Fatigue Test

Question 1

Fatigue

Answer 1

Progressive, localized and permanent structural damage that occurs when a material is subjected to cyclic or fluctuating loading
Maximum stress values are less than UTS and may be below the yield stress limit also

Question 2

Fracture

Answer 2

Separation or fragmentation of a solid body under stress
Cracking can occur in many ways including: slow or rapid application of external load (tension or impact), cyclic or repeated loading (fatigue), and time-dependent deformation under constant load (creep)

Question 3

Fatigue Failure

Answer 3

Fatigue cracks grow at an accelerating rate once initiated and becomes unstable propagating through remaining corss-sectional area

1. cyclic plastic deformation prior to fatigue crack initiation
2. nucleation
3. short crack or small crack phase
4. crack propagation
5. final instability or failure

Question 4

3 common ways stress can be applied

Answer 4

axial, torsional, flexural stresses

Question 5

3 stress cycles loads can be applied

Answer 5

reversed, repeated, varying stress and frequency stress cycles

Question 6

Factors Affecting Fatigue Life

Answer 6

Geometry, stress concentration, residual stresses, size and distribution of internal defects, direction of loading, grain size, environment, temperature, surface quality, material type

Question 7

S-N plot

Answer 7

Stress vs cycles to failure
fatigue life: number of cycles that will cause failure at a certain stress level
fatigue limit: a characteristic of the material and its geometry.