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Development and Evaluation of Carbon-Carbon Threaded Fasteners for High Temperature Applications
Abstract
Carbon-Carbon (C-C) threaded fasteners have been developed for joining C-C composites experiencing temperature above 1500 °C. The fasteners were fabricated from spun yarn graphitized carbon fabric through resin route and from needle punched carbon felt through pitch route techniques. The preforms were processed with multiple cycles of impregnation, carbonisation, and graphitisation up to densities of 1.78 gcm -3 and 1.90 gcm -3. Densification process cycles were repeated to obtain composites with reduced porosity and improved thermo-mechanical properties. Material evaluation of C-C fasteners is discussed and compared with existing graphite fasteners used in industrial and aerospace sectors. Scanning electron microscopy was also carried out to study microstructure of fractured specimens.
... Mei et al. (2010) reported carbon fiber cloth reinforced 2D C/SiC bolts with the tensile strength of 210-230 MPa by CVI process. Kushwaha et al. (2012) fabricated carbon-carbon (C/C) threaded fasteners from spun yarn graphitized (SYG) carbon fabric through resin route and from needle-punched (NP) carbon felt through pitch route techniques with tensile strengths of 102 MPa and 103 MPa, respectively. ...
... Researchers worldwide have studied one or the other preforms mostly using PIP, LSI and CVI + PIP process for making composite fasteners (Verrilli et al. 2002;Böhrk et al. 2010;Wan 2005;Zhang et al. 2011;Mei et al. 2010;Kushwaha et al. 2012), but to the best of our knowledge, a comparison amongst different possible orientations of continuous fibre preform architectures for realizing nearnet-shaped composite fasteners using CVI process is not reported. There are different methodologies available for fabrication of continuous fibre preforms such as alternate stacking of carbon fabric plies in the order of 0°/90°/ ± 45° followed by stitching (termed as 2D stitched preform), weaving of carbon fibres along mutually orthogonal directions (3D woven preform) and NOOBing (Non-interlacing, Orienting Orthogonally and Binding) technique described by Khokar (2002) as a non-woven three-dimensional fabric-forming process which could be utilized for fabrication of near-net-shaped composite fasteners (4D/5D NOO-BED preform). ...
Continuous carbon fibre-reinforced silicon carbide (C/SiC) ceramic matrix composites (CMCs) are one of the most promising candidate materials for many high-temperature applications, particularly as thermo-structural hardware for aerospace and aircraft applications. However, the major challenge lies in joining these composites to the airframe for their application as re-usable thermal protection systems for re-entry vehicles. This necessitates development of suitable fastening mechanisms which can withstand the aero-thermal loads of structures during re-entry conditions. Conventionally used high-temperature fasteners are molybdenum based and they suffer from problems related to oxidation at temperatures above 800 °C in air. Thus for such applications, C/SiC fasteners are considered more reliable due to the oxidation resistance offered up to 1650 °C. This study highlights the importance of fibre orientation in continuous C/SiC composite used for fabricating C/SiC fasteners for futuristic re-entry launch vehicles. The study describes fabrication of four different types of continuous fibre-oriented C/SiC composites viz., 2D stitched, 3D woven, 4D NOOBED and 5D NOOBED configurations via chemical vapour infiltration (CVI) route, and compares their tensile property at room temperature so as to find out a suitable preform for fabrication of C/SiC fasteners. It was found that 2D stitched preform-based C/SiC specimen gave the highest tensile strength (157 ± 14 MPa), followed by 3D woven preform-based specimen (130 ± 25 MPa), while the tensile strength of 4D- and 5D-based specimens was very low. Through this study, two carbon fibre preforms viz., 2D stitched and 3D woven are selected for realizing C/SiC fasteners. The role of pyrocarbon interphase coating on carbon fibres, in obtaining high mechanical properties is also understood.
... 13 C/SiC based M6 and M8 fasteners using different types of fiber reinforcements such as carbon fiber cloth reinforced, 14 3D needled preform, 15 and alternately stacked stitched carbon fiber cloth with unidirectional carbon fiber tows 16 densified by CVI 14 and PIP 15,16 processes have been reported. Carbon-carbon (C/C) threaded fasteners realized from spun yarn graphitized carbon fabric through the resin route and from needle punched carbon felt through pitch route techniques 17 have also been reported. But to the best of our knowledge, the importance of critical dimensions such as fillet radius and thread root radius in understanding the tensile failure mode of such ceramic composite fasteners is not reported. ...
Continuous carbon fiber reinforced silicon carbide (C/SiC) ceramic matrix composites are the candidate materials for high-temperature structural applications owing to their high specific strength, low coefficient of thermal expansion, and moderate thermal conductivity. C/SiC based fasteners provide reliability with oxidation resistance up to 1,650°C for joining such C/SiC structural components used in reusable launch vehicles for space applications. The present study describes the methodology to realize C/SiC based M8 fasteners by isothermal-isobaric chemical vapor infiltration process using 2D-stitched carbon fabric preforms. The realized fasteners exhibited a density of 2.10 g/cm3, a tensile strength of 191 ± 3 MPa, a shear strength of 230 ± 69 MPa in non-threaded and 150 ± 86 MPa in threaded regions of shank at room temperature, a high-temperature tensile strength of 170 ± 12 MPa, and a tensile modulus of 70 ± 8 GPa at 1,100°C in the atmospheric conditions. The tensile failure of the C/SiC bolts was observed to depend upon the relative dimensions of fillet radius and thread root radius, wherein a small fillet radius was observed to be detrimental, as it resulted in failure at the head-shank interface of the bolts. The scanning electron microscope images of tensile tested C/SiC bolts indicate extensive fiber pullout, characteristic of quasi-ductile failure of bolts. It is clearly evident from the studies that the C/SiC fasteners are a promising alternative over the currently used molybdenum alloy fasteners.
The paper presents results of studying the impact of the strength and stiffness scaling effects in modern spatially reinforced carbon-carbon composite materials on bearing capacity of the products made from them. These materials are widely used in equipment operating under extreme conditions of simultaneous loading with force and temperature factors. When designing such products, it becomes necessary to understand the influence degree of the frame damaged during machining on observed properties of the material used, including dimensions, at which it is required to consider reduction in strength and stiffness, as well as the value, which could reduce the considered properties.
A method was proposed to test the pull-through mechanical behavior of fastener threads, which were fabricated from weave carbon/carbon (C/C) composites. The damage morphologies of the C/C fastener threads were observed through an optical microscope and high-resolution micro-CT systems. The acoustic emission (AE) technique was utilized to track the damage progression of threads during loading up to fracture in terms of AE event rate which has an exponential type profile. Finally, A 3D finite element damage evolution model of composite threads was established based on continuum damage mechanics to calculate the thread load distribution and damage progression. The relations between the pitch and the load distribution, as well as between different fabrication directions and ultimate loads, were investigated by using this model. The stress in the first thread was analyzed based on the tapered cantilever assumption. The results show that, the first thread is brittle fracture at the root where is the higher stress level region of the threads and it is the initial damage. The load distribution in C/C threads is not uniform and not improved as the value of pitch decreases. Load capacity of C/C threads is different result from the fabrication direction. Numerical results agree well with experimental results.
Fasteners made of the anisotropic carbon/carbon (C/C) composite material have been developed for joining C/C composite material components in the high-temperature environment. The fastener specimens are fabricated from the C/C composites which are made from laminated carbon cloths with Z-direction carbon fibers being punctured as perform. Densification process cycles such as the thermal gradient chemical vapor infiltration (CVI) technology were repeated to obtain high density C/C composites fastener. The fasteners were machined parallel to the carbon cloths (X-Y direction). A method was proposed to test pull-through mechanical behavior of the countersunk-head C/C composite material fasteners. The damage morphologies of the fasteners were observed through the charge coupled device (CCD) and the scanning electron microscope (SEM). The internal micro-structure were observed through the high-resolution Mirco-CT systems. Finally, an excellent simulation of the C/C composite countersunk-head fasteners were performed with the finite element method (FEM), in which the damage evolution model of the fastener was established based on continuum damage mechanics. The simulation is correspond well with the test result . The damage evolution process and the relation between the countersunk depth and the ultimate load was investigated.
We determined the phase diagram involving diamond, graphite, and liquid carbon using a recently developed semiempirical potential. Using accurate free-energy calculations, we computed the solid-solid and solid-liquid phase boundaries for pressures and temperatures up to 400 GPa and 12 000 K, respectively. The graphite-diamond transition line that we computed is in good agreement with experimental data, confirming the accuracy of the employed empirical potential. On the basis of the computed slope of the graphite melting line, we rule out the hotly debated liquid-liquid phase transition of carbon. Our simulations allow us to give accurate estimates of the location of the diamond melting curve and of the graphite-diamond-liquid triple point.
A comparative study has been carried out on mechanical behavior of two dimensionally (2D), three dimensionally (3D) and four dimensionally (4D) reinforced carbon/carbon composites (C/Cs) having 50, 48 and 37vol.% carbon fibers, respectively. The tensile and flexural strengths of 2D- and 3D-C/Cs, found as ∼25% higher than that of 4D-C/C, appear related to fiber volume fraction. The load–displacement plots obtained from three-point bend tests on single edge notch bend specimens appear non-linear, suggesting graceful failure. Scanning electron microscopy studies of crack paths have shown high tortuousity due to crack deflection, branching as well as fiber debonding and breakage. The results indicate that total fracture energy release rate (Jc) and displacement (δ0.6) at 60% of peak load are suitable parameters for evaluation of fracture resistance and damage tolerance, respectively of multi-directionally reinforced C/Cs. The values of Jc and δ0.6 have been found as maximum for 2D- and 4D-C/C, respectively.
The present paper proposes an approach to characterizing fibre/matrix (F/M) interface in carbon/carbon (C/C) composites with respect to both modes of loading that may be expected: opening or shearing. Push-out and tensile tests were used. The former tests involve the shearing mode whereas the latter ones involve the opening one. Push-out tests use a diamond indenter to load the fibres. The interface sliding shear stress was obtained from the load-fibre displacement curve. The tensile tests were conducted on specimens having fibres oriented at 90° with respect to loading direction in order to preferentially open the interfaces. Interface opening strength was extracted from the composite tensile stress–strain behaviour. The specimens were examined under load and after ultimate failure by optical microscopy (OM). The mechanical properties of the F/M interfaces were then discussed.
In-plane tensile and compressive properties of epoxy resin matrix composites reinforced with carbon fiber woven fabrics and carbon fiber felts have been compared and the influences of weave pattern and needle-punching density have been investigated. The tensile and compressive strengths of the woven laminates were derived as increasing functions of the radius of curvature of yarns, and the resulting equations well represented the measured values. The strengths of the felt/resin composites were influenced by needle-punching density as well as the weave pattern of base fabrics. Although the felt/resin composites showed lower strengths than the woven laminates, the felt reinforcement had the advantage of improving interlaminar properties as will be shown in a succeeding paper [Compos. Sci. Technol., submitted]. The compressive strength of the felt reinforced composites utilizing more brittle carbon matrix has also been investigated.
The effects of needle-punched felt structure, including mass ratio of non-woven cloth to short-cut fiber web, PAN-based carbon fiber types of non-woven cloth and thickness of unit (one layer of non-woven cloth and short-cut web was named as a unit), on the flexural properties of C/C composites from pressure gradient CVI are discussed. Results show that flexural strength and modulus increase when mass ratio of non-woven cloth to short-cut fiber web changes from 7:3 to 6:4 and that PAN-based carbon fiber types of non-woven cloth strongly influence the flexural properties. The strength of C/C composites is not linear with the strength of non-woven cloth carbon fiber because of the important interface between carbon fiber and matrix carbon. It is suitable to choose T300 or T700 as reinforcing carbon fiber for C/C composites in the present study. An optimum unit number per cm of the needle-punched felts for higher flexural properties exists.
Oxidized PAN-fiber felt was carbonized to 600, 1000, and 1800 °C, respectively. Different carbon/carbon composites (C/C composites) were prepared from oxidized PAN-fiber felt, the carbonized felts, and resol-type phenol–formaldehyde resin. These composites were then carbonized and graphized at temperatures of between 600 and 2400 °C. The C/C composite made with oxidized PAN-fiber felt showed a strong fiber/matrix bonding, and those developed from the carbonized felt (heat-treatment of 1800 °C) showed a poor fiber/matrix bonding. The graphitized composites reinforced with the oxidized PAN-fiber felt resulted in having a high flexural strength (325 MPa), and the graphitized composites reinforced with the carbonized felt (carbonized at 1800 °C) had a low flexural strength (9 MPa). It was found that the stress-orientation promoted the formation of the anisotropic texture around the fibers as well as between the fibers. This felt may very well be able to provide a low-cost route for producing multidimensional C/C composites.
This study examines the shear properties of a 2D PAN-CVI carbon/carbon composite whose reinforcement layers are formed from a non-woven duplex cloth comprising a continuous fibre layer needled to a short fibre felt layer. Composites of three lay-ups were tested in several orientations using the Iosipescu (V-notched beam) shear test. Material anisotropy means that shear failure stresses and shear moduli are required in several orientations for structural analysis. It was necessary to mitigate the effect of specimen twisting by using strain gages on both sides of the specimens. The approximate ranges of measured shear failure stresses were 30–45 MPa in-plane and 8– 22 MPa interlaminar. Shear moduli ranged between 6–16 GPa in-plane and 1–3 GPa interlaminar. While the presence of flaws in these composites leads to scatter in properties, the effect of bulk density on interlaminar properties was clearly observed.