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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]

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]

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]

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]