http://yetl.yabesh.ir/yetl1/handle/yetl/19027 2026-04-07T10:20:14Z 2026-04-07T10:20:14Z Chih-Ping Wu Zong-Li Hong Yung-Ming Wang http://yetl.yabesh.ir/yetl1/handle/yetl/4244087 2017-12-30T12:58:32Z 2017-01-01T00:00:00Z

Geometrically Nonlinear Static Analysis of an Embedded Multiwalled Carbon Nanotube and the van der Waals Interaction Chih-Ping Wu; Zong-Li Hong; Yung-Ming Wang On the basis of Reissner’s mixed variational theorem (RMVT), rather than the principle of virtual displacement (PVD), the authors presented a nonlocal Timoshenko beam theory (TBT) for the geometrically nonlinear static analysis of multiwalled carbon nanotubes (MWCNT) embedded in an elastic medium. The embedded MWCNT was subjected to mechanical loads on its outer-most surface, with combinations of free, simply supported, and clamped edge conditions. The van der Waals interaction between any pair of walls constituting the MWCNT was considered, and the interaction between the MWCNT and its surrounding medium was simulated using the Pasternak-type foundation model. In the formulation, the governing equations of a typical wall and the associated boundary conditions were derived, in which von Kármán geometrical nonlinearity was considered. Eringen’s nonlocal elasticity theory was used to account for the small-length scale effect. The deformations induced in the embedded MWCNT were obtained using the differential quadrature method and a direct iteration approach. In the numerical examples, solutions of the RMVT-based nonlocal TBT converged rapidly, and the convergent solutions of its linear counterpart closely agreed with the analytical and numerical solutions of the PVD-based nonlocal beam theories available in the literature.

2017-01-01T00:00:00Z Muhammad Irfan-ul-Hassan Markus Königsberger Roland Reihsner Christian Hellmich Bernhard Pichler http://yetl.yabesh.ir/yetl1/handle/yetl/4244088 2017-12-30T12:58:32Z 2017-01-01T00:00:00Z

How Water-Aggregate Interactions Affect Concrete Creep: Multiscale Analysis Muhammad Irfan-ul-Hassan; Markus Königsberger; Roland Reihsner; Christian Hellmich; Bernhard Pichler Customary micromechanics models for the poroelasticity, creep, and strength of concrete restrict the domain affected by the hydration reaction to the cement paste volume, considering the latter as a thermodynamically closed system with respect to the (chemically inert) aggregate. Accordingly, the famous Powers hydration model appears to be a natural choice for the determination of clinker, cement, water, and aggregate volume fractions entering such micromechanical models. The situation changes once internal curing occurs, i.e., once part of the water present is absorbed initially by the aggregate, and then is sucked back to the cement paste during the hydration reaction. This paper develops an extended hydration model for this case, introducing water uptake capacity of the aggregate and paste void-filling extent as additional quantities. Based on constant values for just these two new quantities, and on previously determined creep properties of cement pastes as functions of an effective water:cement mass ratio (i.e., that associated with the cement paste domain rather than with the entire concrete volume), a series of ultrashort-term creep tests on different mortars and concretes can be very satisfactorily predicted by a standard microviscoelastic mathematical model. This further extends the applicability range of micromechanics modeling in cement and concrete research.

2017-01-01T00:00:00Z Rahnuma Shahrin Christopher P. Bobko http://yetl.yabesh.ir/yetl1/handle/yetl/4244089 2017-12-30T12:58:32Z 2017-01-01T00:00:00Z

Characterizing Strength and Failure of Calcium Silicate Hydrate Aggregates in Cement Paste under Micropillar Compression Rahnuma Shahrin; Christopher P. Bobko A new methodology is proposed for investigating compressive failure behavior of cement paste at the micrometer scale. Micropillar geometries are fabricated by focused ion-beam milling on potential calcium-silicate-hydrate (C-S-H) locations identified through energy dispersive spectroscopy (EDS) spot analysis. Uniaxial compression testing of these pillars is performed using nanoindentation equipment. The compressive strength of C-S-H aggregates (225–606 MPa) measured from microcompression tests is found to be consistent with values from multiscale damage and molecular dynamic models. From posttest images, two primary deformation mechanisms at failure were identified; axial splitting and plastic collapse of the entire sample were observed.

2017-01-01T00:00:00Z Anurag Sharma MD Shahjahan Molla Kalpana S. Katti Dinesh R. Katti http://yetl.yabesh.ir/yetl1/handle/yetl/4244086 2017-12-30T12:58:32Z 2017-01-01T00:00:00Z

Multiscale Models of Degradation and Healing of Bone Tissue Engineering Nanocomposite Scaffolds Anurag Sharma; MD Shahjahan Molla; Kalpana S. Katti; Dinesh R. Katti Biomaterials selection and design, and mechanical properties evolution during degradation and tissue regeneration play a critical role in the successful design of nanocomposite scaffolds for bone tissue regeneration. A new multiscale mechanics-based in silico approach is developed to provide a robust predictive methodology for nanocomposite scaffolds. Scaffolds are fabricated using amino acid–modified nanoclay with biomineralized hydroxyapatite (in situ HAPclay) and polycaprolactone (PCL). Steered molecular dynamics (SMD) simulations of the molecular models of HAPclay and the PCL composite provide a mechanical response of the material and the nature of the molecular interactions among constituents. The mechanical responses obtained from SMD are incorporated into a finite element (FE) model of a PCL/in situ HAPclay scaffold with its microstructure obtained from microcomputed tomography images. The model is validated using experimental results. The stress–strain response from multiscale models and experiments shows good agreement with the consideration of wall porosity correction. The multiscale models incorporate damage mechanics–based degradation and healing behavior to capture the evolution of the mechanical properties as the scaffolds degrade and human osteoblasts grow and proliferate inside the scaffolds. The novel multiscale models provide a robust prediction of the mechanical properties evolution in the scaffolds over the time evolution of cell growth proliferation and tissue formation.

2017-01-01T00:00:00Z