Showing papers in "Journal of Thermoplastic Composite Materials in 2002"
TL;DR: In this paper, the authors performed flexural creep tests on sisal-fiber-PCL composites at different temperatures and found that the creep compliance increased with the increase of temperature and with the decrease of the fiber content.
Abstract: Flexural creep tests were performed on sisal-fiber-PCL (polycapro- lactone)-starch composites at different temperatures. The creep compliance increased with the increase of temperature and with the decrease of the fiber content. However, the fragmentation of the polymer macromolecules and the natural fiber fragmentation have influence on the creep behavior. The curves of compliance versus time were shifted along the logarithmic time scale to develop a creep master curve. Activation energy was determined from the shift factors. A four-parameter model was applied in order to quantify the viscoelastic behavior of the composites.
66 citations
TL;DR: In this paper, the authors used a plain weave and a 4-harness satin weave structure to characterize the deformation properties of the yarns of a thermoplastic/glass fabric.
Abstract: Proper material characterization of woven fabric reinforcement is important for accurate modeling of thermoforming. Thermoforming of commingled thermoplastic/glass fabric relies strictly on material deformation at temperatures above the matrix melting temperature. As the temperature increases, the viscosity decreases allowing for the resin to flow. The yarns are freer to rotate, reducing shear loads in the material. The resistance to deformation depends not only on the matrix viscosity, but also on the fabric architecture. The two types of materials used in this study are a plain weave and a 4-harness satin weave structure. An interesting characteristic of these woven materials is that they exhibit shear deformation with concomitant area changes, enabling them to take on shapes of double curvature. This makes them a great candidate for thermoforming of structural parts. To improve the viability of this manufacturing process, simulations and design tools are needed. A standardized test method must be devis...
54 citations
TL;DR: In this article, an approach employing decohesive models with mixed damaged scale and using total fracture energy was developed to simulate the delamination process of a stiffened fibre-composite panel and a repaired composite sandwich panel.
Abstract: An approach employing decohesive models with mixed damaged scale and using total fracture energy was developed to simulate the delamination process of a stiffened fibre-composite panel and a repaired composite sandwich panel. Two decohesive material models – a bilinear interfacial decohesive function and the other a cubic polynomial interfacial decohesive function – were developed by using total fracture energy Gc, and based on using interface elements. In comparison with traditional numerical methods in fracture mechanics, this approach automatically predicts the failure load, crack path and the residual stiffness in the fracture process. Applications in this article are delamination analysis of a stiffened fibre-composite panel under four-point bending conditions and a repaired composite sandwich panel under four-point bending test. Comparisons between modeling predictions and experimental observations show that these decohesive models perform well. This article compares the problem of numerical convergent failure between two decohesive material models.
52 citations
TL;DR: In this paper, a thermoviscoelastic finite element model was developed to predict residual stresses induced during the placement of thermoplastic composite tapes, where the process, being continuous, was considered to be under a quasi steady state where process conditions do not change with respect to the moving roller.
Abstract: The tape placement for thermoplastic composites involves heating, melting, and cooling steps just as do the other manufacturing processes. Consequently, development of residual stresses is unavoidable due to disparate thermal characteristics of matrix and fiber materials and also due to nonuniform cooling rates. From the product quality standpoint, such as interlaminar strength, dimensional accuracy etc., these stresses should be kept within allowable limits. In this study, a thermoviscoelastic finite element model was developed to predict residual stresses induced during the placement of thermoplastic composite tapes. The process, being continuous, was considered to be under a quasi steady state where process conditions do not change with respect to the moving roller. Relaxation of the residual stresses in previously laid layers was also allowed for. Results were obtained for both unidirectional and cross-ply laminates. They show the residual stress distributions through the thickness for a number of chosen sets of process parameters (e.g., roller velocity and heat input). Therefore, residual stresses in a laminate can be controlled by modifying these process parameters.
47 citations
TL;DR: In this paper, a pull-braiding process combined with a contact preheating system, and a new online forming method for pultruded profiles is presented, leading to profiles with a forming radius of 10 cm.
Abstract: Objective of this study is to present new developments in thermo-plastic pultrusion (a pullbraiding process combined with a contact preheating system, and a new online forming method for pultruded profiles) and a new approach for modelling of the preheating process. After modelling of the preheating process of commingled glass fibre/polypropylene yarn, the preheating of a thermoplastic pultrusion line to produce profiles with unidirectional reinforcement in axial direction was modified by adding contact heating pins. Compared to the convective heating used before, profiles with higher qualities could be produced at three times higher processing speeds. First trials of a combined braiding and pultrusion process, also with contact preheating, led to promising results. Furthermore, a process to post-form pultruded profiles immediately after leaving the heated pultrusion die was developed, leading to profiles with a forming radiusof 10 cm.
42 citations
TL;DR: In this paper, a continuous induction welding process was developed at the Institut fur Verbundwerkstoffe (IVW) GmbH, which is suitable for the fiber reinforced polymers (FRP) market, and is distinguished by great flexibility, small investments and good mechanical quality.
Abstract: With the continuous induction welding process, a joining technology is developed at the Institut fur Verbundwerkstoffe (IVW) GmbH, that is suitable in particular for the fibre reinforced polymers (FRP) market, and is distinguished by great flexibility, small investments and good mechanical quality. To increase the process reliability a process modelling was carried out so that optimum process parameters can be predicted and the manufacturing of quality secured welds is granted. A comparison between different joining techniques show that high quality welded joints can be manufactured by the continuous induction welding process.
42 citations
TL;DR: In this article, a model for simulating the crushing behavior and predicting the energy absorption characteristics of triaxially braided composite tubes is presented. But the model is based on the finite element code ABAQUS along with a material module that describes the constitutive behavior of the braid material.
Abstract: This paper describes a model for simulating the crushing behavior and predicting the energy absorption characteristics of triaxially braided composite tubes. The crushing model uses the finite element code ABAQUS along with a material module that describes the constitutive behavior of the braid material. The constitutive behavior includes the effects of damage accumulation, and scissoring and jamming of the braider tows. To facilitate the model development, extensive material tests and tube crushing experiments were performed.Crushing tests were conducted on braided carbon fiber/epoxy-vinyl ester composite circular tubes, which were supplied by USCAR’s Automotive Composites Consortium. All tests were conducted quasi-statically, and plug-type initiators were used to trigger the progressive crushing. Experimental results show that the profile of the load-displacement curve and the overall energy absorption can be significantly affected by the fiber architecture and the fillet radius of the plug-type initiat...
30 citations
TL;DR: In this paper, the melt rheological properties of short sisal fiber reinforced polypropylene composites have been studied using a capillary rheometer and the dependence of the relative composition of component reinforcements and their aspect ratio and also the extent of chemical modification on the overall rheology behavior have been investigated.
Abstract: The melt rheological properties of short sisal fibre reinforced polypropylene composites have been studied using a capillary rheometer. The dependence of the relative composition of component reinforcements and their aspect ratio and also the extent of chemical modification on the overall rheological behaviour have been studied. Incorporation of sisal fibre into polypropylene results in an increase in melt viscosity and a decrease in melt elasticity. The melt viscosity was found to have increased with fibre loading. Incorporation of fibres decreased the extrudate deformation and die-swell and this improvement was more prominent at higher fibre loading. A comparison was made between the two techniques employed for the preparation of the composites, i.e. melt mixing in a Haake Rheocord and solution mixing using toluene-xylene mixture as the solvent. It is found that composites prepared by solution mixing showed a higher viscosity as compared to melt mixed composites. Various chemical modifications using che...
30 citations
TL;DR: Van de Velde et al. as mentioned in this paper used propyltrimethoxysilane, phenylisocyanate and maleic acid anhydride modified polypropylene (MAA-PP) to treat long flax fibers.
Abstract: Dew retted hackled long flax was treated with propyltrimethoxysilane, phenylisocyanate and maleic acid anhydride modified polypropylene (MAA-PP). The results of these treatments on fiber wetting and interfacial properties have already been reported in a previous article [Van de Velde, K. and Kiekens, P. (2001). J. Thermoplastic Com. Mat., 14: 244-245]. Further characterization of the treated fibers by sorption tests, roughness estimation, and tensile testing was done in order to provide additional information on the fiber properties. Based on these fiber and interface properties, a selection of fibers and matrices was made and some tests were done on the resulting composites. These composites consisted of MAA-PP treated flax fibers or untreated fibers as reinforcement, and MAA-PP or unmodified PP as matrix material. The tests on the composites included flexural, interlaminar shear strength (ILSS) and sorption tests, as well as determination of composite compositions. As could be expected from the earlier ...
28 citations
TL;DR: In this paper, a 13.4 m GRP blade with a wound tube as a transverse load and bending moment transferring spar stump was investigated for static and fatigue integrity at DLR up to 5 million load cycles in a sinusoidal one-step test.
Abstract: Future sizes of wind turbine rotor blades will exceed 50 m. For transportation, it is favourable to make them in two parts and connect them in a suitable way at the operational site. With the co-operation of industry and research institutes in three countries, a spar beam-connection principle was selected as a possible solution.The pre-design, including finite element analysis, for the structural details were carried out at DLR, Stuttgart (Germany). LM Glasfiber A/S (Denmark) realised the concept in a 13.4 m GRP blade with a wound tube as a transverse load and bending moment transferring spar stump. The sectional blade was investigated for static and fatigue integrity at DLR up to 5 million load cycles in a sinusoidal one-step test. Strain gauges were applied at those locations shown by the finite element analysis to be critical.During the fatigue tests, the blade was observed by means of a thermoelastic stress analysis camera (TSA) by CLRC (United Kingdom) with the aim to observe the stress distributions...
26 citations
TL;DR: In this paper, the effects of different types of fibers on the physical and mechanical behavior of isotactic polypropylene (iPP) are reported, in particular, the flow behavior, mechanical properties (tensile, flexural and impact resistance) and morphology are examined.
Abstract: The effects of different types of fibers on the physical and mechanical behavior of isotactic polypropylene (iPP) are reported. In particular, the flow behavior, mechanical properties (tensile, flexural and impact resistance) and morphology are examined. It has been found that all the fibers studied behave as effective reinforcing agents for the polypropylene matrix. In fact, a notable increase of the mechanical properties is observed in presence of the fibers, the aramid ones being the most effective. Moreover, dynamic-mechanical measurements provide a further confirmation of the reinforcement effect of the fibers, where a sensible increment of the storage modulus in presence of the fibers is obtained. The morphology of the composites is analyzed by scanning electron microscopy (SEM). A good fiber-matrix interfacial adhesion is observed, in particular, for aramid and glass fiber-reinforced composites. As expected, a good adhesion at the fiber-matrix interface gives rise to a sensible increment of composi...
TL;DR: In this paper, the thermal and mechanical properties of short glass fiber reinforced polyethylene terephthalate (PET) have been investigated, focusing on the influence of three of the variables.
Abstract: Investigation of thermal and mechanical characteristics of short glass fiber reinforced polyethylene terephthalate (PET) has been carried out, focusing on the influence of three of the variables in...
TL;DR: In this paper, a constitutive model consistent with the geometry of the woven pattern is proposed based on experimental results achieved by biaxial tensile tests, and 3D simulations of the unit woven cell submitted to baoxial tensions are also performed and compared to experiments.
Abstract: Simulation of the forming processes of thin composite structures is necessary at the design level in order to check the feasibility of the shape and to know the position of the reinforcements. A finite element analysis of fabric shaping process needs the knowledge of the mechanical behavior of the woven reinforcement. This behavior is non linear because of the shape variation of the weaving pattern when it is loaded. Experimental results are obtained from biaxial tests in the case of balanced and unbalanced fabric. A constitutive model consistent with the geometry of the woven pattern is proposed. It is based on experimental results achieved by biaxial tensile tests. 3D simulations of the unit woven cell submitted to biaxial tensions are also performed and compared to experiments.
TL;DR: In this paper, low-energy impact characteristics of four different random E-glass fiber reinforced thermoplastic and thermosetting matrix composites are studied and the residual tensile strength of the impact-damaged composites is also determined as a function of the input impact energy.
Abstract: Low-energy impact characteristics of four different random E-glass fiber reinforced thermoplastic and thermosetting matrix composites are studied. Low-energy impact causes dent on the impacted side and surface cracks on the unimpacted side of all four composites. The damage size, maximum impact load, deflection at the maximum load and tup velocity dissipation of the four composites are compared. The residual tensile strength of the impact-damaged composites is also determined as a function of the input impact energy.
TL;DR: In this article, two computational models were used to predict the mode shapes and frequencies of honeycomb sandwich panels, and a good agreement was achieved between the model predictions and the experimental results.
Abstract: Vibration frequencies and mode shapes of honeycomb sandwich panels with various structural parameters were studied using computational and experimental methods. Two computational models were used to predict the mode shapes and frequencies of honeycomb sandwich panels. In the first model, honeycomb core was assumed to be quasi-orthotropic; in the second model, plate elements were used for honeycomb cell walls to reflect the geometric nature of the hexagonal cells. The quantitative effect of the anisotropic core on the vibration properties of the sandwich panels was studied, and the mode shapes and frequencies were presented. A good agreement was achieved between the model predictions and the experimental results.
TL;DR: In this article, a theoretical model based on damage mechanics is proposed to predict the mechanical behavior of the material and the evolution laws of the damage variables are established within a thermodynamic framework using the associated thermodynamic forces.
Abstract: The present study is part of an ongoing research work on damage of random short fiber reinforced composites. First, the tensile behavior of the material was studied. In its initial state, the material is planarly isotropic elastic. As the load increases, damage induces an anisotropic degradation of the material properties. Then, the degradation mechanisms were studied from microscopic observations of polished specimens. Finally, a theoretical model based on damage mechanics is proposed to predict the mechanical behavior of the material. Damage variables are used to evaluate the change of the compliance tensor. The evolution laws of the damage variables are established within a thermodynamic framework using the associated thermodynamic forces. Correlation with the tensile test results is good. However, additional experiments have to be carried out to fully validate the proposed model.
TL;DR: In this article, the response of pultruded glass-graphite/epoxy hybrid composites has been evaluated under two different incident impact energy conditions, i.e., high incident energy (HIE) and low incident energy(LIE) of impact are chosen to cause either complete fracture or induce delamination, respectively, for assessing the energy absorption characteristics and delamination fracture toughness.
Abstract: The response of pultruded glass-graphite/epoxy hybrid composites has been evaluated under two different incident impact energy conditions A high incident energy (HIE) and a low incident energy (LIE) of impact are chosen to cause either complete fracture or induce delamination, respectively, for assessing the energy absorption characteristics and delamination fracture toughness of these hybrid composites From the HIE instrumented drop-weight impact tests, the energies required for damage initiation, propagation, as well as total absorbed energies and other parameters necessary for evaluating the impact performance of composites were derived from the load-deformation behavior of each sample The influence of hybridization on the energy absorption characteristics of pultruded composites was investigated A parametric study also was performed to correlate the energy absorption characteristics with the energy dissipative mechanisms attributed to the inherent material damping capacity of these composites The
TL;DR: In this article, the deformations are categorized as radial and tangential deformations and twist, and for each of the three influences, these deformations were quantified, and an additional outcome was an indication of the level of analysis needed to study each of these three influences.
Abstract: This papa briefly discusses the influences of through-thickness thermal expansion, a misaligned ply, and a resin-rich slightly thicker ply on the deformations of a curved composite laminate during cool down from tbc cure temperature. Both two-dimensional and three-dimensional level finite-element analyses are used. The deformations are categorized as to radial and tangential deformations and twist, and for each of the three influences, these deformations are quantified. An additional outcome of the study is an indication of the level of analysis needed to study each of these three influences.
TL;DR: In this article, a model for prediction of the temperature distribution within a sandwich panel during manufacturing is presented, both for a one-dimensional case using finite difference methods to investigate effects of varying thermal contact conductances, and for a three-dimensional (3D) case using the finite element methods to study temperature edge effects.
Abstract: The key to finding relevant process parameters in manufacturing of thermoplastic sandwich panels is an accurate prediction of the temperature at the interface between core and face during manufacturing, as this temperature is critical for the bond between the constituents. In this paper a model for prediction of the temperature distribution within a sandwich panel during manufacturing is presented. The process of face manufacturing by compression molding also is modeled, both for a one-dimensional case using finite difference methods to investigate effects of varying thermal contact conductances, and for a three-dimensional (3D) case using finite element methods to study temperature edge effects. The models are verified by experiments, in which a preconsolidated glass fiber/polyamide 12 laminate is used, partly as a ply in a thicker laminate, partly as face sheet for a sandwich panel. The core material used is polymethacrylimide foam.
TL;DR: In this article, the expressions for the strain energy release rate associated with local delaminations growing from the tips of angle-ply matrix cracks in orthotropic composite laminates loaded in tension are presented.
Abstract: The expressions for the strain-energy release rate associated with local delaminations growing from the tips of angle-ply matrix cracks in orthotropic composite laminates loaded in tension are presented. The strain energy release rate and the laminate residual stiffness properties are predicted as functions of matrix-crack density and delamination length.
TL;DR: In this paper, a finite element model was developed to investigate the response of a thick composite pressure vessel under hydrostatic pressure for deep ocean applications, where the plug-supported end-caps with contoured-ends and initial radial clearances were modeled as radial simply supported boundary conditions at the ends of the composite cylinder.
Abstract: A finite element model was developed to investigate the response of a thick composite pressure vessel under hydrostatic pressure for deep ocean applications. To verify the finite element model, layer-by-layer stress and strain responses at the mid-length of a composite pressure vessel, i.e., free from the end-cap effects, were obtained and compared with an existing analytical solution. Excellent agreement was obtained between the numerical and analytical solutions. The created model was employed to investigate the performance of an APC-2/AS4 thermoplastic composite pressure vessel using plug-supported end-caps with contoured-ends and initial radial clearances. The plug-supported end-caps with contoured-ends and initial radial clearances were modeled as radial simply supported boundary conditions at the ends of the composite cylinder. The pressure vessel has a thickness of 4.3 cm, an inner diameter of 33 cm, an internal effective length of 45.7 cm, and a symmetric sub-laminate configuration of [(90/90/0)s]...
TL;DR: In this paper, a Generalized Mechanics of Materials (GMM) model is developed for practical approximation to the stiffness of three-phase composites, and three classes of composites considered are unidirected.
Abstract: A Generalized Mechanics-of-Materials (GMM) model is developed herein for practical approximation to the stiffness of three-phase composites. The three classes of composites considered are unidirect...
TL;DR: In this article, a new method applied to this technology reduces manufacturing steps and offers the advantage of producing parts with different thicknesses or to add profiles and inserts to the main sheet.
Abstract: Stamp forming is gaining in importance because of its very low cycle times. Hence, this technology is very suitable for large series production. A new method applied to this technology reduces manufacturing steps and offers the advantage of producing parts with different thicknesses or to add profiles and inserts to the main sheet. Process temperature is the dominant parameter for the forming and joining of continuous fabric reinforced thermoplastics in one step. In order to optimise this new method, bonded parts have been produced and analysed under different process conditions. The results of these investigations are presented in this paper.
TL;DR: In this paper, the authors discuss the manufacturing aspects of such tubular preforms and suggest ways to overcome the complexity of the yarn weaving process and suggest a way to exploit this characteristic of weaving for the composites industry.
Abstract: The versatility of the textile weaving process has made it a popular method for producing structural composite preforms. Enhanced through-thickness strength by multi-layer weaving, good in-plane strength and the ability to produce 2.5D or 3D shapes, are some of the advantages which have made weaving the most commonly used textile process for composite applications. It is also possible to incorporate local modifications to the weave patterns and fibre-densities within the woven structure; although this characteristic of weaving has not been completely exploited by the composites industry. It is easy to produce a tubular structure having good bi-directional mechanical properties. Moreover, the preform also can be molded into bent shapes, making the woven composites more versatile than ever before. Drape behavior of such tubular fabrics is complex and has not previously been investigated. The aim of this paper is to discuss the manufacturing aspects of such tubular preforms and to suggest ways to overcome th...
TL;DR: In this article, a linear analytical model is proposed to evaluate the impact force as a function of the velocity of the impactor, which provides a simple tool for estimating the magnitude of impact load from the impact energy.
Abstract: A linear analytical model is proposed to evaluate the magnitude of the impact force as a function of the velocity of the impactor. This model provides a simple tool for estimating the magnitude of the impact load from the impact energy. For hybrid composites subjected to low- and medium-velocity impacts where elastic deformation is assumed, the effect of cross section material distribution on impact response was investigated. For a hybrid metal/polymer laminate and a hybrid titanium composite laminate, the relative position of the laminate plies has a significant effect on the plate deflection under impact loads. For equal a real weight plates, the number of layers in a hybrid composite laminate does not appear to affect the impact resistance. However, the relative material ratio of metal to polymer (or metal to polymeric composite) in hybrid composites significantly affects the impact response. Furthermore, the relative ply thickness in a laminate does not have significant effect on its impact resistance...
TL;DR: In this paper, the Poisson's ratio and Young's modulus perpendicular to UD fiber directions are used to predict a reasonable set of mechanical properties for sheared fabrics for composite structures.
Abstract: In the last several decades an increase of fiber reinforced plastics as material for structural parts can be observed. For a designer of composites the control of fiber content and fiber placement is therefore becoming more important. With software programs fiber placement can be predicted and used in several fields. One of those fields is the estimation of the mechanical properties of the composite structure. Especially in translating the fabric properties given by suppliers of these materials to FE based programs, assumptions with respect to undulation and shearing need to be made. By using realistic and more or less average values as found in literature for the Poisson’s ratio and Young’s modulus perpendicular to UD fiber directions it is possible to predict a reasonable set of mechanical properties for sheared fabrics.
TL;DR: In this paper, an analytical modeling and experimentally produce idealized composites reinforced with discontinuous fiber tows to evaluate the theoretical upper limits of tensile strength as compared to continuous fiber composites.
Abstract: The purpose of this work is to perform analytical modeling and experimentally produce idealized composites reinforced with discontinuous fiber tows to evaluate the theoretical upper limits of tensile strength as compared to continuous fiber composites. The idealized composite represents a staggered mosaic of prepreg tape strips of equal width and length. Three-dimensional analysis was performed to evaluate the energy release rate of the possible damage accumulation modes, such as vertical splits and delaminations emanating from tape strip ends. Realistic estimates of the failure strain of the discontinued tow composites was obtained by comparing the calculated energy release rates to the critical Mode II energy release for axial cracking in the material system. The predicted failure strain as a function of the strip geometry was also in good correlation with the experimental results.
TL;DR: In this article, a micromechanics model was used to analyze a quarter of unit cell for a unidirectional lamina and the results were compared with the FEM resu...
Abstract: Finite element models are used to analyze a quarter of unit cell for a unidirectional lamina. Effective lamina properties obtained from a micromechanics model were used to compare with the FEM resu...
TL;DR: In this article, a novel composite material has been developed based on thermoplastic polymers and thermoplastically chalcogenide glass on the other hand, which can produce very different structures of the composite, ranging from fibrous to "sandwich" structures.
Abstract: A novel composite material has been developed based on thermoplastic polymers on one hand and thermoplastic chalcogenide glass on the other hand. Extrusion technique and pressing allowed the production of very different structures of the composite, ranging from fibrous to “sandwich” structures. Also obtained were highly homogenous compositions that contain perfectly spherical glass particles of 1-6 mm in diameter dispersed into a polymer matrix.Optical properties of the composite have been studied thoroughly. It was established that extrusion allows the obtaining of composites, which are highly transparent in the 2-25 mm wavelength band when the concentration of the chalcogenide glass does not exceed 33%. When the concentration of chalcogenide glass was as great as 40%, dramatic changes in the transmission spectrum were observed. The extruded films are opaque not only in the visible band but in the near and middle IR as well, while being transparent in the far IR band. Such composite films are suitable as...
TL;DR: In this article, an elastic-plastic thermal stress analysis is carried out on a thermoplastic composite beam made of steel fiber thermoplast carbon fiber matrix composite, which is fixed by two rigid planes at the ends.
Abstract: In this study, an elastic-plastic thermal stress analysis is carried out on a thermoplastic composite beam. Temperature is chosen to vary linearly along the sections of the beam. The beam is made of steel fibre thermoplastic matrix composite. It is fixed by two rigid planes at the ends. The solution is performed for 0°,45°,60° and 90° orientation angles. The orientation angle of 30° does not give any plastic yielding, for it melts before plastic yielding. The intensity of the residual stress component of σx is maximum at the upper and lower surfaces of the beam and is obtained to be the greatest for the orientation angle of 0°. The equivalent plastic strain is found to be the greatest for 0° and 60° orientation angles. Plastic yielding begins on the beam at the highest temperature for 45° orientation angle.