Current research interest in multi-scale modeling of cement paste requires accurate characterization of the time-dependent mechanical properties of the material, particularly the C-S-H phase. Nanoindentation is evaluated as a tool for measuring both the instantaneous and the short-term viscoelastic properties of cement paste. Atomic force microscopy (AFM) based indentation is compared to conventional nanoindentaion in measuring mechanical properties of cement pastes. Time-dependent solutions are derived to characterize creep indentation tests performed on hardened cement paste and to extract the time-dependent properties. The effect of approximating C-S-H viscoelastic properties with a time-independent Poisson's ratio is discussed, and arguments for utilizing a time-independent Poisson's ratio for short-term response are presented. In evaluating AFM as a mechanical characterization tool, various analytical and numerical modeling approaches are compared. The disparities between the numerical self-consistent approach and analytical solutions are determined and reported. The measured elastic Young's modulus values acquired by AFM indentation tests are compared to Young's modulus values from nanoindentation measurements from cement paste. These results show that the calcium silicate hydrate (C-S-H) phase of hydrated portland cement has different properties on the nanometric scale than on the micron scale. Packing density of C-S-H particles is proposed as an explanation for the disparity in the measured results. The AFM measured uniaxial viscoelastic compliance values are compared to similar values obtained with traditional nanoindentation for the same material. The comparison of these results shows that the calcium silicate hydrate (C-S-H) phase of portland cement has similar but distinct properties on the sub micron scale than on the micron scale. Additionally, the effect of moisture is evaluated by controlling the relative humidity (RH) of the testing environment between 40% and 100% plus, or wet. The viscoelastic compliance appears to be highest at 40% RH and the material appears to be less compliant at higher relative humidity levels. Possible mechanisms controlling the viscoelastic deformation are presented and evaluated in conjunction with the moisture related poromechanical effect.

Thesis (Ph. D.)--University of Washington, 2008. / Vita. Includes bibliographical references (p. 91-97).

Thesis--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 77-79).

Thesis (Ph.D)--Aerospace Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Bauchau, Olivier; Committee Member: Hodges, Dewey; Committee Member: Makeev, Andrew; Committee Member: Ozbay, Serkan; Committee Member: Ruzzene, Massimo. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph.D.)--Aberdeen University, 2009. / Title from web page (viewed on Mar. 26, 2010). Includes bibliographical references.

Thesis (Ph. D.)--University of Queensland, 2003. / Includes bibliographical references.

No description available.

O meio corporativo, principalmente quando se trata de montadoras automotivas, é carente de conhecimento dos fatores que podem influenciar o processo de união entre pares tribológicos. Quando há um fim específico, como o tema deste trabalho: assegurar níveis de controle capazes de eliminar os riscos de uma vedação deficiente na câmara de combustão com custo mínimo, tal carência é ainda maior. O estudo da tribologia inerente à união entre cabeçote e bloco do motor diesel é fundamental para se compreender a que ponto é possível garantir a melhor estanqueidade possível, especialmente no que esteja relacionado ao processo rotineiro de aperto na linha de produção. Nesse sentido, a investigação proposta neste trabalho tem o claro objetivo de propor melhores condições técnicas de vedação ao caso particular da união entre cabeçote e bloco do motor de forma a eliminar / minimizar qualquer influência externa durante o aparafusamento do par supracitado. Adicionalmente, o conhecimento aqui exposto poderá ser difundido a muitas outras aplicações similares nas quais a fixação aparafusada está atrelada a funções que não apenas de fixação, podendo estas estarem inclusive em outros universos do produto, tais como motores, cabinas, eixos e transmissão. / The automobile corporate field has a lack of knowledge when the subject is related to tightening specific issues, especially regarding tribological studies. When there is a specific goal as this thesis theme: ensure all the control levels to eliminate sealing deficiency risks inside combustion chamber in a low investment cost, the needs are even higher. The tribological study between diesel engine block and its cylinder heads assembly is essential to comprehend what is necessary to have the best possible sealing, mostly when it\'s related to the routine on the assembly tightening process. Thinking on that, this work has the goal to propose the best condition on fastening technique that guarantees the sealing to any superficial topography roughness. Additionally, the acquired knowledge will be spread to other similar applications that are not unequally associated to bolted joints, but also in other vehicle universes, such as engines, cabs, axles and transmissions.

Dissertation (Ph. D.)--University of Akron, Dept. of Polymer Engineering, 2005. / "December, 2005." Title from electronic dissertation title page (viewed 09/17/2006) Advisor, Arkady I. Leonov; Co-Advisor, Joseph P. Padovan; Committee members, Joseph P. Padovan, Gary R. Hamed, Erol Sancaktar, Rudolph J. Scavuzzo, Jr.; Department Chair, Sadhan C. Jana; Dean of the College, Frank N. Kelley; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

This thesis addresses normal axisymmetric contact of dissimilar elastic solids at finite interfacial friction. It is shown that in the case of smooth and convex but otherwise arbitrary contact profiles and monotonically increasing loading a single stick-slip contour evolves being independent of loading and profile geometry. This allows developing an incremental procedure based on a reduced problem corresponding to frictional rigid flat punch indentation of an elastic half-space. The reduced problem, being independent of loading and contact region, was solved by a finite element method based on a stationary contact contour and characterized by high accuracy. Subsequently, a tailored cumulative superposition procedure was developed to resolve the original problem to determine global and local field values for two practically important geometries: flat and conical profiles with rounded edges and apices. Results are given for relations between force, depth and contact contours together with surface stress distributions and maximum von Mises effective stress, in particular to predict initiation of fracture and plastic flow. It is also observed that the presence of friction radically reduces the magnitude of the maximum surface tensile stress, thus retarding brittle fracture initiation. Hertzian fracture through indentation of flat float glass specimens by steel balls has been examined experimentally for a full load cycle. It has been observed that if the specimen survived during loading to a maximum level it frequently failed at decreasing load. It has been proposed by Johnson et al. (1973) that the underlying physical cause of Hertzian fracture initiation during load removal is that at unloading frictional tractions reverse their sign over part of the contact region. Guided by these considerations a robust computational procedure has been developed to determine global and local field values in particular at unloading at finite friction. In contrast to the situation at monotonically increasing loading, at unloading invariance properties are lost and stick-slip regions proved to be severely history dependent and in particular with an opposed frictional shear stress at the contact boundary region. This causes an increase of the maximum tensile stress at the contour under progressive unloading. It is shown that the experimental observations concerning Hertzian fracture initiation at unloading are at least in qualitative correlation with the effect friction has on the maximum surface tensile stress. A contact cycle between two dissimilar elastic bodies at finite Coulomb friction has been further investigated analytically and numerically for a wider range of material parameters and contact geometries. With the issue of Hertzian fracture initiation in mind, results concerning the influence of the friction coefficient and compliance parameters on the absolute maximum surface tensile stress during a frictional contact cycle are reported along with the magnitudes of the relative increase of maximum tensile stresses at unloading. Based on a critical stress fracture criterion it is discussed how the predicted increases will influence the critical loads required for crack initiation. Fracture loads are measured with steel and tungsten carbide spherical indenters in contact with float glass specimens at monotonically increasing loading and during a load cycle. Computational predictions concerning the fracture loads are given based on Hertz and frictional contact theories combined with a critical stress fracture criterion. The computational results obtained for frictional contact are shown to be in better agreement with experimental findings as compared to the predictions based on the Hertz theory. The remaining quantitative discrepancy was attributed to the well-known fact that a Hertzian macro-crack initiates from pre-existing defects on the specimen’s surface. In order to account for the influence of the random distribution of these defects on the fracture loads at monotonic loading, Weibull statistics was introduced. The predicted critical loads corresponding to 50% failure probability were found to be in close agreement with experimentally observed ones. / QC 20100729