B cavities applied stress from vj colangelo and fa

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Unformatted text preview: e: • Cyclic stresses are introduced by fluctuating thermal stresses • Occurs at elevated temperatures • Thermal stress: l ET – Corrosion fatigue: • Simultaneous action of a cyclic stress and chemical attack • Preventative techniques can be used to reduce the rate of corrosion, including protective surface coatings and using a more corrosion‐resistant material • • m • • – mostly elastic • – Decreasing creep rate – Slope diminishes with time – Material experiences an increase in creep resistance or strain hardening • Secondary creep: – Rate is constant – Longest stage of creep process • Tertiary creep: – Acceleration of rate up to point of failure – Failure is termed “rupture” – Caused by: • Grain boundary separation • Formation of internal cracks, cavities and voids • necking • • Steady‐state creep rate: Qc ss K 2 exp RT n – K2, n and Qc activation energy are material parameters. • Creep fracture: – The lifetime tf of the material also de...
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