Determining reliable edge isopachic data from interior thermoelastic measurements

The maximum stresses in a plane-stressed component typically occur on the boundary. However, it is generally difficult to obtain reliable experimental data at an edge and thermoelastic stress analysis is no exception. The inability to measure reliable edge isopachic stresses has caused many previous thermoelastic stress analyses to be more qualitative than quantitative. This paper develops and implements an effective iterative least-squares method for calculating reliable edge isopachic stresses from measured interior values. The method is based upon the plane-stress isotropic compatibility equation. A regularization scheme is employed to minimize the sensitivity to measurement error and to improve the stability of the algorithm by controlling the rate of convergence. An illustrative example with actual measured thermoelastic data is included. The processes thermoelastically determined results compare well with those obtained using strain gages.Paper was presented at the 1994 SEM Spring Conference held in Baltimore, MD on June 6–8.     

An LDV system for turbulence length scale measurements

An LDV system for making spatial correlation measurements of velocity fluctuations in turbulent nonreacting and reacting flows is presented. The LDV system is the dual beam type and consists of an elongated probe volume and a two-point optical fiber detector. Results are presented of the integral length scale measured in a nonreacting grid generated turbulent flow.A version of this paper was presented at the ASME Winter Annual Meeting of 1984 and printed in AMD, Vol. 66     

Zur Rheologie der Torfbearbeitung

Zusammenfassung Zur rheologischen Charakterisierung nordwestdeutschen Hochmoortorfes genügt allein die Fließgrenze. Sie ist abhängig von der Torfart und bei mechanischer Vorbehandlung von der Gesamtzahl der Rührerumdrehungen. Die Erniedrigung der Fließgrenze durch Bearbeitung wird mit Hilfe eines einfachen Strukturmodells gedeutet.Der Vergleich zweier Bearbeitungsmaschinen bei jeweils gleichen Fließgrenzen des Torfes ergibt, daß das Momentenverhältnis nur von der Rührerbauart, nicht von der Torfart abhängt. Damit ist die Bestimmung der Fließgrenze durch Rührertypen möglich, bei denen die Meßsehwierigkeiten des Rotationsviskosimeters nicht auftreten. Weiter folgt daraus, daß das Verhältnis der spezifischen Arbeiten zweier Rührer, die gleichen Torf bis zur gleichen Fließgrenze bearbeiten, ebenfalls von der Torfart unabhängig ist. Die Abhängigkeit von der Rührerbauart ist relativ gering.Die kraftwirtschaftliche Bewertung verschiedener Rührerkonstruktionen läßt sieh infolge der geringen Unterschiede der spezifischen Arbeiten und der großen Versuchsstreuung nur durch sehr viele Einzelmessungen sichern.     

An experimental and analytical investigation of the rail shear-test method as applied to composite materials

This report presents the results from an experimental and analytical investigation of the stress distributions occurring in a rail shear test. The effects of nonuniform stresses induced by differential thermal expansion, rail flexibility and specimen aspect ratio on measured shear modulus and ultimate strength of composite laminates are shown. A two-dimensional linearly elastic finite-element model was used to analytically determine how various geometric parameters influenced the magnitude and distribution of inplane normal and shear stresses in a tensile-rail-shear specimen. Rail shear tests were conducted at room temperature and 589 K (600°F) on selected graphite-polyimide composite laminates using two titanium rail configurations. The analysis and test methods are discussed, and the results of the effects of the various parameters on shear modulus and ultimate strength are presented.     

Response of circular clamped plates to square-wave stress pulses

An account is given of an experimental investigation of the reeponse of clamped circular mild-steel plates of various thicknesses subjected to rectangular stress pulses over a small circular region. The stress pulses were transmitted to the plates through a 1/2-in.-diam shock bar and the strain-time responses of the plates were measured. The stress-wave interactions between the bar and the plates were measured for a number of thicknesses and the effect of the applied stress on the extent of the plastic deformation was determined. It was found that the elastic response was accurately predicted by the theory of Sneddon and the plastic response behaved according to a simple modification of this theory. The interaction between the stress pulse and plates of various thickness was theoretically predicted and found to be in excellent agreement with experimental measurements. The final plate deflections were theoretically predicted using a rigid viscoplastic theory and was in substantial agreement with the data. From this theory, the data were analyzed to determine the visco-plastic constant or relaxation time of the material. It is proposed that this testing arrangement is a suitable and convenient method for determining dynamic yield properties under biaxial-loading conditions.     

Experimental study of multiple interior impacts

In this paper, experiments involving interior impacts on soft, lead targets are described. The term “interior impact” refers to the impact of a projectile at the bottom of a predrilled hole in the target. It is known that impact of low-velocity projectiles into such soft targets results in plastic flow and cavities similar to those obtained in high-velocity impact of hard targets. Therefore, comparatively simple rifle-propelled projectile impacts on soft targets may yield useful information for high-speed hard-target impacts. Double impacts with a short-time interval, on the order of microseconds, between projectile arrivals were conducted. The leading projectile creates a plastic flow in the target which partially seals the entrance hole. The trailing projectile must first force open the passage hole before achieving additional penetration. The total penetration was measured for different time intervals between the projectiles. A method was developed to obtain double impacts at the same point. The method utilizes a duplex round, which is made up of two separate projectiles fired from the same cartridge. With this round, a series of impact experiments was conducted. It was learned that occlusion, or the close up of the hole, is negligible for nearly simultaneous projectiles (less than 10 μs between impacts), and greatest with about 80 to 100 μs between impacts. The projectile velocity was measured by the use of properly placed photodiodes.     

A note on duality in finite elasticity

The duality between stress and deformation fields for plane deformations of a compressible isotropic hyperelastic material established by J. M. Hill [1]is generalized to deformations of a homogeneous elastic material without the restrictions of isotropy and hyperelasticity. At the same time a clarification of Hill's results is achieved.     

The non-uniform transformation strain problem for an anisotropic ellipsoidal inclusion

The problem of an anisotropic ellipsoidal inclusion which undergoes a stress-free transformation strain (in the sense of J.D. Eshelby) is considered, and the following theorem is proved: If an ellipsoidal region in an infinite anisotropic linear elastic medium undergoes, in the absence of its surroundings, a stress-free transformation strain which is a polynomial of degree M in the position coordinates x_t, then the final stress and strain state in the transformed inclusion, when constrained by its surroundings, is also a polynomial of degree M in x_t.     

Strain-optic law for a certain class of birefringent composites

A strain-optic law for a certain class of birefringent fiber-reinforced composite materials is developed. The strain-optic law requires both mechanical and optical characterization of the material. Previous investigations have hypothesized the existence of three independent optical properties for the anisotropic birefringent material. The strain-optic relation developed in this study, however, requires only a single strain-optic coefficient, coupled with four independent mechanical material properties, for prediction of the optical response of a birefringent anisotropic material. Experimental results are presented which show good agreement with the developed strain-optic relation. Finally, the isoclinic parameter is investigated and preliminary evidence is presented which indicates a correspondence between principal-strain direction and optical isoclinic angle.     

The buckling load of an elastically supported cantilevered column with continuously varying cross section and distributed axial load

Summary The solution for the buckling load of an elastic supported cantilevered column with continuously varying cross section and distributed axial load is developed. Boundary conditions are formulated for fixed and elastic support. The critical loads are tabled for an usual variation in cross section and axial load distribution as function of the ratio between respectively rigidities and axial forces at fixed and free end, the variation of the rigidity and axial forces given by their degrees of the polynomial variation and rotation stiffness of the elastic support.

---

Übersicht Es wird die Knicklast für eine elastisch gelagerte, freitragende Säule mit stetig veränderlichem Querschnitt und stetig verteilter Axiallast berechnet. Die Randbedingungen sind für feste sowie für elastische Lagerung formuliert worden. Für einen übliczen Bereich von Querschnitten und Axiallasten werden die kritischen Lasten in Tabellen angegeben. Dabei wurde das Verhältnis zwischen der Steifigkeit und den Axiallasten am festen und freien Ende variiert.