Snap-back instability of double cantilever beam with bridging

Abstract

Adhesive bonding community shows a continued interest in using bridging mechanisms to toughen the interface of secondary bonded joints, especially in the case of laminated composites. Due to snap-back instability that occurs during fracture, confusions may exist when identifying the toughening effect experimentally. The true toughening effect may be overestimated by lumping all energy contributions (kinetic energy included) in an overall effective toughness. Here, fundamentals for bridging to enhance fracture resistance are explored through the theoretical analysis of the delamination of a composite double cantilever beam (DCB) with bridging. Specifically, we establish a theoretical framework on the basis of Timoshenko beam theory and linear elastic fracture mechanics to solve the fracture response of DCB in the presence of discrete bridging phases. We elucidate the crack trapping and the snap-back instability in structural response during the crack propagation. We identify the contribution to the overall toughness observed numerically/experimentally of both the physical fracture energy and other types of dissipation.The associated toughening mechanisms are then unveiled. Furthermore, we study the effects of property of the bridging phases on the snap-back instability, based on which, we propose a dimensionless quantity that can be deployed as an indicator of the intensity of snap-back instability. Finally, we identify the role of geometrical properties, i.e. the substrate thickness and the arrangement spacing of the bridging phases, in the snap-back instability and the macroscopic fracture toughness of a DCB. This work provides, from a theoretical point of view, an essential insight into the physics related to the structural response of DCB with discrete toughening elements.

Snap-through Crack Propagation in Architected Bonded Interfaces Analyzed Using a Mechanoluminescent SAO/E Coating

“…We did not observe such an event in any of our tests. However, as reported elsewhere, it may likely occur when the stored energy during the trapping/arrest phase is large enough, such as in the case of bridging in composites and adhesive joints …”

“…However, as reported elsewhere, it may likely occur when the stored energy during the trapping/arrest phase is large enough, such as in the case of bridging in composites and adhesive joints. 38 ML Emission Patterns. In the current study, the crack tip approaching the wall between consecutive channels experiences an acceleration as the crack growth becomes unstable.…”

Improving the crack propagation response of layered and bonded structures through dissipation mechanisms at different length scales

“…While a single ligament was considered in the discussion up to now, the ligaments distribution and variability also play a crucial role in the crack propagation response. Concerning the ligaments distribution, while the presence of small, densely distributed ligaments can be effectively modelled as an equivalent macroscopic CZM, the effect of few, distant ligaments is best described with discrete cohesive "springs", similar to those considered in [21]. As it was…”

“…shown in [22,21], the denser the ligaments are, the more ligaments are active simultaneously during crack propagation, resulting in a more progressive and stable global behaviour. On the other hand, few large ligaments may result in multiple global instabilities, one for each ligament failure, even if the local ligament behaviour is stable.…”

“…The CZM modelling approach discussed in this paper, eventually completed with a discrete bridging vision similar to [21] and an appropriate description of dynamic effects, could play a very important role in the understanding of the role of these multiple microscopic bond features.…”