Resources

Research papers based on recent work

A novel approach to the qualification of nonmetallic pipe systems

This paper discusses the possibilities offered by ramp pressure loading tests to generate data for determining the long term load-bearing characteristics of plastics pipe systems. In addition to ramp pressure loading, procedures are also considered where the pressure is held at a constant value for a period of time, after which the product is subjected to a ramped pressure burst test. The method discussed relies on the material in question obeying Miner’s law in its static fatigue behaviour. The pipe system to which the procedure has been applied is Reinforced Thermoplastic Pipe (RTP), in which the reinforcement is aramid fibre. However the results are expected to apply to any polymeric system where there is evidence of conformity to Miner’s law. A set of ramp loading tests, and constant pressure plus burst tests are reported and compared with the results of conventional ‘constant pressure’ stress rupture tests and a method is proposed for converting these results into ‘equivalent’ constant pressure values. The results obtained on RTP using this new approach lie close to those generated using constant pressure.

Composite angle ply laminates and netting analysis

This paper relates to the ‘netting-analysis’ approach, often used in calculations of the behaviour of helically wound reinforced pressure vessels and tubes. Numerical calculation of the stress–strain relations for angle ply composite laminates often gives the impression of unexpected instability in the underlying equations. For instance, when the in-plane principal stresses are in the ratio 2:1 and the fibres are inclined at an angle close to θ ≈ ±arctan√2, the stress–strain relations are very sensitive to the value of θ and to the relative stiffness of the fibres and matrix. There is a simple explanation for this, which is most clearly understood by developing analytical approximations for the stress–strain relations.

Modelling residual mechanical properties of polymer composites after fire

A thermomechanical modelling approach is proposed for estimating the residual properties of fibre reinforced polymer composites damaged by fire. The modelling was carried out in two parts: (i) prediction of the extent of thermal decomposition (or charring) using a thermal model; and (ii) prediction of the post-fire behaviour using a two layer model that combines the properties of the undamaged laminate and the residual char. Fire experiments were performed on glass–polyester, vinyl ester, and phenolic laminates using a cone calorimeter operated at heat fluxes in the range 25–100 kW m−2, for times up to 30 min. After cooling to room temperature the thickness of the thermal damage layer was determined, along with values of the residual tensile, compressive and flexural properties. For the ‘two layer’ model it was found that the effective boundary between char material and undamaged laminate corresponded to the point where the residual resin content (RRC) of the laminate was 80%. Surprisingly, this value was found to hold for all three resin types tested. Using this RRC value, excellent agreement was found between the measured and predicted post-fire char thickness and the residual mechanical properties. The approach presented is the first reliable method for accurately predicting the residual properties of composites after fire.

The Cost Effective Use of Fibre Reinforced Composites Offshore

This report reviews areas where composites are finding application in the oil and gas industry, onshore and offshore. The most significant advances have been made in the areas of pipework and fluid handling, driven by light weight and corrosion resistance compared to metals. Modest, but significant progress has also been made in structural applications. Lessons are being learned from successful applications with the result that operators, design houses and contractors are now beginning to take a serious interest in their wider use. Expansion is therefore expected to continue into all sectors of the oil and gas industry.

The Integrity of Polymer Composites During and After Fire

This paper reports on changes to the mechanical properties of woven glass laminates with polyester, vinyl ester and phenolic resins during fire exposure. Two sets of experiments were carried out. First, unstressed laminates were exposed to a constant one-sided heat flux (50kWm-2) for various times, and the residual post-fire strength at room temperature was reported. In a second series of experiments, laminates were tested under load. The times corresponding to a given loss of properties were 2–3 times shorter than in the previous case. It was found in both cases that modes of loading involving compressive stress were more adversely affected by fire exposure than those involving tension.

Vacuum bag moulding of large thermoplastic parts in commingled glass/PET copolymer

This paper describes the development of a thermoplastic composite system for structural application in the chassis of an electrically propelled bus. The work involved the characterisation and modelling of a vacuum bag moulding process using a woven commingled thermoplastic composite precursor. The matrix materials were PET and a PET copolymer. The process employs an ambient pressure oven, with tooling that can be made from composite, metal or ceramic. The process results in good quality laminates, with a void content generally lower than 1%. The temperature profile through the part and the consolidation behaviour were characterised and modelled. It was found that the thermal profile could be modelled with adequate accuracy using ‘single point’ values of thermal properties. Experimental measurements showed, for the first time, that consolidation occurs in two stages: a low temperature solid state debulking near to Tg, followed by full melt impregnation at a higher temperature (above Tm in the case of the homopolymer). Both stages in the consolidation process were modelled separately using a simplified version of the Kamal equation.

PowerPoint Presentations

Composites In Fire - Introductory presentation

This is the presentation given at the start of Composites In Fire 4, which several delegates requested.

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