Microindentation is performed on hot isostatic pressed (HIP) Mg-Al (AM40) alloysamples produced by high-pressure die cast (HPDC) process for the purpose ofquantifying the mechanical properties of the α-Mg grains. The processof obtaining elastic modulus and hardness from indentation load-depth curves iswell established in the literature. A new inverse method is developed to extractplastic properties in this study. The method utilizes empirical yieldstrength-hardness relationship reported in the literature together with finiteelement modeling of the individual indentation. Due to the shallow depth of theindentation, indentation size effect (ISE) is taken into account whendetermining plastic properties. The stress versus strain behavior is determinedfor a series of indents. The resulting average values and standard deviationsare obtained for future use as input distributions for microstructure-basedproperty prediction of AM40.

Thin metal films on compliant polymer substrates are of major interest forflexible electronic technologies. The suitability of a film system for flexibleapplications is based on the electro-mechanical performance of the metalfilm/polymer substrate couple. This study demonstrates how a 10 nm Cr interlayerdeteriorates the electro-mechanical performance of 50 nm Au films on polyimidesubstrates by inducing the formation of cracks in the ductile layer. Combinedin-situ measurements of the film lattice strains with x-raydiffraction and electrical resistance with four point probe of the Au-Cr and Aulayers during uniaxial straining confirmed different electro-mechanicalbehaviours. For Au films with a Cr interlayer the film stress decreases rapidlyas cracking initiates and reaches a plateau as the saturation crack spacing isreached. Crack formation and stress drop correspond to a rapid increase in thefilm resistance. Without the interlayer the Au film stress reaches a maximumaround 2% engineering strain and remains constant throughout the experiment. Thefilm resistance is unaffected by the applied elongation up to a maximum strainof 15%, giving no sign of cracking in the metal layer. The outstandingelectro-mechanical performance of the gold film indicates that adhesion layers,like Cr, may not be necessary to improve the performance of ductile films onpolymers.

InP membranes have been bonded oxide mediated onto a patterned and unpatterned Sisubstrate. Indentation is shown to allow local testing on patterned areas. Bothresponses on patterned and unpatterned are compared and placed in reference tooxide free bonded membranes. Delamination of the membrane was observed to dependon the presence of patterns in the Silicon substrate. It occurs when theindenting load reached 55 mN for an oxide mediated bonded unpatterned structureand 42 mN for an oxide mediated bonded patterned one. This is in both casesbelow the value of 80 mN obtained for an oxide free bonded membrane(unpatterned). Weibull analysis of these events yielded a modulus m of magnitude6 to 10, indicating that delamination fracture is relatively predictable with aweaker resistance obtained in patterned oxide mediated bonding. Delamination ofthe membrane is the result of constraint of plastic flow by the InP/Siinterface. Membrane rotation is induced and increases with the indentation load,until it is sufficient to initiate and propagate an interfacial crack.

Two approaches have been employed in the preparation of hierarchical compositelaminates with a carbon nanotube (CNT) phase. Glass fibers were coated with CNTsusing electrophoretic deposition (EPD) prior to infusion with epoxy resin. TheCNTs were functionalized using an ultrasonicated-ozone process followed byreaction with polyethyleneimine (PEI) to enhance CNT to fiber and matrixadhesion. Chemical vapor deposition (CVD) was also used to grow CNTs onto quartzfibers, prior to infusion with an epoxy resin modified with a thermoplasticnanophase. The mechanical performance of the two CNT laminates types weresimilar, however, the fracture surfaces indicated distinct differences. The EPDlaminates showed fracture in the CNT-rich interphase region, whereas, the CVDlaminates showed that strength was limited by adhesion failure at the CNT-fiberinterface. The electrical conductivity of CVD laminates was 100 times higherthan EPD laminates. For the EPD laminates the PEI functionalization increasesthe CNT-CNT distance resulting in reduced conductivity, while the high CNTpacking density and residual iron catalyst on the fiber surface in the CVDlaminates creates conducting pathways resulting in higher conductivities.

This study presents a combine experimental and analytical investigation of thetoughening behavior in natural fiber-reinforced earth-based composites. Aspecially designed single fiber pullout apparatus was used to provide aquantitative determination of interfacial properties that are relevant totoughening brittle materials through fiber reinforcement. The parametersinvestigated included a specially designed high strength earth-based matrixcomprising of 60% laterite, 20% clay and 20% cement. The toughening behavior ofwhisker-reinforced earth-based matrix is analyzed in terms of a whisker bridgingzone immediately behind the crack tip and interface strength. This approach isconsistent with microscopy observations which reveal that intact bridgingwhiskers exist behind the crack tip as a result of debonding of thewhisker-matrix interface. Debonding with constant frictional stress was obtainedand this formed the basis for the analytical model considered and the underlyingcrack-microstructure interactions associated with Resistance-curve behavior wasstudied using in situ/ex situ optical microscopy to account for the bridgingcontribution to fracture toughness. The effect of multiple toughening mechanisms(debonding and crack bridging) was elucidated and the implications of theresults are considered for potential applications in the design of robustearth-based building materials for sustainable eco-friendly homes.

Multilayered film stacks, with length scales less than 10 nm are commonly used ina variety of devices, but present significant challenges to mechanical testingand evaluation. This is due to property convolution of the different layers.Both the properties of the individual layers and the combined response of thefilm stack are important input for design optimization. Here, we presentex-situ nanoindentation of a film stack representative of aperpendicular magnetic recording (PMR) hard disc drive (HDD), with more than 10layers. We then compare this with in-situ transmission electronmicroscopy indentation to visualize deformation of individual layers of thestack. The ex-situ testing reveals early plastic deformation,with an initially high contact pressure (13 GPa) and modulus ( >160GPa), followed by significant softening (8 GPa contact pressure and 140 GPamodulus), then slight hardening to 9 GPa. From in-situ testing,it is revealed that the metallic layer directly under the diamond like carbon(DLC) contributes the majority of the deformation and plastic flow, which is inturn constrained by a metallic oxide.

This work presents a preliminary experimental study on the possibility toinitiate growth of whiskers on the surfaces of some technologically importantmetals utilizing the enhanced electric field of surface plasmon polaritons(SPPs). The results provide evidence that a relatively high concentration ofwhat appear to be whisker nuclei form in the region where SPPs were excited,whereas no such changes are observed on the untreated surface.

It is well-known that dual phase (DP) steels composed of ferrite and martensitehave good ductility and plasticity as well as high strength. Due to theirexcellent mechanical properties, DP steels are widely used in the industrialfield. The mechanical properties of DP steels strongly depend on several factorssuch as fraction, distribution and grain size of each phase. In this study, thegrain size effect on mechanical properties of DP steels was investigated. Inorder to obtain DP structures with different grain sizes, intercritical heattreatment in ferrite + austenite two-phase region was carried out forferrite-pearlite structures having coarse and fine ferrite grain sizes. Theseferrite-pearlite structures with coarse and fine grains were fabricated by twotypes of heat treatments; austenitizing heat treatment and repetitive heattreatment. Ferrite grain sizes of the specimens heat-treated by austenitizingand repetitive heat treatment were 47.5 µm (coarse grain) and 4.5µm (fine grain), respectively. The ferrite grain sizes in the final DPstructures fabricated from the coarse-grained and fine-grained ferrite-pearlitestructures were 58.3 µm and 4.1µm, respectively. Themechanical behavior of the DP structures with different grain sizes wasevaluated by an uniaxial tensile test at room temperature. The local straindistribution in the specimens during tensile test was obtained by a digitalimage correlation (DIC) technique. Results of the tensile test showed that thefine-grained DP structure had higher strength and larger elongation than thecoarse-grained DP structure. It was found by the DIC analysis that thefine-grained DP structure showed homogeneous deformation compared with thecoarse-grained DP structure.