Stiffness and hysteretic energy loss of a reinforced-concrete shear wall

A static, cyclic test of one of the largest reinforced concrete shear walls to be investigated in a laboratory is reported. The test was performed to study the dynamic characteristics (stiffness and hysteretic energy loss) of the shear wall. Very sensitive displacement gages are needed to measure the small deformations. The large forces required to load the structure make the test results susceptible to deformation of the support fixture. With these concerns in mind, instrumentation and data-reduction methods were developed that could separate model deformations from displacements caused by support motion. Also, model displacements were separated into shear and bending components. Results showed that prior to cracking, overall stiffness as well as the individual components of stiffness are accurately predicted by mechanics of materials beam theory that accounts for shear deformation. Equivalent viscous damping ratios that were determined from the hysteretic energy before and after cracking were similar.     

Torsion pendula with electromagnetic drive and detection system for measuring the complex shear modulus of liquids in the frequency range 80–2500 Hz

An apparatus for the measurement of liquid complex shear viscosity in the frequency range 80–2500 Hz, with the use of a torsion pendulum operating in forced oscillation, is described. The drive and detection system consists of a magnet inside the pendulum, two excitation and two measuring coils. The determination of the complex shear viscosity is based on the measurement of the resonance frequency and the damping of the torsion pendulum.The feasibility of this method is demonstrated with a number of Newtonian liquids in the viscosity range 0.3 to 60 m Pa s. Results for a viscoelastic polymer solution are presented. A comparison is made with other apparatus working in the same frequency range. a coil height - A apparatus constant - B magnetic induction - C ₁,C ₂ apparatus constants - d diameter torsion rod - D pendulum damping - E apparatus constant - F ₀ top frequency - G shear modulus torsion rod - G ^* =G + iG complex shear modulus - h length torsion rod - H transfer function - i - I moment of inertia - J ₀ excitation-current amplitude - J _exc excitation current - K torsion spring constant - l length pendulum mass - M torque - n number of coil turns - p dipole moment - Q = ₀/ mechanical quality - r radius pendulum mass - R Re {Z} - t time - T temperature - U induction voltage - U ₀ induction-voltage amplitude - x distance - X Im {Z} - Z = R + iX liquid impedance - Z _cyl characteristic cylindrical impedance - Z _pl characteristic plane impedance - angle - _M coefficient of linear expansion of the pendulum mass - _R coefficient of linear expansion of the torsion rod - rate of shear - penetration depth - steady-state viscosity - _s solvent viscosity - angular displacement - ₀ angular-displacement amplitude - µ ₀ =4 10^–7 Vs/Am - density - phase angle - angular frequency - ₀ top angular frequency - band-width     

An analytical-experimental estimation of elastic linear zone for photoelastic mode I SIF extraction

The traction continuity condition is used to delineate the elastic linear zone (ELZ) for the extraction of the Mode I stress intensity factor (SIF) from photoelastic data. The procedure requires an estimation, with the aid of experimental data, of some non-dimensional quantities which are the ratios of unknown parameters of the LEFM equations and the corresponding ones for an infinite body problem. Furthermore, the crack tip nonlinear zone is assumed to admit of plastic deformation with small-scale yielding.The estimation of the ELZ thus obtained seems to predict well the experimentally observed one.     

Cyclic-deformation behavior of notched mild-steel plates in plane stress

Notched rectangular SAE 1015 mild-steel plates were subjected to controlled cyclic nominal stresses or strains in a closed-loop servo-controlled fatigue-testing machine. Resistance strain gages were used to measure strains at the notch roots. These strains showed that large mean strains and strain ranges prevailed at these notches, though nominal strains were fully reversed and small. Inelastic stress- and strain-concentration factors calculated at various cycles were used to check the accuracy of the Neuber relation between these concentration factors and elastic stress-concentration factor. Limitations of this relation and characteristic notch-strain behavior mentioned above are discussed with reference to the peculiarities of the stress-strain relationships of this material.     

Dynamic-stress concentration using photoelasticity and a laser light source

Since experimental techniques using dynamic photoelasticity are, in general, limited by suitably intense monochromatic light sources, it was of primary importance to describe a ruby-laser system which would completely remove this particular aspect of the problem. Modulation of the system, in this case by a Kerr cell, provides the necessary control of the light output such that a complete series of results can be obtained by putting together the results of many individual tests recorded on a conventional still camera. In this case, the dynamic-stress-concentration factor in a strut with a symmetrically located circular discontinuity was determined to establish definitely the potential of the system.     

The low Reynolds number turbulent flow and mixing in a confined impinging jet reactor

Turbulent mixing takes an important role in chemical engineering, especially when the chemical reaction is fast compared to the mixing time. In this context a detailed knowledge of the flow field, the distribution of turbulent kinetic energy (TKE) and its dissipation rate is important, as these quantities are used for many mixing models. For this reason we conduct a direct numerical simulation (DNS) of a confined impinging jet reactor (CIJR) at Re = 500 and Sc = 1. The data is compared with particle image velocimetry (PIV) measurements and the basic flow features match between simulation and experiment. The DNS data is analysed and it is shown that the flow is dominated by a stable vortex in the main mixing duct. High intensities of turbulent kinetic energy and dissipation are found in the impingement zone which decrease rapidly towards the exit of the CIJR. In the whole CIJR the turbulence is not in equilibrium. The strong mixing in the impingement zone leads to a rapid development of a monomodal PDF. Due to the special properties of the flow field, a bimodal PDF is generated in cross-sections downstream the impingement zone, that slowly relaxes under relaminarising conditions. The time required for meso-mixing is dominating the overall mixing performance.     

Energy release rates in a constrained epoxy disc with Hookean and Mooney–Rivlin materials

Assuming that the disc material can be modeled either as Mooney–Rivlin or as Hookean and the steel ring enclosing the disc as Hookean, the energy release rates as a function of the crack length are evaluated and compared. Two loadings are considered––one in which the surface of the star shape hole in the disc is loaded by a uniform pressure and the other in which the temperature of the composite body is uniformly raised. It is found that the linear and the nonlinear analyses give qualitatively similar results for the two loadings. For each load, the energy release rate increases with an increase in the starter crack length, reaches a maximum value and then decreases gradually.     

在封闭结构中水对爆炸冲击波的削波、减压作用

采用数值方法计算了封闭矩形空间中布置在炸药周围的水对爆炸冲击波的削波作用以及对于气室压力的削减作用。计算结果显示 ,在各种不同的载荷密度和水 /药质量比参数条件下 ,冲击波峰值压力和气室压力均得到明显的削减。还计算了一个具有开口的模型隧道中水的削波作用 ,并将计算结果与实验测量数据进行了比较。     

含夹杂和微裂纹复合材料的损伤演化和分析

利用细观力学的Ｅｓｈｅｌｂｙ和Ｍｏｒｉ－Ｔａｎａｋａ理论，考虑纤维和微裂纹之间的相互作用，研究了定向分布微裂纹的演化规律及其对材料力学性能的影响，分析了纤维体积份数，弹性系数、微裂纹密度，纤维不同取向与基体开裂强度之间的变化关系，并给出了许多有意义的结论。