Materials Science Forum Vols. 654-656

Abstract: A dual-cooled fuel (i.e. annular fuel) has been proposed to substantially increase in power density and safety margins compared to a solid fuel in operating PWR plants. As this fuel rod has larger outer diameter than the conventional solid rod to accommodate sufficient internal flow, new supporting structure geometries should be designed and their reliabilities (i.e. vibration characteristics, fretting wear resistance, etc.) are also examined with both analytical and experimental methods. In this study, the supporting structure characteristics and fretting wear behaviors are analyzed and examined by using two kinds of simulated supporting structures that have embossing and cylindrical shapes. Their supporting structure characteristics were examined by using a specially designed test rig and their results were compared with that of analytical method. Also, fretting wear behaviors of simulated supporting structures were experimentally examined with considering the effect of contact shapes and their stiffness values. Based on the test results, the relationship between the supporting structure characteristics and their fretting wear behaviors was discussed in detail.

Abstract: The influences of solution treatments, prior cold drawings and aging treatments on mechanical properties in Corson alloy with high contents more than 8.0 mass% of Ni and Si have been investigated. As a result of the optimization of conditions, the maximum hardness and tensile strength reached 306HV and 968MPa, respectively. Effects of temperatures of solution treatment and aging on the mechanical properties were analyzed based on solid solute concentrations in matrix phase, which were estimated by using the linear analysis and calculated from the electrical conductivity. The solute concentrations were also measured directly by SEM-EDS. Consequently, the precipitation hardening of the alloys was governed mainly by the solute concentrations of Ni and Si in matrix phase in solution treatment. The hardness depended on not only the solute concentrations but also the excess of Ni and Si in the alloys.

Abstract: Thermo-physical properties of diamond reinforced Al composites were investigated. Volume fraction of diamond particles was up to 55%. In order to improve the interfacial bonding between diamond and aluminum, diamond particles were pre-coated with titanium using molten salt method. XRD and SEM observation showed that the Ti coating on diamond consists of carbide layer and metal layer, which mainly depend on temperature and time. The influences of the Ti coating on interfacial characteristic and the thermo-physical properties of the composites were studied. The interfacial characterization and thermal diffusivity measurements indicated that Ti coated diamond was more favorable on interfacial bonding and thermal properties. Ti coating on diamond resulted in an increase of thermal conductivity of the composites, from 200 to 430 W/mK along with a coefficient of thermal expansion of 6.40 × 10-6/K.

Abstract: This paper presents a computational and experimental investigation of the influence of self-healing micro-vessels on the structural properties of laminated composites. Embedded self-healing system is rapidly emerging as an important technology for improving the damage resistance of laminated composites. Introduction of hollow fibres or hollow spheres can, however, potentially weaken the structure and lead to excessive reduction in mechanical performance of composites. In this research, computational simulation is carried out to investigate the effect of embedded microvascular vessels on the mechanical properties of self-healing composite, focusing on the stress concentrations around self-healing vessels and delamination cracking.

Abstract: The bond strength of various metal multilayers produced by cold rolling of metal foils with different thermal conductivity was investigated. Results indicated that under the same conditions of deformation and surface preparation, the metallic multilayer system with low thermal conductivity exhibited relative high bond strength while high thermal conductivity metal system may fail to be roll-bonded together. The relationship between the deformation-induced localized heating and the bond strength were discussed. The deformation-induced localized heating in the low thermal conductivity metal multilayer systems may provide opportunities for achieving a successful accumulative roll bonding or a “cold roll/heat treatment/cold roll” process to synthesize metallic multilayer materials.

Abstract: In this study, the fatigue characteristics and life of woven glass fabric/epoxy laminate composites applied to railway vehicle were evaluated. The fatigue test was conducted by tension-tension load with stress ratio R of 0.1 and frequency of 5Hz. The material used to fatigue test was two types of woven glass fabric/epoxy laminate composite with and without the reinforcement of carbon/epoxy ply. Also, the fatigue life of woven glass fabric/epoxy laminate composite was compared with that of aluminum 6005 used to the car-body and under-frame structures of railway vehicle. The test results showed that the failure strength and life of woven glass fabric/epoxy laminate composite with the reinforcement of three carbon/epoxy plies had a remarkable improvement in comparison with that of bare specimen without reinforcement.

Abstract: Approaches to detect, assess, monitor and repair damage in critical aircraft components fabricated from composite materials are essential for safe and cost effective operation. In metallic aircraft structures, it is common to leave some fractures in situ for a prescribed period until it is convenient to repair, provided strict inspection and verification processes are in place. Under current military aircraft structural management guidelines, visible damage to critical composite components requires either immediate repair or replacement. Much has been learnt about the behaviour of damaged composite structures, but further investigation is required to develop validated residual strength and life prediction tools. A preliminary review of an early physically based, residual strength prediction method was conducted. The accuracy of this method for use in predicting the strength of composite following a complex damage was tested by comparing the results with compression-after-impact test data for a composite laminate representative of F/A 18 fracture critical structure.

Abstract: In the conventional DCB test, test is usually conducted by observing the crack growth with a microscope, in this paper, new technique is tried to monitor the crack propagation in real time using optical fiber attached in the Kevlar/epoxy specimen. Crack tip position was monitored using strain distribution field data from the optical fiber and compared with the microscope data. BOCDA (Brillouin Optical Correlation Domain Analysis) system was used to measure the strain distribution of the optical fiber and spatial resolution, strain accuracy were about 9mm, ±20με each.

Abstract: Carbon fibre composites are being used in the structure of new generation helicopters in order to reduce weight. Helicopters such as armed reconnaissance vehicles, are potentially vulnerable to small arms fire. As a result a series of ballistic tests were carried out on laminate test specimens using 7.62mm and 12.7mm small arms fire. These specimens are representative of typical helicopter composite structure. These ballistic tests were followed by ultrasonic ‘A’ scans, hammer tap and thermography techniques to determine the extent of delamination damage.

Abstract: Many modern military aircraft are constructed from composite and bonded structure, such as thin carbon-epoxy laminate bonded to Kevlar® and Nomex® honeycomb. Operation of these platforms in Australian and global conditions will subject the structure to potentially high levels of humidity, extremes in temperature, and for maritime operations, exposure to salt spray conditions. The thin composite laminate is likely to rapidly absorb moisture in a humid environment and enable permeation of moisture into the adhesive and core. In addition to the chemical influence of moisture on the composite structure, the moisture trapped in the honeycomb structure may freeze and expand with changes in altitude during operations or simply due to daily temperature fluctuations at the resident airbase. The combination of moisture ingress in the honeycomb structure and thermal cycling may lead to deteriorated strength of the honeycomb panels over time that would not be observed for long term humid exposure alone. Long term salt water absorption may also have an adverse effect on composites structures. This study investigates the effects of humid environments and thermal cycling on the mechanical properties of composite and honeycomb structures.