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Granitic rocks usually exhibit strongly anisotropy due to pre-existing microcracks induced by long-term geological loadings. The understanding of anisotropy in mechanical properties of rocks is critical to a variety of rock engineering applications. In this thesis, the anisotropy of tension-related failure parameters involving tensile strength, flexural strength and Mode-I fracture toughness/fracture energy of Barre granite is investigated under a wide range of loading rates. Three sets of dynamic experimental methodologies have been developed using the modified split Hopkinson pressure bar system; Brazilian test to determine the tensile strength; semi-circular bend method to determine the flexural strength; and notched semi-circular bend method to determine the Mode-I fracture toughness and fracture energy. For all three tests, a simple quasi-static data analysis is employed to deduce the mechanical properties; the methodology is assessed critically against the isotropic Laurentian granite. It is shown that if dynamic force balance is achieved in SHPB, it is reasonable to use quasi-static formulas. The dynamic force balance is obtained by the pulse shaper technique. To study the anisotropy of these properties, rock blocks are cored and labeled using the three principal directions of Barre granite to form six sample groups. For samples in the same orientation group, the measured strengths/toughness shows clear loading rate dependence. More importantly, a loading rate dependence of the strengths/toughness anisotropy of Barre granite has been first observed: the anisotropy diminishes with the increase of loading rate. The reason for the strengths/toughness anisotropy can be understood with reference to the preferentially oriented microcracks sets; and the rate dependence of this anisotropy is qualitatively explained with the microcracks interaction. Two models abstracted from microscopic photographs are constructed to interpret the rate dependence of the fracture toughness anisotropy in terms of the crack/microcracks interaction. The experimentally observed rate dependence of the anisotropy is successfully reproduced.

No description available.

Granitic rocks usually exhibit strongly anisotropy due to pre-existing microcracks induced by long-term geological loadings. The understanding of anisotropy in mechanical properties of rocks is critical to a variety of rock engineering applications. In this thesis, the anisotropy of tension-related failure parameters involving tensile strength, flexural strength and Mode-I fracture toughness/fracture energy of Barre granite is investigated under a wide range of loading rates. Three sets of dynamic experimental methodologies have been developed using the modified split Hopkinson pressure bar system; Brazilian test to determine the tensile strength; semi-circular bend method to determine the flexural strength; and notched semi-circular bend method to determine the Mode-I fracture toughness and fracture energy. For all three tests, a simple quasi-static data analysis is employed to deduce the mechanical properties; the methodology is assessed critically against the isotropic Laurentian granite. It is shown that if dynamic force balance is achieved in SHPB, it is reasonable to use quasi-static formulas. The dynamic force balance is obtained by the pulse shaper technique. To study the anisotropy of these properties, rock blocks are cored and labeled using the three principal directions of Barre granite to form six sample groups. For samples in the same orientation group, the measured strengths/toughness shows clear loading rate dependence. More importantly, a loading rate dependence of the strengths/toughness anisotropy of Barre granite has been first observed: the anisotropy diminishes with the increase of loading rate. The reason for the strengths/toughness anisotropy can be understood with reference to the preferentially oriented microcracks sets; and the rate dependence of this anisotropy is qualitatively explained with the microcracks interaction. Two models abstracted from microscopic photographs are constructed to interpret the rate dependence of the fracture toughness anisotropy in terms of the crack/microcracks interaction. The experimentally observed rate dependence of the anisotropy is successfully reproduced.

Šiuo metu medžiagų poreikis gamybai yra labai išaugęs.Todėl inžinieriai stengiasi atrasti vis naujų arba tobulesnių medžiagų. Daugiasluoksnės konstrukcijos įgauna vis didesnę paklausą, dėl savo savikainos ir pritaikymo galimybės.Naudojant šias medžiagas galima gauti norimas masės ir stiprumo konstrukcijas. Daugiasluoksniams konstrukciniams elementams gaminti naudojamos tokios medžiagos kaip:stiklo, boro, plastiko pluoštai ir t.t. Mes išanalizavome 6 metrų sijas iš dviejų medžiagų. Mes analizavome skirtingus skerspjūvius ir skirtingus sluoksnių storius, paskaičiavome skerspjūvių stiprumą ir standumą. Taip pat analizavome racionalių sijų pranašumus. Nustatyta kurie skerspjūviai yra pranašiausi. Taip pat nustatyta, kad racionalios sijos yra pranašesnės už vientiso skerspjūvio. Gavome, kad racionalios sijos yra pigesnės iki 30 procentų. / Dolieba M. Influence of analysis of Strength and Stiffness of Two- Ply Beam: Master thesis of mechanical engineer / research advisor Assoc. Prof. habil. Dr. J. Bareišis; Šiauliai University, Technological Faculty, Mechanical Engineering Department.- Šiauliai, 2007. Materials for construction needful more and more. Engineers trying to get more perfection materials. Multiplayer construction is very popular at this time, because it is cheaper, we can reduce the weight and the forse. Different products and constructions elements using multiplayer constructions from glass, carbon, boric plastic and other materials. We analysing six meters beam from two ply. We take different cross-section and different high of ply and analysing strength and stiffness. After we calculating how less material need for rational beam. In result we see which cross-section are best for using. At first we see that multiplayer constructions have the advantage before common beams. We get that rational beam are thirty percent cheaper.

Composite materials are formed by combiing two or more materials that have quite different properties. The different materials work together to give the composite unique properties, but within the composite you can easily tell the the different materials apart – they do not dissolve or blend into each other. Modern aviation, both military and civil, is a prime example. It would be much less efficient without composites. In fact, the demands made by that industry for materials that are both light and strong has been the main force driving the development of composites. The greatest advantage of composite materials is strength and stiffness combined with lightness. By choosing an appropriate combination of reinforcement and matrix material, manufacturers can produce properties that exactly fit the requirements for a particular structure for a particular purpose. In general, composite materials are very durable. The downside of composites is usually the cost. Although manufacturing processes are often more efficient when composites are used, the raw materials like steel, but in many cases they are just what we need.

Šiame baigiamajame magistro darbe išanalizuota įstrižai lenkiamos daugiasluoksnės sijos standumo priklausomybė nuo medžiagos tamprumo modulio ir sijos stiprumas nuo sijos geometrinių parametrų. Tyrimo objektu buvo pasirinkti du nelygiašoniai kampuočiai 100x63x6, 100x63x10 ir vienas lygiašonis 100x100x6. Kampuočiai užpildomi skirtingo tamprumo modulio medžiagomis. Sijos galas apkraunamas 10 kN jėga. Sijoje įstrižas lenkimas susidaro dėl kampučio ir užpildo tamprumo modulio skirtumo, todėl sijos standumo centro koordinatės nebesutampa su geometrinio centro koordinatėmis. Užpildytas kampuotis pasirinktas dėl praktinės naudos, nes jį užpildžius kita pigesne medžiaga, padidinamas jo standumas įstrižam lenkimui. Sija tampa kvadrato ar stačiakampio formos, kas leidžia lengviau montuoti siją jai skirtoje vietoje. Tyrimui atlikti panaudojami du metodai - tai analitiniai skaičiavimai ir BEM (Baigtinių Elementų Metodas). Rezultatuose palyginami rezultatai gauti iš analitinių skaičiavimų ir iš BEM. / In this Master of Science thesis was analyzed skew bended multilayer beams stiffness dependence on material elastic modulus and strength of the beam from the beam geometrical parameters and elastic modulus. As the Objects of investigation was selected two scalene angles 100x63x6, 100x63x10, and one isosceles 100x100x6. Scalene angles were filled with different materials of different elastic modulus. End of the beam was loaded 10 kN force. Skew bend in this multilayer beam arise because the elastic modulus of angles and filled materials are different, and then the coordinate system of stiffness center do not coincident with geometrical coordinate system. Filled angle was chosen for practical use, because when we filled it with another cheaper material, it could be increased the skew bending stiffness. Beam become square or rectangular, that allows easier installation of the beam in place. Survey used two methods - the analytical calculations and FEA (Finite Element Analysis). The results were obtained from analytical calculations and the FEA, and compared.

The finite element method is used to investigate the effects of welding-induced residual stress and distortion on the strength and behaviour of ship hull structures. A finite element welding simulation consisting of sequentially coupled transient thermal and nonlinear structural analyses is used to predict the three-dimensional residual stress and distortion fields in welded stiffened plates. Three types of stiffener commonly used in commercial and naval applications are considered. The welding simulation is followed by a 'shakedown' analysis to study the possibility of residual stress relief caused by cyclic loads. The strength and behaviour of stiffened plates under axial load is characterized by normalized plots of average axial stress versus axial strain, commonly referred to as load-shortening curves. These curves are used to evaluate the effects of welding-induced residual stress and distortion on stiffened plate behaviour with and without considering stress relief by shakedown. Load-shortening curves generated by finite element analysis are also compared with load-shortening curves produced using analytical methods including those prescribed in ship structural design standards published by the International Association of Classification Societies (IACS). To conclude, a hull girder ultimate strength analysis is carried out using Smith's method with load-shortening curves generated by several different methods. Results indicate that welding-induced residual stress and distortion decrease the ultimate strength of flat-bar, angle, and tee-stiffened plates investigated in this study by as much as 17%, 15% and 13%, respectively. Stiffened plate ultimate strength values calculated using IACS common structural rules agreed reasonably well with results from numerical models in most cases. There was however, a significant discrepancy between the numerical load-shortening curves and the IACS curves in the post-ultimate regime, where the IACS curves overestimated the post-ultimate strength of stiffened plates by as much as 30%. To investigate stress relief by shakedown, axial stresses of 25% and 50% of the yield stress were applied and residual stresses were reduced by approximately 20% and 40%, respectively. In some cases, these reductions in residual stress led to increases in stiffened plate ultimate strength as high as 7%. Analysis of a box girder using load-shortening curves from a finite element model including residual stresses and distortions predicted by welding simulation predicted a bending moment capacity within 2.7% of the experimentally measured value. Using load-shortening curves from the IACS common structural rules, the ultimate strength was overestimated by 17%. / Thesis .pdf/A

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