151-0535-00L  Optical Methods in Experimental Mechanics

SemesterAutumn Semester 2016
LecturersE. Hack, R. Brönnimann
Periodicityyearly recurring course
Language of instructionEnglish


AbstractThe lecture introduces a variety of optical methods to assess the mechanical behaviour of a structure, to determine material parameters, or to validate results from numerical analysis. Focus is on camera-based techniques for deformation, strain and stress analysis. Applications and limitations will be discussed. The lecture includes two afternoons of hands-on experience at Empa in Dübendorf.
ObjectiveThe students are able to designsimple optical set-ups and describe the process of image formation. They understand the working principle of various camera-based 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 or 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 dedicated 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 imaging 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, dynamic measurements and vibration analysis are explained in the context of modal analysis or transient events. The calibration of imaging optical methods and their application to the validation of numerical simulations are described.

The content is structured as follows:
1. Imaging methods: an introduction
2. Digital Image Correlation
3. White light moiré methods
4. Interferometry
5. Deformation analysis: Speckle pattern interferometry
6. Strain analysis: Shearography
7. Modal analysis
8. Measurement of transient deformations
9. Stress analysis: Photoelasticity
10. Stress analysis: Thermoelasticity
11. Validation of FEA results and calibration of optical full-field methods
12. Fibre based methods

The lecture includes two afternoons of laboratory experience at Empa, where the student will take the first steps with optical methods. Hands-on experience includes 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. You will be invited to a private blog which will stimulate the discussion of the lecture and the exercises.
LiteratureA good overview on the optical methods is presented in the following text books:

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

Kjell J. Gasvik: Optical Metrology, 3rd ed.
2002, John Wiley & Sons, Ltd.
(available on-line through NEBIS)
Prerequisites / NoticeBasic knowledge of optics and interferometry as taught in basic physics courses are advantageous .
Every week exercises will be distributed. Solving them is warmly recommended .
The two afternoons with hands-on experience are central elements of the lecture.