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In this presentation, fracture mechanisms caused by the combined effect of mechanical, electrical and environmental stresses in composite high voltage insulators are discussed. In particular, the effect called brittle fracture as well as damage/fracture mechanisms caused by improper crimping are demonstrated. Several experimental procedures developed to simulate the brittle fracture process under...
In this paper some peculiarities of fatigue crack growth are considered, ones referred to curves of a crack length vs. a number of cycles or the rate of propagation vs. the range of stress intensity factor, i.e. curves typical of tests with overloads applied in cycles. Difficulties with the model-based description (based on the Wheeler retardation model) of fatigue crack growth have been shown. The...
Present paper deals with the concept of prediction short and long fatigue crack growth in notched member using linear elastic fracture mechanics (LEFM) and invokes the stochastic nature of fatigue process. Probabilistic approach to modelling of crack growth in the depth of component links the previous authors' works which considered surface crack growth description in notched and unnotched samples...
Damage accumulation is evaluated according to a cumulative damage hypothesis, and the residual life is predicted with respect to a fatigue failure criterion. The estimation of cumulative damage under service loading is significantly influenced by a time loading history. The problem of the history effect can be converted to the problem of investigation of equivalent loading with non-zero stress/strain...
In the CAD and CAX design and technologies of modern engineering structures -equipment, machines and their parts, professional engineers are frequently called upon to solve problems of a complex character, in which dynamic loads produced by a number of factors and agents play an increasingly part. The phenomenon of fatigue crack closure is known to strongly influence fatigue crack growth rates, hence...
A number of effects of hydrogen both as gas and dissolved in metal on the fatigue crack growth in steels, especially at the near threshold load, has been analysed: 1) the effect of gas adsorption on the effective fatigue threshold [delta]Kth eff; 2) analysis of hydrogen effect on the fatigue crack growth in structural steels in dependence of its strength and test temperature; 3) application of fracture...
This presentation summarizes recent activities in the Center for Advanced Materials and Structures at the University of Denver toward the development of experimental and computational methodologies to facilitate the analyses of failure/fracture mechanisms and residual thermal stresses in unidirectional and woven graphite/PMR-15 composites subjected to biaxial shear dominated loads. Over the last three...
The present paper deals with the assessment of strength of a structure with a crack located between two different elastic materials subjected to extensional and in-plane non-uniform loading. Some problems concerned with the complex exponent of the stress field, oscillatory singularity range near the crack tip and interpretation of stress intensity factors KI and KII are discussed. New modified stress...
Corrosion fatigue emanating from semicircular notches is considered. The studies are focused on the relationship between stress field and electrochemistry in notches with the aim of understanding and prediction of the corrosion fatigue crack nucleation and growth behaviour from notch surface. It has been done for typical corrosive active system "low strength carbon steel - 3% NaCl solution",...
The paper concerns application of the energy parameter, being a sum of the elastic and plastic strain energy density in the critical plane, for description of experimental data obtained from the fatigue tests of 35NCD16 steel, GGG40 and GGG60 cast irons subjected to constant amplitude cyclic tension-compression, torsion and variable-amplitude tension-compression, torsion and combined tension with...
The classical methods of the life prediction and residual life evaluation of cyclically loaded materials and structures are briefly summarised. The principal mechanisms leading to the fatigue damage evolution in crystalline materials are analysed. The stages of fatigue damage evolution are given and their importance in fatigue life is discussed. The role of fatigue crack initiation in materials free...
Principles of the statistical approach to the stability of microtortuous cracks under the remote mode I loading are presented within the framework of linear elastic fracture mechanics. The basic idea of this approach lies in the suggestion that branching occurs only at those sites along the crack front, where the characteristic structural parameter (grain size, interparticle distance) is comparable...
The paper presents problems of fatigue life prediction and technical state assessment on the example of chosen materials and components working under mechanical and thermal loading. The following problems have been discussed: methods of mechanical behaviour investigation of materials in specific operating conditions, modelling the object from the point of view of solids mechanics using FEM, relationship...
As is well-known, the fatigue strength of materials decreases by increasing the specimen size. Such a decrease can be remarkable when very large structures are considered. An overview of experimental findings and theoretical studies on this phenomenon is presented. Then size effect in fatigue is explained by considering the fractal nature of the reacting cross sections of t structures, that is, the...
Some common fatigue criteria applicable to generic plane stress states under sinusoidal loading are reviewed with emphasis to those based on the so-called critical plane approach. Then a multiaxial high-cycle fatigue criterion recently proposed by the authors and based on the critical plane approach is discussed. Such a criterion can be applied to the case of sinusoidal plane stress states, and an...
The problem of evaluation and computer modelling of operational processes with both continuous and discontinuous nature is presented in the paper. We suppose the knowledge of statistical characteristics of the continuous component in the frame of correlation theory - frequency probability density function of the distribution and power spectral density or autocorrelation function respectively. A simulation...
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