[Paper Review] Elastic and Fracture Behavior of Three-Dimensional Ply-to-Ply Angle Interlock Woven Composites: Through-Thickness, Size Effect, and Multiaxial Tests

Weixin Li, Yao Qiao+5 more|arXiv (Cornell University)|Dec 10, 2020

Mechanical Behavior of Composites134 references18 citations

TL;DR

This study investigates the elastic and fracture behavior of 3D ply-to-ply angle interlock woven composites using novel out-of-plane fracture tests, size effect analysis on SENT specimens, and multiaxial Arcan rig tests with X-ray micro-CT. It provides the first objective characterization of intra-laminar fracture energy via Bažant’s Type II Size Effect Law, revealing strong damage tolerance due to significant size effects and transition zone behavior across specimen sizes.

ABSTRACT

This work presents a comprehensive investigation of the elastic and fracture behavior of ply-to-ply angle interlock three-dimensional woven composites. The research investigated novel splitting and wedge-driven out-of-plane fracture tests to shed light on the tensile fracture behavior in the thickness direction and to provide estimates of the out-of-plane tensile strength and fracture energy. In addition, size effect tests on geometrically-scaled Single Edge Notch Tension (SENT) specimens were performed to fully characterize the intra-laminar fracture energy of the material and to study the scaling of structural strength in this type of three-dimensional composites. The results confirmed that size effect in the structural strength of these materials is significant. In fact, even if the range of sizes investigated was broader than in any previous size effect study on traditional laminated composites and two-dimensional textile composites, all the experimental data fell in the transition zone between quasi-ductile and brittle behavior. This implies strong damage tolerance of the investigated three-dimensional composites. The analysis of the data via Bazant's Type II Size Effect Law (SEL) enabled the objective characterization of the intra-laminar fracture energy of three-dimensional composites for the first time. Finally, Arcan rig tests combined with X-ray micro-computed tomography allowed unprecedented insights on the different damage mechanisms under multi-axial nominal loading conditions, particularly tension-dominated and shear-dominated conditions.

Motivation & Objective

• To characterize the out-of-plane tensile strength and fracture energy of 3D ply-to-ply angle interlock woven composites using novel splitting and wedge-driven fracture tests.
• To investigate the size effect on structural strength in 3D woven composites through geometrically scaled Single Edge Notch Tension (SENT) specimens.
• To apply Bažant’s Type II Size Effect Law (SEL) to objectively quantify the intrinsic fracture energy of 3D composites for the first time.
• To explore multi-axial damage mechanisms under tension- and shear-dominated loading using Arcan rig tests combined with X-ray micro-computed tomography.
• To understand the scaling behavior and damage tolerance of 3D woven composites across a broad range of specimen sizes.

Proposed method

• Conducted novel splitting and wedge-driven out-of-plane fracture tests to measure out-of-plane tensile strength and fracture energy.
• Performed geometrically scaled Single Edge Notch Tension (SENT) tests to study size effect on structural strength across multiple specimen dimensions.
• Applied Bažant’s Type II Size Effect Law (SEL) to extract the intrinsic fracture energy $ G_f $ from experimental data, using the relationship $ \sigma_{Nu} = \sqrt{\frac{E^* G_f}{D g(\alpha_0) + c_f g'(\alpha_0)}} $.
• Used the equivalent elastic crack concept to relate nominal strength to fracture energy, distinguishing apparent fracture toughness $ K_{IcA} $ and apparent fracture energy $ G_{fA} $ from material properties.
• Employed Arcan rig tests with X-ray micro-computed tomography to visualize and analyze damage mechanisms under multi-axial loading conditions.
• Calculated dimensionless functions $ g(\alpha) $ and $ g'(\alpha) $ numerically using finite element methods and quarter-point element techniques for accurate stress intensity factor estimation.

Experimental results

Research questions

• RQ1 What is the out-of-plane tensile strength and fracture energy of 3D ply-to-ply angle interlock woven composites, and how do they compare to in-plane properties?
• RQ2 How does specimen size influence the structural strength of 3D woven composites, and does the size effect follow a predictable scaling law?
• RQ3 Can Bažant’s Type II Size Effect Law be successfully applied to 3D woven composites to extract intrinsic fracture energy $ G_f $?
• RQ4 What are the dominant damage mechanisms under multiaxial loading (tension-dominated and shear-dominated), and how do they evolve with load?
• RQ5 How does the transition between quasi-ductile and brittle behavior manifest in 3D woven composites across a wide range of specimen sizes?

Key findings

• The out-of-plane tensile strength of the 3D woven composite was measured via novel splitting and wedge-driven fracture tests, providing direct estimates of fracture properties in the thickness direction.
• All experimental data from geometrically scaled SENT specimens fell within the transition zone between quasi-ductile and brittle behavior, indicating strong damage tolerance.
• The size effect on structural strength was significant and well described by Bažant’s Type II Size Effect Law, enabling the first objective characterization of intrinsic intra-laminar fracture energy $ G_f $ for 3D woven composites.
• The apparent fracture energy $ G_{fA} $ decreased with decreasing specimen size, confirming the size-dependent nature of fracture response in these materials.
• Arcan rig tests combined with X-ray micro-CT revealed distinct damage mechanisms under tension- and shear-dominated loading, including matrix cracking, fiber-matrix debonding, and fiber bundle reorientation.
• The analysis showed that for large specimens, the effective fracture energy $ G_f $ approached a constant value, confirming that $ G_f $ is a material property independent of specimen size when $ D \to \infty $.