Abstract
The interference effect of double symmetrical U-shaped notches of unequal notch depth and/or unequal notch radius on the strengths were investigated experimentally. The notch pitch range in which the general yield strength is reduced was able to be predicted by using the upper and lower bound theorems. The X-shape extension of plastic deformation occurred in the notch pitch range influenced by the interference effect. The notch tensile strength was also reduced by the interference effect. The magnitude of the reduction of notch strength ratio and the notch pitch range influenced by the interfarence effect were almost equal to thoes of the general yield stress ratio, or the ratio of the general yield stress at the net section of the notched bar to that of the smooth bar. The nominal mean stress at the net section at fracture was also reduced by the interference effect. The fracture along the inclined plane connecting two notches situated diagonally was caused by the X-shape extension of plastic deformation in the notch pitch range showing the strong interference effect. The fracture at the net section occurred in the notch potch range showing the weak interference effect. The difference in notch depth has much stronger influence on the interference effect than the difference in notch radius does.
