Showing papers by "Paul Robinson published in 2016"
TL;DR: In this article, the translaminar fracture toughness of 0° plies has been investigated using thin-ply pre-pregs, and it was shown that the in-situ, property of the fracture toughness depends strongly on the 0° ply-block thickness.
Abstract: The concept of translaminar fracture toughness of 0° plies has enabled the development of a considerable number of ply-level numerical models for structural failure of laminated composites. Using thin-ply pre-pregs, this paper demonstrates that this translaminar toughness is not an absolute, but rather in-situ, property and depends strongly on the 0° ply-block thickness, even in situations where delamination and diffuse damage are inhibited. We used two different grades of a thin-ply carbon-epoxy system to produce four different 0° ply-block thicknesses ranging from 0.03 mm to 0.12 mm, and measured the respective translaminar fracture toughness using compact tension tests. SEM and X-ray analysis showed no delamination nor diffuse damage. Yet, the translaminar fracture toughness increased from 46 to 104 kJ/m2 (initiation), and from 49 to 160 kJ/m2 (propagation), for the thickness range above. This finding has significant implications for the development and use of ply-level numerical failure models, for structural design with thin-ply composites, and for the development of thin-ply material systems.
61 citations
TL;DR: In this paper, gas-texturing and non-constrained annealing were used to introduce fibre waviness into UD polyamide 12 composites produced by wet-impregnation hoping to produce composites with a more gradual failure mode and increased failure strain.
Abstract: Unidirectional (UD) carbon fibre reinforced polymers offer high specific strength and stiffness but they fail in a catastrophic manner with little warning. Gas-texturing and non-constrained annealing were used to introduce fibre waviness into UD polyamide 12 composites produced by wet-impregnation hoping to produce composites with a more gradual failure mode and increased failure strain. Both methods increased the variation of fibre alignment angle compared to the control samples. The composites containing wavy fibres exhibited a stepwise, gradual failure mode under strain controlled uniaxial tension rather than a catastrophic failure, observed in control samples. Gas-texturing damaged the fibres resulting in a decrease of the tensile strength and strain to failure, which resulted in composites with lower tensile strength and ultimate failure strain than the control composites. Non-constrained annealing of carbon fibre/PA-12 produced wavy fibre composites with ultimate failure strain of 2%, significantly higher than 1.6% of the control composite.
25 citations
TL;DR: In this article, a modification of the interleaf layer improves the interlaminar shear strength of the laminates without affecting the stiffness loss at elevated temperatures, and two poly(styrene-co-maleic anhydride) (SMA) films were prepared and used as interleaf films.
11 citations
02 Sep 2016
TL;DR: In this paper, the authors show how fiber/matrix interface modification can be used to develop a range of novel carbon fibre reinforced polymer (CFRP) composites that open up new applications far beyond those of standard CFRPs.
Abstract: We show how fibre/matrix interface (or interphase) modification can be used to develop a range of novel carbon fibre reinforced polymer (CFRP) composites that open up new applications far beyond those of standard CFRPs. For example, composites that undergo pseudo-ductile failure have been created through laser treatment of carbon fibres. Composites manufactured with thermo-responsive interphases can undergo significant reductions in stiffness at elevated temperatures. Additionally, structural supercapacitors have been developed through a process that involves encapsulating carbon fibres in carbon aerogel.
10 citations
01 Jan 2016
TL;DR: In this article, the post-impact behavior of composite fuselage panels subjected to multi-site low-velocity impacts was investigated, which showed a good agreement with both the impact damage and subsequent compression performance.
Abstract: This research investigates the post-impact behaviour of composite fuselage panels subjected to multi-site low-velocity impacts. Large curved stiffened panels (1.2 m × 0.8 m, with composite skins/stiffeners and aluminium frames) of two different skin thicknesses were subjected to sequential drop-weight impacts at locations previously determined to be critical in FE simulations. After assessment of the impact damage, each panel was tested in compression. High-speed video, strain gauges, digital image correlation and acoustic emission were used to monitor the failure development and to provide data for comparison with the FE simulations. The FE models, which were based on a mesomechanical approach, showed a good agreement with both the impact damage and the subsequent compression performance.
7 citations
01 Jan 2016
TL;DR: In this article, the post-impact behavior of CFRP coupon specimens subjected to multisite impacts was investigated, and the experimental results were used to validate a finite element mesomechanical modelling approach which accounts for both intralaminar damage and interlaminar damage.
Abstract: This research investigates the post-impact behaviour of CFRP coupon specimens subjected to multisite impacts. Sequential low-velocity impacts at different locations were performed on coupons with different thicknesses. The impact load history was recorded, and the extent of damage was assessed by ultrasonic inspection. The residual strength in compression was then measured in a compression after impact rig which was specially modified for the testing of thin composites. High-speed video and digital image correlation records were taken for a number of specimens during testing. The experimental results were used to validate a finite element mesomechanical modelling approach which accounts for both intralaminar damage and interlaminar damage.
1 citations