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The effect of patterns on image-based modelling of texture-less objects

Hafeez J., Jeon H.-J., Hamacher A., Kwon S.-C., Lee S.-H.

Metrology and Measurement Systems

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2018

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Vol. 25, nr 4

755--767

EN

The task of generating fast and accurate three-dimensional (3D) models of objects or scenes through a sequence of non-calibrated images is an active field of research. The recent development in algorithm optimization has resulted in many automatic solutions that can provide an accurate 3D model from texture-full objects. Structure-from-motion (SfM) is an image-based method that uses discriminative point-based feature identifier, such as SIFT, to locate feature points in the images. This method faces difficulties when presented with the objects made of homogenous or texture-less surfaces. To reconstruct such surfaces a well-known technique is to apply an artificial variety by covering the surface with a random texture pattern prior to the image capturing process. In this work, we designed three series of image patterns which are tested based on the contrast and density ratio which increases from the first to the last pattern within the same series. The performance of the patterns is evaluated by reconstructing the surface of a texture-less object and comparing it with the true data. Using the best-found patterns from the experiments, a 3D model of a Moai statue is reconstructed. The experimental results demonstrate that the density and structure of a pattern highly affects the quality of the reconstruction.

2

Microstructure and Mechanical Properties of AA1050/ AA6061/AA1050 Multi-Layer Sheet Fabricated by Cold Roll Bonding Process

Lee S.-H.

Archives of Metallurgy and Materials

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2018

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Vol. 63, iss. 3

1489--1492

EN

A cold roll-bonding process was applied to fabricate an AA1050/AA6061/AA1050 multi-layer sheet. Three Al sheets in which an AA6061 sheet is inserted inside two AA1050 sheets of 2 mm thickness, 40 mm width and 300 mm length were stacked up after surface treatment, and the material was then reduced to a thickness of 1.0 mm by multi-pass cold rolling. The AA1050/AA6061/AA1050 laminate complex sheet fabricated by roll bonding was then hardened by a natural aging (T4) and an artificial aging (T6) treatments. The microstructures of the as-roll bonded and the age-hardened Al complex sheets were revealed by optical microscope and electron back scatter diffraction analysis, and the mechanical properties were investigated by tensile and hardness testing. The strength of the as-roll bonded complex sheet was found to increase by 2.6 times, compared to that value of the starting material. Both AA1050 and AA6061 showed a typical recrystallization structure in which the grains were equiaxed after heat treatment. However, the grain size was smaller in AA6061 than in AA1050.

3

Characteristics Of The Porous Body Sintered By Nano-Sized Fe-Cr-Al Alloy Powder

Lee S.-I., Lee S.-H., Gu B.-U., Lee D.-W., Kim B.-K.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2B

1275--1279

EN

Porous metal with uniform honeycomb structure was successfully produced by sintering using Fe-Cr-Al nano powder, which was prepared by the pulsed wire evaporation (PWE) in ethanol. Its process consisted of the several steps; 1) coating on the surface of polyurethane sponge with the liquid droplets generated from the ethanol-based slurry where the Fe-Cr-Al nano powders were uniformly dispersed, 2) heat treatment of debinding to remove the polyurethane sponge and 3) sintering of the porous green body formed by Fe-Cr-Al nano powders. The strut thickness of porous Fe-Cr-Al was increased by the increase of spraying times in ESP step. Also, The shrinkages and the oxidation resistance of the sintered porous body was increased with increase of sintering temperature. The optimal sintering temperature was shown to 1450°C in views to maximize the oxidation resistance and sinterability.