5. Notched material: tensile and compressive responses for deep sharp notches
The effect of notch length a0 upon the tensile and compressive strengths of deep double edge notched specimens are shown in Fig. 5(a) for Alporas foam and in Fig. 5(b) for the Alcan foam. The plots display the net section stress versus the plastic displacement, Du=u− uel (whereuisthetotaldisplacementacrossthenotchand
uel is the elastic load-line displacement). For both tensile and compressive tests, the net section stresses exceed the yield strength of the unnotched materials, which implies a small degree of notch strengthening associated with plastic constraint. The increased strength with reduced net section may also be due to a reduced probability of material imperfection with diminishing stressed volume. It is noted from Fig. 5(a) and (b) that the net section stress drops to zero in the tensile tests at an opening