Crack Propagation Speed in the Drying Process of Paste

1. The mechanism of the effect of the frequency and form of trajectory of cyclic loading upon the speed of crack propagation was examined from the fracture mechanics viewpoint. 2. In steel 00Kh12N3D a reduction in sinusoidal loading frequency of 20 times (from 2000 to 100 cycles/min) leads to an increase of 1.6 times in the speed of crack development. 3. The speed of fatigue crack propagation in steel 00Kh12N3D is expressed by the following experimentally obtained relationship:C=1.61.10−10‡K3.07n−0.22 4. In steel 15Kh2NMFA the speed of crack growth does not depend upon the frequency of sinusoidal loading and is expressed by the relationshipC=3.86.10−11‡K3.16. 5. A reduction in the frequency of loading with a rectangular form of trajectory leads to a reduction in the speed of crack development in steels 00Kh12N3D and 15Kh2NMFA. 6. The speed of the fatigue crack is less with impact loading than with a sinusoidal form of load trajectory.

This paper deals with a non-destructive detection method of the generation time, the crack length and the propagation speed of fatigue crack in spot-welded joints under tensile-shear load.In case of spot-welded joints, fatigue cracks generate usually at the neighborhood of nugget tips of the weld interface, and propagate toward outer surfaces of the sheets. Accordingly, it is very difficult to observe and measure the crack length, consequently the generation time and the propagation speed of crack by using conventional measuring devices.Authors developed a non-destructive method of fatigue crack, which the generation time, the crack length and the propagation speed of fatigue crack can be quantitatively estimated by utilizing infomation obtained from the strain gages bonded on the electrode indentations of spot welds. Specimens used in this experiment are made of various kinds of thin steel sheets.Main conclusions obtained in this study are as follows:(1) The propagation length of fatigue crack is related with both mean strain and strain range of out-put of the strain gage, and the changing rate of strain range is specially useful for fatigue crack detection.(2) The generation time and the propagation speed of fatigue crack can be estimated easily from relationship between the number of cycles and the crack length, which is established in advance for an individual test piece.

Experimental observations on the effect of thermal treatment on the crack speed and mode I and II fracture toughness in brittle and ductile rocks

Study on dynamic fracture behavior of mode I crack under blasting loads

Fracture of brittle and ductile crystals in the generalized stress state. Strength and strain fracture criteria

Since the tensile fracture is governed by the load rate, the unstable crack fracture must be observed under the condition in which the load rate is smaller than crack speed. In this paper, the time-dependent stress caused by the compression wave emanated from the rupture section of a notched round bar is observed by the strain gauge method, while the problem of the same condition is theoretically analysed by postulating the crack growth models. The crack speed is determined from a comparison of the experimental result with theoretical result. Furthermore, the present paper experimentally distinguishes the effect of various factors, load rate and stress intensity factor, strain hardening, and area contraction of the material on the crack speed in tensile fracture, and suggests the experimental condition in observing the unstable crack fracture by the tensile test.

Analyses of the multiple cracking behaviour of brittle hollow cylinders under internal pressure

Crack propagation speed in ceramic during quenching

Following earlier observations of multiple micro-crack formation accompanying crack propagation under dynamic conditions, the question regarding the discrepancy between the ‘theoretically anticipated’ maximal crack (Rayleigh wave) speed and those observed typically in amorphous, isotropic solids is examined experimentally. It is shown that if the production of these multiple micro-cracks ahead of the main fracture is suppressed by fabricating a material possessing a thin uniform region of vanishing intrinsic (molecular/atomic) material strength, the crack speed is materially increased to the point of approaching the Rayleigh wave speed. Moreover, it is also shown that the presence of small discreet flaws of sufficient spatial density similarly ‘weakens’ the material to produce fracture speeds comparable to the Rayleigh wave speed. One deduces, therefore, that for a single crack front the linearized theory of elastodynamics correctly predicts the dynamic crack propagation behavior of a solid with sufficiently low material strength.

A Yoffe-type moving crack in one-dimensional hexagonal piezoelectric quasicrystals

Controlling factors for roughness increases on cleavage fracture surfaces and crack branching in polycrystalline steel

An earlier developed numerical model for three‐dimensional propagation in horizontally stratified fluid/elastic media [H. Schmidt and J. Glattetre, J. Acoust. Soc. Am. 78, 2105–2114 (1985)] has been modified to incorporate seismic moment representations for compact cracks of tensile, dip‐slip, and strike‐slip types. The applied global matrix approach first yields the depth‐dependent Green's function simultaneously in all layers for an arbitrary number of individual source depths. The frequency domain solution for a three‐dimensionally propagating crack is then determined by wavenumber integration over a spatial grid of superpositions of individual source contributions multiplied by the proper phase terms. Finally, the time domain solution over the spatial grid is obtained by simple Fourier synthesis. The present Fourier transform approach has the advantage that many crack propagation scenarios can be treated with only a single computer intensive solution of the wave equation. Once the depth‐dependent Green's function has been determined for the relevant crack type and depths, the field can be evaluated very efficiently by superposition for any crack propagation direction and speed. The developed model has been applied to theoretical analysis of the sound field produced in an Arctic environment by ice cracking, demonstrating the effect of cracking mechanisms, propagation speed as well as environmental parameters in general. [Work supported by ONR.]

The author has studied the relationship between the stress and the propagating speed of fatigue crack by analysing shelly pattern on fracture surface of shoulder fillet specimens obtained by the tests described in Part 3. This analysis was based upon the assumption of the stress σ on the cros section of fillet as follows : [numerical formula] where η : distance from neutral axis for bending C1, C2 : constants given by stress concentrating factor. As the results of above studies, it has been presumed that the propagating speed of fatigue crack may be reduced due to coaxing effect and strain harding at the tip of fatigue crack, where the speed is smaller than 0.2μ/c. When the speed exceed 0.2μ/c, it may be obtained from the following formula ; [numerical formula] where υσn : stress on edge line of fracture surface kg/mm2. υc : speed of fatigue crack propagation μ/c. σo : fatigue strength of specimen having fine crack kg/mm2. Φr : stress gradient on surface layer of cracking part kg/mm2/mm.

Evolution of Crack Propagation Rate in Notched Specimens Using XFEM Method under Bending Load Condition

Dynamic crack propagation and bifurcation phenomena are investigated analytically by utilizing the strain energy density fracture criterion in the framework of catastrophe theory. The effect of biaxial stress, loading imperfections (mixed-mode loading), Poisson's ratio, state of stress as well as crack tip propagation speed on the crack path directional stability is analyzed. Special crack path stability charts for (un)stably propagating cracks are obtained, and their connection with the experimentally recorded crack tip stress field is addressed. It is shown that a slight change of the normal stress acting parallel to a crack at its tip (crack-parallel stress) may be able to affect the crack surface roughening and/or branching velocity considerably. It is also indicated that under small tensile crack-parallel stress, the crack propagation is stable only when the crack propagation speed is less than about 30% of the relevant shear wave speed. The crack becomes unstable, and its surfaces roughen severely at a higher speed, and the crack bifurcates at the highest propagation speed, some 45% of the shear wave speed. It is suggested that superimposing mode-II (shear) loading will enhance the dynamic crack path stability while increasing crack propagation speed will reduce the stability of crack propagation. It is expected that under compressive crack-parallel stress no crack surface roughening will occur before the crack stably bifurcates.