A simple method for measuring surface strains around cracks

A simple system has been developed to measure surface strains that occur during in situ deformation of mechanical test specimens. The system uses photolithographically deposited displacement markers and computer image recognition routines to determine in-plane displacements and strains from digital images. The strain calculating routines are integrated into a simple mouse-driven software package that facilitates the transformation from digital images to useful strain field information. Additional routines have been developed to determine crack tip stress fields and J integrals. Crack tip stress intensities have been calculated from strain maps obtained for traction-free cracks in stainless steel. The J integrals were found to be independent of contour and consistent with applied stress intensities. Crack tip stress intensities were calculated for bridged cracks in lamellar TiAl. The toughening effect of the bridging zones was determined by including the bridged region in the contours. Resistance curves generated from strain maps were consistent with those measured during mechanical testing.     

A simple method for measuring local buckling of thin plates

A simple computer-interfaced optical system for measuring the dynamic-local-buckling deformation of thin-walled metal structural-plate elements is described in this paper with two sets of experimental results. The major advantage of this system is its simplicity and economy as well as its speedy automated process for data scanning, acquisition, and analyses by using a microcomputer.Paper was presented at the 1986 SEM Spring Conference on Experimental Mechanics held in New Orleans, LA on June 8–13.     

Visual receiver for the phase contrast refractometer

Summary The accuracy of a visual photometric meter is limited by the luminance discrimination ratio ΔB/B of the eye, which, in the present case, is about 2 per cent. The unit, utilizing polarizers, measures optical paths to within 0.003 λ. The efficiency is compared with that of the photoelectric receiver, and accuracy values for some applications, including analyses of the isotope mixtures D₂O¹⁶/H₂O¹⁶ and H₂O¹⁸/H₂O¹⁶, are given.     

A Wollaston prism interferometer implemented with a digitizer

Objective of this work was to implement a Wollaston prism interferometer with a digitizer so as to perform the evaluation procedure of interferograms automatically by means of a microcomputer. The adopted opto-electronic sensing device is a linear array of 1,024 bar-shaped (15 m × 26 m) silicon photodiodes with center-to-center spacing 25 m. A stepping motor can move the array board in order to investigate the whole interferometric image. Scanning time is about 10 ms/line. Application of the system to measurements of concentration profiles in some mass diffusion processes of a binary gas mixture proves the ability of the digitizer to accurately measure gas densities. The performance and the potentiality of the sensor are analyzed and discussed.     

Rankine combined vortex interaction with a rectangular prism

Large eddy simulation is utilised to study the three-dimensional interaction between a travelling Rankine combined vortex and a rectangular prism. The study examines the strength and the topology of a vortex during the interaction with a prism that is much wider than the vortex core diameter. The physics of the interaction is revealed for the straight (β = 0°) and the oblique (β = 45°) impacts. For both cases, the low-level portion of the vortex undergoes displacements in the streamwise and the lateral directions. Also the vortex shape and the core vorticity are substantially disrupted. Behind the prism the full vortex circulation is recovered after a considerable distance. This created a low-velocity region. The sheltering effect of the prism is noticed for both straight and oblique impacts. The flow velocities in the sheltering region, right behind the prism, are reduced by more than 42% compared to the maximum flow speeds before the interaction.     

小型高压引爆装置冲击电流简易测量方法

依据脉冲放电电路的等效电路及其微分方程,采用Levenberg-Marquarat算法对主电容放电电压测试波形数据进行衰减系数识别,从而获得模拟电流波形。该方法克服了分流器法和Rogowski线圈法等直接测量小型高压引爆装置冲击电流时,因附加电路引起的电流波形失真。MATLAB模拟结果表明,该方法得到的电流模拟波形与真实电流波形拟合精度高,可用于直列式引信电子安全与解除保险装置和低能冲击片雷管的优化匹配设计。     

The crumbling of a viscous prism with an inclined free surface

Summary We study the two-dimensional instantaneous Stokes flow driven by gravity in a viscous triangular prism supported by a horizontal rigid substrate and a vertical wall. The oblique side of the prism, inclined at an angle α with respect to the substrate, is a fluid-air interface, where the stresses are zero and surface tension is neglected. We develop the stream function ψ in polar coordinates (r,θ) centered at the vertex of α and split it into an inhomogeneous part, which accounts for gravity effects, and a homogeneous part, which is expressed as a series expansion. The inhomogeneous part and the first term of the expansion may be envisioned, respectively, as self-similar solutions of the first kind and of the second kind for r→0, each one holding in complementary α domains with a crossover at α _c =21.47^∘, which we study in some detail. The coefficients of the series are calculated by truncating the expansion and using the method of direct collocation with a suitable set of points at the wall. The solution strictly holds for t=0, because later the free surface ceases to be a plane; nevertheless, it provides a good approximation for the early time evolution of the fluid profile, as shown by the comparison with numerical simulations. For 0<α<45^∘, the vertex angle remains constant and the edge remains strictly at rest; the transition at α _c manifests itself through a change in the rate of growth of the curvature. The time at which the edge starts to move (waiting time) cannot be calculated since the instantaneous solution ceases to be valid. For α>45^∘, the instantaneous local solution indicates that the surface near the vertex is launched against the substrate so that the edge starts to move immediately with a power law dependence on time t. However, due to the high value of the exponent, the vertex may seem to be at rest for some finite time even in this case. Received 29 August 1997; accepted for publication 21 January 1998     

Vibrations and self-heating of a viscoelastic prism with a cylindrical inclusion

The vibrations and self-heating of a viscoelastic prism with a cylindrical inclusion under harmonic loading are studied through numerical simulation. The effects of the stiffness of the inclusion and the mechanical and kinematic types of loading on kinetics, spatial temperature distribution, and thermal instability parameters are examined __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 6, pp. 73–81, June 2007.     

Photoelectric intensity ratio meter as receiver for the phase contrast refractometer

Summary The phase contrast refractometer converts optical phase differences into intensity differences, and thus the receiver is a photometer. The present design is photoelectric with one phototube and a grey wedge, an electronic device acting as a null indicator. The ratio between the intensities of the two areas to be measured is accurate to 0.3%, corresponding to a difference in optical path in the phase object of 0.0004 λ.     

Small-diameter parallel plate rheometry: a simple technique for measuring rheological properties of glass-forming liquids in shear

The rheological characterization of glass-forming liquids is challenging due to their extreme temperature dependence and high stiffness at low temperatures. This study focuses on the special precautions that need to be taken to accommodate high sample stiffness and torsional instrument compliance in shear rheological experiments. The measurement errors due to the instrument compliance can be avoided by employing small-diameter parallel plate (SDPP) rheometry in combination of numerical instrument compliance corrections. Measurements of that type demonstrate that accurate and reliable rheological data can be obtained by SDPP rheometry despite unusually small diameter-to-gap (d/h) ratios. Specimen preparation for SDPP requires special attention, but then experiments show excellent repeatability. Advantages and some current applications of SDPP rheometry are briefly reviewed. SDPP rheometry is seen as a simple and versatile way to measure rheological properties of glass-forming liquids especially near their glass transition temperature.     

Stress state of a cross-base prism under torsion

The stress state of a cross-base prism under torsion is analyzed. The lower- and upper bounds for stresses are found by solving an infinite system of linear algebraic equations and using Koyalovich’s limitants method. It is proved that the infinite system is regular and that its solution exists and is unique. The asymptotic behavior of the unknowns is established. The convergence of the series for stresses is accelerated Translated from Prikladnaya Mekhanika, Vol. 44, No. 11, pp. 79–93, November 2008.     

Autorotation dynamics of a low aspect-ratio rectangular prism

This paper presents two previously unreported aspects of the autorotation dynamics of low aspect ratio rectangular prisms, observed during an experimental study of the dynamics of helicopter underslung loads. Low-speed wind tunnel tests of a simplified container model free to rotate on a fixed axis demonstrated (a) that autorotation rate can lock-in to a structural mode and (b) that static hysteresis in autorotation rate can occur at low speeds. Autorotation lock-in behaves in a similar manner to vortex-shedding lock-in, suggesting that a similar feedback flow process between vortex wake dynamics and body motion is operating, and may provide a partial explanation for the complex changes in behaviour of rotating slung loads at high airspeeds. Static hysteresis at low speeds results in a bifurcation diagram for autorotation which is similar to that for cross-wind galloping of a square prism, including the effects of friction and inertia. The similarity in bifurcation behaviour seems likely to indicate similar dynamics rather than flow physics, suggesting that it may be possible to apply techniques developed to model the effect of non-linear damping characteristics in galloping to the modelling of autorotation.     

On a connectivity matrix formula for tensegrity prism plates

This paper considers tensegrity structures constructed from repetition of simple fundamental units. The tensegrity prism is chosen as a fundamental unit, which allows us to build plates, columns, towers, and their variations. The connectivity matrix plays a central role in analysis and design of tensegrity structures. This paper provides a systematic way to construct connectivity matrices for tensegrity structures constructed from repetition of tensegrity prisms. The number of units and node locations (shape) can be chosen arbitrarily. As an application of the connectivity matrix, a minimal-mass design subjected to force equilibrium (force balance) and yield and buckling stress constraints is shown.     

材料的双轴拉伸的规律的研究

汽车车身覆盖件是冲压成型的,其覆盖件的高精度回弹量计算非常困难,并少见有研究和报道。由于冲压成型过程是一个大应变和塑性屈服,常规的拉伸试验机无法测出其应力应变曲线,而目前汽车工业领域还没有建立用于修正回弹量的数据库,所以必须通过数值模拟和实验的方法对汽车车身覆盖件进行弹性模量、屈服强度和硬化规律进行研究。本实验研究的目的是通过对规定材料的双轴拉伸试验,应用数字图像处理的光测方法,确定材料屈服强化阶段复杂本构模型的材料特性常数,以达到正确合理描述复杂材料的硬化行为。试验中采用机械式拉伸试验机实现材料的双轴拉伸行为,利用数字相关光测方法获得拉伸材料屈服面屈服过程中大应变全场的数据,通过数字图像相关处理,得到材料在屈服强化阶段复杂本构模型的特性参数。实验研究的设备和仪器包括(1)双轴拉伸试验机;(2)计算机,高分辨率CCD和摄像头,图像卡,图像处理软件;(3)其它辅助设备等。实验研究设备的规范标准根据国家现行实验规范标准对本实验研究设备进行标定和计量审核。