In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

The Helioseismic and Magnetic Imager (HMI) instrument and investigation as a part of the NASA Solar Dynamics Observatory (SDO) is designed to study convection-zone dynamics and the solar dynamo, the origin and evolution of sunspots, active regions, and complexes of activity, the sources and drivers of solar magnetic activity and disturbances, links between the internal processes and dynamics of the corona and heliosphere, and precursors of solar disturbances for space-weather forecasts. A brief overview of the instrument, investigation objectives, and standard data products is presented.

/pdf/the-helioseismic-and-magnetic-imager-hmi-investigation-for-2omq27f3k3.pdf

The Helioseismic and Magnetic Imager (HMI) Investigation for the Solar Dynamics Observatory (SDO)

https://cyberleninka.org/article/n/768408.pdf

Mechanical properties of graphene and graphene-based nanocomposites

Highly stretchable graphene-nanocellulose composite nanopaper is fabricated for strain-sensor applications. Three-dimensional macroporous nanopaper from crumpled graphene and nanocellulose is embedded in elastomer matrix to achieve stretchability up to 100%. The stretchable graphene nanopaper is demonstrated for efficient human-motion detection applications.

Highly Stretchable Piezoresistive Graphene–Nanocellulose Nanopaper for Strain Sensors

Sensing strain of soft materials in small scale has attracted increasing attention. In this work, graphene woven fabrics (GWFs) are explored for highly sensitive sensing. A flexible and wearable strain sensor is assembled by adhering the GWFs on polymer and medical tape composite film. The sensor exhibits the following features: ultra-light, relatively good sensitivity, high reversibility, superior physical robustness, easy fabrication, ease to follow human skin deformation, and so on. Some weak human motions are chosen to test the notable resistance change, including hand clenching, phonation, expression change, blink, breath, and pulse. Because of the distinctive features of high sensitivity and reversible extensibility, the GWFs based piezoresistive sensors have wide potential applications in fields of the displays, robotics, fatigue detection, body monitoring, and so forth.

Wearable and Highly Sensitive Graphene Strain Sensors for Human Motion Monitoring

The capability of embedded piezoelectric wafer active sensors (PWAS) to perform in‐situ Nondestructive evaluation (NDE) for structural health monitoring (SHM) of fiber reinforced polymer (FRP) composite plate like structures is explored The basic principles of Lamb wave transmission and reception with PWAS transducers were verified with simple laboratory experiments, performed on both isotropic and anisotropic plates In the second case, Noncontact measurements for Lamb wave sensing using Laser Doppler Velocimeter were explored

In‐Situ Damage Detection in Plate Structures Using PWAS and Non‐Contact Laser Doppler Velocimeter

Inspection of rail welds has always been a challenge to the Railways. The conventional ultrasonic methods which are employed now for the detection of defects are not found to be good enough for defects that exist in different parts of the weld. Phased Array Ultrasonics which performs sectorial scanning could be used effectively for detection of defects in rail welds. The analysis of phased array images basically concentrates on defects that are volumetric in rail. The feasibility studies conducted in parts of rail other than welds were promising. Defect indications were seen very much separately from its surroundings. Accurate positioning of the defect is possible. Close lying defects can be seen separately which assures better resolution. Linear normal scans were very much suitable to detect cracks of complex geometries, as it gives a specific indication pattern each time when it is present.

Rail weld inspection using phased array ultrasonics

Condition Monitoring of Internal combustion engines is becoming more and more crucial as the engine designers try to achieve better fuel efficiency and/or more power while adhering to the stringent pollution control norms practiced today. Most of the condition monitoring practices follows a periodic maintenance model or in case of cheaper engines, none at all. Keeping in mind the importance of continuous monitoring of critical parts of engine like piston rings and cylinder liner there are a number of real time condition monitoring methods in practice. Our work deals with an unconventional use of signal processing tools on Acoustic Emission (AE) from engine cylinder liner to identify or enhance the features associated with various faults commonly found in critical engine components. Experimental data is obtained from a small petrol engine in which various fault conditions are recreated. Signals collected from the engine running with bad piston, worn out piston rings and under lubricant oil level were analyzed.

A novel use of signal processing tools for fault detection in IC engines

The study reports on the characterization of interfacial disbonds in an elastic-viscoelastic (steel-rubber) adhesively bonded bilayer structure where the elastic material (steel) has a significantly higher impedance than the viscoelastic material (rubber). The study uses the A0 mode guided wave at a low frequency of 100 kHz, which was generated and detected using non-contact air-coupled ultrasound. The A0 mode could be generated and detected from both steel and rubber sides, despite the high viscoelasticity of the rubber layer. However, the A0 mode guided wave propagation is sustained only in the steel layer and not in the rubber layer. The mode travelling along the steel layer leaks into the rubber layer and hence can be detected from the rubber side in the bonded region. When the disbond is below either the transmitter or the receiver, a better sensitivity in the disbond detection was achieved from the rubber side rather than the steel side. Using the experimental and 2D frequency-domain finite element simulation results, a linear correlation between the extent of disbond and the amplitude, time-of-flight (ToF) difference of the A0 mode arrival in the disbond region on the steel side was also established. The results show the potential to characterize interfacial disbonds regardless of the position with respect to the transmitter or receiver in elastic-viscoelastic multilayered structures using air-coupled guided wave inspection from single-side access.

Guided A0 wave mode interaction with interfacial disbonds in an elastic-viscoelastic bilayer structure

When subjected to continuous tensile loads, a material cools in the elastic regime and heats up in the plastic regime. Temperature changes are also observed when metals are subjected to cyclic stresses of amplitude below the yield strength. The insights into the use of thermomechanical phenomenon as a NDE technique are presented here based on experimental and computational evidence. Infrared thermal camera has been used to monitor the temperature changes in the materials. Measured temperature changes for tensile load on a material subjected to different levels of plastic deformation and for cyclic load on material are presented. Existing theoretical basis to explain the thermomechanical response is discussed in terms of (a) thermoelastic effect for the elastic regime in tensile load, (b) Taylor–Quinney coefficient for the plastic regime in tensile load, and (c) phenomenological models for the cyclic load. For the case of monotonic tensile loading, the extent of initial plastic deformation of a material is experimentally correlated with the observed decrease in temperature in the elastic regime. For the case of cyclic loading leading to stresses below the yield strength, the Kelvin–Voigt model has been found to be sufficient to explain the temperature changes. Amount of plastic deformation accumulated in the material can be deduced based on the decrease in temperature during tensile loading. Closeness between the parameters of Kelvin–Voigt model and that of the grain make this model suitable for understanding the thermomechanical response of polycrystalline materials subjected to stresses below the yield strength. To fully explain the thermoplastic effect beyond the Taylor–Quinney coefficient, a phenomenological model that accounts for the grain resizing, along with rotation and sliding, during the plastic deformation needs to be developed.

Krishnan Balasubramaniam

Papers

In‐Situ Damage Detection in Plate Structures Using PWAS and Non‐Contact Laser Doppler Velocimeter

Rail weld inspection using phased array ultrasonics

A novel use of signal processing tools for fault detection in IC engines

Guided A0 wave mode interaction with interfacial disbonds in an elastic-viscoelastic bilayer structure

Thermomechanical Phenomenon: A Non-destructive Evaluation Perspective