Da Jesson

The Interface and Interphase in Polymer Matrix Composites: Effect on Mechanical Properties and Methods for Identification

The interface between the matrix and reinforcing phases can have a significant effect on the mechanical properties of the resulting composite material. The interface can be studied by a number of surface analysis techniques and the interaction modelled. Such studies, and such modelling, can help understanding of the mechanisms which composites undergo during their lifetime. The current review discusses the role of the interface and the methods by which it can be studied; two case studies are presented which illustrate these methods and the value that such knowledge of the interface has brought to larger investigations.

Green composites: sustainability and mechanical performance

Abstract This study considers the mechanical properties of a range of thermosetting resin systems, including systems with bioderived content, and associated natural fibre composites. The bioderived resin systems (22 and 40% biocontent) demonstrated similar tensile strength to standard resin systems, indicating their potential to be a substitute for such systems. To optimise the performance of the natural fibre composites, the reinforcement needed to be dried before composite processing. The stiffness and strength of the natural fibre systems improved with degree of alignment, as expected, and with the use of a semiprocessed fibre; in this way, the properties approached those of chopped strand mat E-glass composites. Even the natural fibre composite with the lowest tensile performance still demonstrated a fracture toughness that was halfway in between the E-glass composite and the resin system.

Characterisation of the fatigue properties of cast irons used in the water industry and the effect on pipe strength and performance

As part of an on going programme to characterise the residual properties and understand the failure mechanisms of in-service grey cast iron water pipes, the fatigue crack propagation behaviour of grey cast iron samples has been studied. Specimens were sourced from three ex-service pipes. For each pipe the microstructure and composition were characterised and the fracture toughness was determined. The fatigue behaviour was investigated in terms of the crack growth rate (da/dN) as a function of the applied stress intensity factor range. Clear differences in the fatigue behaviour of the samples from different pipes were observed. The result from these investigations, which indicate that microstructural differences play a role in mechanical behaviour, will support the development of asset management tools for use in the water industry.

Graphitic Corrosion Of A Cast Iron Trunk Main:Implications For Asset Management

Failures of (large diameter) cast iron trunk water mains can be catastrophic in the damage they can cause and it is therefore imperative to understand how cast iron deteriorates in order to help predict those areas of a water supply network which are at greatest risk of failure. Cast irons undergo a localized form of corrosion known as graphitic corrosion. Although a well reported phenomena, the mechanisms of graphitic corrosion are not fully understood. Scanning electron microscopy, in conjunction with energy dispersive x-ray spectroscopy, was used to characterise the microstructure and chemistry of the graphitic corrosion that occurs on the external surface of the pipe during time in service. It was found that that the graphite flakes within the cast iron are deteriorating during the corrosion process. High levels of chlorides are often found at the corrosion interface, within graphitic pits in the pipe wall. The implications of these observations on the development of models used to predict the remaining service life of buried trunk main are discussed.

Tensile characterisation of thick sections of Engineered Cement Composite (ECC) materials

Engineered Cement Composite (ECC) materials have the potential to be used in applications where a level of pseudo-ductility under tensile stress is required. Most previous work has focussed on comparatively thin specimens. For future civil engineering applications, however, it is imperative that the behaviour of thicker specimens is understood. In the present work, specimens containing cement powder, water, polymeric fibres and admixtures were manufactured following two different processes and tested in tension. Multiple matrix cracking was observed during tensile testing, leading to a pseudo-ductile behaviour. Complementary measurements of sample density and porosity suggest that a high porosity could be linked with an enhanced tensile strain-to-failure whereas high density is associated with a high maximum stress. The fibre dispersion, assessed by scanning electron microscopy, indicated that mechanical performance was enhanced with increasing proportion of fibres aligned along the tensile test axis, and this orientation can be linked to the manufacturing process.

Derivation of Uniaxial Stress-Strain curves for Cast iron from Samples tested in flexure

Cast iron is a material that still has significant usage in the water industry. Although cast iron pipes, both distribution and trunk mains, are being phased out, a significant portion of current pipe networks are still comprised of the aging cast iron infrastructure that can be 50 to 150 years old. The cast iron pipes display a range of microstructures which, unsurprisingly, is related to their manufacturing process (pit cast and spun cast). Since it is prohibitively expensive, time consuming and too disruptive to replace this infrastructure in one programme of work, it is necessary to understand the properties of the remaining pipes so that replacement work can be focused in the first instance on areas of critical importance (Rajani and Makar [1]).

Do production processes influence the mechanical properties of bleached alfa pulpboard

This study was conducted to determine and analyse the influence of production process on the mechanical properties of bleached alfa pulpboard. Scanning electron microscopy showed that the industrial process currently used to produce the pulpboard causes small-scale and large-scale deformations in the alfa fibres. The same process results in a preferred orientation of the alfa fibres, leading to alignment in the rolling direction and hence there is some variation in the mechanical performance of the pulpboard in the different directions. Indeed, the mechanical properties show that the pulpboard loses its isotropic nature, mainly in the high-deformation regions. The pulpboard does not have the same mechanical characteristics in the longitudinal, 45°, and transverse directions. The samples taken in a longitudinal direction, which corresponds to the rolling direction, have better mechanical performance than in samples taken in the other two directions. Furthermore, the alkali (NaOH) treatment that is used to extract the alfa fibres from the alfa stems did not succeed in removing all of the non-cellulosic materials initially present in the alfa stems.