Ishan Karnik

Fiber-reinforced composites (FRCs) are valued for their high specific properties. However, FRCs are vulnerable to difficult-to-predict damage growth and complex failure modes thereby motivating the need for robust structural health monitoring (SHM). Self-sensing via nanofiller-induced piezoresistivity has much potential for this. Research in piezoresistivity to date has overwhelmingly focused on the direct current (DC) response. This is important because alternating current (AC) has important… Show more

Fiber-reinforced composites (FRCs) are valued for their high specific properties. However, FRCs are vulnerable to difficult-to-predict damage growth and complex failure modes thereby motivating the need for robust structural health monitoring (SHM). Self-sensing via nanofiller-induced piezoresistivity has much potential for this. Research in piezoresistivity to date has overwhelmingly focused on the direct current (DC) response. This is important because alternating current (AC) has important benefits such as improved data density, potential for greater sensitivity, and reduced power requirements. In light of the potential of AC-based methods, this work explores AC transport responsiveness to high-cycle fatigue loading in carbon nanofiber (CNF)-modified glass fiber/epoxy laminates via equivalent circuit analyses. These results show that equivalent circuit behavior is significantly affected by fatigue-induced damage accumulation suggesting a mechanism for monitoring fatigue. However, clear circuit parameter evolution-load cycle trends were not observed suggesting further work is needed to fully realize the potential of AC-based monitoring. Show less

A modified truncated Maclaurin series (MMS) formulation is presented in order to gain additional probability density function (PDF) parameters over the usual two or three associated with classical PDFs, such as Gauss, log-normal, Weibull, beta, etc. Such a protocol results in a higher fidelity match of experimental or other observational data due to the practically almost unlimited increase in number of available PDF parameters. Additionally, such a power series expression is readily… Show more

A modified truncated Maclaurin series (MMS) formulation is presented in order to gain additional probability density function (PDF) parameters over the usual two or three associated with classical PDFs, such as Gauss, log-normal, Weibull, beta, etc. Such a protocol results in a higher fidelity match of experimental or other observational data due to the practically almost unlimited increase in number of available PDF parameters. Additionally, such a power series expression is readily analytically integrable in order to produce its associated cumulative distribution function (CDF), expectation and probability as well as all statistical moments. An illustrative example is included to exhibit a pattern of series convergence and errors of least square (LSQ) statistical data fits. Additionally, the relation between the Fischer sufficiency index, LSQ fit errors and number of series parameters is also investigated. Results have direct aerospace applications in failure probability analysis, statistical characterization of material properties, optimal design of systems of systems, random loads, sizing, thermal effects, etc. Show less