Resistance-type Strain Research Articles

Strains in flat plates from moiré-displacement patterns

Surface strains in flat plates subjected to static loads were accurately determined from projection-moire displacements. The moire displacements and strains were evaluated by comparison with the dial-gage deflections and strains measured by resistance-type strain gages. The moire diflections and strains were further evaluated by comparison with the values predicted by three analytical methods—small-deflection beam theory, large-deflection beam theory, and small-deflection plate theory. It was found that strains in flat-plate structures can be determined from projection-moire displacements to an accuracy better than 10 percent.

On the Measurement of Strain Distribution in Wood under the Axial Tension Force by X-Ray Diffraction

Under the axial tensile force in the fiber direction the distribution of crystal lattice strain in the b-axis direction of the cellulose (I) in the cell wall of tracheids were measured by the X-ray diffraction technique using (040) reflection of cellulose micelles.In this study the transit X-ray method was used and the diffraction profiles were obtained by 40sec fixed time and θ-2θ method. The macroscopic surface strains of the specimens in the fiber direction were measured by the electrical strain meter and resistance type strain gage, pasted on both sides of the specimens.The lattice strain in the fiber direction was a little smaller than the surface strain of the specimens, but the average ratio of the lattice strain to the surface strain was in the range of 0.90∼0.97 below the surface strain level of 3000×10-6.The lattice strains decreased with the increasing inclination from the fiber axis.In the inclined direction from the fiber axis, the lattice strains were a little smaller than the normal strains of the specimen calculated from Eq. (10), of homogeneous orthogonal anisotropic body, but the appearance of distribution of lattice strains in the cell wall was similar to that of the normal strains of the specimens.From those results it is considered that the micelles which were arranged in the cell wall have actually taken over a portion of the applied stress and acted an effective role in the mechanical properties of wood.It is qualitatively observed that the micelles have largely been improved in their orientation by the axial extension in the fiber direction.

A Clamp-On Strain Transducer for Use on Geologic Materials

Abstract The design, calibration and application of a clamp-on type strain transducer for the simultaneous monitoring of axial and transverse strain under both uniaxial and triaxial test conditions is described The transducer attaches directly to the test specimen and utilizes a number of linear variable differential transformers to provide average strain data. Tests have been carried out on specimens of a number of metallic (steel, brass and aluminum) and geologic materials (granite, limestone and sandstone) at confining pressures of up to 5,000 psi. No difficulties are contemplated in using the psi. No difficulties are contemplated in using the transducer at confining pressures of 10,000 psi and higher. Introduction In order to determine the deformation characteristics of a solid, the requirements are: a suitably shaped test specimen; a system for applying the necessary loads to the test specimen; and a system for monitoring the resulting strains. This paper is concerned with the third requirement and describes the development of a clamp-on strain transducer for the measurement of both axial and transverse strain in specimens of geologic material under both uniaxial and triaxial loading conditions. For studies under uniaxial test conditions several workers have designed transducers for specific research projects. In many cases sufficient time was not available to develop and qualify these transducers for general use. At least one commercial firm manufactures a clamp-on type axial and transverse-strain transducer that utilizes differential transformers and is designed specifically for use on geologic materials. The development of suitable strain transducers for use on geologic materials under triaxial test conditions** has been extremely limited. Several methods have been utilized in which axial specimen strain was determined by external measurement of loading piston displacement. Although such methods have proved more or less satisfactory for experiments where large strains were involved, their use in experiments where small strains (less than 0.5 percent) and small strain increments ( 0.001 percent) are of interest are unsatisfactory due to a percent) are of interest are unsatisfactory due to a number of factors. For example, even with extremely fine polishing of specimen end-surface will compress surface will contain a large number of asperities. Under a compressive load the surface will compress rapidly upon initial loading due to failure or the development of plastic deformation in the individual asperities. Strain values based on deformation measurements made across such a surface would be seriously in error, particularly at low loads. Furthermore, the mechanical stability and accuracy of an external strain measuring system, although not too difficult to achieve in large strain experiments, becomes a major difficulty when small strains are being considered. Bonded resistance-type strain gauges provide one means of conveniently measuring axial and transverse strain in both uniaxial and triaxial tests. These have been used successfully for the investigation of the mechanical behavior of geologic materials. The inability to calibrate directly this type of gauge and the cost of gauges required for any extensive test program suggests that considerable effort should be directed toward the development of a clamp-on type strain transducer that could be utilized under both uniaxial and triaxial test conditions. Besides the transducer described, we are familiar with two other clamp-on transducers designed for use under triaxial test conditions one a purely experimental unit, incorporating bonded resistance strain gauges, being utilized by Mazanti, and the other made by Structural Behavior Engineering Laboratories in Phoenix that utilizes linear differential transformers as sensing elements.

Effect of Pressure on Creep in Tin

Bending creep of tin is reported with an activation volume of approximately 8.5×10−24 cm3, essentially independent of temperature between 0° and 57°C, and pressures to 8 kbar. The pressure dependence of the output of resistance-type strain gauges is given.