Automated Tape Placement Research Articles

On the investigation of quasi-static crack resistance of thermoplastic tape layered composites with multiple delaminations: Approaches for quantification

The present study is devoted to the quantitative characterisation of the interlayer bonding in unidirectional carbon fibre reinforced thermoplastic laminates produced by automated tape placement with in-situ consolidation (ATPisc). Two different manufacturing protocols were applied to produce the laminates that were further characterised using the quasi-static mode I double cantilever beam (DCB) test. Regardless of the manufacturing approach, the laminates exhibited multiple cracking accompanied by fibre bridging during testing, which affected the main mid-plane crack propagation. This effect was examined by comparing the crack length visually measured during testing with both the crack length back-calculated from the compliance and the crack length calculated using the flexural modulus and the compliance. In addition, the investigation of the evolution of the effective flexural modulus E1 and the damage parameter φ throughout testing was performed for a better understanding of the damage accumulation in the specimens.

Gap filling mechanisms during the thin ply Automated Tape Placement process

Automated Tape Placement (ATP) is one of the attractive automated composite manufacturing processes as it reduces labor cost, increases production rate and improves repeatability. In this method, the part is built by consolidating one unidirectional prepreg tape layer at a time with a placement head using a compaction roller. Defects such as gaps between neighboring tapes during lay up are inevitable. This challenge becomes even more critical in the ATP of the thin ply prepreg tapes as the ratio of the gap width to the tape thickness increases. The filling process of such gaps during the process cycle results in resin-rich areas and fiber waviness. In this paper, we present a model to numerically simulate the gap-filling process by coupling the squeeze flow behavior within the tapes to fill the gap with the deformation of the top layers into the hollow space within the gap. First, the experimental results clarify the microstructural physics of the gap-filling process. This is followed by proposing a model to predict the flow front of resin that moves to fill the gap and the gap thickness. The predictions of the model are compared with experimental results and validated by the micrographs of fabricated samples.

Quantification Approaches for Fatigue Crack Resistance of Thermoplastic Tape Layered Composites with Multiple Delaminations.

Automated tape placement with in-situ consolidation (ATPisc) is a layer-wise manufacturing process in which the achievement of proper interlayer bonding constitutes one of the most challenging aspects. In the present study, unidirectional carbon fiber reinforced thermoplastic laminates were produced following different manufacturing protocols using ATPisc. The interlayer bonding of the laminates produced was characterized by mode I fatigue fracture tests with double cantilever beam (DCB) specimens. Independent of the manufacturing approach, the laminates exhibited multiple cracking during DCB testing, which could not be evaluated simply following standard methods. Thus, various data analysis methodologies from literature were applied for the quantitative assessment of the fracture behavior of the laminate. The examination of the evolution of the damage parameter and the effective flexural modulus throughout testing enabled a better understanding of the damage accumulation. The Hartman-Schijve based approach was revealed to be a convenient method to present fatigue crack growth curves of laminates with multiple delaminations. Moreover, a preliminary attempt was made to employ a ‘zero-fiber bridging’ methodology to eliminate the effect of additional damage processes on the fatigue crack growth that resulted in large-scale, partially massive fiber bridging.

Heat transfer modelling of flashlamp heating for automated tape placement of thermoplastic composites

Flashlamp systems introduce pulsed and broadband heating to automated tape placement (ATP) offering greater control and optimisation potential. A thorough understanding of the role of operation parameters on the process is necessary to unlock these capabilities. A 2D finite element model of the heat conduction, able to analyse the temperature field evolution in the time scales of short high-energy pulses, was developed and combined with ray tracing analysis in this work. The model was validated against experimental data from ATP trials of AS4/PEEK composites. Parametric studies showed that pulse duration and frequency influence significantly both the surface and bulk temperature profiles. Longer pulses lead to higher irradiation temperatures, whilst the profiles converge to the behaviour of a continuous source of equivalent power at high frequency. The versatility of flashlamp heating enhances the processing envelope through expanding the feasible combinations of maximum temperature and depth of penetration achievable in ATP processing.

Fibre Alignment and Void Assessment in Thermoplastic Carbon Fibre Reinforced Polymers Manufactured by Automated Tape Placement.

Automated Tape Placement (ATP) technology is one of the processes that is used for the production of the thermoplastic composite materials. The ATP process is complex, requiring multiple melting/crystallization cycles. In the current paper, laser-assisted ATP was used to manufacture two thermoplastic composites (IM7/PEEK and AS4/PA12). Those specimens were compared to specimens that were made of thermoset polymeric composites (IM7/8552) manufactured while using a standard autoclave cycle. In order assess the quality, void content, fibre distribution, and fibre misalignment were measured. After manufacturing, specimens from the three materials were assessed using optical microscopy and computed tomography (CT) scans. The results showed that, as compared to the thermoset composites, thermoplastics that are manufactured by the ATP have a higher amount of voids. On the other hand, manufacturing using the ATP showed an improvement in both the fibre distribution inside the matrix and the fibre misalignment.

Solving the Boundary Value Problem of Curves With Prescribed Geodesic Curvature Based on a Cubic B-Spline Element Method

Composite manufacturing processes such as automated tape placement (ATP) and filament winding process (FW) put forward specific requirements for the geodesic curvature along the layup paths of the composite tows and tapes. In this paper, a non-uniform cubic b-spline element method is proposed for solving the boundary value problem of curves with prescribed geodesic curvature. The differential equation system of the target curve is discretized through the point collocation method, and a quasi-Newton iteration scheme is adopted to approach the real solution from an initial approximation. The proposed method is proved to have third order accuracy, which shows more superiorities comparing with existing numerical methods. Simulations and experiments on a series of parametric surfaces are performed to investigate the performance of the proposed approach and the results verify the high efficiency. The proposed method could cope with the BVP for curves no matter their geodesic curvature vanishes or not. At the same time, the computed curves are natural and smooth such that interpolation technique is unnecessary to ensure the continuity of target curves. One potential application of this method is trajectory optimization for automated tape placement process.

Modeling and Numerical Simulation of Laminated Thermoplastic Composites Manufactured by Laser-Assisted Automatic Tape Placement

A comprehensive numerical model is developed for the simulation of the laser-assisted automated tape placement process of carbon fiber/thermoplastic composites. After being heated with a laser, the thermoplastic is welded with the help of a consolidation roller onto a substrate made up of layers of tapes bonded onto one another. Under the pressure applied by the roller, the thermoplastic flows and the tape reaches its final thickness. The numerical model is developed in three sequential steps that can be used to identify the required pressure and temperature distribution to achieve a good bond. Firstly, a heat transfer simulation is performed to determine the temperature distribution into the incoming tape under the consolidation roller. Secondly, a rheological model is developed to examine the polymer flow under the roller and to obtain the pressure field. Finally, the consolidation level between the substrate and the tape is investigated through the degree of intimate contact, which is related to the processing parameters such as the roller velocity, the laser power density and the compaction force.

Comparison of progressive damage between thermoset and thermoplastic CFRP composites under in-situ tensile loading

The in-situ damage progression in three carbon fibre reinforced cross-ply composite systems under tensile loading is examined, namely, carbon IM7/epoxy, carbon IM7/PEEK and carbon AS4/polyamide. Epoxy is a thermoset polymer while polyether ether ketone (PEEK) and polyamide are thermoplastic. The thermoset composite is manufactured in an autoclave using matrix pre-impregnated with unidirectional carbon fibres, while the thermoplastic composites are manufactured using laser-assisted automated tape placement (LATP). A tensile microtester is mounted in a scanning electron microscope to observe the damage mechanisms in-situ under tensile loading. X-ray computed tomography scans are also carried out to examine porosity in the material systems. IM7/epoxy and IM7/PEEK displayed similar damage mechanisms: transverse cracking in 90° plies followed by fibre breakage in the 0° plies at the fillets and interlaminar fracture. AS4/polyamide displayed a different mechanism with fibre fracture appearing first in the 0° plies, followed by transverse cracking and interlaminar fracture. The effect of autoclave treatment on the materials manufactured by LATP has also been examined.

Modeling and Numerical Simulation of Laminated Thermoplastic Composites Manufactured by Laser-Assisted Automatic Tape Placement

Abstract A comprehensive numerical model is developed for the simulation of the laser-assisted automated tape placement process of carbon fiber/thermoplastic composites. After being heated with a laser, the thermoplastic is welded with the help of a consolidation roller onto a substrate made up of layers of tapes bonded onto one another. Under the pressure applied by the roller, the thermoplastic flows and the tape reaches its final thickness. The numerical model is developed in three sequential steps that can be used to identify the required pressure and temperature distribution to achieve a good bond. Firstly, a heat transfer simulation is performed to determine the temperature distribution into the incoming tape under the consolidation roller. Secondly, a rheological model is developed to examine the polymer flow under the roller and to obtain the pressure field. Finally, the consolidation level between the substrate and the tape is investigated through the degree of intimate contact, which is related to the processing parameters such as the roller velocity, the laser power density and the compaction force.

Mechanical evaluation and failure analysis of composite laminates manufactured using automated dry fibre tape placement followed by liquid resin infusion

Automated tape placement is seen as a promising technique for the manufacture of net-shape dry fibre preforms using carbon fibre tapes. However, most of the dry fibre tapes (DFT) available on the market are proprietary and aimed mainly at the aerospace sector. In the current study, two different binders (polyurethane and phenoxy water based binder) were used to coat and hence stabilise the carbon fibre tows. A net shaped preform was manufactured using Laser-Assisted Dry Fibre Tape Placement (LDFTP) and subsequently infused by vacuum assisted liquid resin infusion. The mechanical properties of the resulting laminates were compared to the laminates where the preform was manually laid up by hand with and without a coating (baseline). Failure mechanism analysis was carried out using scanning electron microscopy (SEM). The LDFTP process improved cured ply thickness (17–20% reduction) and fibre volume fraction (+9%). Interlaminar shear strength (ILSS) showed a significant improvement of 35–48%. However, only laminates manufactured using phenoxy coated LDFTP manufactured preforms showed comparable flexural strength to the uncoated baseline. Flexural modulus reduced in all cases. Further optimisation of binder content and process parameters (layup rate, consolidation temperature) is required for high speed deposition, better consolidation and improvements in mechanical properties.

Influence of repass treatment on carbon fibre-reinforced PEEK composites manufactured using laser-assisted automatic tape placement

Laser-assisted automated tape placement (LATP) in-situ consolidation of thermoplastic composites offers an efficient solution for production of large, high performance composite structures. The present work investigates laser repass treatment as a method of enhancing surface roughness and mechanical properties of LATP processed CF/PEEK laminates. Three laminate stacking sequences were studied, viz. [0°]16, [−45°/0°/45°/90°]2s and [±45°]4s. Four repass treatments were performed, including single, double, perpendicular and tool-side repasses. The effect of these repasses on interlaminar shear strength (ILSS), open-hole compression (OHC), in-plane shear (IPS), density, fibre volume fraction, void content and surface roughness was investigated. Surface roughness tests confirmed the improvement of the surface finish due to repass treatment. However, insignificant differences in ILSS values were observed across all repass treatments, but a single laser repass did appear to improve the OHC and IPS performance. Autoclave treated samples were used as a benchmark to compare with LATP processed laminate properties.

Annealing Effects on the Crystallinity of Carbon Fiber-Reinforced Polyetheretherketone and Polyohenylene Laminate Composites Manufactured by Laser Automatic Tape Placement

In situ consolidation of thermoplastic composites by Automated Tape Placement (ATP) is challenging. High quality ATP grade pre-preg material and tape head equipped with an efficient heat sources like lasers offer an opportunity towards high deposition rates and improved mechanical properties of composite materials. In this study uni-directional carbon fiber/ polyphenylene sulfide (UD tape prepreg CF/PPS), carbon fiber/polyetheretherketone (UD tape prepreg CF/PEEK) as well as blend of carbon fiber/polyetheretherketone/polyphenylene sulfide (UD tapes prepregs CF/PEEK/PPS) laminates are compared in terms of their properties after beeing processed by ATP technology. CF/PPS, CF/PEEK and blend CF/PPS/PEEK laminate specimens were processed using in-situ laser-assisted ATP (LATP) process. LATP processing parameters used in this study were chosen based on a preliminary trials; the results provide a basis for refinement of these parameters and prepreg material with an optimal and balanced set of final mechanical properties. This study showed an attempt how to manage the processing parameters for LATP process and to obtain composite materials with tailored properties. The process for production of thermoplastic plates with LATP head in general is a process that is governed by many parameters such as: laser power, angle of incidence, roller pressure and temperature, placement speed, tool temperature, then types of the roller material and the tool material. These parameters are not subject of discussing in this paper; they are kept constant, and the goal of the paper is to manage the crystallinity level within the composite thermoplastic material during annealing step at different temperatures after LATP process. Also, the void content during the production process could be controlled. More particularly, the authors showed that composites based on PPS matrix manufactured with LATP process possess higher flexural strength, with less void content compared to samples based on PEEK matrix. These samples showed also higher crystallinity after annealing step.

Static test of a variable stiffness thermoplastic composite wingbox under shear, bending and torsion

AbstractAutomated manufacturing of thermoplastic composites has found increased interest in aerospace applications over the past three decades because of its great potential in low-cost, high rate, repeatable production of high performance composite structures. Experimental validation is a key element in the development of structures made using this emerging technology. In this work, a $750\times640\times240$ mm variable-stiffness unitised integrated-stiffener out-of-autoclave thermoplastic composite wingbox is tested for a combined shear-bending-torsion induced buckling load. The wingbox is manufactured by in-situ consolidation using a laser-assisted automated tape placement technique. It is made and tested as a demonstrator section located at 85% of the wing semi-span of a B-737/A320 sized aircraft. A bespoke in-house test rig and two aluminium dummy wingboxes are also designed and manufactured for testing the wingbox assembly which spans more than 3m. Prior to testing, the wingbox assembly and the test rig were analysed using a high fidelity finite element method to minimise the failure risk due to the applied load case. The experimental test results of the wingbox are also compared with the predictions made by a numerical study performed by nonlinear finite element analysis showing less than 5% difference in load-displacement behaviour and buckling load and full agreement in predicting the buckling mode shape.

A Multi-level Trajectory Planning Method Based on Quasi-geodesic for Automated Tape Placement

A Multi-level Trajectory Planning Method Based on Quasi-geodesic for Automated Tape Placement

Operation of the Collaborative Composite Manufacturing (CCM) System.

The automated tape placement and the automated fiber placement (AFP) machines provide a safer working environment and reduce the labor intensity of workers than the traditional manual fiber placement does. Thus, the production accuracy, repeatability and efficiency of composite manufacturing are significantly improved. However, the current AFP systems can only produce the composite components with large open surface or simple revolution parts, which cannot meet the growing interest in small complex or closed structures from industry. In this research, by employing a 1-degree of freedom (DoF) rotational stage, a 6-RSS parallel robot, and a 6-DoF serial robot, the dexterity of the AFP system can be significantly improved for manufacturing complex composite parts. The rotational stage mounted on the parallel robot is utilized to hold the mandrel and the serial robot carries the placement head to mimic two human hands that have enough dexterity to lay the fiber to the mandrel with complex contour. Although the CCM system increases the flexibility of composite manufacturing, it is quite time-consuming or even impossible to generate the feasible off-line path, which ensures uniform lay-up of subsequent fibers considering the constraints like singularities, collisions between the fiber placement head and mandrel, smooth fiber direction change and keeping the fiber placement head along the norm of the part's surface, etc. Moreover, due to the existing positioning error of the robots, the on-line path correction is needed. Therefore, the on-line pose correction algorithm is proposed to correct the paths of both parallel and serial robots, and to keep the relative path between the two robots unchanged through the visual feedback when the constraint or singularity problems in the off-line path planning occur. The experimental results demonstrate the designed CCM system can fulfill the movement needed for manufacturing a composite structure with Y-shape.

Parameter Selection for Peel Strength Optimization of Thermoplastic CF-PA6 for <i>Humm</i>3<sup>TM</sup>

For Automated Tape Placement process, degree of bond varies with variation in process parameters and material. Interlaminar bond strength characterization is one of the most important criteria in determining the quality of bond between two layers of thermoplastic tapes. Depending on the bond strength achieved using different process parameters, a process window is defined. Based on the process window an iterative procedure is adopted to find optimum parameters to realize maximum bond strength. This paper aims to investigate the interlaminar bond strength of thermoplastic CF-PA6, during Automated Tape Placement process. A fairly new heating source, a pulsed light solution, i.e. a humm3TM system, which delivers uniform, highly controllable heat to the nip point is used. Experiments were conducted for different process parameters and results obtained using wedge peel test were analyzed. Results acquired help in assessing the material and the heating source in terms of capabilities and efficiency.

Multi-Scale Modeling and Simulation of Thermoplastic Automated Tape Placement: Effects of Metallic Particles Reinforcement on Part Consolidation.

This paper concerns engineered composites integrating metallic particles to enhance thermal and electrical properties. However, these properties are strongly dependent on the forming process itself that determines the particle distribution and orientation. At the same time, the resulting enhanced thermal properties affect the reinforced resin viscosity whose flow is involved in the intimate contact evolution. Thus, a subtle and intricate coupling appears, and the process cannot be defined by ignoring it. In this paper, we analyze the effects of particle concentration and orientation on the process and processability. For this purpose, three main models are combined: (i) a multi-scale surface representation and its evolution, by using an appropriate numerical model; (ii) flow-induced orientation, and (iii) the impact of the orientation state on the homogenized thermal conductivity.

Investigation of the effects of femtosecond laser metal surface texturing on bonding of PA 6 to steel

Abstract This paper investigates the effects of femtosecond laser surface texturing on the interfacial bond strength of steel and a thermoplastic polymer PA 6 film. Ultimately the textures will be used for hybrids that are manufactured using a near-infrared (NIR) laser-assisted automated tape placement (ATP) process and carbon fibre / PA 6 composites, therefore the NIR absorptance of the textured metal substrate is also of interest. To identify the influence of different surface structures on the bonding strength, lap shear samples were manufactured with laser textures varying in pulse length, hatch distance and ablated depth and tested by ASTM D 3165. The surface structures were analysed with white light interferometry (WLI) and scanning electron microscopy (SEM). Additional optical measurements in the infrared radiation range of 900 nm to 1100 nm were executed with a spectrophotometer to evaluate the laser absorptance for the NIR automated tape placement process. The lap shear strength increased to the highest value of 31.9 MPa with a tooth shaped laser texture using a 275 fs laser pulse width, a hatch distance of 600 μm an ablated depth of 40 μm. Also the absorptance for this sample increased by approximately 13% to 73% compared to the unprocessed pickled steel.

Steel-CF/PA 6 hybrids manufactured by a laser tape placement process: Effect of first-ply placement rate on lap shear strength for garnet blasted substrates

Abstract This paper investigates the manufacture of selectively reinforced metal/composite hybrids in a laser-assisted automated tape placement process. Unidirectional carbon fibre/PA 6 composite tapes were applied to 1.9 mm hot rolled steel substrates. The bonding of the first ply to the substrate is critical to the success of the metal-composite hybrid. This work investigates the effect of increasing the first-ply placement rate for speeds of 25 mm/s, 50 mm/s and 100 mm/s. The steel substrates were pre-treated by garnet blasting and then coating with a 60 μm layer of PA 6. The garnet blasted surface texture was quantified using white light interferometry. The thermal history for bonding of the first ply was measured with fine wire thermocouples. The interfacial bond strength of the hybrid laminates was assessed by ASTM D 3165 lap shear tests. The lap shear strength increased to the highest value of 22.4 MPa at 50 mm/s. Analysis of the fracture surfaces and thermal history suggest that the lower strengths at 25 mm/s and 100 mm/s are due to lower adhesion of the PA 6 coating to the metal substrate, most probably due to lower levels of crystallization.

Design, Manufacture and Test of an In-Situ Consolidated Thermoplastic Variable-Stiffness Wingbox

Thermoplastic composites offer the potential for reducing the overall manufacturing costs of aircraft structures by allowing continuous production methods to be applied without the ancillary need for ovens or autoclaves by using in situ consolidation techniques. In the last 10 years, carbon-fiber/polyether-ether-ketone-based composites have become available with desirable combinations of strength, stiffness, and toughness properties. By combining the latest manufacturing techniques with these new materials and with new design methods, cheaper, lighter, and better-performing aircraft structures become a viable prospect. As such, a variable-stiffness unitized integrated-stiffener thermoplastic composite wingbox was developed, which was manufactured by laser-assisted automated tape placement with winding and in situ consolidation. The wingbox loads were determined by assuming its location to be at 85% of the wing semispan of a B737/A320-size aircraft. At this load, the wingbox was designed to buckle elastically. A full-scale structural test using a bespoke testing frame with representative bending moment and shear load was undertaken. Indeed, the wingbox buckled elastically at a load close to that predicted numerically. The current results highlight the potential advances that become possible in primary aerospace structures by combining fiber steering and in situ consolidation of carbon-fiber thermoplastic composites together with new blended, unitized structural concepts.