Experimental Assessment of the Glued Laminated Timber Beams in 4-Point Bending Tests and Photoelastic Coating Technique

The paper presents the results of investigation on seven glued laminated timber (GL24h class) bending beams. Bending strength and modulus of elasticity were determined. The beams were tested for four-point bending by loading them at a constant speed deflection. The strain gauge method and photoelastic coating technique were applied for strain distributions determination in selected cross-sections of the beams. Good agreement of the measurement results was obtained with both techniques. Application of the photoelastic coating technique enabled more detailed analysis of the beams failure mode, including timber defects influence on the strain distributions.

Utilisation Possibilities of PhotoStress Method in Determination of Residual Stresses

The presented paper demonstrates the determination of residual stresses by means of PhotoStress® method. The identification was performed on a drilled and subsequently loaded sample of a split ring. Through drilling and subsequent loading of the sample we were able to simulate residual stresses throughout the surface of the split ring. Using the values of residual stresses, a gradient of residual stresses was specified. The 3 mm thick split ring was laser-cut from a non-alloyed fine-grained structural steel sheet suitable for welding, i.e. steel 11 523. It was coated with 3.125 mm thick photoelastic coating PS-1A with fringe constant.

Small Oblique Angle Technique for Principal-Strain Separation in Luminescent Photoelastic Coating

To determine the individual values of the two strain components by separate principal strains, a theoretical model of strain separation by oblique incidence with a new luminescent photoelastic coating configuration is presented. Considering the non-strain related refraction effect included in the total optical response at oblique incidence, the small incidence angle technique for simplifying the post-processing complexity is given. To affirm the validity of this strain separation method based on small oblique angles, the signal-to-noise ratio for providing sufficient signal intensity has been theoretically analyzed.

Experimental Analysis of Propagation of Plastic Zones in Two-Dimensional Problems

In the paper, the author presents experimental analysis of propagation of plastic zones in two-dimensional models with different stress concentrators. The experimental tests were carried out by photoelastic coating method on duralumin stripes loaded by tensile stresses. For various levels of loading, the photographs of isochromatic pattern were taken under loading and after removing loading. On the basis of isochromatic pattern recorded for loaded models, the boundaries of plastic zones were determined using the Treska-Coulomb yield condition. The isochromatic pattern taken for the unloaded, but previously partly plastified elements, show the picture of the residual strain remaining in the material. A discussion of the results is presented.