Creep life time

Fig. 2b shows the variation of the time to fracture with the stress for the same specimens tested in Fig. 2a. The results for AZ 91 alloy and its composite demonstrate the creep life-times of the composite may be up to one order of magnitude longer than those for the monolithic alloy although this difference decreases with increasing applied stress so that ultimately there is very little difference at stresses >100 MPa. By contrast, the creep life of the QE 22 + Saffil composite is markedly shorter than that of the unreinforced alloy at stresses > 100 MPa. The presence of a reinforcement leads to a substantial decrease in the overall ductility of matrix alloy. Thus,...

The life-time of a component - its time-to failure, tf - is related to the rate at which it creeps. As a general rule ... 

Improvements in all processing steps, and quality of powders allow the increased use of refractive additives, e.g., rare earths which result in remarkable increases of creep resistance, strength and life time of Si3N4 ceramics (Figs. 30 and 31) [411-415, 420],... 

Figure 25 shows that, in the case of a stable crack-craze growth with breakage of fibrils in the midrib, the oldest part of a fibril (the part having carried the craze stress for the longest time) is just at the middle Hence, if the breakage is due to some additional creep phenomena, it must break in the midrib. A straightforward consequence is that the life-time tq of the fibril under a load cs may be easily defined as ... 

It has been shown that the life time in the creep process of rubbery polymers scatters largeley but obeys the specified statistical distribution which are introduced theoretically based on some assumptions. Two assumptions are made here that "one crack leads the body to failure" and "the v th crack leads the body to failure". The former assumption leads the exponential distribution of tg, and the latter the unimodal distribution when v>2. It has been explained from experiments that the distribution of tg for pure rubbers of vulcanized SBR and NR are the exponential, type and for filled systems the unimodal type. Theory introduced here can be applied not only to the creep failiire but also to the failure process varing stress level such as uniaxial extension with constant strain rate. It has been demonstrated that the distribution of Xg, the stretch ratio at breedc in the constant rate of extension, is well estimated by the theory substituting the parameters n and c which are obtained from creep failure experiment to eq(l9). 

Deca-bromodiphenyl ether, 471 Decay fungi, 412 Dechlorane Plus , 473 Deck boards, 207, 208, 215, 225 Catastrophic damage, 207 Commercial, 215 Flame spread, 208 Half-life time, 207 Higher density, 207 Ignition time, 208 Lower density, 207 Span rating, 225 Deckjoists, 288, 289 Deck Lok, 60 Deck surface, 21, 206 Temperature, 21, 206 Deflection and creep of composite deck boards, 291... 

Si-C-0 fibers are prone to creep above 1100°C (Figure 14). The creep rate does not reach steady state prior to failure during tensile tests performed in argon. It decreases continuously with time, indicating that primary (or logarithmic) creep dominates the entire creep life of the fibers. The strain-time curves obey the following classical law ... 

Creep life is limited by the rate of crack propagation. Critical crack size development depends on the stress dependence of the failure time. The time-to-failure at stresses under tension below a certain limit (82 MPa for alumina) is a consequence of an increase in failtrre strain at the crack tip. Basically, failure is... 

The extent of the probable damage and the remaining life time of the furnace tubes operating at the creep range may be assessed on the basis of material examinations, including replica techniques, and confirmed taking into account the service records and corrosion rates, according to Appendix E of the American Petroleum Institute s Reconunended Practice [8]. 

After most of the life time has passed, the creep rate strongly increases until final fracture ensues. In this region of tertiary creep (region III), massive inner damage occurs in the material as we will discuss in detail in section 11.3. This strongly reduces the load-bearing cross section and thus explains the strong increase of e. 

With a required life time of the shaft of 200 000 h, it is not sensible to wait for creep data measured experimentally at comparable times, for this would require about twenty years. To avoid this, data at shorter testing times, which are partially measured at temperatures beyond the service temperature, are extrapolated to larger service times. This is frequently done using the so-called Larson-Miller parameter, moti-... 

Creep strain/time curves have been determined for a range of SiCf/SiC type composites, " for various types of SiC fibre and for other CFCMCs. However, the faetors eontrolling the creep properties of different composites have usually been diseussed by reference to only a few standard parameters, such as the minimum creep rate (Sm), and the creep rupture life (tf). For this reason, the present projeet seeks to demonstrate that evidence derived from analyses of creep curve shape is relevant to interpretation of the detailed manner in which specific material variables influence strain aecumulation and damage evolution during tensile creep of CFCMCs. 

These methods determine tensile creep resistance (fracture stress) values as functions of service life (time to fracture) [162]. 

Corrosion creep of diecast Mg-5A1 and Mg-9Al-lZn alloys anodized by a 8p.m thick coating showed that anodic coating delays metal dissolution facilitating plastic deformation of the stressed metal, and for this reason alone increases the corrosion creep life of metals (Fig. 9.15). For instance, time-to-fracture of anodized Mg-5A1 alloy increases from 340 to 637 hours... 

Figore 17.10 (a) Fatigue life reduction factor as a function of creep holding time for different 316L(N) plates [32], (b) Creep-fatigue interaction diagram in RCC-MRx and ASME codes [21]. 

The above considerations on the dependence of t on the size of inherent flaws have been extended by various authors [13, 16—17] to a method of predicting the creep life of glassy polymers. It is assumed that the size of the largest intrinsic flaw can be determined from the breaking stress in short time loading according to Eq. (9.4) ... 

All-oxide CMCs based on alumina fibers and matrices are favorable materials for use at high temperature in oxidizing atmospheres. One possibility for CMCs is the application as combustion liner. As a major drawback oxide fibers show the lowest creep resistance of all ceramic fibers due to their predominant ionic bonds. Therefore, the knowledge of the creep behavior becomes important for construction and dimensioning of components undergoing creep deformation over the life time. 

Values in the Reduced Electrical Power Range/Options column represent ranges of values to evaluate reduced power operations. One JIMO level 2 requirement, from JPL Document 982-00115, Revision 2, Prometheus Project Multi-mission Project Derived Requirements , dated July 15,2005, is the project shall use a nuclear reactor whose thermal power output is adjustable to allow long-term operation at any reactor level down to the minimum of full power output required to support the minimum required electrical power. A reduced power mode may be used when electrical demand is reduced for long periods of time. The period of reduced electric demand may allow reactor power and/or temperature to be reduced, which allows fuel and clad temperature reduction (increased creep life) and burn up reduction (increased core life). The reduced power options are further discussed in Section 8, Operational Strategy . 

Generally speaking, when it comes to evaluating conventional materials, test samples for service life time estimation, quality, and safety analyses are collected. Data showing material characteristics are typically secured by means of optical and electron microscopes through destructive tests such as pull, compression, bending, torsion, creep, fatigue, impact, and corrosion. The same methods may be applied to a nanoscaled material. 

Extend the safe useful operation life of major HT/HP power plant items, subject to time-dependent creep and thermal fatigue damage, with benefits in terms of delayed costs for component replacement. 

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