Naslov
The Effect of Constraint on the Fracture Toughness of Adhesively Bonded Joints

Autori
Cooper, Vincent ; Ivanković, Alojz ; Karač, Aleksandar ; McAuliffe, D ; Murphy, Neal ; Tuković, Željko

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Skup
32nd Annual Meeting of the Adhesion Society

Mjesto i datum
Savannah (GA), Sjedinjene Američke Države, 15.02.2010. - 20.02.2010

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
adhesive; joints; constraint; fracture; finite volume method; OpenFOAM

Sažetak
Although many testing methods and procedures have been standardised and used to characterize adhesive bond toughness, the accurate transfer of laboratory results to complex structures remains questionable. The difficulty arises from the existence of strong bond-line thickness effects on the fracture toughness. We aim to address this problem by examining the level of constraint within the bond-line and hence its effects on the global bond toughness. In addition, attempts are made to relate the microstructural features on the fracture surfaces with the constraint level and fracture toughness. The current work examines the fracture behaviour of adhesively bonded joints by conducting a series of low rate tapered double cantilever beam (TDCB) tests with various bond gap thicknesses. The dependence of the value of the adhesive fracture energy, GIC, for a crack propagating cohesively through the adhesive layer upon the thickness and width of the joint is investigated. A single part, nano-rubber toughened, structural epoxy adhesive was used throughout the research. Tests were carried out using two different TDCB setups: (i) Steel substrates of width 25mm (ASTM D3433) and (ii) 10mm wide aluminium 2014 substrates following the BS2001:7991 testing protocol. In order to accurately calculate the fracture toughness, numerical modelling of the TDCB experiments was performed using the finite-volume (FV) approach with a Dugdale shape traction-separation law. Numerical results were compared with experimentally recorded load-displacement and crack-length data. In addition, the mean hydrostatic stress across the crack front, prior to crack initiation, for various bond thicknessesis numerically quantified. This is used as an estimate of the geometric constraint, i.e. stress tri-axiality. Numerical results indicate that the crack tip stress field is affected by the constraint and hence bond thickness. Higher level of constraint promotes voiding (debonding) of rubber-particles in the local damage region in front of the crack, but it also restricts global plastic deformation of the adhesive. A detailed analysis of the fracture surfaces, using field emission gun scanning electron microscopy (FEG-SEM), revealed apparent variations of the microstructural features with bond gap thickness. By analysing the density and size of voids on the fracture surfaces we aim to explain the source of dependency of GIC with constraint (i.e. bond thickness and width), hence verifying the numerical results.

Izvorni jezik
Engleski

Znanstvena područja
Strojarstvo

POVEZANOST RADA