Modified rolled homogeneous armor (RHA) steels were designed and produced to characterize the effects of niobium additions and accompanying heat treatments on microstructure and mechanical properties. This study combines in-house steel production and property analysis to advance the understanding of niobium on enhanced hardenability and weldability in a chemistry-process-structure-property relationship paradigm. For steel production, designed alloys were cast in a vacuum induction melting furnace and thermo-mechanically processed. Optimal heat treatment conditions were determined by utilizing a thermo-mechanics calculation software. Microstructures were investigated by optical and electron microscopy while hardenability was characterized by Jominy end-quench tests. Mechanical tests were performed at various stress states, strain rates, and temperatures to understand deformation behavior under complex loading conditions. Encouraging results in performance were observed in the micro-alloyed armor steels as compared to reference materials from earlier studies.

A design of experiments methodology was used to investigate the effect of vaporgrown carbon nanofiber (VGCNF) weight fraction, high-shear mixing time, and ultrasonication time on the Izod impact strength of vinyl ester (VE) based nanocomposites. A response surface model (RSM) was developed for predicting impact strengths using a regression analysis approach. The RSM predicts a maximum increase in impact strength of 18% at a VGCNF weight fraction of 0.17 parts per hundred parts resin (phr) (a volume percent of ~0.1) and 100 min high-shear mixing when compared to that of neat VE. The impact strength predictions show an initial increase for low VGCNF weight fractions and extended high-shear mixing. However, a marked decrease in impact strength occurred as the VGCNF weight fraction increased above 0.45 phr. Scanning electron micrographs of the fracture surface of several specimens suggest that the impact strength of VGCNF/VE nanocomposites is directly related to nanofiber dispersion.

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<p>  </p> <p>Materials performance under extreme conditions is pivotal to the design of advanced nuclear reactor materials. Nanocrystalline metals possess improved radiation resistance and superior mechanical properties. However, it remains a major challenge to stabilize the fine grains in nanocrystalline materials at elevated temperatures. The response of abundant interfaces and triple junctions to thermal annealing, plastic straining and radiation damage profoundly influence the overall performance of nanocrystalline metals. The objective of this thesis is to illustrate a new alloy design strategy via engineering the interfaces and triple junctions of triphase nanocomposites to enhance the thermal stability, mechanical strength and radiation tolerance of nanocrystalline metallic materials simultaneously. </p> <p>In triphase nanocomposites where each phase is nearly immiscible to the others, the triple junctions and phase boundaries form a 3D interlocking network that could significantly increase the thermal and radiation stability. In this thesis, two distinct triphase architectures were explored: nanolaminate and nanocrystalline Cu-Ag-Fe composites fabricated by magnetron sputtering. The effectiveness of Cu-Ag-Fe triphase triple junctions in mitigating thermal grooving was evaluated by considering grooving kinetics. Additionally, micropillar compression tests on Cu-Ag-Fe nanolaminate composites demonstrated substantial enhancement of strength and strain hardening capability comparing to Cu/Fe multilayers. The nanocrystalline Cu-Ag-Fe composites exhibited a distinct texture evolution and greatly enhanced resistance to grain coarsening. In situ sequential dual beam (He + Kr) irradiation studies show nanocrystalline Cu-Ag-Fe composites have a remarkable bubble swelling resistance, suggesting the strong He storage and defect annihilation capability of the triphase nanocomposites. The results obtained from this thesis provide innovative perspectives on the design of high strength nanostructured metals with enhanced thermal stability and radiation tolerance.</p>

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No / Long glass fibre (LGF) composites are extensively used in manufacturing to produce components with enhanced mechanical properties. Long fibres with length 12 to 25mm are added to a thermoplastic matrix. However severe fibre breakage can occur in the injection moulding process resulting in shorter fibre length distribution (FLD). The majority of this breakage occurs due to the melt experiencing extreme shear stress during the preparation and injection stage. Care should be taken to ensure that the longer fibres make it through the injection moulding process without their length being significantly degraded. This study is based on commercial 12 mm long glass-fibre reinforced polypropylene (PP) and short glass fibre Nylon. Due to the semi-flexiable behaviour of long glass fibres, the fibre orientation distribution (FOD) will differ from the orientation distribution of short glass fibre in an injection molded part. In order to investigate the effect the change in fibre length has on the fibre orientation distribution or vice versa, FOD data was measured using the 2D section image analyser. The overall purpose of the research is to show how the orientation distribution chnages in an injection moulded centre gated disc and end gated plaque geometry and to compare this data against fibre orientation predictions obtained from Autodesk Moldflow Simulation Insight.

Yes / This paper studied the effect of different types of multi-walled carbon nanotubes (MWCNTs) on the dynamic mechanical properties of cementitious composites. Impact compression test was conducted on various specimens to obtain the dynamic stress-strain curves and dynamic compressive strength as well as deformation of cementitious composites. The dynamic impact toughness and impact dissipation energy were, then, estimated. Furthermore, the microscopic morphology of cementitious composites was identified by using the scanning electron microscope to show the reinforcing mechanisms of MWCNTs on cementitious composites. Experimental results show that all types of MWCNTs can increase the dynamic compressive strength and ultimate strain of the composite, but the dynamic peak strain of the composite presents deviations with the MWCNT incorporation. The composite with thick-short MWCNTs has a 100.8% increase in the impact toughness, and the composite with thin-long MWCNTs presents an increased dissipation energy up to 93.8%. MWCNTs with special structure or coating treatment have higher reinforcing effect to strength of the composite against untreated MWCNTs. The modifying mechanisms of MWCNTs on cementitious composite are mainly attributed to their nucleation and bridging effects, which prevent the micro-crack generation and delay the macro-crack propagation through increasing the energy consumption.