Stress Concentration at Notches

510 Pages·2017·12.67 MB·English

by  Mykhaylo P. Savruk

Mykhaylo P. Savruk · Andrzej Kazberuk
Stress
Concentration
at Notches
Stress Concentration at Notches
Mykhaylo P. Savruk Andrzej Kazberuk
(cid:129)
Stress Concentration
at Notches
123
MykhayloP. Savruk Andrzej Kazberuk
Bialystok University of Technology Bialystok University of Technology
Bialystok Bialystok
Poland Poland
and
Karpenko Physico-Mechanical Institute
ofthe National Academy of Sciences
ofUkraine
Lviv
Ukraine
ISBN978-3-319-44554-0 ISBN978-3-319-44555-7 (eBook)
DOI 10.1007/978-3-319-44555-7
LibraryofCongressControlNumber:2016948284
©SpringerInternationalPublishingSwitzerland2017
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Preface
Studies of stress and displacement fields in solids with crack-like defects play the
key role in fracture mechanics. Such defects include both cracks or thin notches
themselves and sharp V-shaped notches, which originate infinite stresses in their
tips in the frames of linearelasticity theory, aswellas rounded notches with small
radiioftipcurvature.Inthetipsofsuchnotches,evensmallloadsgeneratestresses
higher than the ultimate strength of material that precludes application of classical
criteria to the estimation of carrying capacity of structural members. To date,
solution schemes for fracture mechanics problems are best developed for solid
bodieswithcracks.FractureproblemsforsolidbodieswithsharpV-shapednotches
are studied to a much lesser extent. This situation can be explained by analytical
difficulties arising in solving problems of elasticity theory for bodies with rounded
notches.Tosolveproblemsofsuchclassstartingfromdataonstressconcentration
intheroundednotchtipwithasignificantradiusofcurvature,approximatemethods
are therefore of great importance. To find a solution, one must know how stress
concentration factor for rounded notch tip with a small radius of curvature
asymptotically depends on stress intensity factor for similar sharp stress concen-
trator. The authors had obtained such dependencies by solving singular integral
equations that describe the singular boundary value problem of semi-infinite
rounded V-shaped notch in elastic isotropic or orthotropic plane under ordinary
boundary conditions, and assuming the respective asymptotic behavior of stress
fieldatinfinity.Obtainedsolutionsdemonstratedtheasymptoticbehaviorforfinite
notched bodies, i.e., the smaller relative radius of curvature the notch tip has, the
more precise they are. Based on the developed unified approach to determining
stress concentrations near sharp or rounded V-shaped notches in elastic bodies,
stressconcentrationfactorsnearroundedV-shapednotcheswerederivedandstress
intensity factors for respective sharp V-shaped notches were found using a limit
transition. The approximating functions were built for stress concentration factors
near a rounded notch with arbitrary tip curvatureradiusand stress intensity factors
for sharp notches in specimens of different configurations. Along with original
achievementsofauthors,thebookcontainsmostestablishedresultsfromtheworld
literature in the field. The book is partially based on translated Ukrainian edition
v
vi Preface
entitled ‘Stress Concentration in Solid Bodies with Notches’ by M.P. Savruk and
A. Kazberuk issued in 2012 by the SPOLOM Publishing House, Lviv, Ukraine.
Presenteditioncontainsextrachaptersconcerningstressconcentrationnearnotches
in anisotropic bodies. The book consists of 12 Chapters.
Chapter 1 outlines the method of singular integral equations in application to
two-dimensional problems of elasticity theory for multiply connected regions with
holes and/or cracks. Basics of quadrature method for numerical solution of the
singular integral equations along either open or closed contours are considered.
Chapter 2 presents analysis of stress fields in elastic plane with a semi-infinite
notch under condition either of plane stress state or plane strain state. Well-known
boundaryvalueproblemsolutionsforeigenvaluesofawedgeintheplaneelasticity
theory are considered at first. Then the same solutions are constructed for the
semi-infiniteroundedV-shapednotchandtherelationbetweenstressconcentration
and stress intensity factors in elastic bodies with rounded or sharp V-notches have
been established.
Chapter3isdevotedforthesolutionstoelasticityproblemforaplaneweakened
by a sharp or rounded V-notch with edge cracks propagating from the notch tip.
TherelationshipbetweenstressintensityfactorsinthesharptipofV-notchandthe
crack tip has been derived.
FracturecriteriafornotchedsolidbodiesarediscussedintheChap.4.Themost
attentionhereisfocusedonthedeformationcriterion.Themodelofplasticitybands
in fracture mechanics was adopted as a basis. Under this model, the solutions to
elastic–plastic problems for a plane with sharp or rounded V-shaped notches have
been obtained.
Chapter 5 comprises results of studying stress concentration around the curvi-
linear openings in an elastic plane. A well-known analytical solution for the
ellipticalholeispresentedanddiscussed.Thelimittransitiontotheparabolicnotch
is performed. Numerical values of stress concentration factors in the tips of a slot,
oval, or rectangular openings with rounded vertices are calculated by solving
respectivesingularintegralequations.Usingthelimittransitiontozerotiprounding
radius, we derived stress intensity factors for respective sharp-angled holes.
Chapter 6 proceeds with the periodic elasticity theory problem for a plane
weakened by an infinite row of closely spaced identical curvilinear holes. Stress
concentrationfactorsinthetipsofbilateralparabolicorroundedV-shapednotches
were found for the limit case of infinitesimal holes spacing. These results are
comparedwithknownexpressionsforhyperbolicnotches.Usingthelimittransition
the solution for bilateral sharp V-shaped notches was derived.
Edgenotchesinelastichalf-planearestudiedintheChap.7.Analysisisgivento
single sharp or rounded V-shaped notches as well as periodic systems of such
notches. A solution to periodic elasticity theory problem for a half-plane with
sinusoidalboundaryispresented.Thecaseofedgenotchwithacrackgrowingfrom
its tip is included as well.
In Chap. 8, we quote stress concentration factors and stress intensity factors for
rectangularspecimenswithedgeroundedorsharpV-shapednotches.Unilateraland
Preface vii
bilateraledgenotchesareincluded.WidelyknowninterpolationNeuberformulafor
stress concentration factors is generalized to sharp and rounded V-shaped notches.
Chapter9isdevotedtothediscspecimenswithnotches.Calculationsweremade
for tensile disc specimen with edge U-shaped notch either without crack or with
crack growing from the notch tip. Analysis was made also for compression disc
specimens with the slots or rhombic holes. The solution was obtained for
ring-shaped specimens with inner edge U-shaped notches as well.
Antiplane deformation of elastic bodies with notches or cracks is studied in the
Chap. 10. The elastic problem solution for eigenvalues of a semi-infinite rounded
V-notchintheantiplanetheoryofelasticitywasconstructed.Basedonthissolution,
the relation between stress concentration factor and stress intensity factor for
rounded or sharp V-shaped notches under longitudinal shear had been established.
The longitudinal shear of elastic wedge with cracks or notches was analyzed.
Elastic–plastic interaction of sharp V-notch with a circular hole was examined.
Solutions were found for stress concentration near curvilinear holes (including
narrow slot, oval, rhombic, and rectangular holes) with either sharp or rounded
vertices under antiplane deformation.
Chapter 11 covers results of studying stress concentration near notches in an
anisotropicbody.Themethodofsingularintegralequationsinapplicationtoplane
anisotropicelasticityproblemsispresented.Basedonknownclosedformsolutions
toproblemofanisotropicplanewithellipticalholeundertension,stressdistribution
in the plane with stress-free parabolic notch is determined for the case when the
stress field is asymptotically given at infinity through the stress intensity factor in
the tip of respective semi-infinite crack. A solution to plane eigenproblem for an
orthotropic wedge with the bisecting line parallel to orthotropy axis is ensured.
Usingmethodofsingularintegralequations,thesimilarsolutionwasobtainedfora
rounded V-shaped notch in the orthotropic plane. The relation between stress
concentrationfactorandstressintensityfactorinorthotropicplanewithroundedor
sharp V-shaped notches was established.
Chapter 12 concerns with studying stress concentration near notches in
quasi-orthotropicbodies,thatis,bodieswiththespecialtypeoforthotropywhenthe
characteristic equation has multiple roots. Basic relationships of plane elasticity
theory for such media are presented and singular integral equations of first basic
problemoftheoryofelasticityforaregioncontainingcurvilinearcracksarestated.
Solutions for eigenvalues of a quasi-orthotropic wedge were obtained.
Correspondingsolutionsforquasi-orthotropicplanewitharoundedV-shapednotch
were constructed. The relation between stress concentration factor and stress
intensityfactorinquasi-orthotropicplane with rounded orsharp V-shaped notches
had been established. On this basis, the stress intensity factors in V-shaped tip of
two-sectional kinked crack using the superposition technique were derived.
The authors gratefully acknowledge the funding by National Science Centre
(Poland) under the project 2011/03/B/ST8/06456.
Bialystok, Poland; Lviv, Ukraine Mykhaylo P. Savruk
Bialystok, Poland, November 2015 Andrzej Kazberuk
Contents
1 Method of Singular Integral Equations in Application to
Problems of the Theory of Elasticity .... .... .... .... ..... .... 1
1.1 Basic Relationships of the Plane Theory of Elasticity..... .... 2
1.1.1 Basic Equations.. .... .... .... .... .... ..... .... 2
1.1.2 Complex Representation of General Solution
for Equations of Plane Theory of Elasticity. ..... .... 5
1.2 System of Curvilinear Cracks in Elastic Plane . .... ..... .... 8
1.2.1 Selected Information Concerning the Theory
of Analytical Functions.... .... .... .... ..... .... 8
1.2.2 Single Curvilinear Crack... .... .... .... ..... .... 12
1.2.3 System of Curvilinear Cracks ... .... .... ..... .... 16
1.3 System of Curvilinear Holes and Cracks in Elastic Body.. .... 18
1.3.1 Multiply Connected Region with Holes.... ..... .... 18
1.3.2 Multiply Connected Region with Holes and Cracks ... 21
1.4 Numerical Solution of Singular Integral Equations Using
Quadrature Method. ..... .... .... .... .... .... ..... .... 24
1.4.1 Quadrature Formulas.. .... .... .... .... ..... .... 24
1.4.2 Integral Equation on an Open Contour .... ..... .... 33
1.4.3 Integral Equation on a Closed Contour.... ..... .... 43
References. .... .... .... ..... .... .... .... .... .... ..... .... 51
2 Stress Distribution in Elastic Plane with a Semi-infinite Notch .... 57
2.1 Methods for Stress Analysis in Notched Bodies.... ..... .... 57
2.2 Eigensolutions of Elasticity Theory Plane Problem
for Wedge.... .... ..... .... .... .... .... .... ..... .... 60
2.2.1 Characteristic Equations ... .... .... .... ..... .... 60
2.2.2 Stress Intensity Factors in V-Notch Tip.... ..... .... 63
2.2.3 Constructing General Solution Using
Eigenfunctions... .... .... .... .... .... ..... .... 68
ix
x Contents
2.3 Semi-infinite Curvilinear Notches in Elastic Plane .. ..... .... 70
2.3.1 Parabolic Notch.. .... .... .... .... .... ..... .... 70
2.3.2 Hyperbolic Notch .... .... .... .... .... ..... .... 75
2.3.3 Curvilinear Notch of Special Shape... .... ..... .... 78
2.4 Rounded V-Notch Under Symmetrical Loading.... ..... .... 82
2.4.1 Problem Definition and Reduction to Singular
Integral Equation. .... .... .... .... .... ..... .... 82
2.4.2 Symmetrical Stress Distribution in Plane with
Rounded V-Notch.... .... .... .... .... ..... .... 88
2.5 Rounded V-Notch Under Mixed Loading. .... .... ..... .... 92
2.5.1 Antisymmetric Stress Distribution.... .... ..... .... 92
2.5.2 Complex-Stressed State.... .... .... .... ..... .... 98
References. .... .... .... ..... .... .... .... .... .... ..... .... 102
3 Elastic Plane with Semi-infinite Notch and Cracks. .... ..... .... 113
3.1 Elastic Wedge with Edge Crack at Notch Tip . .... ..... .... 113
3.1.1 Solutions Obtained Using Wiener–Hopf Method.. .... 114
3.1.2 Approximate Closed-Form Solution
for Symmetrical Loading... .... .... .... ..... .... 118
3.2 Edge Crack System in Semi-infinite Rounded V-Notch Tip.... 123
3.2.1 Reduction of Problem to Singular Integral
Equations.. ..... .... .... .... .... .... ..... .... 123
3.2.2 Numerical Solution of Singular Integral Equations .... 125
3.3 Symmetrical Edge Crack in Rounded V-Notch Tip . ..... .... 128
3.4 Two Symmetrical Edge Cracks in Rounded V-Notch Tip . .... 130
References. .... .... .... ..... .... .... .... .... .... ..... .... 134
4 Deformation Fracture Criterion for Bodies with Notches..... .... 137
4.1 Fracture Criteria for Notched Solid Bodies.... .... ..... .... 137
4.2 Model of Plasticity Bands in Fracture Mechanics... ..... .... 140
4.2.1 Plane Stress State .... .... .... .... .... ..... .... 141
4.2.2 Plane Strain State .... .... .... .... .... ..... .... 145
4.3 Infinite Wedge with Plasticity Bands .... .... .... ..... .... 149
4.3.1 Plane Stress State .... .... .... .... .... ..... .... 150
4.3.2 Plane Strain State .... .... .... .... .... ..... .... 154
4.4 Plasticity Band Near Rounded V-Notch.. .... .... ..... .... 158
4.5 Two Plasticity Bands Near Rounded V-Notch . .... ..... .... 163
References. .... .... .... ..... .... .... .... .... .... ..... .... 170
5 Stress Concentration Near Hole in Elastic Plane .. .... ..... .... 181
5.1 Elliptical Hole. .... ..... .... .... .... .... .... ..... .... 181
5.1.1 Stress Concentration Near Elliptical Hole .. ..... .... 182
5.1.2 Limit Transition to Parabolic Notch .. .... ..... .... 184
5.1.3 Stress Distribution Around Notch Tip. .... ..... .... 186
Contents xi
5.2 Oval Hole.... .... ..... .... .... .... .... .... ..... .... 191
5.2.1 Stress Concentration Near Narrow Slot.... ..... .... 191
5.2.2 Stress Concentration Near Oval Hole . .... ..... .... 196
5.2.3 Limit Transition to Two-Tip Lens-Like Hole .... .... 197
5.3 Rhombic Hole .... ..... .... .... .... .... .... ..... .... 201
5.3.1 Stress Concentration Near Rhombic Hole .. ..... .... 201
5.3.2 Stress Concentration Near Square Hole
with Rounded Vertices .... .... .... .... ..... .... 204
5.4 Rectangular Hole .. ..... .... .... .... .... .... ..... .... 207
5.4.1 Stress Concentration Near Rectangular Hole
with Rounded Vertices .... .... .... .... ..... .... 207
5.4.2 Stress Intensity Factors in Vertices of Rectangular
Hole . .... ..... .... .... .... .... .... ..... .... 211
5.4.3 Semi-infinite Rectangular Notch . .... .... ..... .... 212
5.5 Elastic Plane with Circular Hole and Edge U-Notches.... .... 214
5.5.1 First Basic Problem for Plane with Circular Hole. .... 214
5.5.2 Cracks in Elastic Plane with Circular Hole . ..... .... 214
5.5.3 Edge U-Notch in Plane with Circular Hole. ..... .... 216
5.5.4 Elastic Plane with Circular Hole and Two Edge
U-Notches. ..... .... .... .... .... .... ..... .... 219
References. .... .... .... ..... .... .... .... .... .... ..... .... 220
6 Periodic System of Closely Spaced Holes in Elastic Plane .... .... 227
6.1 Integral Equation of the Problem ... .... .... .... ..... .... 228
6.2 System of Elliptical Holes .... .... .... .... .... ..... .... 232
6.3 System of Narrow Slots .. .... .... .... .... .... ..... .... 234
6.4 Systems of Rhombic or Oval Holes. .... .... .... ..... .... 236
6.5 Bilateral Rounded Notch.. .... .... .... .... .... ..... .... 239
6.5.1 Bilateral Hyperbolic Notch . .... .... .... ..... .... 239
6.5.2 Bilateral Parabolic Notch... .... .... .... ..... .... 240
6.5.3 Bilateral U-Notch .... .... .... .... .... ..... .... 242
6.5.4 Bilateral Rounded V-Notch. .... .... .... ..... .... 243
6.6 Bilateral Sharp V-Notch.. .... .... .... .... .... ..... .... 245
References. .... .... .... ..... .... .... .... .... .... ..... .... 247
7 Edge Notches in Elastic Half-Plane . .... .... .... .... ..... .... 249
7.1 Edge Notch... .... ..... .... .... .... .... .... ..... .... 249
7.1.1 Edge Notch in the Shape of Circular Segment ... .... 249
7.1.2 Semi-elliptical Notch.. .... .... .... .... ..... .... 251
7.1.3 Rounded V-Notch.... .... .... .... .... ..... .... 251
7.1.4 Sharp V-Notch .. .... .... .... .... .... ..... .... 256
7.2 Edge Notch with Cracks.. .... .... .... .... .... ..... .... 259
7.2.1 Edge Semi-elliptical Notch with Crack .... ..... .... 260
7.2.2 Edge V-Notch with Crack Growing from Its Tip . .... 262