Compression test data

Figure 8. Example of typical compression test data...

A mathematical model was developed by Smith et al. (1998) to extract data on the elastic Young s modulus and some criteria of failure of stationary phase Baker s yeast from compression testing data. A mean Young s modulus of 150+ 15 MPa with a corresponding mean von Mises strain at failure of 0.75 + 0.08 and a mean von Mises stress at failure of 70+ 4 MPa (Smith et al., 2000b) were obtained. 

Figure 13. Example of typical compression test data. (Reproduced with permission from Ref. 45. Copyright 1968y Forest Products Research...

FIGURE 17 Example of bulk density versus consolidation pressure plot from compressibility test data. 

Figure 11.7. Example of typical compression test data for basswood impregnated with poly(methyl methacrylate). (Adapted from Langwig et al, 1968.)...

Carbon fibers exhibit up to 50% lower compressive than tensile strengths. The compressive strength of fibers is calculated from compressive test data recorded from composite materials. A critical analysis of the compressive tests and compressive strength data for a variety of PAN based and mesopitch based carbon fibers can be found in reference [43]. 

Clech analyzed creep data from Pb-free solders (and baseline Sn-Pb solder) using the lesser known obstacle-controlled creep model developed by Frost and Ashby (Ref 75). That analysis examined tensile and compression test data as well as creep results derived from shear creep tests of soldered joints (Ref 76). The basic mathematical representation is ... 

Plastic deformation is commonly measured by measuring the strain as a function of time at a constant load and temperature. The data is usually plotted as strain versus time. Deformation strain can be measured under many possible loading configurations. Because of problems associated with the preparation and gripping of tensile specimens, plastic deformation data are often collected using bend and compression tests. 

Most ceramics have enormous yield stresses. In a tensile test, at room temperature, ceramics almost all fracture long before they yield this is because their fracture toughness, which we will discuss later, is very low. Because of this, you cannot measure the yield strength of a ceramic by using a tensile test. Instead, you have to use a test which somehow suppresses fracture a compression test, for instance. The best and easiest is the hardness test the data shown here are obtained from hardness tests, which we shall discuss in a moment. 

The compressive data are of limited design value. They can be used for comparative material evaluation and design purposes if the conditions of the test approximate those of the application. The data are of definite value for materials that fail in the compressive test by a shattering fracture. On the other hand, for those that do not fail in this manner, the compressive information is arbitrary and is determined by selecting a point of compressive deformation at which it is considered that a complete failure of the material has taken place. About 10% of deformation are viewed in most cases as maximum. 

The test can provide compressive stress, compressive yield, and modulus. Many plastics do not show a true compressive modulus of elasticity. When loaded in compression, they display a deformation, but show almost no elastic portion on a stress-strain curve those types of materials should be compressed with light loads. The data are derived in the same manner as in the tensile test. Compression test specimen usually requires careful edge loading of the test specimens otherwise the edges tend to flour/spread out resulting in inacturate test result readings (2-19). 

Stress-strain relationships for soil are difficult to model due to their complexity. In normal practice, response of soil consists of analyzing compression and shear stresses produced by the structure, applied as static loads. Change in soil strength with deformation is usually disregarded. Clay soils will exhibit some elastic response and are capable of absorbing blast-energy however, there may be insufficient test data to define this response quantitatively. Soil has a very low tensile capacity thus the stress-strain relationship is radically different in the tension region than in compression. 

DIF values vary for different stress types in both concrete and steel for several reasons. Flexural response is ductile and DIF values are permitted which reflect actual strain rates. Shear stresses in concrete produce brittle failures and thus require a degree of conservatism to be applied to the selection of a DIF. Additionally, test data for dynamic shear response of concrete materials is not as well established as compressive strength. Strain rates for tension and compression in steel and concrete members are lower than for flexure and thus DIF values are necessarily lower. 

The static modulus and dynamic storage modulus were investigated for some open-celled PE foams by static compression tests and dynamic viscoelastic measurements in compression mode. Experimental data were compared with theoretical predictions. 8 refs. 

Sharma (90) has examined the fracture behavior of aluminum-filled elastomers using the biaxial hollow cylinder test mentioned earlier (Figure 26). Biaxial tension and tension-compression tests showed considerable stress-induced anisotropy, and comparison of fracture data with various failure theories showed no generally applicable criterion at the strain rates and stress ratios studied. Sharma and Lim (91) conducted fracture studies of an unfilled binder material for five uniaxial and biaxial stress fields at four values of stress rate. Fracture behavior was characterized by a failure envelope obtained by plotting the octahedral shear stress against octahedral shear strain at fracture. This material exhibited neo-Hookean behavior in uniaxial tension, but it is highly unlikely that such behavior would carry over into filled systems. 

The ISO standard clearly differentiates between bonded and unbonded test pieces and in an appendix gives the stress strain relationships, taking account of shape factor. In the scope it is pointed out that comparable results will only be obtained for bonded test pieces if they are of the same shape, and that lubricated and bonded test pieces do not give the same results. There is, however, a very curious little introduction that gives a very narrow view of when compression data is needed and makes a dubious claim about use on thin samples when hardness measurement would be difficult - so is an accurate compression test on thicknesses below 2 mm. 

The stress-strain data can be generated from either tension or from compression tests. For soft solids, compression tests are preferred since it avoids the need to clamp the sample ends. Consequently, compression tests are widely used in testing foods. However, the friction between the loading plates can be significant, as noted by several investigators (58-61). 

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