The mechanisms of energy dissipation in the non-propagating fatigue cracks in metallic materials

The sources of heat generation in vibrothermography

“…Frictional rubbing between contacting asperities has generally been accepted as a source of heat generation in vibrothermography [1,8,9]. However, there is controversy with this claim since it has also been argued that frictional rubbing between crack faces is not responsible for heat generation or energy dissipation, but that crack heating is entirely due to interactions in the elastoplastic region of a crack [10]. Despite numerous finite element simulations and theoretical explanations, no definitive experimental validation of either theory has been presented and no single theory has been universally accepted to date to explain the source-or sources-of heat generation in vibrothermography.…”

Approximate analytical determination of vibrodiagnostic parameters of a cracked elastic body under subharmonic resonance. Part 1. Weak resonance

“…2 shows the functions À ( ) α calculated by formulas (12), (14) through (18) for the subharmonic resonance case with h ω = 0.0016 and 0.0032 which roughly correspond to the values of the logarithmic decrement of free vibrations δ = 0.01 and 0.02 (h ω δ π = 2 ). It is evident that the A values determined by formulas (15) are too high and those by formulas (17), (18) are too low in comparison to the initial values calculated by (12) and (14). The results of calculations by formulas (17) and (18) are fully coincident over the entire α range.…”

“…The ever increasing interest in studying vibrations of elastic bodies with a fatigue crack-like damage is motivated by the necessity of assessing any possible changes in the vibration status of structural elements during their long-term operation as well as by the need to develop efficient methods of vibrodiagnostics for such damage. The related research efforts are pursued along the following three main directions: (i) conventional, i.e., the determination of changes of natural frequencies of structural elements in the presence of cracks [1-7] and tracing a variation of the mode shape [8,9], (ii) determination of parameters of nonlinear effects of vibration processes, which are due to the presence of a closing or "breathing" crack [10][11][12][13][14], and (iii) assessment of the influence of a crack on the damping characteristics of elastic bodies [15][16][17][18].Establishing relations between a closing crack parameters and vibration parameters of an elastic body in crack-induced nonlinear resonances is still one of the less explored lines of inquiry as it is difficult to analytically solve the problem and set up a correct experiment.The previously performed analysis of available methods for calculating the forced vibrations of an elastic body with a closing crack [19] suggests that there are considerable difficulties associated with finding easy-to-use solutions. The resultant sets of complex constitutive equations did eventually require a numerical solution.…”

“…The ever increasing interest in studying vibrations of elastic bodies with a fatigue crack-like damage is motivated by the necessity of assessing any possible changes in the vibration status of structural elements during their long-term operation as well as by the need to develop efficient methods of vibrodiagnostics for such damage. The related research efforts are pursued along the following three main directions: (i) conventional, i.e., the determination of changes of natural frequencies of structural elements in the presence of cracks [1-7] and tracing a variation of the mode shape [8,9], (ii) determination of parameters of nonlinear effects of vibration processes, which are due to the presence of a closing or "breathing" crack [10][11][12][13][14], and (iii) assessment of the influence of a crack on the damping characteristics of elastic bodies [15][16][17][18].…”

The effect of damping and force application point on the non-linear dynamic behavior of a cracked beam at sub-and superresonance vibrations

“…The data o f direct experimental investigations [9][10][11][12][13] attest that the fatigue crack growth is accompanied by a considerable increase o f damping characteristic of cracked specimens. Consequently, the determination o f the relationship between the crack parameters and non-linear effects must be realized while taking into account the change of damping in a vibrating system, rather than assuming constant damping which has been the case in the past; if the increase in damping is neglected, the prediction of damage magnitude will be in error.…”