Institute of Fundamental Technological Research

Upper bounds on the yield point load factor for notched bars with finite thickness and small shoulder ratio c/h, are presented and later compared with experimental results. Five sets of specimens of aluminium alloys were tested. It was found that the yield point load generally coincides with the theoretical upper bound, although the influence of the notch geometry and ductility of the material can be observed.

Experimental results for fifty-six specimens of an aluminium alloy are presented in a study of the effect of the prestraining path on the shape of the yield surfaces. A special experimental technique has been applied, consisting of cutting out flat specimens from the prestrained sheet material. Experimental results show that if two various loading paths have different initial sectors and a common final sector, the influence of these initial sectors on the yield surface is the smaller the longer is the final common sector. A theoretical analysis of that problem on the basis of the kinematic workhardening rule is also presented.

Theoretical and experimental results are presented for plastic flow of axially symmetric notched bars. The slip-line fields have been calculated numerically using the Shield theory of axially symmetric plastic flow. The load factors obtained from the theoretical solutions differ only slightly from those for plane strain conditions. Two sets of specimens were investigated in order to obtain the actual load factors for V-shaped and rounded notches. The agreement between the theory and experimental results is satisfactory. In the last series of experiments the influence of the diameter of the bar outside the notch was investigated and later compared with the theoretically estimated value of that diameter.

Experimental results for twenty-eight tubular specimens of a M-63 brass, subjected to combined biaxial tension, are presented in the study of the effect of prestraining on the shape of the yield surface. Yield surfaces are found for various definitions of the yield locus. The strain increments are also shown in the stress plane in order to compare their orientation with the normality criterion. Moreover, the lengths of elastic and plastic strain increment vectors are compared at different moments of loading.

Experimental results for twenty-eight tubular specimens of a M63 brass, subjected to combined biaxial tension are presented in the study of the effect of prestraining on the shape of the yield surface. Yield surfaces are found for various definitions of the yield locus. The strain increments are also shown in the stress plane in order to compare their orientation with the normality criterion. Moreover, the lengths of elastic and plastic strain increment vectors are compared at different moments of loading.