共查询到20条相似文献,搜索用时 0 毫秒
1.
2.
声波在奥氏体不锈钢焊缝中传播时声束弯曲,为超声成像带来了困难。基于Ogilvy焊缝模型,建立了奥氏体不锈钢焊缝非均匀各向异性声场仿真模型,采用Dijkstra路径搜索算法对各向异性条件下的声传播路径和声传播时间进行了数值模拟和分析。在此基础上,采用Verasonics超声相控阵成像系统,进行了奥氏体不锈钢焊缝的全聚焦成像实验,采集全矩阵回波数据,并结合理论模型计算的声传播路径和相应的传播时间,进行了成像结果修正。结果表明,与均匀介质模型的全聚焦成像结果相比,基于该文模型的焊缝全聚焦成像检测结果具有更高的缺陷定位精度和分辨率,验证了该方法的可行性,为奥氏体不锈钢焊缝成像检测提供了新的思路。 相似文献
3.
The reflection properties of planar anisotropy Fe50Ni50 powder/paraffin composites have been studied in the microwave frequency range.The permeability of Fe50Ni50 powder/paraffin composites is greatly enhanced by introducing the planar anisotropy,and can be further enhanced by using a rotational orientation method.The complex permeability can be considered as the superposition of two types of magnetic resonance.The resonance peak at high frequency is attributed to the natural resonance,while the peak at low frequency is attributed to the domain-wall resonance.The simulated results of the microwave reflectivity show that the matching thickness,peak frequency,permeability,and permittivity are closely related to the quarter wavelength matching condition.The Fe50Ni50 powder/paraffin composites can be attractive candidates for thinner microwave absorbers in the L-band(1-2 GHz). 相似文献
4.
核电阀体唇焊焊缝熔深不足可能导致其在服役期内无预期断裂,由此引起的流质泄露将引起严重的安全事故。因此,极有必要在阀体焊接完成后进行熔深测量以保证足够的焊缝强度。本研究针对阀体唇焊缝粗糙余高曲面声学耦合差、熔深测量难的问题,提出基于喷水式超声聚焦检测技术的唇焊焊缝熔深测量方法。首先,根据核电阀体唇焊焊缝结构特点提出唇焊熔深的超声聚焦测量方法;其次,通过构建检测过程的有限元模型分析焊缝余高曲率对声场聚焦能力的影响,给出余高曲率各异的焊缝检测时的水距修正方法,以便在预定熔深范围内形成高能聚焦声场;最后,分析和提取与唇焊结构相关的检测信号特征,结合金相分析方法修正声速。研究结果显示:通过水距修正可改善焊缝曲率半径变化对聚焦声场的不利影响,曲率半径28.5 mm时焦区声压幅度仅下降11%,基于特征脉冲时间间隔及声速修正可测定焊缝熔深;与金相试验对比,绝对误差小于0.06 mm,满足核电阀门唇焊焊缝熔深测量的需求。 相似文献
5.
6.
本文系统地研究了不同形状(三方、四方及六方) 的孔缺陷对锯齿形石墨烯纳米条带电学特性的影响. 结果表明: 孔缺陷形状对于石墨烯纳米条带的电导及电流特性影响显著, 其可能源于不同形状的孔缺陷边界对于电子散射的不同; 另外, 当缺陷悬挂吸附氢或氮原子, 将引起孔缺陷形状改变, 因此不同孔缺陷吸附对于石墨烯纳米条带的电学特性的影响也各不相同. 本研究将为石墨烯基电子器件失效分析及石墨烯孔结构器件设计提供有价值的理论指导.
关键词:
石墨烯
孔缺陷
电学特性 相似文献
7.
针对奥氏体不锈钢焊接构件安全评价需要,对各向异性结构中超声波传播特性进行了研究,利用射线追踪法确定了各向异性介质中声波传播路径。在传统全聚焦成像基础上,发展了一种用于各向异性焊缝中缺陷检测的超声阵列全聚焦成像方法。通过数值仿真和实验,研究了介质材质对超声阵列成像的影响,结果表明,发展的全聚焦成像方法可以很好实现各向异性焊缝中缺陷检测,缺陷定位更准确。项目研究工作为奥氏体不锈钢焊缝检测提供了可行的技术方案. 相似文献
8.
由于可有效降低高热负载的影响, Laue弯晶是插入件辐射高通量密度硬X射线(30 keV以上)聚焦、 准直和单色化的最有效的光学元件.研究其聚焦光学特性,对发展高性能、高稳定的Laue弯晶单色器具有重要意义. 采用自行发展的光线追迹软件较为系统地研究了Laue弯晶的聚焦特性, 分析了入射光性质及弯晶参数对聚焦光斑、焦距、发散度等主要光学参数的影响. 结果表明,衍射能量越高,聚焦光斑越小,并趋于稳定值;弯曲半径越小,聚焦光斑越小, 并在其达到一阈值时得到聚焦光斑的极小值,之后随着弯曲半径的变小,由于像差等因素的影响, 聚焦光斑反而变大;晶体越厚,聚焦光斑越大,呈线性正比关系.对于衍射光发散度, 其随着衍射能量的增大而变小,并趋于稳定值;其与晶体曲率呈线性正比关系. 同时通过研究得到弯晶各参数的合理选择范围. 相似文献
9.
The coefficients of reflection and refraction on interface of the crystals in the Savart polariscope
According to the boundary conditions of the electromagnetic field, the coefficients of reflection and refraction on the interface of crystal in the Savart polariscope are obtained for ordinary ray (o-ray) and extraordinary ray (e-ray).The coefficients of reflection and refraction are different from an isotropic medium and have more complicated forms than isotropic medium. 相似文献
10.
11.
The reflection properties of planar anisotropy Fe50Ni50 powder/paraffin composites have been studied in the microwave frequency range. The permeability of Fe50Ni50 powder/paraffin composites is greatly enhanced by introducing the planar anisotropy, and can be further enhanced by using a rotational orientation method. The complex permeability can be considered as the superposition of two types of magnetic resonance. The resonance peak at high frequency is attributed to the natural resonance, while the peak at low frequency is attributed to the domain-wall resonance. The simulated results of the microwave reflectivity show that the matching thickness, peak frequency, permeability, and permittivity are closely related to the quarter wavelength matching condition. The Fe50Ni50 powder/paraffin composites can be attractive candidates for thinner microwave absorbers in the L-band (1-2 GHz). 相似文献
12.
ABSTRACTInfrared thermometry is a widely used technique for contactless temperature measurement, which is often conducted through semi-transparent media. In the present work, influences on the measurement results stemming from semi-transparent media and from the optical characteristics of the measurement setup are discussed. Results of two experimental setups, containing low, medium, and high transmission media are presented and compared to calculated data using a one-dimensional analytical approach and a three-dimensional ray-tracing algorithm. It is shown through modeling and experiments that the surroundings and, in particular, the (semi)transparent materials within the optical path are critical for accurate temperature measurements. 相似文献
13.
14.
Lattice vibration and thermodynamical properties of a single-layer graphene in the presence of vacancy defects 下载免费PDF全文
The phonon density of states(PDOS) and the thermodynamical properties including the heat capacity, the free energy,and the entropy of a single-layer graphene with vacancy defects have been studied theoretically. We first analytically derive the general formula of the lattice vibration frequency, and then numerically discuss the effect of the defects on the PDOS. Our results suggest that the vacancy defects will induce the sawtooth-like oscillation of the PDOS and the specific oscillation patterns depend on the concentration and the spatial distribution of the vacancies. In addition, it is verified that the vacancy defects will cause the increase of the heat capacity because of the vacancy-induced low-frequency resonant peak. Moreover, the influences of the vacancies on the free energy and the entropy are investigated. 相似文献
15.
Marie-Aude Ploix Philippe Guy Bertrand Chassignole Joseph Moysan Gilles Corneloup Rachid El Guerjouma 《Ultrasonics》2014
Multipass welds made of 316L stainless steel are specific welds of the primary circuit of pressurized water reactors in nuclear power plants. Because of their strong heterogeneous and anisotropic nature due to grain growth during solidification, ultrasonic waves may be greatly deviated, split and attenuated. Thus, ultrasonic assessment of the structural integrity of such welds is quite complicated. Numerical codes exist that simulate ultrasonic propagation through such structures, but they require precise and realistic input data, as attenuation coefficients. This paper presents rigorous measurements of attenuation in austenitic weld as a function of grain orientation. In fact attenuation is here mainly caused by grain scattering. Measurements are based on the decomposition of experimental beams into plane-wave angular spectra and on the modeling of the ultrasonic propagation through the material. For this, the transmission coefficients are calculated for any incident plane wave on an anisotropic plate. Two different hypotheses on the welded material are tested: first it is considered as monoclinic, and then as triclinic. Results are analyzed, and validated through comparison to theoretical predictions of related literature. They underline the great importance of well-describing the anisotropic structure of austenitic welds for UT modeling issues. 相似文献
16.
基于第一原理电子结构和输运性质计算,研究了585双空位拓扑缺陷对锯齿(zigzag)型石墨纳米带(具有椅型(armchair)边)电子结构和输运性质的影响.研究发现,585双空位缺陷的存在使得锯齿型石墨纳米带的能隙增大,并在能隙中出现了一条局域于缺陷处的缺陷态能带,双空位缺陷的取向也影响其能带结构.另外,585双空位缺陷对能隙较小的锯齿型石墨纳米带输运性质的影响较大,而对能隙较大的锯齿型石墨纳米带影响很小,缺陷取向并不显著影响纳米带的输运性质.
关键词:
石墨纳米带
585空位缺陷
电子结构
输运性质 相似文献
17.
18.
基于第一性原理电子结构和输运性质计算,研究了单空位缺陷对单层石墨纳米带(包括zigzag型和armchair型带)电子性质的影响.研究发现,单空位缺陷使石墨纳米带在费米面上出现一平直的缺陷态能带;单空位缺陷的引入使zigzag型半导体性的石墨纳米带变为金属性,这在能带工程中有重要的应用价值;奇数宽度的armchair型石墨纳米带表现出金属特性,有着很好的导电性能,同时,偶数宽度的armchair型石墨带虽有金属性的能带结构,但却有类似半导体的伏安特性;单空位缺陷使得奇数宽度的armchair石墨纳米带导电
关键词:
石墨纳米带
单空位缺陷
电子结构
输运性质 相似文献
19.
The reflection in the Savart polariscope is different from the isotropic medium. The double reflection of rays in the Savart
polariscope is analyzed and discussed on the basis of the Snell law. The double reflection formulae of the extraordinary ray
and the ordinary ray are given. These results may provide a theoretical and practical guide for studying, developing and engineering
polarization interference imaging spectrometers.
Supported by the National Natural Science Foundation of China (Grant Nos. 40375010 and 60278019), the Science and Technology
Plan Foundation of Shaanxi Province (Grant No. 2005K04-G18), and the Special Research Project of Shaanxi Provincial Educational
Department (Grant No. 07JK261) 相似文献