Zhenyu Jiang

Deformation in magnetorheological elastomer and elastomer-ferromagnet composite driven by a magnetic field

Magnetorheological elastomer (MRE) is a new class of smart materials, whose modulus can be controlled by the applied magnetic field. In this paper, using a white light speckle technique for deformation analysis, we present the real-time dynamic deformation progress (the vector diagram of the displacement or the whole-field quantitative displacement distribution) of the MRE and the elastomer?ferromagnet composite (EFC) while the magnetic field is turned on. The experimental results verify the prediction presented in a recently published paper, (Borcea and Bruno 2001 J.?Mech.?Phys.?Solids 49 2877?919), and reveals some interesting phenomena which will give us a deeper understanding for such smart materials.

Effects of Meso Shape Irregularity of Metal Foam on Yield Features under Triaxial Loading

Metallic foam is a typical porous material with heterogeneous meso structures that affect the metallic foams mechanical properties, in which shape irregularity of meso structures (porous cells) is the key. Shape irregularity of a porous cell reflects the deviation the cell shape from a sphere having the same volume. This paper examines the effects of meso shape irregularity of metallic foam on yield features based on three-dimensional (3D) Voronoi model and the finite element (FE) method. Three cubic foams designed by 3D Voronoi technique were constructed to furnish different statistics of shape irregularity but with the same initial density. Three normal stresses were applied on cubic metallic foam proportionally to implement the triaxial proportional loading in triaxial compression and tension. The yield surface of each 3D Voronoi foam under triaxial loading was calculated, and the influence of shape irregularity on the yield surface was investigated. The results show that the yield surface in (σe, σm) space may be depicted by an ellipse for metallic foams with different shape irregularities. The meso shape irregularity does clearly affect the yield surface with larger shape irregularity producing a smaller yield surface. This means that the metallic foam with larger shape irregularity yields more easily, and this feature is also reflected in the normalized yield surface for metallic foams with different irregularities.

Thermoforming carbon fibre-reinforced thermoplastic composites

The use of carbon fibre composites is growing in many sectors but their use remains stronger in very high value industries such as aerospace where the demands of the application more easily justify the high energy input needed and the corresponding costs incurred. This energy and cost input is returned through gains over the whole life of the product, with for example, longer maintenance intervals for an aircraft and lower fuel burn. Thermoplastic composites however have a different energy and cost profile compared to traditional thermosets with notable differences in recyclability, but this profile is not well quantified or documented. This study considers the key process control parameters and identifies an optimal window for processing, along with the effect this has on the final characteristics of the manufactured parts. Interactions between parameters and corresponding sensitivities are extracted from the results.

Research on the energy absorption properties of aluminum foam composite panels with enhanced ribs subjected to uniform distributed loading

A new design of aluminum foam composite panels with enhanced ribs was proposed, and the energy absorption property of it was analyzed by combining dynamic testing and numerical simulation. The optimization of aluminum foam composite panels with enhanced ribs was investigated assuming that the panels had the same total mass. An Instron drop hammer test machine was used to study the dynamic compressive behavior of the new composite panels and the impact deformation characteristics of the components. Finite element method (FEM) software was employed to simulate the loading process, and the simulation results were compared with the experimental data for validating the reliability of the model. The effect of rib-mass ratio on the energy absorption property was investigated, and the energy absorption capacities of the new composite panels and conventional sandwiches were compared at different impact velocities. The analysis shows that, compared with conventional sandwich panels, aluminum foam composite panels with enhanced ribs have better energy absorption subjected to uniform distributed loading; and both rib-mass ratio and impact velocity have an effect on the normalized energy absorption. The results of this study can be a reference for related academic research and engineering application.

Low Velocity Penetration Mechanical Behaviors of Aluminum Foam Sandwich Plates at Elevated Temperature

This paper presents the low-velocity impact tests on the sandwich plates with aluminum foam core and aluminum skins at elevated temperatures. A furnace, attached to an Instron Dynatup 9250 HV drop hammer system, was designed to accomplish the penetration tests at temperatures up to 500°C. In order to process the experimental data accurately, the numerical vibration analysis was conducted to determine the threshold frequencies of the fast Fourier transform (FFT) filter for the original impact data. The experimental results showed that the failure modes of the sandwich, peak load and absorbed energy varied obviously with temperatures. Furthermore, the results showed that the failure modes of the top skin and metal foam core showed minor changes with respect to temperatures. Whereas the failure mode of the bottom skin and peak loads changed significantly with respect to temperatures. Also, the absorbed energy revealed a three-stage variation with the change of temperature.

Mechanism of the Strain Rate Effect of Metal Foams with Numerical Simulations of 3D Voronoi Foams during the Split Hopkinson Pressure Bar Tests

With the demand of lightweight structure, more and more metal foams were employed as impact protection and efficient energy absorption materials in engineering fields. But, results from different impact experiments showed that the strain rate sensitivity of metal foams were different or even controversial. In order to explore the true hiding behind the controversial experimental data about the strain rate sensitivity of metal foams, numerical simulations of split Hopkinson pressure bar (SHPB) tests of the metal foams were carried out by finite element methods. In the analysis, cell structures of metal foams were constructed by means of 3D Voronoi, and the matrix metal was assumed to be no strain rate sensitivity, which helps to learn the strain rate effects quantitatively by the foam structures. Numerical simulations showed that the deformation of the metal foam specimen is not uniform during the SHPB tests along the specimen, and the strain–stress relations of the metal foams at two ends of the specimen are different; there exists strain rate sensitivity of the metal foams even the matrix metal has no strain rate sensitivity, when the strain of the metal foams is defined by the displacement difference between the ends of the specimen; localized deformation of the metal foams and the inertia effect of matrix metal are the two main contributions to the strain rate sensitivity of the metal foams.

DESIGN AND MECHANICAL PROPERTIES OF LIQUID RUBBER-BASED CONCRETE

A new type of concrete was developed using liquid rubber (polyurethane) as binder and graded stones as aggregate. The mechanical properties of the prepared liquid rubber-based concrete (LRBC) were systematically investigated through flexural and compressive tests. The dynamic response of LRBC to impact was studied using a spit Hopkinson pressure bar system, which demonstrates a non-monotonic strain rate sensitivity of LRBC. Furthermore, three typical pavement performance tests, i.e., rutting, seepage and sanding tests, were carried out to evaluate the potential of LRBC for the applications in pavement systems. According to the experimental study, the optimum rubber-aggregate ratio was found to be 17% (weight of binder by that of aggregate). The LRBC prepared with this recipe showed the superiority in most pavement performance indicators to other three types of conventional asphalt concrete.

A Variable Mass Meso-Model for the Mechanical and Water-Expelled Behaviors of PVA Hydrogel in Compression

Static uniaxial compressive experiments were conducted to study the mechanical behaviors of polyvinyl alcohol (PVA) hydrogels in ambient conditions. It was found that water is expelled during the compression of hydrogels that have high water contents. It means hydrogels may be a mass variable under the compression. In order to depict the mechanical properties intrinsically, a variable mass model with meso-scale cells was proposed to simulate PVA hydrogels. In the model, there are uniform cells with frames of polymer fibers and water, and a virtue membrane designed to wrap up the boundary of the model. The model not only depicts the behaviors of the compressive mechanics and the expelled water, but also explains the nonlinear stress–strain relation of PVA hydrogels and why the hydrogels with high water content demonstrate a modulus considerably lower than the bulk modulus of water.

Modeling and computing parameters of three-dimensional Voronoi models in nonlinear finite element simulation of closed-cell metallic foams

ABSTRACT Modeling and computing parameters in nonlinear finite element simulations significantly affect simulation accuracy and efficiency even when it is carried out using commercial software, such as ABAQUS, ANSYS, etc. Yet comprehensive effects of these parameters on simulation results have seldom been reported. In this article, we explore the effects of several important parameters, such as mass scaling type and value, element type and size, and loading velocity, on the accuracy and efficiency of nonlinear finite element simulation of metallic foams based on three-dimensional Voronoi mesostructures. Analysis indicated that these parameters did affect simulation accuracy and efficiency, and three optimized nondimensional parameters were recommended. Based on the verified model and optimized parameters, effects of cell-wall thickness distribution on the uniaxial properties of metallic foams were also investigated. Simulation results showed that the different distribution of cell-wall thickness in modeling may induce varied elastic moduli and yield stress of metal foams. Our analysis showed that modeling and computing parameters must be paid attention to in the nonlinear FE simulation, and that the recommended parameters constitute a good reference for numerical simulation of metallic foams in predicting mechanical behaviors.

Numerical Analysis on Usability of SHPB to Characterize Dynamic Stress–Strain Relation of Metal Foam

Split Hopkinson pressure bar (SHPB) technique is the most important test method to characterize dynamic stress–strain relations of various materials at different strain rates, and this technique re...