Influence of the Stacking Angle on the Strength and Stiffness Properties of Tiled Laminates for Civil Applications: A DIC Based Approach

Abstract

Tiled Composites (TC) are a bio-inspired oblique layered material, composed of stacking individual plies in a tiled fashion and joining them together with a polymer to form a rigid structural material. This concept has great potential in different sectors (i.e. bridge building, offshore construction, ship building, lock gates, fire resistance panels, …) as it allows the manufacturing of composite plates from tiled strips of fabric which opens up the door for robotised production of panels of any shape and size. Because this is a relatively new concept, less is known about the mechanical properties of the material such as the strength, the local and global stiffness and the fracture mechanics properties. Further, the classic laminate theory does not fully describe Tiled Laminates (TL) as opposed to plane-parallel laminates and international literature is virtually non-existent. Although numerical finite element (FE) models are available, experimental data is needed to validate, calibrate and corroborate these models. In previous research, the longitudinal stiffness was described by strain gauges and extensometers, leading to scatter/variation in the results due to the specific location of the measurement equipment on the laminate, which cannot be justified by the FE models. This paper studies the full strain field in a TL under uniaxial tension by digital image correlation (DIC) and compares the results to the numerical FE models. Furthermore the influence of the stacking angle and laminate lay-up will be assessed. As a guidance for the uniaxial tensile tests, ASTM D3039 was used even though the specimens are not symmetric or balanced as prescribed by this standard. The results show that the strains along a path in the FE models on the top and bottom of the TL show large variations and that the peak values at the free edges in the FE models need to be averaged out over a relatively large distance. Further, the stacking angle and laminate lay-up have a significant influence on the stress distribution along the specimen and the failure mechanism. Finally, the tests allow for good local and global stiffness characterisation of a TL and will make it possible to establish a set of verified material parameters for the considered TL composites, which will serve as an input to the verification of the FE models.