Application of Aligned Carbon Nanotube-Reinforced Polymer Composite to Electrothermal Actuator

Electrothermal bimorph actuators have been widely researched, comprising two layers with asymmetric expansion that generate a bending displacement. Actuation performance greatly relies upon the difference of the coefficients of thermal expansion (CTE) between the two material layers. Since traditionally used bimorph materials have positive CTE values, the generated displacements are restricted because of their relatively low CTE difference. Currently, the synthesis and characterization of carbon nanotube (CNT)/polymer composite actuators are topics of intense research activity. CNTs have been attracting much interest because of their superior electrical, thermal and mechanical properties. In addition, the negative CTE value of CNTs in the axial direction has been investigated analytically, leading one to expect that the CTE of the composites in a direction parallel to the CNT alignment will drastically decrease by containing the aligned CNTs into polymer materials. In this chapter, an experimental method for determining the CTE of a CNT in the axial direction is discussed. Based on this result, we demonstrate an electrothermal bimorph actuator having a large bending displacement and high force output using an aligned CNT-reinforced epoxy composite and thin aluminum foil. Performance characteristics including power and work output per unit volume versus frequency are also reviewed

Mechanical and Fracture Properties of Carbon Nanotubes

Carbon nanotubes (CNTs) have attracted much interest because of their superior electrical, thermal, and mechanical properties. These unique properties of CNTs have come to the attention of many scientists and engineers worldwide, eager to incorporate these novel materials into composites and electronic devices. However, before the utilization of these materials becomes mainstream, it is necessary to develop protocols for tailoring the material properties, so that composites and devices can be engineered to given specifications. In this chapter, we review our recent studies, in which we investigate the nominal tensile strength and strength distribution of multi-walled CNTs (MWCNTs) synthesized by the catalytic chemical vapor deposition (CVD) method, followed by a series of high-temperature annealing steps that culminate with annealing at 2900°C. The structural-mechanical relationships of such MWCNTs are investigated through tensile-loading experiments with individual MWCNTs, Weibull-Poisson statistics, transmission electron microscope (TEM) observation, and Raman spectroscopy analysis

Molecular Dynamics Simulations and Theoretical Model for Engineering Tensile Properties of Single-and Multi-Walled Carbon Nanotubes

To apply carbon nanotubes (CNTs) as reinforcing agents in next-generation composites, it is essential to improve their nominal strength. However, since it is difficult to completely remove the defects, the synthesis guideline for improving nominal strength is still unclear, i.e., the effective strength and the number of nanotube layers required to improve the nominal strength has been undermined. In this study, molecular dynamics simulations were used to elucidate the effects of vacancies on the mechanical properties of CNTs. Additionally, the relationships between the number of layers and effective and nominal strengths of CNTs were discussed theoretically. The presence of extensive vacancies provides a possible explanation for the low nominal strengths obtained in previous experimental measurements of CNTs. This study indicates that the nominal strength can be increased from the experimentally obtained values of 10 GPa to approximately 20 GPa by using six to nine nanotube layers, even if the increase in effective strength of each layer is small. This has advantages over double-walled CNTs, because the effective strength of such CNTs must be approximately 60 GPa to achieve a nominal strength of 20 GPa