Showing papers in "Composites Part B-engineering in 2000"

Cement reinforced with short carbon fibers: a multifunctional material

Abstract: This is a review of cement-matrix composites containing short carbon fibers. These composites exhibit attractive tensile and flexural properties, low drying shrinkage, high specific heat, low thermal conductivity, high electrical conductivity, high corrosion resistance and weak thermoelectric behavior. Moreover, they facilitate the cathodic protection of steel reinforcement in concrete, and have the ability to sense their own strain, damage and temperature. Fiber surface treatment can improve numerous properties of the composites. Conventional carbon fibers of diameter 15 μm are more effective than 0.1 μm diameter carbon filaments as a reinforcement, but are much less effective for radio wave reflection (EMI shielding). Carbon fiber composites are superior to steel fiber composites for strain sensing, but are inferior to steel fiber composites in the thermoelectric behavior.

Tests and modeling of carbon-wrapped concrete columns

Abstract: There is an urgent need for models that can accurately predict performance of fiber-wrapped concrete columns. Axial compression tests on a total of 45 carbon-wrapped concrete stubs of two batches of normal and high-strength concrete and five different number of wraps were used to verify a confinement model, which was originally developed for concrete-filled glass FRP tubes. Also, a nonlinear finite element model with a non-associative Drucker–Prager plasticity was developed. Both models compared favorably with test results. It was concluded that the adhesive bond between concrete and the wrap would not significantly affect the confinement behavior. Moreover, the same confinement model can be applied to carbon and glass fibers, as long as the model has incorporated the dilation tendency of concrete as a function of the stiffness of the jacket. However, it is of utmost importance to establish the effective hoop rupture strain of the wrap through a reliability analysis by setting proper confidence level for design purposes.

Three-dimensional thermoelastic deformations of a functionally graded elliptic plate

Abstract: A new solution in closed form is obtained for the thermomechanical deformations of an isotropic linear thermoelastic functionally graded elliptic plate rigidly clamped at the edges. The through-thickness variation of the volume fraction of the ceramic phase in a metal–ceramic plate is assumed to be given by a power-law type function. The effective material properties at a point are computed by the Mori–Tanaka scheme. It is found that the through-thickness distributions of the in-plane displacements and transverse shear stresses in a functionally graded plate do not agree with those assumed in classical and shear deformation plate theories.

Ultrasonic evaluation of matrix damage in impacted composite laminates

Abstract: Conventional ultrasonic inspection methods are largely used for detection of delaminations in composite materials while only recently new techniques have been proposed to identify matrix cracks in simple tension loaded coupon specimens. In this study delaminations and matrix cracking caused by low-energy impacts on quasi-isotropic carbon/PEEK laminated plates are examined by means of different pulse-echo techniques: conventional time-of-flight and amplitude C-scans at normal incidence are used to check for the presence of delaminations, while backscattering C-scans (in which the transducer is set at an angle to the laminate plane) allow the detection of matrix cracks through the laminate thickness. Selected results from full waveform ultrasonic analysis of impacted carbon/PEEK laminates are discussed and compared with X-ray data in order to demonstrate the efficiency of the proposed inspection technique.

Performance of glass fiber reinforced plastic bars as a reinforcing material for concrete structures

Abstract: The increasing use of fiber reinforced plastic (FRP) bars to reinforce concrete structures necessitates the need for either developing a new design code or adopt the current one to account for the engineering characteristics of FRP materials. This paper suggests some modifications to the currently used ACI model for computing flexural strength, service load deflection, and the minimum reinforcement needed to avoid rupturing of the tensile reinforcement. Two series of tests were conducted to check the validity of the suggested modifications. The first series was used to check the validity of the modifications made into the flexural and service load deflection models. The test results of the first series were also analyzed to develop two simple models for computing the service load deflection for beams reinforced with glass FRP (GFRP) bars. The second series was used to check the accuracy of the modification suggested into minimum reinforcement model. Test results of the first series indicate that the flexural capacity of the beams reinforced by GFRP bars can be accurately predicted using the ultimate design theory. They also show that the current ACI model for computing the service load deflection underestimates the actual deflection of these beams. The two suggested models for predicting service load deflection accurately estimated the measured deflection under service load, and the simpler of the two pertains better predictions than those of the models available in the literature. Test results of the second series reveal that there is an excellent agreement between the predicted and recorded behavior of the test specimens, which suggests the validity of the proposed model for calculating the required minimum reinforcement for beams reinforced by GFRP bars.

Impact damage characterisation of carbon fibre/epoxy composites with multi-layer reinforcement

Abstract: Low-velocity impact tests were performed to investigate the impact behaviour of carbon fibre/epoxy composite laminates reinforced by short fibres and other interleaving materials. Characterisation techniques, such as cross-sectional fractography and scanning acoustic microscopy, were employed quantitatively to assess the internal damage of some composite laminates at the sub-surface under impact. Scanning electron microscopy was used to observe impact fractures and damage modes at the fracture surfaces of the laminate specimens. The results show that composite laminates experience various types of fracture; delamination, intra-ply cracking, matrix cracking, fibre breakage and damage depending on the interlayer materials. The trade-off between impact resistance and residual strength is minimised for composites reinforced by Zylon fibres, while that for composites interleaved by poly(ethylene-co-acrylic acid) (PEEA) film is substantial because of deteriorating residual strength, even though the damaged area is significantly reduced. Damages produced on the front and back surfaces of impact were also observed and compared for some laminates.

Rapid thermal non-destructive testing of aircraft components

Abstract: This paper compares the use of different thermal non-destructive testing techniques to rapidly inspect carbon fibre composite aircraft components. Samples were prepared to simulate inclusions and barely visible impact damage in carbon fibre reinforced plastic laminate which represent faults in the manufacturing process and in-service environment respectively. The limits of material fault detection were then compared for transient and lock-in thermography and the results were verified with underwater ultrasonic c-scans. The paper concludes that lock-in thermography is a more powerful technique to detect impact damage and that transient thermography is more suitable for detecting inclusions. Thermal non-destructive testing is up to 30 times quicker than underwater ultrasonic c-scanning and may ultimately provide the solution to the problem of rapid quantitative in-service and manufacturing process inspection of commercial aircraft components.

Numerical Analysis and Experimental Correlation of Composite Shell Buckling and Post-Buckling

Abstract: This paper deals with the buckling and post-buckling behaviour of carbon fibre reinforced plastic cylindrical shells under axial compression. The finite element analysis is used to investigate this problem and three different types of analysis are compared: eigenvalue analysis, non-linear Riks method and dynamic analysis. The effect of geometric imperfection shape and amplitude on critical loads is discussed. A numerical–experimental correlation is performed, using the results of experimental buckling tests. The geometric imperfections measured on the real specimens are accounted for in the finite element model. The results show the reliability of the method to follow the evolution of the cylinder shape from the buckling to the post-buckling field and good accuracy in reproducing the experimental post-buckling behaviour.

Composite degradation due to fluid absorption

Abstract: This experimental study investigated the combined effects of liquid (water, Skydrol, fuel, and dichloromethane) absorption, impact damage and drilling on aramid and carbon fibre/epoxy composites. The static and fatigue behaviour of the composite samples was determined after the treatments. The response to impacts was analysed, and elastic and absorbed energy were measured. The mechanism of moisture diffusion into the composites was studied and a method for the accelerated ageing of the composites applied. Penetrant radio-opaque dye and stereo-radiography were used to determine the onset and growth of damage during fatigue life and the decay of mechanical characteristics. Optical microscopy was used to investigate the microscopic mechanisms of absorption and damage, in order to propose interpretative models.

Behavior of full-scale reinforced concrete beams retrofitted for shear and flexural with FRP laminates

Abstract: Four full-scale reinforced concrete beams were replicated from an existing bridge. The original beams were substantially deficient in shear strength, particularly for projected increase of traffic loads. Of the four replicate beams, one served as a control and the remaining three were implemented with varying configurations of carbon fiber reinforced polymers (CFRP) and glass FRP (GFRP) composites to simulate the retrofit of the existing structure. CFRP unidirectional sheets were placed to increase flexural capacity and GFRP unidirectional sheets were utilized to mitigate shear failure. Four-point bending tests were conducted. Load, deflection and strain data were collected. Fiber optic gauges were utilized in high flexural and shear regions and conventional resistive gauges were placed in eighteen locations to provide behavioral understanding of the composite material strengthening. Fiber optic readings were compared to conventional gauges. Results from this study show that the use of fiber reinforced polymers (FRP) composites for structural strengthening provides significant static capacity increases approximately 150% when compared to unstrengthened sections. Load at first crack and post cracking stiffness of all beams was increased primarily due to flexural CFRP. Test results suggest that beams retrofit with both the designed GFRP and CFRP should well exceed the static demand of 658 kN m sustaining up to 868 kN m applied moment. The addition of GFRP alone for shear was sufficient to offset the lack of steel stirrups and allow conventional RC beam failure by yielding of the tension steel. This allowed ultimate deflections to be 200% higher than the pre-existing shear deficient beam. If bridge beams were retrofit with only the designed CFRP failure would still result from diagonal tension cracks, albeit at a 31% greater load. Beams retrofit with only the designed shear GFRP would fail in flexure at the mid-span at an equivalent 31% gain over the control specimen, failing mechanism in this case being yielding of the tension steel. Successful monitoring of strain using fiber optics was achieved. However, careful planning tempered by engineering judgement is necessary as the location and gauge length of the fiber optic gauge will determine the usefulness of the collected data.

Prediction of failure thermal cycles in graphite/epoxy composite materials under simulated low earth orbit environments

Abstract: In order to evaluate the changes in the mechanical properties, mass and coefficient of thermal expansion of composites in space, graphite/epoxy composite specimens were exposed to simulated low earth orbit (LEO) environmental conditions including ultraviolet radiation, thermal cycling and high vacuum. Surface morphology was investigated by using a scanning electron microscope, and outgassed products were analyzed with a quadrupole mass spectrometer. The failure cycle of composite laminates exposed to the attack of LEO environmental factors was predicted by using four modified failure criteria. The modified failure criteria were expressed as a function of stresses as well as thermal cycles.

Modeling of composite/concrete interface of RC beams strengthened with composite laminates

Abstract: In this paper a finite element model for predicting shear and normal stresses in the adhesive layer of plated reinforced concrete beams has been developed. The numerical results carried out agree with those obtained in previous studies by other authors. It is found that shear stresses and high concentrations of peeling forces are present at the ends of the plates when the composite beam is loaded in flexure. These concentrations can produce premature failure of the strengthened beam because of debonding of the plate or cracking of the concrete cover along the level of internal steel reinforcement. The numerical simulation captures the actual interfacial stresses and, in particular, the maximum values of shear and normal stresses.

Bending, compression, and shear behavior of woven glass fiber/epoxy composites

Abstract: The mechanical properties and failure mechanisms of through-the-thickness stitched plain weave glass fabric‐epoxy composites were studied. Unstitched plain weave and biaxial non-crimp fabrics were used for comparison. Composite panels were fabricated using Resin Transfer Molding. Z-directional stitching increased the delamination resistance and lowered the bending strength of the composites. Composites made from through-the-thickness stitched fabrics demonstrated improved compression after impact behavior as compared to the unstitched fabrics. The results presented in this investigation should be useful in tailoring textile composites to achieve specific property goals. q 2000 Elsevier Science Ltd. All rights reserved.

Aspects of residual thermal stress/strain in particle reinforced metal matrix composites

Abstract: The influence of inclusion geometry and thermal residual stresses and strains on the mechanical behaviour of a 20 vol% Al 2 O 3 particulate reinforced 6061-T0 Al alloy metal matrix composite is investigated through finite element analysis. The introduction of residual thermal stresses/strains prior to external loading leads to a decrease of the proportional limit, 0.2% offset yield stress and the apparent stiffness. The residual stresses/strains are shown to have a greater effect on the composite behaviour under compressive loading than tensile loading. The residual stresses/strains have little effect on the cyclic behaviour of the composite. In only the second cycle, the difference between the cyclic curves, with and without a thermal history, was 2 MPa. Use of a cube shaped particle, with sharp corners and edges, in the unit cell model led to much greater initial hardening behaviour than spherical inclusions, and therefore a greater 0.2% offset yield stress due to stress/strain localisation at the particle corners and edges. This results in regions of constrained plasticity and high stress triaxiality in the matrix around the particle, producing improved load transfer in the composite. It is shown that inclusion aspect ratio, in the range of 0.5–2.0, has an impact on the yield stress. A minimum yield stress occurred at an aspect ratio of approximately 0.9 with significant increases on either side of this point. The influence of residual stress/strain had a similar effect throughout the aspect ratio range except tensile loading, following thermal treatment, on unit cells with inclusion aspect ratios greater than 1.5 resulted in the highest yield stresses.

Strengthening concrete beams for shear using CFRP-materials: evaluation of different application methods

Abstract: This paper presents different methods and tests for the application of carbon fibre reinforced plastic (CFRP) fabrics and tapes to concrete beams. The purpose of the tests were twofold; first to study the shear force capacity of the beams both before and after strengthening; and second, to examine three different ways of applying the fabrics. These were: two hand lay-up systems, one vacuum injection system and one pre-preg system. The total number of beams tested was eight. The test results proved that a very good strengthening effect in shear could be achieved by bonding fabrics to the face of concrete beams. However, a lot of energy was released at failure, which led to brittle failures. The tests also showed that the techniques which used hand lay-up were preferable as compared to other systems, even though the fibre weight fraction was considerably less. However, the vacuum injection system was the most environmentally friendly method.

Ultrasonic technique for the evaluation of delaminations on CFRP, GFRP, KFRP composite materials

Abstract: In the present paper an ultrasonic NDI technique for the delaminations evaluation on several composite materials is described. The methodology, based on an ultrasonic test apparatus in the form of reflection, allows us to determine the position along the thickness and extension of delaminations on several CFRP, GFRP and KFRP laminates subjected to low-velocity impact test. The experiments have been performed in two distinct phases. During the first phase typical aerospace materials such as thermoset and thermoplastic CFRP thin laminates and sandwich were inspected, in order to validate the ultrasonic NDI system and the original test methodology. Then, in the second phase, tests have been performed on glass fiber and polyester resin systems, where the fiber was in the form of woven fabric or woven roving, and Kevlar and polyester resin system, where the Kevlar is in the form of woven fabric. All the specimens are made by RTM technology and the thickness are comprised between 5 and 6 mm. Moreover, the NDI analysis was performed using two different probes (5 and 15 MHz), in order to evaluate the importance of the probe frequency for the reliable evaluation of delaminations on composite materials. The results show the NDI system capabilities in terms of damage detection, location and evaluation.

Statistical analysis of the mechanical properties of composite materials

Abstract: The Weibull statistic is currently used in designing mechanical components made of composite materials. This work presents useful formulae to describe the behaviour of the Weibull modulus estimator, which in turn may be described by means of a three-parameter Weibull distribution. Expressions for the parameters of this latter distribution, dependent on the sample size, are also given in the paper, so, the percentage points, published until now in tabular form, may be directly calculated. Empirical expressions are derived for determining the A-basis and the B-basis material properties as a function of the sample size.

An evaluation of different models for prediction of elastic properties of woven composites

Abstract: A critical analysis of two simple and convenient analytical models for calculation of elastic properties of woven fabric composites is performed. Predictions of these models are compared with results obtained using the method of reiterated homogenization and with experimental data for plain weave glass fiber and carbon fiber polyester composites. Three different scales are identified in the analysis. The first scale predictions, which are the tow properties (obtained by applying Hashin's concentric cylinder model, the Halpin–Tsai expressions or mathematical homogenization technique), are the most critical because they form the input information for woven composite modeling. It appears that the uncertainty in this information causes larger differences in predictions than the deviations between models of different degree of accuracy. This fact sets limits on the required accuracy of the models. Model comparisons reveal that the woven composite model based on isostrain assumption in the composite plane and isostress assumption for out-of-plane components is in very good agreement with both experimental data and the reiterated homogenization method, whereas the modified mosaic parallel model fails to describe composites with large interlaced regions.

Shape control of NITINOL-reinforced composite beams☆

Abstract: The shape of composite beams is controlled by sets of flat strips of a shape memory nickel–titanium alloy (NITINOL). The strips are embedded in the composite fabric of these beams inside sleeves, which are placed on the neutral axes. Prior to their insertion inside the beams, the NITINOL strips are thermally trained to provide and memorize controlled transverse deflections. Proper activation of the shape memory effect of the appropriate strips is utilized to produce controlled shapes of the NITINOL-reinforced beams. A mathematical model is developed to describe the behavior of this class of SMART composites. The model describes the interaction between the elastic characteristics of the composite beams and the thermally induced shape memory effect of the NITINOL strips. The effect of various activation strategies of the NITINOL strips on the shape of the composite beams is determined. The theoretical predictions of the model are validated experimentally using a fiberglass composite beam made of 8 plies of unidirectional BASF 5216 prepregs, which are 9.75 cm wide and 21.20 cm long. The beams are provided with four NITINOL-55 strips, which are 1.2 mm thick and 1.25 cm wide. The time response characteristics of the beam are monitored and compared with the corresponding theoretical characteristics. Close agreement is obtained between the theoretical predictions and the experimental results. The obtained results suggest the potential of the NITINOL strips in controlling the shape of composite beams without compromising their structural stiffness.

A systematic analysis and design approach for single-span FRP deck/stringer bridges

Abstract: There is a concern with worldwide deterioration of highway bridges, particularly reinforced concrete. The advantages of fiber reinforced plastic (FRP) composites over conventional materials motivate their use in highway bridges for rehabilitation and replacement of structures. In this paper, a systematic approach for analysis and design of all FRP deck/stringer bridges is presented. The analyses of structural components cover: (1) constituent materials and ply properties, (2) laminated panel engineering properties, (3) stringer stiffness properties, and (4) apparent stiffnesses for composite cellular decks and their equivalent orthotropic material properties. To verify the accuracy of orthotropic material properties, an actual deck is experimentally tested and analyzed by a finite element model. For design analysis of FRP deck/stringer bridge systems, an approximate series solution for orthotropic plates, including first-order shear deformation, is applied to develop simplified design equations, which account for load distribution factors under various loading cases. An FRP deck fabricated by bonding side-by-side box beams is transversely attached to FRP wide-flange beams and tested as a deck/stringer bridge system. The bridge systems are tested under static loads for various load conditions, and the experimental results are correlated with those by an approximate series solution and a finite element model. The present simplified design analysis procedures can be used to develop new efficient FRP sections and to design FRP highway bridge decks and deck/stringer systems, as shown by an illustrative design example.

Numerical evaluation of failure mechanisms on composite specimens subjected to impact loading

Abstract: Composite panels are in common use, especially in aeronautic and aerospace structures due to their high strength/weight and stiffness/weight ratio. The out-of-plane impact loading is considered potentially dangerous mainly because the damage may be left undetected and because the loading itself acts in the through-the-thickness direction of the laminated composite panel. This direction is the weakest in the composite since no fibres are present in that direction. The impact loading can lead to damage involving three modes of failure: matrix cracking, delamination and eventually fibre breakage for higher impact energies. Even when no visible impact damage is observed at the surface on the point of impact, matrix cracking and delamination can occur, and the residual strength of the composite is considerably reduced. The objective of this study is to determine the mechanisms of the damage growth of impacted composite laminates when subjected to impact loading. For this purpose a series of impact tests were carried out on composite laminates made of carbon fibre reinforced epoxy resin matrix. An instrumented drop-weight-testing was used together with a C-scan ultrasonic device for the damage identification. Two stacking sequences of two different epoxy resins and carbon fibres, representative of four different elastic behaviours with a different number of interfaces were used. A numerical evaluation of these specimens was also carried out, using static analysis only. Results showed that the delaminated area due to impact loading depends on the number of interfaces between plies. Two failure mechanisms due to impact were identified, which are influenced by the stacking sequence and by the thickness of the panels.

Investigation on the effects of fiber composites at concrete joints

Abstract: This investigation involves parametric studies of the application of fiber-reinforced polymer (FRP) composite laminates to exterior beam–column joints to increase their moment capacity. Three beam–column joint models were examined using various fiber composite laminates and wraps, and various thickness. Composite laminates and wraps considered were made out of epoxy and fibers such as E-glass, carbon, and kevlar. One beam–column joint model without FRP reinforcement was used as a control specimen for comparison. The other two beam–column joint models studied included laminates bonded to the tensile faces with and without wraps. The wraps were provided to prevent the peeling of the laminates. The finite element analysis results indicated that the choice of the fiber composite materials, the laminate and wraps arrangement and thickness affected the enhancement of the structural joint performance significantly. Furthermore, an increase in the moment capacity of up to 37% was observed when the joints were reinforced with FRP laminates and were compared to the control specimen.

Strength and ductility of reinforced concrete moment frame connections strengthened with quasi-isotropic laminates

Abstract: Zusammenfassung This paper introduces an innovative technique using polymer composites for repair and retrofit of reinforced concrete (RC) moment frame connections. In this pilot study, a total of six half-scale reversal cyclic tests were preformed. The tests were conducted on half-scale specimens simulating interior beam-to-column sub-assemblages of a typical RC structure. Two connection specimens were used as control specimens and were tested to failure. These two “repairable” damaged specimens were re-tested under a similar loading regime after being repaired with both epoxy injection as well as carbon–epoxy and E-glass–epoxy quasi-isotropic laminates. To investigate the performance of the composite systems as retrofit schemes, two other half-scale tests were conducted on undamaged specimens strengthened with both E-glass–epoxy and carbon–epoxy quasi-isotropic laminates. Test results indicated that the use of composite overlays has led to an appreciable increase in stiffness, strength, and ductility of these connections. The ductility and strength of the repaired specimens were increased up to 42 and 53% respectively, as compared to the control specimens. Discussion on the advantages and disadvantages of using E-glass–epoxy vs. carbon–epoxy laminates is also presented.

Behavior of CFRPC strengthened reinforced concrete beams with varying degrees of strengthening

Abstract: This paper summarizes the results of experimental and analytical studies on the flexural strengthening of reinforced concrete beams by the external bonding of high-strength, light-weight carbon fiber reinforced polymer composite (CFRPC) laminates to the tension face of the beam. Four sets of beams, three with different amounts of CFRPC reinforcement by changing the width of CFRPC laminate, and one without CFRPC were tested in four-point bending over a span of 900 mm. The tests were carried out under displacement control. At least one beam in a set was extensively instrumented to monitor strains and deflections over the entire range of loading till the failure of the beam. The increase in strength and stiffness provided by the bonded laminate was assessed by varying the width of laminate. The results indicate that the flexural strength of beams was significantly increased as the width of laminate increased. Theoretical analysis using a computer program based on strain compatibility is presented to predict the ultimate strength and moment-deflection behavior of the beams. The comparison of the experimental results with theoretical values is also presented, along with an investigation of the beam failure modes.

Damage, deformation and residual burst strength of filament-wound composite tubes subjected to impact or quasi-static indentation

Abstract: Thin-walled filament-wound E-glass fibre-reinforced epoxy tubes were subjected to lateral indentation in quasi-static and low speed impact tests and were then tested under internal pressure to determine their residual burst strength. The behaviour of tubes subjected to quasi-static and low velocity impact loading tests was found to be the same. Experimental strain measurements in quasi-static indentation tests showed a large degree of redistribution of strain with increasing deflection which resulted in local buckling failure away from the indentation point. Damage in the form of matrix cracking resulted from low energy indentation but did not reduce the residual burst strength of the tube. Higher energy indentation, which produced buckling failure, reduced the tubes’ burst strength by 60%.

Dynamics of active piezoelectric damping composites

Abstract: A finite element model is developed to investigate the dynamic characteristics of beams treated with discrete patches of Active Piezoelectric Damping Composites (APDC) The APDC patches, under consideration, consist of piezoelectric rods that are obliquely embedded in a viscoelastic matrix to actively control its shear and compression damping characteristics With such active and passive control capabilities, the energy dissipation mechanism of the viscoelastic layer can be enhanced and the dynamic behavior of the system can be improved The effectiveness of the APDC in damping the vibration of beams is compared with the performance of the conventional Passive Constrained Layer Damping (PCLD) The effect of the inclination angle of the piezoelectric rods on the performance of the APDC is presented The results obtained demonstrate that the APDC, with their inherent active and passive capabilities, are an effective means for controlling structural vibrations over a broad frequency band

On a moderate rotation theory of thin-walled composite beams

Abstract: A small strain and moderate rotation theory of laminated composite thin-walled beams is formulated by generalizing the classical Vlasov theory of sectorial areas. The proposed beam model accounts for axial, bending, torsion and warping deformations and allows one to predict critical loads and initial post-buckling behaviour. A finite element approximation of the theory is also carried out and several numerical applications are developed with reference to lateral buckling of composite thin-walled members. The sensitivity of critical load to second-order effects in the pre-buckling range is pointed out.

Modeling of progressive damage in aligned and randomly oriented discontinuous fiber polymer matrix composites

Abstract: Damage constitutive models based on micromechanical formulation and a combination of micromechanical and macromechanical damage criterions are presented to predict progressive damage in aligned and random fiber-reinforced composites. Progressive interfacial fiber debonding models are considered in accordance with a statistical function to describe the varying probability of fiber debonding. Based on an effective elastoplastic constitutive damage model for aligned fiber-reinforced composites, micromechanical damage constitutive models for two- and three-dimensional (2D and 3D) random fiber-reinforced composites are developed. The constitutive relations and overall yield function for aligned fiber orientations are averaged over all orientations to obtain the constitutive relations and overall yield function of 2D and 3D, random fiber-reinforced composites. Finally, the present damage models are implemented numerically and compared with experimental data to show the progressive damage behavior of random fiber-reinforced composites. Furthermore, the damage models will be implemented into a finite element program to illustrate the dynamic inelastic behavior and progressive crushing in composite structures under impact loading.

Free vibration of symmetric angle-ply thick laminated composite cylindrical shells

Abstract: Analytical solutions for the vibrations of thick symmetric angle-ply laminated composite cylindrical shells are established using the first-order shear deformation theory. The complex method is developed to deal with the partial differential governing equations of thick symmetric angle-ply laminated composite cylindrical shells. Numerical results are provided for comparison, and coincide with existing results in the literature. The frequency characteristics for thick symmetric angle-ply laminated composite cylindrical shells with different H/R and L/R ratios are studied in comparison with those of symmetric cross-ply laminates. Also, the influence of lamination angle and number of lamination layers on frequency is investigated in details.

On the statical behaviour of fibre-reinforced polymer thin-walled beams

Abstract: The work deals with the formulation of a one-dimensional kinematical model that is able to study the static behaviour of fibre-reinforced polymer thin-walled beams. The proposed model allows us to take into account the effects of shear deformability. Some numerical results obtained via the finite element method are provided and comparisons with the results obtained by Vlasov's classical theory are also presented.