Determination of the critical loads of shells by nondestructive methods

Two methods for determining the location of and load level to produce instability of compressed cylindrical shells are presented. The first relates the variation in the wall normal stiffness as a function of applied compressive force to the critical load. It uses the distribution of stiffness over the surface of the shell as a guide to buckle location. The second method associates the local dynamic mass with instability behavior. The test data presented show that either method will give excellent prediction capability from low-load-level data for shells of orthodox form. Neither method appears to apply to spirally stiffened shells. This is thought to be due to the fact that there is a substantial difference between the buckle pattern under axial compression and the imperfection shape induced by the normal displacement which is used to ascertain the wall stiffness and the dynamic mass.     

Evaluation of effective absorption coefficient during laser irradiation using of metals martensite transformation

The paper presents a method for determination of effective absorption coefficient of irradiation during action of a pulsed laser. For this purpose the solution of some axisymmetrical boundary value problem of heat conduction for half-space and the experimentally obtained polymorphous zones of transformation in the exposed materials are applied. The verification of the methodology is given for St 45 steel and the monocrystal cobalt samples.     

Nonpremixed flame control with microjets

The hydrodynamic control of buoyant nonpremixed flames is investigated by injecting high-momentum fluid through a central microjet. The resulting flame characteristics are mapped for jets of different strengths. The flame height decreases linearly with an increase in the microjet Froude number as the flow changes from a buoyancy-dominated to a momentum-controlled regime. The flame luminosity is reduced by injecting stronger microjets. The jets alter the flame structure by establishing strong entrainment of the ambient air from the quiescent surroundings. The introduction of an inert species as the microjet fluid has a similar qualitative effect as air. Microjet assistance is as effective as partial premixing for reducing the flame height and luminosity.     

Critical needs of fringe-order accuracies in two-color holographic interferometry

Two-color holographic interferometry is a promising technique for separating simultaneous concentration and temperature variations in solution for crystal-growth experiments on earth and in microgravity conditions in space. The ultimate success depends on two linearly independent fringe patterns due to the different wavelengths. With available practical lasers and typical crystal-growth experimental conditions the two interference fringe patterns (other than scale effects) may not be too different. The slight error in the measured fringe order can then yield large uncertainty in temperature and concentration determination. This aspect is analytically considered for the first time in this article. A simple cell (rectangular parallelpiped) is considered containing the fluid. For simplicyt, we assume a constant field along the object-wave-propagation direction in the cell. The two reconstructed fringe patterns are then represented in terms of temperature and concentration variations. Solving two equations theoretically yields the desired temperature and concentration. However, once the fringe-postition measurement error is introduced, error in the temperature and concentration results. These errors are analytically determined. A particular case of TGS (triglycine sulfate) aqueous solution with HeNe (λ=632.8 nm) and HeCd (λ=441.6 nm) lasers for holography is critically discussed. It is found that a high degree of accuracy in the fringe order is required in this particular case. To improve fringe-position measurements, special techniques such as electronic phase measurement or heterodyne detection may be necessary. The study provides the analytical guidelines for designing the experiments and critical needs of desired physical parameters. Paper was presented at the 1990 SEM Fall Conference on Experimental Mechanics held in Baltimore, MD on November 5–8.     

Electromagnetic disturbance created by an expanding conducting cylinder in a magnetic field

We examine the electromagnetic disturbance created by a linearly expanding, ideally conducting cylinder in an external uniform magnetic field with account for effects of order v/c (v is the boundary velocity).The problem of uniform magnetic field compression in a contracting cylindrical cavity with ideally conducting walls with radius decreasing linearly with time was solved in [1]. As far as we know the corresponding external problem has not been investigated.     

Fracture data and stress-strain behavior of rocks in triaxial compression

Test results are reported for a recently completed experimental research program on rocks subjected to triaxial compression. Sandstone, marble, granite and shale specimens were tested at confining pressures as high as 90,000 psi corresponding to mean stresses of up to 143,000 psi. Recognizing that the largest potential experimental error in such tests results from making strain and load measurements external to the vessel, special load and strain-measuring devices were designed and fabricated for use inside the pressure vessel. The specimens were carefully machined cylinders with length-to-diameter ratios of two and with diameters ranging from 4/16 in. to 1 in. The confining pressure was held constant during each run, but varied from 0 to 90,000 psi over the tests. Results are reported in the form of:

1. Stress-strain curves for individual specimens
2. Maximum shear stress at fracture vs. mean-stress curves for each rock type tested
3. Tabulation of results for 59 specimens

A number of tests were run on granite specimens which had been previously fractured. Results from these tests showed good agreement with tests on intact granite, providing the confining pressure was above 30,000 psi.     

Rigidity of tube sheet structure

The shear displacement of a tube sheet relative to a parallel stationary sheet depends not only on the stiffness of the tubes connecting the two sheets, but also on the play of the tubes within the holes of the sheets. This dependence is non-linear and extremely sensitive.     

On the propagation of generalized transverse waves in heat-conducting elastic materials

A generalized transverse wave is a propagating acceleration discontinuity on which the temperature and the entropy, together with their gradients, are continuous. In a heat-conducting elastic material the propagation and growth of such waves are uninfluenced by thermomechanical interaction. It is shown in this paper that in any given plane there is at least one direction in which a generalized transverse wave may propagate, and the existence is also proved of at least one direction in which a pair of generalized transverse waves may travel. Necessary and sufficient conditions are established for the speeds of propagation of these waves to be real. Relationships between transverse and generalized transverse waves are also studied, and in the last two sections of the paper the directions in which generalized transverse waves may propagate in an isotropic heat-conducting elastic material are systematically worked out and classified.     

What are gene patents and why are people worried about them?

This article examines what it means to patent a gene. Numerous ethical concerns have been raised about the effects of such patents on clinical medical practice as well as on research and development. We describe what kinds of inventions are covered by human gene patents, give several examples and summarize the small body of empirical research performed in the US examining the effects of these patents. There is little evidence that early fears about gene patenting placing substantial restraints on research and clinical medicine have come to fruition. Nonetheless, there are areas of concern, and policy makers, physicians and the public should be alert to ensure that the net social benefits of patenting human genes are maintained.     

Strain analysis for moiré interferometry using the two-dimensional continuous wavelet transform

In this paper, we introduce the two-dimensional continuous wavelet transform for the automated strain analysis of the moiré interference fringe pattern. The Fourier transform method has been widely used for automated analysis of an optical interference fringe pattern. However, this method is hardly applicable to the analysis of the fringe pattern, which includes large displacement range or discontinuities. We show the advantages of the wavelet transform method by applying it to experimental results on composite laminates.