Showing papers by "Peter Davies published in 2020"

Influence of Seawater Ageing on Fracture of Carbon Fiber Reinforced Epoxy Composites for Ocean Engineering

Abstract: Carbon fiber reinforced composite materials are finding new applications in highly loaded marine structures such as tidal turbine blades and marine propellers. Such applications require long-term damage resistance while being subjected to continuous seawater immersion. However, few data exist on which to base material selection and design. This paper provides a set of results from interlaminar fracture tests on specimens before and after seawater ageing. The focus is on delamination as this is the main failure mechanism for laminated composites under out-of-plane loading. Results show that there are two contributions to changes in fracture toughness during an accelerated wet ageing program: effects due to water and effects due to physical ageing. These are identified and it is shown that this composite retains over 70% of its initial fracture properties even for the worst case examined.

Towards More Representative Accelerated Aging of Marine Composites

Abstract: Polymer and composite materials are being considered for marine applications where long term durability is critical. Unfortunately, for most of these applications it is not possible to perform test programs for ten or more years in order to verify performance, so accelerated testing is widely used. This chapter describes the parameters that can be used to accelerate aging tests and discusses their limitations. Two examples are shown from campaigns lasting over 6 and 8 years, in order to provide data that reveal long term behavior.

Evaluating Mooring Line Test Procedures through the Application of a Round Robin Test Approach

Abstract: Innovation in materials and test protocols, as well as physical and numerical investigations, is required to address the technical challenges arising due to the novel application of components from conventional industries to the marine renewable energy (MRE) industry. Synthetic fibre ropes, widely used for offshore station-keeping, have potential application in the MRE industry to reduce peak mooring line loads. This paper presents the results of a physical characterisation study of a novel hybrid polyester-polyolefin rope for MRE mooring applications through a round robin testing (RRT) approach at two test facilities. The RRT was performed using standard guidelines for offshore mooring lines and the results are verified through the numerical modelling of the rope tensile behaviour. The physical testing provides quantifiable margins for the strength and stiffness properties of the hybrid rope, increases confidence in the test protocols and assesses facility-specific influences on test outcomes. The results indicate that the adopted guidance is suitable for rope testing in mooring applications and there is good agreement between stiffness characterisation at both facilities. Additionally, the numerical model provides a satisfactory prediction of the rope tensile behaviour and it can be used for further parametric studies.

Using video clubs to develop teachers’ thinking and practice in oral feedback and dialogic teaching

Abstract: The authors report outcomes of an evaluation of a ‘video club’ intervention to improve the feedback and dialogic teaching practice of 91 teachers from 11 primary schools in England. Participating t...

The fatigue performance of titanium alloys joined via the powder interlayer bonding method

Abstract: This study investigated the fatigue performance of two forged variations of α + β titanium alloys, namely Ti-6Al-4V (Ti-6-4) and Ti-6Al-2Sn-4Zr-6Mo (Ti-6-2-4-6) joined via the powder interlayer bonding (PIB) process. Both alloys were bonded at relevant temperatures in the specific alloy’s α + β region. Modifications to the microstructure during the bonding process where it recrystalised into a bi-modal structure, resulted in improved low cycle fatigue (LCF) response for the Ti-6-4 alloy. This improvement is seen throughout the fatigue curve when compared to the LCF performance of the as received Ti-6-4 material. The improvement in LCF performance resulting from the microstructure transformation overcomes any reduction in performance that can be attributed to retained porosity after the bonding cycle. While the HCF performance of the Ti-6-2-4-6 alloy joined via the PIB process fell below that of the as received β-forged billet material, the fatigue performance compares well with previous HCF results for welded material. Unlike the Ti-6-4 alloy, the β-forged Ti-6-2-4-6 alloy does not benefit from the transformation of its microstructure throughout the bond region.

The joining of gamma titanium aluminides via the powder interlayer bonding method

Abstract: Powder interlayer bonding (PIB) is a joining technique originally developed to enable high-integrity repairs of aerospace components. The technique has previously been employed for the joining of titanium and nickel alloys utilised in the aerospace industry. This study expands on the application of the novel joining technique known as powder interlayer bonding (PIB), to the bonding of γ titanium aluminide (TiAl) material. PIB has been used to facilitate high-integrity joints in gamma titanium aluminides (TiAl), where full densification of the joint was achieved. The PIB technique described here used a metallic powder interlayer between the two faying surfaces of γ TiAl specimens. Bonds were formed in an inert atmosphere under induction heating. The PIB technique proved capable of producing high-integrity bonds in terms of microstructural evaluation, with very limited porosity retained after the bonding cycle. A brittle Ti2Al phase can be produced with heavily oxidised powder which is susceptible to cracking and will negatively affect mechanical properties.

Temperate rocky reef on the southeast Australian continental shelf

Abstract: Recent multibeam and towed video surveys at Port Stephens have disclosed additional information on habitat extent and diversity on Australia’s temperate southeast coast. Multibeam identified previously undescribed soft-sediment features at Seal Rocks and Broughton Island while also confirming broader geomorphological characteristics including the presence of a shelf sand body. While soft unconsolidated sediments dominate the seabed, reef, and mixed habitats covered 20%–40% of the seafloor over the inner- and mid-shelf and supported morphologically diverse sponge communities. Kelp, urchins, branching algae, and encrusting sponges were common to shallow sites (20–40 m) where depth variability was greatest. Sponges dominated over mid to deep-reef and mixed substrate areas and coexisted with ascidians (50–70 m) or sea whips and gorgonians (80–100 m). Multibeam was effective for identifying reef (82%) and soft-sediment (71%) areas but relatively less accurate at identifying mixed seabed. Further subdivisions within the current classification scheme are warranted if a more detailed and park-specific scheme is required.