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NOTCH EFFECTS INTRODUCTION OF A NOTCH AFFECTS THE FRACTURE PROCESS Eg: INCREASES THE DUCTILE-BRITTLE TRANSITION TEMPERATURE OF STEEL NOTCH CREATES A LOCAL STRESS PEAK AT THE ROOT OF THE NOTCH WHEN THIS LOCAL STRESS REACHES THE YIELD STRENGTH, PLASTIC FLOW BEGINS THIS RELIEVES THE HIGH ELASTIC STRESS, LIMITS THE PEAK STRESS TO THE YIELD STRESS ALSO PRODUCES A TRIAXIAL STATE OF STRESS AT THE NOTCH

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(a). Elastic stresses under a notch in a thin plate (plane stress). (b). Elastic stresses under a notch in plain strain (c ). Distribution of σ y with z at x= 0 (plain strain) (d). Distribution of stresses during local yielding (plain strain)

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Intersection of flow curve and fracture curve as per Ludwik theory

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Strength V/s Transition temperature plot

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Fracture criteria for biaxial state of stress in ductile metals Biaxial fracture criterion for brittle cast iron – Shaw’s criterion for brittle materials

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Log-log plot of true stress-strain curve

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Forms of power curve σ = Kε n

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Interpretation of necking criterion

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Considere’s construction to determine point of maximum load

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Geometry of a necked region Stress acting on element at point O O

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Plot of variation of local elongation with position along gauge length of a tensile specimen

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Strain rate change test to determine strain rate sensitivity

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Relaxation curve determined at σ o, ε o

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Representation of long range and short range stress fields

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Thermal activation barrier

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Temperature dependence of the hardness of copper

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Relationship between reduction of area and angle between the longitudinal direction in forging and the specimen axis

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Effect of forging on longitudinal and transverse reduction of area for tensile strength 810 MPa

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W.A. Wood’s concept of microdeformation leading to formation of fatigue crack (a) static deformation (b) fatigue deformation leading to surface notch(intrusion) (c) fatigue deformation leading to slip-band extrusion

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Plastic blunting process for growth of stage II fatigue crack

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S-N curve for notched and un-notched specimen using Goodman line

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Superposition of applied and residual stresses

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Notch stress analysis based on Neuber’s analysis

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Role of corrosive environment on fatigue crack propagation

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Effect of frequency on fatigue life at constant elevated temperature

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Fold formation at a triple point

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Intergranular cracks formation due to Grain Boundary Sliding (GBS)

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Fatigue - creep interaction diagram for constant temperature

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