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Fracture process zone and crack migration in pure mode II bonded composite joints

influence of pre-crack, stacking sequence, normalized crack-geometry

Journal Article (2026)
Author(s)

Ishan Manoj (TU Delft - Aerospace Engineering)

Daniel Bernardes de Castro (TU Delft - Aerospace Engineering)

John Alan Pascoe (TU Delft - Aerospace Engineering)

René Alderliesten (TU Delft - Aerospace Engineering)

Research Group
Group Alderliesten
DOI related publication
https://doi.org/10.1016/j.compstruct.2026.120440 Final published version
More Info
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Publication Year
2026
Language
English
Research Group
Group Alderliesten
Journal title
Composite Structures
Volume number
389
Article number
120440
Downloads counter
21
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Abstract

This study examines how loading mode during pre-cracking, stacking sequence, and initial delamination ratio (a0/L) influence Mode II fracture characterization (GIIC) of bonded composite joints. 3-point End-Notched Flexural tests were performed on Unidirectional (UD) and Quasi-Isotropic (QI) carbon fibre/epoxy laminates bonded with AF163-2 K adhesive. Results reveal that fracture toughness and crack migration are governed by the morphology of the Fracture Process Zone (FPZ). In UD laminates, Mode I pre-cracking forms localized FPZ, requiring intense plastic deformation to transition into shear-dominated FPZ, capturing the upper-bound fracture resistance. Conversely, Mode II pre-cracked specimens exhibited diffused shear FPZ, resulting in lower GIIC. In QI laminates, diffused FPZ by Mode II pre-cracking delays crack migration into the weaker interlaminar, promoting growth within the bond-layer. However, localized FPZ from Mode I pre-cracks requires intense plastic deformation and shear cracks for the crack to grow in the bond-layer, triggering earlier migration. The crack migration was sensitive to the “a0/L” ratio: a ratio of 0.4 induces independent interlaminar delamination, while 0.6 displays angular crack-migration. These mechanisms remained invariant when the span-length was scaled, provided the normalized crack length was preserved. This study demonstrates that GIIC is process-dependent, underscoring the need to characterize fractures based on FPZ evolution.