Damage cycle ratio

As to the damage progression during the application of a train or history of loads of equal amplitude cr, or Si the first hypothesis that comes to mind is that damage is related to the ratio between the number of applied cycles n,- and the allowable cycles Ni at that stress or strain amplitude, known as cycle ratio... 

Note that it is not done, at this time, any hypothesis about the time history of load spectra application that can be arbitrary. Fatigue failure occurs when this summation reaches the value of the critical damage D r for the particular material. Consider, for example, a block of three-step spectra of constant amplitude stress S > S2> Sj. Values of the respective cycle ratios n/V,-, with i = 1, 2, 3, can be deducted from the S-N diagram of the material, as shown in Fig. 8.16. Fatigue failure occurs when, as said, the total damage introduced by the three load spectra reaches the value of the critical damage... 

Grover, H.J. An observation concerning the cycle ratio in cumulative damage. ASTM STP 274, 120-124 (1960)... 

In a previous work (1), we established that the damage factor evolution is independent of load level and number of cycles to failure, provided the tests duration remains short enough (pure fatigue tests). Under these conditions, the damage factor gains continuously increasing values that depend only on the cycle ratio to failure (Fig.2) ... 

FIGURE 2 Damage factor in terms of cycle ratio to failure (1),... 

Although its applicability to repeated sequences of identical loading cycles is not ensured, recent advances assert its validity for random cyclic loading (4). For concrete subjected to stress reversals, we assume that the cycle ratio to failure accumulates separately for the compressive part of the cycle on the one hand, and for the tensile part on the other hand. In the latter case, we introduce a tensile damage factor increasing as the cumulative cycle ratio to failure. Thus, tensile failure occurs as soon as the tensile damage factor reaches unity. 

A Diesel cycle has a compression ratio of 18. Air-intake conditions (prior to compression) are 72°F and 14.7 psia, and the highest temperature in the cycle is limited to 2500° F to avoid damaging the engine block. Calculate (a) thermal efficiency, (b) net work, and (c) mean effective pressure (d) compare engine efficiency with that of a Carnot cycle engine operating between the same temperatures. 

Acetazolamide can produce severe lactic acidosis, with an increased lactaterpyruvate ratio, ketosis with a low beta-hydroxybutyrateracetoacetate ratio, and a urinary organic acid profile consistent with pyruvate carboxylase deficiency. The acquired enzymatic injury that results from inhibition of mitochondrial carbonic anhydrase V, which provides bicarbonate to pyruvate carboxylase, can damage the tricarboxylic acid cycle. 

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