Contrary to pyramids and domes, elongated huts on a Si(001) substrate are commonly considered as kinetically limited structures. In this work, however, based on detailed scanning tunneling microscopy observations of Ge huts growing on Si(001) at temperatures below 550 degrees C and finite element analysis, the possibility of an equilibrium-driven elongation is raised, where hut-preceding pits are thought to lift the energetic degeneracy of {105} facets and cause elongation along energetically preferred directions.

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Experiments are carried out to determine the delamination toughness for a crack along the interface between two transversely isotropic materials. The material chosen for study consists of carbon fibers embedded within an epoxy matrix. A crack is introduced between two layers of this material, with fibers in the upper layer along the +45 • -direction and those in the lower layer along the −45 • -direction both with respect to the crack plane. The Brazilian disk specimen is employed in the testing. To calibrate the specimens, stress intensity factors are obtained which result from the applied load, as well as residual curing stresses. It may be noted that all three modes are coupled, leading to a three-dimensional problem. The finite element method and a mechanical M-integral are employed to determine the stress intensity factors arising from the applied load. For the residual stresses, a three-dimensional conservative thermal M-integral is presented for stress intensity factor determination. The stress intensity factors found for the applied load and residual stresses are superposed to obtain a local energy release rate, together with two phase angles. From the load at fracture, the critical interface energy release rate or interface toughness G ic as a function of phase angles ψ and φ is determined. Results are compared to a fracture criterion.

A methodology has been developed for accurately measuring the mechanical properties of materials used on the micro-scale. The direct tension test method using a dog bone-type specimen has been employed, as it is the most effective and straightforward method to obtain results including a full stress-strain curve. The goal of this investigation was to develop a universal, yet simple and reliable, methodology to be used for accurate characterisation of mechanical properties for a wide variety of materials. Specimens from single crystal silicon were fabricated using photolithography by means of deep reactive ion etching. This material was chosen as it is expected that on both the micro-and macro-scales, Young's modulus will have the same value. Hence, the accuracy of the methodology may be unambiguously examined. The test set-up includes a small test machine containing a load cell whose maximum capacity is 5 N and is capable of direct gripping and displacement control. The specimens were found to have a trapezoidal cross-section that was accurately measured using a scanning electron microscope. The strains were obtained by means of digital image correlation using images obtained via optical microscopy. The quantities measured include Young's modulus E, the fracture strength r f and the fracture strain f . The average value of E obtained in the micro-tests agrees well with the reference value obtained on the macro-scale. Figure 1: (A) Direct tensile specimen and frame; dimensions in millimetres. (B) Gauge; dimensions in micrometres (t ¼ thickness) Ó