PSA 1.2 — Stress & Strain: the Language of the Course
Pull a specimen and plot σ–ε:
The problem: most steels don't have a sharp "knee" where yielding obviously starts — the curve just bends gradually. So where exactly is "yield"? Standards had to define it.
Method 1 — 0.2 % offset (Rp0.2), the default. Draw a line parallel to the elastic slope E, but starting at ε = 0.002 (that's the 0.2 %). Where this line cuts the curve = yield. Meaning: the stress that leaves 0.002 permanent stretch after unloading — a small, agreed, measurable amount of "permanent damage" chosen as the boundary. Used by most ASTM/ASME materials.
Method…
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