Point Of Maximum Depth Research Articles

Diving behaviour of gentoo penguins,Pygoscelis papua; factors keeping dive profiles in shape

The foraging ecology of seven Gentoo penguins,Pygoscelis papua, breeding at Ardley Island, Antarctica was studied using animal-attached devices which recorded swimming speed, heading and dive depth. Reconstruction of the foraging routes by vectorial analysis of the data indicated that at no time did the birds forage on the sea bed. Swimming speed was relatively constant at 1.7 m s-1, but rates of descent and ascent in the water column during dives increased with increasing maximum dive depth due to changes in descent and ascent angles. The amount of time spent discending and ascending in the water column increased with maximum dive depth as did the duration spent at the point of maximum depth. Dive profiles were essentially either U-shaped (flat-bottomed dives), or V-shaped (bounce dives). Development of a model based on simple probability theory indicated that the optimal dive profile to maximize the chances of prey acquisition depends on vertical prey distribution and on the visual capabilities of the birds with respect to descent and ascent angles.

Stress intensity factors for an inclined surface crack under biaxial stress state

A simplified analytical model for an inclined surface crack subjected to a system of biaxial stresses has been proposed and closed-form solutions for the mode I and mode III stress intensity factors at the maximum depth point of an inclined surface crack have been derived. The variation patterns of the mode I and mode III normalized stress intensity factors with angle of crack inclination and biaxial load ratio are given quantitatively.

CRACK GROWTH AND CLOSURE BEHAVIOUR OF SURFACE CRACKS UNDER AXIAL LOADING

Abstract— Crack growth and closure behaviour of surface cracks in 7075‐T6 aluminium alloy are investigated under axial loading, noting the difference in fatigue growth behaviour at the maximum crack depth point and at the surface intersection point and also with through‐thickness crack growth behaviour. The plane strain closure response at the point of maximum depth of a surface crack is monitored using an extensometer spanning the surface crack at the midpoint of its length. The plane stress closure at the surface intersection point is observed by multiple strain gauges placed at appropriate intervals ahead of the crack tip and continuously monitored without interrupting the fatigue test. The crack opening ratio is found to be about 10% greater at the maximum depth point than at the surface intersection point. Under axial loading, the difference in plane strain crack closure behaviour between the surface crack and the through‐thickness crack is relatively small. Growth rates of surface cracks can be well described by the effective stress intensity factor range based on the closure measurements made in this study. The growth rates in terms of the effective stress intensity factor range seem to be slightly slower in surface cracks than in through‐thickness cracks.

Simplified Estimation Equations of J-Integral for Surface Crack Under Bending Loads.

This paper presents the simplified estimation equations of J-integral at the surface and maximum depth point of a surface crack. These equations are based on finite element analysis with the surface cracked large plate specimen. The equations are expressed as the functions of crack length, crack depth, plate thickness and plate width for bending loads. The J-integral equations are used to develop the analysis given by finite element method for semielliptical surface cracks in finite elastic plastic plate subjected to bending loads. A wide range of configuration parameters was included in the equations. The ratios of crack depth to crack length ranged from 0 to 1 and the ratios of crack depth to plate thickness ranged from 0 to 0.75. The effects of plate width on the J-integral variations along the crack front were also included. Comparing the values of J-integral computed by the equations with those from the finite element analysis, the mean errors are within ±2.6 percent. The equations were used to predict patterns of surface crack propagation under bending fatigue loads for a SUS304 steel at 550°C. The curves of crack length, crack depth vs number of cycles predicted by the equations describe the experimental data well.

Oblique semi-elliptical surface crack in semi-infinite solid subjected to tension

This note is concerned with a semi-elliptical surface crack arbitrarily inclined to the free surface of a semi-infinite solid subjected to tension. The analysis is performed by the body force method, and the stress intensity factor at the maximum depth point on the crack front are given for various shapes and inclination angles of the crack. The numerical results are fitted to a reliable polynomial for convenience in engineering applications.

Monitoring of surface fatigue crack growth and crack tip closure behavior by the ultrasonic isoscanning technique.

The ultrasonic isoscanning technique using shear waves is employed to monitor the surface fatigue crack growth under a constant stress intensity factor range. It is shown that this technique has the potential to become an effective tool for the evaluation of quantitative surface fatigue crack growth characteristics. Not only can the three-dimensional crack profile be continuously measured with fairly high accuracy during fatigue crack growth testing, but this study indicates that the crack tip closure can be detected at the maximum depth point and near the surface. The surface regions under plane-stress conditions are closed for a greater portion of the fatigue load cycle than the maximum depth point under a predominantly plane-strain condition. The plane-strain crack tip opening load is smaller than the plane stress crack tip opening load.

Monitoring of surface fatigue crack growth and crack tip closure behavior by the ultrasonic isoscan technique.

The ultrasonic isoscan technique using shear waves is employed to monitor the surface fatigue crack growth under a constant stress istensity range. It is shown that this technique has the potential to become an effective tool for quantitative surface fatigue crack growth characteristics. Not only can the three dimensional crack profile be continuously measured with fairly high accuracy during fatigue testing, but this study indicates that the crack tip closure can be detected at the maximum depth point and near the surface. The surface regions under plane-stress conditions are closed for a greater portion of the fatigue load cycle than the maximum depth point under a predominantly plane-strain condition. The plane strain crack tip opening load is smaller than the plane stress crack tip opening load.

CLOSURE BEHAVIOUR OF SURFACE CRACKS

Abstract— The fatigue crack closure response was investigated for a surface crack in BS4360 50B structural steel, subjected to (1) constant amplitude loading and (2) constant amplitude loading interrupted by a single peak overload. A variety of compliance techniques was employed to determine closure behaviour. The crack mouth gauge measured the bulk, plane strain closure load, while the near tip strain gauge indicated the surface, plane stress closure response. For constant amplitude loading it was found that the surface regions of a surface crack are closed for a greater portion of the load cycle than the maximum depth point. A single peak overload caused different closure and growth rate transients at the surface of the thumbnail crack and at the maximum depth point. For growth rates above 10‐6 mm/cycle, such behaviour agrees with the response of a through crack when subjected to constant amplitude loading, and a single peak overload.

Three-dimensional elastic-plastic finite element analysis of small surface cracks

Three-dimensional, elastic and elastic-plastic finite element analysis of small surface cracks was performed. The elastic analysis is in good agreement with other solutions. For a round surface with a radius equal to six times the crack depth, the K at the surface is about 4% higher than the K for a flat surface. The results of the elastic-plastic analyses show a unique variation of the effective K (J-integral) along the crack front with a decrease in K at the surface due to a lack of plane strain constraint and an increase in the effective K at the maximum depth point with increasing plasticity. Similar behavior was observed for a semielliptical crack. Increasing the strain hardening exponent from 10 to 20 produced similar results with slightly higher effective A's for high applied strains. These results are useful in understanding the fracture behavior of small surface cracks.

On the front surface correction factor for semi-elliptical surface cracks

In general, the maximum SIF for the semi-elliptical cracks (a/c <I) occurs at the point of maximum depth (~=~/2). Probably that is why many investigators have dealt with this point in detail and a good number of solutions is available for F at ~=~/2 [5-10]. However, Chell [9] suggested a simple linear interpolation for general value of ~ considering that the value of F for a/c÷0 was independent of and equals that of F for ~ =~/2. But one should note that although this later result is evidently true for a/c=0 (case of an edge crack, @ ceases to have real significance and can be considered constant ~=~/2),F is not independent of ~ for a/c÷0 as we shall see from various results obtained by several investigators. The expression proposed by Chell would seem therefore to be incorrect. The purpose of this note therefore is to examine various solutions for F in the light of the more recent data [10-14] and to propose expressions for the edges ~=0 and ~=~/2 which correlate better with this data. Finally we shall propose an approximation for the general value of F(~, a / c ) .