Dynamic Stress Intensity Factor and Scattering of SH Wave by Circle Canyon and Crack

The dynamic stress intensity factor (DSIF) and the scattering of SH wave by circle canyon and crack are studied with Green's function. In order to solve the problem, a suitable Green's function is constructed first, which is the solution of displacement fields for elastic half space with circle canyon under output plane harmonic line loading at horizontal surface. Then the integral equation for determining the unknown forces in the problem can be changed into the algebraic one and solved numerically so that crack DSIF can be determined. Last when the medium parameters are altered, the influence on the crack DSIF is discussed partially with the displacement between circle canyon and crack.

Effect of Blasting Stress Wave on Dynamic Crack Propagation

Stress waves affect the stress field at the crack tip and dominate the dynamic crack propagation.Therefore,evaluating the influence of blasting stress waves on the crack propagation behavior and the mechanical characteristics of crack propagation is of great significance for engineering blasting.In this study,ANSYS/LS-DYNA was used for blasting numerical simulation,in which the propagation characteristics of blasting stress waves and stress field distribution at the crack tip were closely observed.Moreover,ABAQUS was applied for simulating the crack propagation path and calculating dynamic stress intensity factors(DSIFs).The universal function was calculated by the fractalmethod.The results show that:the compressive wave causes the crack to close and the reflected tensile wave drives the crack to initiate and propagate,and failure mode is mainly tensile failure.The crack propagation velocity varies with time,which increases at first and then decreases,and the crack arrest occurs due to the attenuation of stress waves and dissipation of the blasting energy.In addition,crack arrest toughness is smaller than the crack initiation toughness,applied pressure waveforms(such as the peak pressure,duration,waveforms,wavelengths and loading rates)have a great influence on DSIFs.It is conducive to our deep understanding or the study of blasting stress waves dominated fracture,suggesting a broad reference for the further development of rock blasting in engineering practice.

SCATTERING OF SH-WAVE BY CRACKS ORIGINATING AT AN ELLIPTIC HOLE AND DYNAMIC STRESS INTENSITY FACTOR

The method of complex function and the method of Green's function are used to investigate the problem of SH-wave scattering by radial cracks of any limited length along the radius originating at the boundary of an elliptical hole, and the solution of dynamic stress intensity factor at the crack tip was given. A Green's function was constructed for the problem, which is a basic solution of displacement field for an elastic half space containing a half elliptical gap impacted by anti-plane harmonic linear source force at any point of its horizontal boundary. With division of a crack technique, a series of integral equations can be established on the conditions of continuity and the solution of dynamic stress intensity factor can be obtained. The influence of an elliptical hole on the dynamic stress intensity factor at the crack tip was discussed.

SCATTERING OF THE HARMONIC STRESS WAVE BY CRACKS IN FUNCTIONALLY GRADED PIEZOELECTRIC MATERIALS

The present paper considers the scattering of the time harmonic stress wave by a single crack and two collinear cracks in functionally graded piezoelectric material （FGPM）. It is assumed that the properties of the FGPM vary continuously as an exponential function. By using the Fourier transform and defining the jumps of displacements and electric potential components across the crack surface as the unknown functions, two pairs of dual integral equations are derived. To solve the dual integral equations, the jumps of the displacement and electric potential components across the crack surface are expanded in a series of Jacobi polynomials. Numerical examples are provided to show the influences of material properties on the dynamic stress and the electric displacement intensity factors.

Dynamic stress concentration of an elliptical cavity in a semi-elliptical hill under SH-waves

The method of wave-function expansion in elliptical coordinates,elliptical cosine half-range expansion and Mathieu function were applied to obtain an exact analytical solution of the dynamic stress concentration factor(DSCF)around an elliptical cavity in a shallow,semi-elliptical hill.An infinite system of simultaneous linear equations for solving this problem was established by substituting the wave expression obtained by the Mathieu function including the standing wave expression of elliptical lining given herein into the boundary condition obtained by the region-matching method.The finite equations system with unknown coefficients obtained by truncation were solved numerically,and the results in the case of an ellipse degenerating into a circle were compared with previous results to verify the accuracy of the method.The effects of different aspect ratios,incident wave angles and aperture ratios on the dynamic stress concentration around the elliptical cavity were described.Some numerical results,when the elliptical hill was changed into a circular one,were analyzed and compared in detail.In engineering,this model can be regarded as a semi-cylindrical hill with an elliptical cylindrical unlined tunnel under the action of SH waves,and the results are significant in aseismic design.

Research Review of Principles and Methods for Ultrasonic Measurement of Axial Stress in Bolts

Bolts are important fasteners indispensable in the manufacturing field for their advantages, which include convenient assembly and disassembly, easy maintenance, refastenability to prevent looseness, and the avoidance of a phase change in the connected material composition. The precise control of the tightening force in bolts is closely related to the safety and reliability of the connected equipment or structure. Although there are many methods for estimating the tightening force applied to a bolt during assembly, poor accuracy in controlling the preload during the tightening process and a lack of monitoring to determine the residual axial force in service remain issues in evaluating the safety of bolted assemblies. As a nondestructive testing technology, ultrasonic measurement can be applied to successfully address these issues. In order to help researchers understand the theoretical basis and technological development in this field and to equip them to conduct further in-depth research, in this review, the basic knowledge describing the state of stress and deformation of bolts, as well as conventional testing methods are summarized and analyzed. Then, through a review of recent research of the ultrasonic measurement of the axial stress in bolts, the influence of the e ective stressed length and temperature are analyzed and proposed methods of calibration and compensation are reviewed. In order to avoid coupling errors caused by traditional piezoelectric transducers, two newly proposed ultrasonic coupling technologies, the electromagnetic acoustic transducer(EMAT) and the permanent mounted transducer system(PMTS), are reviewed. Finally, the new direction of research of the detection of residual axial stress in in-service bolts that have been assembled to yield is discussed.

SHEAR WAVE SCATTERING FROM A PARTIALLY DEBONDED PIEZOELECTRIC CYLINDRICAL INCLUSION

The scattering of SH wave by a cylindrical piezoelectric inclusion partially debonded from its surrounding piezoelectric material is investigated using the wave function expansion method and singular integral equation technique. The debonding regions are modeled as mul- tiple arc-shaped interface cracks with non-contacting faces. By expressing the scattered ?elds as wave function expansions with unknown coe?cients, the mixed boundary value problem is ?rstly reduced to a set of simultaneous dual series equations. Then dislocation density functions are introduced as unknowns to transform these dual series equations into Cauchy singular integral equations of the ?rst type, which can be numerically solved easily. The solution is valid for arbi- trary number and size of the debonds. Finally, numerical results of the dynamic stress intensity factors are presented for the cases of one debond and two debonds. The e?ects of incidence direc- tion, crack con?guration and various material parameters on the dynamic stress intensity factors are respectively discussed. The solution of this problem is expected to ?nd applications in the investigation of dynamic fracture properties of piezoelectric materials with cracks.

Scattering of elastic wave by a cylindrical shell deeply embeded in saturated soils

The compression of soil grain and pore fluid as well as viscid coupling of pore fluid and soil skeleton is considered, the scattering problem of incident plane P1 wave （fast compressional wave） by an infinite cylindrical shell deeply embedded in isotropic saturated soils is studied by adopting the amended Biot model, amplitude equations about potential functions of scattering and refracting fields are obtained, and the effect of dimensionless frequencies and shell thickness on the back-scattering spectra and dynamic stress concentration factors of two types of cylindrical shells with high and low rigidity are numerically computed and analyzed.

Scattering of SH-wave from interface cylindrical elastic inclusion with a semicircular disconnected curve

Scattering of SH wave from an interface cylindrical elastic inclusion with a semicircular disconnected curve is investigated. The solution of dynamic stress concentration factor is given using the Green＇s function and the method of complex variable functions. First, the space is divided into upper and lower parts along the interface. In the lower half space, a suitable Green＇s function for the problem is constructed. It is an essential solution of the displacement field for an elastic half space with a semi-cylindrical hill of cylindrical elastic inclusion while bearing out-plane harmonic line source load at the horizontal surface. Thus, the semicircular disconnected curve can be constructed when the two parts are bonded and continuous on the interface loading the undetermined anti-plane forces on the horizontal surfaces. Also, the expressions of displacement and stress fields are obtained in this situation. Finally, examples and results of dynamic stress concentration factor are given. Influences of the cylindrical inclusion and the difference parameters of the two mediators are discussed.

SCATTERING OF ANTI-PLANE SHEAR WAVES BY A SINGLE CRACK IN AN UNBOUNDED TRANSVERSELY ISOTROPIC ELECTRO-MAGNETO-ELASTIC MEDIUM

A theoretical treatment of the scattering of anti-plane shear(SH) waves is provided by a single crack in an unbounded transversely isotropic electro-magneto-elastic medium. Based on the differential equations of equilibrium, electric displacement and magnetic induction intensity differential equations, the governing equations for SH waves were obtained. By means of a linear transform, the governing equations were reduced to one Helmholtz and two Laplace equations. The Cauchy singular integral equations were gained by making use of Fourier transform and adopting electro-magneto impermeable boundary conditions. The closed form expression for the resulting stress intensity factor at the crack was achieved by solving the appropriate singular integral equations using Chebyshev polynomial. Typical examples are provided to show the loading frequency upon the local stress fields around the crack tips. The study reveals the importance of the electro-magneto-mechanical coupling terms upon the resulting dynamic stress intensity factor.

Surface Effects on the Scatter of SH-Wave by a Shallow Buried the Elliptical Hole

The methods of complex function, multi-polar coordinate system, and conformal mapping are used to solve dynamic stress concentration factor. The surface elasticity theory is applied to obtain the stress boundary conditions on the surface. The effects of frequency and the ration of the major and minor axis of the ellipse on the dynamic stress concentration factor around the elliptical nano-hole are discussed in detail. When the size of elliptical hole shrinks to nanometers, the numerical results show that the surface effect has a significant effect on the scattering of SH-wave.

Dynamic Analysis of Nanosized Arbitrary Shape Inclusion under SH Waves

The scattering of shear waves (SH waves) by nano-scale arbitrary shape inclusion in infinite plane is studied by complex variable function theory. Firstly, the governing equation and the relationships between stress and displacement are given by classical elastic theory. Secondly, the arbitrary shape inclusion in the two-dimensional plane is transformed into a unit circle domain by conformal mapping, the incident wave field and the scattered wave field are presented. Next, the stress and displacement boundary conditions are established by considering surface elasticity theory, The infinite algebraic equations for solving the unknown coefficients of the scattered and standing waves are obtained. Finally, the influence of surface effect, non-dimensional wave number, Shear modulus and hole curvature on the dynamic stress concentration factor are analyzed by some examples, the numerical results show that the surface effect weakens the dynamic stress concentration. With the increase of wave number, the dynamic stress concentration factor (DSCF) decreases. Shear modulus and hole curvature have significant effects on DSCF.

INTERACTION OF ELASTIC WAVES WITH A PERIODIC ARRAY OF COLLINEAR INPLANE CRACKS

A boundary integral equation method is applied to the study of the interaction of plane elastic waves with a periodic array of collinear inplane cracks.Numerical results are presented for the dynamic stress in- tensity factors.The effects of the wave type,wave frequency,wave incidence angle,and crack spacing on the dynamic stress intensity factors are analyzed in detail.

含裂纹声子晶体能带分析的改进局部径向基函数配点法

基于直接法局部径向基函数配点法(local radial basis function collocation method,LRBFCM)提出了含裂纹声子晶体反平面弹性波的能带结构计算方法,分析了其能带结构特性,并通过有限元法计算对比验证该数值结果的准确性和有效性.在边界上采用直接法沿方向取局部节点,解决了边界求解不稳定问题,讨论了数值方法的处理技巧对结果的影响.并通过考虑不同声阻抗比、散射体形状(方形、圆形)和裂纹情况,验证了该方法计算含裂纹声子晶体能带结构的适用性.研究了形状参数、配点数对计算结果的影响.最后深入分析了不同长度和位置的裂纹对声子晶体能带结构的影响特性,并进行了对比分析.文章的创新性在于用直接法局部径向基函数配点法解决了含裂纹声子晶体能带结构计算的问题,极大增加了声子晶体的应用价值.研究结果显示:随着裂纹的扩展,能带结构带隙逐渐变窄;当裂纹扩展到一定程度时,金散射体的声子晶体带隙数量会增加,且新增带隙会随着裂纹扩展而变宽,但铝散射体的声子晶体带隙数量会减少;直接法局部径向基函数配点法可以大大提高含裂纹声子晶体能带结构的计算效率和计算精度.

自体富血小板血浆联合超短波治疗膝骨性关节炎对患者炎症因子和氧化应激反应的影响

目的探讨对膝骨性关节炎(knee osteoarthritis,KOA)患者予以自体富血小板血浆(platelet rich plasma,PRP)联合超短波治疗对炎症因子和氧化应激反应的影响。方法选取2022年1—12月抚州市中医医院骨伤科收治的64例KOA患者作为研究对象,随机分为观察组与对照组,每组32例。对照组予以药物治疗(倍他米松联合利多卡因)治疗,观察组予以自体PRP联合超短波治疗。比较两组临床疗效及血清炎症因子[肿瘤坏死因子α(tumor necrosis factorɑ,TNF-α)、白细胞介素-1β(interleukin-1β,IL-1β)、基质金属蛋白酶-3(matrix metalloproteinase-3,MMP-3)]、氧化应激反应指标[超氧化物歧化酶(superoxide dismutase,SOD)、谷胱甘肽过氧化物酶(glutathione peroxidase,GSH-Px)、丙二醛(malondialdehyde,MDA)、一氧化氮(nitric oxide,NO)]水平。结果观察组治疗总有效率为96.88%,高于对照组的75.00%,差异有统计学意义(P<0.05);治疗后,观察组血清TNF-α、IL-1β、MMP-3水平均低于对照组,差异有统计学意义(P<0.05);治疗后,观察组血清SOD、GSH-Px水平均高于对照组,MDA、NO水平均低于对照组,差异有统计学意义(P<0.05)。结论自体PRP联合超短波治疗KOA患者效果显著,可有效抑制炎症细胞因子分泌,改善氧化应激障碍,值得临床推广应用。

爆炸应力波作用下层理介质断裂的动焦散实验分析

利用爆炸加载动焦散试验系统,进行了有机玻璃的透射式动焦散试验.记录了含层理介质裂纹扩展的全过程,发现裂纹穿过层理偏移一定距离后继续扩展的现象.给出了爆炸荷载作用下裂纹尖端应力强度因子随时间的瞬态变化曲线.对爆炸应力波在层理介质中引起断裂的机理进行了进一步的研究,讨论了层理对应力波传播的影响.利用应力波传播理论分析,得出层理中裂纹与层理后裂纹产生的机理不同,为层理岩体定向断裂控制爆破研究提供了新方法.

爆破地震波作用下隧道围岩动应力集中系数分析

将爆破地震波进行合理近似简化,采用波函数展开法,推导了无限岩石介质中爆破地震波作用下隧道围岩动应力集中系数的表达式,结合具体算例,从理论上定量分析了围岩不同位置上爆破地震波主频和围岩物理力学指标对动应力集中系数的影响。分析结果表明:隧道围岩迎爆侧的动应力集中系数整体上大于背爆侧,动应力集中系数峰值偏向于迎爆侧;在不同主频爆破地震波作用下,动应力集中系数的影响存在最大值;隧道围岩的弹性模量对动应力集中系数的影响较大,而泊松比对动应力集中系数的影响较小。

基于应力波因子的金属材料表面塑性损伤检测

提出了一种基于应力波因子的金属材料表面塑性损伤检测方法。将AZ31镁铝合金试件加载到不同的拉伸载荷后,利用Ritec SNAP非线性超声测试系统激发和接收Rayleigh表面波,通过实验测试在不同载荷作用后基于应力波因子的声学非线性系数与应力的关系。研究结果表明,当加载应力接近材料的屈服极限时,基于应力波因子的声学非线性系数随着应力的增加明显增大,因此可以利用基于应力波因子的声学非线性系数对金属材料表面的塑性损伤进行非线性超声无损评价。

应用应力波技术的蜂窝结构损伤监测

蜂窝夹层复合材料结构是复合材料在飞机上所采用的一种重要形式。文中采用基于压电元件的应力波技术对蜂窝夹层结构的脱粘损伤进行了监测研究 ,研究采用梁及板两种典型结构试件 ,并采用小波分析对应力波检测信号进行了数据处理 ,提取了两种可有效表征脱粘损伤的应力波因子 ,初步实现了一套蜂窝夹层结构损伤的实时在线监测系统。

爆炸应力波作用下缺陷介质裂纹扩展的动态分析

采用透射式焦散线测试系统,进行爆炸应力波作用下缺陷介质裂纹扩展试验,研究了含与炮孔共线的预制裂隙介质裂纹扩展速度、加速度、裂纹尖端动态应力强度因子和动态能量释放率的变化规律以及它们之间的变化关系。试验结果表明,在爆炸应力波作用下裂隙两端产生了两条翼裂纹A、B,翼裂纹A的长度较翼裂纹B长,两条翼裂纹向相反的方向扩展;在翼裂纹扩展过程中,存在着加速与减速的过程,扩展速度瞬间达到峰值,其后逐渐振荡下降;动态应力强度因子也呈现瞬间达最大值到逐渐减小连续振荡变化的趋势,动态应力强度因子KId>KIdI;翼裂纹尖端的动态能量释放率对裂纹扩展具有驱动作用。