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941.
Sub-surface cracks present difficulties for eddy current methods as the skin effect causes currents to flow preferentially near the surface. This work examines graphite as a case study for the qualitative assessment of sub-surface cracks and employs multi-frequency eddy current techniques. The research has particular relevance to Advanced Gas-Cooled Reactors (AGR׳s) as during their operation there is the potential for cracks to develop within moderator bricks. This work reports that subsurface slots of 18% brick thickness can be detected. This work confirms these results with a parametric 3D finite element study. 相似文献
942.
M. Kargar M. Mashinchi A. Parchami 《Quality and Reliability Engineering International》2014,30(5):615-621
Process capability indices provide numerical measures to compare the output of a process to client's expectations. However, most of the existing researches have used traditional distribution frequency method by using a single sample due to assess process capability. An alternative to this approach is to use the Bayesian method. In this paper, we utilize a Bayesian approach based on subsamples to check process capability via capability index Cpk. As a new suggestion, we used the informative normal prior distribution and the characteristics of sufficient statistic of the parameter to drive the posterior distribution. The capability test is done, and the posterior probability p, for which the process under investigation is capable, is derived both based on the most popular index Cpk. Finally, a numerical example is given to clarify the method. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
943.
Although several research studies have been conducted on simply supported concrete elements reinforced with fibre reinforced polymer (FRP) bars, there is little reported work on the behaviour of continuous elements. This paper reports the testing of four continuously supported concrete slabs reinforced with carbon fibre reinforced polymer (CFRP) bars. Different arrangements of CFRP reinforcement at mid-span and over the middle support were considered. Two simply supported concrete slabs reinforced with under and over CFRP reinforcement and a continuous concrete slab reinforced with steel bars were also tested for comparison purposes. All continuous CFRP reinforced concrete slabs exhibited a combined shear–flexure failure mode. It was also shown that increasing the bottom mid-span CFRP reinforcement of continuous slabs is more effective than the top over middle support CFRP reinforcement in improving the load capacity and reducing mid-span deflections. The ACI 440.1R–06 formulas overestimated the experimental moment at failure but better predicted the load capacity of continuous CFRP reinforced concrete slabs tested. The ACI 440.1R–06, ISIS–M03–07 and CSA S806-06 design code equations reasonably predicted the deflections of the CFRP continuously supported slabs having under reinforcement at the bottom layer but underestimated deflections of continuous slabs with over-reinforcement at the bottom layer. 相似文献
944.
Ultrasonic pulse-echo methods for flaw detection have been widely employed as an effective strategy for nondestructive evaluation, and flaw detection plays an important role due to its ability to detect localized damage in structures. In practice, flaw damage typically occurs in a few areas in the material, resulting in only a few echoes that exist in a received signal, which motivates us to detect flaws using sparse representation methods. In this study, the noisy signal is modelled by a linear combination of modulated Gaussian pulses, which form an over-complete dictionary. The over-complete dictionary is designed such that the sparseness of the representation is expected. A robust sparse Bayesian learning framework is employed with the goal of enforcing model sparseness and reducing the source of ill-conditioning in the inversion problem for flaw detection. Useful information, including the range of frequency and bandwidth parameters of the flaw echoes, is also estimated. Based on this information, we propose a post-processing scheme for structure noise elimination and flaw detection. The capability of the proposed method is quantitatively evaluated by simulation studies and is further validated by the experimental data. 相似文献
945.
可靠性是机械设备质量的核心与重要表征之一,为了对机械设备可靠性进行表达与评价,就需要进行试验。文章就机械可靠性试验及发展问题,进行了较为细致的探讨。 相似文献
946.
947.
Taking tests enhances learning. But what happens when one cannot answer a test question—does an unsuccessful retrieval attempt impede future learning or enhance it? The authors examined this question using materials that ensured that retrieval attempts would be unsuccessful. In Experiments 1 and 2, participants were asked fictional general-knowledge questions (e.g., “What peace treaty ended the Calumet War?”). In Experiments 3–6, participants were shown a cue word (e.g., whale) and were asked to guess a weak associate (e.g., mammal); the rare trials on which participants guessed the correct response were excluded from the analyses. In the test condition, participants attempted to answer the question before being shown the answer; in the read-only condition, the question and answer were presented together. Unsuccessful retrieval attempts enhanced learning with both types of materials. These results demonstrate that retrieval attempts enhance future learning; they also suggest that taking challenging tests—instead of avoiding errors—may be one key to effective learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
948.
J. Akrman L. Kubá H. Bendová D. Jírová K. Kejlová 《International journal of cosmetic science》2009,31(2):119-129
Testing plate made of optical quartz has been developed for the purpose of determination of sun protection factor (SPF) in vitro by the method of diffusion transmission spectroscopy; the plates were coarsened by sanding and grinding to surface roughness values (Ra) of 18 μm. The plate was coated with a film of sunscreen by an application of 2 mg cm−2 as that used for determination of SPF in vivo by the COLIPA method. The transmission values measured were converted into the SPF in vitro and the protection factor in ultraviolet A light, UVAPF in vitro . The testing plate was tested with commercial sunscreens. The found values of SPF in vitro fit well with the values determined by means of the COLIPA method in vivo . The plates coated with sunscreen film were irradiated with light simulating the sun radiation. The values of protection factors obtained before and after irradiation were compared, and the differences were used for estimation of photostability of the UV filters included. 相似文献
949.
异种金属扩散焊接接头存在多种类型的缺陷,这些缺陷严重影响焊接结构的完整性和零部件本身的使用性能。利用超声波扫描成像技术获得试样的扫描图样,然后从扩散焊接界面的显微结构和界面超声回波信号等角度,阐述了扩散焊接接头的原材料裂纹、接头裂纹、未焊合缺陷和焊接良好区域的特征。通过有效的无损检测手段,可以准确地评价缺陷的类型、大小和位置。 相似文献
950.