Showing papers in "Advanced Composite Materials in 1999"
TL;DR: In this article, SiC and Si3N4 materials were tested under various turbine engine combustion environments, chosen to represent either conventional fuel-lean or fuel-rich mixtures proposed for high speed aircraft.
Abstract: SiC and Si3N4 materials were tested under various turbine engine combustion environments, chosen to represent either conventional fuel-lean or fuel-rich mixtures proposed for high speed aircraft. Representative CVD, sintered, and composite materials were evaluated in both furnace and high pressure burner rig exposure. While protective SiO2 scales form in all cases, evidence is presented to support paralinear growth kinetics, i.e. parabolic growth moderated simultaneously by linear volatilization. The volatility rate is dependent on temperature, moisture content, system pressure, and gas velocity. The burner tests were used to map SiO2 volatility (and SiC recession) over a range of temperature, pressure, and velocity. The functional dependency of material recession (volatility) that emerged followed the form: exp(-Q/RT) * Px * vy. These empirical relations were compared to rates predicted from the thermodynamics of volatile SiO and SiOxHv reaction products and a kinetic model of diffusion through a moving ...
151 citations
TL;DR: In this article, a method for prediction of fatigue strength under temperature environment was proposed for polymer composites and its validity was confirmed for the flexural fatigue strength of satin-woven CFRP laminates and others.
Abstract: A method for prediction of fatigue strength under temperature environment was proposed for polymer composites and its validity was confirmed for the flexural fatigue strength of satin-woven CFRP laminates and others. This method is based upon the four hypotheses: (A) same failure process under constant strain-rate (CSR), creep, and fatigue loadings, (B) same time-temperature superposition principle for all failure strengths, (C) linear cumulative damage law for a nondecreasing stress process, and (D) linear dependence of fatigue strength upon stress ratio. Data are provided for tensile CSR, creep, and fatigue tests at various loading rates, frequencies, and temperatures in the longitudinal direction of unidirectional CFRP. In this paper, experimental verification of the prediction method is discussed for the tensile fatigue strength of unidirectional CFRP.
68 citations
TL;DR: In this paper, the material design of ceramic matrix composites (CMCs) is discussed in terms of fiber nature and architecture, interphases (pyrocarbon, BN, multilayers), matrices and seal-coating, taking into account lifetime considerations.
Abstract: The material design of ceramic matrix composites (CMCs) is discussed in terms of fiber nature and architecture, interphases (pyrocarbon, BN, multilayers), matrices and seal-coating, taking into account lifetime considerations. CMCs are processed by liquid or gas phase routes. Besides the well established processing routes, such as polymer impregnation and pyrolysis (PIP), slurry impregnation/hot pressing (SIHP) and isothermal/isobaric chemical vapor infiltration (I-CVI) techniques, emerging processes allowing densification times of the order of a day, are discussed.
61 citations
TL;DR: In this paper, the authors discuss recent advances in oxide-oxide composite technology and present a review of these advances in Advanced Composite Materials: Vol. 8, No. 1, pp. 17-23.
Abstract: (1999). Recent advances in oxide-oxide composite technology. Advanced Composite Materials: Vol. 8, No. 1, pp. 17-23.
17 citations
TL;DR: In this article, the authors investigated the correlation of the damage resistance under low velocity impact and Mode II interlaminar fracture toughness in five material systems, namely, T800/3631 (CF/Epoxy), UT500/PEEK (CF,PEEK), AS4/PEK (CF), IM7/PIX-A (CF polyimide), and T 800/3900-2 (Toughened Epoxy).
Abstract: Investigated in this study was the correlation of the damage resistance under low velocity impact and Mode II interlaminar fracture toughness in five material systems, namely, T800/3631 (CF/Epoxy), UT500/PEEK (CF/PEEK), AS4/PEEK (CF/PEEK), IM7/PIX-A (CF/Polyimide) and T800/3900-2 (CF/Toughened Epoxy). These materials can be roughly divided into two types. One is a compatible type, which shows high impact resistance under low velocities with high Mode II delamination resistance. The other type is a non-compatible type, which has poor impact resistance at low velocities, even though it has superior Mode II delamination resistance. As for the system of T800/3631, T800/3900-2 and IM7/PIX-A composites, the Impact Energy (IE)/Damage Area (DA) ratio correlates well with GIIC(0 : PMAX), Mode II energy release rate characterized at PMAX, and GIIR(0), Mode II energy release rate in propagation, for the 0/0 interface. The system of these materials is the compatible type. On the other hand, as for the system of T800/...
16 citations
TL;DR: In this paper, a semi-solid magnesium alloy was squeeze-cast into an aluminum borate whisker preform, and the dependence of the binder types, which were the SiO2, Al2O3, and TiO2 sols, was measured.
Abstract: To develop a new kind of composite material, 'graded morphology MMCs', a semi-solid magnesium alloy was squeeze-cast into an aluminum borate whisker preform. Currently, to increase the interfacial tensile/shear strength between MMCs and some metal parts, the joining processes have been studied. However, a suitable process has not yet been found. In this study, we first studied the optimum manufacturing condition to increase the preform compressive strength which should be necessary to prevent the preform from deformation in the squeeze cast process. The dependence of the binder types, which were the SiO2, Al2O3, and TiO2 sols, the binder content (0-5 mass% vs whisker amount), and the sintering temperature (1000- 1 160°C) of the preform were measured. We then examined the microstructure of the obtained material which was in situ joined with the semi-solid magnesium alloy (Mg-9 mass% Al-1 mass% Zn). The results were as follows: (1) The SiO2 sol was the most effective as a binder to increase the preform comp...
16 citations
TL;DR: In this article, the minimum weight design of composite plates in the presence of cutouts undergoing large amplitude oscillations was investigated. And the optimal value was found by using a genetic algorithm with tournament selection.
Abstract: The present investigation concerns minimum weight design of composite plates in the presence of cutouts undergoing large amplitude oscillations. The Ritz finite element model using a nine-noded C0 continuity, isoparametric element along with a higher order displacement theory which accounts for parabolic variation of transverse shear stresses is used to predict the dynamic behavior. The optimal value is found by using a Genetic Algorithm with tournament selection. Results have been obtained for various cutout geometries like square, rectangular, circular and elliptical in the large amplitude range.
11 citations
TL;DR: The various standards for CFCCs are reviewed and additional areas requiring normalization are discussed (e.g. mechanical, thermal, electrical, electro-magnetic, optical, and biological testing).
Abstract: Ceramic matrix composites (CMCs) and, in particular, continuous fibre ceramic composites (CFCCs) are targeted for industrial, aerospace and other high-technology applications that require the high-temperature properties and the wear/corrosion resistance of advanced ceramics while providing inherent damage tolerance (i.e. increased 'toughness') without the volume/ surface area-dependent strengths of monolithic ceramics. To utilize CFCCs designers need reliable and comprehensive data bases (and the design codes that contain them). Generating reproducible information for these data bases requires standards. Presently, there are relatively few (compared to metals) national (e.g. ASTM, CEN, JIS, etc.) or international standards (e.g. ISO) for testing CFCCs. In this paper, the various standards for CFCCs are reviewed and additional areas requiring normalization are discussed (e.g. mechanical, thermal, electrical, electro-magnetic, optical, and biological testing). 'Design codes' such as the ASME Boiler and Pres...
10 citations
TL;DR: In this article, the authors evaluated the strength of two-and three-ply FRP composite with artificial damage under internal pressure using the ring burst test developed by the authors [1, 2], and they confirmed that AE analysis is exellent for monitoring the propagation of delamination in an FRP pressure vessel with damage.
Abstract: The strength of two- and three-ply FRP composite with artificial damage under internal pressure was evaluated using the ring burst test developed by the authors [1, 2]. Ring specimens were fabricated by a filament winding (FW) machine. In this study, the simulated damage of the scratch and the combination of scratch and pre-existing interlaminar delamination, i.e. teflon sheet inserted between the outermost and the inner FRP layers, were introduced artificially into the FW-FRP specimen. The fracture behavior during the tests of damaged FRP was characterized by observation using an 8-mm video camera and a high magnification video scope, strain measurements and AE analysis. It was confirmed that AE analysis is exellent for monitoring the propagation of delamination in an FRP pressure vessel with damage. The pressure of a notched specimen showed the maximum when the delamination propagated to the half region of the specimen. The maximum pressure was larger than the predicted pressure based on the premise tha...
10 citations
TL;DR: In this paper, a new peeling test of FRP sheets bonded on mortar and concrete was proposed to characterize the peeling strength and examine the effects of different surface treatment and primer.
Abstract: A new peeling test of FRP sheets bonded on mortar and concrete was proposed to characterize the peeling strength and examine the effects of different surface treatment and primer. A simple data reduction method was proposed for the energy release rate due to peeling from the viewpoint of fracture mechanics and theory of thin membrane. The effect of surface treatment and primer was compared by energy release rate, initiation load, and maximum load. Observing energy release rate and initiation load, it was shown that there were some differences between non-primer and primer, and observing maximum load, it was shown that there were some differences among different surface treatments.
9 citations
TL;DR: In this article, the authors present a methodology to measure the strength of monofilaments which are commonly used for fiber-reinforced composite materials using a so-called loop test.
Abstract: This paper presents a methodology to measure the strength of monofilaments which are commonly used for fiber-reinforced composite materials. A so-called loop test is adopted for the present test. B...
TL;DR: In this article, the three-dimensional finite element method (FEM) is applied to a quasi-isotropic carbon fiber reinforced plastic (CFRP) laminate to investigate the interlaminar free edge stresses and ply stresses under combined thermal and mechanical loadings.
Abstract: Tensile tests of quasi-isotropic (0/45/-45/90)s Carbon Fiber Reinforced Plastic (CFRP) laminate at low (-100°C), room (25°C), and high (150°C) temperatures showed that the transverse crack propagation and interlaminar delamination growth behavior are obviously affected by the temperature. In the present study, the three-dimensional finite element method (FEM) is applied to a quasi-isotropic CFRP laminate to investigate the interlaminar free edge stresses and ply stresses under combined thermal and mechanical loadings. The mechanical properties of a lamina (T800H/#3631 ) are obtained experimentally as a function of temperature and both the temperature-dependent mechanical properties and the idea of stress-free temperature are taken into account. Resulting stresses, including initial residual thermal ones due to the stress-free temperature, are used to discuss the above mentioned experimental results, which leads to the temperature-dependent critical properties for damages such as transverse crack and delam...
TL;DR: In this article, the authors proposed that the design of parts must take into account the geometrical singularities, where fiber orientations, fiber ratio and matrix content may vary rapidly.
Abstract: Thermostructural Composites are made of inorganic fibers, like carbon or ceramic fibers, associated with an inorganic matrix. So, they are able to sustain high temperatures. Many combinations and even more processing routes may be implemented. Fibers and matrix are usually brittle materials, but the composite may present a much higher toughness and a good strain to failure. Mechanical loads on thermostructural composites generate cracks which propagate under monotonous or alternate loadings. The crack pattern governs most of the composite properties. Furthermore, it allows the penetration of oxidative or corrosive agents, thus affecting the long-term properties. Design of parts must take into account the geometrical singularities, where fiber orientations, fiber ratio and matrix content may vary rapidly. Special tests on technological samples are the more efficient way to ascertain the design in these areas. Thermostructural composites are more and more used in high temperature and aggressive atmospheres,...
TL;DR: In this paper, a creep model for cross-ply laminate in which the transverse crack density is increasing was established. Viscoelasticity theory and shear lag analysis were employed for this creep model and the tracer was used to evaluate the transversal crack density.
Abstract: A creep model is established for a cross-ply laminate in which the transverse crack density is increasing. Viscoelasticity theory and shear lag analysis are employed for this creep model and the tr...
TL;DR: In this article, the effect of heat conduction from inner layers induced by the thermoelastic effect was evaluated numerically for two stacking sequences of CFRP laminates based on an analytical equation and finite element analysis.
Abstract: In an infrared stress measurement for multi-lamina CFRP, it is important to evaluate the effect of heat conduction from inner layers induced by the thermoelastic effect. Although a temperature amplitude at a specimen surface is measured in the infrared stress graphic system, the heat flux from the inner layers influences the surface temperature state because it has the same frequency as the applied loads. As a preliminary step of analysis, thermoelastic coefficients of unidirectional CFRP were investigated first. Then, the effects of heat conduction were evaluated numerically for two stacking sequences of CFRP laminates based on an analytical equation and finite element analysis. These calculated results were compared with the experimental results. Two kinds of theoretical results, analytical and finite element analysis, agreed well with experimental results. It was clearly indicated that the thermal conduction must be considered for the infrared stress measurement of multi-lamina CFRP.
TL;DR: In this article, three ceramic matrix composites (CMCs) were investigated after creep tests and the damage features of each one were identified, using optical and scanning electron microscopy (SEM), and the complete damage sequences were presented.
Abstract: Three ceramic matrix composites (CMCs) were investigated after creep tests: a 2D SiCf-MLAS, a 2D SiCf-SiC and a 2.5D Cf-SiC. The damage features of each one are identified, using optical and scanning electron microscopies (SEM), and the complete damage sequences are presented. As a result of its time-dependence, damage in CMCs may be considered as slow crack growth in the temperature and stress fields investigated. But the quantification of damage, through the classical damage mechanics, appears as a complex issue, due to the architecture effects in composite materials.
TL;DR: In this article, an anomalous stress-strain behavior is explained by the presence of an axial residual stress state which differs from that induced by the thermal expansion mismatch between the fibres and the matrix.
Abstract: Continuous fibre reinforced ceramic matrix composites (CFCCs) show a scatter in parameters such as first matrix cracking stress, initial elastic modulus, ultimate strength, etc. which characterise their mechanical behaviour. This scatter can be attributed to a large extent to variations in the axial residual stress state from specimen to specimen. Under some circumstances even negative strain accumulation with increasing stress has been observed during tensile loading of CFCCs. Examples of such anomalous stress-strain behaviour are shown, and its occurrence is explained by the presence of an axial residual stress state which differs from that induced by the thermal expansion mismatch between the fibres and the matrix. Microstructural features leading to the establishment of such an abnormal residual stress state are indicated. Combining these observations it appears that variation in the residual stress state explains both the scatter observed in tests exhibiting normal behaviour, and in tests with anomal...
TL;DR: In this article, the changes in energy absorption and crush mechanism using internal and external mandrels were investigated based on the formulation of the total energy absorbed by each fracture to control the energy absorption capabilities.
Abstract: Tapered composite tubes have high energy absorption performance under the axial compressive load. We have tried to formulate the total energy absorbed by each fracture to control the energy absorption capabilities. In this paper, the changes in energy absorption and crush mechanism using internal and external mandrels were investigated based on the formulation. Specific energy absorptions of the tubes using mandrels were higher than that of tubes compressed with flat plates because many of the fractures depended on energy absorption generate by the use of mandrels. For example, the glass cloth/epoxy tube using an external mandrel displayed specific energy absorption of 116 kJ/kg, which was the highest value recorded for any glass reinforced plastics.
TL;DR: In this article, a statistical-probabilistic approach to the mechanical behavior of CMCs is proposed, based on a statistical probabilistic description of multiple matrix cracking and fiber failures.
Abstract: The approach to the mechanical behavior of CMCs that is proposed, is based on a statistical-probabilistic description of multiple matrix cracking and fiber failures. It is applied to unidirectional and woven SiC/SiC composites. The predicted stress-strain behaviors were in good agreement with available experimental data. The influence of various factors including porosity, loading conditions and constituent properties is anticipated.
TL;DR: The Si-C-O fiber has high tensile strength and relatively high heat resistance as mentioned in this paper and has been applied as reinforcement for aluminum wire, glass-ceramics, or silicon carbide matrix composite materials.
Abstract: Several kinds of SiC-based ceramic fibers are presently fabricated on an industrial scale using precursor polymers. The Si-C-O ceramic fiber that was first developed in 1975, has high tensile strength and relatively high heat resistance. The Si-Ti-C-O fibers emerged after the Si-C-O fiber was developed. These fibers have been applied as reinforcement for aluminum wire, glass-ceramics, or silicon carbide matrix composite materials. Through the research work on these fiber reinforced metal or ceramic matrix composites, these fibers have increased heat resistance. In the past ten years, a new fabrication process of the fiber, a radiation curing method, has been developed. In addition, the conversion process of polymer precursors to ceramics and the thermal stability of the fibers have been widely studied at high-temperatures ranging above 1500 K. These research works have successfully produced excellent SiC-based ceramic fibers with high-temperature resistance. These fibers are mainly prepared from polycarbo...
TL;DR: In this paper, a singular finite element method is formulated utilizing the asymptotic solutions for displacements and stresses near the tip of the interface crack between dissimilar anisotropic materials and the variational principle of a hybrid functional.
Abstract: A singular finite element method is formulated utilizing the asymptotic solutions for displacements and stresses near the tip of the interface crack between dissimilar anisotropic materials and the variational principle of a hybrid functional. The interfacial crack problem can be analyzed by the singular hybrid element at the interfacial crack tip and the conventional displacement-based elements surrounding the crack element. Analyzing a small central interfacial crack between two large anisotropic composite layers with different fiber orientations subjected to uniform tensile load, we demonstrate that the present numerical solutions are in good agreement with the analytical ones for an interfacial crack between two semi-infinite anisotropic solids. Then, we apply the present method for the analysis of delamination originating from the transverse crack tip in laminates under plane strain extension, antiplane shear and plane strain bending.
TL;DR: In this paper, a damage mechanics model to predict the nonlinear behavior of laminated composites due to crack evolution is developed, where a cracking layer can be replaced with an equivalent uniform work-softening layer.
Abstract: A damage mechanics model to predict the nonlinear behavior of laminated composites due to crack evolution is developed. We propose a new concept that a cracking layer can be replaced with an equivalent uniform work-softening layer. With this new concept, the constitutive equations for a cracking layer are constructed according to modem plasticity theory. A lamina damage surface, i.e. a threshold of crack evolution, is defined in the stress space of each lamina, and the constitutive equations for a cracking layer are constructed by applying the defined damage surface to the associated flow rule. Then, the derived constitutive equations for a cracking layer are introduced with classical lamination theory to predict laminate constitutive behavior in the damage process. Comparisons are made between the predictions and experimental results for some laminate configurations, and reasonable agreements are shown for all laminates.
TL;DR: In this article, the design of textile preforms for reinforcing ceramic matrix composites is studied, using the concepts of micro-and macro-cells to analyze the thermo-mechanical behavior of textile composites.
Abstract: Two and three dimensional fiber preforms produced by textile forming techniques have been used successfully for reinforcing ceramic-based composites. The focus of this paper is on the design of textile preforms for reinforcing ceramic matrix composites. The research work consisted of the following tasks: (1) identification of typical loading conditions on composite structural elements; (2) determination of the requirements on the orientation and volume content of fiber reinforcement; (3) identifying the fiber preforms suitable for each loading condition; (4) identifying the preforming technologies available for producing the preforms; (5) analysis and modeling of the thermo-mechanical behavior of the textile composites, using the concepts of micro- and macro-cells; and (6) characterization of textile composite performance.
TL;DR: In this paper, a pulse CVI-slurry joint process was applied to carbon-fiber/SiC composites, which consisted of slurry infiltration, polymer infiltration and pyrolysis.
Abstract: In order to construct a suitable process for fabricating small and medium size CMC parts, attempts have been made to try to apply a pulse CVI-slurry joint process for making 3D carbon-fiber/SiC composites. The joint process consisted of slurry infiltration, polymer infiltration and pyrolysis, and pulse CVI. In the polymer infiltration and pyrolysis process, polycarbosilane was used as a preceramic polymer. The pulse CVI was carried out in a reaction temperature between 1323 K and 1423 K, using a source gas system of SiCl4-CH4-H2. The deposited phase varied with reaction temperature, gas concentration and reacting time. At 1373 K, a large amount of mass filling into a porous-matrix was observed. The flexural strength of the composite remarkably increased after the pulse CVI application. The joint process is effective for fabrication of thin and relatively simple shape parts.
TL;DR: A new concept for the R&D of advanced materials such as CMCs is proposed, namely, the Cost-Effectiveness Concept (CEC), which is one way to bring together scientific and technological targets.
Abstract: Now that the aerospace industry is no longer a dream, but a promising market, high performance structural materials are in great need. For such applications, Ceramic Matrix Composites (CMCs) are hopeful candidates. However, one of the most important problems actually hindering CMC research and development is the high cost of common process routes. To try to solve such problem, a new concept for the R&D of advanced materials such as CMCs is proposed, namely, the Cost-Effectiveness Concept (CEC). This concept is one way to bring together scientific and technological targets. In this work, this strategy will be defined and then illustrated in the case of the elaboration of 3D CMCs and of the development of oxidation protection materials.
TL;DR: In this article, a twin screw extruder was used to extract sheets from blends containing liquid crystalline polymer (LCP) and bisphenol-A polycarbonate (PC) at various take-up speeds.
Abstract: Sheets from blends containing liquid crystalline polymer (LCP) and bisphenol-A polycarbonate (PC) were prepared using a twin screw extruder at various take-up speeds. Thermal behavior, mechanical properties, and viscoelastic properties of sheets with various compositions were investigated using differential scanning calorimetry (DSC), dynamic mechanical analysis measurement (DMTA), and sonic velocity measurement. DMTA studies showed the blends to have two glass transition temperatures (Tg) corresponding to those of the PC-rich and LCP-rich phases. Blends of PC and LCP were immiscible, although their Tgs varied slightly with composition. The dynamic and sonic moduli increased with increasing LCP content owing to the high modulus of LCP. The modulus remained unchanged with increasing LCP content at low LCP wt% (<20 wt% LCP).
TL;DR: In this paper, the static strength and fatigue life of graphite/epoxy laminates were measured using a tensile coupon and Hwang and Han's MFLPE I (modilized fatigue life prediction equation (1)), which is based on the fatigue modulus degradation model and reference modulus, was chosen for predicting the repaired specimen and compared with the conventional fatigue life equations such as S-N curve and Basquin's relation.
Abstract: The static strength and fatigue life of repaired graphite/epoxy laminates was observed using a tensile coupon. The lay-up of investigated laminates was [0°/±45°/90°]s. Static strength was measured from the specimens prepared by various repair techniques such as cosmetic treatment, precured-single patch, precured-double patch and cure-in-place patch methods. The strength was recovered to the extent of 60-70% of unnotched case. Fatigue life was also measured from the laminates repaired with cure-in-place patch method. Hwang and Han's MFLPE I (modilied fatigue life prediction equation (1)), which is based on the fatigue modulus degradation model and reference modulus, was chosen for fatigue life prediction of the repaired specimen and compared with the conventional fatigue life equations such as the S-N curve and Basquin's relation. The MFLPE 1 agrees more closely with experimental data than the S-N curve or Basquin's relation.