Photoelastic Determination of Elastic and Plastic—Elastic Strain Distributions in Tube Plates

Abstract

These tube plates are the parts of boiler drums that contain triangular arrays of holes for the water (or steam) tubes. These drums are thin enough to be treated as flat plates in biaxial tension. Photoelastic coatings were bonded to eight models made of two boiler steels and the strain distributions around the holes and in the ligaments between the holes were determined for several loads. The results showed confined yielding around the holes before failure of the diagonal or axial ligaments under the 2:1 load ratio, which occurs due to pressure without ‘beam’ bending of the boiler drum. A frozen stress test was also carried out to determine the elastic principal stresses in the ligaments of one geometry. The results showed that, in this diagonal ligament, along the straight line joining points of greatest elastic stress at the holes, the smaller principal stresses in the plane of the plate were also tensile, but only about 10 per cent of the greater principal stresses. This shows that, along these lines of likely failure, the photoelastic coatings underpredict the onset of yielding slightly.