Digital stereomicroscopy for measurements of deformations, velocity fields and microstructural changes of paper

Sammanfattning: There is a strongly increasing request of measuring systems for mechanical properties studies, for example in the paper industry. Paper research is today not only concentrated to flock studies, weight and quality controls of the paper but also focussing of mechanical behaviours in the fibre scale. For this purpose, an optical metrology system for measurements of mechanical response in the µm-range of loaded sub-mm objects is developed, but the system could also be used for materials like polymer composites, wood or steel. The system is full-field, non-touching and all-electronic. The main components in the system are a stereomicroscope and a speckle correlation technique called digital speckle photography. Either a random structure pattern exists naturally on the sample or a dot pattern must be attached on its surface. Using white light illumination, 2-D and 3-D deformation fields as well as velocity fields can be measured. The standard deviations are about 60 nm in plane and about 170 nm out of plane, depending on the magnification and quality of the pattern. Information of the topography of the sample is provided in the calibration routine for 3-D measurements. By using laser illumination, measurements of microstructural changes on the object surface are possible through a technique called laser speckle decorrelation. Examples of measurements of micro-flow, 3D deformations and microstructural changes in printing paper are given in this thesis.