Function Of Cycle Number Research Articles

Interference optical measurements during continuous and discontinuous crack propagation in fatigue loaded polymers

Continuous and discontinuous fatigue crack propagation behaviour have been investigated in PMMA and PVC, respectively, using the optical interference method. Thus craze zone sizes at the crack tip have been measured as functions of cycle number and relative stress intensity factor during crack propagation and between crack jumps. The results obtained give new and improved information on the material behaviour in the micro-region at the crack tip and also lead to modifications of a previously proposed model on crack and craze propagation behaviour during fatigue.

Thermal energy storage materials — a DSC study

A DSC investigation of a thermal energy storage, first-order phase change system has been carried out. The material is a borax—common salt modified sodium sulfate decahydrate system, distributed throughout a fumed silica supporting matrix. The qualitative features of the thermal behavior of the material can be explained in terms of the phase diagram of the sodium sulfate—water peritectic system, modified by the presence of a low-temperature eutectic. Fusion and recrystallization enthalpies have been measured as a function of cycle number. The thermal conversion efficiency of the system is high. Combining these data with specific heat measurements, the calculated storage capacity is in good agreement with published engineering information.

The effect of cyclic stress on dilatancy: Another look

Twelve granite and gabbro cylinders have been stress-cycled under confining pressures of 0.5, 1.5, and 5.0 kbar. No consistent trend appeared in the minimum stress required for dilatancy as a function of cycle number at the highest pressure, but at 1.5 kbar and below a decrease was indicated. Dilatant volumetric strain at differential stresses corresponding to the frictional strength of the rock persists at a value of a few parts in 104 at all confining pressures and is essentially unaffected by cycling.

Technical note: Characteristic of fatigue changes of hardened and soft annealed aluminum alloy of AIMg5 type

Investigations weremade to evaluate the basic fatigue properties of an aluminum alloy (A1Mg5) in tests made on samples of a thickness of 2 mm. in both the hardened and annealed conditions (Appendix I). Surface microscopic observations were used as the basic method of investigation. The loss of reserve of material plasticity was observed by estimating a hysteresis loop and measuring the strengthening rate as a function of cycle number (Fig. 1-4 and Appendix II). A generalized description of fatigue damage was deduced from the results of the investigations. Two basic periods of this process were identified: (1) a preliminary period of a generation of deformations characterized by an appearance of plastic displacements in some grains of major material parts, and (2) a permanent damage period of the appearance and spread of progressive microcracks (loss of cohesion) in material. The generation period is characterized by an appearance of considerable strengthening. In soft materials this increase was very intense particularly during the first 1000 cycles. In hardened materials the strengthening progress was much lower and was observed clearly