PSA 2.1 — Stress Categories: Sustained, Displacement, Occasional
Two kinds of loading exist, and they fail differently:
The hanging-weight vs stretched-bolt picture: a weight on a rope (primary) will keep pulling through any amount of yielding until the rope parts. A bolt stretched 1 mm too far (secondary) yields, loses its excess load, and stops — it fails only if you cycle it thousands of times. Thermal expansion is the stretched bolt.
Plus a fourth the codes fold in via SIFs rather than a separate bucket: peak/local stresses at discontinuities — they drive fatigue and are captured inside S_E through i-factors (2.4).
100 MPa of weight-bending on a…
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