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Experimentálne zistenie radiálných modulov pružnosti jarného a letného dreva smreku obyčajného métodou DIC
Vido, Michal
The aim of this work is to find radial modulus of elasticity in stress, and comparison between methods of detecting modulus of elasticity by transom and by digital image corellation (DIC). A transverse Reuss model of the composite deformation was used to calculate overall modulus of elasticity by DIC. Furthermore, the individual modules of elasticity between spring and summer wood of Norway spruce (Picea abies L.) were compared. The average value of modulus of elasticity detected by transom is 270,57 MPa. The value of modulus of elasticity of the whole sample detected by DIC is, on average, for all twenty samples 993,88 MPa. Another value is modulus of elasticity of the whole sample detected by DIC, which is converted by Reuss model and its average value is 969,7 MPa. Samples of summer wood detected by DIC have an average value of modulus of elasticity 1226,67 MPa and samples of summer wood detected by transom have an average value of modulus of elasticity 1036,53 MPa. The last value is modulus of elasticity of spring wood measured by DIC, which has on average 909,67 MPa.
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Analýza deformací dřeva smrku ztepilého zatíženého tlakem v tangenciálním směru
Šotner, Martin
The main goal of this bachelor thesis consists in analysis of mechanical features of timber spruce (Picea abies L.) under compressive mechanical deformation in tangential direction. Basic theory about the microscopic structure of wood and an overview of traditional and modern methods for analysis and evaluation of mechanical phenomena were introduced in recent literature as well as cited in experimental part of this work. Results of the work elastic moduli and strengths of early and late wood are obtained from experiments based on electromechanical material testing systems Tinius and Zwick and digital image correlation (DIC) simultaneously. Modulus of elasticity and mechanical strength are processed by Voigt model. Obtained results are statistically evaluated. The average value of modulus of elasticity (late wood) considering influence of method inaccuracy (mechanical testing device) is specified as 807.12 MPa (experimentally obtained value of target parameter). The value 807.12 MPa approximates value (929.32 MPa) obtained from Voigt model (estimated value of target parameter). Both values of modulus of elasticity have 15% difference. Similar approach (Voigt model) is used for evaluation of average stress of early (5.47 MPa) and late (10.25 MPa) wood.
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Snímání deformací dřeva s vysokou vlhkostí a výskytem vad pomocí metody DIC
Piňos, Pavel
The diploma thesis is fucused on scanning deformations of wood which has high value of humidity and defects in its structure. The experiment was carried out on standard trial corpuscles. Beech, oak and poplar were chosen as experimental timber species. The influence of high humidity and defects on mechanic qualities and deformations on this tiber species was examined and studied. The aim of thesis is to find out mutual difference and compare the results between defornations measured by standardly used conventional methods and contactless digital image correlation (DIC) and also verify of application of this optical method. The thesis includes also numerical model.
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Analysis of the mechanical behavior of wood by means of digital image correlation
Brabec, Martin
The full-field optical techniques such as e.g. a digital image correlation are capable to fully reflect the natural wood heterogeneity. Therefore, this thesis aspires to contribute to the experimental mechanics of wood and wood-based composites by the implementation of the full-field optical technique based on the digital image correlation to the standard mechanical tests. A supplementation of the conventional displacement sensors should help to obtain more precise mechanical characteristics and to do more sophisticated analyses of the deformation behaviour of wood and wood-based composites. The experimental part of the thesis is divided into the five independent case studies listed as the original papers. The measurements were carried out on the most wide-spread wood species in central Europe such as European beech (Fagus sylvatica, L.) and Norway spruce (Picea abies, L. Karst). Beside the solid wood, the new wood-based sandwich structure, which consists of a core made from birch plywood and the particleboard facings, was investigated too. The loading of the samples was carried out using of the standard mechanical tests such as tension, compression, three-point bending and torsion test. In the first study, the full-field deformation data were used to indentify reasons for the non-standard deformation behaviour of spruce and beech wood during compression parallel to grain. Reason for this was recognized in the abrubt compression of damage zones located near the compression plates, which induced the expansion of the middle zone located between them. The second study aimed to find out neutral axis position in native and thermally modified beech wood during the conventional three-point bending test. The relative neutral axis position was obtained from mutual position of the neutral axis and centroidal axis, which was determined based on the appropriate image processing methods. It was found that the neutral axis and centroidal sample axis are almost coincident. Objective of the third study was to determine both longitudinal shear moduli of beech wood with help of the full-field shear strains, obtained from a single torsion test, together with use of the appropriate analytical solutions for the calculation of the stress distribution within the radial and tangential direction on the longitudinal-radial and longitudinal-tangential sample surfaces. Both longitudinal shear moduli increasingly mutually differed as the load increases. Within the fourth study, verification of the elastic material model used in finite-element analyses was carried out with help of full-field deformations induced around notches within dog-bone shaped sample during the uniaxial tension. Great correlation was found between numerically predicted and experimentally measured strain data sets for both longitudinal-radial and longitudinal-tangential shear planes. The fifth study dealed with the characterization of elastic deformation behaviour of newly developed wood-based composite with a sandwich structure. Based on the full-field strain analysis the local strain concentrations were identified. They took place within the core during flatwise compression, and within the facings, when the edgewise compression test was done. A variety of presented results confirmed widespread applicability of optical methods in the mechanics of materials. Therefore, the utilization of full-field optical method based on digital image correlation in experimental mechanics of wood and wood-based composites can be highly recommended.
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Mechanické vlastnosti vláknových uhlíkových kompozitů
Začal, Jaroslav
Carbon fibre reinforced composites (CFRP) are construction material, which is viewed as a perspective for its ratio of mechanical properties to weight. In recent years the research was focused on implementing the carbon-based composites among smart materials. Nevertheless, extent and volume of use of these composites in technical practice is still not up to the potential, which this modern material offers. One of substantial reasons is the lack of adequate instruments for continuous manufacturing quality control and for mechanical condition monitoring of ready-made construction parts. For this reason the presented dissertation thesis is focused on effectiveness enhancement of detection of deformation response in composites subjected to mechanical loading with uniaxial tension with employment of passive acoustic emission (AE) detection, optical method for detection of surface deformation fields digital image correlation (DIC) and electron microscopy scanning electron microscopy (SEM). Combination of used methods proved as a robust instrument for identification and monitoring of entire degradation process in composite material in course of mechanical loading.
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Numerická a experimentální analýza vybraného celodřevěného tesařského spoje
Zámečník, Petr
The major task of this topic is evaluation of the birdsmouth carpentry joint by various approaches employing finite element method and DIC. The numerical modeling is carried out to predict mechanical performance of the joint and the DIC as reference measurement has been established. There are proposed few achievements in introducing of effective way to give sufficient comparison. (1) The model in several variations is presented whereas gluing and contact analysis in ANSYS is in research scope. (2) The DIC was viably established with the real mechanical measurement in the same time. Although there were found some differences in comparison o FEM with DIC, the results present similarities especially when the contact analysis was carried out.
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Aplikace metod optické analýzy při zkoušení nábytku
Štábl, Jakub
This thesis deals with the use of digital image analysis during the chair testing. The thesis aim is to show and compare different analytic programs and two optical methods of measurement. Selected optical analysis are Digital Image Correlation and Motion Capture. These non-contact measurement methods are used during the chair testing, specifically static test of the seat and backrest. The measured values are statistically evaluated and the results of different methods and softwares are compared. The chair testing follows relevant standards.
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