406 research outputs found

    Full-field Vibration Measurement for Vibrothermography

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    Vibrothermography is a nondestructive technique for finding defects through vibration‐induced heating imaged with an infrared camera. To model the crack heating process in Vibrothermography, it is essential first to understand the vibration that causes heat generation. We describe a method for calculating internal motions from surface vibrometry measurements. A reciprocity integral and Gauss\u27s law allow representation of internal motion by a surface integral of boundary motion times the Green\u27s Function. We present experimental results showing internal motions calculated from measured surface motions of a vibrating sample. This will ultimately allow estimation of the detectability of a hypothetical crack at an arbitrary location in a specimen

    An ideological content analysis of corporate manifestos:a foundational document approach

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    This project involves a socio-linguistic look at corporate discourse in the form of “mission statements.” The analysis is performed by utilizing the foundational document model (FDM) as a theoretical framework for performing ideological content analyses. The FDM is a semantic grammatical model consisting of five sociological categories (ethical norms, folklore narrative, utopian schemes, strategic planning, and role attribution). Stark contrasts are observed between manifestos produced by the two most successful companies in the soft beverage industry (Coca-Cola and PepsiCo.). The comparative analysis performed in this study shows great potential regarding a possible extension and application of the content-analytical framework for those primary texts used when mobilizing collective action

    Frequency Dependence of Vibrothermography

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    It has long been postulated that vibrothermographic heating—the heating of cracks due to sound or vibration‐induced rubbing—may be frequency dependent. It has been difficult to factor out the innate frequency dependence of the heat‐generation process from the geometry‐dependent mode structure. We present experiments showing the heating of cracks in slender Inconel∕Titanium specimens at transverse resonance. Different resonant modes vibrate at different frequencies but load the crack in the same way (Mode I). The results show a clear increase of heating with vibration frequency

    Measurement of dynamic full-field internal stresses through surface laser Doppler vibrometry

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    We present a method for evaluating internal dynamic stresses in a solid vibrating body from measurements of surface motion. The method relies on the same mathematics as boundary element method: A boundary reciprocity integral represents interior motion as a surface integral of boundary motion times the Green’s function. The surface motions are measured with a laser vibrometer rather than simulated, giving a direct measurement of internal motions and internal dynamic stresses. Experimental results on a flexing beam demonstrate that stresses measured in this fashion match those calculated from elementary theory

    Toward a Viable Strategy for Estimating Vibrothermographic Probability of Detection

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    Vibrothermography is a technique for finding cracks and delaminations through infrared imaging of vibration‐induced heating. While vibrothermography has shown remarkable promise, it has been plagued by persistent questions about its reproducibility and reliability. Fundamentally, the crack heating is caused by the vibration, and therefore to understand the heating process we must first understand the vibration process. We lay out the problem and begin the first steps toward relating detectability to the local motion around a crack as well as the crack size. A particular mode, the third‐order free‐free flexural resonance, turns out to be particularly insensitive to the presence of clamping and transducer contact. When this mode is excited in a simple bar geometry the motions of the part follow theoretical calculations quite closely, and a single point laser vibrometer measurement is sufficient to evaluate the motion everywhere. Simple calculations estimate stress and strain anywhere in the bar, and these can then be related to observed crack heating
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