EngArc - L - Modified Goodman Diagram

Modified Goodman Diagram

Fig1.

The following table shows the bounds on regions in the modified Goodman range-of-stress diagram shown in Fig1.

Region	Limiting Value of σ_m
a	−σ_yp ≤ σ_m ≤ σ_ab
b	σ_ab < σ_m ≤ 0
c	0 < σ_m ≤ σ_cd
d	σ_cd < σ_m ≤ σ_yp

The modified Goodman range-of-stress diagram shown above is a failure locus for the case of uniaxial fatigue stressing. Any cyclic loading that produces a stress amplitude that exceeds the bounds of the locus will cause failure in fewer than N cycles. Any stress amplitude that lies within the locus will result in more than N cycles without failure. Stress amplitudes that just touch the locus produce failure in exactly N cycles.

A modified form of the Goodman relationship is recommended for general use under conditions of high-cycle fatigue. This form is represented by the modified Goodman diagram. Any given Goodman diagram is constructed for a single fatigue lifetime of N cycles. The Goodman Diagram is only good for one point on the fatigue curve. The Goodman Diagram will change for different points on the fatigue curve. The amplitude stress line σ_a represents the Goodman equation. The diagram may also be called a 'range-of-stress' diagram or a 'modified Goodman range-of-stress' diagram.

Fig2.