Determination of yield point and yield strength of ASTM A572Gr.50 high strength steel plate

During the tensile test of ASTM A572Gr.50 high strength steel plate, the elastic deformation of A572Gr.50 sample increases with the increase of tensile load.

When the two load does not increase or decrease, the deformation of ASTM A572Gr.50 high strength steel plate sample suddenly increases, and the sample seems to give up to load and self elongation. This phenomenon is called yield phenomenon.

The stress caused by the yield phenomenon is called the yield point and can be calculated according to the following formula:
Sigma S = Ps / S0
The form, the sigma S yield point, MPa;
Ps - yield load, N;
S0 - the original cross section area of the sample, mm2.

The emergence of the yield point marks the transition of ASTM A572Gr.50 high strength steel plate sample. It  changes from elastic deformation to plastic deformation. Because when the applied force reaches or exceeds the yield point of A572Gr.50 steel material, if the external force is eliminated, the length of the sample is partially restored, but it can no longer be restored to the original length.  That is, partial deformation or elongation is permanently retained.