18.7 :  플라스틱 행동

Materials under stress due to tensile loading exhibit elastic and linear behavior until the yield point. Removing the load at the yield point, stress and strain decrease linearly. The strain does not return to zero, indicating plastic deformation.

Plastic deformation is influenced by the maximum stress value and the time elapsed before load removal.

Upon re-loading, the specimen follows the previous unloading curve until near the yield point, then aligns with the original stress-strain curve, implying a higher yield point than the initial strain-hardening.

However, the rupture point remains unchanged, suggesting reduced ductility.

If the initial loading is large enough to cause strain-hardening of the material at C', unloading occurs along line C'D'.

If a compressive load is applied, yield strength decreases to a maximum point H' via a curved path, yielding the material along H'J'.

While the compressive stress is less than the yield stress, the total change in stress between the maximum tensile and the compressive stress equals twice the yield stress.