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1.
Inspection of austenitic stainless steel weldments by conventional ultrasonic means is fundamentally limited by the textured, columnar grain structure of the weld metal. It is shown that, for selected angles of incidence, shear waves normally polarized with respect to the columnar grains can pass through the weld metal-base metal interface without partial reflection. As a consequence, the inspectability of stainless steel weldments can be improved. The operation of a low frequency, ultrasonic system for stainless steel butt weldments is demonstrated.  相似文献   

2.
All nine elastic moduli of an orthotropic composite material, namely, polypropylene reinforced with glass fiber, are determined from the measured values of the bulk acoustic wave velocities along specific directions in the planes of symmetry of the material. These data are used to calculate the angular dependences of phase velocities, polarization vectors, and directions of ray velocities of bulk waves in the composite. It is demonstrated that the difference in the velocities of shear waves polarized along and across the glass fiber gives rise to an acoustic birefringence and can lead to an elliptical polarization of waves. The measurement of the phase velocities of shear waves as functions of the wave polarization is suggested as a method for the determination of the fiber orientation in a composite material.  相似文献   

3.
A. Singh 《Ultrasonics》1983,21(6):270-274
Refracted shear waves in extruded stainless steel pipes were found to change their velocity and direction (beam skewing) as they propagated through the pipe thickness. These variations in refracted angles and velocities result in flaw location errors during ultrasonic examination. Two techniques, one using refracted shear waves in pitch-catch mode and the other refracted longitudinal waves in pulse-echo mode, are discussed as to their feasibility in determining the flaw location accurately in these pipes. The result of the work was that a two-scan approach using refracted shear waves in pulse-echo for flaw detection and refracted longitudinal waves in pulse-echo for flaw location was recommended.  相似文献   

4.
J.A. Ogilvy 《Ultrasonics》1986,24(6):337-347
A model for ultrasonic wave propagation in anisotropic and inhomogeneous materials is applied to the case of ultrasonic inspection of an austenitic V-butt weld manufactured by the downhand Manual Metal Arc technique. We examine the propagation behaviour of waves within the weld region and, in addition, model beam divergence behaviour. From this work we predict directions of low inspection sensitivity and also identify regions of material to which no ultrasound penetrates. The relative merits of the three different wave modes are examined, showing clearly the advantages of horizontally polarized shear waves for austenitic steel inspection. Vertically polarized shear waves are shown to be the least effective for such inspections. We discuss the relevance of this work to the ultrasonic non-destructive testing of austenitic steel components, concluding that care is needed over the choice of wave modes and angles, to ensure sensitive inspection of the whole weld material.  相似文献   

5.
魏勤  卫婷  宋广三 《应用声学》2011,30(3):220-226
本文在研究超声测试应力的过程中为了减小材料组织结构以及残余应力对应力测试结果的影响,对45#钢试样进行再结晶退火热处理,并用超声双折射法研究试样的再结晶退火组织,分析其微观组织和各向异性。实验结果表明,试样中横波声速随其偏振化方向改变而变化,存在声速快轴和慢轴且两者相互垂直;试样经650℃炉温,保温40分钟炉冷再结晶退火热处理后,声各向异性因子小,表现出材料微观组织均匀,晶粒细,各向异性小,并与金相实验结果一致。  相似文献   

6.
Ultrasonic transit times may be used to locate the interface between molten weld metal and parent plate as a weld is formed. These transit times will lead to errors in interpretation of the location of the weld interface if account is not taken of the variation of ultrasonic velocity with temperature. We assess the magnitude of these errors using a theoretical model based on the Green's function to obtain the temperature distribution at any time and then convert the temperatures into elastic constants through empirical fits to high temperature data. A ray tracing method and a semi-analytical approach are used to estimate the effects of the changes in elastic constants on the ray paths and transit times. From these theoretical predictions we conclude that the location errors incurred by assuming ultrasonic velocities appropriate to cold metal are less than 0.5 mm for a 3.5 mm radius weld in austenitic steel or in iron. Experimental values tend to be larger than this, possibly suggesting that the solid-liquid interface is not as perfect as in the theoretical model. Under all of the conditions investigated, predicted errors are smaller with compression waves than with shear waves.  相似文献   

7.
A new ultrasonic technique for the determination of residual stresses in steel, intended to correct for the effects of variable texture and microstructure, is proposed. The method is based upon the use of the compressional wave time delay in addition to the time delays of two orthogonally polarized shear waves used in the shear wave birefringence technique. This method is justified theoretically using expressions for the ultrasonic velocities in an aggregate of orthorhombic symmetry composed of cubic crystallites.Measurements of the three time delays for propagation in the through thickness direction have been made on a large number of steel plates selected at random. The measurements are found to fall on two lines, and reveal that two types of texture are present in rolled steel plates. In the presence of a stress, the measured points deviate from the lines and this effect is quantified theoretically using elastic constants obtained by applying a uniaxial compressive stress to one of the samples.The usefulness of the technique to determine a residual stress distribution is demonstrated by measurements near the tip of a crack in a compact tension specimen.  相似文献   

8.
超声双折射法测试铝合金的内部应力   总被引:1,自引:0,他引:1       下载免费PDF全文
声各向同性的金属材料在应力作用下表现出声各向异性,这是用声弹性法分析材料内部应力的基础。本文用偏振方向平行或垂直于应力方向的超声纯横波对LY11型铝合金进行测试。实验结果表明:材料在拉、压单轴应力作用下,偏振方向平行和垂直于应力方向的超声纯横波的声速都发生了变化。实验在分析材料声各向异性的基础上计算材料声弹性双折射系数,得到测试LY11型铝合金内部应力的理论公式,并对其内部的残余应力进行评估。实验中利用双换能器回振法测量声速,时间测试精确度可达10-11s,可精确测量声速的微小变化量。  相似文献   

9.
兰姆波在搭接焊缝上的反射和透射   总被引:2,自引:0,他引:2       下载免费PDF全文
李阳  蔡桂喜  董瑞琪 《声学学报》2017,42(4):495-503
采用数值模拟方法和实验研究了兰姆波在搭接焊缝上的反射和透射。数值模拟了频率500 kHz的兰姆波S0与.A0模态,分别在2 mm厚不锈钢板上的不同宽度搭接焊缝模型上的反射和透射,并计算了相应的反射系数和透射系数。发现:当搭接焊缝宽度小于4 mm时,S0模态的反射系数和焊缝宽度具有近似的线性关系,而焊缝余高和两板之间的间隙对S0模态反射系数的影响很小。基于兰姆波S0模态反射系数与焊缝宽度的线性关系。提出了通过测量S0模态反射系数快速测量搭接焊缝宽度的方法。实验测得的2 mm厚不锈钢板上不同宽度搭接焊缝对500 kHz的入射兰姆波S0模态的反射系数,验证了上述线性关系,说明了可用兰姆波反射回波测量搭接焊缝宽度。  相似文献   

10.
J.A. Ogilvy 《Ultrasonics》1988,26(6):318-327
Reflection of ultrasonic beams from the faces of planar weld defects is affected by the anisotropic nature of the weld material. The simple laws of geometrical reflection no longer hold and energy may be strongly reflected into unexpected directions. This has important consequences for ultrasonic inspection techniques relying on specular signals for defect detection. In this Paper a ray tracing approach is used to study, theoretically, the expected patterns of defect reflection behaviour for several weld types and several defect locations and orientations. In general we find that when the ultrasonic beam is generated in the austenitic weld material without first passing through the base metal then the strongly reflected specular signal travels in very unexpected directions. If, however, the ultrasonic beam travels into the weld metal via the base metal then reflected signals usually occur close to the expected directions, except for vertically polarized shear waves. Furthermore, for a given weld type it is obviously useful to minimize ultrasonic ray paths within the weld material, to minimize both attenuation and curvature of ray paths.  相似文献   

11.
In this paper, a kind of bi-layered asymmetrical split ring metamaterial was proposed as a circular polarization converter. Simulations and experiments at the microwave regime showed that the proposed structures can achieve the conversions from right-handed circularly polarized electromagnetic waves to left-handed ones and the reversed conversions in the opposite propagating direction. The linear to circular polarization transmission coefficients and the surface currents were investigated to understand the mechanism of the circular polarization conversions. Moreover, we optimized the proposed metamaterials by increasing the distance between the two metal layers. The proposed circular polarization converters have applications in microwave wave plates and metamaterial antennas.  相似文献   

12.
In this paper, an ultra-wideband chirality selective metastructure absorber is proposed that enables differential absorption and reflection of circularly polarized waves in the terahertz (THz) range. The structure achieves circular dichroism (CD) by using asymmetrically split metal rings as fundamental meta-atoms. Most critically, the high impedance surface and air-resonant cavities are inserted separately in the meta-atoms and dielectric substrate to enhance CD and broaden the bandwidth of absorption. The metastructure absorber can achieve more than 90% absorption of right circularly polarized waves at 0.675–1.244 THz, and it can maintain more than 90% reflection of left circularly polarized waves at 0.607–1.229 THz without changing the direction of rotation. Besides, its CD can reach more than 80% at 0.687–1.213 THz with a relative bandwidth of 55.3%. Spin-selective absorption, which is closely related to breaking chiral symmetry, is investigated through power loss distribution, wide-angle incidence, and scan parameter optimization. The proposed strategy is further validated in the THz band, and the polarization selection and manipulation techniques can be applied to chiral sensing/radio-thermometry, circular polarization detectors/lasers, and molecular spectroscopy.  相似文献   

13.
The reflection and transmission of Lamb waves at overlap joints are researched by the numerical method and the experiments. The numerical method is used to simulate the reflection and transmission of Lamb waves at welds with different widths on 2 mm-thick stainless steel plates. The reflection and transmission coefficients are calculated as well. When the welds width is less than 4 mm, a quasi-linear correlation is observed between the reflection coefficient of SO mode and the weld width. In contrast to the weld width, both the gap between two plates and the reinforcement height of weld do not have obvious effect on the reflection coefficient. Based on the results, we propose that the weld width could be rapidly measured through examining the echo amplitude of SO mode. Experiments further confirm the quasilinear correlation and the feasibility of our proposed method.  相似文献   

14.
高喜  余行阳  曹卫平  姜彦南  于新华 《中国物理 B》2016,25(12):128102-128102
An ultrathin micro-split Jerusalem-cross metasurface is proposed in this paper, which can efficiently convert the linear polarization of electromagnetic(EM) wave into the circular polarization in ultra-wideband. By symmetrically employing two micro-splits on the horizontal arm(in the x direction) of the Jerusalem-cross structure, the bandwidth of the proposed device is significantly extended. Both simulated and experimental results show that the proposed metasurface is able to convert linearly polarized waves into circularly polarized waves in a frequency range from 12.4 GHz to 21 GHz, with an axis ratio better than 1 d B. The simulated results also show that such a broadband and high-performance are maintained over a wide range of incident angle. The presented polarization converter can be used in a number of areas, such as spectroscopy and wireless communications.  相似文献   

15.
韩江枫  曹祥玉  高军  李思佳  张晨 《物理学报》2016,65(4):44201-044201
根据各向异性媒质理论, 设计了一种宽带、反射型超材料极化旋转体, 能够将线极化波极化方向旋转90°, 极化转化率大于90%的工作带宽为5.5–14.5 GHz. 该极化旋转体由两层介质板、金属双开口谐振环和金属底板周期排列构成, 具有各向异性的特点, 单元两对角线方向的电场分量反射系数相同, 反射相位相差180°, 导致其极化旋转特性. 利用表面电流分布图, 分析不同极化波入射时该极化旋转体的谐振状态, 实验和仿真结果符合较好. 该极化旋转体在新型天线设计和隐身技术等方面具有广阔的应用前景.  相似文献   

16.
From the measurement of a low frequency (50-150 Hz) shear wave speed, transient elastography evaluates the Young's modulus in isotropic soft tissues. In this paper, it is shown that a rod source can generate a low frequency polarized shear strain waves. Consequently this technique allows to study anisotropic medium such as muscle. The evidence of the polarization of low frequency shear strain waves is supported by both numeric simulations and experiments. The numeric simulations are based on theoretical Green's functions in isotropic and anisotropic media (hexagonal system). The experiments in vitro led on beef muscle proves the pertinent of this simple anisotropic pattern. Results in vivo on man biceps shows the existence of slow and fast shear waves as predicted by theory.  相似文献   

17.
The strong elastic anisotropy of the discrete unidirectional plies in a composite laminate interacts sensitively with the polarization direction of a shear ultrasonic wave propagating in the thickness direction. The transmitted shear wave can therefore be used to detect errors in the ply orientation and stacking sequence of a laminate. The sensitivity is particularly high when the polarization directions of the shear wave transmitter and receiver are orthogonal to each other. To understand the interaction between normal-incident shear waves and ply orientations in a laminate, a complete analytical model was developed using local and global transfer matrices. The model predicted the transmitted signal amplitude as a function of polarization angle of the transmitter and time (or frequency) for a given laminate and input signal. To alleviate the experimental problems associated with shear wave coupling, electromagnetic acoustic transducers (EMATs) and metal delay lines were used in the angular scan of the transmitted signal. The EMAT system had the added advantage of being applicable to uncured composite laminates. Experiments were performed on both cured and uncured laminates with common layups for model verification. The sensitivity of the measured shear wave signals to fiber misorientation and stacking sequence errors was also demonstrated.  相似文献   

18.
本文采用光纤激光器在不锈钢表面上制备圆形阵列结构来增强不锈钢与塑料的连接强度。研究了激光制备的圆形阵列结构参数以及连接参数对不锈钢与塑料连接强度的影响。结果表明,不锈钢表面经过激光扫描构形处理后能显著提高不锈钢与塑料的连接强度,在压力作用下,熔融塑料渗入激光构造微孔形成的机械互锁是增强不锈钢与塑料连接强度的主要机制。激光构形后不锈钢表面上的毛刺高度、数量以及覆盖率对连接接头的连接强度有重要影响。毛刺高度为10~20μm,毛刺数量占比Tm小于14.82%时,不锈钢与塑料在连接面处断裂,剪切力随着Tm的增加而增加;当Tm值高于14.82%时,在塑料处断裂,且剪切力数值在塑料的平均拉伸断裂力(950 N)上下浮动。不锈钢与塑料连接接头断裂于塑料处时所对应的最小覆盖率为38.5%,此时剪切力为900 N。此外,激光扫描处理过程中不锈钢与塑料连接的温度与压力对连接强度有重要影响,在加热温度为400℃时,不锈钢与塑料连接接头的剪切力最强;当压力为75 kN时,不锈钢与塑料连接接头的剪切力最强。  相似文献   

19.
陈龙天  程用志  聂彦  龚荣洲 《物理学报》2012,61(9):94203-094203
电磁波的极化特性在通信、导航和雷达等方面已逐渐得到应用.为了有效控制电磁波的极化状态, 本文设计了一种基于开口环结构的人工异向介质.该人工异向介质由开口环结构,电介质基底和金属背板组成, 可以将入射的线性极化波完整地转换为圆极化波,椭圆极化波以及和入射波极化方向垂直的线极化波. 本文通过实验和仿真验证了本文的设计,实验结果和仿真结果符合较好.  相似文献   

20.
Sasaki Y  Hasegawa M 《Ultrasonics》2007,46(2):184-190
The ultrasonic velocity of shear waves propagating through radial direction of a wood plate specimen, transversely to the loading direction, was measured. By rotating an ultrasonic sensor, the oscillation direction of the shear waves was varied with respect to the wood plate axis and loading direction. The relationship between shear wave velocity and oscillation direction was examined to discuss the effect of anisotropy on the acoustoelastic birefringence in wood. The results obtained were summarized as follows. When the oscillation direction of the shear wave corresponded to the tangential direction of the wood specimen regardless of the stress direction, shear wave velocity decreased markedly and the relationship between shear wave velocity and rotation angle tended to become discontinuous. That is, when the shear waves oscillated in the anisotropic axis of the wood, the shear wave velocity peaked unlike in the case of oscillation in the stress direction. In an isotropic material (acrylic, aluminum 5052), on the contrary, when the shear waves oscillated in the stress direction of the specimen, the shear wave velocity peaked regardless of the main-axis direction of the specimen. On the basis of the discussion of these results, the ultrasonic shear wave propagating in wood under stress is confirmed to be polarized in the anisotropic axis of the wood.  相似文献   

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