OS-V: 0900 Constant Amplitude Stress-Life Analysis

A notched test specimen is subjected to tensile loading and a Constant Amplitude Stress-Life Analysis is performed using OptiStruct.

The Stress-Life result from OptiStruct is compared with the results from eFatigue calculator, for the element 215576.
Figure 1. Model with Loading Conditions

Model Files

Before you begin, copy the file(s) used in this problem to your working directory.

Benchmark Model

The model is a test specimen of thickness 9.5 mm, subjected to tensile loading of 1150 N at circular holes, normal to the notch. The model was meshed with first-order shell elements and the loading is applied to RBE3 elements that are connected to the holes. The Signed Von Mises (SGVON) combined stress was used.

The material used is Steel RQC-100:
Material Properties
Young's modulus
203000 MPa
Poisson's ratio
Ultimate tensile strength (UTS)
863.0 MPa
Fatigue strength coefficient (SRI1)
1101.0 MPa
First fatigue strength exponent (B1)
Cycle limit of endurance for one segment SN curve (NC1)
1000000 cycles
A constant amplitude load is applied in the FATLOAD entry with a scale factor of 14.1332, whose variation is:
Time Points
Load Curve Point
Figure 2. Load Curve used in FATLOAD

All the modifying factors (Surface Roughness and Fatigue Strength Reduction factor) are set to 1.0.


Comparison of the Stress-Life results between OptiStruct and eFatigue calculator for element 215576.
Result eFatigue

(Target Value)

OptiStruct Normalized with the Target Value
Life (Nf) 152000 cycles 151881 cycles 1.0008