Abstract: Fiber reinforced polymer (FRP) laminates are prone to delamination damage during the production and use. To understand the effect of delamination damage on the residual compression strength of FRP laminates, this article has conducted compression tests and modal testing on composite beams with precast mid-plane delamination of different sizes. The effects of different delamination on the natural frequencies and the compressive strength of FRP beams are studied and the correlation between frequencies and compressive strength are investigated. The finite element model of delaminated FRP laminates was established in ABAQUS, and the simulation analysis results were compared with the testing results to validate the simulation model. The finite element method is used to analyze the influence of the delamination size on the frequency and compressive strength. The results show that the natural frequencies of the FRP beams decreases with the increase of the delamination area. Compared with those without initial damage, the FRP beams with delamination were mainly fractured in the interface where the delamination occurs. The delamination has expanded to different extent depending on the initial delamination sizes. With the increase of delamination size, the decrease of compressive strength of composite laminates has increased. When the layups of the FRP specimen changes, with the increase of the delamination sizes, there still exists the correlation between the structural frequencies and the residual compressive strength. Experiments and simulations both show that the natural frequencies are closely correlated to the residual compression strength of the FRP beams with delamination, and an exponential relationship is observed. However, if the layups changes, the exponential relationship will be changed accordingly between the frequencies and the residual compression strength.

Key words: composites, delamination, frequency, residual compressive strength, vibration