Pullout tests are a common experimental and analytical tool commonly used for the characterization of bonding and debonding behavior of composite, layered and sandwich structural components. A survey of the literature indicates that uncertainty regarding the physical properties of the problem is rarely considered in the analysis of the structural response. However, such uncertainties are expected to play a significant role following the potentially brittle and unstable nature of the debonding process. In the context of the pullout test, as well as in other structural configurations, the effect of the entire bonding layer is usually assumed to be properly described by a single bond-slip law (traction-separation, or cohesive interface, law) which analytically connects relative displacements between the two structural layers and the tractions they develop. This assumption has been examined in several studies where a high order model for the adhesive layer together with two cohesive interfaces were suggested as a more accurate modeling approach. However, in the context of the pullout configuration, and, particularly, in the context of the uncertainty involved in the structural failure mechanism, the significance of such richer modeling approach was not examined.In the current work, a stochastic analysis of the debonding process during a pullout test on a layered composite structure is presented. The effect of explicitly modelling the adhesive layer is specifically examined, and the coupled effect of considering both uncertainty and an explicit modeling of the adhesive layer is highlighted. For this purpose, a single composite sheet attached to a rigid substrate and subjected to a prescribed axial displacement is examined. Following the concepts of the high-order sandwich beam theory, the adhesive is modeled as a deformable linear elastic layer of finite thickness obeying presumed high order displacement fields. Cohesive interfaces are used to model separately the two interfaces of the adhesive. For comparison, a simplified (and commonly used) model is considered, in which the composite strip is mathematically attached to the rigid substrate through a single cohesive interface. Physical uncertainty is considered in both models by a random field representation of geometrical, material, and interfacial properties. The stochastic structural analysis is carried out by the perturbation-based Stochastic Finite Element Method and its augmentation to incorporate a pseudo-arc-length method. The latter aims to take care of the highly nonlinear character of the problem and the resulting snap back folds.The stochastic results describe the way uncertainty in various input quantities evolves along the debonding process, the hierarchy of the contributions of these uncertainties to the uncertain structural response, and the impact of explicitly modeling the adhesive layer on these predictions. The comparison to the simplified model points at significant differences between the two modeling approaches that can be seen both in the deterministic and in the stochastic analyses.

Stochastic Analysis of Layered Structure's Pullout Test and the ‎Significance of Modeling the Adhesive Layer

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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