Chapter 8 - Failure Flashcards
Engineering Failure
It is often seen as extreme behavior that must be avoided or predicted.
Ductile Fracture
The more plastic deformation a material experiences at fracture, the more ductile the material is.
Mechanisms behind ductile fractures
Necking, Small cavity formation, Coalescence of cavities to form a crack, Crack propagation, Final shear fracture at 45.
Brittle Fraction
Fractures without plastic deformation.
Cleavage
For most brittle crystalline materials, crack propagation corresponds to the successive and repeated breaking of atomic bonds along specific crystallographic planes.
Transgranular
The crack propagates through the grains.
Intergranular
In some alloys, crack propagation is along the grains.
Stress Concentration
The presence of a crack or defect will amplify the applied stress on a system.
Fracture Toughness
Measure of a material’s resistance to fracture.
Impact Testing technique
Chanpy test, Izod test.
Cyclic Stress
Cyclic stresses arrise from loading and unloading a given system.
Fatigue Life
Number of cycles up to failure.
Fatigue Limit
Stress amplitude under which the fatigue life is infinite.
Fatigue Strength
Stress level at which failure will occur for a specific number of cycles.
Factors that affect fatigue life
Mean stress, Surface effects, Design factors, Surface treatment.
