Uniaxial compressive creep tests

Uniaxial compressive creep tests were carried out for granite sampled from Three Gorges Project (TGP) site in China at seven temperatures from 20°C to 300°C in order to determine the parameters C , Ci, Cr and Cj in eq. (25). The curves of creep compliance vs. time in logarithmic coordinates... 

Type of stress. A uniaxial tensile creep test would not be expected to give the required data if the designer was concerned with torsional or compressive creep. 

The testing of polymers requires unique understanding of the viscoelastic nature of polymers. For example in a creep test it is required to suddenly apply a constant tensile, compression, or torsion stress to a bar of material. The most common description of a uniaxial tensile creep test is shown in Fig. 5.5(a). Several questions may arise one of which is How is the load to be applied suddenly without causing dynamic effects. One answer is for the load to be applied as ramp input as shown in Fig. 5.5(b). Obviously, the latter case is not a correct creep test. How big an error is involved A solution of the differential equation representative of the material for the ramp input of Fig 5.5(b) can be obtained and it can be shown that the error in the strain output is negligible if the loading time, to, is small compared to the retardation time of the material, x. 

Experimental creep data for ceramics have been obtained using mainly flexural or uniaxial compression loading modes. Both approaches can present some important difficulties in the interpretation of the data. For example, in uniaxial compression it is very difficult to perform a test without the presence of friction between the sample and the loading rams. This effect causes specimens to barrel and leads to the presence of a non-uniform stress field. As mentioned in Section 4.3, the bend test is statically indeterminate. Thus, the actual stress distribution depends on the (unknown) deformation behavior of the material. Some experimental approaches have been suggested for dealing with this problem. Unfortunately, the situation can become even more intractable if asymmetric creep occurs. This effect will lead to a shift in the neutral axis during deformation. It is now recommended that creep data be obtained in uniaxial tension and more workers are taking this approach. 

The simplest test used to study the deformation behaviour of asphalts was the static unconfined uniaxial compression test, termed the creep test, developed in the 1970s by Shell Bitumen (Hill 1973). The specimen was subjected to static axial compressive load over a long period (1 h). The test procedure was very simple and required low-cost equipment. In addition. Shell Bitumen developed a rut prediction procedure based on results of the creep test but soon realised that it underestimated rut depths measured in trial pavements (Hill et al. 1974). This was attributed to the effects of dynamic loading producing higher deformation in the wheel-tracking test (Van de Loo 1974). 

Special specimen preparation as with tensile testing. However, the extraction of intrinsic mechanical parameters from creep indentation data is analytically complex [3, 4]. Confined compression or unconfined compression tests require preparation of cylindrical cored specimens of tissue and underlying bone. With unconfined compression, the free draining tissue edges and low aspect ratio, layered nature of the test specimen may introduce error. Compression of a laterally confined specimen by a porous plunger produces uniaxial deformation and fluid flow. Confined compression creep data has been analyzed to yield an aggregate equilibrium compressive modulus and permeability coefficient [5] and uniaxial creep compliance [6]. 

D5520-94 Standard Test Method for Laboratory Determination of Creep Properties of Frozen Soil Samples by Uniaxial Compression... 

The results from creep or relaxation compression test are evaluated and represented on the same way as for tensile creep or relaxation tests. After the applying of the weight m to the specimen accompanying load generates a uniaxial stress ffco (Eq. 4.53) in the initial cross-section area Aq. At this moment the extens-ometer monitors the increase in time-dependent compression AL (t) from which normative compression... 

Test method A determines the creep characteristics of bituminous mixtures by means of a uniaxial cyclic compression test with some confinement present. To achieve a certain... 

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