Compressive measurement uniaxial compression

The statistical models for estimating the stones durability against salt crystallization using both the porosity and mechanical properties were proposed. These models were developed by multiple regression analysis and the statistically checked. The application of the models is that a physical properties (prosity) and mechanical properties measurement (uniaxial compressive strength, point load index and P-wave velocity) of the stone can used for... 

In order to determine which is the most appropriate yield criterion for a particular polymer it is necessary to follow the yield behaviour under a variety of states of stress. This is most conveniently done by working in plane stress = 0) and making measurements in pure shear (o- = -0-2) and biaxial tension (o-i, 02 > 0) as well as in the simple uniaxial cases. The results of such experiments on glassy polystyrene are shown in Fig. 5.28. The modified von Mises and Tresca envelopes are also plotted. In both cases they have been fitted to the measured uniaxial tensile and compressive yield stresses, oy, and oy. It can be seen that the von Mises... 

When an isotropic material is subjected to planar shock compression, it experiences a relatively large compressive strain in the direction of the shock propagation, but zero strain in the two lateral directions. Any real planar shock has a limited lateral extent, of course. Nevertheless, the finite lateral dimensions can affect the uniaxial strain nature of a planar shock only after the edge effects have had time to propagate from a lateral boundary to the point in question. Edge effects travel at the speed of sound in the compressed material. Measurements taken before the arrival of edge effects are the same as if the lateral dimensions were infinite, and such early measurements are crucial to shock-compression science. It is the independence of lateral dimensions which so greatly simplifies the translation of planar shock-wave experimental data into fundamental material property information. 

The structure/property relationships in materials subjected to shock-wave deformation is physically very difficult to conduct and complex to interpret due to the dynamic nature of the shock process and the very short time of the test. Due to these imposed constraints, most real-time shock-process measurements are limited to studying the interactions of the transmitted waves arrival at the free surface. To augment these in situ wave-profile measurements, shock-recovery techniques were developed in the late 1950s to assess experimentally the residual effects of shock-wave compression on materials. The object of soft-recovery experiments is to examine the terminal structure/property relationships of a material that has been subjected to a known uniaxial shock history, then returned to an ambient pressure... 

The microstructure/property relationships observed in shock-recovered samples have been often tacitly assumed to result solely from the shock compression, duration, and rarefaction due to the imposed uniaxial-strain shock. Recent shock-recovery studies have, however, shown that the degree of residual strain in the sample significantly influences the measured struc-... 

A strength value associated with a Hugoniot elastic limit can be compared to quasi-static strengths or dynamic strengths observed values at various loading strain rates by the relation of the longitudinal stress component under the shock compression uniaxial strain tensor to the one-dimensional stress tensor. As shown in Sec. 2.3, the longitudinal components of a stress measured in the uniaxial strain condition of shock compression can be expressed in terms of a combination of an isotropic (hydrostatic) component of pressure and its deviatoric or shear stress component. 

In the perfectly elastic, perfectly plastic models, the high pressure compressibility can be approximated from static high pressure experiments or from high-order elastic constant measurements. Based on an estimate of strength, the stress-volume relation under uniaxial strain conditions appropriate for shock compression can be constructed. Inversely, and more typically, strength corrections can be applied to shock data to remove the shear strength component. The stress-volume relation is composed of the isotropic (hydrostatic) stress to which a component of shear stress appropriate to the... 

The first group of tests is carried out on specimens generally fabricated into a dumb-bell shape, with forces applied uniaxially. The usual apparatus consists of a machine with a pair of jaws, which during the test are moved relative to each other, either together or apart, in a controlled manner. A chart recorder is employed to give a permanent record of the results obtained, so that the force at fracture can be determined. Whether this kind of set up measures tensile, compressive, or flexural strength depends on how the sample is oriented between the jaws, and on the direction that the jaws are set to travel relative to one another. 

An initial attempt was made to correlate the structural properties of the kl-(BEDT-TTF)2M(CF3)4(TCE) salts with their superconducting transition temperature [31]. The relationship between Tc and any single unit cell parameter failed to show any discemable trend. The best correlation was obtained by plotting Tc as a function of the b/c ratio, where b is the interlayer and c is an intralayer direction. A similar conclusion was reached through the determination of uniaxial pressure coefficients of p -(BEDT-TTF)2SF5CH2CF2S03 and k-(BEDT-TTF)2Cu(NCS)2 through the measurement of thermal expansion [32]. These results also indicated that expansion of the interlayer direction and compression of an intralayer direction... 

Gas compression in closed-cell polymer foams was analysed, and the effect on the uniaxial compression stress-strain curve predicted. Results were compared with experimental data for a foams with a range of cell sizes, and the heat transfer conditions inferred from the best fit with the simulations. The lateral expansion of the foam must be considered in the simulation, so in subsidiary experiments Poisson s ratio was measured at high compressive strains. 13 refs. 

Texture has a number of component attributes, and some of them can be assessed by mechanical means. The texture or firmness of cooked potatoes is evaluated by subjecting each sample to a compression test using a universal testing machine equipped with a load cell. Cooked potato cylinders are compressed in a single-cycle compression-decompression test. Uniaxial compression is measured with an Instron machine with a lOON load cell. Measurements are performed on hot potato cylinders (depth 12 mm, height 10 mm) from 15 potatoes immediately after cooking, at a deformation rate of 20 mm/min. Stress and strain at fracture are calculated by the Instron series IX version 7.40 software and means of 15 repetitions are calculated. 

In the same way that close-packed directions in a crystal have larger refractive indices, so too can the application of a tensile stress to an isotropic glass increase the index of refraction normal to the direction of the applied stress. Uniaxial compression has the reverse effect. The resulting variation in refractive index with direction is called birefringence, which can be used as a method of measuring stress. 

Uniaxial tension testing with superposed hydrostatic pressure has been described by Vernon (111) and Surland et al. (103). Such tests provide response and failure measurements in the triaxial compression or tension-compression-compression octants. 

Deformational measurements were carried out in a uniaxial compression of cylindrical samples and the equilibrium shear modulus G was determined from [11]... 

The failure characteristics of a food or food material can be measured using compression, tension, or torsion. Of all the available deformation tests, possibly the most common is uniaxial compression (Lelievre et al, 1992). Bulk compression is another type of compression test, but it is seldom used due to the difficulty inapplyingforceby means of hydraulic pressure (Bourne,, 1982). The experimental... 

Uniaxial compression of a cylindrical shape is a method of measuring the behavior of a Hookean solid. Hooke s law is represented by the following relationship ... 

The time required for one TPA test of a sample is 5 to 10 min, which includes sample positioning and instrument cleaning. It is usually the case that sample preparation (e.g., cooking) requires much more time than TPA measurements. Most uniaxial compression instruments offered to the food industry are computer controlled and have software to immediately calculate the TPA parameters. 

This method has been used to obtain force-separation curves for block copolymers adsorbed on planar substrates and subjected to uniaxial compression. Block copolymers are adsorbed from solution onto atomically flat substrates (e.g. mica, quartz) and the force between the plates measured for separations ranging from —0.1 to contact. Further details of the experiments are given in Section 3.8.2. 

It is worth pointing out that the most reliable stress-strain curves are obtained by uniaxial compression or shear, in order to avoid the craze formation that can occur in tensile measurements. 

In addition to the compression loading, uniaxial extension of entangled PDMS chains have been investigated by pulling a small portion of the material and measuring elastic response before the rupture happens [419]. The multiple ruptures observed in the force-distance curves (Fig. 43) have been interpreted as fractures of an entangled network of PDMS chains formed between the tip and the silica grafted surface. At small deformations, also the capillary forces were shown to contribute in the force. The elastic part of the curves was described us-... 

In this study, uniaxial confined swelling and compression experiments were performed on a hydrogel that mimics the behaviour of biological tissues. The deformation of the sample and the electrical potential difference over the sample, caused by varying mechanical and chemical loads, were measured successfully. 

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