The diffractographic strain gage

A method for measuring strain using diffraction of light from a single aperture is described, and results of a comparison tensile test with an electrical-resistance strain gage are presented. The “diffractographic strain gage” is shown to have high sensitivity, linearity, accuracy and temperature compensation and the ability to operate in a variety of hostile environments. It is furthermore simple, inexpensive, and the data can be collected by eye without assistance from further instrumentation.     

Radiation effects on creep rupture and fatigue strength of pure aluminum

Paper describes an experimental investigation on the effect of nuclear radiation on the creep rupture and fatigue strength of pure aluminum for the ratios of alternating stress to mean stress ranging from zero to infinity. It was found that not only was the strength of the material tested affected by radiation over a range of ratios of stresses, but also the brittle-ductile transition was influenced.Based upon the experimental results obtained, an analytical model was developed to correlate creep rupture, fatigue strength and radiation effect for various ratios of stresses. This information may prove to be valuable in dealing with the stress analysis of nuclear reactors.Paper was presented at 1966 SESA Annual Meeting held in Pittsburgh, Pa., on November 6–9.     

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.     

A complex potential method for plate problems with bending extension coupling

Summary Within the framework of linear elasticity a complex plate analysis method is presented which includes bending extension coupling as it appears for example in laminates. Four complex potentials are introduced from which the resultant forces and moments and the accompanying deformations can be determined in a rather simple way. The underlying bending extension coupling is reflected by the actual numerical value of some constants. The usefulness of the introduced complex potentials is demonstrated by the example of a cracked plate under inplane and bending forces.

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Eine Methode komplexer Potentiale für Scheiben/Platten-Probleme mit Biege-Dehn-Kopplung

Übersicht Im Rahmen linearer Elastizität wird eine komplexe Scheiben/Platten-Analyse-Methode vorgestellt, die Biege-Dehn-Kopplung erfaßt, wie sie beispielsweise in Laminaten vorkommt. Es werden vier komplexe Potentiale eingeführt, aus denen die resultierenden Kräfte und Momente in einer recht einfachen Weise bestimmt werden können. Die zugrundeliegende Biege-Dehn-Kopplung spiegelt sich im tatsächlichen numerischen Wert einiger Konstanten wieder. Die Nützlichkeit der eingeführten komplexen Potentiale wird am Beispiel einer rißbehafteten Scheibe/Platte demonstriert, die in ihrer Ebene und durch Biegung belastet ist.

     

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.     

Rheologische Messungen an Kunststoff-Schmelzen mit einem neuen Rotationsrheometer

Zusammenfassung In der vorliegenden Arbeit wird ein neues Rotationsrheometer vorgestellt und über Messungen an zwei Polymethylmethacrylat-Formmassen berichtet. Bei dem Rheometer handelt es sich um ein Couette-Rheometer mit feststehendem Innenzylinder als Meßkörper. Der Meßkörper ist beidseitig eingespannt. In dem geschlossenen Meßraum können die Schmelzen bis zu einem Druck von 500 bar belastet werden.Der zeitliche Verlauf der Schubspannung in den Schmelzen wird in Abhängigkeit von Temperatur und Druck aufgezeichnet.

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Summary A new type of rotational rheometer is described, and results for two samples of polymethylmethacrylate are reported. The rheometer consists of a Couette system with fixed inner cylinder, supported at both ends for torque measurements. Pressure may be varied up to 500 bar. Shear stresses have been recorded as a function of time, temperature and pressure.

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Nomenklatur C [kp cm^–2 s^–1] Steigung der Anlaufkurve im Nullpunkt - D [kp cm rad^–1] Direktionsmoment - E ₀ [kcal mol^–1] Aktivierungsenergie der Newtonschen Viskosität - G [kp cm^–2] Schubmodul - G [—] Griffith-Zahl - l [mm] Länge des Meßkörpers - p [kp cm^–2] Druck - R _i [mm] Radius des Innenzylinders - R _a [mm] Radius des Außenzylinders - t _max [s] Zeit, bei der das Maximum in der Anlaufkurve auftritt - T [°C] Temperatur - ₀ [cm² kp^–1] Druckkoeffizient der Newtonschen Viskosität - [s^–1] Schergeschwindigkeit - ₀ [kp s cm^–2] Newtonsche Viskosität - (g cm²] Trägheitsmoment des Meßkörpers - v ₀ [s^–1] Eigenfrequenz des Meßsystems - _max [kp cm^–2] maximale Schubspannung - _st [kp cm^–2] stationäre Schubspannung Mit 7 Abbildungen und 1 Tabelle     

An introduction to dynamic photoelasticity

The general area of elastodynamics is divided into four more limited topics including, stress-wave propagation, vibration and impact, fracture propagation and quasi-static transients. The application of dynamic photoelasticity to each topic is discussed. Recording methods used in dynamic photoelasticity which are reviewed include the high-speed framing camera, the Cranz-Schardin system, Q-switched ruby lasers, and a stopaction strobe system. Advantages and disadvantages of each method of recording are covered. Analysis procedures used in interpreting the dynamic isochromatic-fringe patterns are described. Examples are illustrated where separation of the principal stresses is possible and a calibration method for determining the dynamic material-fringe valuef _σ ^* is reviewed. Finally, four applications of dynamic photoelasticity to problems arising in geophysics, fracture mechanics, flaw detection and mining are briefly reviewed to show the versatility of the dynamic photoelastic method are described.     

Some observations of the permanent set of cross-linked natural rubber samples after heating in a state of pure shear

Experimental evidence is presented to show that when cross-linked natural rubber samples are heated in air whilst subject to a pure shear strain and subsequently freed of all forces the new force-free or set state is not related to the original force-free state by a pure shear. During a pure shear linear elements along one of the principal directions of strain remain unchanged in length; it is shown that these elements undergo an increase in length as a result of the recovery after heating. The results are compared with the predictions of the two-network theory of permanent set propounded by previous workers.

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Zusammenfassung Vernetzte Naturkautschuk-Proben, in Luft erhitzt, zeigen bei gleicher Beanspruchung mit reiner Scherung und anschließender Entlastung einen neuen spannungsfreien (oder gesetzten) Zustand, der mit dem ursprünglichen spannungsfreien Zustand nicht durch eine reine Scherung in Beziehung steht. Durch eine solche bleiben lineare Elemente entlang einer der Hauptachsen der Spannung in ihrer Länge unverändert; es. wird gezeigt, daß diese Elemente an Länge bei der Erholung nach dem Aufheizen zunehmen. Die Resultate werden mit den Voraussagen der Zweinetzwerk-Theorie des permanent set der Autoren verglichen.

     

A torsional creep apparatus

Summary This paper describes a torsional creep apparatus for the determination of the creep compliance in shear as a function of time. The instrument is suitable for the measurement of compliances below 5·10^–8 m²/N, in the time range between 1 and 10⁵ seconds. Within five minutes and with an accuracy of 1 C, the temperature of the specimen can be adjusted to any value between –175 and –200 C. From the torsional creep measurements can be calculated the dynamic shear modulus and the corresponding damping. The lowest damping, determined in this way, is several times 10^–3.

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Zusammenfassung Ein Apparat zur Messung des Torsions-Kriechverhaltens wird beschrieben. Das Instrument ist zur Bestimmung von Nachgiebigkeiten kleiner als 5·10^–5 m²/N im Zeitbereich zwischen 1 und 10⁵ Sekunden geeignet. Die Temperatur der Probe läßt sich innerhalb 5 Minuten und mit einer Genauigkeit von 1 C auf jeden Wert zwischen –175 und –200 C einstellen. Aus der gemessenen Kriechfunktion können der dynamische Schubmodul und die dynamische Dämpfung berechnet werden. Eine untere Grenze für die Dämpfung, die man auf diese Weise noch bestimmen kann, ist einige Male 10^–3.

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The work was partly sponsored by the Office of Naval Research, Washington, D. C., under contract number N 62558-3884.     

Experimental and theoretical determination of frequencies of elastic toroids

Experiments are described which determine natural frequencies of five toroidal models whose major diameters are of 10 in. and whose minor diameters vary from 0.25 to 2 in. The experimentally determined frequencies are compared with the theoretical frequencies derived using the elementary theories for the in-plane and out-of-plane vibrations of circular rings of R. Hoppe and J. H. Michell, as well as the method of internal constraints. The comparative results for the frequencies are presented in tabular form.