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Digitale Medien

A Hierarchical Surface Measurement Strategy Using Non-Repeating Patterns (2000)

Zhou, M. ; Fraser, C. S.

Oxford, UK : Blackwell Publishing Ltd

The @photogrammetric record 16 (2000), S. 0

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ISSN: 1477-9730

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Architektur, Bauingenieurwesen, Vermessung

Notizen: Hierarchical approaches for automated photogrammetric surface measurement invariably employ image pyramids and image matching at multiple resolutions. Such an approach is also applicable in industrial photogrammetry where projected light patterns are used to provide texture on an otherwise texture-free surface. This paper describes a novel strategy for hierarchical surface measurement in which projected non-repeating target patterns are employed, rather than the lower-resolution levels of an image pyramid. Thus, although the final derived digital surface model is obtained by image matching, preliminary surface models which support the matching are obtained using the non-repeating patterns. These projected patterns allow a simplification of the triangulation phase since they offer the potential of a fast and unambiguous solution to the image point correspondence problem. Following an introduction to the non-repeating pattern strategy, integration of the approach into a multi-camera vision metrology system is described and some experimental measurements are summarized

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/0031-868X.00154

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Digitale Medien

Finite element analysis of micromechanical failure modes in a heterogeneous ceramic material system (2000)

Zhai, J. ; Zhou, M.

Springer

International journal of fracture 101 (2000), S. 161-180

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ISSN: 1573-2673

Schlagwort(e): Micromechanical modeling ; cohesive force ; fracture ; heterogeneous materials ; elasticity ; fracture modes ; failure modes ; numerical simulation ; crack propagation ; ceramic composites.

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau

Notizen: Abstract A micromechanical model that provides explicit accounts for arbitrary microstructures and arbitrary fracture patterns is developed and used. The approach uses both a constitutive law for the bulk solid constituents and a constitutive law for fracture surfaces. The model is based on a cohesive surface formulation of Xu and Needleman and represents a phenomenological characterization for atomic forces on potential crack/microcrack surfaces. This framework of analysis does not require the use of continuum fracture criteria which assume, for example, the existence of K-fields. Numerical analyses carried out concern failure in the forms of crack propagation and microcrack formation. Actual microstructures of brittle alumina/titanium diboride (Al2O3/TiB2) composites are used. The results demonstrate the effects of microstructure and material inhomogeneities on the selection of failure modes in this material system. For example, the strength of interfaces between the phases is found to significantly influence the failure characteristics. When weak interfacial strength exists, interfacial debonding and microcrack initiation and growth are the principal mode of failure. When strong interfacial strength is derived from material processing, advancement of a dominant crack and crack branching are observed.