The load-strain curves of thin-walled hollow cylinders of mild steel under compression, bending or torsion and rectangular cross-sectional beams with small height under bending deviate from the elastic line before reaching the lower yield point. In this paper these experimental results are attributed to yielding of the surface layer of the material. It is concluded that the surface yeild stress is 3/4 of the inherent yield stress of bulk material under uniform stress such as simple tension or compression.

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