Showing papers by "Ramin Sedaghati published in 2019"

On the properties of magnetorheological elastomers in shear mode: Design, fabrication and characterization

Abstract: Magnetorheological elastomers (MREs) are novel class of magneto-active materials comprised of micron-sized ferromagnetic particles impregnated into an elastomeric matrix, which exhibit variable stiffness and damping properties in a reversible manner under the application of an external magnetic field. Characterization of highly complex behavior of these active composites is a fundamental necessity to design adaptive devices based on the MREs. This study is mainly concerned with in-depth experimental characterizations of static and dynamic properties of different types of MREs using methods defined in related standards. For this purpose, six different types of MRE samples with varying contents of rubber matrix and ferromagnetic particles were fabricated. The static characteristics of the samples were experimentally evaluated in shear mode as a function of the magnetic flux density. The particular MRE sample with highest iron particles content (40% volume fraction) was chosen for subsequent dynamic characterizations under broad ranges shear strain amplitude (2.5–20%), excitation frequency (0.1–50 Hz) and applied magnetic flux densities (0–450 mT). The results revealed nearly 1672% increase in the MRE storage modulus under the application of a magnetic flux of 450 mT, which confirms the potential of the novel fabricated MRE for control of vibration and noise in various engineering applications.

Experimental characterization and microscale modeling of isotropic and anisotropic magnetorheological elastomers

Abstract: In this research, a systematic study is conducted on the sample preparation, characterization and microscale modeling of magnetorheological elastomers (MREs) with isotropic and anisotropic particle distributions. Different MRE specimens with silicone rubber as the matrix material and varying content of carbonyl iron particles as magnetizable fillers are fabricated. The quasi-static properties of the samples are characterized experimentally using an advanced rheometer equipped with a magnetorheological device. The elastic response of the MREs at zero magnetic field is first investigated theoretically and experimentally. A microscale modeling approach is then used for predicting the response of the MREs under an external magnetic flux density. The approach is based on the idealized distribution of particles inside the matrix according to the regular lattice models or chain-like structure for isotropic and anisotropic dispersions, respectively. Several lattice types are proposed, and performance of each lattice is compared with their counterparts. Detailed explanation is provided on the behavior of the proposed lattices and changes in the properties of the MREs are described from the microstructure point of view. The results for different lattice models are then compared with the experimental measurements for both isotropic and anisotropic MRE samples.

Modeling and dynamic analysis of a vehicle-flexible pavement coupled system subjected to road surface excitation

Abstract: Increased road traffic combined with heavy vehicle loads leads to deterioration of pavements and reduces the life span of the paved roads. As a result, large amounts of financial resources are spent each year to improve and maintain road infrastructure around the world. Vehicle dynamics and pavement dynamics are strongly coupled through their contact points. This research focuses on the dynamic analysis of pavement-vehicle interaction system and the effect of coupling action on the response. The system response due to the moving vehicular load on rough road supported by a linear visco-elastic foundation was investigated. The vehicle is modeled as a two-degree-of-freedom quarter-vehicle model, and the pavement-foundation system is described by a simply supported Euler-Bernoulli beam resting on Pasternak foundation, while the tire is coupled to the flexible pavement with a single point contact. Galerkin method was used to develop a system of governing differential equations for a coupled system in the time domain. Direct numerical integration method using Newmark-β based on linear average acceleration method was then used to solve the governing equations and evaluate the response of the coupled system. The results were validated with previous research works and compared with conventional uncoupled systems. Finally, the effects of parameters such as vehicle speed, road roughness, soil stiffness and suspension damping on the responses were investigated.

Investigation on thermal relaxation of residual stresses induced in deep cold rolling of Ti–6Al–4V alloy

Abstract: In the present study, a finite element model has been developed to simulate the deep-cold rolling process on Ti-6Al-4V specimens and the following short term exposure of the treated components to elevated temperature. The developed model can be effectively used to predict the residual stress profiles induced by the process at room temperature and the following residual stress relaxation at the elevated temperature. In the present study, the thermal relaxation stage is performed using a viscoplastic model which couples the creep and plasticity deformation mechanisms to predict the state of residual stresses at the elevated temperature. For this purpose, a new set of hyperbolic creep law coefficients are identified in order to describe the primary creep at 450 °C. The accuracy of the developed finite element model to predict residual stresses is validated by comparison with the experimental data available in the literature. It has been shown that the finite element predictions correlate well with experimental results with error generally less than 10%. The developed model can be effectively utilized for parametric studies to understand the effect of different process parameters on the induced residual stresses without performing expensive experimental tests.

Modeling pavement damage and predicting fatigue cracking of flexible pavements based on a combination of deterministic method with stochastic approach using Miner’s hypothesis

Abstract: Distress in flexible pavements has been a problem in many countries due to the increase in road traffic and vehicle loads. One of the most important distress modes in the design of pavements is fatigue cracking. Despite the fact that there have been considerable efforts in recent years in fatigue performance evaluation and the design process of flexible pavements, there is still a need for further studies to overcome the difficulty in predicting fatigue cracking in terms of damage distribution considering the uncertainty associated with the input parameters of pavement life and traffic repetitions. The purpose of this paper is to develop a methodology for modeling pavement damage and predicting fatigue cracking of flexible pavements based on a combination of deterministic method with stochastic approach using Palmgren–Miner’s hypothesis. Four predictive models are introduced and used in a comprehensive case study to estimate the fatigue life of the pavement surface layer. The solutions are obtained through numerical integration based on Gaussian quadrature method. The results reveal that pavement damage has a broad range of distribution in which the actual traffic load repetitions has a Poisson distribution, while the traffic repetitions to failure follows a lognormal distribution.