Reduced-time composite curves

Fig. 3. Composite curve of tme stress at break at 40°C vs reduced time to break tjfor polypropylene fibers of three draw ratios (15) (—...

Effective corrosion inhibitors will increase the time to initiation of severe corrosion currents and detrimental concrete admixtures will reduce the time to initiation of severe corrosion. A composite curve from the ASTM round robin is given in Fig. 3. The integrated macrocell current (Coulombs) is a measurement of the total corrosion due to the macrocell. The test is not designed to evaluate materials such as silica fume that increase the resistance between the steel bars and significantly decrease chloride ingress. 

A damage calculation based upon this composit curve yielded a projected time to failure of 4.7 years. Correspondingly, an accounting for the initial, unintended overload cycles reduces this to 4.2 years. Comparison of this value... 

It should be noted again that the proportionality of moduli to Tp/ToPo (and of compliances to Topo/Tp) and the applicability of a single friction coefficient fo are more general principles than the detailed predictions of any specific theory, and these principles can be applied without assuming that the form of the time or frequency dependence follows any prescribed function. There have been some otha-schemes for constructing composite curves in which it was assumed at the outset that log Ot was a linear function of reciprocal absolute temperature (by analogy with the theory of rate processes ), and it has sometimes been erroneously believed that the method of reduced variables implies a specific form such as this for the temperature dependence. On the contrary, the shape of the curve in Fig. 11-4 is determined empirically from the data, although it may be useful to fit it subsequently to a suitable analytical expression (Section B below). 

An example of nonlinear stress relaxation is shown in Fig. 16-17, where the ratio of time-dependent tensile stress to tensile strain is plotted logarithmically against time for different strains for cellulose monofilaments. (In this case the structure is no doubt preoriented.) The differences can be interpreted as due to a decrease in relaxation times with increasing stress, and the curves can be combined approximately into a composite curve by plotting with reduced variables, with a shift factor Os which decreases very rapidly with increasing strain. It is doubtful, how-ever, 2 whether the latter can be entirely related to fractional free volume in crystalline polymers as it is for amorphous polymers (Section Cl of Chapter 15). 

The a—time curves for the oxidation reactions [60] of both nickel maleate (534—568 K) and nickel fumarate (548—583 K) were similar to those characteristic of each reactant in vacuum, though E values were reduced to 150 10 kJ mole-1. It was concluded that the distributions of nucleation sites and subsequent patterns of product development were little altered by the change in composition of product from Ni/C (and Ni3C) to NiO. This difference, however, significantly changed the temperature coefficient and stoichiometry of the interface processes, since all carbonaceous material in the reactants was converted to CO2. A constant value of E (150 kJ mole-1) was thus found for the oxidations of the four nickel salts studied [60], the maleate, fumarate, formate and malonate. 

The techniques of monomolecular rate theory easily transform measured reaction data into a form where we can analyze apparent kinetics and the effects of intracrystalline diffusion by the use of selectivity data. Time dependency has been eliminated. Since selectivity is extremely reproducible and is independent of short-term aging effects, the number of experimental runs is reduced while data reliability is maintained. For catalyst evaluation at any temperature, it is necessary to determine the equilibrium composition and the straight-line reaction path. With this information any catalyst can be evaluated at this temperature with simply the additional information from a curved-line reaction path. The approach used in the application of monomolecular rate theory to the xylene isomerization selectivity kinetics is as follows. Reference is made to the composition diagram, Figure 1. 

The HRR curves for six formulations were collected over 20min using the RCC (Figure 16.16). In a previous publication [36], we showed that the absolute pHRR values measured from the conventional cone and the RCC were not the same however, the trends as a function of different compositions were aligned. For this reason, the RCC is primarily used as a screening tool and it reduces the sample size and experiment time from 50 g and 45 min per sample to 0.5 g and 1.5 min per sample. This is an approximate order of magnitude improvement. 

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