Factors Influencing Yield Stress
The stress at which yield occurs is dependent on both the rate of deformation (strain rate) and, more significantly, the temperature at which the deformation occurs. In general, the yield strength increases with strain rate and decreases with temperature. When the latter is not the case, the material is said to exhibit yield strength anomaly, which is typical for superalloys and leads to their use in applications requiring high strength at high temperatures.
Early work by Alder and Philips in 1954 found that the relationship between yield stress and strain rate (at constant temperature) was best described by a power law relationship of the form
where C is a constant and m is the strain rate sensitivity. The latter generally increases with temperature, and materials where m reaches a value greater than ~0.5 tend to exhibit super plastic behaviour.
Later, more complex equations were proposed that simultaneously dealt with both temperature and strain rate:
where α and A are constants and Z is the temperature-compensated strain-rate - often described by the Zener-Hollomon parameter:
where QHW is the activation energy for hot deformation and T is the absolute temperature.
Read more about this topic: Yield (engineering)
Famous quotes containing the words factors, influencing, yield and/or stress:
“The goal of every culture is to decay through over-civilization; the factors of decadence,—luxury, scepticism, weariness and superstition,—are constant. The civilization of one epoch becomes the manure of the next.”
—Cyril Connolly (1903–1974)
“A physician’s physiology has much the same relation to his power of healing as a cleric’s divinity has to his power of influencing conduct.”
—Samuel Butler (1835–1902)
“The face of nature and civilization in this our country is to a certain point a very sufficient literary field. But it will yield its secrets only to a really grasping imagination.... To write well and worthily of American things one need even more than elsewhere to be a master.”
—Henry James (1843–1916)
“A society which is clamoring for choice, which is filled with many articulate groups, each urging its own brand of salvation, its own variety of economic philosophy, will give each new generation no peace until all have chosen or gone under, unable to bear the conditions of choice. The stress is in our civilization.”
—Margaret Mead (1901–1978)