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Fracture Mechanics An IntroductionProf. Ir. Eko Budi Djatmiko, MSc., PhD.Nur Syahroni, ST., MT.Fatigue & Fracture Mechanics (MO-091334)Teknik Kelautan FTK- ITS1Why structures failDesign ApproachesStress Analysis for Member with CrackStress Concentration FactorThree Modes Deformation of CrackStress Intensity Factor

Fatigue & Fracture Mechanics (MO-091334)2OutlineWhy structures fail

Fatigue & Fracture Mechanics (MO-091334)3Brittle fracture of the World War II Liberty shipsWhy structures failNegligible during design, construction or operation of structures:Poor workmanshipInappropriate or substandard materialsError in stress analysisOperator errorApplication of a new design or material, which produces an unexpected (an undesirable) resultExample: Brittle fracture of World War II Liberty shipsBroken completely in two while sailing between Siberia-Alaska in 1943Totally 2700 ships, 400 fractures, 90 serious failure, 20 ships broken completely in twoThe first ship applied all-welded hull which were much faster and cheaper in fabricationFatigue & Fracture Mechanics (MO-091334)4Design ApproachesThe strength of material approachThe fracture mechanics approachFatigue & Fracture Mechanics (MO-091334)5

Stress Analysis for Member with CracksStress concentration factor (Kt)

For very sharp cracks

Fatigue & Fracture Mechanics (MO-091334)6

Stress Intensity Factor (KI)By using a method developed by Westergaard , Irwin found that the stress and displacement fields in the vicinity of crack tips subjected to the three modes of deformation are given by:Fatigue & Fracture Mechanics (MO-091334)7

Stress Intensity Factor (KII)By using a method developed by Westergaard , Irwin found that the stress and displacement fields in the vicinity of crack tips subjected to the three modes of deformation are given by:Fatigue & Fracture Mechanics (MO-091334)8

Stress Intensity Factor (KIII)By using a method developed by Westergaard , Irwin found that the stress and displacement fields in the vicinity of crack tips subjected to the three modes of deformation are given by:Fatigue & Fracture Mechanics (MO-091334)9

Stress Intensity Factor EquationsFatigue & Fracture Mechanics (MO-091334)10SIF for Through-Thickness CrackFatigue & Fracture Mechanics (MO-091334)11

SIF for Single Edge CrackFatigue & Fracture Mechanics (MO-091334)12

Infinite widthFinite width

Free surface correction factor SIF for Embedded Elliptical or Circular Crack in Infinite PlateFatigue & Fracture Mechanics (MO-091334)13

If b=p/2, KI max for embedded elliptical crack:Q= flaw shape parameterFor circular cracka=c, Q~2.4

SIF for Surface CrackFatigue & Fracture Mechanics (MO-091334)14Q= flaw shape parameter

Mk: back surface correction factorfor values of a/t0.5 SIF for Crack Growing from HoleFatigue & Fracture Mechanics (MO-091334)15

for very short crack, a/r0, f(a/r) ~ 3 (=kt)for large a/r become through thickness crackSIF for Crack in Bending BeamFatigue & Fracture Mechanics (MO-091334)16

ReferencesBarsom, JM. & Rolfe, ST., Fracture & Fatigue Control in Structures, Applications of Fracture Mechanics, Pretince-Hall, New Jersey, 1987.Anderson T.L., Fracture Mechanics, Fundamental and Application, CRC Press, Boca Raton, 1991

Fatigue & Fracture Mechanics (MO-091334)17Example problemsFatigue & Fracture Mechanics (MO-091334)18

Example problemsFatigue & Fracture Mechanics (MO-091334)19