151-0535-00L  Optical Methods in Experimental Mechanics

SemesterAutumn Semester 2019
LecturersE. Hack, R. Brönnimann
Periodicityyearly recurring course
Language of instructionEnglish

AbstractThe lecture introduces optical methods to assess the mechanical behaviour of a structure, to determine material parameters, and to validate results from numerical simulations. Focus is on camera-based techniques for deformation, strain and stress analysis. Applications, strengths and limitations are discussed. The lecture includes two afternoons of hands-on experience at Empa in Dübendorf.
ObjectiveThe students are enabled to design basic optical set-ups and to describe the process of image formation. They understand the working principle of various optical techniques for shape, deformation and strain measurement. Most notably, they can explain how the measurand is transformed into an interference signal, a change of polarization state or of surface temperature. They know the main application fields of the individual techniques. They are able to choose the most appropriate technique for solving a measurement task and to estimate its expected resolution. Through the hands-on experience the students gain a deeper and sustained understanding of the content by applying the theoretical foundations to tangible measurement tasks.
ContentAfter an introduction into optics and image acquisition the lecture explains how to transform mechanical quantities such as strain, stress or deformation into an image content. The measurement techniques make use of a variety of optical principles:

- Triangulation (Digital Image Correlation, Fringe Projection)
- Interference (Speckle Pattern Interferometry, Shearography)
- Diffraction (Moiré-Interferometry, Fiber Bragg Gratings)
- Birefringence (Photoelasticity)
- Infrared radiation (Thermal Stress Analysis)

In addition, time-resolved measurements in the context of modal analysis and transient events are explained. The calibration of imaging optical instruments and their application to the validation of numerical simulations are discussed.

The content includes:
- Introduction to optics and imaging
- Digital Image Correlation
- Structured light techniques
- Diffraction and interferometry
- Speckle pattern interferometry
- Modal analysis and transient deformations
- Applications to microsystems and interfaces
- Stress analysis: Photoelasticity
- Stress analysis: Thermoelasticity
- Calibration and validation of numerical models
- Fibre based methods

The lecture includes two afternoons at Empa, where the student will gain first-hand experience with optical methods. These hands-on laboratory classes may include e.g. Digital Image Correlation, Speckle pattern interferometry, Thermal Stress Analysis, Fibre optic sensors, Fringe projection, depending on availability of the equipment and the interest of the students.
Lecture notesCopies of the presented slides will be made available on-line through ILIAS. Each lecture contains a set of exercises. You will be invited to a private blog which shall stimulate the discussion of the lecture content and the exercises. Standard solutions for the exercises will be posted with a time shift.
LiteratureA good overview on the optical methods is presented in the following text books:

Toru Yoshizawa, Ed., Handbook of Optical Metrology, 2nd edition, 2015, CRC Press, Boca Raton
ISBN 978-1-4665-7359-8

Pramod Rastogi, Erwin Hack, Eds., Optical Methods for Solid Mechanics: A Full-Field Approach
2012, Wiley-VCH, Berlin
ISBN 978-3-527-41111-5

W. N. Sharpe Jr., Ed., Handbook of Experimental Solid Mechanics
2009, Springer, New York
ISBN 978-0-387-26883-5
Prerequisites / NoticeBasic knowledge of optics and interferometry as taught in basic physics courses are advantageous.