The fracture of epoxy- and elastomer-modified epoxy polymers in bulk and as adhesives

Abstract

SynopsisThe fracture behavior of a piperidinemisphenol A diglycidyl ether (A) resin has been determined in bulk a q l as an adhesive using the linear elastic fracture methods developed by Mostovoy. The effect of adding carboxy-terminated butadiene-acrylonitrile (CTBN) elastomer to resin A was investigated. The opening-mode fracture energy (91~) of resin A was 120 to 150 J/m2, and largely attributable to plastic deformation. Fractographic evidence was obtained for plastic flow a t the crack tip during crack initiation. Propagation was unstable due to the rate dependence of the plasticity. There were no significant differences in the bulk and adhesive fracture behavior. Addition of 5-15% CTBN to resin A produced minute elastomer particles which increased Sic to -4000 J/m2 (at 15%). Further CTBN addition resulted in an elastomerepoxy blend and a decrease in fracture energy. Fractography again indicated that crack initiation involved plastic deformation but that the elastomer had greatly increased the volume in which the deformation occurred. The adhesive fracture of the elaatomer-epoxy was found to be strongly dependent on the crack-tip deformation zone size (ryJ in that 9 1~ was a maximum when bond thickness was equal to 2 rye. At bond thicknesses less than 2 r,, there was a restraint on the development of the plastic zone resulting in lower 91. values.

Effects of bond gap thickness on the fracture of nano-toughened epoxy adhesive joints

“…Mostovoy et al [5] investigated the effects of adhesive joint geometry on the toughness of commercial toughened epoxy adhesives with aluminium adherends and found that an increase in bond gap thickness resulted in an increase in toughness. Bascom et al [1] also investigated the behaviour of rubber--modified epoxy resin using the tapered double--cantilever beam (TDCB) configuration and found that the fracture energy is maximized when the bond thickness equals the diameter of the plastic zone formed ahead of the crack tip.…”

A multiscale parametric study of mode I fracture in metal-to-metal low-toughness adhesive joints

“…In Regime III, for ℎ ℎ >0.45 mm, the adhesive fracture energy decreases somewhat at first and then reaches a plateau value with a magnitude significantly larger than the lowest value which is exhibited for very thin adhesive layers. In previous experimental studies, Regime I has been observed by Chai (1986Chai ( , 1988, and Regimes II and III by Bascom et al (1975), Kinloch and Shaw (1981) and Chai (1986). Fig.…”

“…As might be expected, experimental studies have been carried out with a view to ascertain these effects. In particular, several researchers (Bascom et al, 1975;Chai, 1986Chai, , 1988Kinloch and Shaw, 1981) have shown that the adhesive fracture energy, , is a nonlinear function of the thickness of the adhesive layer. This effect was qualitatively explained by Kinloch and Shaw (1981) from the magnitude of the plastic dissipation in the adhesive layer being dependent upon the degree of constraint, which was supported by some experimental evidence (Hunston et al, 1989).…”

A finite element modelling methodology for the non-linear stiffness evaluation of adhesively bonded single lap-joints: Part 1. Evaluation of key parameters

“…Azari, Papimi and Spelt [27] reported in 2009 that certain researchers had found that increasing t a caused an increase in joint strength [28,29], some observed a strength decrease [5,30,31] and some no significant change at all [31,32]. A second 2009 investigation by Grant et al [26] with joints subjected to four-point bending concluded that the strength was "independent of the adhesive thickness", an "increase in adhesive thickness causes the joint overlap section to be stiffer" and that, for tension loading the strength increases with increased t a .…”