Strength improvement of a smart adhesive bonded joint system by partially integrated piezoelectric patches

In order to reduce the stress concentration in the adhesive layer of an adhesively bonded joint, a smart adhesive joint system was developed by integration of piezoelectric sensors/actuators patches, bonded to the surfaces of the adherends, near the ends of the joint area. By adjusting the applied electric field on the piezoelectric layer in the developed smart joint system, one can produce additional forces and moments which would act oppositely to those developed internally, thereby alleviating the stress concentration in the joint edges. This would, in turn, improve the performance of the adhesively bonded joint. In our work, the strength enhancement of the developed smart bonded joint system was first evaluated by an experimental investigation. In addition, a theoretical analysis model was developed for predicting the effect of the applied electric field on the surface-bonded piezoelectric patches.     

Wood-dowel rotation welding – a heat-transfer model

The relationship between temperature, time of friction and thermal flux for high-speed rotational wood-dowel welding has been modelled through a heat-transfer model. It was shown that the interface temperature could be estimated as a function of the friction time by the general equation T ₀ = T _i + 2βuτ√α/h√π √t, where T ₀ – temperature at the welding interface, T _i – initial temperature of the wood, t – time, τ – the friction stress, u – the rate of rotation or vibration, β – the fraction of mechanical energy convertible into thermal energy, and h and α are, respectively, the thermal conductivity and diffusivity of the wood. For both the rotation welding and linear welding systems, the value of β is found to be 0.080±0.01. The results obtained for dowel rotation welding indicate that a temperature of 180°C is optimal for rotational dowel welding. The model was validated from experimental data on rotational dowel welding for the portion of the curve in which temperature increased as a function of time. Furthermore, it was also validated from experimental data for linear vibration welding.     

A Rate-Dependent Cohesive Zone Model for Adhesively Bonded Joints Loaded in Mode I

The present work investigates the rate-dependent failure behaviour of structural adhesive joints loaded in mode I. Butt joint and tapered double cantilever beam (TDCB) specimens were tested at velocities ranging over more than six orders of magnitude. A rate-dependent extension of the bi-linear cohesive zone model is proposed and implemented into the finite element code LS-DYNA via an user-defined subroutine. The parameters for the implemented cohesive zone model are found directly by evaluation of experimental data. The comparison of simulations with experimental results for different specimen types and test velocities validates the proposed model. The critical energy release rate of adhesively bonded joints is usually measured in (tapered) double cantilever beam tests, and evaluated using the Irwin–Kies equation. In this paper a different evaluation method is proposed, which provides additional information on the energy dissipated during crack initiation. The results of this method agree with the results obtained using the Irwin–Kies equation. The investigations have focussed on thin adhesive layers. Parameter identification and validation have been performed using the crash-optimized adhesive Terokal 5077 from Henkel.