Constitutive Models
A constitutive model relates stress to strain. Implementing one correctly is a different problem from writing down its yield surface. These articles work through the parts that decide whether an implementation converges: return mapping at corners and apexes, consistent tangent operators, and the parameters that quietly control the answer.
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What a Mohr circle actually tells you
The Mohr circle turns a stress state into geometry. The angles on it are doubled, the envelope touches it once, and both facts are derived here from scratch.