Fracturing Behavior and Size Effect of Discontinuous Fiber Composite Structures with Different Platelet Sizes

TL;DR

This paper explores the fracture behavior and size effect in Discontinuous Fiber Composites, revealing how platelet size influences strength, fracture energy, and failure modes across different specimen sizes using experimental and modeling approaches.

Contribution

It introduces a combined fracture mechanics and stochastic finite element model to estimate fracture energy and analyze size effects in DFCs with varying platelet sizes.

Findings

Strength decreases with increasing specimen size.

Large specimens follow LEFM and fail in a brittle manner.

Fracture energy increases linearly with platelet size.

Abstract

This study investigates the mode I intra-laminar fracture and size effect in Discontinuous Fiber Composites (DFCs). Towards this goal, the results of fracture tests on geometrically-scaled Single Edge Notch Tension (SENT) specimens are presented and critically discussed for three platelet sizes. The results clearly show a decrease in nominal strength as the specimen size increases. This effect becomes more important as the structure size increases. It is found that, when the specimen is sufficiently large, the structural strength scales according to Linear Elastic Fracture Mechanics (LEFM) and the failure occurs in a very brittle way. In contrast, small specimens exhibit a more pronounced pseudo-ductility with a limited scaling effect and a significant deviation from LEFM. To characterize the fracture energy and the effective length of the fracture process zone, an approach combining equivalent fracture mechanics and stochastic finite element modeling is proposed. The model accounts for the complex random mesostructure of the material by modeling the platelets explicitly. Thanks to this theoretical framework, the mode I fracture energy of DFCs is estimated for the first time and it is shown to depend significantly on the platelet size. In particular, the fracture energy is shown to increase linearly with the platelet size in the range investigated in this work.