Effect of the asymmetry factor on the nature of failure and deformation of the surface of fatigue fractures

Electron and x-ray fractography were used to examine fracture surfaces of 38KhN3MA structural steel produced in tests of cyclic cracking resistance with different asymmetry factors of the load cycle. The variation of the failure mechanism in crack propagation was determined: from striated to ductile in the fatigue zone of fractures, brittle, quasicleavage in the zone of uncontrolled failure, and back to ductile in the final fracture zone. The experiments show that the strain, on the fracture surface rapidly increases in the zone of uncontrolled failure. The minimum deformation on the surface, of all fractures corresponds to the same values of the range of the stress intensity factor and the crack growth rate. These values are similar to the coordinate of the points of intersection of the kinetic diagrams of fatigue failure of specimens tested at different asymmetry factors of the load cycle.Translated from Problemy Prochnosti, No. 5, pp. 56–61, May, 1990.The authors are grateful to V. G. Kudryavsho for discussing the experimental results.     

Product and process innovations: How are they defined? How are they quantified?

This paper considers the alternative meanings attributed to the terms product and process innovation, and demonstrates, on the basis of the SPRU database on innovations in Great Britain, how the total number of product and process innovations varies according to the definition adopted. Only 3.1% of the innovations monitored can be univocally labelled as either products or processes, whilst as many as 96.9% of them fall into a grey zone. The authors conclude that these terms, although useful tools of analysis, should be defined more precisely in the studies of the economics of technological change.     

Repeated plastic deformation as a cause of mechanical surface damage in fatigue, wear, fretting-fatigue, and rolling fatigue: A review

After studying statements bringing together essential features of the fatigue behaviour of metal structures in service, it is shown that the elementary phenomena of plastic deformation and fatigue crack propagation, which explain the fatigue behaviour of notched parts, also play an important role in other modes of damage of machinery parts. This is the case for mechanical surface damage under repeated bearing pressures in the absence of any apparent lateral sliding, for fretting-fatigue in which there is alternating lateral displacement of very low amplitude, and for false-brinelling marks in ball or roller bearings. It is also the case for unidirectional friction wear and for rolling damage, either with friction in gears or with very low friction in ball or roller bearings.     

The fatigue failure criterion of the mixed model

A new fatigue failure criterion is proposed in the view of the modern fracture theory in this paper. Under the fatigue loading of the fully mixed model for the body including the penetrable cracks. A general expression in quadrate approximation is established, which includes the important equations obtained by experience or the classical theories. The valid conditions of the expression are also presented.     

Static fatigue of rubbery polymers: statistical approach to the failure process

A phenomenological theory of a stochastic process was applied to the study of the failure mechanism of static fatigue of rubbery polymers. Static fatigue, namely, creep and stress relaxation experiments, were made on two specimens, pure vulcanizate and carbon-reinforced vulcanizate of acrylonitrile-butadiene rubber (NBR). The distributions of the lifetime were analysed by means of the function in the form of the Weibull distribution, which is an improvement of the stochastic theory proposed by Kawabataet al. The experiments proved the validity of the theory. Furthermore, the experimental results suggest that, in pure vulcanizate, a critical crack initiates and propagates unstably (random process at Weibull modulus of unity), and that, in carbon-reinforced vulcanizate, multi-cracks initiate and propagate stably due to the presence of carbon black particles (wear-out process at Weibull modulus of 1 to 3). The scattering in the lifetime of pure vulcanizate seems to reflect the inherent characteristics of the polymer.