Showing papers in "Journal of Composite Materials in 1985"
TL;DR: In this article, a systematic classification of the effects of transverse cracking on the stress-strain response of composite laminates is presented, and an assessment of the ply discount method for predicting stiffness reductions at crack saturation is also made.
Abstract: A systematic classification of the effects of transverse cracking on the stress-strain response of composite laminates is presented. Stiffness reductions resulting from transverse cracking in glass/epoxy and graphite/epoxy laminates from crack initiation to crack saturation are predicted using the stiffness-damage relationships developed by the author in a previous work. Good agreement with the experimental results is found. An assessment of the ply discount method for predicting stiffness reductions at crack saturation is also made.
369 citations
TL;DR: In this article, an analytical model is developed to assess the compressive strength criticality of near-surface interlaminar defects in laminated composites, where the growth conditions and growth behavior of this defect are studied by breaking the overall problem into an elastic stability problem and a fracture problem.
Abstract: An analytical model is developed to assess the compressive strength criticality of near-surface interlaminar defects in laminated composites. The delaminated region is elliptic in shape, separating a thick isotropic plate from a thin orthotropic layer whose material axes coincide with the ellipse axes. The growth conditions and growth behavior of this defect are studied by breaking the overall problem into an elastic stability problem and a fracture problem. Post-buckling solution for the elliptic section is obtained using the Rayleigh-Ritz method while an energy balance criterion based on a self-similar disbond growth governs the fracture. The parameters controlling the growth or arrest of the delamination damage are identified as the fracture energy, disbond depth and elastic properties of the materials from both sides of the delaminating interface. By varying the degree of material anisotropy relative to the loading axis a range in growth behavior was found including stable or unstable crack growth parallel to or normal to the loading axis.
311 citations
TL;DR: In this article, a one-dimensional transient thermal model with an nth order ap proximation for the rate of decomposition of a polymer composite material undergoing decomposition was applied.
Abstract: The thermal response of a polymer composite material undergoing decomposition has been modeled. A one-dimensional transient thermal model with an nth order ap proximation for the rate of decomposition was applied. The model was tested by ex perimentally measuring the temperature profiles during decomposition for a glass- filled phenol-formaldehyde polymer composite. Additionally, the specific heat and thermal conductivity of the virgin and char components, heat of decomposition, and the kinetic parameters were experimentally determined and used as input to the model. The predicted temperature profiles are in good agreement with experimental temperatures obtained using a radiant heat flux apparatus.
266 citations
TL;DR: In this paper, the impact response behavior of initially stressed composite laminates is investigated using the finite element method, where an experimentally established contact law is incorporated into the program and the Newmark time integration algorithm is used for solving the time dependent equations of the plate and the impactor.
Abstract: The impact response behavior of initially stressed composite laminates is investigated using the finite element method. An experimentally established contact law is incorporated into the finite element program. The Newmark time integration algorithm is used for solving the time dependent equations of the plate and the impactor. Numerical results, including the contact force history, deflection, and strain in the plate, are presented. Effects of impact velocity, initial stress, and the mass and size of the impactor are discussed.
252 citations
TL;DR: In this paper, the stress field in a coated continuous fiber composite subjected to thermo- mechanical loadings is calculated by use of four concentric circular cylinders model and the target material is Ni- or SiC-...
Abstract: The stress field in a coated continuous fiber composite subjected to thermo- mechanical loadings is calculated by use of four concentric circular cylinders model. The target material is Ni- or SiC-...
229 citations
TL;DR: Experimental data of the three-dimensional problem of impact of a flat strip by a spherical impactor are presented and interpreted qualitatively by comparison with a plane-strain numerical analysis of an infinitely wide plate impacted by a cylindrical impactor.
Abstract: Experimental data of the three-dimensional problem of impact of a flat strip by a spherical impactor are presented and interpreted qualitatively by comparison with a plane-strain numerical analysis of an infinitely wide plate impacted by a cylindrical impactor. The role of transverse shear stress in proximal and middle layer crack initiation is established. A detailed presentation of damage is provided with exact delamination zones. The basic conclusions drawn establish a basis for further research in understanding impact induced fracture in composites.
215 citations
TL;DR: In this paper, the buckling of an elliptic delamination embedded near the surface of a thick quasi-isotropic laminate was predicted using finite element and Rayleigh-Ritz methods.
Abstract: The buckling of an elliptic delamination embedded near the surface of a thick quasi-isotropic laminate was predicted. The thickness of the delaminated ply group (the sublaminate) was assumed to be small compared to the total laminate thickness. Finite-element and Rayleigh-Ritz methods were used for the analyses. The Rayleigh-Ritz method was found to be simple, inexpensive, and accurate, except for highly anisotropic delaminated regions. Effects of delamination shape and orientation, material anisotropy, and layup on buckling strains were examined. Results show that: (1) the stress state around the delaminated region is biaxial, which may lead to buckling when the laminate is loaded in tension; (2) buckling strains for multi-directional fiber sublaminates generally are bounded by those for the 0 deg and 90 deg unidirectional sublaminates; and (3) the direction of elongation of the sublaminate that has the lowest buckling strain correlates with the delamination growth direction.
196 citations
TL;DR: In this paper, the authors evaluated stiffnesses and compliances, thermal expansion coefficients, and stress and strain averages for a fibrous composite lamina which contains a given density of open transverse cracks and is subjected to uniform mechanical loads and thermal changes.
Abstract: Overall stiffnesses and compliances, thermal expansion coefficients, and stress and strain averages are evaluated for a fibrous composite lamina which contains a given density of open transverse cracks and is subjected to uniform mechanical loads and thermal changes. The evaluation procedure is based on the self-consistent method and is similar, in principle, to that used in finding elastic constants of unidirectional com posites.
193 citations
TL;DR: In this article, a conceptually simple mixed mode fracture analysis method is presented for the prediction of tensile matrix failure in composite laminates, which makes use of a mixed mode s...
Abstract: A conceptually simple mixed mode fracture analysis method is presented for the prediction of tensile matrix failure in composite laminates. The analysis technique, which makes use of a mixed mode s...
144 citations
TL;DR: In this article, the elastic moduli of fabric composites are con ducted in order to evaluate the theoretical predictions developed by the authors in their previous work, and the experimental results coincide very well with the theory for 8 harness satin carbon/epoxy systems.
Abstract: Some experiments for measuring the elastic moduli of fabric composites are con ducted in order to evaluate the theoretical predictions developed by the authors in their previous work. Experimental results coincide very well with the theory for 8 harness satin carbon/epoxy systems. There exists some discrepancy between theories for con strained and unconstrained local warping in the case of plain weave composites. Ex perimental results are bounded by these two theories. The dependency of elastic moduli on laminate ply number is discovered in plain weave composites. The ratio of ply thickness to thread width is also a very important parameter, which strongly affects the elastic moduli of plain weave composites. The in-plane shear modulus of fabric composites is mainly influenced by fiber volume fraction, which varies linearly with ng. Off-axis properties of fabric composites are measured and compared with theories. The experimental results essentially confirm the validity of the author's theoretical predict...
105 citations
TL;DR: In this article, a formulation, an efficient solution procedure, a microcomputer program, and a graphics routine for an anisotropic symmetrically laminated beam finite element in cluding the effect of shear deformation is introduced.
Abstract: A formulation, an efficient solution procedure, a microcomputer program, and a graphics routine for an anisotropic symmetrically laminated beam finite element in cluding the effect of shear deformation is introduced. The emphasis of the formulation and solution procedure is for simplicity, efficiency, and easy implementation on microcomputers. The element possesses six d.o.f.'s at each of the two nodes: trans verse deflection and slope due to bending and shear, respectively, and a twisting angle and its derivative with respect to the beam axis. The formulation, solution procedure, and the program have been evaluated by performing a systematic choice of examples; whenever possible, the present solutions are compared with alternative existing solu tions.
TL;DR: In this paper, a criterion for predicting the direction of crack extension in orthotropic composite materials is presented, based upon the normal stress and the anisotropic tensile strength on arbitrary planes about the tip of a crack.
Abstract: A criterion for predicting the direction of crack extension in orthotropic composite materials is presented. The criterion is based upon the normal stress and the anisotropic tensile strength on arbitrary planes about the tip of a crack. Results are obtained, via finite element solutions, for: (1) isotropic mixed mode fracture, (2) cracks in unidirectional off-axis slotted composite tensile coupons and (3) cracks in cross plied laminates. Comparisons are made with other theories and experimental results.
TL;DR: In this article, a review of recent experimental work on the macroscopic rheological properties of suspensions of rod-like particles in Newtonian and non-Newtonian fluids is reviewed.
Abstract: Recent experimental work on the macroscopic rheological properties of suspensions of rodlike particles in Newtonian and non-Newtonian fluids is reviewed. Correlations are proposed for the shear viscosity-shear rate relationship for semi-concentrated and concentrated suspensions. In the former case, shear thinning behavior is found with the slope of the power law region depending upon fiber aspect ratio. For the concen trated systems, the data are substantially independent of volume fraction and aspect ratio and show slight shear thinning.
TL;DR: In this paper, two analytical methods are developed for studying the buckling stability of the delaminated composites. But they are based on the well-known Rayleigh-Ritz method, including transverse shear in the composite and distorsional deformation in the ligament.
Abstract: The compressive stability of delaminated random short-fiber composites is con sidered. A mechanistic model is introduced for the problem. Both buckling stability and crack stability (i.e., delamination growth) are investigated. Two analytical methods are developed for studying the buckling stability of the delaminated com posites. The first is formulated on the basis of the well-known Rayleigh-Ritz method, including transverse shear in the composite and distorsional deformation in the delaminated ligament. The second method employs a plane-elasticity, finite-element buckling analysis. Both local buckling and coupled global and local buckling are ex amined. A fracture mechanics approach is used to study the possible compressive crack growth at buckling. The validity of the model and the accuracy and efficiency of the methods of analysis are demonstrated and discussed.
TL;DR: In this article, a quasi-static thermal stress response and failure behavior of graphite/epoxy lam inated plates under combined intense thermal and mechanical loadings was investigated, and the temperature field is obtai...
Abstract: Quasi-static thermal stress response and failure behavior of graphite/epoxy lam inated plates under combined intense thermal and mechanical loadings are investigated. The temperature field is obtai...
TL;DR: In this paper, the basic mechanics and mechanisms of compressive stability of delaminated random short-fiber composites are studied, and an experimental program, employing an SMC-R50 composite with built-in delaminations, is conducted to evaluate the validity of the mechanistic model and to demonstrate further the accuracy of the methods of analysis developed in the associate paper.
Abstract: The basic mechanics and mechanisms of compressive stability of delaminated random short-fiber composites are studied. An experimental program, employing an SMC-R50 composite with built-in delaminations, is conducted to evaluate the validity of the mechanistic model and to demonstrate further the accuracy of the methods of analysis developed in the associate paper [1]. Excellent agreement between experimen tal results and analytical solutions is observed. Based on the analytical development, the fundamental compressive stability behavior of delaminated short-fiber composites is investigated by a comprehensive parametric study. The influence of delamination length, crack position, number of delaminations, and composite plate length on the critical compressive stress and buckling modes is analyzed in detail. Possible crack growth in the delaminated composite subjected to in-plane compression is also studied.
TL;DR: In this paper, the use of double cantilever beam specimens for measuring the mode I in terlaminar fracture toughness was critically evaluated, and experiments were performed with unidirectional composites to measure the fracture toughness.
Abstract: The use of slender double cantilever beam specimens for measuring the mode I in terlaminar fracture toughness was critically evaluated. Experiments were performed with unidirectional composites to ...
TL;DR: In this article, the effect of the volume ratio of the consti tuents and the degree of dispersion of the types of fibers is considered and the existence of the "hybrid effect" for strain is shown along with its sensitivity to volume ratio and dispersion.
Abstract: The basic chain-of-bundles probability model is modified so that any unidirectional intraply hybrid composite consisting of two types of fibers can be modeled. The method of analysis is the Monte Carlo simulation technique which allows for many dif ferent types of hybrids to be analyzed. The effect of the volume ratio of the consti tuents and the degree of dispersion of the types of fibers is considered. The existence of the "hybrid effect" for strain is shown along with its sensitivity to volume ratio and dispersion. The Weibull distribution function is shown to be a good representation for the hybrid breaking strain.
TL;DR: In this article, the static and dynamic stress concentration factors in three dimensional intermingled and interlaminated hybrid composites were derived using the inverse Laplace transform and the first six terms of the asymptotic expression.
Abstract: HE KNOWLEDGE OF STRESS CONCENTRATIONS INDUCED BY FIBER BREAKTages in composites is basic to the understanding of the strength and fracture characteristics of composites. Fukuda, Fukunaga and Chou, among others, [1-3] have studied the static stress concentration factors in unidirectional fiber composites. They applied the results to examine the statistical failure behavior of hybrid and non-hybrid composites with continuous fibers. Hikami and Chou [4] have also investigated the static stress concentration in discontinuous fiber composites arising from the arrays of fiber-ends. The problem of dynamic stress concentration due to fiber breakage in a composite sheet was first considered by Hedgepeth [5] using the shear-lag theory. Ji, Hsiao and Chou [6] adopted this approach and applied it to calculate the stress concentration factors in a two-layered interlaminated hybrid composite. The result was used to explain the &dquo;hybrid effect&dquo; often observed in hybrids composed of low elongation and high elongation fibers. Tai [7] further extended this approach to consider static and dynamic stress concentration factors in three dimensional intermingled and interlaminated hybrid composites. Tai introduced the asymptotic approach for inverse Laplace transform and used the first six terms of the asymptotic expression.
TL;DR: In this article, an approximate theory of the bending of cross-ply fiber-reinforced composites that is simpler than the exact theory of elasticity but is capable of accommodating any given displacement boundary conditions and arbi trarily varying side loads is presented.
Abstract: The Saint-Venant theory of beams cannot account for constraints against cross- sectional warping, and for this reason it gives results that are inaccurate near fixed ends and at points where the warping changes abruptly, as under concentrated side loads. In highly anisotropic materials such as fiber-reinforced composites, the cumulative effect of such inaccuracies may be significant in some circumstances.In the present paper we present an approximate theory of the bending of cross-ply fiber-reinforced composites that is simpler than the exact theory of elasticity but is capable of accommodating any given displacement boundary conditions and arbi trarily varying side loads. As an illustration, the theory is applied to the problem of a tip-loaded cantilever with a fixed end. In this problem the theoretical results agree with elementary beam theory (with a particular choice of the shear correction factor) except in a relatively long end-effect region near the clamped end.To test the theory, cantilever specim...
TL;DR: In this article, the stresses in transparent glass-epoxy plates loaded by a steel pin through a hole were determined experimentally using photoelasticity, and the stresses around the hole edge, across the net section, along the shear-out line, and on the centerline below the hole for quasi-isotropic, unidirectional, and angle-ply plates were shown.
Abstract: The stresses in transparent glass-epoxy plates loaded by a steel pin through a hole were determined experimentally using photoelasticity. The paper presents the stresses around the hole edge, across the net section, along the shear-out line, and on the centerline below the hole for quasi-isotropic, unidirectional, and angle-ply plates. Stresses in an isotropic comparison specimen are also presented. Stress concentration factors for several locations around the plates are tabulated. The paper discusses the experimental approach and the isochromatic and isoclinic fringe patterns for the four plates are shown.
TL;DR: In this article, the effects of impactor size on the damage-growth and the degree of damage in SMC-R50 composite plates were investigated and it was found that the damagezone size as well as the tensile strength and stiffness are strongly dependent on the impactors size.
Abstract: An experimental investigation was carried out to study effects of impactor size on the damage-growth and the degree of damage in SMC-R50 composite plates. Plane- ended cylindrical steel impactors of 9.7 mm in diameter were chosen to inflict impact damage in the impact energy range from 15 to 52 N-m using a gas gun facility. The im pact velocity range was adjusted for each impactor corresponding to their sizes (25.4, 38.1 and 50.8 mm long) such that the impact energy levels can be maintained constant. The damage-zone size as well as the tensile strength and stiffness are found to be strongly dependent on the impactor size. Impact energy is found not to be a governing parameter for damage-growth and degree of damage that can take into account the im pactor size.
TL;DR: In this paper, the effects of pressure and temperature on time-dependent changes in physical/ mechanical properties of graphite/epoxy composites were investigated and an explanation was offered in terms of types and mechanisms of molecular events that occur in the glassy state.
Abstract: Effects of pressure and temperature on time-dependent changes in physical/ mechanical properties of graphite/epoxy composites were investigated. Samples from an eight-ply thick laminate of commercially used composites were cured, post-cured and then quenched to environments of various temperature and pressure. Time- dependent changes in their properties were analyzed by calorimetric and dynamic mechanical measurements. An increase in the glass transition temperature was found to occur at longer aging times. The rate of this process was enhanced by an increase in temperature and/or a decrease in pressure. An explanation was offered in terms of types and mechanisms of molecular events that occur in the glassy state. Physical aging, i.e. a time-dependent decrease in free volume (and enthalpy) takes place during the first stage of aging, but is not the sole mechanism responsible for the observed in crease in T g. Here, experimental results were checked against theoretical predictions based upon the free volum...
TL;DR: In this paper, the load-deformation behavior of braided ±45-deg graphite/epoxy cylinders with integrally-formed braided and machined holes has been investigated.
Abstract: The load-deformation behavior of braided ±45-deg graphite/epoxy cylinders with integrally-formed braided and machined holes has been investigated. Axial tension or compression was applied to the cylinders via pairs of diametrically-opposed holes at the mid-length of the specimens. Pin-joint bearing tests were conducted on another set of specimens. Strains were measured around the hole and at a range of locations along the cylinder length and circumference. The strain concentration effects and failure modes are illustrated and discussed. Integrally-formed braided holes are seen to provide an in creased joint bearing strength compared with machined holes in the composite materials studied.
TL;DR: In this article, the authors investigated the transient thermal stress problem of a rectangular slab, which possesses both thermal and elastic orthotropy, when held at a con stant temperature is suddenly subjected to an arbitrary temperature variation along one of its edges.
Abstract: This paper investigates the transient thermal stress problem of a rectangular slab, which possesses both thermal and elastic orthotropy. The slab initially held at a con stant temperature is suddenly subjected to an arbitrary temperature variation along one of its edges. Based upon the solution of transient temperature field, the thermal stress analysis is performed based upon the further development of a displacement- potential approach. The complete stress field has been obtained in closed forms. Numerical results for a typical unidirectional fiber composite have demonstrated high concentration of thermal stresses far exceeding those generated in steady state thermal environment.
TL;DR: In this paper, a theoretical model for estimating the effective elastic modulus of particulate hybrid composites is proposed, in which a concept of equivalent virtual volume fraction is introduced to take interaction among a matrix and inclusions into account.
Abstract: A theoretical model for estimating the effective elastic modulus of particulate hybrid composites is proposed. A concept of "equivalent virtual volume fraction" is in troduced in order to take interaction among a matrix and inclusions into account. The model is illustrated by the effective shear modulus of particulate hybrid composites based upon a modified self-consistent method for two-phase composites. The obtained results reflect the influence of the matrix phase geometry more adequately than simple "self-consistent" models.
TL;DR: In this article, a stress-based finite element analysis is used to analyze a Kevlar 49/epoxy monolayer containing a single, preexisting fiber break and a residual frictional interface stress after the primary bond fails.
Abstract: A stress-based finite element analysis, formulated within the context of a shear-lag theory, is used to analyze a Kevlar 49/epoxy monolayer containing a single, preexisting fiber break. The highest and most localized stress concentration occurs when the epoxy matrix is idealized as linearly elastic and perfectly bonded to the fibers. This calculation suggests, however, that the fiber-matrix bond strength will be exceeded at relatively low load levels and fiber-matrix debonding will occur. Calculations which permit debond ing and also consider a residual frictional interface stress after the primary bond fails are presented. When there is no residual frictional stress, the fiber stress concentration is fully relieved and debonding occurs along the entire fiber length at loads only slightly higher (∼ 10%) than that needed to initiate bond failure. A residual frictional stress stabilizes debond growth. The fiber stress concentration factor decreases as the magnitude of the residual frictional stress decrease...
TL;DR: In this article, the validity of the loading path assumption is examined in the context of fiber reinforced composite material failure criteria, where the failure criteria assume explicitly or implicitly that the state of failure stress is independent of loading path, provided that the path intercepts the failure surface at that given point first.
Abstract: on the failure surface. Most of the failure criteria assume explicitly or implicitly that the state of failure stress is independent of loading path [6], provided that the loading path intercepts the failure surface at that given point first. For fibre reinforced composite materials there are many failure mechanisms which can be activated along different loading paths. The macroscopic failure behavior reflects these various failure mechanisms. Consequently, the validity of the aforementioned assumption needs to be studied carefully. A loading path defines, with respect to time, the unique state of stress to which a given material is subjected. As an example, consider the 0,-02 stress
TL;DR: In this paper, the authors employed thermal, ultrasonic and limited x-ray radiography techniques to identify fatigue damage in alumina fiber reinforced aluminum plates with a centered circular hole.
Abstract: Thermography, ultrasonic and limited x-ray radiography techniques were employed to identify fatigue damage in alumina fiber reinforced aluminum plates with a centered circular hole. Metallographic examination identified the damage as longitudinal and transverse cracks, which were frequently associated with striation markings in the metal matrix. These striation markings suggest that the aluminum matrix was plastically deformed within a damage zone adjacent to the hole. The length of the cracks iden tified by the ultrasonic techniques varied between 0.40-6.50 mm. There are indications that the size and the location of the fatigue damage may be assessed thermographically.
TL;DR: In this article, a model for predicting reliability of brittle composite structures with complex multiaxial stress states is presented for predicting the probability of material fracture in an off-axis geometry and a center through-hole offaxis geometry using several different material systems.
Abstract: A model is presented for predicting reliability of brittle composite structures with complex multiaxial stress states. This model allows all of the stress components to con tribute to the probability of material fracture. The model is applied to an off-axis geometry and to a center through-hole off-axis geometry using several different material systems. Results for the off-axis geometry demonstrate the importance of using the correct specimen configuration when performing a reliability analysis. Stresses induced by the end-constraint may cause an over prediction of reliability or an underutilization of material strength, depending on the overall stiffness and strength characteristics of the material. Results for the center-notched off-axis geometry demonstrate the effect of strength variability on the localization of fracture prob ability. Low variability materials exhibit a localization of high probability of failure regions, implying a high repeatability of fracture initiation site. High variability mat...