From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Journal page discussing the dynamic fatigue life of rubber, including testing machinery and graphical data.
| Identifier | ExFiles\Box 178\2\ img017 | |
| Date | 15th January 1940 guessed | |
| 22 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 12, NO. 1 FIGURE 6 (Left) DeMATTIA FATIGUE MACHINE WITH RUBBER SAMPLES (Right) HIGH-SPEED DYNAMIC FATIGUE MACHINE, 0.25-INCH STROKE S R C plotted to cover most of the rubber stocks with which the authors worked. The ratio of fatigue life at a given temperature to that at 100° F.{Mr Friese} is plotted as ordinate along a logarithmic scale. The temperature of the rubber is plotted as abscissa. The ordinate of the graph, in other words, gives the factor by which the fatigue life of rubber vibrating at a rubber temperature of 100° F.{Mr Friese} must be multiplied in order to give the fatigue life which would result for rubber vibrating under the same oscillation conditions but at the rubber temperatures given along the abscissa. The temperature of the rubber under the imposed vibration has a pronounced effect on its fatigue life. Consider a sample vibrating under certain oscillation conditions and at a rubber temperature of 100° F.{Mr Friese} It will have a given fatigue life corresponding to the ratio =1. If an identical sample is vibrating under the same oscillation conditions but at a much higher rubber temperature, its fatigue life will be less because its deterioration results from several causes. There is first the effect which would result from merely the vibration at 100° F.{Mr Friese} Then there is the deterioration due to heat aging which would result from keeping the sample at this high temperature without vibration. The total deterioration in all probability is not the sum of these two parts. For example, there may be an interaction between temperature and oscillation which alters the amount of deterioration. Since the relative importance of these variables as well as their interaction cannot be given an evaluation applicable to all cases of rubber testing and compounding, the ratio for high temperatures is indicated as a broad band in Figure 9. Likewise, in the low-temperature region a broad band is also plotted. At the low temperatures the fatigue life depends, among other things, upon the chill characteristics of the rubber stock and the total time during which the rubber member is being fatigued at the low temperature. Linear Dynamic Fatigue Life under Constant Load Conditions Figure 5 (center) shows a high-speed constant-load fatigue machine which vibrates the rubber samples at 1800 cycles per minute. The oscillation stroke on this machine can be varied from 0.125 to 0.75 inch. In this type of testing the rubber samples, R, are loaded with dead weights, W. The top of the sample is vibrated up and down, the weights remaining stationary, owing to the mismatching of frequencies—that is, the frequency of the imposed vibration is very much greater than the natural mechanical frequencies of the weights sprung on the rubber samples. The distinction between this type of fatigue testing and the constant-strain fatigue testing is that in this case the rubber samples are allowed to drift, or extend in length with time, as they are being dynamically fatigued. However, the general nature of the fatigue life curves obtained under dead loading is similar to the fatigue life curves for constant strain oscillation; and the dynamic fatigue life under “constant load” fatigue conditions can be calculated from data obtained on constant-strain fatigue if changes in length accompanying dynamic drift are taken into account. Dynamic Fatigue Life of Rubber Vibrated in Shear Until now we have considered only the dynamic fatigue of rubber worked under linear strains. Similar dynamic fatigue relations have been found for rubber vibrated in shear. FIGURE 7. DYNAMIC FATIGUE LIFE CURVE FOR SMALL OSCILLATION STROKES GRAPH 1: TITLE: DYNAMIC FATIGUE LIFE CURVE FOR SMALL OSCILLATION STROKES Y-AXIS: DYNAMIC FATIGUE LIFE, AVERAGE NUMBER OF CYCLES FOR COMPLETE BREAK X-AXIS: % LINEAR STRAIN AT MINIMUM = (L_MIN - L_0) / L_0 * (100)% DATA: Curve shows a small peak at -100% strain labeled 'COMPRESSION BREAK ON FIRST CYCLE', then a large curve peaking around 200-250% strain. A note indicates 'CONSTANT OSCILLATION STROKE ≈ 25% = ¼ L₀'. Another note indicates 'ELONGATION BREAK ON FIRST CYCLE' at high strain values. FIGURE 8. EXPERIMENTAL DATA ON 50 DUROMETER STOCK GRAPH 2: TITLE: EXPERIMENTAL DATA ON 50 DUROMETER STOCK Y-AXIS: DYNAMIC FATIGUE LIFE (LOG SCALE), ranging from 1 to 1000, with labels for KILO CYCLES and MEGA CYCLES. X-AXIS: % MINIMUM STRAIN = (L_MIN - L_0) / L_0 * (100)% DATA: Multiple curves are plotted for different %ΔL values: 25%, 33%, 50%, 125%, 200%, 235%, 300%, 350%. | ||