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.     

Rheometers in scanning mode for cure of rubbers with low enthalpy: effect of heating rate and rubber–die contact

Abstract

Rheometers are usually run under isothermal conditions for the cure of rubbers, in spite of the following drawbacks: three experiments at least are necessary at different temperatures selected within a narrow temperature window, and it takes some time for thermal equilibrium to establish between the rubber sample initially at room temperature and the dies. In scanning mode, the dies of the rheometer and the sample should be heated from room temperature up to the selected final temperature at a constant rate. The effect of the value given to the heating rate, which is the main factor in this new method, is especially studied, as well as the quality of the contact between the dies and the sample. The rubber used in the present study is a natural rubber vulcanised with 2% sulphur with a low enthalpy. The kinetic parameters of this cure reaction have been previously determined by isothermal rheometry, and the enthalpy measured by calorimetry. The state of cure–temperature curves in scanning mode have been calculated using a numerical model taking into account the conduction heat transfer through the rubber, the coefficient of heat transfer at the die–rubber interface, and the kinetics of the heat evolved from the cure reaction with the enthalpy. The kinetic parameters are determined from the state of cure–temperature curves, which are similar to the torque–temperature curves, using a least squares method. The values of the kinetic parameters obtained by this last calculation, based on the mathematical treatment of these curves, are the same as those introduced for obtaining these curves using the numerical model. Thus, whatever the heating rate, ranging from 2 to 10 K min ^–1 , and the value of the coefficient of heat transfer at the die–rubber interface expressing the quality of the contact, in scanning mode the moving die rheometer (MDR) can be used to determine the kinetics of the cure of rubbers.     

Evidence that attitude accessibility augments the relationship between speeding attitudes and speeding behavior: A test of the MODE model in the context of driving

According to the MODE model of attitude-to-behavior processes, attitude accessibility augments attitude–behavior correspondence, reflecting an automatic influence of attitudes on behavior. We therefore tested whether attitude accessibility moderates the attitude–behavior relationship in a context that is governed by characteristically automatic behavior, namely driving. In study 1 (correlational design), participants (N = 130) completed online questionnaire measures of the valences and accessibilities of their attitudes towards speeding. Two weeks later, online questionnaire measures of subsequent speeding behavior were obtained. Attitude valence was a significantly better predictor of behavior at high (mean + 1SD) versus low (mean – 1SD) levels of attitude accessibility. In study 2 (experimental design), attitude accessibility was manipulated with a repeated attitude expression task. Immediately after the manipulation, participants (N = 122) completed online questionnaire measures of attitude valence and accessibility, and two weeks later, subsequent speeding behavior. Increased attitude accessibility in the experimental (versus control) condition generated an increase in attitude–behavior correspondence. The findings are consistent with the MODE model’s proposition that attitudes can exert an automatic influence on behavior. Interventions to reduce speeding could usefully increase the accessibility of anti-speeding attitudes and reduce the accessibility of pro-speeding attitudes.     

Design and realization of a mobile wheelchair robot for all terrains

A novel design of a mobile wheelchair robot for all terrains, especially for staircases and inclines, is proposed. Toachieve the required locomotion, a pair of multi-limbed structures, comprised of a lift coxae, rotation femurs and support tibiae, are pivotally mounted on the opposite sides of the body and actuated to rotate through epicyclic gear trains. A dual-footing mode with a set of wheel and crawler tractors in each support tibia permits the locomotion mode depending on various terrains, and hence the mobile wheelchair robot can navigate on a flat surface, and climb up and down stairs or inclines with its body kept horizontal. The implemented design is verified experimentally using our first manufactured prototype mobile wheelchair robot and it is shown that it could be suitable for applications to wheelchairs or others.     

Multi-Sensor-Based Control Strategy for Initiating and Maintaining Interaction Between a Robot and a Human

This paper presents a multi-sensor-based control strategy allowing a mobile robot to safely navigate with respect to a given human being. Two sensors are embedded in our robot: a vision system that is able to detect and track the person of interest, and a RFID antennas belt that can locate the tag worn by the latter. Thus, our control strategy will be built using image features (when the user is visible) and RFID information (when not). In the first case, a robust visual servoing control will be designed, while in the second case a suitable RFID controller will be proposed. Experimental results demonstrate the efficiency of the proposed control strategy.     

27—THE RôLE OF WATER IN THE SETTING OF WOOL: A STUDY OF SETTING AT TEMPERATURES ABOVE 100°C: PART II: FABRIC PROPERTIES

An account is given of a study of the changes in fabric properties caused by setting with steam in autoclaves. Dimensional stability, shear angles, thickness, and breaking strength were measured, and the influence of variations in setting conditions, such as humidity, temperature, time, pH, and mechanical pressure, was investigated. The controls necessary for eliminating end-to-end effects in whole pieces are discussed.