# HL-T: 1100 Stress Life (S-N) Using Stress History Created from Modal Participation Factors (via a *.pch file) and Modal Stress

- Import a model to HyperLife
- Select the SN module with a Modal Superposition loading type and define its required parameters
- Create and assign a material
- Assign a *.pch file (containing modal participation factors) to modal stresses
- Evaluate and view results

- Create stress history from modal participation factors and modal
stresses.For the complete time interval, stress history is given by:
$${\sigma}_{ij}(t)={\sum}_{k}{P}_{k}(t)*{\sigma}_{ij,k}$$ Where,- $${\sigma}_{ij}(t)$$
- Stress history for the given time interval of an element
- $${P}_{k}(t)$$
- Participation factor per mode at time
`t`(via mrf/pch file) - $${\sigma}_{ij,k}$$
- Modal stress of an element per mode (via h3d file)
- $$k$$
- Mode

- Perform an SN uniaxial calculation for the above stress history.The above pch file is generated from OptiStruct from a modal transient run.