Shan Yi Du

Significantly reducing electrical resistivity by forming conductive Ni chains in a polyurethane shape-memory polymer/carbon-black composite

We demonstrate an approach to significantly reduce the electrical resistivity in a polyurethane shape-memory polymer (SMP) filled with randomly distributed carbon black (CB). With an additional small amount of randomly distributed Ni microparticles (0.5vol%) in the SMP/CB composite, its electrical resistivity is only reduced slightly. However, if these Ni particles are aligned into chains (by applying a low magnetic field on the SMP/CB/Ni solution before curing), the drop of the electrical resistivity is significant. This approach, although demonstrated in a SMP, is applicable to other conductive polymers.

Electrical conductivity of thermoresponsive shape-memory polymer with embedded micron sized Ni powder chains

The electrical resistivity of a thermoresponsive polyurethane shape-memory polymer (SMP) filled with micron sized Ni powders is investigated in this letter. We show that, by forming conductive Ni chains under a weak static magnetic field (0.03T), the electrical conductivity of the SMP composite in the chain direction can be improved significantly, which makes it more suitable for Joule heat induced shape recovery. In addition, Ni chains reinforce the SMP significantly but their influence on the glass transition temperature is about the same as that of the randomly distributed Ni powders.

Solution-Responsive Shape-Memory Polymer Driven by Forming Hydrogen Bonding

Recently, there is interest in triggering shape recovery of shape-memory polymers(SMPs) by novel non-external heating. In this paper, many hard works have been carried out to make SMP induced by solution. The main challenge in the development of such polymer systems is the conversion of solution-induced effects at the molecular level to macroscopic movement of working pieces. This paper presents a systematic study on the effects of solution on the glass transition temperature (Tg). The results reveal that the hydrogen bonding of shape memory polymer (SMP) was aroused by the absorbed solution that significantly reduces Tg of polymer. The mechanism behind it is solution firstly intenerates polymeric materials till the Tg of polymer lowered down to the temperature of ambient, then hydrogen bonding interaction improves the flexibility of polymeric macro-molecular chains. Thus, the shape memory effect (SME) can undergo solution-driven shape recovery. In addition, it provides a new approach that the SMP can be induced by applying non-energy stimulus. The Dynamic Mechanical Analyzer (DMA) results reveal that the modulus of polymer was softened gradually with immersion time increasing. The experimental result is approximate to the theory.

Active vibration control of smart composites featuring electro-rheological fluids

Our experimental investigations are focused on evaluating the elastodynamic response characteristics of a beam fabricated in an electrorheological fluid when the beam is subjected to forced vibration. The beam which is designed in this experiment is composed of three kinds of materials, i.e. structural material, damping material and sealant material. Different ratios of structural material to damping material have been tested in an applied electric field. The results demonstrate clearly the ability to significantly change the vibrational characteristics of a beam fabricated in a smart composite by changing the electric field intensity imposed on the fluid domains. The ASTM standard E756-83 equations are used to evaluate the Youngs modulus of the beam.

Investigate of Electrical Conductivity of Shape-Memory Polymer Filled with Carbon Black

A new system of thermoset styrene-based shape-memory polymer (SMP) filled with carbon black (CB) is investigated. To realize the electroactive stimuli of SMP, the electrical conductivity of SMP filled with various amounts of CB is characterized. The percolation threshold of electrically conductive SMP filled with CB is about 3% (volume fraction of CB), which is much lower than many other electrically conductive polymers. When applying a voltage of 30V, the shape recovery process of SMP/CB(10 vol%) can be realized in about 100s. In addition, the thermomechanical properties are also characterized by differential scanning calorimetery (DSC).

Improving the electrical conductivity by forming Ni powder chains in a shape-memory polymer filled with carbon black

We demonstrate a simple approach to significantly reduce the electrical resistivity of thermo-responsive shape-memory polymers (SMPs), so that they can be easily triggered for shape recovery by Joule heating at a low electrical voltage. After adding a small amount of Ni micro particles into a polyurethane SMP filled with carbon black (CB), the electrical resistivity is slightly reduced. However, if these Ni particles are aligned into chains (by applying a low magnetic field on SMP/CB/Ni solution and then drying to fix the conductive chains), the drop of electrical resistivity is significant. This kind of SMP composites is suitable for cyclic operation as only micro/nano particles are used. A sample (40×15×1mm) with 10vol% of CB and 0.5vol% of chained Ni can be heated to 80°C for shape recovery at 30 V (1.2 W) of power. This approach is generic and applicable for producing other conductive polymers.

Design of a Deployable Antenna Actuated by Shape Memory Alloy Hinge

This paper is concerned about a design of a new deployable antenna actuated by 6 shape memory alloy (SMA) hinges. The antenna consists of 6 radial, tensioned, parabolic, deployable ribs connecting to a central hub. The hinge, located at each rib, is used of the Nitinol SMA material due to the ability to generate large strains and electrical resistive actuation. The elongated SMA wire is heated by an electrical current, caused to contract in response to a converse thermally-induced phase transformation. The resulting tension creates a moment, imparting rotary motion between two adjacent beams. The concept and operation of deployable antenna system are discussed in detail, and a dynamic simulation is presented. A series of experiments are performed on the SMA actuator to investigate the system behavior in the process of deployment. Results indicated that the hinge with low speed rotation and easy fabrication achieves reliable actuation for the deployment of the antenna, and the antenna demonstrates a high deployment-to-stowage volume ratio.

Dynamic characteristics of a beam specimen featuring electrorheological fluids

The experimental investigations are focused on evaluating the elastodynamic response characteristics of beams fabricated in electrorheological (ER) fluids when the beams are subjected to forced vibration. The beams used in this experiment are composed of three kinds of materials: structural material, damping material and sealant material. Beams with different ER fluids and different structural material are made and tested. The results demonstrate clearly the ability to significantly change the vibrational characteristics of beams fabricated in smart composites by changing the electric field intensity imposed on the fluid domains. With the ASTM standard E756-83 equations, the Youngs modulus of the beams and the shear modulus of ER fluids are evaluated.

Numerical and Experimental Studies on Cured Shape of Thin Unsymmetric Carbon/Epoxy Laminates

An analytical model was established by means of Ritz method to calculate the cured shape of cross-ply unsymmetric composite laminates. A number of experiments of Carbon/Epoxy laminates were conducted. It was found in the experiment that the warped surface could be a multiple-value function, which should be studied further. The result of calculation correlates well with the experimental result except the regions very near the laminate edge. The conclusion is instructive to manufacture of composite laminates.

Fabrication of AlN-SiC-TiB2 Ceramics by Self-Propagating High Temperature Synthesis and Hot Isostatic Pressing

The fabrication of AlN-SiC-TiB2 ceramics with powder mixtures of Al, 6H-SiC and TiB2 was investigated by self-propagating high temperature synthesis (SHS) and hot isostatic pressing (HIP). The powder mixtures were shaped by isostatic cool pressing method and the combustion reaction was carried at the pressure of 100-200 MPa N2 by an ignitor. The compositions and morphologies of the combustion product were studied by XRD and SEM. The determined bending strength and the fracture toughness of the ceramics were 350 MPa and 3.5 MPa⋅m1/2 respectively.