Showing papers in "Journal of Reinforced Plastics and Composites in 1990"
TL;DR: In this paper, the effect of interlaminar strength on the delami nation resistance was discussed and it was found that through-the-thickness stitching could reduce the delamination area in a composite plate.
Abstract: The delamination resistance of a composite plate subjected to low-velocity impact is dependent on the interlaminar strengths and the level of interlaminar stress. The former is strongly influenced by the material properties such as matrix toughness and fiber-matrix bonding strength while the latter can be affected by the specimen geometry and loading parameters. In this study, some thin composite plates were fabricated and sub jected to low-velocity impact. The delamination in every specimen was examined. Experi mental results revealed that the delamination area was proportional to the lamina thickness and the difference of fiber angle between adjacent laminae. A Mismatch Theory based on the difference of bending stiffness between adjacent laminae was used to interpret the cause of high interlaminar stress level. The effect of interlaminar strengths on the delami nation resistance was also discussed. It was found that through-the-thickness stitching could reduce the delamination area in a composite plate ...
119 citations
TL;DR: In this article, a method to determine the complete state of stress at free edges of composite laminates under combined loads (uniaxial tension or compression, moment, and out-of-plane shear) is presented.
Abstract: A method to determine the complete state of stress at free edges of com posite laminates under combined loads (uniaxial tension or compression, moment, and out-of-plane shear) is presented. Based on the principle of minimum complementary en ergy, two coupled ordinary differential equations are derived with use of calculus of varia tions. The stresses are determined in closed form and are in good agreement with other solutions published in the literature for uniaxial tension and applied moment. This solu tion is applicable to general laminates with straight free edges and is computationally very efficient.
69 citations
TL;DR: The Modified Rule of Mixtures has been verified to effectively predict the axial tensile strength of glass fiber reinforced injection molding compounds (IMC). Nylon, polypropylene, and polybutylene as mentioned in this paper.
Abstract: The Modified Rule of Mixtures has been verified to effectively predict the axial tensile strength of glass fiber reinforced injection molding compounds (IMC). Nylon, polypropylene, and polybutylene...
48 citations
TL;DR: In this article, several finite element models suitable for delamina tion damage analysis have been used and frequency shift diagrams for modes up to 24 with severity of damage up to 15 % have bee used.
Abstract: In the present paper several finite element models suitable for delamina tion damage analysis have been used. Frequency shift diagrams for modes up to 24 with severity of damage up to 15 % have bee...
44 citations
TL;DR: In this article, a group of cross-plied graphite/epoxy laminates with and without adhesive layers were examined by sectioning the impacted specimen and examining the sections with an optimal microscope.
Abstract: Impact experiments on a group of cross-plied graphite/epoxy laminates with and without adhesive layers were conducted. Impact-damage modes were examined by sectioning the impacted specimen and examining the sections with an optimal microscope. The effectiveness of using adhesive layers to suppress impact-induced delamination was investigated. It was found that the presence of adhesive layers could toughen the interface between two laminae and also reduce matrix cracking. A guide to the optical use of adhesive layers for improving impact resistance properties was proposed.
36 citations
TL;DR: In this paper, the normalized change in ultrasonic "natural" velocity as a function of stress and temperature was measured in a unidirectional laminate of T300/5208 graphite/epoxy composite using a pulsed phase locked loop ultrasonic interferometer.
Abstract: The normalized change in ultrasonic "natural" velocity as a function of stress and temperature was measured in a unidirectional laminate of T300/5208 graphite/epoxy composite using a pulsed phase locked loop ultrasonic interferometer. These measurements were used together with the linear (second order) elastic moduli to calculate some of the nonlinear (third order) moduli of this material.
32 citations
TL;DR: Simplified procedures are described to design and analyze single and multi-bolt composite joints as discussed by the authors, and several design variables associated with composite bolted joints are summarized in the appendix of this paper.
Abstract: Simplified procedures are described to design and analyze single and multi-bolt composite joints. Numerical examples illustrate the use of these methods. Factors affecting composite bolted joints are summarized. References are cited where more detailed discussion is presented on specific aspects of composite bolted joints. Design variables associated with these joints are summarized in the appendix.
31 citations
TL;DR: In this paper, an example of two-dimensional to three-dimensional finite element analysis of a laminated composite plate with a hole is presented, where displacements of the global/local interface from the 2D global model are applied to the edges of the 3D local model.
Abstract: An example of two-dimensional to three-dimensional global/local finite element analysis of a laminated composite plate with a hole is presented. The 'zoom' technique of global/local analysis is used, where displacements of the global/local interface from the two-dimensional global model are applied to the edges of the three-dimensional local model. Three different hole diameters, one, three, and six inches, are considered in order to compare the effect of hole size on the three-dimensional stress state around the hole. In addition, three different stacking sequences are analyzed for the six inch hole case in order to study the effect of stacking sequence. The existence of a 'critical' hole size, where the interlaminar stresses are maximum, is indicated. Dispersion of plies at the same angle, as opposed to clustering, is found to reduce the magnitude of some interlaminar stress components and increase others.
30 citations
TL;DR: In this paper, a micromechanics theory for the prediction of the nonlinear behavior of unidirectional fiber-reinforced materials and composite laminates is presented.
Abstract: A micromechanics theory for the prediction of the nonlinear behavior of unidirectional fiber-reinforced materials and composite laminates is presented. The method relies on the properties of fibers and matrix, and involves two parameters which describe the nonlinear response of the unreinforced matrix. These two parameters can be backed-out from the nonlinear axial shear response of the unidirectional lamina. The predicted behavior of boron/epoxy, glass/epoxy, and graphite/polyimide composites is compared with available measured data, and good agreement is obtained in most cases. 22 refs.
21 citations
TL;DR: In this article, the mechanical properties of continuous graphite fiber reinforced composites containing filler modified epoxy matrix have been investigated and a modification of epoxy resin with either thermoplastic p...
Abstract: The mechanical properties of continuous graphite fiber reinforced com posites containing filler modified epoxy matrix have been investigated. Modification of epoxy resin with either thermoplastic p...
19 citations
TL;DR: In this article, a thermo-formable thermoplastic composite sheet product is described, which consists of aligned discontinuous reinforcing fibers in a thermoplastics resins, and is drawable to 50 % or more axial draw ratio.
Abstract: A thermoformable thermoplastic composite sheet product is described. The sheet consists of aligned discontinuous reinforcing fibers in a thermoplastic resin. It is drawable to 50 % or more axial draw ratio and has mechanical properties close to those of straight continuous fiber composite sheets. Development and preservation of fiber alignment enables the achievement of high fiber volume fraction (FVF) and mechanical properties. In general, tensile modulus and strength are 90% or better of continous fiber composites at the same FVF. Fatigue and creep properties are also comparable. This paper details the mechanical and formability characteristics of the sheets and presents various applications that show the processing advantages of this advanced composite sheet concept over straight continuous fiber or woven fabric sheets.
TL;DR: In this paper, the hygrothermal influence on the flexural properties of unidirectional Kevlar 49-graphite/epoxy hybrid composite was investigated in the temperature range -50°C to 150°C.
Abstract: The hygrothermal influence on the flexural properties of unidirectional Kevlar 49-graphite/epoxy hybrid composite was investigated in the temperature range -50°C to 150°C. Moisture was introduced into the specimen by immersion in distilled water. Two material lay-ups were used in this investigation. In Kev 49/T-300/Kev 49, Kevlar 49 and graphite prepreg are used as outer and center layer, respectively and in T-300/Kev 49/T-300, it was vice-versa. In both cases the tapes were alternated until the total thickness was achieved. Data for the determination of flexural strength and modulus were generated at various temperatures for both dry and saturated specimens. The results show that both flexural strength and modulus change with the ply sequence of hybrid lami nates. The flexural strength and modulus of Kev 49/T-300/Kev 49 are relatively higher than those of T-300/Kev 49/T-300. The apparent flexural strength decrease with the in crease of temperature in the range 23°C to 150°C. The addition of moisture furt...
TL;DR: In this article, the performance of various coated chemithermomechanical pulp-filled polystyrene composites has been evaluated by evaluating the mechanical properties of the composite materials.
Abstract: The performance of various coated chemithermomechanical pulp-filled polystyrene composites has been judged by evaluating the mechanical properties of the composite materials. When fibers were coated with only polymers, e.g., polystyrene or PVC, or a mixture of polymer and Na-silicate, the performance of the composites is re vealed to be very poor. But when an isocyanate (coupling agent) was used along with the above compositions, mechanical properties improved compared to those of both the origi nal polymer and non-treated composites. PS 525-based composites showed better perfor mance compared to PS 201-based composites as far as mechanical properties (other than impact strength) were concerned. Impact strength of PS 201-based composites improved the most compared to even that of the original polymer when silicate along with isocyanate were used as a coating component of the fiber.
TL;DR: In this article, it was shown that interlaminar normal tension is possi fble if the wavy layers are near the inner radius, despite the compressive nature of the problem.
Abstract: Further details are reported regarding the stresses around wavy layers in thick multilayer cylinders loaded with external hydrostatic pressure. Modelling strategies, as well as new results are presented. It is shown that interlaminar normal tension is possi ble if the wavy layers are near the inner radius. This despite the compressive nature of the problem.
TL;DR: In this paper, the buckling of shallow sandwich shells with thick faces was studied in the case of general anisotropy and a closed form solution was derived for the determination of buckling load, which can be applied for a wide range of cases.
Abstract: The paper presents the differential equation system of buckling of shallow sandwich shells with thick faces in the case of general anisotropy. A closed form solution is derived for the determination of the buckling load which can be applied for a wide range of cases. It is also shown that, in the case of isotropic shells, the effect of shearing defor mation can be taken into account in many cases analogously to Foppl's formula.
TL;DR: In this article, a new approach to the fracture mechanics analysis of unidirectional composites has been formulated, where material heterogeneity, material anisotropy, finite width effects, and various possible failure modes are all specifically taken into account.
Abstract: A new approach to the fracture mechanics analysis of unidirectional com posites has been formulated. First, using the shear-lag model, we obtained an approximate stress-analysis for composites containing cracks and longitudinal splits. From this new stress analysis, we derived expressions for the energy release rate due to both self-similar crack propagation and to longitudinal splitting. The new expressions are easy to use. Be cause material heterogeneity, material anisotropy, finite width effects, and various possible failure modes are all specifically taken into account, we suggest that these new expressions should replace conventional fracture mechanics for analyzing fracture data in unidirec tional composites. Experimental work has verified that the new expressions fit experimen tal data significantly better than conventional fracture mechanics expressions.
TL;DR: In this paper, the effect of the squeeze casting conditions on the impregnation of fibrous ceramic preforms by light alloys has been approached by using a suitable model with continuous aligned fibers.
Abstract: The various features of squeeze casting are first described and discussed. The effect of the squeeze casting conditions on the impregnation of fibrous ceramic preforms by light alloys has been approached by using a suitable model with continuous aligned fibers. The processing parameters influencing the impregnated length and the required squeeze casting pressure have been pointed out. According to the modeling and taking into account the capillary effect, the numerical computation of the general equations of heat and fluid flows with specified boundary conditions emphasized the parameters which predominantly control the processing technique: mainly the preform temperature, the reinforcement volume fraction, the impregnation speed and the wettability of the ceramic fibers by the liquid aluminum alloys. 7 refs.
TL;DR: In this article, the authors determined the mode I interlaminar fracture toughness of unidirectional poly(phenylene oxide)/carbon fiber composites using the double cantilever beam test.
Abstract: Mode I interlaminar fracture toughness was determined on a series of unidirectional poly(phenylene oxide)/carbon fiber composites using the double cantilever beam test Initial toughness for growth of a delamination from an insert depends on fiber type, and ranges from 190 to 440 J/sq m, with intermediate modulus fibers tending to give lower values than high-strain fibers Low toughness values are attributed to poor fiber-matrix adhesion As a delamination progress down the beam, fiber bridging increases the apparent toughness by up to a factor of 7, depending on the fiber
TL;DR: In this paper, the weldline strength of injection molded polypropylene containing spherical and irregularly shaped fillers (glass spheres, calcium carbonate), or reinforcements such as glass flakes and fibers, talc, and mica were investigated.
Abstract: Weldlines represent potentially fatal sources of weakness in injection molded thermoplastic parts. This is particularly true for filled and reinforced composi tions where usual remedies consisting in a modification of processing conditions such as increase of melt temperature, injection speed, and pressure do not always work. This paper deals with weldline strength of injection molded polypropylene containing spherical and irregularly shaped fillers (glass spheres, calcium carbonate), or reinforcements such as glass flakes and fibers, talc, and mica. Two types of weldline will be considered: weldlines formed when two melt streams meet head-on and those formed as a result of flow around an insert. It will be shown that the loss of strength is greatest in compositions reinforced with flakes and fibers. This is due to flow induced filler orientation in the weldline zone. Approaches to reduce the loss of strength which make use of known flow behavior of suspensions of fibers and flakes will be illustrated.
TL;DR: In this paper, the authors compared the performance of block copolymerization and chemical reaction with dynamic test and morphology study, and the mechanical properties of their sheet molding compounds were studied.
Abstract: Toughened unsaturated polyesters were prepared by chemical reaction, physical blending, and block copolymerization method, respectively. Mechanical proper ties of thus formed unsaturated polyesters after curing were compared. The superior per formance of block copolymers was explained with dynamic test and morphology study. Mechanical properties of their sheet molding compounds were studied as well.
TL;DR: In this article, a finite element formulation for the analysis of thin to moderately thick composite shell structures is presented, with shear effects included by relaxing the Kirchhoff-love hypothesis and prescribing the neu tral surface displacements independently from the rotations.
Abstract: A finite element formulation for the analysis of thin to moderately thick laminated composite shell structures is presented. A plate type element is developed with shear effects included by relaxing the Kirchhoff-Love hypothesis and prescribing the neu tral surface displacements independently from the rotations. The in-plane layer stresses are calculated using the constitutive equations. Once the in-plane stress variation has been obtained, the equilibrium equations are integrated to obtain the transverse shear and nor mal stresses. Two example problems are considered herein. For symmetric angle-plied or unidirectional winding it has been found that a pressurized cylinder, in addition to expand ing radially, also rotates about its axis. This contradicts the assumption that a symmetri cally wound cylinder under pressure exhibits axisymmetric deformation; thus a full cylin der model must be analyzed to produce the actual deformation. Laminated circular cylindrical shells are also analyzed with both clamped ...
TL;DR: In this paper, the fatigue failure mechanisms of three unidirectional laminated composite material systems (consisting of a common fiber in varying resin matrices) were investi gated.
Abstract: The fatigue failure mechanisms of three unidirectional laminated compos ite material systems (consisting of a common fiber in varying resin matrices) were investi gated. Static tensions tests of the pure resins and composites in the axial direction were analyzed in conjunction with fatigue test data to determine failure characteristics. The resins with the highest strain energy density and ultimate strain exhibited the best fatigue properties. A comparison of fatigue curves for both pure resins and composites data showed that the dominant failure mechanism in fatigue is a combination of matrix cracking and interface debonding.
TL;DR: In this paper, the authors studied the matrix cracking sequence in graphite epoxy laminates that contain a small central hole and provided a quantitative measurement and a physical analysis of matrix cracking patterns near the hole.
Abstract: This paper studies the matrix cracking sequence in [02/90 2]s graphite epoxy laminates that contain a small central hole. Experiment was performed first using specimens loaded in uniaxial, quasi-static tension, followed by inspections of the speci men at several prescribed loading increments by means of x-radiography. The inspection provides a quantitative measurement and a physical analysis of matrix cracking patterns near the hole.
TL;DR: In this article, a higher order beam theory is used to analyze two Mode II interlaminar bending specimen geometries, based on second order displacements in the thickness coordinate and derived in conjunction with Reissner's variational principle.
Abstract: A higher order beam theory is used to analyze two Mode II interlaminar bending specimen geometries. The theory is based on second order displacements in the thickness coordinate and is derived in conjunction with Reissner's variational principle. Homogeneous orthotropic materials are considered. Both the inplane normal stress and the interlaminar shear stress distributions exactly satisfy the equilibrium equations of clas sical theory of elasticity. The resulting field equations are applied to an analysis of the end notch flexure (ENF) specimen and end notch cantilever (ENC) specimen. Numerical results from the present theory are compared to those obtained from finite elements for the end notch flexure specimen. Excellent agreement is obtained.
TL;DR: In this article, an empirical modification in the one-dimensional Fickean solution of moisture absorption by composites has been suggested, which can be used to account for the differences between the theoretical prediction and the observed be havior.
Abstract: In this paper an empirical modification in the one-dimensional Fickean solution of moisture absorption by composites has been suggested. Certain physical factors due to which actual process of moisture diffusion in composites differs from the classical diffusion descnbed by Fick's law have been discussed. It is shown that most of the factors which attnbute to the differences between the theoretical prediction and the observed be havior can be accounted for, just by incorporating some parameters in the Fickean solution itself.
TL;DR: In this article, the effects of damage growth caused by humidity cycling between 95% RH and 0% RH at 40°C on AS4/3502 graphite/ epoxy composite material were investigated.
Abstract: Experiments were conducted to determine the effects of damage growth caused by humidity cycling between 95% RH and 0% RH at 40°C on AS4/3502 graphite/ epoxy composite material. Tests were performed to measure tensile and compressive moduli, Poisson's ratios, and ultimate strengths. Fracture behavior was determined from double cantilever beam tests in which energy release rates were measured. In virtually all cases it was found that the cycling conditions utilized in this work did not lead to any sig nificant changes in moduli, Poisson's ratio, ultimate strength, or energy release rates de spite the fact that micro-level damage was known to be present.
TL;DR: In this article, analytical solutions for the developing temperature profile of a power law fluid in pure drag flow are presented for three sets of boundary conditions: 3) the boundary conditions are considered:
Abstract: Analytical solutions are presented for the developing temperature profile of a power law fluid in pure drag flow. Three sets of boundary conditions are considered:
TL;DR: In this article, the authors used a modified form of the shear coefficient that accounts for the different in-plane properties of the panels to find the minimum attainable deflection, which depends on finding an optimal combination of the contribu tions from the bending deflection and the beam deflection.
Abstract: The deflection of a thin-walled fiber-reinforced anisotropic composite ma terial beam under the action of an applied transverse load is given as a function of the elas tic constants of the composite material panels that form the beam cross-section. A Timoshenko beam theory, that uses a modified form of the shear coefficient that accounts for the different in-plane properties of the panels, is used to find the beam deflection. The minimum attainable deflection depends on finding an optimal combination of the contribu tions from the bending deflection and the shear deflection of the beam. Numerical and graphical results obtained from a computer code allow the user to investigate the effects of different composite material systems and layup configurations in the panels of the beam.
TL;DR: In this article, the authors discuss the matrix cracking sequence in a [02/90 2]s graphite epoxy laminate with double-side notches and show that the matrix cracks are caused by stress concentration near the notched region.
Abstract: This paper discusses the matrix cracking sequence in a [02/90 2]s graphite epoxy laminate with double-side notches. Experiments were performed on specimens loaded in uniaxial, quasi-static tension. The specimens were inspected at ascending load increments by x-radiography for patterns of matrix cracks caused by stress concentration near the notched region.
TL;DR: In this article, the authors measured the stress acoustic constants (SACs) of unidirectional graphite/epoxy composites under tensile load and the SAC was defined as the slope of the normalized change in ultrasonic "natural" velocity as a function of stress.
Abstract: Previously, the stress acoustic constants (SAC''s) of unidirectional graphite/epoxy composites were measured to determine the nonlinear moduli of this material. These measurements were made under compressive loading in order to obtain the sufficient number of values needed to calculate these moduli. However, because their strength in tension along fiber directions can be several times greater, most composites are used under tensile loading. Thus, it is important to characterize the nonlinear properties of these materials in tension as well. The SAC''s which are defined as the slope of the normalized change in ultrasonic "natural" velocity as a function of stress were measured in a unidirectional laminate of T300/5208 graphite/epoxy. Tensile load was applied along the fiber axis with the ultrasonic waves propagating perpendicular to locked loop ultrasonic interferometer with the nominal frequency of the ultrasonic waves being 2.25 MHz.