Use of the flexure test for determining environmental behavior of fibrous composites

Use of the unidirectional flexure test for assessing environmental effects on organix matrix composites is investigated. Results show that moisture and temperature induce a change in failure mode from filament dominated to matrix dominated. Thus, the flexure test provides a simple means for determining environmental conditions which induce significant changes in mechanical behavior related to flexure-stress conditions. Environmental test procedures are also emphasized.     

An analogue technique for determining torsion and flexure functions of uniform beams

This paper describes an extremely simple, and yet accurate technique, based on electric analogy, for determining torsion and flexure functions of beams of uniform section, acted upon by terminal loads. Equations governing the torsion and flexure of such beams have been expressed to state the problem as a Neumann-type boundary-value problem; thus, the problem reduces to finding a function (or functions), which is harmonic within the cross section of the beam, and whose normal derivatives at the boundary of the section are prescribed. Prescribed current densities are introduced at the boundary, and consequent voltages are obtained as the analogue of required functions. Instrumentation is very simple and, once what has been described here as the “influence matrix” of voltages is obtained, both torsion and flexure functions can be obtained simply by multiplying the “influence matrix” by vectors of appropriate normal derivatives at the boundary. None of the usual drawbacks of membrane analogy arise here. Use and accuracy of the technique have been demonstrated by a number of examples.     

瞬态对流-扩散方程的变分多尺度解法

根据变分多尺度思想,求解了瞬态线性和非线性对流-扩散方程。文中为了简化细尺度方程的求解,忽略了该方程的瞬态性,分别用高阶多项式泡函数(High-order Polynomial Bubble)和自由残量泡(Residual Free Bubble)函数近似细尺度解,进而引入了消除数值伪振荡的稳定化结构。数值算例验证了本文方法的精确性、稳定性和对高Peclet数问题的适应性,证明了上述对细尺度模型的简化是可行的。     

Linearization as a method for determining parameters of relaxation spectra

A new method for determining parameters of a relaxation spectrum of visco-elastic bodies is proposed. The basic idea of the method consists of presenting measured frequency dependencies of the dynamic modules components by the power series. The coefficients of these series are found by comparing varying values with experimental data by linear functional of errors. The parameters of a spectrum are then calculated from the coefficients of the series. This procedure allows us to overcome the main problem of finding relaxation times, i.e. to pass from non-linear to linear functional of errors. It gives us the unique possibility of unambiguously estimating weights (partial moduli) of lines in a discrete relaxation spectrum and relaxation times because there is only a single minimum in the functional of errors. Received: 8 December 1999/Accepted: 10 December 1999     

On a method for determining the fixing conditions for a rectangular plate from the natural frequencies

We prove the duality of solutions for the problem of determining the boundary conditions on two opposite sides of a rectangular plate from the frequency spectrum of its bending vibrations. A method for determining the boundary conditions on two opposite sides of a rectangular plate from nine natural frequencies is obtained. The results of numerical experiments justifying the theoretical conclusions of the paper are presented. Rectangular plates are widely used in various technical fields. They serve as printed circuit boards and header plates, bridging plates, aircraft and ship skin, and parts of various mechanical structures [1–4]. If the plate fixing cannot be inspected visually, then one can use the natural bending vibration frequencies to find faults in the plate fixing. For circular and annular plates, methods for testing the plate fixing were found in [5–7], where it was shown that the type of fixing of a circular or annular plate can be determined uniquely from the natural bending vibration frequencies. The following question arises: Is it possible to determine the type of fixing of a rectangular plate on two opposite sides of the plate from the natural bending vibration frequencies if the other two sides are simply supported? Since the opposite sides of the plate are equivalent to each other, a plate with “rigid restraint—free edge” fixing will sound exactly the same as a plate with “free edge—rigid restraint” fixing. Hence we cannot say that the type of fixing of a rectangular plate on two opposite sides can be uniquely determined from its natural bending vibration frequencies. But it turns out that we can speak of duality in the solution of this problem. Here we observe an analogy with the problem of determining the rigidity coefficients of springs for elastic fixing of a string [8]: the rigidity coefficients of the springs are determined by the natural frequencies uniquely up to permutations of the springs.     

Variational method for solving problems of the plasticity of compressible media

Variational methods used in the theory of plastic flow are formulated on the assumption of the incompressibility of the deformable medium. In solving problems of the mechanics of soils and friable media and technological problems of the plastic shaping of uncompacted materials it is very important to take account of irreversible volumetric change. Extremum and variational theorems are proved in [1, 2] for rigid-plastic and viscoplastic expanding bodies. A variational equation equivalent to a complete system of differential equations is derived for a compressible plastic body.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 5, pp. 153–155, September–October, 1977.     

A method for determining ultrahigh temperatures

The problem of determining high and ultrahigh temperatures is urgent in connection with mastering the technology of new high-power energy sources. The known methods of measuring temperatures by using thermocouples, ultrasound, or optical devices can either be used only over limited temperature ranges or are very difficult to apply in practice. The present article describes a method of determining temperature based on the phenomenon of rethermalization of neutrons. The neutron is used as an agent interacting with the hot medium. When neutrons are scattered by atoms of a hot medium there is a change in their energy spectrum which is uniquely related to the kinetic temperature of the medium. In principle there is no apparent upper limit of the temperatures which can be measured by this method.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 8–11, May–June, 1979.The authors thank G. A. Ilyasova and M. Ya. Bankrashkova for their kind assistance in calculating the neutron energy spectra.     

New method for determining strain on the surface of a body with photoelastic coatings

An experimental method has been developed for determining the strains at all points on the surface of a structure. Narrow epoxy-resin strips on a thin film are cemented to the surface of the body under study. Photoelastic studies show that the birefringent pattern of these strips is dependent only on the longitudinal strain parallel to their axes. When the strips are used in conjunction with a continuous photoelastic coating, the surface strain can be determined at all points from direct observation of the fringe patterns. Paper was presented at 1964 SESA Annual Meeting held in Cleveland, Ohio, on October 28–30.     

Approximate method for determining the maximum temperature during quasistationary heating of a piecewise-homogeneous half-space

A method is proposed to calculate the maximum temperature of the surface of a piecewise-homogeneous half-space heated by a uniformly moving, locally distributed heat flow. Analytical solutions of the corresponding quasistationary heat-conduction problems are obtained for small and large values of the Peclet number. These solutions are used to derive formulas for calculating the maximum temperature in the case of intermediate (moderate) values of the Peclet number. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 3, pp. 85–97, May–June, 2005.     

An experimental method for determining the dynamic contact law

An experimental method is investigated whereby the strain response from an impacted beam is sufficient to determine the contacting force. Once the force is known, it is shown how the contact law can be determined. Experimental results for an impacted aluminum beam are demonstrated.     

简支梁中截面挠度计算的一种简易方法

介绍了一种首先利用简支梁的对称性找出等价悬臂梁, 然后利用叠加法求出等效悬臂梁自由端的挠度, 从而得到一般载荷作用下简支梁中间截面挠度的方法.     

Comment on the Clauser chart method for determining the friction velocity

A known difficulty with using the Clauser chart method to determine the friction velocity in wall bounded flows is that it assumes, a priori, a logarithmic law for the mean velocity profile. Using both experimental and DNS data in the literature, this note explicitly shows how friction velocities obtained using the Clauser chart method can potentially mask subtle Reynolds-number-dependent behavior.

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