Siddhant Datta

High-Speed Surfactant-Free Fabrication of Large Carbon Nanotube Membranes for Multifunctional Composites

AbstractA high-speed manufacturing process for multiwalled carbon nanotube (MWNT) buckypaper is presented, and its application as an embedded strain sensor for composite materials is demonstrated. This manufacturing method enables the production of sizable carbon nanotube (CNT) membranes with significantly reduced processing time and less manufacturing complexity than other contemporary techniques. The use of surfactants and chemical functionalization of MWNTs was completely avoided in this method because functionality of carbon nanotubes can be hampered by such surface treatments. Microstructure, mechanical properties, and piezoresistive response of the fabricated buckypaper were characterized, and its sensitivity as a strain sensor was analyzed. Stable piezoresistive response could be achieved at low strains, and a high sensitivity to strain was observed when buckypaper was embedded in glass fiber epoxy laminates for strain sensing.

In-situ Strain and Damage Sensing in Glass Fiber Laminates Using Embedded CNT

Carbon nanotube (CNT) membranes manufactured by a novel slurry compression process have been used to introduce self-sensing capability in glass fiber reinforced polymer matrix (GFRP) laminates. The CNT membranes were embedded in the interlaminar region of the laminates and piezoresistive characterization studies were conducted under monotonic and cyclic loading. High sensitivity to strain was observed. A measurement model, developed using the resistance measurements obtained under fatigue loading, was used to quantify fatigue crack length in real time. The fatigue crack growth rates and the nature of crack propagation in baseline and self-sensing GFRP (SGFRP) specimens were compared. The results show that the average crack growth rate reduced by an order of magnitude by the introduction of CNT membrane. The SGFRP laminates developed in this study exhibited crack tip blunting during fatigue, while facilitating real time strain and damage sensing. doi: 10.12783/SHM2015/213

Identification of material damage precursors using nonlinear ultrasonics

The primary goal of this research effort is to develop nondestructive evaluation techniques capable of detecting material damage precursors mainly for turbine engine materials under low and high-cycle fatigue testing. The experimental results presented in this paper show a significant increase of the relative acoustic nonlinearity, βr, in aluminum and Ni-based superalloy fatigued specimens. While in agreement with the prior research, the main advantage of the current technique over the previous methods is that the ultrasonic beam may be focused to inspect the presence of damage precursors at localized stress concentrator site. For example, when the ultrasonic beam travelled through the root of the round-notched specimens, the acoustic nonlinearity exhibited an increase of approximately 450% as compared to the pristine specimens. This procedure will be further developed to detect damage precursors in propulsion components undergoing thermo-mechanically fatigue to quantify their remaining useful life.

A novel methodology for self-healing at the nanoscale in CNT/epoxy composites

Self-healing materials have the potential to repair induced damage and extend the service life of aerospace or civil components as well as prevent catastrophic failure. A novel technique to provide self-healing capabilities at the nanoscale in carbon nanotube/epoxy nanocomposites is presented in this paper. Carbon nanotubes (CNTs) functionalized with the healing agent (dicyclopentadiene) were used to fabricate self-healing CNT/epoxy nanocomposite films. The structure of CNTs was considered suitable for this application since they are nanosized, hollow, and provide a more consistent size distribution than polymeric nanocapsules. Specimens with different weight fractions of the functionalized CNTs were fabricated to explore the effect of weight fraction of functionalized CNTs on the extent of healing. Optical micrographs with different fluorescent filters showed partial or complete healing of damage approximately two to three weeks after damage was induced. Results indicate that by using CNTs to encapsulate a healing agent, crack growth in self-healing CNT/epoxy nanocomposites can be retarded, leading to safer materials that can autonomously repair itself.

A multiscale model coupling molecular dynamics simulations and micromechanics to study the behavior of CNT-enhanced nanocomposites

A comprehensive, point-information-to-continuum-level analysis framework is presented in this paper to accurately characterize the behavior of CNT-enhanced composite materials. Molecular dynamics (MD) simulations are performed to study atomistic interactions of the CNT with the polymeric phase. The effect of crosslinking between the epoxy resin and the hardener on the mechanical properties of the polymer is investigated; furthermore, the effect of CNT weight fraction on the most likely polymer cross-linking degree is also studied through stochastic models. The stochastic distributions obtained from MD simulations provide a basis to simulate local variations in the matrix properties at the fiber-centered continuum model at the microscale. The interfaces at nanoscale (CNT and matrix) and microscale (fiber and CNT-dispersed matrix) are characterized by performing CNT pullout simulations, and a single fiber pullout simulation, respectively.