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电磁超声表面波被广泛用来检测表面或近表面缺陷。双向表面波电磁超声换能器(ElectromagneticAcoustic Transducer, EMAT)会在两侧同时产生能量较低且均衡的超声波,而微小缺陷(缺陷深度远小于表面波波长)的反射信号非常微弱,易被噪声淹没,根据回波信号,难以识别和定位缺陷。为此基于惠更斯叠加原理设计了单向表面波EMAT,对其声场进行了有限元分析;研究了增强侧表面波遇到不同缺陷的响应特性,得出缺陷深度、角度与反射波幅值的关系;并对含不同微小缺陷的铝板进行了实验研究。仿真和实验结果表明,所提方法提高了表面波检测微小缺陷的灵敏度,并实现了缺陷位置及深度的量化。 相似文献
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《中国测试》2019,(11):84-89
针对U型电磁超声表面波换能器(electromagnetic acoustic transducer,EMAT)换能效率低的问题,提出一种基于三维仿真的研究方法。首先,在Maxwell软件中建立U型电磁超声无损检测激发探头三维有限元模型并进行仿真分析,研究电磁超声换能器中线圈间距、截面积以及提离距离和磁铁类型及几何参数对换能效率的影响。结果表明:在使用蛇形线圈和U型磁铁作为电磁超声表面波换能器的情况下,减小线圈的提离距离、线圈截面积,适当增大线圈间距可以提高EMAT换能效率;此外,正交方差分析法对U型永磁铁的几何参数研究表明,U型永磁铁的宽度对换能效率的影响显著。 相似文献
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为探索破片冲击作用对地铁车辆车轮廓形表面变形的影响,本文建立了破片冲击车轮侧面、车轮踏面和车轮轮缘的有限元模型。通过圆柱形破片冲击车轮的仿真计算,得到了破片在不同位置以不同速度冲击车轮后车轮各表面的变形量,经过分析确定了造成车轮变形量最大的破片冲击位置和破片冲击速度。利用最终结论,结合地铁车辆日常检修中对车轮廓形的要求,得出了车轮防护的重点区域和车轮防护的性能要求,同时对战时车轮快速检修标准提出了新的建议。 相似文献
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电磁超声换能器的非接触、信号重复性好等特点使得其在高温自动检测、材料特性测量等领域有着广泛的应用前景。利用电磁超声技术激发表面波更是行之有效的方法,论文着重于理论分析,对表面波电磁声换能器的物理结构、电声学特性作了较为全面和深入的研究,并用等效电路模型探讨了阻抗匹配的方法。结果表明,电磁声换能器为感性负载,不同于压电器件的容性负载特性,因此对换能器的设计和优化也有着独自的特性;随着提离距离的增大,相应的换能效率也将急剧下降;阻抗匹配对于提高信号的输出强度,抑制谐波分量有着重要的作用,而采用电容并联匹配相比串联匹配,能够提供更高的转换效率。 相似文献
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本市某重型机械加工企业的1台最大额定起重量为200t的通用桥式起重机,在进行年度定期检验的过程中发现,在经过2年时间的使用之后,该起重机的大车车轮及小车车轮均出现不同程度的裂纹。为避免裂纹继续扩大,导致严重事故的发生,笔者要求该企业立刻联系生产厂家对这批车轮进行探伤处理,并要求探伤不合格的车轮必须报废。本文对该起重机车轮裂纹产生的原因进行了分析,并提出了相关的预防措施。 相似文献
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《International journal for numerical methods in engineering》2018,113(9):1488-1506
In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method. 相似文献
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Standards are the basis for production enterprises to organize production ex-factory inspection trade 《中国标准化(英文版)》2008,25(1):24-25
Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.…… 相似文献
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A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa. 相似文献
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On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.…… 相似文献
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Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß. 相似文献
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C. Qihong W. Zhan‐Wen J. Yi J. Yehua L. Fei F. Hanguang 《Materialwissenschaft und Werkstofftechnik》2014,45(7):582-590
In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M2(B,C), (W,Mo)2(B,C), M3(B,C), M23(B,C)6 type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm2. The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K1 mill housing of bar mill. 相似文献
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《中国标准化(英文版)》2014,(4)
正Responding to ISO’s appeal for survey for the to-be-developed ISO Strategy Plan for 2016-2020,SAC hosted a special workshop over the needs and comments of various fi elds on June 8 in Beijing.The workshop was attended by ISO President-elect and Ansteel General Manager Zhang Xiaogang,SAC Vice-Administrator Yu Xinli,and 30 experts from 相似文献
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《中国标准化(英文版)》2014,(5)
正The review group of Asia Pacific Laboratory Accreditation Cooperation(APLAC)carried out a 4-day peer review of the proficiency testing provider(PTP)for China National Accreditation Service for Conformity Assessment(CNAS)from July 28 to 31,2014.CNAS passed the PTP review with excellent performance.Two senior peer reviewers of APLAC made a comprehensive,rigorous and detailed review of CNAS’s PTP accreditation activities,and made the on-spot inspection of the review groups in Shanghai and Shenzhen respectively. 相似文献
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《中国标准化(英文版)》2014,(4)
正China and Greece Sign the Standardization Cooperation Agreement Witnessed by Chinese Premier Li Keqiang and Greek Prime Minister Antonis Samaras,AQSIQ Minister Zhi Shuping and ELOT Chairman and Executive Director Angelos Tolkas signed the SAC-ELOT Standardization Cooperation Agreement.The Agreement is one of the critical cooperation documents signed during Li Keqiang’s visit in Greece,encouraging China and Greece to 相似文献