Influence of test parameters on the interlaminar shear strength of FRP bars

At present, the interlaminar shear test is increasingly used as a supplementary test to determine the mechanical characteristics of FRP bars. This is mainly due to its simplicity and its ability to quantify the properties of the fibre/matrix interface. These tests are performed according to ASTM D4475. However, there are several pa-rameters in ASTM D4475 that are not directly specified. Due to this, studies that use such tests feature a variety of different boundary conditions and, consequently, suffer from limited comparability. Furthermore, no study is available in which the effects of changes in selected parameters are comprehensively determined. This paper presents an experimental study that investigated the capabilities and limitations of the short-beam test. In this study a total of 338 specimens from three different manufacturers were tested. The study was focused on the influence of different bar diameters, span-to-diameter ratios and loading speeds. It was found experimentally that the calculated interlaminar shear strength is strongly affected by the applied span-to-diameter ratio. Therefore, the article offers a conversion relationship that takes the span-to-diameter ratio into account. The suitability of the conversion relationship was also verified for alkali-conditioned specimens.