Tensile creep strain

Log-log plot of tensile creep strain rate against applied stress for alumina and an alumina-17vol%SiC nanocomposite tested in tension at 1200°C. 

A cross-plot can be made of the tensile creep strains for a specific time versus the creep stress. When a smooth curve is fitted to the discrete... 

C1291-95 Test Method for Elevated Temperature Tensile Creep Strain, Creep Strain Rate, and Creep Time-to-Failure for... 

E s % s nominal tensile creep strain rate daVdf according to ISO 899-1... 

Note GF-PP has the following properties at 20 C. Density - 1120 kgm . Tensile creep strain (measured on end-gated injection moulded bars) can be expressed as... 

Two test cases are used to validate the linear viscoelastic analysis capability implemented in the present finite-element program named NOVA. In the first case, the tensile creep strain in a single eight-noded quadrilateral element was computed for both the plane-stress and plane-strain cases using the program NOVA. The results were then compared to the analytical solution for the plane-strain case presented in Reference 49. A uniform uniaxial tensile load of 13.79 MPa was applied on the test specimen. A three-parameter solid model was used to represent the tensile compliance of the adhesive. The Poisson s ratio was assumed to remain constant with time. The following time-dependent functions were used in Reference 49 to represent the tensile compliance for FM-73M at 72 °C ... 

Figure 3.27. Tensile creep strain vs. test duration-curves of PP and its composites under 80% of the static ultimate tensile strength (UTS) at room temperature [57]...

Figure 10. Tensile creep strain behavior ofALSP/HCF gels for...

Strain gages were used to monitor the tensile creep strain, with computerized data acquisition. The resolution (of the strain gauge system) was 0.0001 cm/cm. The load-line displacement measurement was made using a dial gage with a resolution of0.0006 cm. 

It should also be noted that in this case the material was loaded in compre-sion whereas the tensile creep curves were used. The vast majority of creep data which is available is for tensile loading mainly because this is the simplest and most convenient test method. However, it should not be forgotten that the material will behave differently under other modes of deformation. In compression the material deforms less than in tension although the efrect is small for strains up to 0.5%. If no compression data is available then the use of tensile data is permissible because the lower modulus in the latter case will provide a conservative design. 

Although the creep behavior of a material could be measured in any mode, such experiments are most often run in tension or flexure. In the first, a test specimen is subjected to a constant tensile load and its elongation is measured as a function of time. After a sufficiently long period of time, the specimen will fracture that is a phenomenon called tensile creep failure. In general, the higher the applied tensile stress, the shorter the time and the greater the total strain to specimen failure. Furthermore, as the stress level decreases, the fracture mode changes from ductile to brittle. With flexural, a test specimen... 

Fig. 2-37 Tensile stress-strain-time correlation resulting from creep for PC.

For tensile creep, TJ would be the tensile viscosity. When the viscosity is high (e.g., when working at relatively low temperatures or with very high-molecular-weight polymers) it can be difficult to determine tl-x accurately, so creep recovery measurements are made. Here the load is released after a given creep time and the strain is followed as the specimen shrinks back toward its new equilibrium dimensions. 

For elastomers, factorizability holds out to large strains (57,58). For glassy and crystalline polymers the data confirm what would be expected from stress relaxation—beyond the linear range the creep depends on the stress level. In some cases, factorizability holds over only limited ranges of stress or time scale. One way of describing this nonlinear behavior in uniaxial tensile creep, especially for high modulus/low creep polymers, is by a power... 

Figure 3.7. (a) Creep strain versus time example of polypropylene at 23°C under 10 MPa in tensile loading (b) Creep strain... 

A typical creep experiment involves measuring the extent of deformation, called the creep strain, e, over extended periods of time, on the order of thousands of hours, under constant tensile loads and temperature. The resulting plot of creep strain versus time (Figure 5.43) shows the resulting creep rate, e = dejdt, which is the slope of the... 

Lofaj, F., Okada, A., and Kawamoto, H., Cavitation strain contribution to tensile creep in vitreous bonded ceramics , J. Am. Ceram. Soc, 1997, 80, 1619-23. 

FIG. 13.44 Typical tensile creep behaviour of a glassy amorphous polymer (a modified PMMA at 20 °C), where strain is plotted vs. log time, for various values of tensile stress. From bottom to top 10, 20, 30, 40, 50 and 60 MPa. From Haward (1973). Courtesy Chapmann Hall. 

FIG. 13.47 Small strain tensile creep curves of rigid PVC quenched from 90 °C (i.e. about 10 °C above Tg) to 40 °C and further kept at 40 0.1 °C for a period of 4 years. The different curves were measured for various values of time te elapsed after the quench. The master curve gives the result of a superposition by shifts that were almost horizontal the arrow indicates the shifting direction. The crosses refer to another sample quenched in the same way, but only measured for creep at a te of 1 day. From Struik (1977,1978). Courtesy of the author and of Elsevier Science Publishers. 

FIG. 13.48 Small-strain tensile creep of rigid PVC. Left short-time tests (t < 1000 s) at a te of 2 h after quenches from 90 °C to various temperatures (f/fe < 0.13). The master curve at 20 °C was obtained by time-temperature superposition (compare Section 13.4.8) the dashed curves indicate the master curves at other temperatures. Right, long-term tests (t = 2 x 106 s, fe = 1/2 h, t/te = 1100). The dashed lines are the master curves at 20 and 40 °C for a te of 1/2 h they were derived from the left-hand diagram. From Struik (1977,1978). Courtesy of the author and of Elsevier Science Publishers. 

Fig. 4.1 Tensile creep curves for siliconized silicon carbide (Carborundum KX01). Over most of the data range, these data can be represented by a constant creep rate there is a short primary creep stage, and almost no tertiary creep. The rupture strain decreases with increasing creep rate. The strain to failure, =1.5%, indicates brittle behavior even at low rates of creep detormation. Figure from Ref. 28.

Fig. 5.5 Effect of changing the elastic modulus ratio and constituent creep stress exponents on the total strain rate of a 1-D composite subjected to tensile creep loading.31 In both (a) and (b), the dashed lines represent the composite behavior, and the thin solid lines the constituent behavior. In the calculations, it was assumed that the creep load was applied instantaneously.

Fig. 5.8 Influence of initial loading rate on the 1200°C tensile creep life of 0° SCS-6 SiCf/HPSN composites crept in air at a nominal stress of 250 MPa. The creep curves include the elastic strain on loading. For each loading rate, duplicate tests were performed to provide a rough indication of the scatter in the results, (a) Creep load applied in 1000 s, and (b) creep load applied in 2.5 s. After Holmes et al.38...

A constant tensile-stress method is outlined in ISO 6252, in which a test specimen is exposed to a constant tensile force while immersed in a stress cracking agent so as to determine the time to rupture under a specified stress. This uniaxial test leads to the determination of the lifetime of the specimen with accuracy, but it is time consuming and requires complex equipment. Variations of this test include a tensile creep test that monitors the strain and a monotonic creep test that uses a constant stress rate instead of a fixed stress [1]. 

The first quantitative study of deformation mechanisms in ABS polymers was made by Bucknall and Drinkwater, who used accurate exten-someters to make simultaneous measurements of longitudinal and lateral strains during tensile creep tests (4). Volume strains calculated from these data were used to determine the extent of craze formation, and lateral strains were used to follow shear processes. Thus the tensile deformation was analyzed in terms of the two mechanisms, and the kinetics of each mechanism were studied separately. Bucknall and Drinkwater showed that both crazing and shear processes contribute significantly to the creep of Cycolac T—an ABS emulsion polymer—at room temperature and at relatively low stresses and strain rates. 

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