Tensile fatigue

Bunsell and Hearle (1971) showed that cyclic loading of nylon commonly gave tensile breaks after the same time as for creep rupture at the peak cyclic load. The exception was when the fibres were cycled from zero load to about 50% of break load. In these circumstances, the break showed a tail on one end, which is typically about five fibre diameters long and had stripped off the other end. Fig. 9a,b. The sequence of failure was first the development of a small transverse crack, which then turned and ran along the fibre at an angle of about 5° to the fibre axis. Fig. 9c. When the crack had crossed half the fibre, the stress on the residual cross-section caused final ductile rupture, Fig. 9d. 

A similar loading sequence caused failure in polyester fibres, but on some polyester fibres studied later by Oudet and Bunsell (1987) a low critical minimum load gave the same form of break. An important, and unexplained difference from nylon is that the axial cracks are closely parallel to the fibre axis. Consequently, the tails are extremely long. Fig. 9e,f. In one example, the crack had propagated beyond the final break zone, which was effectively a creep rupture failure from a central flaw. Fig. 9g. 

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Fig. 4. Tensile fatigue, the Monsanto fatigue-to-failure FTF test, for several elastomers D, FZ A, ethylene—acryflc O, nitrile (NBR) and, FVMQ.

Attempt to ensure that residual and operational tensile or oscillatory tensile (fatigue) stresses in components are kept moderate so far as reasonably practicable. 

Fig. 7-4 Example of long-term tensile fatigue curves.

It is noted, however, that both of the above CaF2 and Ti02 nanoceramics had some amount of porosity. This may account for an apparent soft behavior related to the superplastic deformation at low temperature, which does not yet reveal the plastic deformation characteristics in nanoceramics. Localized superplastic deformation under cyclic tensile fatigue tests was observed by Yan et al. on 3Y-TZP nanoceramics at room temperature [25], The micromechanism behind this phenomenon is argued to be essentially governed by grain-boundary diffusion. The contribution of dislocation slip might be in operation as a parallel mechanism to develop slip band-like microfeatures. 

It was shown that, after cyclic tensile fatigue fracture at room temperature in a narrow region within a couple of micrometers of each side of the fractured surfaces, the morphology of grain elongation appeared to be general. Viewed... 

J. W. Holmes, A Technique for Tensile Fatigue and Creep Testing of Fiber-Reinforced Ceramics, J. Comp. Mat., 26[6], 916-933 (1992). 

This combined analysis of AoA and Ar, therefore establishes that the main cracks that nucleate close to the contact edge correspond to predominantly tensile fatigue cracks. This conclusion remains valid whatever the contact condition (partial slip or gross slip). In addition, the distribution of within the contact plane is of interest (Fig. 15). The maximum amplitude... 

Tensile Fatigue - Progressive localized permanent structural change occurring in a material subjected to cyclic tensile stress that may culminate in cracks or complete fracture after a sufficient number of cycles. See also Fatigue, Flexural Fatigue. 

Battelle Memorial Institute [ ], Kaiser Aluminum and Chemical Corporation [-], Aluminum Company of America [ ], and Martin-Denver [ ] have all contributed to the slowly increasing amount of low-temperature fatigue testing information. The only true tensile fatigue testing at 20°K among these is being done by Martin and, to date, has been applied to metals only. 

Table I. Tensile Fatigue Tests on Epon 828/181 Glass Laminate...

The complex of equipment developed for tensile fatigue tests consists of four basic items. The first is the closed-loop liquid-hydrogen testing system of which, the cryostat, the second item, becomes an integral part. The modified fatigue machine and the instrumentation system form the third and fourth items. 

A tensile fatigue test is carried out on a polyethylene, with the strain varying from 0 to 1% at 300 Hz. Calculate the rate of energy dissipation per unit volume if E = 1.0 GPa, E" — 20 MPa, and hence the initial heating rate, if the product of density and specific heat is 1.2x 10 Jm- K- ... 

The following Table 4.19 shows a summary of available tensile fatigue strength values of thermoplastics ... 

Table 4.19 Alternate and swell tensile fatigue strength of thermoplastics materials. ...

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