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Wood fibers are of the order of a few millimeters in length and a hundred micrometers in width, which makes it difficult to mechanically characterize them using standard methods, such as tensile testing. This work, builds on the development of a novel method to evaluate the stiffness of wood fibers, which uses the cantilever of an atomic force microscope (AFM) to carry out three-point bending. This is done by placing the fibers across a two millimeter trench, whereupon the AFM engages to the center and both applies loads and records the resulting displacements. Testing using this method has been confined to a single species of wood, pinus sylvestris (Scots pine), but there is a significant spread in the modulus of the fibres tested. This is not entirely surprising as a sample of wood consists of several different types of fibre, including, for example, heartwood and sapwood, early wood and latewood. These different fibres vary slightly in size and wall thickness. Here, Weibull statistics is used to investigate the correlation between samples in a dataset, and describe the magnitude of the correlation, in order to distinguish between fibre types and to provide greater clarity of the modulus associated with different types of fibre.

Timber is a composite material ordered over many length scales. The basic building blocks of timber are wood fibres, hollow tube like elements which are responsible for both water transport and load bearing within trees, (Ansell, 2015). The fibres can be separated from bulk timber in a process known as defibrilation, a key industrial process for the production of Medium Density Fibreboard (MDF). MDF is a composite material formed of fibres and adhesive, which is used widely in the construction industry among innumerable others.

Armour which is manufactured and distributed for personnel, vehicle and structural protection, primarily for military or policing applications, undergoes stringent testing to ensure that it can meet the demands of a range of impact scenarios. However, the effects of repetitive low-level damage are not fully understood and, in order to maintain a given level of protection, armour is recalled and replaced periodically, which is costly, and may be unnecessary. This paper reports preliminary studies on the relationship between minor damage and the resulting impact resistance of a woven fabric reinforced composite laminate (E-glass with epoxy resin). Specimens were subjected to displacement-controlled fatigue tests to introduce dispersed damage before being subjected to quasi-static indentation testing. The results showed that during penetration of the specimens, the peak load was reduced by approximately 10% for the pre-fatigued specimens, compared to the non-fatigued specimens, and there was some indication the energy absorption also reduced. It is proposed that the development of fibre fractures during the pre-fatigue of the specimens is the origin of these changes.

Digital Image Correlation (DIC) can be used to obtain full-field strain information on specimens under load. Through analysis of the resultant strain-contours, defects such as delaminations in composite materials can be detected, based on their effect on the deformation behaviour. This work focusses on the use of the DIC technique and two variations of active thermography (lock-in thermography and pulse thermography) for determining the lengths of delaminations in “milled-slot” specimens; for each technique, the measured delamination lengths have been compared with visually observed (i.e. photographed) delaminations grown under fatigue loading in transparent woven fabric GFRP specimens. In addition, the DIC results have been interpreted with the aid of a finite element model of the strain distribution in the milled-slot specimens. It has been found that the DIC technique provides a reasonably good method for measuring the length of the fatigue-grown delaminations after an empirical fit is applied, with the aid of the FE analysis, to overcome complications caused by fibre-bridging. On the other hand, the results using both lock-in and pulse thermography showed reasonable correlations with the visually observed (i.e. photographed) delamination lengths without the need for an empirical fit, although some post-processing of the data was required. For both thermography techniques, there were difficulties in determining the delamination lengths close to the edge of the milled slot.

Grey cast iron water pipe networks have been installed around the world, often 100–180 years ago. Cohorts (which can be defined by age, size, casting technology and geographical location, to specify but a few groups) degrade at different rates due to environmental and in-service issues, which can lead to a significant loss in mechanical performance. Hence, the management of these assets can be extremely problematic in terms of identifying priorities. The current paper considers the causes of such degradation, the consequences for defining accurate and up-to-date condition assessment protocols and hence the type and urgency of rehabilitation strategies. It follows that understanding the integrity/life expectancy of water networks requires non-destructive evaluation (NDE) of large-diameter cast iron trunk mains, with particular reference to the kinds of defects that are likely to be present and the issues that make assessment difficult. From this, recommendations are outlined for asset managers required to specify NDE protocols, based on an understanding of the nature of the material and conditions in the field.

Learning activities intended to offer children practice in careful mathematical logical thinking are described. (DT)

The effect of various organically modified silica (ormosil) nano-particle additions on the mechanical properties of a polyester resin has been investigated. For materials produced on such a fine scale, surface properties are known to dominate the manner in which they behave. This thesis presents results from two complementary areas of study: surface analysis and mechanical testing. The surface properties of the nano-particles and the interactions of the nano-particles with a polyester and adsorbed water have been investigated. These analyses have led to the development of a model which shows that the small organic groups grafted to the silica surface (methyl, ethyl and vinyl) are able to pack comparatively densely at the surface, effectively forming a continuous monolayer. This layer is sufficiently thick to prevent interaction of retained silanol groups with the polyester resin. When the silica is modified with phenyl functionality, however, the larger size leads to a more dispersed organic coverage that cannot be considered as a complete monolayer. Hence this layer reduces, but will not completely prevent interaction of the matrix with retained silanols of the silica. The particles have been dispersed in a polyester resin successfully. The dispersion process is an important step in producing viable nano-composites. Mechanical testing of such nano-composites has found a significant improvement in the toughness properties of the phenyl ormosil modified polyester, compared with the unmodified resin, whilst the other modified polyesters show smaller improvements. When considered with the surface analysis investigation, it is argued that the improvement is a result of a reduction of the strength of the interface (with reference to a commercial nano-silica) between the particles and the matrix. The phenyl ormosil is more strongly bonded than the other ormosils. Whilst these other ormosils are able to contribute to toughness through a crack pinning mechanism, the phenyl ormosil absorbs energy through debonding and promotes plastic deformation in the matrix, around and between particles, mechanisms which lead to a greater toughness enhancement.