Fatigue testing diagram

Permanent structural changes that occur in a material subjected to fluctuating stress and strain, which cause decay of mechanical properties. See S-N diagram. The ability of a material to plastically deform before fracturing in constant strain amplitude and low-cycle fatigue tests. See S-N diagram. ... 

Plot of stress, S, vs. number of cycles, N, required to cause failure of similar specimens in fatigue test. Data for each curve on the S-N diagram are obtained by determining fatigue life of a number of specimens subjected to various amounts of fluctuating stress. The stress axis may represent stress amplitude, maximum stress, or minimum stress. A log scale is usually used, especially for the N-axis. 

The fatigue limit is the stress below which a material can be stressed cyclically for an infinite number of times without failure. The fatigue strength is the cyclic stress a material can withstand for a given number of cycles before failure. The S-N diagram is the plot of stress (S) against the number of cycles (N) required to cause failure of similar specimens in a fatigue test of exactly the same conditions. 

The fatigue resistance of nano- and microcomposites was also compared by Mallick and co-workers [46,56]. In particular, th performed stress-controlled tension-tension fatigue tests on PP nanocomposites reinforced with 5 wt% of organoclay and on 40 wt% talc-filled PP. As reported in Figure 9.15, the S-N diagram of nanocomposites was slightly better than that of neat PP and much higher than that of talc-filled composites. 

S-N diagram Plot of stress (S) against the number of cycles (N) required to cause failure of similar specimens in a fatigue test. 

Figure 1.10 Diagram of an eccentric machine for tensile and compressive oscillation fatigue tests.

The diagram in O Fig- 46.18 illustrates this case. Spot weld bonded H-samples (see O Fig. 46.15) start the fatigue test at a stress level of around 60 kN and end after six million cycles at around 30 kN, which is the starting level of the Metal Active Gas (MAG)-welded sample. 

For rotating-bending fatigue tests, schematic diagrams of (a) a testing apparatus, and (b) a test specimen. 

To ensure that blade stress levels are within the fatigue life requirements of the eompressor, it is usual praetiee to strain-gauge the blading on one or two prototype maehines, measure the stress levels, and generate a Campbell diagram showing the plotted test data. To measure data, an impeller ean also be mounted on a shaker table with a variable frequeney output (0-10,000 Hz). Aeeelerometers ean be mounted at various positions on the... 

The data on which Fig. 8.74 is based are for tests carried out in carbonate well-water. McAdam made the further interesting discovery that if mild steel were tested in condenser water and a similar graph constructed, the set of contours corresponded more closely to the right-hand side of Fig. 8.74, i.e. the behaviour of mild steel in condenser water was similar to that of Monel in carbonate water. The apparent universality of this diagram is an interesting observation, but it has not provoked a basic theory of corrosion fatigue. 

As for the epoxy polymers, a quantitative comparison of the contact fatigue behaviour was attempted on the basis of an estimate of the maximum tensile stress at the edge of the contact. The coefficient of friction of the copolymers increased as the tests proceeded, with a variation which was dependent upon the level of the normal loading. As a first approach, the value of //. at crack initiation was taken into account in the calculation of a . The results are reported in a S-N fatigue diagram giving the maximum applied tensile stress as a function of the number of cycles to crack initiation (Fig. 23). These data show a marked increase in the contact fatigue resistance of the GIM copolymers compared with the MIM material. 

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