Novel experimental design for two-dimensional delamination in FRP laminates

Abstract: The two-dimensional (2D) delamination behavior of composite laminates under quasi-static out-of-plane opening loads has been experimentally investigated. A novel design and experimental set-up for fiber-reinforced polymer (FRP) laminated plates with a circular embedded pre-crack was developed. Increasing load-displacement curves were obtained due to the increasing crack front length during propagation. Throughout the loading process, stiffening and softening mechanisms were activated. The stretching of delaminated part of the laminates constituted the main stiffening mechanism. Once the crack started growing, a corresponding softening due to crack propagation occurred together with a secondary stiffening mechanism, fiber-bridging. These stiffness-related mechanisms were reflected in the compliance.

Numerical modeling of two-dimensional delamination growth in composite laminates with in-plane isotropy

Thomas Keller, Anastasios Vassilopoulos, Congzhe Wang

The two-dimensional (2D) delamination growth in fiber-reinforced polymer (FRP) laminates with in-plane isotropy under Mode I loading condition was numerically investigated using finite element analyses. Two sizes of plate models were developed, focusing on different fracture stages. Cohesive elements were employed to simulate the fracture behavior in the presence of large-scale bridging (LSB). The influences of the pre-crack shape/area, loading zone shape/area and fracture resistance were parametrically studied. It was found that either a flatter pre-crack shape or a flatter loading zone shape could result in higher initial structural stiffness and less uniform distribution of the strain energy release rate (SERR) along the pre-crack perimeter during crack initiation and early propagation. However, they had only a minor effect on the stiffness after full fiber bridging development in all directions. The plates finally achieved constant stiffness, which increased linearly with the fracture resistance. The final crack shape was dependent on the loading zone shape and area, but the effects were relatively weak.

2021

Thin ply composites: Experimental characterization and modeling of size-effects

Robin Amacher, John Botsis, Joël Cugnoni, Larissa Sorensen

Thin-ply composites are rapidly gaining interest in the composite industry, not only because of the larger design possibilities that they offer, but also because of positive size effects that have been shown to improve performance in various loading conditions [1]. In this work, carbon fiber-epoxy composites of different ply thicknesses (30-300 g/m(2) fiber areal weight) were produced from the same batch of Toray M40JB fiber and NorthTPT TP80ep matrix to study the influence of ply thickness on the ultimate strength and on the onset of damage in lamina, laminates and components. Uniaxial tension, open-hole compression and open-hole tensile fatigue tests on quasi isotropic 45 degrees/90 degrees/-45 degrees/0 degrees laminates showed very significant improvements regarding the on-set of damage, and in some cases ultimate strength, when decreasing the ply thickness. These performance improvements are the result of major changes in the damage progression and failure modes of the laminates caused by a systematic delay or near suppression of transverse cracking and delamination growth in thin-ply composites. On the component level, thin-ply laminates enabled a marked improvement for bolted-joint bearing, especially in hot-wet conditions. Under impact, the 30 mu m thin ply laminate exhibited a quasi-brittle failure with extensive translaminar cracking while a ply thickness of 100 mu m was found as optimum to minimize the projected damage area. Ply thickness scaling of transverse and in-plane shear strength was identified based on classical laminate theory and unnotched tensile tests on quasi-isotropic specimens. The empirical scaling was found to follow a linear trend over a range of ply thicknesses from 30 to 250 mu m. Due to the near suppression of delamination, the strength of thin-ply composites could then be modeled more effectively than thick ply composites using classical laminate theory or standard multilayer shell modeling. (C) 2014 Elsevier Ltd. All rights reserved.

Elsevier2014

Thin ply composites: Experimental characterization and modeling of size-effects

Robin Amacher, John Botsis, Joël Cugnoni, Larissa Sorensen

Elsevier2014