共查询到20条相似文献,搜索用时 15 毫秒
1.
S. M. Abo-Dahab 《先进材料力学与结构力学》2017,24(14):1145-1158
The present article is concerned with the investigation of the propagation of shear waves in a nonhomogeneous anisotropic incompressible medium under the effect of the electromagnetic field, gravity field, rotation, and initial stress taking into account a comparison between presence and absence of magnetic field, initial stress, and rotation. Analytical analysis reveals that the velocity of propagation of the shear waves depends upon the direction of propagation, the anisotropy, magnetic field, rotation, gravity field, nonhomogeneity of the medium, and the initial stress. The frequency equation that determines the velocity of the shear waves has been obtained. Some special cases are also deduced from the present investigation. In fact, these equations are an agreement with the corresponding classical results when the medium is isotropic. Numerical results have been given and illustrated graphically in each case considered. The results indicate that the effects of gravity field, initial stress, magnetic field, electric field, anisotropy, and rotation are very pronounced. Also, the absence of initial stress, magnetic field, and rotation tends to increasing of the S-waves velocity compared with presence of them. 相似文献
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In the present context, we consider the propagation of shear waves in the transverse isotropic fluid saturated porous plate.
The frequency spectrum for SH-modes in the plate has been studied. It is observed that the frequency of the propagation is
damped due to the two-phase character of the porous medium. The dimensionless phase velocities of the shear waves have also
been calculated and presented graphically. It is interesting to note that the frequency and phase velocity of shear waves
in porous media differ significantly in comparison to that in isotropic elastic media. 相似文献
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预应力梁横向振动分析的模态摄动方法 总被引:13,自引:2,他引:11
以预应力简支梁为例,分析了预应力在梁的横向振动过程中的变化,建立了预应力梁横向弯曲振动的微分方程。采用模态摄动法,进一步推导出预应力梁模态特性的近似分析方法,把复杂的变系数微分方程的求解转化为线性代数方程组的求解,从而有效地简化了计算过程。最后通过算例,讨论了预应力对梁的横向振动特性的影响。计算结果表明:当施加预应力的位置有较大的偏心距时,预应力对梁的自振特性有较大的影响。 相似文献
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针对钢绞线锈蚀导致混凝土开裂现象,开展了不同应力状态下混凝土的锈胀开裂试验,基于红外和热重分析研究了预应力钢绞线锈蚀产物的膨胀率,分析了预应力对保护层临界开裂时间和裂缝宽度的影响,综合考虑预应力、铁锈膨胀率和混凝土开裂损伤等因素,建立了开裂初始和发展全过程的锈胀裂缝预测模型,并通过试验结果进行了验证。结果表明:预应力会加速混凝土的锈胀开裂,在钢绞线抗拉强度75%的预应力水平下,保护层初始开裂时间降低了22%,裂缝扩展速率增加了9%;建立的模型具有较好的精度,可以合理地预测预应力混凝土的锈胀开裂。 相似文献
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预应力FRP加固工程结构技术研究进展 总被引:2,自引:0,他引:2
围绕国内外预应力FRP加固技术的研究现状以及最新进展,从预应力FRP加固混凝土结构、预应力FRP加固钢结构、预应力FRP加固中关键技术的研究等方面进行了综述。试验研究表明:预应力FRP加固混凝土能显著提高构件的开裂荷载、屈服荷载和极限荷载,改善受弯构件在长期荷载的力学性能,提高构件的疲劳寿命;预应力CFRP加固钢梁后,其屈服荷载和极限荷载相对于对比梁都有明显的提高,其提高的程度随着预应力CFRP的用量和预应力水平的提高而增大;预应力CFRP加固对钢梁的刚度提高作用也比较明显,对低强度的钢材,提高效果更明显;采用预应力FRP加固工程结构的关键问题在于预应力的施加体系、预应力控制值、预应力损失和端部的锚固。 相似文献
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M.D. Sharma 《International Journal of Engineering Science》2011,49(2):191-202
This study aims to calculate the wave-field characteristics of four attenuating waves in anisotropic thermoviscoelastic medium. An energy balance equation relates the complex-valued energy flux vector to the time-averaged densities of kinetic energy, strain energy and dissipated energy of plane harmonic waves in the medium. A complex slowness vector defines the inhomogeneous propagation of an attenuating wave in the medium. This slowness vector is specified with the phase velocity and the two non-dimensional attenuation parameters of the wave. One of the attenuation parameter defines the inhomogeneity strength of the wave as a measure of its deviation from homogeneous propagation. The phase velocity, attenuation parameters, polarizations of particles, propagation direction are combined to define the group velocity, ray direction and quality factor of attenuation of an inhomogeneous wave in the medium. Numerical examples are considered to study the variations of these characteristics of energy flux with propagation direction and inhomogeneity strength for each of the four attenuating waves in the medium. The effects of anisotropic symmetries are analyzed on the velocities of waves. The decay-rate of energy densities is exhibited with offset in the propagation-attenuation plane. 相似文献
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氯离子扩散系数是评价沿海环境中核电厂预应力混凝土安全壳耐久性的重要参数。该文基于两尺度方法,通过分析双轴等压下水泥浆基体、界面和混凝土细观结构,建立了水泥浆基体和界面毛细孔隙率与预应力之间的定量关系。为了量化预应力对微裂纹闭合、产生和扩展的影响,提出了临界毛细孔隙率与预应力之间的经验公式。将混凝土模拟成由骨料、界面和水泥浆基体组成的三相复合材料,获得预应力混凝土氯离子扩散系数比。通过与试验结果比较,校正了经验公式中的两个参数。用三组试验数据初步验证了该预测方法的有效性。 相似文献
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Giorgio Carta 《Acta Mechanica》2011,220(1-4):209-215
The paper deals with wave propagation in an elastic homogeneous bar that includes a prestressed segment in it. The prestress in that segment may be due to some distortion forces acting upon the bar. The end surfaces of the segment act as discontinuity surfaces inside the medium. They partially reflect and partially transmit any pressure wave impinging on them. It is found that the coefficients of reflection and transmission are functions both of the prestress of the segment and of the frequency of the wave. This produces a prestress-induced dispersion-like phenomenon, which in principle should be capable of revealing the state of internal stress of the body. 相似文献
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以两片安装竖向筋试验简支梁为基础,进行了预应力混凝土箱梁桥竖向预应力孔道对腹板截面削弱的研究,试验表明在不灌浆情况下梁开裂荷载提前,箍筋应力、混凝土表面主拉应增加明显,同时对试验梁进行了有限元分析,试验结果与有限元分析一致。研究表明加强竖向预应力灌浆质量的检测与管理对防止预应力混凝土箱梁桥的开裂有重要意义,同时为分析这类桥的开裂原因提供了理论与试验依据。 相似文献
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The transfer of prestress force from prestressing strands to the surrounding concrete is dependent on the bond between the two materials. Understanding the actual bond stress distribution along the transfer length results in optimized design of the transfer zone of prestressed concrete members. Equations of estimating the transfer length in ACI 318 code and AASHTO LRFD bridge design specifications simply take into account the effect of the strand diameter only. The objective of this study is to provide a generalized procedure for determining the bond stress–slip relationship accurately by incorporating the effects of additional parameters, such as concrete compressive strength at prestress release, center-to-center strand spacing, and concrete bottom cover. First, the bond stress distribution along the transfer length of a prestressed concrete member is formulated based on longitudinal slip–strain compatibility, force equilibrium and invariable bond stress–slip relationship along the transfer length. Second, a generalized Inverse Problem-Solving approach is introduced to determine best parameter coefficients through minimizing the discrepancy between the calculated and measured results. Two types of measurements (i.e., transfer length and end slip) reported in the literature are utilized to demonstrate the proposed approach. Predicted transfer length and end slip values using the calibrated bond stress–slip relationship show better agreement with the test data compared to those predicted by ACI 318 code and AASHTO LRFD bridge design specifications. Third, a computational procedure is developed and an example is presented to assist engineers using the developed formulae for determining the bond stress distribution along the transfer length of prestressed concrete members. 相似文献
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随着声学技术的快速发展,界面波在无损检测及环境参数反演领域的应用越来越广泛,但是目前理论与实践之间还存在一些差距,首先对基于Biot理论的流体饱和多孔介质声传播特性的理论进行了仿真分析,然后运用势函数结合多孔介质固体-流体边界条件建立了两半无限空间流-固界面Scholte波理论模型,最后对这一理论模型进行了实验验证。仿真结果表明:声波频率对各种波速几乎没有影响,但各种波速随孔隙度的变化较大;通过实验验证:Scholte波波速理论值与实际测量值之间的相对误差不超过0.24%。 相似文献
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不引入解析法中体外筋预拉力增量与梁中点振动位移成正比的假设,提出用能量法分析体外预应力梁动力特性。由于不引入解析法中的假设,梁自振频率也更准确,与数值解吻合良好。计算结果表明:解析法低估了体外筋对第1自振频率效应;高估了对第2自振频率效应;体外预应力筋对第1自振频率影响较大,对高阶的频率影响很小,可以不考虑其影响;随着体外筋面积和偏心距的增加,梁的第1自振频率也随之增加。在理论上,体外预应力能减小梁的自振频率,而体内预应力对梁的自振频率没有影响 相似文献
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目的 获得2024铝合金在不同喷丸参数下壁板外表面的变形规律。方法 选取喷丸气压、移动速度、预应力3个工艺参数作为正交试验因素进行预应力喷丸成形正交试验,研究在不同参数组合下单筋件的变形规律。结果 工艺参数按对单筋件变形量影响程度从大到小的顺序依次为:移动速度、预应力和喷丸气压。获得了2024铝合金单筋试验件喷丸成形后曲率半径与气压、移动速度和预应力之间的回归方程,其拟合值与试验值偏差小于12.6%。结论 获得了喷丸成形工艺参数对单筋件弯曲变形的影响规律,建立了工艺参数与曲率半径的回归方程,可为今后带筋壁板零件的喷丸成形工艺设计提供参考。 相似文献
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Kinking of a crack in a prestressed body under the influence of incident stress waves is investigated on the basis of the balance of rates of energies. It is assumed that the crack tip will choose to propagate at a time, in a direction, and at a speed for which the energy flux into the propagating crack tip attains a maximum value with respect to variation of the kinking angle. It is shown that the balance of rates of energies implies that the crack tip speed is zero at the onset of fracture. Consequently, the conditions for the onset of crack kinking and for the computation of the kinking time and kinking angle are completely defined by the elastodynamic field around the original crack tip. Examples of the incidence of step stress waves on a semiinfinite crack in a prestressed body have been investigated. It is shown that for an incident antiplane wave with Mode III fracture, kinking is generally not possible. For an incident inplane wave with mixed Mode I–II fracture, kinking may happen. For that case curves are presented which relate the kinking time and the kinking angle to the state of prestress and to the parameters of the incident wave. 相似文献
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Baljeet Singh 《Acta Mechanica》2010,211(3-4):337-344
Reflection of plane waves at a traction-free and electrically shorted/charge-free surface of a prestressed piezoelectric medium is studied. The reflection coefficients of qP and qSV waves are derived for electrically shorted and charge-free cases. The effect of initial stress on the reflection coefficients is discussed for a particular example of Lithium niobate. 相似文献