Application of Probability to Mechanical Design
113
Condition 1. Table 2.3
1
Pf = ~ t -- -4.7534
96,000 4- 72,226
S~
0.96789
s2 -- 173,806 psi safety device
Condition 2. Table 2.3
s~ = 24,563 structural member
1
Pf = 1~ t = -2.3263
96,000 4- 35,765
S~
0.99231
s2 = 132,786 psi safety device
s I ~ 60,702 structural member
Now
~ Ec
S=Sl2
r
1
~¢~Ec ~ 30 x 1060"0015 2
2 s~
2
60,702 psi
2r = d = 0.5242" q5
1
Pf = 106
.v/~ 30 × 1060"0015 2
2
24,563
2r = d = 1.2954"
0.64772
= 0.26210
This curve is shown in Fig. 2.41.
F. Monte Carlo Fatigue Calculations
The computer fatigue calculations
using the Gaussian and Weibull
distributions are set up as in Fig. 2.6 with t (Eq. (2.42)) set to obtain
low probability of failure. The computer randomly picks a value for the
unknown variable and calculates the load or stress while for the capacity
or strength of a part or material the computer picks a value with in the
distribution found previously. If the capacity is greater than the load or
stress the selection is good, however, if load or stress is greater than