Rupture time

Plm = Larson-Miller parameter T = temperature, °R t = rupture time, hr... 

Finally, the rupture time follows from Equation A7 by setting H... 

Upon setting E - 0.1 and 7 - 0, we recover the characteristic rupture time listed in the main text. 

If the area under the vessel is provided with adequate drainage capability credit may also be taken for a reduced heat input due to the runoff of any flammable liquids producing the fire exposure. Usually drainage requirements to NFPA 30 (Flammable and Combustible Liquids Code), would have to be met, namely 1 percent to a 15.2 meter (50 ft.) radius. Published literature suggests that an uninsulated vessel rupture time could be increased 100% for a highly effective drainage system. 

Figure 12.1 Creep-rupture (time to failure plotted horizontally against applied hoop stress) of polyethylene pipes under pressure at different temperatures...

Fig. 7.27 Rupture time sequence of a carbon black agglomerate (R0 = 30 pm) in a styrene-cobutadiene rubber (SBR) in simple shear flow. The shear rate was 13.5 s 1 resulting in a shear stress of 130,000 Pa. [Reprinted by permission from V. Collin, Etude Rheo-optique des Mecanismes de Dispersion du Noir de Carbone dans des Elastomeres, Doctoral Dissertation, Ecole des Mines de Paris, Sophia, Antipolis, France (2004).]...

Alloy Formula Steady state creep rate (h-1) Rupture [time (h)] Creep rupture ductility (%)... 

In the calculation of the rupture time (the time required to achieve a contact between the surfaces of the two menisci), it is assumed that the particle occupies a symmetrical position with respect to the film surfaces. Fig. 9.8 shows the contact region between the film and particle, and gives also the symbols of the quantities used to calculate the rupture time. 

Fig. 9.8. Schematic presentation of parameters used to calculate the film rupture time.

To analyse bond breakage under steady loading, we take advantage of the enormous gap in time scale between the ultrafast Brownian diffusion (r 10 — 10 s) and the time frame of laboratory experiments ( 10 s to min). This means that the slowly increasing force in laboratory experiments is essentially stationary on the scale of the ultrafast kinetics. Thus, dissociation rate merely becomes a function of the instantaneous force and the distribution of rupture times can be described in the limit of large statistics by a first-order (Markov) process with time-dependent rate constants. As force rises above the thermal force scale, i.e. rj-t> k T/x, the forward transition... 

Figure 12.26 Double logarithmic plot showing the creep rupture time, tf, as a function of the applied stress, a, for poly(methyl methacrylate) at 24°C. Data obtained for (A) freshly quenched samples and (O) samples aged at 24°C for 5 years. (From Ref. 30.)...

Mechanisms of Single-Foam Film Stability. Soap bubbles and soap films have been the focus of scientific interest since the days of Hooke and Newton (2—9). The stability and structure of foams are determined primarily by the relative rate of coalescence of the dispersed gas bubbles (10). The process of coalescence in foams is controlled by the thinning and rupture of the foam films separating the air bubbles. Experimental observations suggest that the lifetime (stability) of foam films is determined primarily by the thinning time rather than by the rupture time. Hence, if the approaching bubbles have equal size, the process of coalescence can be split into three stages ... 

Jain and Ruckenstein (27) and Gumerman and Homsy (28) reported that surface rheological properties may also considerably stabilize a thin film by imparting a rigidity to liquid-film surfaces. The differences between estimated rupture times for films with mobile surfaces and immobile surfaces may also be very high. 

With a high enough stress, complete failure, or rupture, will be virtually instantaneous, while with suitably low stresses, in the absence of other effects, the time to failure will be elTecthely infinite. In between there are clearly levels of stress that will cause failure in measurable time. scales. By choice of loading, a creep test, without the need to measure strain, will yield stress rupture times. Such tests are not commonly carried out under normal atmospheric conditions, but where they are used, tension is the usual mode of stressing. 

Since experimental creep rupture times rarely exceed 10" h, it is necessary to extrapolate the data, using a straight line extension of the ductile rupture line on the log-log graph. The British Gas Specification for polyethylene pipe required the 50 year creep rupture stress cr o > 10 MPa. The International Standard ISO 9080 classifies polyethylene as PE80 if the lower confidence limit of the 50 year creep rupture strength lies between 8.0 and 9.9 MPa, and as PEIOO if it lies between 10.0 and 11.9 MPa. 

Fig. 14.2 shows creep rupture data for a particular MDPE, for ductile failure at a range of temperatures. An Arrhenius plot, of the logarithm of the creep rupture time versus the reciprocal of the absolute test temperature, is usually a straight line graph. This can be used to estimate the creep rupture times at lower temperatures. If there is ductile failure in the higher temperature tests, it is unlikely that brittle failure will occur at long times at low temperatures. 

As experience with creep rupture testing of polyolefins has been gained, elevated temperature tests have been used for quality control purposes, and standards set using such tests, i.e. the creep rupture time for pipes for natural gas distribution must exceed 170 h at 80 °C and a hoop stress of 3 MPa. Care must, however, be exercised if a polyethylene made by a different process is introduced, because the use temperature is close to 10 °C when the pipe is buried in the ground the slope of the Arrhenius plot varies between different polyethylenes. 

The parameter is a function of fiber rupture time (<) and temperature 7). Here D = log (Go) = 22 for the SiC and AI2O3 fibers in the high-temperature range where creep cavitation... 

Here Qr is the effective stress-dependent activation energy for fiber rupture T (kelvin) is the absolute temperature for the rupture test and tr (hours) is the fiber mpture time. Complete q-maps covering a wide range of temperatures and stresses are shown in Fig. 4a for two types of oxide fibers Nextel 610 and Nextel 720, and for three types of SiC fibers Hi-Nicalon, Sylramic, Sylramic-iBN. Here the curves represent best-fit averages of the fiber rupture times as measured for a 25 mm gauge length. 

Fig. 1), fairly consistent MG lines can still be constructed for the fibers based on their minimum creep rate at rupture. For example, Fig. 5 shows best-fit MG lines for average rupture time versus minimum creep rate (or mstantaneous rate at rupture) for four SiC fibers at 1200°C in air [19]. Also included are the MG results forthe Hi-Nicalon fiber tested at 1400°C in air. 

Tensile creep tests were conducted at 1000 and 1100 °C in air and in steam. Results are summarized in Table II, where creep strain accumulation and rupture time are shown for each creep stress ievel, test temperature and environment. Creep-rupture results from prior work obtained at 1200 °C are included in Table 11 for comparison. Creep curves obtained at 1000 and 1100 °C ate shown in Figs. 3 and 4, respectively. Creep curves from prior work obtained at 1200 °C are shown in Fig. 5. Note that at each temperature creep tests were conducted both in air and in steam. The time scale in Fig. 5(b) is reduced to clearly show the creep curves obtained at stress levels > 125 MPa. 

Fig. 13. Adherence of a glass ball (R = 5.042 cm) on a glass plate through castor oil. influence of rupture time (from ref. 48). ...

Pritchard, G. and Speake, S,D., Effects of temperature on stress rupture times in glass polyester composites. Composites, 19, 29-35, 1988. 

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