Strength variability

The largest design dependent strength variable is material strength, either ultimate tensile strength (Su), uniaxial yield strength (Sy), shear yield strength (Ty) or some... 

A high shape faetor in the 2-parameter model suggests less strength variability. The Weibull model ean also be used to model duetile materials at low temperatures whieh exhibit brittle failure (Faires, 1965). (See Waterman and Ashby (1991) for a detailed diseussion on modelling brittle material strength.)... 

In fact, the strength variability of a given fiber-resin combination may be significantly different from the strength variability of a different combination of the same fiber with another resin system [35]. This is particularly the case when environmental and fatigue loading (long-term durability) are considered. 

Figure 6 The effect of increasing the ionic strength on the EOF mobility of Nucleosil C-18 wide-pore octadecylated silica stationary phases. Conditions column 55 cm (40 cm packed length) x 100 pm i.d. Eluent actonitrile-Tris (pH 9.0) (60 40, v/v) ionic strength variable. Temperature 25°C. Dectection 214 nm. Voltage 30 kV. (o) 7-pm Nucleosil 4000 A, ( ) 7-pm Nucleosil 500 A, (A) 5-pm Nucleosil 120 A, and ( ) 3-pm Spherisorb ODS-1, 80 A. (Reprinted with permission from Ref. 46, copyright 2001, with permission from Elsevier Science.)...

Medium dark Dark brown to medium brown High to medium wood content. Often large pieces Some gelification but not extensive Strength variable, hardiness and sp gr above average... 

Figure 6. Dielectric constant values corresponding to the peak values of tan 8 in the T plane (as an approximate relaxation strength variable) as a function of salt concentration (9) ZnClt (O) ZnBr2 (M) Znls.

The strength variability of ceramic materials can be evaluated using Weibull stahshc, which is based on the weakest-link theory, where the more severe flaw results in fracture propagation and determine the strength [69]. The Weibull two-parameter distribution is given by [14] ... 

Jiang, B. C., Smith, J. L., and Ayoub, M. M., Psychophysical Modelling of Manual Materials Handling Capacities Using Isoinertial Strength Variables, Human Factors, Vol. 28, No. 6, 1986,... 

The reliability computations for other distributions, such as exponential, lognormal, gamma, Wei-buU, and extreme value distributions, have also been developed (Kapur and Lamberson 1977). In addition, the reliability analysis has been generalized when the stress and strength variables follow a known stochastic process. The references cited in this subsection also contain simple design examples illustrating the use of the probabihstic approach to design. 

Houston SL, Houston WN, Anderson TW (1995) Moisture and strength variability in some Arizona subgrades. Transp Res Rec 1481 35... 

R.F. Cook, D.R. Clarke, Fracture stability, R-curves and strength variability, Acta Mater., 36 [3] 555-62 (1988)... 

U. Ramamurty, F. W. Zok, F. A. Leckie, and H. E. Deve, Strength variability in alumina fiber reinforced aluminum matrix composites, Acta Afater., 45 [11] 4603 613 (1997). 

The partial factor for steel reinforcement, covering resistance uncertainties, yield strength variability and deterioration effects, varies within the range from 1.15 to 1.35. 

Creep measurements of PRD 49 (PpBA) fibers at 65 °C and 150 °C exhibit logarithmic creep, as is also observed for PpPTA and PpBAT fibers at room temperature, and the creep rate increases with temperature [190]. Wu et al. determined Weibull parameters of the strength and lifetime distributions of PpPTA fibers at room and elevated temperatures [207]. They found that the mean filament strength (and Weibull scale parameter) varies inversely with temperature, while the strength variability (and Weibull modulus) remains practically constant over... 

The higher is m and the lower represents strength variability. Ve is the effective volume of the specimen and may be expressed as ... 

The lines are not completely linear one of the reasons may be the probability of the different distribution, amount and size of cracks. Specimens containing larger flaws will break or fail at lower stresses than those predicted. As indicated above, the higher the m, the lower the strength variability. 

A higher strength variability is foimd in ceramic fibers (such as alumina), which have a relatively low Weibull shape parameter. Typical Weibull parameters for commercial fibers are shown in Table 1. The statistical variability of bundles and composites is a function of the fiber variability but is generally lower than... 

R. Tandon, D.J. Green and R.F. Cook, Strength Variability in Brittle Materials with Stabilizing and Destabilizing Resistance Fields, Acta metall. 41 399 408 (1993). 

Manufacturers Comments Fast-curing and flexible with good aqueous Manufacturers Comments High-strength. Variable rate cure and ... 

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