Ratio Of Stress Intensity Factor Research Articles

Comparison of Compliance Results for the Wedge-Loaded Compact Specimen

Abstract Results of the ratio of stress intensity factor to crack-mouth displacement as a function of crack length are presented for the wedge-loaded compact specimen. Comparisons are made between experimental compliance results, numerical results from collocation methods, and deep-crack limit-solution results. Applications are for crack-arrest and stress-corrosion-cracking tests for metals and other materials under predominantly linear elastic conditions.

Quasistatic propagation of a normal fault: A fracture mechanics model

We have carried out boundary element calculations to simulate quasistatic propagation of a normal fault in the earth's crust under a horizontal tensile loading. Byerlee's frictional law is employed to describe the mechanical behavior of the fault surface. We hypothesize that in order for a normal fault to grow quasistatically, the mixed-mode effective shear stress intensity factor must exceed a threshold value (fracture toughness), a crustal material property. We suggest that the fault grows in a direction of local maximum shear stress. The direction of fault propagation thus depends on the ratio of tensile and shear stress intensity factors. A listric normal fault is likely to form in crustal material with a small shear fracture toughness. A listric normal fault is also more likely to form in crustal material with a high degree of plasticity. The propagation trajectory of an incrementally growing normal fault is examined. As the normal fault extends to a greater depth, the shear stress intensity factor drops, owing to an increase in fault surface friction. The equilibrium depth to which a normal fault will grow is controlled by the far field loading and the fracture mechanical property of the crustal material. The decrease of shear stress intensity with fault length also stabilizes the fault growth.

Effect of Stress Ratio on Crack Extension Rate of Fine-Grained Isotropic Nuclear Graphite

Effect of stress ratio on the crack extension rate da/dN was examined for an iso-tropic nuclear graphite IG-11, using tapered double cantilever beam specimens. Loads were applied to the specimens cyclically at a loading rate of 251 N/s in the load range where the stress ratio R range of 0∼0.8. Here R is defined as the ratio of the minimum stress intensity factor K min to the maximum stress intensity factor K max. The rate da/dN was measured optically using a comparator. Conclusions derived as 1. For a given value of R, crack extension rate da/dN can be expressed as da/dN = C(ΔK)n. here, ΔK is a stress intensity factor range, i.e. ΔK = Kmax − Kmin , and C and n are constants and strongly dependent on R value respectively.2. Threshold stress intensity factor range ΔKth which was defined as the point below which no crack extension more than 10 μm was observed after loadings of 105 cycles was related with R-values as ΔKth /ΔKtho = (1 − R)0.89, (ΔKtho = ΔKth at R = 0).

Effect of Stress Ratio on Crack Extension Rate of Fine-Grained Isotronic Nuclear Granhite

Effect of stress ratio on the crack extension rate da/dN was examined for an iso-tropic nuclear graphite IG-11, using tapered double cantilever beam specimens. Loads were applied to the specimens cyclically at a loading rate of 251 N/s in the load range where the stress ratio R range of 0∼0.8. Here R is defined as the ratio of the minimum stress intensity factor K min to the maximum stress intensity factor K max. The rate da/dN was measured optically using a comparator. Conclusions derived as 1. For a given value of R, crack extension rate da/dN can be expressed as da/dN = C(ΔK)n. here, ΔK is a stress intensity factor range, i.e. ΔK = Kmax − Kmin , and C and n are constants and strongly dependent on R value respectively. 2. Threshold stress intensity factor range ΔKth which was defined as the point below which no crack extension more than 10 μm was observed after loadings of 105 cycles was related with R-values as ΔKth /ΔKtho = (1 − R)0.89, (ΔKtho = ΔKth at R = 0).

Assessment of stress intensity factor and aspect ratio variability of surface cracks in bending plates

In this paper, a closed-form solution for the stress intensity factor ( K) of semielliptical surface cracks in plates subjected to pure bending, obtained by Newman and Raju using 3D finite elements, is critically evaluated. This solution is compared to a recommended solution by the Society of Experimental Stress Analysis (SESA). It is also compared to photoelastic K measurements. In addition, in this study the aspect-ratio variability of surface cracks under fatigue loading is predicted and compared with experimental data and also with the predictions of other empirical equations proposed by Porten, Kawahara and Kurihara, and lida. Finally, the usefulness of this equation for the prediction of fatigue life of surface cracks is evaluated by a comparison with experimental results.

Strength of ceramic materials containing small flaws

Ceramic strength values for different flaw sizes, grain sizes and notch radii are analyzed with a grain-fracture model. The critical stress-intensity factor for small flaws is lower than that for large cracks. Therefore, conventional LEFM is not applicable for estimating ceramic component strength. However, the relationships between the ratio of equivalent crack length and mean grain diameter, a e d ,and the ratio of critical stress-intensity factors for short and long cracks, K c K Ic ,are almost identical for various kinds of ceramic materials. This fact is well expressed by the model. Moreover, both the effect of grain diameter on plain specimen strength and that of notch-root radius on the notch-toughness value are explained well with the model utilizing the K Ic value of materials.

The effect of a single peak overload on fatigue crack propagation rate and crystallographic path in Fe-3%Si single crystals

The effect of a single peak overload on fatigue crack path and propagation rate in a Fe-3%Si single crystal was studied. Two specimen orientations were considered. For the same propagation rate (3 × 10 −6 mm/ cycle), the A specimen was in the threshold regime of the d a/d n- ΔK relationship and the B specimen was in the mid-growth rate regime. Related growth occurred in both types of specimen, when the ratio of the overload stress intensity factor, K ov , to K max due to baseline cycles was set to 2. The direction of crack growth in specimenA was not changed after the overload, but in specimen B, the crack path was changed from noncrystallographic to crystallographic, and produced a crystallographic step. The step was changed from noncrystallographic to crystallographic, and produced a crystallographic step. The step was approximately on the (001) plane. The fatigue crack growth increment associated with the retardation was found to be proportional to the square of K ov . These results suggest that the cause of retardation is not only the overload plastic zone size and decrease of ΔK efl but also the dislocation rearrangement at the crack front associated with plastic deformation caused by the overload.

Some geometrical observations on crack front profiles in PMMA double torsion specimens

The double torsion (DT) technique has proved its usefulness in fracture mechanical testing. Practical considerations make it preferable to other methods in many cases. Nevertheless, it is sometimes considered with reluctance, first because of its curved crack front and secondly because of a misunderstanding of the related problems. Experiments were conducted on polymethylmethacrylate (PMMA) to elucidate the effect of crack velocity and geometry. It was found that the crack front profile does not vary with crack velocity, whereas the geometry of the specimen has a strong influence on it. A simple model is developed, based on a strain fracture criterion. It describes quite well the experimental profiles of PMMA. Crack opening displacement, shear modulus, stress intensity factor and Poisson's ratio are shown to be of importance. The influence of the subcritical crack growth exponent could be effective for some materials but not for PMMA.

Transverse Flexure of a Semi-infinite Plate with a Step and a Crack at an Angular Corner

A semi-infinite plate with a step and a crack originating from its angular corner is analyzed as a thin plate bending problem. Taking uniform bending moment as the load condition, stress distributions are investigated. Stress intensity factors which are important in linear fracture mechanics are analytically calculated for various crack lengths. The influence of the step and the angle of the corner is investigated. The relation between stress intensity factor and Poisson's ratio is also investigated. A rational mapping function which is formed as a sum of fractional expressions and the complex variable method are used for the analysis. By using this mapping function, a closed solution is obtained which is exact for the shape represented by the rational mapping function. By using a rational mapping function of a sum of fractional expressions, the stress analysis for a comparatively arbitrary shape can be carried out.

Mixed‐Mode Fracture from Controlled Surface Flaws in Hot‐Pressed Si3N4

The room‐temperature mixed‐mode fracture of commercial hot‐pressed Si3N4 was examined using controlled surface flaws in 4‐point bending, oriented at various angles 6 with respect to the outer fiber tensile stress direction. Catastrophic fracture paths were non‐coplanar with the initial flaw plane, and the stress intensity factor ratio KI/KIC was < 1 for fracture in modes II and III. A non‐coplanar maximum strain‐energy release rate fracture criterion best described mixed‐mode fracture.

Analysis of Transverse Cracks in an Orthotropic Strip With Edge Stiffeners

The stress analysis of a central transverse crack in a stiffened orthotropic panel under tension is treated in this paper. The existing analytical techniques for the isotropic problem of a crack in an infinite strip, based on the well-known Schwarz alternating method for multiply connected domains, are applied to the present orthotropic problem. The ratio of stress-intensity factors for the finite plate to that of the infinite plate is obtained as a function of the crack length. The results are compared with the isotropic solution.

Fracture of cylindrical and spherical shells containing a crack

Fatigue and fracture of cylindrical and spherical shells containing a through crack and subjected to internal pressure or torsion are considered. The stress intensity factor ratios giving the effect of curvature are obtained as functions of a dimensionless shell parameter. By using the conventional plastic strip model the plastic zone size around the crack tip and the crack opening displacement are calculated. The calculated COD values are shown to be in good agreement with the experimental results. The fracture criterion of critical COD is verified by using the results of the burst tests in titanium and aluminum alloy cryogenic pressure vessels. Modified fatigue crack propagation models taking into account the bending effect in shells are introduced and are applied to the analysis of experimental data obtained from flat plates, and cylindrical shells under axial tension, internal pressure, and torsion. Finally, the paper includes the effect of humidity on the crack growth rate and the effect of load biaxiality on the rupture strength.

A circumferential crack in a cylindrical shell under torsion

The fully anti-symmetric problem for a cylindrical shell with a circumferential crack is considered. The solution of the problem is reduced to that of a system of singular integral equations of the first kind. As an example the torsion of the cylinder is discussed and membrane and bending components of the stress intensity factor ratio are given.