Fatigue Calculations as per ASME Sec. VIII Div. 2 - Annex 3-F

[ashaykadam]

As per ASME Sec. VIII Div. 2 -> Annex 3-F.1.2, following formulae are specified to calculate the "design number of design cycles" (N) from Equation (3-F.1),

N =10^X
where,
X = (C1 + C3.Y + C5.Y^2 + C7.Y^3 + C9.Y^4 + C11.Y^5) / (1 + C2.Y + C4.Y^2 + C6.Y^3 + C8.Y^4 + C10.Y^5)
Y = (Sa / Cus)(Efc / Et)

Following Terms are clearly specified in Code as follows:
1. ET = modulus of elasticity of the material under evaluation at the average temperature of the cycle being evaluated.
2. Cus = conversion factor, 1.0 for ksi & 6.894757 for MPa stress units

However, I am not clear from where to get other values? My queries are as follows:
1. How to calculate Sa (Stress Amplitude)?
2. How to determine EFC = modulus of elasticity used to establish the design fatigue curve
3. I also wish to know how to use "Table 3-F.9" to calculate the "design number of design cycles" (N)

Thanks.



Ashay Kadam
Mechanical Engineer
India.

 

[TGS4]

The stress amplitude is calculated following the procedure in 5.5.3 or 5.5.4.

EFC is shown in each of the applicable Tables. It is explicitly listed as a General Note at the end of each Table.

Your question regarding Table 3-F.9 is unclear. This table is a selection of data points using the equations and the data from the various fatigue curves.