Creep and Fatigue: Understanding Stress and Failure in Materials

Creep and Fatigue 1
CREEP AND FATIGUE
By Name
Course
Instructor
Institution
Location
Date

Creep and Fatigue 2
Q 4
Pressure vessel (p) is given as1.5 Mpa
D:a of the cover plate (D) is given as 450 mm
D:a of bolt (d) = 20mm
Area A = πr2
Which can as well be given as,, Area A = π
4 (D2)
R= 225mm
Number of bolts = 30
Elasticity E = 210×103 Mpa
Area A = π
4 (D2)
A = π
4 (450×450)
A= 159043.12 mm2
Secondary creep rate = 32.2 ×10-17 σ−4h-1
First part
Initial tightening stress in the bolt n is given by
σ = P D2
nd = 1.5× 450 × 450
30 ×20
σ = 303750
600
σ = 506.25Mpa
Second part

Creep and Fatigue 3
Time for tightening
The equation for finding the time for tightening is given below
σ = Pr
t = 1.5× 225
t
506 = 1.5× 225
t
t= 337.5
506.25
t= 0.66 seconds ss
Q 6
From Miner’s rule , failure is witnessed when
n 1
N 1 + n 2
N 2 + ..........................+ ¿
¿ = 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . i
Where ni = number of cycles at ith stress table,
Ni = number of failure links to ith stress relevant. ¿
¿ = damage ratio
Stages
1. 250 cycles at σ 1
2. 250 cycles at σ 2
3. 250 cycle at σ 3