Mehrdad N. Ghasemi Nejhad

Thermal Analysis for Thermoplastic Composite Tow/Tape Preheating and Pultrusion

The on-line consolidation of thermoplastic composites is a relatively new technology that can be used to manufacture composite parts with complex geometries. The localized melting/solidification technique employed in this process can reduce the residual stresses and allow for improved dimensional stability and performance. An additional advantage of this technique is elimination of the curing steps that are necessary in the processing of thermoset-matrix composites. This paper discusses analytical and numerical anisotropic thermal analysis for preheating and/or pultrusion of impregnated composite tows or tapes. Heat of melting/solidification is included in the form of a heat generation term. A separation of variable method is employed to solve the governing equations analytically. In the numerical analysis, the governing equations are discretized using a nonuniform mesh and solved employing a finite difference approach. The processing parameters, such as processing speed, heat intensity, heat source width, etc., as well as material properties are incorporated in the analysis. The maximum error between the analytical solution and the numerical result is found to be 1%.

Experimental and Computational Study of APC-2/AS4 Thermoplastic Composite C-Rings

The mechanical performance of APC-2/AS4 thermoplastic composite C-ring samples with different processing conditions was investigated, and experimental results were compared with numerical results using finite element methods (FEMs). Mandrel/substrate preheating was found to be necessary for good-quality parts. Ten sets of samples, with five samples per set, were manufactured using in-situ thermoplastic composite filament winding. For the first five sets, tape preheated to below the glass transition temperature (Tg ) at 110°C was used, while the consolidation pressure for various sets was 5.5, 12.6, 19.4, 26.0, and 32.4 kN/linear-meter. The same pressures were used for the next five sets while the tape was preheated above the Tg at 170°C. Scanning electron microscopy (SEM) was used for quality control. C-ring tests were performed to evaluate failure stress, strain, and deflection of C-rings at room temperature. Samples failed in compression at ring mid-section and inner radius. Samples made with 12.6 and 19.4 kN/linear-meter consolidation pressures yielded the best results. Non-linear FEM was employed to simulate the C-ring experiment using shell, target, and contact elements. The experimental deflection to failure was applied to the model, and the failure stress, strain, and load were determined. The results from non-linear numerical analysis were slightly higher than those determined from available analytical solution.

Design, Analysis, Manufacture, and Test of APC-2/AS4 Thermoplastic Composite Pressure Vessels for Deep Water Marine Applications

A general design and analysis methodology is presented for the development of thick-wall thermoplastic composite pressure vessels for deep-water marine applications. A parametric study was performed to determine the optimum tapered radius, initial radial clearance, and plug length of the plug-supported end-caps employed here as end-closures since it was found that these optimum parameters could improve the performance of the composite pressure vessels by minimizing bending and shear stresses near the ends. Stress and buckling nonlinear finite element analyses (FEA) were performed taking hygrothermal effects into account. An equivalent coefficient of thermal expansion to model coefficient of moisture expansion for FEA software, where moisture absorption is not an input, is introduced to fully model hygrothermal effects. Based on the FEA results and taking the pressure vessel weight, ease of fabrication, mechanical and environmental performance, and cost into account APC-2/AS4 thermoplastic composite was found to be a suitable material system for the pressure vessel. An in situ thermoplastic composite filament winding/tape laying system employing infrared local and global heaters was developed in the Advanced Materials Manufacturing Laboratory of the University of Hawaii at Manoa, and was employed to manufacture the thick-wall composite pressure vessels. The manufactured pressure vessels had excellent quality, were instrumented by strain gages, and then successfully tested in the Hawaii Institute of Geophysics of the University of Hawaii at Manoa high-pressure water-filled pressure chamber. The strain gage results from the experiments were compared with those obtained from the FEA and excellent agreements were achieved.

Processing and Performance of Continuous Fiber Ceramic Composites by Preceramic Polymer Pyrolysis: I—Filament Winding:

Continuous Fiber Ceramic Composite (CFCC) tubes have been manufactured using cure-on-the-fly and no cure-on-the-fly filament winding by preceramic polymer pyrolysis route. Processing guidelines to effectively use the cure-on-the-fly filament winding technique for the manufacture of CFCCs are introduced in this paper. The preceramic polymer used in thiswork is Blackglas™ (a siloxane polymer). Afilament winding machine was designed to adapt to the brittle nature of the fibers and the relatively low temperature cure of the polymer. Seven reinfiltration/pyrolysis cycles, with about 17 hours per cycle, were necessary to reach a convergence by weight. C-ring tests at both room and high temperature were performed to assess the quality of the manufactured parts. Scanning Electron Microscopy (SEM) was used to further examine the microstructure and quality of the parts. Effects of infrared cure-on-the-fly, fiber coating/material system, part thickness, and service temperature on the processing and mechanical performance of the manufactured CFCCs were studied.

Processing and performance of Nicalon/Blackglas and Nextel/Blackglas using cure-on-the-fly filament winding and preceramic polymer pyrolysis with inactive fillers

Abstract The effects of inert powder inclusion on processing and mechanical performance of Nicalon/Blackglas and Nextel/Blackglas prepared by cure-on-the-fly filament winding with preceramic polymer pyrolysis have been investigated. Ceramic fiber reinforcements were boron-nitride-coated Nextel® and carbon-coated Nicalon™. Blackglas™ preceramic polymer was mixed with the micron size inert fillers in the presence of a surfactant agent, Hypermer PS2, to achieve a good dispersion of the powder during the process. Nextel/Blackglas, Nextel/Blackglas–TiN, Nextel/Blackglas–TiC, Nextel/Blackglas–SiC, Nextel/Blackglas–Si 3 N 4 , Nicalon/Blackglas, Nicalon/Blackglas–TiN, and Nicalon/Blackglas–Si 3 N 4 tubes were manufactured. Scanning electron microscopy revealed the good quality of the parts. Samples with fillers exhibited excellent shape retention by comparison with those without fillers. C-ring tests were performed to evaluate the mechanical performance of the C-rings at room temperature. The production rate of samples composed of Nextel and Nicalon/filler increased by 14–28%. The strength and displacement to failure dropped by 6–28% and 5–33%, respectively, for Nextel-based samples, and the same values for Nicalon-based samples were 22–33% and 30–46%, respectively. No conclusive statement could be made for modulus. Effects of material system were studied and the results revealed that samples composed of BN-Nextel® showed better mechanical performance over samples composed of C-Nicalon™.

Effects of Geometric Optimization of Plug-Supported End-Caps on the Performance of Thick Thermoplastic Composite Pressure Vessels Under External Hydrostatic Pressure

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]4 subjected to an external hydrostatic pressure of 71 MPa. The results of finite element analysis revealed that the performance of the pressure vessel greatly depends on the length of the tapered section as well as the tapered radius of the contoured-end plug-supported end-caps. In addition, it is shown that an initial radial clearance of plug-supported end-caps can also affect the performance of the pressure vessel. The optimum performance of the pressure vessel was obtained when the length of the tapered section and tapered radius were 38.1 mm and 3.3 m, respectively. The best initial radial clearance for this pressure vessel was found to be 0.5 mm; however, sealing issues should also be taken into account when selecting the final amount of an initial radial clearance. The comparisons between the performances of the pressure vessels reveal that the stress factor of safety of the pressure vessels using plug-supported end-caps with optimum tapered and initial radial clearance can be 2 and 2.29 times, respectively, greater than that for the pressure vessel with plug-supported end-caps.

Processing and Performance of Continuous Fiber Ceramic Composites by Preceramic Polymer Pyrolysis: II—Resin Transfer Molding

Vacuum Assisted Resin Transfer Molding (VARTM) was used in conjunction with preceramic polymer pyrolysis to manufacture Continuous Fiber Ceramic Composites (CFCCs). Two VARTM techniques were used: (a) the use of injection pressure in the presence of a vacuum and (b) the use of vacuum only without the injection pressure. After initial testing, eight CFCC tubes were fabricated using these techniques. The matrix material used was Blackglas™. C-Nicalon™ in the form of woven fabric and BN-Nextel ®312 in the form of braided textile were used as reinforcements. C-Nicalon™ CFCC tubes with 4%–6% porosity, 55%–57% fiber volume fraction, and 2.12–2.18 g/cm3 density reached convergence by weight in 10 cycles (with about 17 hours per cycle), while BN-Nexlet ®312 CFCC tubes with 4%–6% porosity, 70%–72% fiber volume fraction, and 2.42–2.48 g/cm3 density converged by weight in 8 cycles. TheVARTMprocessing time averaged 15 minutes for each tube. The mechanical performance of the components was evaluated at room and high temperatures using a C-ring test. Scanning Electron Microscopy (SEM) was employed to study the microstructure of the parts. The results show that the without injection pressure technique offers a promising method to produce tubular CFCCs in terms of lower manufacturing costs, part uniformity, and enhanced mechanical properties. BN-coating performs better at high temperature compared with C-coating. Also, a combination of BN-coating and a textile braided architecture of fiber preform proved to enhance the performance of the manufactured CFCCs. Finally, the mechanical performances of the manufactured CFCC tubes using VARTMtechnique were compared with those using a cure-on-the-fly filament winding technique for a similar geometry using the same materials.

Design, Manufacture, and Characterization of Composites Using On-Line Recycled Thermoplastic Powder Impregnation of Fibers and In-Situ Filament Winding:

Recycled thermoplastic powder impregnated composites using in-situ filament winding and on-line consolidation of fibers have been successfully manufactured with the modified filament winding setup constructed in this study. Reclaimed low density polyethylene (RLDPE), reclaimed low-density polyethylene with polymer additives consisting of 0.25% by weight of Cyasorb® UV-3346 Light Stabilizer, 0.25% by weight of Cyasorb® UV-53 1 Light Stabilizer, and 0.08% by weight of Cyanox® 2777 Antioxidant (RLDPE-PA), and virgin low-density polyethylene (LDPE) were pulverized to ultrafine powders ranging from 20 to 300,um, and utilized to impregnate a separated fiberglass tow. After initial experiments, two powder-impregnated composite tubes were manufactured for each thermoplastic material system. The composites were then tested for tensile (hoop) strength and compressive bending strength under the ASTM D2290-95 and C-ring tests, respectively. This study showed that while the RLDPE composite did not perform well, composite samples made with RLDPE and polymer additives (i.e.. RLDPE-PA) performed better than RLDPE samples but not as well as composites made of virgin LDPE. The impregnation and consolidation steps in the manufacturing process were also effective for all three systems. The composite tubes exhibited very low void contents and high fiber volume fractions, while unmelted and unconsolidated thermoplastic powders were not present in the manufactured parts. The absence of fiber waviness and fiber migration through the thickness of the composite demonstrates that the online consolidation of powder-impregnated fibers was also effective. The collection of the separated powder-impregnated fibers prior to filament winding also seemed to be sufficient.

Development of multifunctional nanocomposites with 3-D printing additive manufacturing and low graphene loading

Fused filament fabrication (FFF) or fused deposition modeling is an additive manufacturing (AM) process commonly used for geometric modeling and rapid prototyping of parts called three-dimensional (3-D) printing. Commonly used thermoplastic materials in FFF 3-D printing AM are acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and polybutylene terephthalate (PBT). However, these materials exhibit relatively low strength and toughness. Therefore, it is desirable to improve various properties of thermoplastics in 3-D printing AM by employing nanotechnology. The combination of 3-D printing and nanotechnology opens new venues for the manufacture of 3-D engineered materials with optimized properties and multifunctionality (e.g. mechanical, electrical, and thermal properties). Hence, in this work, the multifunctional property improvement effects of graphene oxide (GO) on thermoplastic materials suitable for 3-D printing AM are investigated. Low loading of GO with carboxyl and hydroxyl surface functional groups is incorporated into thermoplastic materials suitable for 3-D printing AM by a special mixing technique. ABS is chosen in this study due to its availability. Graphene nanosheets are employed to improve the properties of the developed nanocomposites by 3-D printing AM. GO is chosen to improve the dispersion of graphene nanosheets into the thermoplastic system to increase their interfacial adhesion. A multifunctional property improvement is observed in the developed nanocomposite with less than 0.1 wt% GO. Employing ASTM standard tests, it was found that at a very small loading of 0.06% by weight, GO could improve the properties of the thermoplastic in terms of strength, strain-to-failure, and toughness, while maintaining the stiffness, rendering the developed nanocomposites suitable for various applications of static and dynamic loading. GOs are now commercially available at low prices. At such low loadings, these graphene-type materials become economically feasible components of nanocomposites.

T300HoneySiC: a new near-zero CTE molded C/SiC material

Using an Additive Manufacturing process, Trex Enterprises and teammates were successful in producing a 12-inch by 12-inch by 0.5-inch vented, lightweight, Honeycomb C/SiC ceramic matrix composite (CMC) panel which had a density relative to bulk silicon carbide of 11% (89% lightweighting). The so-called T300HoneySiC™ panel and facesheet stock material were fabricated into ASTM standard coupons and tested at Southern Research Institute to obtain basic materials properties data. The material properties data showed that we had made a near-zero coefficient of thermal expansion (CTE= -0.22 ppm/°C from -196°C to +24°C) CMC C/SiC material with good strength. This material will be ideal for space opto-mechanical structures and optical benches due to its near-zero CTE and light weight. The material is initially molded and then converted to a C/SiC ceramic matrix composite, thus the fabrication time can be less than 3 weeks from start to finish, resulting in low cost.