Publication

Mixed-Mode I/II fracture behavior of asymmetric composite joints

Thomas Keller, Anastasios Vassilopoulos, Moslem Shahverdi
2016
Conference Papers

Abstract

The partitioning of the total strain energy release rate, G(tot), into the Mode I, G(I), and Mode II, G(II), components is challenging, especially in asymmetric cracks. Although many researchers have studied the fracture behavior of composite materials under mixed-mode loading using symmetric and/or asymmetric mixed-mode bending (MMB) specimens, few studies exist in the literature regarding the experimental investigation and analysis of the fracture behavior of asymmetric MMB specimens comprised of orthotropic layered adherends. In this study, a new approach, designated as the "extended global method", was established the fracture mode partitioning. The "extended global method" was applied for the analysis of the experimental data. The mixed-mode fracture behavior of adhesively-bonded composite joints was experimentally investigated using asymmetric mixed-mode bending specimens. Finite element models were developed in order to validate the approach. The virtual crack closure technique was used for the calculation of the fracture components at the crack tip and an exponential traction-separation cohesive law was used to simulate the fiber bridging zone. The crack propagated along paths outside the symmetry plane and, therefore, mode partition could not be performed in commonly accepted ways followed for symmetric specimens. In addition, the experimental compliance method was used for calculating the fracture energy of the examined asymmetric mixed-mode bending specimens. Results obtained using the "extended global method" and the experimental compliance method were in good agreement with the results from FE models. The outcome of this study combined with the results obtained from pure Mode I and Mode II experiments can be used to establish failure criteria for the examined joints, that can be eventually be used for designing structural joints with the same adherends and adhesives. Copyright (C) 2016 The Authors. Published by Elsevier B.V.

Official source

Thomas Keller, Anastasios Vassilopoulos, Moslem Shahverdi
2016
Conference Papers

Abstract

Official source

Related concepts (18)

Fracture mechanics

Fracture mechanics is the field of mechanics concerned with the study of the propagation of cracks in materials. It uses methods of analytical solid mechanics to calculate the driving force on a crack and those of experimental solid mechanics to characterize the material's resistance to fracture. Theoretically, the stress ahead of a sharp crack tip becomes infinite and cannot be used to describe the state around a crack. Fracture mechanics is used to characterise the loads on a crack, typically using a single parameter to describe the complete loading state at the crack tip.

Fracture

Fracture is the separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displacement develops perpendicular to the surface, it is called a normal tensile crack or simply a crack; if a displacement develops tangentially, it is called a shear crack, slip band or dislocation. Brittle fractures occur without any apparent deformation before fracture.

Fracture toughness

In materials science, fracture toughness is the critical stress intensity factor of a sharp crack where propagation of the crack suddenly becomes rapid and unlimited. A component's thickness affects the constraint conditions at the tip of a crack with thin components having plane stress conditions and thick components having plane strain conditions. Plane strain conditions give the lowest fracture toughness value which is a material property.

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