Advanced Materials Research Vols. 47-50

Abstract: This paper presents a novel Adaptive Tuned Vibration Absorber (ATVA) using the enhanced magnetorheological elastomers (MREs) for powertrain vibration reduction. The MRE material used in this application includes micro-sized iron particles enhanced by adding nano-sized magnetic powders. With the enhancement, MRE’s elastic modulus significantly increases due to the MR effect. In the new ATVA, the MRE plays a role as a torsional spring whose stiffness coefficient can be varied with an external magnetic field. Additionally, this ATVA could operate in shearsqueeze mode rather than shear mode. Thus, the frequency range is much wider than that of general MREs. Such property of the enhanced MRE is an advantage for constructing a smart ATVA for powertrain vibration control because the ATVA can work effectively in a wide frequency range instead of a narrow bandwidth as a conventional dynamic absorber does. Numerical simulations of a powertrain system for the second and third gear fitted with the ATVA are used to validate its effectiveness. The obtained results show that the powertrain vibration can be greatly suppressed. Particularly, the ATVA is effective in reducing the powertrain vibration not only in case of the single harmonic excitation but also for the case of the multi-harmonic excitation. Furthermore, the simulation results can be used to optimize the ATVA’s design, which will be our next work.

Abstract: Entangled materials are similar to cellular materials, with regard to their low density and discrete architecture. In this work steel wool (sintered in a furnace for various time at two temperatures) and non sintered steel wool are investigated. Experimental mechanical compression tests were performed on both materials. Compression stress and Young’s modulus are extracted and compared with the time and temperature of sintering, and initial density. The results are analyzed using a classical Toll’s model. A special attention is paid to the value of the exponent which relates stress and Young’s modulus to density. This exponent ranges from 3 to 5 for non sintered wool, and is close to 3 for the stress law and 4 for the Young’s modulus law for sintered wool.

Abstract: Interlocked materials are new examples of “hybrid materials”, mixing materials and structures at a millimetric scale. They consist of periodic assemblies of elementary blocks with specific shapes, maintained in contact by compressive boundary conditions. These “pre-fragmented materials” can simultaneously fulfil antagonistic properties such as high strength together with good damage tolerance. We performed indentation tests on two different structures: (i) an assembly of osteomorphic ice blocks and (ii) an assembly of plaster made cubes. The tests being performed up to the failure, it is found that these structures dissipate much more mechanical energy than similar monolithic plates and preserve their integrity up to much larger deformation. A numerical modelling is then developed in order to reproduce this behaviour. Using finite elements, we simulated the friction contact between two elastic cubes or blocks, for a given lateral load and friction coefficient. The outputs are then introduced as local contact rules in a “Discrete Elements code” specially developed for this study. The discrete code is then used to model the elastic and damage behaviour of assemblies of cubes or osteomorphic blocks. The comparison with experimental results is satisfactory. Finally, the code is used to model larger assemblies of interlocked structures for which the force path is analysed.

Abstract: Guided wave structural damage detection is one of promising candidates for the future aircraft structural health monitoring systems. There are several advantages of guided wave based damage detection: well established theoretical studies, simple sensor devices, large sensing areas, good sensitivity, etc. However, guided wave approaches are still vulnerable to false warnings of detecting damage due to temperature changes of the structures. Therefore, one of main challenges is to find an effective way of compensating temperature changes and to imply it to existing damage detect algorithms. In this paper, a simple method for applying guided waves to the problem of detecting damage in the presence of temperature changes is presented. In order to examine the effectiveness of the presented method, delaminations due to low-velocity impact on composite plate specimens are detected. The results show that the presented approach is simple but useful for detecting structural damage under the temperature variations.

Abstract: This study investigated the effect of the enhancement by addition of Micro Fibrillated Cellulose (MFC) on the static, fatigue and impact properties of plain-woven CFRP. Test results showed that the addition of MFC little contributed to the improvement of static properties. However, the initiation of matrix cracks between woven carbon fiber cloths was prevented under cyclic loading so that the fatigue life of the CFRP was improved by the modification with MFC. The ductility of plain-woven CFRP was also acquired under impact load by the addition of the MFC to the matrix.

Abstract: In this paper, active vibration control performance of the smart hull structure with Macro-Fiber Composite (MFC) is evaluated. The governing equations of motion of the hull structure with MFC actuators are derived based on the classical Donnell-Mushtari shell theory. Subsequently, modal characteristics are investigated and compared with the results obtained from finite element analysis and experiment. The governing equations of vibration control system are then established and expressed in the state space form. Linear Quadratic Gaussian (LQG) control algorithm is designed in order to effectively and actively control the imposed vibration. The controller is experimentally realized and control performances are evaluated.

Abstract: This paper presents control performances of a magnetorheological (MR) fluid-based multifunctional haptic device which is applicable to realization of in-vehicle comfort functions. By combining the functions into a single device, the proposed haptic device can transmit various reflection forces for each comfort function to a driver without requiring the driver’s visual attention. As a multifunctional haptic device, a MR knob is proposed in this work and devised to be capable of both rotary and push motions with a single knob. Based on the optimally determined design parameters to maximize a control torque, the proposed haptic device is manufactured. And in-vehicle comfort functions are constructed in virtual environment which makes the functions to communicate with the haptic device. Subsequently, a feed-forward controller using torque/force maps is formulated for the force tracking control. Control performances such as reflection force of the haptic device are experimentally evaluated via the torque/force map-based feed-forward controller.

Abstract: This paper presents damping force control performances of a magnetorheological (MR) damper via new control strategy considering hysteretic behavior of the field-dependent damping force. In order to achieve this goal, a commercial MR damper which is applicable to passenger vehicle is adopted and its field-dependent damping force is experimentally evaluated. Since the field-dependent damping force shows the hysteretic behavior which significantly affects to control characteristics of the system, Preisach hysteresis model for the MR damper is established and its first order descending (FOD) curves are experimentally identified. Subsequently, a feed-forward compensator strategy for the MR damper is formulated and damping force control is evaluated. In addition, vibration control performances are experimentally evaluated with quarter-vehicle test facility.

Abstract: In this work, a simple but effective approach was reported for preparing natural fiber reinforced plastic foams based on plant oil with excellent compressive performance and biodegradability. Firstly, epoxidized soybean oil (ESO) was converted into its acrylate ester AESO, which can be free-radically copolymerized with reactive diluents like styrene to give thermosetting resins and their foam plastics. Then the bio-foam composites were produced using short sisal fiber as the reinforcement. Effects of fiber loading, length and surface treatment on properties of the foam composites were investigated. It was found that exposure of the fibers to gas cells of the foam reduced the effectiveness of interfacial effect, which is different from conventional bulk composites. As a result, reinforcing ability of sisal fibers became a function of fiber length, loading, etc. Furthermore, the plastic foams based on plant oil resin were proved to be biodegradable in soil burial or in the presence of fungi.

Abstract: This paper presents both theoretical and experimental study of particle motion in a typical interdigitated electrode array. Both finite element method and numerical simulation were performed to predict the movement of particles. The simulation results indicated that the particle motion and separation behaviors strongly depend on the combined contributions of a number of parameters, such as the frequency of the electric field, applied voltage, dielectric properties of the particles and the surrounding medium.