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The continuous resistance welding (CRW) process consists of an end-effector which moves along the length of a weld seam, heating a conductive implant while compacting the joint locally throughout the melt and solidification stages of the thermoplastic material. The performance of the joint has been shown to be highly dependent on the process temperature at the weld interface; however, this cannot be measured directly during the process in a non-invasive manner. Other parameters such as boundary conditions, substructure properties, or part geometry may vary along the length of the weld. As such, a physics-based simulation is developed founded upon an "MSTEP" framework which defines how the materials (M), shape (S), tooling (T), and equipment (E) interact to determine the process (P). Detailed finite element (FE) models are developed for thermal analysis based on the weld geometry, boundary conditions, and previously developed and validated melt/crystallization models for the thermoplastic matrix. Experimental CRW tests are presented to validate simulations and calibrate suitable control variables. [ABSTRACT FROM AUTHOR]

Developing reliable processes is one of the key elements in producing high-quality composite components using an automated fiber placement (AFP) process. In this study, both simulation and experimental studies were carried out to investigate fiber steering and cut/restart under different processing parameters, such as layup rate and compaction pressure, during the AFP process. First, fiber paths were designed using curved fiber axes with different radii. Fiber placement trials were then conducted to investigate the quality of the steered fiber paths. Furthermore, a series of sinusoidal fiber paths were fiber placed and investigated. Moreover, a six-ply laminate with cut-outs in it was manufactured in the cut/restart trials. The accuracy of the fiber cut/restart was compared at different layup rates for both one- and bi-directional layups. Experimental results show that it was possible to layup steered fiber paths with small radii of curvature (minimum 114 mm) designed for this study when the proper process condition was used. It was observed from the cut/restart trials that the quality of tow cut was independent of layup speed; however, the accuracy of tow restart was related to the layup speed. The faster the layup speed, the less accurate was the tow restart.

Comparing manufactured parts to their engineering specifications is the basis for Quality Control. Traditionally, Geometric Dimensioning and Tolerancing (GD&T) standards define how engineering tolerances are used for generating fabrication specifications. Due to the complexities inherent to the composite layup process, Automated Fiber Placement (AFP) machines require a new paradigm of quality control. In addition to the traditional finished part dimension and quality reports, the AFP process requires a ply-by-ply inspection of the as-built laminate to ensure that each laydown remains within the manufacturing allowable specifications. To address this problem, Fives and the National Research Council Canada have proposed an In-Process Inspection system based on Optical Coherence Tomography (OCT) technology capable of performing highresolution surface profilometry and automatic alignment of the as-manufactured measurements to the asdesigned engineering model. With both an accurate surface profile and positioning of the measurement data in the CAD design reference, the differences can be analyzed to detect manufacturing anomalies and minimize process variability. Later on, this information has the fidelity required for an exact digital transformation of the process. This paper will review a few aspects of the Measurement System Analysis performed to validate the sensor's reliability as well as review the high level methodology undertaken to establish the relationship between the IPI system's sensor and the machine tool center point during fabrication. Finally, examples will be used to demonstrate the approach to obtain course, ply, and laminate level aggregations. [ABSTRACT FROM AUTHOR]

There is an emerging interest in the aerospace industry to manufacture components with intricate geometries using discontinuous-fibre carbon/polyether-ether-ketone moulding systems (obtained by cutting unidirectional tape into strands). Great formability and high modulus can be achieved with this type of composites, but the high variability of measured properties can have a detrimental effect on the design allowables. When it comes to prediction of mechanical properties, it is important to capture the average strength and modulus as well as their statistical variability. This article proposes a stochastic finite element technique that uses the concept of randomly oriented strands to model variability, and the application of Hashin’s failure criteria and fracture energies to estimate strength. Overall, the model matches the trends observed during experiments and shows that strength of randomly oriented strand composites is significantly lower than that of continuous-fibre laminates due to the ‘weakest-link’ principle. [ABSTRACT FROM AUTHOR]

The resistance welding technique for thermoplastic composites (TPCs) entails melting the TPC polymer at the joint interface using heat generated by resistive (Joule) heating of a conductive mesh orheating elementplaced between the surfaces to be welded. The continuous resistance welding (CRW) is an automated large-scale resistance welding technique that consists of a moving voltage source along the heating element creating a continuous weld along its path. This paper presents a transient model that is developed to predict the heat transfer in TPCs in all three dimensions during the CRW process. The model is finite element in nature and includes both the resistive and thermal conductivity behaviors of the material involved. The significance of this modeling approach is that it captures the movement of the electrical connection, as well as the nonuniform distribution of the current and resistive heating along the length and width of the weld seam. The modeling results are compared with experimental data obtained by thermocouples and an infrared camera, and exhibit solid conformance for predicting the trend of variations in weld temperature. [ABSTRACT FROM AUTHOR]

A novel approach to automate large-scale resistance welding of thermoplastic composite materials, based on real-time temperature control, is presented in this paper. Resistance welding, a kind of fusion bonding, is a widespread alternative process to mechanical fastening and adhesive bonding in joining thermoplastic composites. A second-order linear observer was identified to estimate the online temperature at the weld interface. A fuzzy logic controller (FLC) was designed to control the weld temperature using both process voltage and linear weld speed as the control inputs and using the temperature estimate as the feedback signal. The FLC was implemented in real time with the experimental setup using an industrial robot—KUKA KR 210. The closed-loop controller was capable of successfully controlling the weld temperature within 10% of the desired temperature, resulting in superior weld quality when compared to open-loop results. The results thus affirm the suitability of the control strategy for large-scale automated welding. [ABSTRACT FROM PUBLISHER]

An experimental investigation of resistance welding of thermoplastic composite double lap shear (DLS) joints is presented. DLS specimens consisting of unidirectional carbon fibre/polyetheretherketone (CF/PEEK), carbon fibre/polyetherketoneketone (CF/PEKK), carbon fibre/polyetherimide (CF/PEI) and 8-harness satin weave fabric glass fibre/polyetherimide (GF/PEI) composites were resistance welded using a stainless steel mesh heating element. The welded specimens were tested under static and fatigue loadings, and the quality of the welds was examined using optical and scanning electron microscopy. Weld strengths of 53, 49, 45 and 34 MPa were obtained for CF/PEEK, CF/PEKK, CF/PEI and GF/PEI DLS joints, respectively. Indefinite fatigue lives were obtained between 20 and 30% of the ultimate static failure loads of the joints. Performances of the resistance-welded DLS and single lap shear (SLS) joints were compared. It was shown that the effect of joint geometry, that is, DLS versus SLS, on the mechanical performance of the resistance-welded joints is minimal, indicating a good resistance of welded joints to peel stresses. [ABSTRACT FROM PUBLISHER]

Compression molding of randomly oriented strands (ROS) composites offers the possibility to manufacture complex parts with a fast processing cycle. In this paper, effects of pressure, strand size, temperature, and material placement in the mold cavity on the quality of a T-shape part were studied experimentally with carbon/polyether ether ketone ROS composites. Minimum filling pressure was obtained for the consolidation of a 25-mm deep cavity. Parts processed at filling pressure showed a void content no greater than 1.2%. Increasing pressure to 70 bar resulted in decreased void content as low as 0.03%. Mechanical testing of the T-shape showed similar strengths for parts processed at filling pressure and higher (70 bar). At the component level, initial strand placement greatly affected mechanical performance as the presence of a knit line was responsible for a reduction of 60% in tensile strength. The main findings show that processing a complex feature at filling pressure Pfill was sufficient to reach nominal mechanical properties. This suggested that moderate porosity was not detrimental to the mechanical performance for the given tests where fatigue performance was not evaluated. [ABSTRACT FROM AUTHOR]

The possibility of assembling through welding is one of the major features of thermoplastic composites and it positively contributes to their cost-effectiveness in manufacturing. This article presents a comparative evaluation of ultrasonic, induction and resistance welding of individual carbon fibre-reinforced polyphenylene sulphide (PPS) thermoplastic composite samples that comprises an analysis of the static and dynamic mechanical behaviour of the joints as well as of the main process variables. The induction welding process as used in this research benefitted from the conductive nature of the reinforcing fibres. Hence, no susceptor was placed at the welding interface. Resistance welding used a fine-woven stainless-steel mesh as the heating element and low welding pressures and times were applied to prevent current leakage. Triangular energy directors moulded on a separate tape of PPS resin were used to concentrate ultrasonic heat at the welding interface. The static single-lap shear strength of the joints was found similar for induction and ultrasonic welding. A 15% drop in the static mechanical properties of the resistance welded joints was attributed to incomplete welded overlaps following current leakage prevention. However, the fatigue performance relative to the static one was similar for the three sorts of joints. A comparative analysis of process variables such as welding time, required power and energy was also carried out. [ABSTRACT FROM AUTHOR]

The use of resistance welding technology to join thermoplastic composite aerospace structures is still contingent upon a better understanding of the heat transfer mechanisms occurring during welding, which govern the joint quality and mechanical performance. In this study, two-dimensional (2D) and three-dimensional (3D) transient heat transfer finite element models were developed to simulate resistance welding of thermoplastic composites. The 2D model was used to investigate the effect of the length of the exposed areas of the heating element to air (clamping distance) on the local overheating at the edges and the effects of the input power level on the thermal behavior of the welds. It is shown that controlling the clamping distance improves the thermal uniformity of the weld. The 3D model shows that heat conduction along the length of the laminates influences the thermal uniformity of the weld interface. An optimization chart is developed in order to minimize the undesirable edge effect and to define the conditions required to obtain a complete weld. The results of the 3D model are compared with experimental data. [ABSTRACT FROM AUTHOR]

The objective of this work is to determine the effects of metal mesh heating element size on resistance welding of thermoplastic composites. The materials to be resistance-welded consisted of carbon fiber/poly-ether-ketone-ketone (CF/PEKK), carbon fiber/poly-ether-imide (CF/PEI) and glass fiber/PEI (GF/PEI). Four different metal mesh sizes were used as heating elements. The samples were welded in a lap shear joint configuration and mechanically tested. Maximum Lap Shear Strengths of 52, 47 and 33 MPa were obtained for the CF/PEKK, CF/PEI and GF/PEI specimens, respectively. The ratio of the heating element’s fraction of open area and wire diameter was shown to be the most important parameter to be considered when selecting an appropriate heating element size. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Joining of thermoplastic composites is an important step in the manufacturing of aerospace thermoplastic composite structures. Therefore, several joining methods for thermoplastic composite components have been under investigation and development. In general, joining of thermoplastic composites can be categorized into mechanical fastening, adhesive bonding, solvent bonding, co-consolidation, and fusion bonding or welding. Fusion bonding or welding has great potential for the joining, assembly, and repair of thermoplastic composite components and also offers many advantages over other joining techniques. The process of fusion-bonding involves heating and melting the polymer on the bond surfaces of the components and then pressing these surfaces together for polymer solidification and consolidation. The focus of this paper is to review the different fusion-bonding methods for thermoplastic composite components and present recent developments in this area. The various welding techniques and the corresponding manufacturing methodologies, the required equipment, the effects of processing parameters on weld performance and quality, the advantages/disadvantages of each technique, and the applications are described. [ABSTRACT FROM AUTHOR]

Six E-glass/Epoxy shallow water composite pressure vessels with effective length of 45.72 cm and inner diameter of 33.02 cm were designed, analyzed, manufactured, and tested for an external hydrostatic design pressure of 1.14 MPa that corresponds to a depth of 91 m in ocean. Composite pressure vessels were designed as composite cylinders fabricated by roll-wrapping and enclosed by two flat plug-supported end-caps due to their ease of manufacturing and cost-effectiveness. The plug-supported end-caps had a combination of tapered contour and initial radial clearance to account for bending and shear stresses in composite cylinders at the end-cap locations. Buckling and stress finite element analyses were performed for the design of the pressure vessels. An eigenvalue buckling analysis was performed to determine a bifurcation buckling pressure (2.51 MPa) and a modal shape of the structure for a wall-thickness of 7.72 mm based on 32 layers of 0.2413 mm thick each. These results were then used to perform a nonlinear buckling analysis. The nonlinear buckling pressure was determined to be 1.42 MPa yielding a buckling pressure factor of safety of 1.25. Stress analysis was performed to investigate the stress response of the structure with the wall-thickness of 7.72 mm under the design pressure. Maximum stress and strain criteria were used and stress and strain factor of safety of 11.95 and 17.17 were achieved, respectively. The composite pressure vessels were made of plain weave E-glass/Epoxy fabric. A comparative study of various materials property modeling for woven materials was performed and reported in this work. The three-dimensional Crimp model was explained and employed in this investigation to model the effective properties of a woven composite material, and the results were compared with other existing models. In addition, general guidelines to model the effective properties of woven hybrid materials are also provided. Tube roll-wrapping with wet-laying... [ABSTRACT FROM AUTHOR]

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)[sub s]][sub 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... [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

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 (T[SUBg]) 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 T[SUBg] 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. [ABSTRACT FROM AUTHOR]

Boron nitride nanotubes (BNNTs) offer complimentary properties to carbon nanotubes (CNTs) and interact more favorably with epoxies than do CNTs. This could make BNNTs the preferred nanotube for reinforcing epoxy when electrical conductivity is not required, and particularly where features such as transparency/color, neutron absorption or electrical insulation are advantageous. Here we report epoxy nanocomposites containing 1–7 wt% raw BNNTs. The elastic modulus and fracture toughness increased progressively with loading up to 5 wt% BNNTs. Adhesive joints (ASTM D1002) indicated average improvements of ~10% in joint strength at 2 wt% raw BNNTs, but substantially reduced strength for a 5 wt% BNNT adhesive joint. Observation of the failure surfaces suggests that BNNTs impede crack propagation leading to increased joint performance despite a mixed-mode failure with a substantial contribution from adhesive failure. BNNTs purified by removing the elemental boron impurity were more effective, yielding 15% joint strength improvements at 1 wt% loading. This nanocomposite is also semi-transparent, showing the potential for reinforced, electrically insulating, transparent adhesives based on BNNTs. [ABSTRACT FROM AUTHOR]