Fundamental Investigation for Tensile Test Using Conical Cupping Die

A number of researches have conducted in order to evaluate the ductile fracture occurrence by using forming limit diagram. However, specimen shape and testing machine for obtaining forming limit diagram of sheet metal have some problems. The problem about specimen shape is occurring at the specimen edge. In uniaxial tensile test, the specimen edge may cause a defused neck in width direction and may have influence on fracture occurrence. In biaxial tensile test by using a cruciform specimen, a uniform biaxial deformation is not obtained because uniaxial tensile stress occurs at the specimen edge. Tensile test by using a specimen which does not have such edges should carry out, for example, in bulge test and multi-axial tube expansion test, specimens without edge are used. However, these methods need special machines. Therefore, new biaxial tensile testing method is required. By this method, materials deform depending on biaxial strain state by using popular pressing machines.

X-Ray Tomography Investigation of Fe-rich Intermetallics in AlSi Alloys

Iron exists as a common impurity element in AlSi foundry alloys. The main consequence of the presence or adding of iron to AlSi alloys is the formation Fe-rich intermetallics with especially deleterious β-Al5FeSi. This work aims to identify the role of fluid flow on the microstructure and intermetallics in Al-9 wt.% Si-0.2/0.5/1.0 wt.% Fe alloys directionally solidified under defined thermal and fluid flow conditions and extensively uses 3D x-ray tomography to get a better insight into their morphology and formation. The results have revealed the growth of larger and more dense β-Al5FeSi intermetallics in the specimen centre as an effect of forced flow. The reconstructions confirmed that the course of number density at the specimen cross section increases from the specimen edge to its centre.

Influence of Specimen Sampling on Internal Residual Stress Test

Using Finite Element Method, the changing rules of residual stresses in the test specimen cut out from a quenched plate were analyzed, and suitable dimensions of the specimen for crack compliance method test was recommended. The results show that cutting has great influences on residual stresses in the specimen edge areas to a range of about one thickness, while it has little influences on stresses at the center part of the specimen; cutting mainly influences stresses normal to the cutting plane, while it has little effect on stresses parallel to the cutting plane; specimen with length bigger than 2.67 times the thickness and width bigger than 2 times the thickness is suitable for crack compliance method test, under these conditions peak stresses losing in crack compliance method results is less than 5% compared with surface stress X-ray diffraction results.

Interpretation of Holographic and Lorentz Images of an Array of Reverse Biased P-N Junctions in a Semi-Infinite Specimen

The problem of observing reverse-biased p-n junctions by means of transmission electron microscopy techniques is very challenging both from the experimental and theoretical points of view. In particular, in addition to standard Lorentz microscopy techniques, whose image contrast is able to give some information on the region of high field, also holographic methods have been successfully applied and an interference map of the twodimensional phase on the specimen plane obtained.In this work we consider, in particular, the theoretical and interpretative aspects, as we have improved a model for the electric field associated to a periodic array of alternating p and n stripes lying in a half plane (physically corresponding to an array of zero-width step junctions) by taking into account that the junctions are tilted with respect to the specimen edge.

Magnetic Deflecting Microscopy: A Novel Visualizing Method of Magnetic Stray Fields for Thick or Non-Transparent Magnetic TEM Samples

For microstructure analysis of magnetic materials, in particular, for a new class of Nd-Fe-B hard magnets, a number of magnetic imaging techniques can be applied to gain different microstructure information. For instance, SEM magnetic imaging can be successfully used for very thick samples from a bulk ones down to a sample thickness of 10-20 μ. Below this limit the resolution of SEM magnetic images generally is too low to visualize fine details of magnetic structure. For very thin samples (less then 0.5 μm) magnetic Lorentz microscopy methods in conventional TEM are very useful tools to reveal magnetic domains and their structure. Therefore, it seems that relatively thick films of 0.5-20 μm in thickness are left out of the experimental limits of the methods discussed.We report on a novel, indirect TEM method that allows us to extend the limits of magnetic imaging for TEM non-transparent magnetic samples by viewing the surface stray fields and fringing fields generated by magnetic domains at specimen edge.

Evaluation of Microscopic Deformation in CFRP Laminates with Delamination by Micro-Grid Methods

Micro-grid methods were applied to measure displacements in 90° ply in CFRP cross-ply laminates with only transverse cracks or with both transverse cracks and delaminations. The COD (crack opening displacement) of the transverse cracks were also measured. Micro-grids were printed on the specimen edge surfaces by using the photo-lithography technique. The displacement fields of the specimen edge surface obtained from the experiment were compared with McCartney's [1] and Lee et al.'s [2] analyses which predicted the displacement field of a cross-ply laminate with only transverse cracks. Furthermore these analyses were modified to consider the existence of delamination.