Preformed Yarn Research Articles

Experimental investigation on Mode-I fracture toughness of Carbon-Carbon composites fabricated by preformed yarn method

Carbon-Carbon composites are one such material that gives designers significant importance for advanced applications over conventional materials. They are applied in applications at very high temperatures (up to 3000 °C), and under extreme conditions. They have a density which is much less than metals and ceramics and thus, make low part weight a significant factor for aerospace applications. Fracturing toughness is a measurable way to express a substance's resistance to fracture in the case of a break.This paper describes the experimental studies done to investigate the Mode-1 fracture toughness of carbon–carbon composites which was fabricated via the preformed yarn method. Fracture toughness was determined for four different (a/w) ratios i.e. 0.45, 0.47, 0.50 and 0.52 respectively. The results showed that with only two cycles of pitch impregnation, HIP and graphitizing, carbon–carbon composites were successfully produced. The specimen having an (a/w) ratio of 0.45 had a higher fracture toughness value in comparison with all values. As the (a/w) ratio was increasing, the fracture toughness value decreased and the fractured surface clearly shows a brittle fracture behavior.

Effect of fiber weight fraction on mechanical properties of carbon–carbon composites

AbstractThis article presents the synthesis of carbon–carbon (C/C) composites by preformed yarn (PY) method, by varying the percentage of carbon fiber weight fraction. The PY used was carbon fiber bundle surrounded by coke and pitch which was enclosed in nylon‐6. Three types of samples with fiber weight fractions of 30, 40, and 50%, respectively, are fabricated and mechanical properties were studied. In each case, the PY was chopped and filled into a die of required shape and hot pressed at 500°C to get the preform composite. To obtain the carbonized and graphitic structure, the specimen was heat treated at 2500°C followed by soaking for 10 to 12 hrs. Further, two cycles pitch impregnation was done by hot isostatic pressing, to eliminate the voids and to increase the density hence to obtain good mechanical properties. The characteristics such as hardness, flexural strength, and impact strengths were studied. It is observed that, as the carbon fiber percentage increases, the properties also get improved, provided sintering is done at fairly higher temperatures such as 2700°C. The superiority of the new class of C/C composites made by the proposed PY technique over those obtained by the conventional methods is also demonstrated. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Development and characterization of carbon-carbon composite for aircraft brake pad using preformed yarn method

This paper presents the synthesizing of carbon-carbon (CC) composites by preformed yarn (PY) method, by varying the percentage of carbon fiber volume. The PY used is carbon fiber bundle surrounded by coke and pitch which is enclosed in nylon-6. Three types of samples with fiber weight fractions of 30%, 40% and 50% respectively, are fabricated and tested. In each case, the PY is chopped and filled into a die of required shape and hot pressed at 600°C to get the carbonized composite. To obtain the graphitic structure, the specimen is heat treated at 1800°C followed by soaking for two hours. Further, one cycle pitch impregnation is done by hot isostatic pressing, to eliminate the voids. The characteristics such as hardness, compressive strength, creep, density and oxidation resistance are studied. It is observed that, as the carbon fiber percentage increases the properties also improved, provided sintering is done at fairly higher temperatures. The superiority of the new class of CC composites made by the proposed PY technique over those obtained by the conventional methods is also demonstrated.

Mechanism of synthesizing dense Si–SiC matrix C/C composites

The following technique is known to synthesize C/C (carbon fiber-reinforced carbon) composites. The organic matter in the preformed yarn (plastic straw covered yarn including bundles of long carbon fibers, carbon powder, and organic binder) is pyrolyzed at 500 °C and concurrently hot-pressed. Then, the carbon ingredient is graphitized in an atmosphere of nitrogen at 2000 °C. The authors used the above mentioned C/C composites as a starting material and developed a dense Si–SiC matrix C/C composites in which most long carbon fibers remain without reacting with Si which is infiltrated in argon at 1600 °C and 100 Pa. As a result, production of 1 × 2 m large size plates free from warps and cracks was attained in NGK Insulators, Ltd. This mechanism consists of three steps. First, a trunk-shaped Si–SiC matrix is synthesized between yarn and yarn. Then a trunk-shaped Si–SiC matrix extends a yarn by force. Only differential gap is made in a yarn surface. Finally, branch-shaped Si–SiC matrix is synthesized so that a trunk-shaped Si–SiC matrix leads to the yarn inside.

Fatigue characteristics of metal impregnated C/C composites with slots for load transfer

An experimental investigation is performed on the quasi-static and cyclic behavior of metal impregnated composites such as Cu–C/C and Si–C/C with a slot together with C/C for comparison. They are expected to be applied to an aircraft brake system. Composites tested are based on a preformed yarn method and their fatigue strength and related characteristics are obtained. Damage mechanisms are discussed and it is concluded that effects of microscopic debonding are quite important to the fatigue response of the present specimen and that the debonding makes the failure mode shift from crack propagation in static loading to bearing in cyclic loading.

Strength of metal impregnated C/C under tensile cyclic loading

An experimental investigation is conducted on the tensile cyclic behavior of metal impregnated composites based on a preformed yarn method such as Cu–C/C and Si–C/C together with C/C. Specimens are loaded cyclically in tension and tension. Their S–N curves and the fatigue strength of about 0.8UTS at around N = 10 4 were obtained. Macroscopic and microscopic characteristics are discussed to yield the cyclic failure mechanism as follows. In a low cycle region, the decrease of shear resistance caused by wear at the fiber/matrix interface increases the probability of fiber break, while after about 10 4 cycles the smoother interface and longer debonding area suppress the decrease of shear resistance. Thus, the probability of fiber break does not increase.

520 プリフォームドヤーン法で作製されたC/C複合材料の強度に関する研究(OS 先端材料の力学特性と計測技術(1))

520 プリフォームドヤーン法で作製されたC/C複合材料の強度に関する研究(OS 先端材料の力学特性と計測技術(1))

Tensile Strength of Carbon/Carbon Composites

In order to identify ruling mechanisms of tensile fracture of Carbon/Carbon composites (C/Cs), tensile tests were carried out for various C/Cs as functions of the density, heat treatment temperature, and interfacial strength between fiber and matrix. Three processing routes of preformed yarn, resin char, and HIP processes were adopted to densify C/Cs. These C/Cs were finally heat-treated at temperatures from 2 273 K to 3 300 K. The interfacial strength between fiber and matrix was varied by the selection of processing routes. As a result, two ruling failure mechanisms were identified. At density lower than 1.6 g/cm 3 , the tensile fracture was controlled by stress transfer capability from the matrix to reinforcing fibers. However, at higher density than 1.6 g/cm 3 , tensile strength was primarily governed by the interfacial strength between the matrix and fibers. Thus the latter mechanism is nearly same as ceramic matrix composites.

234 Tensile strength of Carbon/Carbon Composites

In order to identify ruling mechanisms of tensile fracture of Carbon/Carbon composites (C/Cs), tensile tests were carried out for various C/Cs as a function of the density, heat treatment temperature, and interfacial strength between fiber and matrix. Three processing routes of preformed yarn, resin char, and HIP processes were adopted to densify between fiber and matrix was varied by the selection of processing routes and their conditions. As a result, two ruling failure mechanisms were identified. At low density lower than 1.6g/(cm)^3,the tensile fracture was controlled by stress transfer capability from the matrix to reinforcing fibers. However, at higher density than 1.6g/(cm)^3,tensile strength was primary shown to be governed by the interfacial strength between the matrix and fibers. Thus this mechanism is nearly same as ceramic matrix composites, i.e., strong fiber/matrix interface resulted in low ultimate elongation of C/Cs.

Strength improvement by densification of C/C composites

The tensile strength of carbon/carbon composites (C/Cs) was examined as a function of the density in the range above ρ=1.6 g/cm 3. Three processing routes of preformed yarn, resin char, and HIP processes were adopted to densify the C/C composites. The density was increased to 1.95 g/cm 3 through these routes. The interfacial strength between the fiber and matrix was significantly and unexpectedly varied by repeating the HIP process, though the detailed source mechanisms could not be identified. The tensile strength of the densified C/Cs was shown to be dependent on the processing routes. In particular, opposite tendencies were obtained as a function of ρ, i.e. the monotonic strength increases for the C/Cs with the preformed yarn and resin char treatments, while a monotonic decrease was observed using the HIP process. However, after the tensile strength was re-examined, the ultimate tensile strain was found to be expressed by a monotonic decreasing function of the interfacial strength. This implies that weakening fiber interfaces is a key factor for obtaining C/C composites with the higher tensile strength.

Manufacture of Unidirectional Carbon Fiber Reinforced Carbon Composites by Preformed-Yarn Method

A bundle of polyacrylonitrile-based carbon fibers was included in a matrix precursor composed of fine pitchcoke and mesophase pitch, and was coated with polypropylene, resulting in a preformed yarn (PY). Unidirectional (UD) PY sheets, prepared by aligning the PYs, were stacked. Hot press molding of the staked UD-PY sheets at 600°C and heat treatment up to 2000°C were performed to manufacture a UD-C/C composite. Density, porosity, flexuralstrength and modulus of the resulting UD-C/C composite test pieces were measured. Flexural strength and modulusof the UD-C/C composite test pieces manufactured from PY with 40wt% pitch coke in its matrix precursor were487.3MPa and 125.4GPa, respectively. Even without impregnation, these value were superior by a factor of about 1.3than the UD-C/C composites manufactured by conventional method using phenol resin as a main component of matrixprecursor. Microstructural inspections of cross sections of the test pieces were also carried out. Any kind of pore werehardly recognized and a good fiber/matrix bonding was formed in the matrix of the UD-C/C composites manufactured from PY with 40wt% pitch coke in its matrix precursor.

Evaluation of High-Temperature Oxidation Characteristics of Two Directionally Laminated C/C Composite Fabricated by the Preformed Yarn Method

Oxidation kinetics of as received and preheat-treated C/C composites fabricated by the preformed yarn method were investigated. The weight loss due to gasification was measured with oxidation time. In situ observation of microscopic morphological change due to oxidation was conducted using a laser microscope during heating in flowing air. Then, degraded inner and outer morphologies of C/C composites oxidized at various temperatures were examined through observation by SEM and measurement of pore distribution using a mercury porosimeter. As a result, degraded morphologies due to oxidation were extremely different depending on the oxidation temperature range. The inner structural changes became obvious as the oxidation temperature decreased. Therefore, the rate-determining process of the oxidation was changed from the surface chemical reaction to reactive gas diffusion across the boundary layer of a gaseous oxidation product as the oxidation temperature increased. The oxidation reactivity of C/C composites was related to metallic impurities such as iron and residual stress generated during fabrication.

Flexural and Interlaminar Shear Properties of C/C Composite at Elevated Temperatures

Flexural and interlaminar shear properties of carbon fiber reinforced carbon (C/C) composite, fabricated by “the preformed yarn method”, were evaluated at elevated temperatures up to 2300°C in vacuum. Four point flexure test and short beam test were carried out on the C/C composites of unidirectional, cross-ply and quasi-isotropic laminates. Effect of absorbed gas on the composite strength was also studied. The results revealed that flexural strength increase with increasing temperature, and was not profoundly affected by absorbed gas. On the other hand, interlaminar shear strength (ILSS) was remarkably lowered by absorbed gas at room temperature, and the test on the degased specimen showed that ILSS was kept constant up to 2300°C. Hence the absorbed gas is shown to lower matrix strength but not fiber strength. Young's modulus of C/C composites was kept constant up to 1500°C, then decreased at 2000 and 2300°C, that might be originated form temperature dependence of the Young's modulus of the carbon fiber.

Preformed yarn useful in forming composite articles and process of producing same: Okura, A., Cho, T., Nakagawa, T., Gomi, S. and Ueda, T. (Across Company Limited, Japan) US Pat 4 772 502 (20 September 1988)

Preformed yarn useful in forming composite articles and process of producing same: Okura, A., Cho, T., Nakagawa, T., Gomi, S. and Ueda, T. (Across Company Limited, Japan) US Pat 4 772 502 (20 September 1988)