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Analýza tahové-tlakové asymetrie u koeficientů příčné deformace pomocí metody korelace digitálního obrazu
Zadina, Jan
This thesis deals with the analysis of tensile-compressive asymmetry in the coefficients of transverse deformation (Poisson's ratios) of spruce wood (Picea abies L. Karst) in all three principal directions of growth, i.e. for the complete set of 6 Poisson's ratios. Tensile and compressive stress within one direction was applied to the same test specimen, and the digital image correlation (DIC) method was used to analyze surface deformations. For this purpose, the surface of the test specimens in two adjacent planes was recorded by cameras during mechanical loading, and the deformations were fully evaluated from the digital images, from which the Poisson's ratios were subsequently calculated. The evaluation of Poisson's ratios was performed using statistical tests. Statistical t-tests were performed to test the equality of means to compare the tensile and compressive Poisson's ratios, which showed differences between the compressive and tensile Poisson's ratios only in some cases. A one-way ANOVA and Scheffé's test were also performed to compare the different directions with each other, which showed a distribution of large and small Poisson's ratios mainly in tension. A regression analysis was also performed to determine the degree of correlation between the tensile and compressive Poisson's ratios, and correlation was demonstrated in the radial and tangential directions. Regression analysis was also performed to examine the relationship with wood density, which showed a slight correlation with some of the Poisson's ratios.
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Experimentální mechanická analýza konstrukčního LSL kompozitu ze směsi plochých třísek vybraných druhů dřevin
Šulák, Michal
The diploma thesis deals with the idea of replacing spruce wood in structural elements with another alternative wood type- larch. This work compares 3 variants of experimentally manufactured LSL boards. Boards made only with larch or spruce particles were compared with board which contains a mix of spruce and larch chips in a ratio of 60:40. The effect of board composition on mechanical properties was evaluated using bending (flat- and edge-wise), internal bonding, compression and thickness swelling test. The non-destructive digital Image Correlation (DIC) method was used to evaluate the results strain fields during both bending schemes. To determine the behavior of the glued joint itself was used a modified shear strength test on three types of specimen MD/MD, SM/SM and MD/SM. In the case of bending tests were found any significant differences between the boards. Significant differences weren´t found when the compressive behaviour of the boards was tested. However, a statistically significant difference was found in the density of the tested samples for compression and for IB specimen. In both cases, the density of specimen made from spruce particles was significantly lower. When tested for internal bonding, ANOVAs did not confirm significant differences between specimen groups. A significant influence of the strand combination was found in thickness swelling and water absorption. During the lap shear test, a significantly higher strength of the glued joint was found in the MD/MD samples compared to the other groups of samples.
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Composite aircraft joint experimental testing with digital image correlation
Deák, Péter ; Kowalik, Michał
The main goal was to establish results of the individual joint strength characteristics used in composite laminate structure, in order to be used for design computations in airframe structures. A carbon-epoxy composite specimen includes a brass sleeve that is used to connect other metal parts by a bolt, used on light-weight category aircrafts. 11 specimens were tested and pulled by a tensile test machine. The tension mechanisms associated with failure modes of bolted joints in advanced composites is explained. The work is based on experimental test observations, performed by Instron 8516 servo-hydraulic testing machine and analyzed further by Digital Image Correlation (DIC) technique to define failure load of this metal-composite interconnection. Comparison of DIC results is made in parallel with test recorded data as verification. Conclusions include a failure analysis and observations learned during the experiment.
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