Static creep test

Although the static creep test is not included in ENs, some countries still use it. 

The cylindrical specimen is subjected to a static constant coaxial stress for a certain period, at a certain testing temperature. Testing conditions have been established in an international conference (Colloquium 77 1977), after the basic research carried out by Van der Loo (1974). The established testing conditions are as follows applied constant stress ((To), 0.1 MPa test duration, 1 h temperature, 40°C. Before applying the test stress to the specimen, a pre-loading stress is applied for 2 min (0.01 MPa) in order to ensure good contact between the loading plate and the specimen surface. 

The specimen should have parallel and fairly smooth surfaces, so that the friction between the metal plates and the specimen is eliminated. The latter is ensured by coating the specimen surfaces with graphite grease. The deformation in the specimen is measured at regular intervals, typically after 5,10, 20, 40, 80,120, 300, 600, 2400 and 3600 s. 

The apparatus used is much simpler than the apparatus used in the cyclic compression test (Cabrera and Nikolaides 1987 Jongeneel et al. 1985). It is mentioned that the CRT-UTM-NU (Cooper Research Technology Ltd. 2014) apparatus is also capable of performing the static creep test. 

The resistance to permanent deformation of the bituminous mixture is assessed in terms of creep stiffness modulus, determined using the following equation  

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In addition to the above, the maximum permissible bitumen content is determined by executing the triaxial cyclic compression test according to CEN EN 12697 (2012), Method B, or the unconfined static creep test (see Section 7.6.3). This ensures sufficient resistance of the CAM to permanent deformation. 

The creep coefficient may also be determined by executing the static creep test. In this case, the creep coefficient, b, is the slope of the linear fit on the log 5, versus log 5 ix,creep-The stiffness of the bitumen, is determined from the Van der Poel nomograph, and the static creep stiffness, 5 is determined from the static creep test, at various stages of loading. More information regarding the static creep test is given in Section 7.6.3. 

Two specimens per bitumen content (use five levels of bitumen content), after curing for Marshall testing, are subjected to either the triaxial cyclic compression test or the static creep test at 40°C 0.5 C. 

The inability of the static creep test to simulate the real loading conditions on site and to reflect better the improved performance of binder modifiers led to the establishment of the dynamic (cyclic) loading test at the beginning of the 1980s (Finn et al. 1983 Valkering et al. 1990). 

The use of the static creep test without confining lateral pressure, which was the first to be introduced, is currently almost obsolete. 

The total duration of loading in case the uniaxial static (creep) test is employed is 1 h. 

By conducting the static creep test, it is possible to estimate the oncoming permanent deformation (rutting) of the asphalt layers after n years in service. 

One of the other benefits of incorporating polar monomers in the PSA is the enhancement in cohesive strength. This can be observed in the form of higher shear holding in a static shear test and/or better creep resistance of the adhesive when subject to a constant load. 

Methods G and H are obviously not directly comparable with the other adhesion methods. They could be called static fatigue tests, or perhaps creep... 

For bending experiments either 3 or 4 point bending may be used. For static or creep tests the load is usually applied as a weight on a hanger and the deflection measured using an... 

High peel strength with cohesive failure is possible by increasing the 0K/NC0 ratio. At a higher ratio, slight creep is observed at room temperature in the static shear test., 0H/NC0 ratios above 2.0 for Hycar 2103 and 1.8 for Hycar 2106 result in adhesives having incomplete cures with low peel values and poor static shear strength. 

Figure V demonstrates the effect of adhesive dry coating weight on 180° peel strength and rolling ball tack with OH/NCO ratios of 1.7 and 1.3 for Hycar 2103 and Hycar 2106, respectively. Static shear tests run both at room temperature and 70°C show no creep for both systems throughout the thickness range tested.

In practice, viscoelastic properties can be determined by static and dynamic tests. The typical static test procedure is the creep test. Here, a constant shear stress is applied to the sample over a defined length of time and then removed. The shear strain is monitored as a function of time. The level of stress employed should be high enough to cause sample deformation, but should not result in the destruction of any internal structure present. A typical creep curve is illustrated in Fig. 13A together with the four-element mechanical model that can be used to explain the observations. The creep compliance represents the ratio between shear strain rate and constant stress at any time t. 

For quartz, Scholz (1972) determined the activation energy as about 100 kJ/mol by static fatigue tests. For Westerly granite. Carter et al. (1981) determined as 100 130 kJ/mol by creep tests under high temperature (743 - 1038 K). The value of the activation energy obtained in this study agrees well with above values. 

If a creep test is continued for long enough, complete failure of the test piece can be induced. Such a test is termed static stress rupture or static fatigue and is essentially a creep test with the bother of measuring strain removed. 

The long-term behavior of plastics must, in other words, be investigated using static methods. The best-known method is the time-to-mpture or creep test, whereby a workpiece is subjected to stress CTq at time t = 0 and the stress parameter is maintained at a constant level for the entire duration of the test Time-dependent deformation is then measured. Fig. 26. If the elongation is constant, the stress parameter drops off in time with plastics. This is known as relaxation. This knowledge has applications related, for instance, to screw cmmections (plastic... 

By combining static-creep and dynamic tests, a range of stiffness modulus can be obtained. When measurements of stiffness modulus as a function at time, at various temperatures, are carried out and the results are plotted in logarithmic scales, a graph of the type shown in Figure 4.16 is obtained. 

The device may be used when the test is carried out under static-creep loading, which is the one developed by Shell laboratory at the end of the 1960s (Fenijn and Krooshof 1970), similar to the sliding plate viscometer or the improved version known as AARB elastomer tester (Tredrea 2007). 

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). 

Cycloolefin copolymer (COC) is an amorphous, clear metallocene product of norbomene and ethylene with a spectrum of attractive performance characteristics. Thus, COC (MFI at 190 °C and 2.16 kg = 1.7 dg min, p = 1,020 kg m ) was blended with C2+6 LLDPE (MFI at 190 °C and 2.16 kg = 3.2 dg min , p = 920 kg m ). The mechanical properties of the blends indicate immiscibility, despite the increased LLDPE crystallinity. The presence of COC improved the thermo-oxidative stability. Quasi-static tensile tests showed that increasing fraction of COC in the blends accounts for an enhancement of the elastic modulus and a decrease in the strain at break, while tensile strength passes through a minimum. A significant reduction of the creep compliance of LLDPE could be achieved only for the COC fractions exceeding 20 wt% (Dorigato et al. 2010). 

For example, single-lap shear joints can have a known static load applied, then inserted into a specified environment, and the time-to-failnie of joints noted as a function of variables such as adhesive type, pre-treatment and stress (see Shear tests). Static loads can also be applied to other joint configurations. Many studies have shown that such tests exhibit good discrimination between different surface pre-treatments. The creep performance of adhesives can also be measured by means of static load testing (see Durability creep rupture and Durability sub-critical debonding). 

Static load can result in creep behaviour of the bonded structure. To test this, a lap shear specimen with an adhesive thickness of 3 mm is loaded with a defined weight and the displacement (mm) between the two bonded parts is measured within the period of 1 to 4 years. Fig. 20 shows a creep test of Sikaflex -252 adhesive. 

The creep test was performed to determine the viscoelastic behavior under static conditions. A constant stress (0.3 Pa) was applied for 1 min and the resulting strain was measured (creep), then the stress was released and the strain was measured for 1 min (recovery). The shear creep compliance, J (reciprocal pascals), was calculated by dividing the measured shear strain, y, by the applied stress, r (pascals). 

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