Now showing 1 - 4 of 4
  • Publication
    Effects of bond gap thickness on the fracture of nano-toughened epoxy adhesive joints
    The current work is a combined experimental-numerical study of the fracture behaviour of a nano-toughened, structural epoxy adhesive. The mode I fracture toughness of the adhesive is measured using tapered double-cantilever beam (TDCB) tests with various bond gap thicknesses ranging from 0.25 mm to 2.5 mm. Circumferentially deep-notched tensile specimens are independently employed to measure the cohesive strength of the adhesive as a function of constraint. The experimental TDCB test results are predicted numerically for each bond gap thickness using the Finite Volume method and a Dugdale cohesive zone model. A unique relationship between the fracture energy and the constraint level is established. The effect of bond gap thickness on the fracture behaviour of TDCB joints is hence directly attributed to the variation of the intrinsic fracture energy with constraint and not to the variation of the ‘far field’ plastic zone size with bond gap thickness. Using the well known Rice and Tracey void growth model, a link is established between the voids observed in the fracture process zone, the constraint imposed by the thickness of the adhesive and the resulting fracture energy.
      703Scopus© Citations 57
  • Publication
    Modelling the fracture behaviour of adhesively-bonded joints as a function of test rate
    Tapered-double cantilever-beam joints were manufactured from aluminium-alloy substrates bonded together using a single-part, rubber-toughened, epoxy adhesive. The mode I fracture behaviour of the joints was investigated as a function of loading rate by conducting a series of tests at crosshead speeds ranging from 3.33 × 10−6 m/s to 13.5 m/s. Unstable (i.e. stick–slip crack) growth behaviour was observed at test rates between 0.1 m/s and 6 m/s, whilst stable crack growth occurred at both lower and higher rates of loading. The adhesive fracture energy, GIc, was estimated analytically, and the experiments were simulated numerically employing an implicit finite-volume method together with a cohesive-zone model. Good agreement was achieved between the numerical predictions, analytical results and the experimental observations over the entire range of loading rates investigated. The numerical simulations were able very readily to predict the stable crack growth which was observed, at both the slowest and highest rates of loading. However, the unstable crack propagation that was observed could only be predicted accurately when a particular rate-dependent cohesive-zone model was used. This crack-velocity dependency of GIc was also supported by the predictions of an adiabatic thermal-heating model.
      551Scopus© Citations 82
  • Publication
    The Bond Gap Thickness Effect on the Fracture Toughness of Nano-Toughened Structural Epoxy Adhesives
    (Adhesion Society, 2010-02-19) ; ; ;
    This work employs combined experimental and numerical studies to investigate the effect of bond gap thickness on the fracture behaviour of a nano-toughened epoxy adhesive produced by Henkel. Tapered-double cantilever-beam (TDCB) joints were subjected to a constant low loading rate. The mode I fracture behaviour of the joints was investigated as a function of bond gap thickness, which was varied from 0.25 to 2.5 mm. A detailed analysis of the fracture surfaces was carried out using scanning electron microscopy (SEM) and variations of the microstructural features with the bond gap thickness, and corresponding constraint, were revealed. The Rice and Tracey void growth model is used to relate the local plastic strain calculated by measuring the size of the voids on the fracture surfaces with the constraint calculated numerically for each bond gap thickness. It was shown that the difference in constraint imposed by different bond gap thicknesses is responsible for the observed dependency of GIC.