This study explores the physical ageing of rubber, traditionally associated with temperature changes, with a focus on room temperature effects, particularly in carbon black-filled rubber. Contrary to previous beliefs, experiments reveal that it takes up to four days for the shear modulus to equilibrate at room temperature. The findings have significant implications for the mechanical behavior of systems containing such rubber components during temperature variations. The paper concentrates on modeling torsional energy flow in filled rubber isolator subjected to a temperature shift at room temperature. The constitutive model incorporates a novel approach considering contributions from free volume and configurational changes to represent the impact of physical ageing on the shear modulus. The resulting torsional energy flow exhibits shifts in levels, peak frequencies and trough frequencies across the audible frequency range, persisting even after temperature stabilization. This highlights the crucial role of physical ageing in the design of vibration isolation systems.

A simplified model of magnetomechanical coupling for hard magnetoactive elastomers (h-MAEs) is developed, notable for its computational speed and good agreement with experiments. The model is based on the forces acting on magnetic dipoles in a magnetic field. It utilizes the finite element method, with each element represented as a magnetic dipole. The fabrication process and the simulation of magnetic-field-induced deformation of a soft gripper made of h-MAE are conducted. The mechanical properties are measured using tensile testing and the magnetic characteristics are evaluated through magnetic hysteresis loops. The deformation of the gripper is analyzed with digital image correlation and compared to the simulation results. The model provides efficient and fast computation with reliable results, facilitating the design of soft robots with various functionalities.

The attenuation of the structure-borne sound caused by elevator systems in residential buildings is a priority for manufacturers. This work develops a model of an active control isolation system for the vibrations produced by the elevator drive machine. This solution proposes the substitution of conventional passive isolators by new ones made of a magnetorheological elastomer (MRE), a smart material whose modulus can be modified by applying a magnetic field. To guide the design process, MRE isolators are fabricated and experimentally tested statically and dynamically in compression mode. Subsequently, the parameters of the MRE are fitted to build a nonlinear material sub-model that accounts for the frequency, amplitude, and magnetic field dependency. Afterward, a global model of the elevator drive machine vibration isolation system is developed, which incorporates the drive machine, structure, and MRE-based isolator. To enhance vibration isolation, two active control strategies are designed and assessed. Simulation results predict that active control systems based on MRE isolators improve vibration isolation as compared to traditional passive systems. The excitation amplitude and frequency, along with the control strategy and magnetization of the MRE isolators are shown to be critical parameters when designing an active control solution.

Soft magnetorheological elastomers (s-MRE) are a kind of smart material with soft magnetic particles embedded in an elastomer matrix. Under a magnetic field, there is pronounced magnetostriction and magnetically controllable mechanical properties for s-MRE, offering broad application prospects in soft robotics, surface pattern control and vibration control. While most existing literature on s-MRE focuses on the quasi-static behaviour, neglecting inertia effect, the dynamic behaviour and potential nonlinear oscillation phenomenon in certain scenarios of s-MRE-based actuators remain underexplored. In order to addressing this gap, a novel dynamic model which incorporates the magnetization, nonlinear viscoelasticity and inertia effects of isotropic s-MRE is proposed to explore the interplay among magnetic field, inertia and viscoelasticity on its dynamic behaviour. After developing the corresponding two-dimensional finite element implementation platform, this study examines the magnetic-induced dynamic behaviour of an isotropic s-MRE-based bilayer beam through numerical simulation. The influence of inertia and viscoelasticity on the magnetic-induced deformation as well as the unique nonlinear vibration characteristics of isotropic s-MRE-based system, such as superharmonic and resonance jump, are explored. Furthermore, to further enhance practical applications, novel magnetic field control algorithms aimed at mitigating harmonic distortion and tuning the vibration frequency of isotropic s-MRE-based magnetic actuation systems are introduced. These findings significantly advance the understanding the dynamic behaviour of s-MRE, paving the way for practical applications of s-MRE in magnetic field-driven loudspeakers and active noise control devices.

Filler reinforced rubber is widely used for engineering applications; therefore, a sound characterization of the effects of physical aging is crucial for accurately predicting its viscoelastic properties within its operational temperature range. Here, the torsion pendulum is used to monitor the evolution of the storage and loss modulus of carbon black filled samples for four days after a temperature drop to 30 degrees C. The storage modulus presents a continuous increase, while the loss modulus generally displays a steady decrease throughout the four days that each test was conducted. The relationship of the recovery rates with the carbon black properties is also studied, analysing its dependency on the particle size and aggregate structure. The evolution of the recovery rate seems to depend linearly on the surface area while the carbon black structure appears to have a much weaker influence on the physical aging behavior for the set of compounds tested. The obtained results corroborate the presence of physical aging at room temperature for filler rubber materials and the ability of the torsion pendulum to monitor the storage and loss modulus change, providing pivotal data on the influence of physical aging on the viscoelastic properties of the material.

This work spotlights the experiences from ten years of implementing sustainable development in all educational programs at a technical university. With a focus on the critical issue of involving more academics in the work, experiences are shared through an ethnographic account including focus group interviews. "€˜Sustainable development"€™ has been perceived as both superficial and overwhelming; unclear yet somehow predetermined; it has been perceived to demand non-existent space in the curriculum; and it has challenged the academics regardless of the subjects'€™ relatedness to sustainability. It is concluded that the evolution of a web of interconnected people, key academics, activities, norms and tools has contributed to an increased participation. The work for authenticity, reliability and feasibility, along with institution-wide and long-term academic development tools is presented.

Isotropic soft magneto-rheological elastomers (s-MRE) are polymer-based composites where magnetically soft particles are randomly distributed in the elastomer matrix. Under a magnetic field, a strong modulus magnetic stiffening effect and a magnetostriction performance is exhibited for isotropic s-MRE, offering a wide application potential in vibration control, soft robotics and haptic displays. In the last decades, substantial theoretical work has focused on modelling the magnetostriction behaviour of isotropic s-MRE. Modelling the influence of magnetic fields to the viscoelastic behaviour of isotropic s-MRE has received less attention, despite the magnetic-dependent viscoelasticity is an essential component of the observed magneto-mechanical response and of great importance for the application of isotropic s-MRE. To predict the magneto-mechanical coupling behaviour accurately and provide guidance for the design of isotropic s-MRE-based applications, a multiplicatively-typed magneto-hyperelastic free energy and a new type of process-dependent viscosity evolution law is proposed in this work. Afterwards, the ability of the model to predict the modulus magnetic stiffening effect and magnetic-dependent nonlinear viscoelastic behaviour of isotropic s-MRE is examined. Finally, three sets of finite element case studies are presented to illustrate the feasibility of the model-based simulation and guide the design of isotropic s-MRE-related applications.

The viscoelastic properties of filler reinforced rubber are measured at small strains with the torsion pendulum after a temperature change and the evolution of the storage and loss modulus is measured against the physical ageing time. Physical ageing refers to the state in which the molecules are out of thermodynamic equilibrium after a temperature change. The time needed to achieve equilibrium is the physical ageing time, during which the material displays shifting mechanical properties. For unfilled rubber, physical ageing occurs only after temperature changes below the glass transition temperature, T-g. However, filler reinforced rubber presents physical ageing after a temperature change at temperatures significantly above T-g. Therefore, the existing models of physical ageing are unsuitable for filler reinforced rubber and further characterization of the evolution of their viscoelastic properties after a temperature change is needed. The torsion pendulum is utilised to measure the material properties since it allows measurements in the rheological simple linear viscoelastic small strains and during long periods of time. The impulse response function obtained from the torsion pendulum measurements is used to calculate the storage and loss modulus at different times after a rapid temperature decrease at room temperatures. The resulting evolution shows a progressive stiffening of the material with an increase of storage modulus and decrease of loss modulus with physical ageing time. This investigation on the evolution of the viscoelastic properties after a temperature change sets the path for a proper characterization of the physical ageing phenomena for filler reinforced rubber and this allows a more reliable constitutive model to be derived.

The effect of the lubrication on the mechanical behavior of magnetorheological elastomers (MREs) in compression mode is experimentally studied. According to ISO 7743, there are two procedures to characterize specimens in compression mode. Differences in the properties of these materials between lubricated and nonlubricated conditions must be considered if devices such as vibration absorbers and isolators are to be developed. With lubrication, compression is said to be uniaxial and homogeneous, thus material properties can be obtained. Without lubrication, tests are easier to perform but results are strongly dependent on the piece shape. In this study isotropic and anisotropic MREs with iron particle volume concentrations of 10, 20, 30 and 40% are tested under different strain amplitudes, prestrain and magnetic fields for a frequency range up to 300 Hz, with and without lubrication. Important design parameters like amplitude, frequency and magnetic field dependency are showed to be dependent on lubrication.

Rail accelerations can be used on the defect detection and health monitoring of railway vehicle and track components; therefore, mathematical models that predict this response are of interest for reproducing its behaviour in a wide range of situations. The numerical track models based on the Timoshenko beam theory introduce a non-physical response, which is especially noticeable in the rail accelerations. It is due to the lack of dynamic convergence of the Timoshenko finite element (FE). This paper addresses this phenomenon employing an enhanced formulation of the Timoshenko FE that includes internal degrees of freedom (iDoF). The iDoF shape functions are derived from the Timoshenko beam dynamic governing equations. Firstly, the formulation is presented, and its performance is compared with a similar Timoshenko FE formulation. Secondly, the proposal is assessed in the dynamic modelling of railway track structures. The use of iDoF efficiently corrects the non-physical response of rail accelerations by improving the FE dynamic convergence. Subsequently, a filtering criterion for accelerations is proposed, which removes the remaining non-physical response while guaranteeing the conservation of coherent frequency content. Finally, practical cases are simulated for which the proposed methodology is proved to be more efficient and reliable than the standard approach.