Optical Methods in Experimental Mechanics and Processing Technology

Abstract

The lecture introduces optical methods to assess engineering structures and material parameters, and to validate numerical simulations. Their strengths and limitations in industrial applications are discussed. Selected fabrication technologies are introduced, together with their optical methods of quality control. 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 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 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 the structures. Through the hands-on experiences 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. The measurement techniques make use of a variety of principles such as - Triangulation - Interference - Diffraction - Birefringence - Infrared radiation The techniques rely on cameras, most notably semiconductor sensors as well as micro-bolometers, and make use of incoherent white light and coherent light sources such as halogen lamps and lasers, respectively. The topics of the lecture include: - Optics and imaging - Digital Image Correlation 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 are applied to microsystems as well as large engineering structures. In addition, time-resolved measurements in the context of modal analysis and dynamic events are explained. The lecture includes two afternoons at Empa, where the students will gain first-hand experience with 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, Thermal Stress Analysis, ellipsometry and fringe projection.

Resources