EFFECT OF RIPPLE LOAD ON THE STRESS-CORROSION CRACKING IN STRUCTURAL STEELS
The presence of small ripple loading can, under certain circumstances, significantly reduce time-to-failure and threshold stress intensity for stress-corrosion cracking (SCC) of steels. A predictive framework for such ripple-loading effects (RLE) is developed from concepts and descriptors used in SCC and corrosion fatigue characterisation. The proposed framework is capable of defining critical conditions required for the occurrence of RLE and predicting time-to-failure curves. The agreement between the predicted and laboratory data is excellent.
Effects of Stress Wave Forms on Low Cycle Corrosion Fatigue
by Kichiro ENDO and Kenjiro KOMAI (Faculty of Engineering, Kyoto University, Kyoto) Studies have been made of the influence of stress rate in trapezoidal strain waves on low cycle corrosion fatigue strength. The electrode potential of the specimens has been observed against the saturated calomel electrode during the cycles. The following facts have been made clear; (1) The corrosion fatigue strength is affected by the stress wave forms. The durability of the material gets cut short by the longer strain time in which the strain ranges from zero to maximum, owing to the fact that the corrosion potential of the specimens is retarded and does not follow up to the equilibrium state of stress. (2) The effect similar to the effect made on the strain time is found to be made on the stress rate. In the range of lower stress, however, the stress rate has less effect because the maximum duration of time of stress becomes more effective than the strain time. (3) When lower stresses are applied, the strain time has its effect on the period of pitting formation and of crack propagation, while the effect on the latter is much smaller than on the former under higher stress range. (Received Apr. 22, 1964)
Electrophysiological Studies of Penticainide (CM 7857), a New Antiarrhythmic Agent, in Mammalian Myocardium
The intracellular electrophysiologic properties of a new antiarrhythmic substance, penticainide, were studied in isolated rabbit, dog, and guinea pig myocardial preparations superfused or perfused with oxygenated Tyrode's solution. “Therapeutic” concentrations of penticainide (1.5 to 3 x 10-5 M) had little effect on sinus node automaticity; sinoatrial conduction was slightly delayed. In atrial, Purkinje and ventricular fibers, amplitude, and maximal rate of rise of phase 0 (dV/dtmax) were decreased by penticainide; Purkinje-ventricle conduction velocity was depressed. Penticainide did not significantly modify action potential duration (APD) of rabbit atria and dog ventricle and reduced APD and effective refractory period (ERP) of dog Purkinje and guinea pig ventricular fibers. Penticainide reduced APD heterogeneity of Purkinje-ventricle junction with a preferential effect at the gate and decreased tension amplitude of perfused papillary muscle in dog heart. The effect of penticainide on dV/dtmax was voltage and rate dependent; the resting block was weak. Thus, penticainide is a class 1 antiarrhythmic agent with properties of class 1B agents such as APD reduction and properties of class 1C agents such as slow recovery kinetic of rate-dependent block.