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  • 1
    Electronic Resource
    Electronic Resource
    A Hierarchical Surface Measurement Strategy Using Non-Repeating Patterns (2000)
    Oxford, UK : Blackwell Publishing Ltd
    The @photogrammetric record 16 (2000), S. 0 
    Details
    ISSN: 1477-9730
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying
    Notes: 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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/0031-868X.00154
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  • 2
    Electronic Resource
    Electronic Resource
    Experimental characterization of the dynamic failure behavior of mortar under impact loading (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 2115-2123 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The failure behavior of mortar under dynamic impact loading is characterized through a series of plate impact experiments. The analysis focuses on the spall strength and the shear stress carrying capacity in different regions of the specimen under normal impact loading. Special attention is paid to the possible existence of a failure wave phenomenon that has been widely recognized as an important failure mechanism for glasses during plate impact. The experiments are designed to allow the strengths of the medium at locations behind and ahead of a possible failure wave front to be analyzed. The diagnostics used include velocity interferometer system for any reflector (VISAR) recording of the free surface velocities of targets and monitoring of the internal stresses via polyvinylidene fluoride (PVDF) gauges embedded in the specimen. Experiments conducted do not provide evidence for the existence of a failure wave phenomenon for mortar under plate normal impact loading. While the study suggests that a threshold impact stress must be exceeded for failure to occur, a clearly defined failure wave that propagates behind the loading wave is not observed. Instead, a gradual failure process that initiates upon the arrival of the loading wave and progresses thereafter is observed. This gradual failure process in mortar is in contrast to the well-defined failure front and complete loss of tensile strength associated with the failure wave phenomenon reported for glasses. The study also indicates that, under impact involving high levels of input stresses, attenuation of the loading wave occurs as it propagates through the failed medium. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1340005
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  • 3
    Electronic Resource
    Electronic Resource
    Finite element analysis of micromechanical failure modes in a heterogeneous ceramic material system (2000)
    Springer
    International journal of fracture 101 (2000), S. 161-180 
    Details
    ISSN: 1573-2673
    Keywords: Micromechanical modeling ; cohesive force ; fracture ; heterogeneous materials ; elasticity ; fracture modes ; failure modes ; numerical simulation ; crack propagation ; ceramic composites.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007545105723
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