Flexural behavior of CFRP box beams and strain measurement by image analysis

Abstract

This paper presents an experimental investigation on the flexural behavior of CFRP box beams with four different CFRP laminate structures. Those four laminates have 25 laminas, and they have the proportion of longitudinal, transverse, and diagonal lamina as 1:1:0 (L1T1), 1:0:1 (L1D1), 1:0:2 (L1D2), and 1:1:2 (L1T1D2). In addition to the displacement and strain gauge measurements, image analysis was employed to observe the deformation and strain field near a failure location. Flexural tests showed that L1D1 exhibited the highest flexural strength, followed by L1D2, L1T1D2, and L1T1, where diagonal laminas clearly contributed to the flexural strength more than transverse laminas. All the beams were observed to have a premature damage near a loading plate, and finally they exhibited a brittle failure in upper flange and web. Different failure modes were observed due to the laminate structures. Among them, image analysis clarified the development of shear strain in the web of L1T1 even before the final brittle failure.