scholarly journals Stress analysis of V-notches with and without cracks, with application to foreign object damage

2003 ◽  
Vol 38 (5) ◽  
pp. 429-441 ◽  
Author(s):  
D Nowell ◽  
D Dini ◽  
P Duó
Keyword(s):  
Stress Intensity ◽  
Stress Concentration ◽  
Fatigue Cracks ◽  
Leading Edge ◽  
Foreign Object ◽  
Foreign Object Damage ◽  
Hard Particles ◽  
Notch Stress ◽  
Concentration Factors ◽  
Stress Concentration Factors

Gas turbine engines can be subject to ingestion of small hard particles, leading to foreign object damage. This can take the form of sharp V-notches in the leading edge of blades and there is a need to predict the initiation and propagation behaviour of fatigue cracks growing from the base of the notch. The notch geometry is quite extreme and is not normally covered in standard references for notch stress concentration factors. Similarly, stress intensity factor solutions for this geometry are not widely available. This paper uses the dislocation density approach to solve the two-dimensional elastic problem of a V-notch with a radiused root. Stress concentration factors are found for the notch itself, and stress intensity factors are determined for cracks growing away from the notch for cases of applied and residual stress distributions. Comparisons are made with existing notch solutions from the literature.

Analysis of stress concentration factors for stepped plates based on a crack tip stress intensity approach

1996 ◽  
Vol 31 (3) ◽  
pp. 197-204 ◽  
Author(s):  
T G F Gray ◽  
F Tournery ◽  
J Spence
Keyword(s):  
Finite Element ◽  
Stress Intensity ◽  
Stress Concentration ◽  
Crack Tip ◽  
Finite Width ◽  
Sharp Corner ◽  
Wide Range ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Crack Tip Stress

The analytical equations given for stress concentration factors are based on the results of finite element analysis of stepped plates subject to uniaxial tension loading. The fillet radii at the stepped transitions were varied over a wide range, leading to elastic stress concentration factors between 1.1 and 8.3 (net stress basis). The parametric equations depend on the previously described concept of a ‘notch configuration factor’. This is similar to the crack configuration factor or compliance function used to modify the basic crack tip stress intensity solutions in the case of finite width or other problems. In the present case of the stepped plate, an energy approach was used to relate the sharp corner stress field to the corresponding sharp crack field, leading to a ‘sharp corner configuration factor’. This factor was then applied to the equation for the stress concentration factor at an elliptical hole in an infinite plate, to give a simple analytical expression for the stepped plate with a radiused fillet. The basic expression was refined further to improve the quality of fit, to an accuracy of 2 per cent with respect to the finite element models.

Stress Concentration Factors of Damaged FPSO Side Panels Under Cyclic Loads

2013 ◽  
Author(s):  
Ilson Pasqualino ◽  
Bianca Pinheiro ◽  
Carolina Ferreira
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Fatigue Cracks ◽  
Mechanical Damage ◽  
Element Model ◽  
Compression Load ◽  
Life Study ◽  
Concentration Factors ◽  
Residual Fatigue ◽  
Stress Concentration Factors

FPSO (floating production, storage and offloading) units can be subjected to mechanical damage in their side panels caused by collision with supply vessels. Even if the ultimate strength of the panel is not significantly affected by small damage, the stress concentration in the collided region may lead to the initiation of fatigue cracks, considering the long period of operation undergone by these vessels. The aim of this work is to evaluate stress concentration factors (SCFs) in damaged FPSO side panels and estimate their effect on the fatigue life through a theoretical study. A finite element model is developed to reproduce a supply vessel collision and evaluate resulting SCFs under in-plane compression load. A parametric study is carried out considering different damage magnitudes and the results obtained are used to develop an analytical expression to provide SCFs as a function of dimensions of damage and panel. SCFs provided by this expression could be used in a theoretical fatigue life study that can estimate the residual fatigue life of collided FPSO side panels and help to forewarn a fatigue failure under the event of an accidental collision.

Dynamic Anti-Plane Behavior of the Interaction Between a Crack and a Circular Cavity in a Piezoelectric Medium

2006 ◽  
Vol 324-325 ◽  
pp. 29-32 ◽  
Author(s):  
Tian Shu Song ◽  
Hong Liang Li ◽  
Jung Qiang Dong
Keyword(s):  
Stress Intensity ◽  
Stress Concentration ◽  
Stress Intensity Factors ◽  
Dynamic Stress ◽  
Piezoelectric Medium ◽  
Circular Cavity ◽  
Intensity Factors ◽  
Dynamic Stress Intensity Factors ◽  
Concentration Factors ◽  
Stress Concentration Factors

In this paper, the dynamic interaction is investigated theoretically between a crack and a circular cavity in an infinite piezoelectric medium under time-harmonic incident anti-plane shearing. The formulations are based on the method of complex variable and Green’s function. The resulting dynamic stress intensity factors at the crack’s tip and dynamic stress concentration factors at the cavity’s edge are obtained with crack-division technique. Numerical results are plotted to show how the frequencies of incident wave, the piezoelectric characteristic parameters of the material and the geometry of the crack and the circular cavity influence upon the dynamic stress intensity factors and dynamic stress concentration factors.

The Effect of Adhesive Layers on the Fracture of Laminated Structures

1978 ◽  
Vol 100 (1) ◽  
pp. 2-9 ◽  
Author(s):  
M. R. Gecit ◽  
F. Erdogan
Keyword(s):  
Stress Intensity ◽  
Stress Concentration ◽  
Plane Stress ◽  
Crack Problem ◽  
Adhesive Layer ◽  
Elastic Continuum ◽  
Adhesive Layers ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Laminated Structures

In this paper the effect of the thickness and the elastic properties of the adhesive layers in laminated structures is considered. The structure is assumed to consist of two sets of periodically arranged dissimilar layers which may contain cracks perpendicular to the interfaces. The crack problem is solved under the assumption of plane strain or generalized plane stress and by using two different models for the adhesive layers. In the first model the adhesive layer is approximated by a combination of tensile and shear springs. In the second the adhesive layer is considered to be an elastic continuum, hence involving no approximating assumptions. The results regarding the stress intensity and stress concentration factors obtained from these two models and that found by ignoring the adhesive layers are presented and some comparisons are made.

Determination of Allowable FOD Defects Sizes on the Surface of Gas-Turbine Engine Stator Parts Based on Stress-Concentration Factors

2014 ◽  
Author(s):  
Alexandr Pakhomenkov ◽  
Denis Slobodskoy
Keyword(s):  
Stress Concentration ◽  
Gas Turbine ◽  
Gas Turbine Engine ◽  
Operational Experience ◽  
Foreign Object ◽  
Turbine Engine ◽  
Periodic Inspection ◽  
Concentration Factors ◽  
Stress Concentration Factors

Requirements for reliability and safety of modern aircraft engines are constantly growing [1–2]. Among these requirements is periodic inspection of the engine condition and condition of its individual parts during operation, for the purpose of evaluation of the risk to operation. This is to ascertain possible damage to various engine parts in the course of operation and progressive wear. Damage can occur for a variety of reasons: ingestion of foreign matter in the engine gas path, operation in extreme and off-design conditions, wear, etc. To trace the engine parts condition and detect various damage on the engine parts, periodic inspection is provided. In case of any damage or deviations on parts, the question of their performance and possibility to break during operation are addressed. There are two ways of answering this question: 1 – experimental demonstration of the required strength of parts with damage; 2 – computational demonstration of the required strength of parts with damage. The first way requires a good deal of time and money for carrying out the experiments. It is efficient only with enough operational experience in typical parts with various surface damage. While developing a new engine (having no prototypes) it is more reasonable to use computational methods. To determine the allowable damage of gas-turbine engine parts, a special procedure has been developed. Its main principles consist of the following: - classification of the typical parts damage by foreign object ingestion; - determination of the stress concentration factors (Kt) due to damage for various defect sizes; - determination of strength factors of safety and life for various zones of parts without damage; - determination of Kt values with which minimum allowable values of strength safety factor and life are attained; - determination of allowable sizes of various types of damage for all zones of each part based on previously defined Kt dependencies on typical damage sizes. This methodology is proposed for determination of allowable damage on the surface of gas-turbine engines stator parts caused by foreign object ingestion in order to ensure the required reliability and safety; its experimental verification is foreseen for the future.

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