFGMC-PF approach is proposed for progressive damage analysis of multi-phase heterogeneous composites with evolving microstructure subject to general multi-axial remote loading. New variational equations are introduced to couple the macro/micro deformation and PF variables of the discrete finite volumes (subcells). An iterative computational formulation is also presented for the numerical solution of the overall nonlinear equations. The proposed approach can accommodate various phase-field damage models and fracture energy approximations. Two PF damage laws, available in the literature, are implemented. The proposed PHFGMC-PF model verification is first accomplished by solving the single-edge crack problem under tension and shear and comparing the results to a finite element PF (FE-PF) analysis. Results of the presented case studies demonstrate a comparable ability of the PHFGMC-PF to solve similar FE-PF non-periodic problems. Applications are presented for progressive damage of carbon-fiber-reinforced (CRP) composites. The PHFGMC-PF in-situ elastic and fracture properties are calibrated for the carbon-reinforced polymer IM7/977-3 composite material system at the fiber–interface–matrix constituents. The micromechanics-PF model can capture the composite overall nonlinear mechanical and damage responses compared to experimental data. [ABSTRACT FROM AUTHOR]

Abstract: Stochastic Markov chain methods are applied to model the fatigue damage evolution in composite materials subjected to cyclic mechanical loadings and monitored by infrared thermography (IR-T) techniques. The IR signal from the surface of open-hole S2-glass/E733FR laminates is captured concurrently during constant amplitude fatigue loadings. The IR testing has high thermal sensitivity below 10mK and the image integration is synchronized with the mechanical loading. A thermoelastic stress analysis (TSA) technique using thermomechanics is used to process the IR fields and relate them to surface stresses and strains. Damage metric is developed for the composite samples based on an area stress reduction threshold. The applicability and validity of the proposed TSA damage index is evaluated by comparing it to the classical overall stiffness reduction measured at select fatigue intervals using an extensometer. The IR-TSA damage index at the last fatigue cycle is used to calibrate the Markov chain models (MCMs). The damage predictions of the MCMs are then examined at different fatigue cycles. A new method is proposed to construct a stochastic S–N curve utilizing the MCMs. The proposed IR-TSA with Markov stochastics is shown to be very effective in predicting the damage evolution and allowed constructing a wide-range of stochastic S–N curves for several composite material systems including experimental results from the literature. [Copyright &y& Elsevier]

The parametric high fidelity generalized method of cells (PHFGMC) is an advanced micromechanical method that can be used for the nonlinear and failure analysis of several composite materials. The computational effort required for studying the nonlinear and damage multiaxial behavior is relatively small, depending on the size of the discretized repeating unit cell (RUC). However, it is computationally challenging, if not impossible, to integrate refined nonlinear micromechanical models within a multiscale analysis of composite structures. This is due to the thousands or more RUC models required at the integration points within a multiscale finite-element (FE) model of laminated structures. To that end, we propose a new artificial neural network (ANN) based micromechanical modeling framework, termed ANN-PHFGMC, for exploring the nonlinear behavior of fiber-reinforced polymeric (FRP) materials. Pre-simulated mechanical stress–strain responses and behaviors are determined using the PHFGMC to generate a multiaxial training database for the ANN micromodel. The simulated training data is founded on the PHFGMC-RUC results based on a hexagonal RUC. The PHFGMC effective stress–strain responses for different applied multiaxial strain paths are divided into two sets of data; one for the training and the other for verifying the trained ANN-PHFGMC model. The resulting trained ANN-PHFGMC is accurate, with less than 5% error in the verified predictions. The ANN-PHFGMC can be used as a stand-alone or embedded as a surrogate proxy model within a multiscale analysis of composite structures. Next, the ANN-PHFGMC model is integrated within a commercial explicit FE code for low-velocity impact (LVI) analysis of laminated composite plates. Multiscale LVI analyses are performed for two composite plates with different layups. Further, results are compared to experimental data to demonstrate the new model's ability to integrate refined nonlinear micromechanical models within a multiscale analysis. [ABSTRACT FROM AUTHOR]

Micromechanically doubly periodic parametric High Fidelity Generalized Method of Cells, in conjunctions with continuum damage mechanics considerations, is presented to determine failure envelopes of unidirectional composite materials. The methods is based on an incremental procedure in which the local damage variables and global stresses are monitored during the strain softening to provide the value of the envelopes at which ultimate failure occurs. The micromechanically established failure envelopes are compared with the well known macrolevel based failure surfaces and with experimental data of multiaxial failure stresses found in the literature. It is shown that the new micromechanical failure envelopes are effective in predicting the multi-axis stress failures. [ABSTRACT FROM AUTHOR]

Abstract: This study deals with the mechanical properties of soft polymeric composite laminates made with Ultra-high-molecular-weight polyethylene (UHMWP) fibers, often used for ballistic protection. Two new mechanical test setups, tensile and axial shear, are proposed to characterize the mechanical behavior of a laminated system made of the commercial Dyneema HB26 cross-ply multi-layered plates. The suitable tension setup is found to be close to a bow-tie like geometry while the axial shear is closer to a butterfly shape. The overall linear and nonlinear behaviors under both tension and shear are investigated. Microstructure of the fibers along with results from the mechanical tests, are used to calibrate a micromechanical model for this material system. [Copyright &y& Elsevier]