Presentation on theme: "Fracture and Failure Theory. Defining Failure Failure can be defined in a variety of ways: Unable to perform the to a given criteria Fracture Yielding."— Presentation transcript:
Defining Failure Failure can be defined in a variety of ways: Unable to perform the to a given criteria Fracture Yielding ……
Failure of Structural Materials Yielding is often considered “impending failure” The deformations associated with yield provide a warning The service life is effectively ended if a materials yields under service, in most cases.
Tresca Yield Criterion Ductile Materials Assumes slip occurs during yielding “yielding begins when max. shear stress reaches the shear stress obtained in a simple tension test at yield” max = (σ 1 –σ 2 )/2
Stress Intensity The Stress Intensity Factor is a constant that defines the stress distribution near a crack 2a rr r = distance from crack tip.
Fracture Toughness, K Ic Fracture toughness, K Ic Material property Used to predict the crack size that can be tolerated c = K Ic /( a) 1/2 K Ic increases with thickness K Ic decreases with temperature increase
Stress Concentrations Stress risers occur at discontinuities SCF is related to hole shape and size 2a rr max ave