Use of notched beams to establish fracure criteria for beryllium

Thesis/Dissertation · Mon Jan 01 04:00:00 EST 1979

OSTI ID:5458315

Mayville, R A

Despite the fact that beryllium is brittle, its other properties make it attractive in certain structural applications. In the present investigation, the fracture of an improved form of Brush-Wellman's S-65 grade pure beryllium was studied under triaxial tensile stresses. This state of stress was produced by testing notched beams, which were thick enough to be in a state of plane strain at the center. A plane strain, elastic-incremental plasticity finite element program was then used to determine the stress and strain distributions at fracture. A four-point bend fixture was used to load the specimens. It was carefully designed and manufactured to eliminate virtually all of the shear stresses at the reduced section of the notched beams. The uniaxial properties of the beryllium were obtained by two methods: (1) conventional tension and compression tests, and (2) a bending test developed in 1910. With this latter technique, the uniaxial stress-strain curves in tension and compression can be obtained from a single bending specimen. For the beryllium, however, these conditions were determined by actually measuring the strains at the root of the notch with strain gages for two specimens. A total of 26 beryllium notched beams were tested to fracture. There were nine different geometries, consisting of combinations of four thicknesses and three different root radii. After the specimens were fractured, the location of fracture initiation, which occurred ahead of the notch, was determined by viewing the fracture surfaces in a scanning electron microscope. In this way, the values of the principal stresses and strains at the location of fracture were determined from the finite element analysis. The maximum tensile stress at fracture in the notched beams was significantly greater than in uniaxial tension. The information obtained from the notched beam tests was used to closely predict the plane strain fracture toughness of the beryllium.

• OSTI ID: 5458315
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360103* -- Metals & Alloys-- Mechanical Properties
ALKALINE EARTH METALS
BERYLLIUM
COMMINUTION
COMPRESSION
ELEMENTS
FAILURES
FRACTURE PROPERTIES
FRACTURES
FRACTURING
MATERIALS TESTING
MECHANICAL PROPERTIES
METALS
NOTCHES
STRAINS
STRESSES
SURFACE PROPERTIES
SURFACE TENSION
TESTING