Abstract:Slow crack propagation in adhesive bonded joints has been characterised using an asymmetric wedge test. Crack position was evaluated from strain gauge measurements, both in the debonded part of the joint and in the bonded zone. Test temperature was changed during loading, giving insight into bond evolution. The technique allows accurate, and virtually continuous, determination of crack position to be made, and therefore the evaluation of crack speed versus fracture energy curves, as well as elastic properties … Show more
“…Figure 2.Normalized stress intensity factor comparison with Budzik et al. 21 as a function of c / h .…”
Section: Resultsmentioning
confidence: 91%
“…Budzik et al. 21 studied crack growth in adhesive bonded joints with an asymmetric test specimen. Their adherents were two different sized aluminum alloy beams and they attached so many strain gages to the thinner one.…”
The double cantilever beam specimen is assumed as two finite length beams, connected together, except at the initial delamination length. The energy release rate ( GI) is evaluated analytically by considering a Timoshenko beam on Winkler and Pasternak elastic foundations. The current data reduction methods have a blind spot in calculating GI when crack approaches the end of the ligament, which is considered in this study and, therefore, the simplifying assumption of infinite ligament length is not assumed here. GI will be strongly dependent on the ligament length if it is less than twice the thickness. Furthermore, the R-curves of different layups including their first points (fracture toughness) are drawn using Ρ–δ curves reported in the literature and they are compared to the experimental results. These comparisons show that Timoshenko beam on Winkler foundation gives the best results in comparison with experimental results for unidirectional and angle-ply laminates.
“…Figure 2.Normalized stress intensity factor comparison with Budzik et al. 21 as a function of c / h .…”
Section: Resultsmentioning
confidence: 91%
“…Budzik et al. 21 studied crack growth in adhesive bonded joints with an asymmetric test specimen. Their adherents were two different sized aluminum alloy beams and they attached so many strain gages to the thinner one.…”
The double cantilever beam specimen is assumed as two finite length beams, connected together, except at the initial delamination length. The energy release rate ( GI) is evaluated analytically by considering a Timoshenko beam on Winkler and Pasternak elastic foundations. The current data reduction methods have a blind spot in calculating GI when crack approaches the end of the ligament, which is considered in this study and, therefore, the simplifying assumption of infinite ligament length is not assumed here. GI will be strongly dependent on the ligament length if it is less than twice the thickness. Furthermore, the R-curves of different layups including their first points (fracture toughness) are drawn using Ρ–δ curves reported in the literature and they are compared to the experimental results. These comparisons show that Timoshenko beam on Winkler foundation gives the best results in comparison with experimental results for unidirectional and angle-ply laminates.
“…Details of the instrumented SCB test are reported elsewhere. [56] In the pre-crack stage of the experiment, upon which this work is focussed, we consider a(t) = a(0) = const., although F(t) is increased at constant rate to some final value F 0 (t) = const. Provided F 0 causes a retarded deformation in the adhesive layer, Δ(t) increases with time.…”
Retarded deformation at the bond line edge of a thick, viscoelastic adhesive layer is observed using digital image correlation. Such information is required for proposing physical crack onset/propagation parameters which take into account viscoelastic and viscous mechanisms in the evaluation of dissipated energy. A complex stress/strain redistribution is observed in the early stage after specimen loading. The results illustrate that viscoelasticity dissipates a considerable amount of energy prior to crack nucleation and the lack of predictive models to account for that phenomenon.
“…There has been controversy on whether the adhesive properties in the thin film form (adhesive joint) are the same as the corresponding bulk properties. However, in many applications, it is crucial to take into account the intrinsic properties of adhesive joint [15] because it conditions the assembly strength, stiffness and durability [16]. In several mechanical investigations, a good agreement between the two configurations has been found [17][18][19][20][21].…”
International audienceA new sample configuration has been developed in order to study molecular mobility of an adhesive in a bonded assembly configuration by dynamic mechanical analysis. The torsional rectangular mode is used to provide a shear solicitation all along the adherend/adhesive interface. The initial mechanical properties of each assembly's constituent are first investigated as reference. The modulus of aluminum foils used as substrates exhibits a classic elastic component and a slight viscous part due to microstructural changes or stress relaxation. Four relaxation modes are highlighted and identified for epoxy adhesive tested as a bulk material. Its viscoelastic behavior is compared to the one of adhesive tested in assembly configuration. The relaxation modes of the adhesive remain visible in spite of the sample stiffening by aluminum foils. Relaxation modes comparison shows that the temperature of loss modulus associated with the mechanical manifestation of glass transition slightly increases for the assembly configuration. Energy losses during this relaxation are much higher in the assembly configuration. Influence of rigid aluminum substrates is discussed in terms of the adhesively bonded joint solicitation mode
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