Flexure creep in three and four point bending tests of unidirectional glass/urethane composites
Publication Name: Materials and Processing Technology - 60 years of SAMPE Progress
Specimens of unidirectional E-glass/polyurethane composite materials were tested in three-point and four-point flexure tests. First, the short-term flexure properties obtained by each test were compared and the effect of the span-to-depth ratio and the diameter of the loading roller on the failure mode were assessed. Second, long-term flexure creep tests were performed at various stress levels. It is found that the creep rupture strengths obtained from the three-point tests are significantly lower than creep rupture values obtained from the four-point tests. It is postulated that shear effects play a dominant role in the viscoelastic creep properties determined by the three-point test, and that these effects depend on the type of the matrix material in the composite. The additional complexity in the fixture required for the four-point creep test has the merit of reducing the shear effects in the flexure creep properties of these materials.