Time dependent resistance degradation

Relatively stable substances that resist degradation at high temperatures (>140°C) are suitable candidates for dry heat sterilization. A 2-h exposure at 180°C or 45 min at 260° C kills spores as well as vegetative forms of micro-organisms. These exposure periods do not include the lag time from loading of the oven until sterilization temperature is reached. The lag time depends on the geometry and operating features of the oven and the characteristics of the load. 

In [9], it is suggested to explicitly represent considered degradation phenomena in a nominal bond graph of the system once a mathematical model for them is available. However, if a mathematical model of a degradation process derived from first principles is not available, if a nominal parameter in the constitutive equation of an element is then replaced by a function of time so that measured data is fitted and can be extrapolated into the future, a bond graph representation might be a problem. If a resistance becomes time-varying as of sometime point to then this may be simply captured by a nonlinear modulated resistor. If the nominal capacitance Co in the constitutive equation q t) = Co e(t) of a capacitor is replaced by a time-dependent capacitance C t) then... 

Long-term durability of adhesively bonded joints may require resistance to a number of individual or combined degradation modes, including environmental attack, fatigue and time-dependent failures. Time-dependent failure mechanisms are often characterized nsing either a strength approach, involving creep and creep-rupture tests, or a fracture approach, in which debond rate is determined. In creep-rupture tests, adhesive joints are subjected to... 

Fig. 18.11 (a) The time-dependent degradation of segment-in-series cells by Mitsubishi heavy industry, (b) Correlation of electrode reaction resistivity and the amount of accumulated chromium at the three phase boundaries... 

Environmental stress cracking resistance. Behaviour of poiy-carbonate in different chemicals by determination of the time-dependence of stress at constant strains. Polymer Degradation and Stability, 82 (2003), p. 451 -461... 

Service lifetime prediction of polymers and/or polymer based materials may be undertaken from different types of tests, such as creep behavior tests (linear and non-linear creep, physical aging, time-dependent plasticity), fatigue behavior tests (stress transfer and normalized life prediction models, empirical fatigue theories, fracture mechanics theory and strength degradation) and standard accelerated aging tests (chemical resistance, thermal stability, liquid absorption) [32]. 

Issues of importance include corrosion (not all materials employed are fully corrosion resistant), time-dependent creep of polymeric parts under high load, gravity creep of fluid lubricants, increased moisture absorbance or oxidation of dry lubricant films, and too much ground testing which can lead to premature lubricant degradation or particle generation. 

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