Optical Methods in Experimental Mechanics and Processing Technology

Abstract

The lecture introduces optical and imaging methods to assess structures and material parameters, or to validate numerical simulations. Selected fabrication technologies are discussed, together with their optical methods of quality control. Their strengths and limitations in industrial applications are discussed. The lecture includes two afternoons of hands-on experience at Empa in Dübendorf.

Objective

The students are able to describe the process of imaging and image acquisition. They know how to design simple experiments based on optical and imaging methods. They understand the working principle of the optical techniques. Specifically, they can explain how a mechanical measurand such as shape, deformation and strain is transformed into an optical signal such as an interference, a change of the polarization state or a change of surface temperature. They know the main application field of the individual techniques. They are able to choose the most appropriate technique for solving a specific measurement task and to estimate its expected resolution. In addition, they understand the basics of processing technologies from the clean room or from 3D printing and how they can assess the quality of layers and structures. Through the hands-on experience the students gain a deeper and sustained understanding by applying the theoretical foundations to tangible measurement tasks.

Content

After an introduction into optics and image acquisition, the lecture explains how to transform mechanical quantities such as shape, deformation, strain or stress into an image content. Selected applications to clean room processes for the fabrication of layered structures are explained. The measurement techniques make use of basic principles such as - Triangulation - Interference - Diffraction - Birefringence - Infrared radiation Imaging techniques rely on area detectors, most notably CCD cameras, infrared sensors as well as micro-bolometers. Natural white light and halogen lamps, as well as coherent light sources such as lasers will be used and demonstrated. The topics of the lecture include: - Optics and imaging - Digital Image Correlation (DIC) in 2D and 3D - Fringe Projection and structured light techniques - Diffraction and holography - Speckle pattern interferometry - Terahertz (THz) techniques - Thin film processes and 3D printing - Photoelasticity and ellipsometry - Thermoelastic Stress Analysis - Validation of numerical models We show how the methods can be applied to microsystems as well as large engineering structures. In addition, time-resolved measurements in the context of modal analysis and dynamic events are explored. The lecture includes two afternoons at Empa, where the students will gain first-hand experience with several optical methods in the laboratory. Depending on availability of the equipment and the interest of the students, these hands-on classes may include e.g. Digital Image Correlation, speckle pattern interferometry, THz holography, Time-domain spectroscopy, Thermal Stress Analysis, ellipsometry and fringe projection.

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