Fracture Toughness
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Fracture Toughness

Fracture ToughnessAlexander Werf , Guangmei Wu

1. DefinitionContent2. Fracture toughness value-- Stress Intensity Factors of Cracks (K IC )3. Notch-Impact tests4. Factors influence on toughness

DefinitionToughness:the ability of a material todeform plastically and toabsorb energy in theprocess before fractureThe key to toughnessis a good combinationof strength and ductility

Fracture toughness valueStress Intensity Factors of Cracks K C aCK C is the fracture toughness in unit ofMPamY is a dimensionless factor dependingon the geometry of the specimen orstructural componentσ is the remote loading stress in MPa or psia is the crack length in meters or inches

Fracture toughness valuesStress Intensity Factors of Cracks K CK IC , K IIC , K IIICMode I :opening modeMode II :sliding modeMode III :tearing mode

Fracture toughness valueStress Intensity Factors of Cracks K CCrit. stress :acC1YK ICKaCrit. crack length :ICYa C = critical crack length (surface crack),one half crack length (intenal crack)σ = the remote loading stressK IC = the fracture toughness, when thesample has a thickness less than BY = a dimensionless factor dependingon the geometry of the specimenσ C = critical applied loading stressthat causes the material to fail

Toughness tests Charpy testIzod testCompact tension specimen

Charpy testK imp is the impact toughnessK QW/SW is the work, required for breaking the specimenm is the pendulum massS is the cross section area of the specimen at thenotch

Izod test and ct-probe testIzod testct-probe

Factors influence on toughness‣ Temperature‣ Strain rate (rate of loading)‣ Thickness‣ Microstructure

Temperature‣ toughness decrease as the temperature lowered

Strain rate (rate of loading)‣ toughness decrease as the rate of loading increase

ThicknessB2.5KICY2‣ toughness decrease with increasing samplethickness B

MicrostructureDuctile matrixBrittle phaseDuctile matrixBrittle phase

References• Script HVAT Metalle, W. Reimers• Mech. Behaviors of Materials, N. E. Dowling• Mech. Verhalten der Werkstoffe, J. Rösler, H.Harders, M. Bäker• Werkstoffkunde, Bargel, Schulze• Werkstofftechnik 1, W. Bergmann•••ähigkeit

Thanks for your attention !


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