151-0535-00L  Optical Methods in Experimental Mechanics

SemesterAutumn Semester 2020
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 esperiments based on optical methods and to describe the process of image acquisition. They understand the working principle of the 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 the polarization state or a change 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 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 shape, deformation, strain or stress into an image content. The measurement techniques make use of a variety of basic principles such as
- Triangulation
- Interference
- Diffraction
- Birefringence
- Infrared radiation

The techniques are based on cameras, most notably CCD and CMOS sensors as well as micro-bolometers, and make use of incoherent white light and coherent light sources such as lasers.

The lecture includes:
- Introduction to optics and imaging
- Digital Image Correlation in 2D and 3D
- Fringe Projection and structured light techniques
- Diffraction and holography
- Speckle pattern interferometry
- Photoelasticity
- Thermoelastic Stress Analysis
- Validation of numerical models
- Fibre based methods

We show that 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 explained.

The lecture includes two afternoons at Empa, where the student will gain first-hand experience with optical methods in the laboratory. These hands-on 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 includes 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.