Fracture of beryllium under biaxial states of stress has been studied in the past using thin-walled tubes loaded by combinations of axial load, torsion, and internal pressure. In the present investigation to obtain a triaxial state of stress, notched beams of beryllium with varying dimensions were tested in plane strain four-point bending. The conditions necessary to ensure plane strain are discussed in detail and plane strain finite element analyses are used to determine the stresses and strains at fracture in the notched specimens. Based on the test results a strain dependent, maximum tensile stress fracture criterion is proposed for parts without macroscopic cracks. In addition, the plane strain fracture toughness of beryllium is estimated from the notched bar tests using the RKR model.

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