Bondline thickness: Fracture mechanics perspective

Sofia Teixeira de Freitas, Michal K. Budzik

Research output: Chapter in Book/Conference proceedings/Edited volumeChapterScientificpeer-review

1 Citation (Scopus)
63 Downloads (Pure)


The bondline thickness is a crucial parameter affecting the strength and toughness of adhesive joints. This parameter is responsible for the stress distribution, and thus, the efficiency of the stress transfer between the adherends, the failure modes, and the correspondent failure loads. However, the available literature reports different trends and relationships during testing between the thickness and strength, or thickness and toughness. In this chapter, the effect of adhesive thickness on the mechanical properties of adhesive joints is explored using the fracture mechanics framework. Two testing cases are discussed in detail: (i) soft bondlines joining rigid adherends, that is, butt joint and single end notch testing specimens, and (ii) rigid bondlines joining flexible adherends, that is, double cantilever beam geometry. These cases represent two extremes in terms of where the energy is stored while testing: in the first one, the energy is stored in the adhesive while in the second, the energy is stored in the adherends. From this discussion, the bondline thickness emerges as a critical geometrical parameter dictating transition between the two extreme cases. A single theoretical framework is provided that merges the two cases and is used to disclose the recently obtained experimental results.

Original languageEnglish
Title of host publicationAdvances in Structural Adhesive Bonding, Second Edition
Number of pages27
ISBN (Electronic)9780323912143
ISBN (Print)9780323984379
Publication statusPublished - 2023

Bibliographical note

Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project
Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.


  • Adhesive thickness
  • Crack onset
  • Poisson’s ratio effect
  • Singular stress fields
  • Thick bondlines


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