2D Volumetric Strain Imaging Through Thz Time-Domain Spectroscopy of Strontium Titanate Flexible Composite Acting as Remote Passive Sensor
Abstract
Strain field imaging can have important applications in the fields of material characterization and structural health monitoring. In the former, this analysis is used for the experimental assessment of mechanical behavioral laws; and in the latter, it is applied for damage prediction purposes in many industries where good structural maintenance increases the safety and productivity of operations. Terahertz Time-Domain Spectroscopy (THz TDS) is a relatively new technique capable of measuring the amplitude and phase of an electromagnetic pulse (EMP) in the THz band, which is characterized by very low absorbance in most dielectric materials and allows to study small variations in a material’s electromagnetic properties. The following thesis defends how applying a composite of Strontium Titanate (STO) particles dispersed in a low dielectric matrix to a structural component, a material that changes its dielectric constant when loaded, and sensing the change in dielectric properties of the coating at different loadings, a new non-destructive and remote sensing method of strain field mapping can be achieved. This method has made possible to correlate strain to changes in the time of arrival (TOA) of the EMP, and then use this correlation to measure the localized strain fields through previous material-specific calibration. The following thesis contains a deep literature review of current state of the art methods for strain field mapping such as Holography or Digital Image Correlation (DIC) and how these relate to strain sensing through THz TDS spectroscopy in terms of advantages and disadvantages. Other methods of sensing strain with THz TDS are also reviewed. Afterwards, a theoretical analysis of our strain sensing method is performed, attending to all the physical factors in the passive sensor that affect THz TDS readings when strained and therefore explaining the physics in which our sensor is based. A mathematical model is also produced that allows to study how different material parameters will affect the sensitivity of the composite. Finally, strain mappings of different geometries that produce strain concentrations are obtained through THz TDS and compared with FEA and DIC to show the current capabilities of the method, together with a discussion of the results and setting the basis for future work.
Degree
M.Sc.
Advisors
Tomar, Purdue University.
Subject Area
Physics|Remote sensing|Acoustics|Electromagnetics|Materials science|Mathematics|Optics
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