The behavior of glass fiber reinforced plastics (GRP) under bending load was investigated by using unsaturated polyester resin reinforced by roving cloths or chopped strand mat. The influence of glass content on their behavior was also investigated. The results obtained were as follows.
(1) The GRP under bending load exhibited microcracks in their tension side at low stress level similarly as the behavior in their tensile tests. So, the strain in the tension side was slight larger than the strain in the compression side.
(2) The elastic modulus in bending increases in proportion to the volumetric content of glass fiber β. But in M-GRP (reinforced by chopped strand mat), the effect of β on their elastic modulus was little.
(3) For R-GRP specimens (reinforced by roving cloths) breaking usually occurred in the compression side, while for M-GRP it is in the tension side.
(4) The bending strength increased in proportion to β to a limit value of β in the same way as the tensile strength, but the limit value for each specimen was slightly lower than that of the tensile strength.
