Fatigue tests reverse bending

Fig. 7.16 Fatigue of Ce-TZP ceramics in static and cyclic (pulsating and reversed bending) tests a Ce-TZP-11, b Ce-TZP-IV, and c Ce-TZP-V. The applied stress values are given as statie stress Ss and maximum stress Smax for R = 0.2 and stress amplitude Sa for R = —1 Cf and

Reversed bending fatigue tests were made at 75 and -300 F for each of the three test materials selecting appropriate stress levels so that smooth S-N curves could be developed from 10 cycles to 10 cycles at 75 F and to 10" cycles at 300°F. With few exceptions two specimens were tested at each stress level. 

The appearance of the fatigue fractures in specimens tested at both 75 and -300 F are quite typical of those stressed in reversed bending (Fig. 16). All fractures disclosed the characteristic mother-of-pearl" or "oyster shell" appearance. The nucleus of the fracture almost invariably is at die surface. The bead-on specimens fractured invariably at the plate, weld bead interface at both test temperatures. This is expected, since there is a geometrical or mechanical notch created by the bead. TTie bead-off specimens fractured either in the weld deposit or heat-affected zone when tested at 75 F. The location of the fracture appears unrelated to stress level and may merely represent the statistical chance of failing in either one of those two locations. At -300 F, the bead-off specimens fractured in the weld, indicating that the metallurgical notch, created by the weld deposit and heat-affected zone, has become relatively unimportant at this low temperature. 

Fig. 4.23 Histogram showing fatigue life distribution of 57 specimens of 75S-T aluminum alloy tested in reversed bending at 206,7 MPa (30 ksi) [11]...

FIQ. 14 fretting fatigue test contguralions. (a) Cantilever beam reverse bending with single pads. 

Fig. 36 Results of reverse bending fatigue tests showing the effect of surface treatments on fatigue life of wmed...

Flex life n. Informally, the number of bending-reversal cycles causing a part to fail in a particular service. Most specifically, the number of cycles to failure of a test specimen repeatedly bent in a prescribed manner. The ASTM test for plastics is D 671. The specimen, molded or cut from sheet, is subjected to load reversal at 30 Hz at a predetermined level of outer-fiber stress until it either fails or the test is discontinued. By setting up different stresses for successive specimens, one can develop a graph of stress at failure versus number of cycles to failure (usually plotted on semi-logarithmic coordinates), i.e., the flex-life curve of fatigue curve. 

Glogowski and Castillo [37] used the reverse plate bending test to evaluate cast bronze alloys in paper mill white waters. Rectangular bars with holes drilled to simulate those in suction rolls were tested in accordance with TAPPI Technical Information Paper 0402-08 with simulated white water containing thiosulfate wicked into the holes [33], This test is better than the rotating beam test as a simulation of the fatigue that occurs at suction roU holes, since it incorporates a drilled hole geometry. 

K 7082 1993 Testing method for complete reversed plane bending fatigue of carbon fibre reinforced plastics... 

Figpre 8.20 Maximum stress (S) versus logarithm of the number of cycles to fatigue failure (N) for seven metal alloys. Curves were generated using rotating-bending and reversed-cycle tests. 

A cylindrical bar of 1045 steel having the S-N behavior shown in Figure 8.20 is subjected to rotating-bending tests with reversed-stress cycles (per Figure 8.18). If the bar diameter is 15.0 mm, determine the maximum cyclic load that may be applied to ensure that fatigue failure will not occur. Assume a factor of safety of 2.0 and that the distance between loadbearing points is 60.0 mm (0.0600 m). 

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