Journal Publications

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.


Authors: Victoria Zinnecker, Christopher Stokes-Griffin, Steve Madden, Andrei Rode, Paul Compston
Year: 2019
Journal name: Procedia Manufacturing
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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.


Authors: Chris Stokes-Griffin, Andreas Kollmannsberger, Paul Compston, Klaus Drechsler
Year: 2019
Journal name: Procedia Manufacturing
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Online Monitoring and Prediction of Thermo-Mechanics of AFP Based Thermoplastic Composites


Abstract: Precision sensing in the characterization of complex additive manufacturing processes such as the Automated Fibre Placement (AFP) technique is important since the process involves a significant level of uncertainty in terms of quality and integrity of the manufactured product. These uncertainties can be monitored by embedding optical fibre Bragg grating (FBGs) sensors which provide accurate and simultaneous measurement of strain and temperature during the AFP process. The embedded sensors have been shown to remain resilient in continuous health monitoring after manufacturing. The thermal history obtained from the FBG sensors demonstrates a reduction of temperature on the bottom ply by up to 25% when the plies are laid one above the other. A numerical tool is developed to identify the physical parameters which may be responsible for the rise/fall of the temperature during ply layup. The numerical findings agree well with the sensor data and is extended to capture a breadth of parametric studies through the layup simulation. The model provides a comprehensive insight to the characteristics of the laid and the laying ply from a thermo-mechanics perspective.


Authors:Ebrahim Oromiehie, Nilanjan Das Chakladar, Ginu Rajan, and Gangadhara Prusty
Year: 2019
Journal name:Sensors
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Automated fibre placement based composite structures: Review on the defects, impacts and inspections techniques


Abstract: Automated fibre placement (AFP) offers high throughput, efficient and accurate manufacturing methods for making multi-stiffened laminated composites. However, processing conditions, machine tolerances and steering of tape can induce small random defects within the laminate, which may compromise the structural integrity. Thus, this paper presents a comprehensive review on the processing/steering-induced defects in AFP and their influence on the quality of the final product. Three key processing parameters in AFP, specifically consolidation force, lay-up speed and curing/melting temperature are attempted elaborately. Additionally, the paper attempted to present the discussions on in-situ process monitoring as well as the Machine Learning (ML) based predictive models for AFP based composites.


Authors: Ebrahim Oromiehie, Gangadhara Prusty, Paul Compston, Ginu Rajan
Year: 2019
Journal name: Composite Structures
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Structural performance of a shape-adaptive composite hydrofoil using automated fibre placement


Abstract: This paper presents an investigation into structural performance of a shape adaptable composite hydrofoil which was manufactured using Automated Fibre Placement (AFP). The methodology and procedure developed for the complex manufacture using AFP is first described here. A mould originally designed for resin transfer moulding (RTM) was used as a tooling surface for AFP layup. An in-house developed optimisation process for tailored bend-twist behaviour was used to obtain the layup sequence and subsequent tool path creation for AFP fabrication of the hydrofoil. The AFP fabricated hydrofoil was experimentally tested for its structural response using a static cantilever experiment whereas for the dynamic behaviour experimental modal analysis (EMA) was used. Finally, a comparison was made between the structural responses of the optimised hydrofoils manufactured by AFP and using the traditional RTM process.


Authors: P.Maung, B.G.Prusty, J.M.White, M.David, A.W.Phillips, N.A.St John
Year: 2019
Journal name: Engineering Structures
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Manufacture of steel–CF/PA6 hybrids in a laser tape placement process: Effect of first-ply placement rate on thermal history and lap shear strength


Abstract: This paper investigates the manufacture of selectively reinforced metal/composite hybrids in a laser-assisted automated tape placement process. Carbon-fibre/PA6 composite tapes were applied to PA6-coated steel substrates. The bonding of the first-ply to the substrate is critical to the success of the hybrid; the effect of first-ply placement rate was investigated for speeds of 25 mm/s, 50 mm/s, 100 mm/s. The interfacial bond strength of the hybrid laminates was determined by ASTM D3165 lap shear tests. A 3D finite element thermal model was formulated to elucidate the thermal behaviour for increasing first-ply placement rate. A method for increasing model efficiency was shown to significantly decrease the computational difficulty while maintaining solution accuracy. Raising the first-ply placement rate from 25 mm/s to 100 mm/s resulted in a fourfold increase in lap shear strength with a maximum value of 22 MPa. The greater strength at higher speeds is attributed to improved synchronisation of the temperature and consolidation pressure history.


Authors: Stokes-Griffin, C.M., Kollmannsberger, A., Ehard, S., Compston, P., Drechsler, K.
Year: 2018
Journal name: Composites Part A: Applied Science and Manufacturing
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In-situ simultaneous measurement of strain and temperature in automated fiber placement (AFP) using optical fiber Bragg grating (FBG) sensors


Abstract: There has been a tremendous growth of utilizing automated fiber placement (AFP) to manufacture highly precise components and large structures like fuselage panels and wing skins for high-end applications in aircrafts and next generation of spacecrafts. Consequently, in-situ identification of potential defects and strain level within the laminates is critical to ensure the quality and integrity of the final product. In this study, optical fiber Bragg grating sensors (FBGs) have been implemented as an on-line monitoring technique for simultaneous measurement of strain and temperature in AFP. In addition, it is also shown that, the embedded FBG sensors can remain within the laminate for continuous health monitoring after manufacturing process toward the identification of crack induced acoustic emissions.


Authors: Oromiehie, E., Prusty, B.G., Compston, P. and Rajan, G.
Year: 2017
Journal name: Advanced Manufacturing: Polymer & Composites Science
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