Magnetically aligned carbon nanotube in nanopaper enabled shape-memory nanocomposite for high speed electrical actuation

A new shape-memory nanocomposite that exhibits rapid electrical actuation capabilities is fabricated by incorporating self-assembly multiwalled carbon nanotube (MWCNT) nanopaper and magnetic CNTs into a styrene-based shape-memory polymer (SMP). The MWCNT nanopaper was coated on the surface to give high electrical conductivity to SMP. Electromagnetic CNTs were blended with and, vertically aligned into the SMP resin upon a magnetic field, to facilitate the heat transfer from the nanopaper to the underlying SMP. This not only significantly enhances heat transfer but also gives high speed electrical actuation

Cooperative dynamics of heuristic swelling and inhibitive micellization in double-network hydrogels by ionic dissociation of polyelectrolyte

In this study, a cooperative model has been proposed for the double network (DN) hydrogel, which synchronously undergoes heuristic swelling and inhibitive micellization by the ionic dissociation of polyelectrolyte. Flory-Huggins solution theory is initially employed to identify the working mechanism of dielectric constants on swelling behavior of the DN hydrogel. Then a free-energy function is introduced to formulate the constitutive relationship of the DN hydrogels, in which the first hydrotropic network undergoes a heuristic swelling and the second hydrophobic network undergoes an inhibitive micellization. Finally, the proposed model has been verified using the experimental results reported in the literature. A good agreement between the theoretical results and experimental ones has been achieved. This study provides a fundamental approach to formulate the constitutive relationship and to understand the cooperative dynamics of two types of networks in DN hydrogels induced by the polyelectrolyte

Synergistic effect of carbon nanofiber and carbon nanopaper on shape memory polymer composite

The present work studies the synergistic effect of carbon nanofiber (CNF) and carbon nanopaper on the shape recovery of shape memory polymer (SMP) composite. The combination of CNF and carbon nanopaper was used to improve the thermal and electrical conductivities of the SMP composite. The carbon nanopaper was coated on the surface of the SMP composite in order to achieve the actuation by electrical resistive heating. CNFs were blended with the SMP resin to improve the thermal conductivity to facilitate the heat transfer from the nanopaper to the underlying SMP composite to accelerate the electroactive responses

Collective and cooperative dynamics in transition domains of amorphous polymers with multi-shape memory effect

Multi-shape memory effect (multi-SME) in amorphous shape memory polymers (SMPs) linked with collective and cooperative rearrangements and accommodations of monomeric segments, thus leading to generation of complex thermodynamic modes. In this study, an extended domain size model is initially formulated to describe various temperature-dependent relaxation behaviors and domain transitions in amorphous SMPs. According to the Adam-Gibbs theory, a cooperative model is employed to identify the principle role of domain size in the collective dynamics of multi-SME in amorphous SMPs. The phase transition theory is then combined with multi-branch Kelvin model to describe the collective and cooperative relaxation behaviors of the SMPs with multiple transition domains. It is shown that the proposed model is able to characterize the thermomechanical transitions and multiple shape recovery processes. Finally, the model is applied to predict shape recovery behavior of SMPs with triple- and quadruple-SME, respectively, and the theoretical results are well validated by the experimental ones

Coupled Thermo-Electro-Magneto-Mechanical Cracking of Non-Homogeneous Media

In recent years, among numerous advanced composite materials, non-homogeneous materials, such as functionally graded materials and laminated media, have received considerable attention in the field of structural design subjected to external thermo-electro-mechanical loads. Such non-homogeneous materials are composed of two or more materials of different properties or functions. The gradual change of properties can be tailored to different applications and service environments. It is possible with these materials to obtain a combination of properties that cannot be achieved in conventional monolithic materials. A typical example of non-homogeneous materials is the composites fabricated by combining piezoelectric ceramics with other materials. Such non-homogeneous materials are usually used for constructions of intelligent systems. The thermo-electro-mechanical properties of these advanced materials change with spatial positions. The knowledge of fracture behavior of non-homogeneous materials is important in order to evaluate their structural integrity. A key feature of fracture which distinguishes non-homogeneous materials from homogeneous materials is that the resistance of the former to fracture and damage tolerance varies spatially. Consequently, analyses of fracture in non-homogeneous materials are considerably more complex than in the corresponding homogeneous case of the same specimen and crack geometry subjected to the same loading conditions. Associated complications involving spatially varying material constants have demanded the re-examination of the elastic crack problem. This new book brings together the diverse achievements in the field

Thermoelastic fracture mechanics for nonhomogeneous material subjected to unsteady thermal load

This article provides a comprehensive treatment of cracks in nonhomogeneous structural materials such as functionally graded materials. It is assumed that the material properties depend only on the coordinate perpendicular to the crack surfaces and vary continuously along the crack faces. By using a laminated composite plate model to simulate the material nonhomogeneity, we present an algorithm for solving the system based on the Laplace transform and Fourier transform techniques. Unlike earlier studies that considered certain assumed property distributions and a single crack problem, the current investigation studies multiple crack problems in the functionally graded materials with arbitrarily varying material properties. The algorithm can be applied to steady state or transient thermoelastic fracture problem with the inertial terms taken into account. As a numerical illustration, transient thermal stress intensity factors for a metal-ceramic joint specimen with a functionally graded interlayer subjected to sudden heating on its boundary are presented. The results obtained demonstrate that the present model is an efficient tool in the fracture analysis of nonhomogeneous material with properties varying in the thickness direction