Lingyu Sun

The dynamic performance of magnetic-sensitive elastomers under impact loading

This work presents the impact response of magnetic-sensitive elastomer (MSE) under combined mechanical and magnetic loads. Two types of MSE specimens with iron particles (spheres) embedded uniformly or in chain-like arrangement in a rubber matrix are prepared by our group. Their dynamic behaviors are studied by a drop hammer-based experimental set-up with magnetic field generator. A numerical simulation method based on magneto?structural coupling is also provided. Both the experimental measurement and the numerical simulation demonstrate that the peak acceleration increases, and oscillation period and the total mitigation time decreases with increasing magnetic field intensity, for any type of MSE. Also, the chain-like structure enhances the trend above further. The failure mode for both types is matrix crushing, which occur at the positions between adjacent spheres within a chain where the impact and magnetic forces are superimposed.

Tunable isolator based on magnetorheological elastomer in coupling shear–squeeze mixed mode:

In this article, the systematic design, construction, and testing of a novel tunable isolator based on magnetorheological elastomers in coupling shear–squeeze mixed mode have been studied. The influence of magnetic particle volume fraction on field-induced properties of magnetorheological elastomer isolator is studied, and the performance of vibration mitigation of magnetorheological elastomer isolator is evaluated experimentally. The results show that the frequency-shift property of magnetorheological elastomer isolator is linearly proportional to the magnetic particle volume fraction and applied current, and vibration mitigation capacity of magnetorheological elastomer isolator is remarkably enhanced by increasing the applied current. The design of magnetorheological elastomer isolator in coupling mixed mode may provide a new insight for using magnetorheological elastomers in vibration reduction applications.

Impact Damage and Residual Strength of Composite Joints in Car Bodies

With the weight reduction requirements for vehicles and the cost reduction tendency for carbon fibers, carbon fiber reinforced plastics (CFRPs) will be applied more and more in automobile bodies in place of some steel materials. However, the structural design method using CFRPs is much different from that using steel. For example, the anisotropic material properties and the brittle plastics matrix need to be considered, and the connection between components is through adhesive joints, which is possibly weaker than the traditional spot welding. These features make CFRPs sensitive to impact loads, especially the repeated low-energy impact.This paper presents a damage-based residual modulus and strength prediction method, which may be utilized in the design of composites components subject to repeated impact loads.First, the CFRPs samples were impacted repeatedly by the pendulum hammer at a constant kinetic energy, 2J, and then, the residual bending modulus and strength were measured by static three-point bending machine. According to the test data, the relationship between impact number and residual stiffness and residual strength were established, and the damage factors after each impact were calculated. In subsequent numerical simulation, the damage accumulation effect was included in the one-step prediction model through replacing the initial modulus by the degradation modulus, and this method was verified numerically by comparison with N-step prediction results after N-times impact calculations. Finally, two kinds of composite joints were analyzed numerically, which provides theoretical guide for the design of composite joints in automobile body.© 2013 ASME

Shock attenuation mechanisms of magnetorheological elastomers absorbers: A theoretical analysis

To predict the dynamic response of shock absorbers based on magnetorheological elastomers and investigate the contributions of various possible energy dissipation mechanisms, a modified four-parameter model of magnetorheological elastomers was proposed, which includes the viscoelastic characteristics of rubber matrix, the variable stiffness and damping property, and the interfacial bond conditions of magnetorheological elastomers under the applied magnetic field. The constitutive equations of magnetorheological elastomers were derived and all parameters were identified based on a published literature. It is theoretically demonstrated that the maximum response force under an impulse input could be attenuated approximately 30% when the magnetic field with 0.57 T is applied. Using the proposed theoretical model, it is shown that the energy dissipation mechanisms mainly come from the interfacial friction between particles and matrix, and the increment on stiffness and dynamic viscosity of the rubber matrix provides reverse contributions to the shock mitigation, while the interfacial bond stiffness has little influence on the response force amplitude. Hence, when magnetorheological elastomers are utilized in shock absorbers, it is suggested to take advantage of the interfacial friction energy.

Investigation on Field-Response Performance of Magnetic-Sensitive Rubber by Impact Experiments With Adjustable Magnetic Fields

A magnetic-sensitive rubber (MSR) can change its stiffness and damping characteristics with variant magnetic intensity. Hence, it is possible to use it in dissipating the impact energy adaptively. Although the relationships between elastic modulus, damping ratio and magnetic intensity have been investigated extensively by static tensile, compression or shear experiments as well as vibration tests, few literatures have shown the effectiveness of MSRs on energy dissipating during impact. In this present paper, a group of magnetic-sensitive specimens, composed by ferromagnetic particles with various volume fraction, particle dimensions at millimeter-scale or micrometer-scale, particle arrangement in chain-like or uniform distributions, and rubber matrix with three different types were manufactured. Then, a series of impact experiments aimed to test the capability of MSRs in mitigating shock was conducted by a self-developed drop hammer device with adjustable homogeneous magnetic field. The influences of the above factors on the acceleration responses were investigated. To explain the mechanism, the mathematical model of the impact process was established, and based on it; the acceleration response was obtained by MATLB software. The numerical solutions are validated by comparing with the corresponding test results. It is found that the volume fraction of particles and magnetic intensity has the obvious influences on the dynamic acceleration response, while the arrangement of macro-particle in matrix affects less. Micro-particles can change the characteristics of matrix more significantly than the macro-particles.Copyright

An Equivalent Method for Optimised Design of Nested Tube Energy Absorber Under Space Constraints

This paper investigates the relationship of energy absorption between individual tube and nested tubes system in order to provide an equivalent design method for engineers. Firstly, both analytical and numerical methods were presented to analyze single tube under lateral point-loading compression, and the influences of material model and tube dimensions on energy absorption was studied. Secondly, an energy absorption system consisted of nested tubes was equivalently modeled by the combination of single tube in parallels or/and in series, and the resultant deformation and energy absorption were derived analytically by the present method. Several typical examples were verified numerically. It also discussed the relationship between structural effectiveness and solidity ratio for tube system and its components. Finally, a nested tubes system was optimized based on the requirements of installation space, crush distance and energy absorption capability.Copyright