Strain aging

A yield drop may be caused by mechanisms other than the dislocation multiplication of unpinning. In a system of dislocations, which may be or are pinned in position, instability is produced in the stress-strain curve. This instability takes the form of a negative slope, as observed in the yield drop. 

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Nitrogen in steel, insufficient aluminum to take up nitrogen (Al N2) strain-aging is aging intensified by cold working. 

From these considerations, Cottrell demonstrated that the rate at which solute atoms diffuse to dislocations and subsequently pin them in place is proportional to time2/3 (this time dependence is derived by an approximate method in Exercise 3.9). This provided the first quantifiable theory for the strain aging caused by solute pinning of dislocations [22]. 

A.H. Cottrell and B.A. Bilby. Dislocation theory of yielding and strain ageing of iron. Proc. Phys. Soc. A, 49 49-62, 1949. 

In the Encyclopedia of Twentieth Century Physics, R.W. Cahn describes A.H. Cottrell and B.A. Bilby s result that strain aging in an interstitial solid solution increases with time as t2/3 as the coming of age of the science of quantitative metallurgy [25]. Strain aging is a phenomenon that occurs when interstitial atoms diffuse to dislocations in a material and adhere to their cores and cause them to be immobilized. Especially remarkable is that the t2/3 relation was derived even before dislocations had been observed. 

Assume that the degree of the strain aging is proportional to the number of interstitials that reach the dislocation. 

Typical doses are in the range of 2.5-5 i.u. per mouse. Optimal dose varies by strain, age, and weight of the mouse. Extending the oocyte collection window beyond 14 h post-hCG may reduce fertilization rates and compromise embryo quality due to oocyte aging. 

Analyte levels are compared both to the concomitant control group (using appropriate statistical methods of the group size is large enough) and additionally to laboratory-specific reference intervals for the species, strain, age and sex in question. 

Today, MPTP represents the most important and most frequently used Parkinsonian toxin applied in animal models (Beal, 2001 Przedborski et al., 2001). The major advantage of the MPTP is that it directly causes a specific intoxication of dopaminergic structures and it induces in humans symptoms virtually identical to PD (Przedborski and Vila, 2003). The major drawback of MPTP is that the cell loss is strain-, age-, and gender-dependent in mice (Smeyne et al., 2005 Sundstrom et al., 1987). 

Ratsof any strain aged 10-12 wk, BALB/c mice aged 6-8 wk (5ee Notes 1 and 2). 

The level and activity of specific enzymes involved in biotransformation can differ depending on the species, strain, age, and sex of the test animal. For example, cats cannot carry out glucuronidation reactions, newborn rats have relatively low cytochrome P450 activity, and male rats are more sensitive to carbon tetrachloride toxicity than female rats. These differences are important to consider when interpreting the results from toxicological studies. The observation that age, sex, and genetics can significantly influence biotransformation reactions in animals raises the question of whether these characteristics also affect the biotransformation capacity of humans. 

Strain aging can also occur in susceptible steels by welding near a crack, causing embrittlement (called dynamic strain aging). For this and other reasons, many users require that plate material intended for pressure-containing components be scanned by ultrasonic inspection equipment for cracks and flaws near edges to be welded. 

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