Compressive load testing

Strength Properties of Adhesive Bonds in Shear by (Compression Loading, Test for (D 905)... 

Another measure of refractoriaess is the hot-compressive strength or hot-load test for refractory bricks or formed specialties. The specimen carries a static load from 69 kPa (10 psi) to 172 kPa (25 psi). It is heated at a specific rate to a specific temperature which is then held for 1.5 h, or it is heated at a specific rate until it fads. The percent deformation or the temperature of fadure is measured. The procedure is described ia ASTM C16. 

Under compression loading, the long flexible tension specimens would simply buckle. Thus, lateral support to prevent buckling is necessary as shown in the compression test fixture with side-support plates in Figure 2-24. There, the specimen is essentially as long as the fixture is tall, and only a small portion of the specimen can be seen where it is not supported. 

Data are generated by placing a test specimen between the two flat, parallel faces of a testing machine and then moving these faces together at a specified rate (ASTM D 695). A displacement transducer may be used to measure the compression of the specimen, while a load cell measures the compressive force exerted by the specimen on the testing machine. Stress and strain are computed from the measured compression load, and these are plotted as a compressive stress-versus-strain curve for the material at the temperature and strain rate employed for the test. 

Several criticisms of these parameters have recently been pointed out. First, they have no specific association with a material plane (i.e., they are scalar parameters), despite the fact that cracks are known to nucleate on specific material planes. With traditional parameters it is difficult to account for the effects of crack closure under compressive loading. Traditional parameters have not been successful at unifying experimental results for simple tension and equibiaxial tension fatigue tests. Finally, a nonproportional loading history can always be constmcted for a given scalar equivalence parameter that holds constant the value of the scalar parameter, but which results in cyclic loading of material planes. For such histories, scalar parameters incorrectly predict infinite fatigue life. 

The diametral compressive strength has been used to estimate the tensile strength of certain AB cements (Smith, 1968). In this test, the load is applied diametrically across a cylinder of cement. Theoretical consideration of the test geometry shows that for a perfectly brittle material the failure that occurs is tensile in character. The difficulty in applying this test to AB cements is that they are not sufficiently brittle for this to hold true. In particular, the zinc polycarboxylate and glass-ionomer cements show sufficient plastic character to make the relationship between diametral compressive and tensile strength vary between AB cements of different types like the compressive strength test, this test is valid only as a means of comparison between similar materials (Darvell, 1990). 

The Vicat softening temperature is the temperature at which a standard deflection occurs for defined test samples subjected to a given linear temperature increase and a compression loading from a defined indenter of a specified weight. The load used is often ION (Vicat A) or SON (Vicat B) and must be indicated with the results. In either case the polymer cannot be used under this compression load at this temperature. 

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. 

The strain-control test has the advantage that information on the strain capacity is obtained, as well as the maximum stress that can be sustained, the latter value being similar to that obtained in a conventional test with constant loading rate. In the following we shall discuss behaviour in compression in tests with a constant strain rate. 

The Firestone flexometer method in D623 is not very specific. The standard test pieces are in the shape of a frustum of a rectangular pyramid but the use of any suitable shape is permitted when cut from products. The apparatus operates at 800 cycles/min and a range of compression loads and amplitudes of oscillation are possible, but no particular conditions are specified. The test piece is fatigued until a definite, but unspecified, decrease in the height of the test piece is reached, which is supposed to represent the onset of internal porosity. Parameters such as temperature rise and changes in compression are reported. 

In the compression modulus test, the movement of the crosshead can be taken. Precautions also must be taken to prevent overrun of the crosshead by having stops installed to prevent damaging the load cell with an overrun. 

A fixed compressive load is applied to the entire cell stack-up between the alumina cell holder and the HastX top plate by means of weights, as shown in the test stand overview, Figure 15. This load must simultaneously compress the cell against the mesh, flow field and foil on the steam/hydrogen side and against the seal around the outer edge of the cell. The outer edge of the cell rests on a window... 

Creep deformation. The deformation of single crystals of wet synthetic quartz under a constant compressive load at atmospheric pressure has been studied by McCormick (1977), Kirby and McCormick (1979), and Linker et al. (1984). The creep curves for all samples loaded almost immediately after the test temperature had been reached are characterized by an incubation period that decreased rapidly with increasing axial stress and increasing temperature. A typical creep curve is shown in Figure 9.5. 

Denser foams behave differently in compression tests. The brittle failure of samples involves cracking along the inclined and longitudinal planes (Fig. 29 d). When compressive load is applied to a material of high apparent density, such as polyurethane foam (Fig. 29 e), the load will go on increasing continuously even after has been attained. At the same time, the cross-section of the sample will increase and the sample assume a barrel-like shape. The foam cells will begin to crumple at the same time. 

A compaction simulator must be able to mimic the full compression cycle of the unit operation. Early attempts at compaction simulation utilized mechanical property testing equipment (e.g., Instron and Lloyd type machines) to compact powders into compacts. Although these machines were well suited to apply appropriate compression loads, they were not designed for the high velocities and accelerations necessary to simulate the double-ended compression cycle of a rotary tablet press (2). 

For this test 3-in. by 6 in. (75-mm by 150-mm) concrete cylinders were cast following the method described in ASTM C 39-86. Mix designs No. 1 and No. 2 were evaluated under axial compressive load. 

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