Inelastic Deformation of Metal Matrix Composites

The deformation mechanisms of a Ti 15-3/SCS6 (SiC fiber) metal matrix composite (MMC) were investigated using a combination of mechanical measurements and microstructural analysis. The objectives were to evaluate the contributions of plasticity and damage to the overall inelastic response, and to confirm the mechanisms by rigorous microstructural evaluations. The results of room temperature experiments performed on 0 degree and 90 degree systems primarily are reported in this report. Results of experiments performed on other laminate systems and at high temperatures will be provided in a forthcoming report. Inelastic deformation of the 0 degree MMC (fibers parallel to load direction) was dominated by the plasticity of the matrix. In contrast, inelastic deformations of the 90 degree composite (fibers perpendicular to loading direction) occurred by both damage and plasticity. The predictions of a continuum elastic plastic model were compared with experimental data. The model was adequate for predicting the 0 degree response; however, it was inadequate for predicting the 90 degree response largely because it neglected damage. The importance of validating constitutive models using a combination of mechanical measurements and microstructural analysis is pointed out. The deformation mechanisms, and the likely sequence of events associated with the inelastic deformation of MMCs, are indicated in this paper

Inelastic deformation of metal matrix composites: Plasticity and damage mechanisms, part 2

The inelastic deformation mechanisms for the SiC (SCS-6)/Ti-15-3 system were studied at 538 C (1000 F) using a combination of mechanical measurements and detailed microstructural examinations. The objectives were to evaluate the contributions of plasticity and damage to the overall MMC response, and to compare the room temperature and elevated temperature deformation behaviors. Four different laminates were studied: (0)8, (90)8,(+ or -45)2s, and (0/90)2s, with the primary emphasis on the unidirectional (0)8, and (90)8 systems. The elevated temperature responses were similar to those at room temperature, involving a two-stage elastic-plastic type of response for the (0)8 system, and a characteristic three-stage deformation response for the (90)8 and (+ or -45)2s systems. The primary effects of elevated temperatures included: (1) reduction in the 'yield' and failure strengths; (2) plasticity through diffused slip rather than concentrated planar slip (which occurred at room temperature); and (3) time-dependent deformation. The inelastic deformation mechanism for the (0)8 MMC was dominated by plasticity at both temperatures. For the (90)8 and (+ or -45)2s MMCs, a combination of damage and plasticity contributed to the deformation at both temperatures

Design, fabrication and testing of sandwich panel decking use in road freight trailers

This paper investigates the potential of sandwich structures in the novel application of road freight trailer decking. Sandwich panels are developed to be lightweight replacements to conventional birch plywood hardwood decking, which is the norm in European road freight trailers. A tailored material selection process is used to identify the most advantageous sandwich panel material combinations with respect to flexural properties and material cost. Sandwich panels with woven glass fibre reinforced polyester and an end-grain balsa are found to be the most advantageous material combination in terms of both raw material cost and mechanical performance. These panels are fabricated using a single shot fabrication technique and are approximately 30% lighter than conventional birch plywood trailer decking. This weight saving corresponds to approximately 165 kg in a standard 13.6 m long European road freight trailer. Three point bend testing has shown that these sandwich panels have superior flexural strength and comparable flexural stiffness to birch plywood. Large panel testing confirmed that these panels can withstand roughly four times the forklift wheel load likely to be seen in-service. The shear properties of two grades of rigid end-grain balsa core are also studied to illustrate the importance of using a higher density balsa core. Practical considerations, such as joining and recyclability, for using sandwich panels in this application are also discussed.Centre for Sustainable Road Freight, Engineering and Physical Sciences Research Council (Grant ID: EP/K00915X/1

Wide-Area Impact Damage Evaluation with Sonic Infrared Imaging NDE in Advanced Composite Structures

Abstract Sonic Infrared (IR) imaging is a relatively new member in the NDE technology family. This method combines a short pulse of ultrasound excitation, typically a fraction of a second, and infrared imaging. It has been shown its great advantage as a NDE technology to detect defects such as cracks in metal/metal alloy structures. As an imaging technology, Sonic IR is capable of wide area evaluation. Composite materials have been used in broader applications due to its light weight and stiffness. However, composites suffer more to impact than metal structures. Such damage in composites may not present at the surface but severe damage could have occurred in deeper layers. In such case, the structure strength is greatly weakened. We have been studying impact damages in composite structures with Sonic Infrared Imaging, and evaluating how structures affect thermal signatures in defect characterization. In this paper, we will present our study on composite panels containing structures such as doublers and beams or stiffeners, which were subjected to impacts from varying energy projectiles

Energy Conservation in Passive Optical Networks: A Tutorial and Survey

The Passive Optical Network (PON) has been evolving continuously in terms of architecture and capacity to keep up with the demand for high-speed Internet access in the access network segment. Recently, integration of Software-Defined Networking (SDN), which provides programmable and (logically) centralized network control, with PON has attracted intensive research interest to further enhance PON performance and reduce operational and capital expenditure. Although PON is regarded as an energy-efficient a ccess n etwork s olution, it is a major contributor for increasing energy consumption in the access network segment because of its higher penetration rate than other access network technologies. Over the past several years, the major standardization bodies like IEEE and research communities have engaged in introducing energy-efficient PON solutions. This article familiarizes readers with PON evolution in terms of capacity, architecture, and its integration with virtualization and SDN based control. We present a comprehensive survey of the energy conservation research efforts in PON starting from conventional PON to SDN based PON leveraging virtual and physical network functions. This article also presents contemporary energy-efficient standardization activities in IEEE and ITU. To the best of our knowledge, to date, this article is the first most comprehensive survey on energy saving research and standardization on PON. We summarize the lessons learned from the recent advancements, identify important challenges ahead and outline several future research directions that can contribute to further advancement of energy-efficient PON