D. Roy Mahapatra

A spectral finite element model for analysis of axial–flexural–shear coupled wave propagation in laminated composite beams

A spectral finite element model (SFEM) for analysis of axial–flexural–shear coupled wave propagation in thick laminated composite beams is presented. Range of validity of the first order shear deformation in the context of higher order Lamb wave modes is discussed. Concept of spectral element shape function, dynamic strain–displacement matrix and dynamically consistent force vector are derived. An exact dynamic stiffness matrix is derived, which is used in finite element (FE) analysis. Computation is performed in the Fourier domain at FFT sampling points over broad frequency band. Post-processing of the response is performed in both the frequency domain as well as in the time domain, which is suitable for structural diagnostics and broad-band wave propagation problems. To extend the range of engineering applications of SFEM, linear damping models are formulated. Effect of viscous damping on group speeds and wave amplitudes are studied for graphite–epoxy composite beams. Response under impact type loading is compared with time domain FE results. Numerical examples are presented, where the effect of axial–flexural–shear coupling is characterized. Efficient application of the model is shown considering laminated beam with ply-drops. Also a global/local model for estimation of Mode-II crack tip field in a delaminated thick composite beam is presented.

FINITE ELEMENT ANALYSIS OF FREE VIBRATION AND WAVE PROPAGATION IN ASYMMETRIC COMPOSITE BEAMS WITH STRUCTURAL DISCONTINUITIES

A new refined locking free first-order shear deformable finite element is presented, and its utility in solving free vibration and wave propagation problems in laminated composite beam structures with symmetric as well as asymmetric ply stacking is demonstrated. The paper also illustrates the application of the element to handle different types of structural discontinuities such as ply-drops, multiply connected beams with rigid joints, lap joints and the beams with delaminations. The developed finite element has a static stiffness matrix that is obtained by exactly solving the axial–flexural–shear coupled governing homogeneous differential equations. Results from the analysis show that the formulated element predicts response that compares very well with the available results reported in the literature. A novel way of modeling structural discontinuities such as delamination is given which significantly reduces the modeling effort to determine static, dynamic and wave propagation responses quickly and accurately.

Integrating strong and weak discontinuities without integration subcells and example applications in an XFEM/GFEM framework†

Partition of unity methods, such as the extended finite element method, allows discontinuities to be simulated independently of the mesh (Int. J. Numer. Meth. Engng. 1999; 45:601-620). This eliminates the need for the mesh to be aligned with the discontinuity or cumbersome re-meshing, as the discontinuity evolves. However, to compute the stiffness matrix of the elements intersected by the discontinuity, a subdivision of the elements into quadrature subcells aligned with the discontinuity is commonly adopted. In this paper, we use a simple integration technique, proposed for polygonal domains (Int. J. Nuttier Meth. Engng 2009; 80(1):103-134. DOI: 10.1002/nme.2589) to suppress the need for element subdivision. Numerical results presented for a few benchmark problems in the context of linear elastic fracture mechanics and a multi-material problem show that the proposed method yields accurate results. Owing to its simplicity, the proposed integration technique can be easily integrated in any existing code. Copyright (C) 2010 John Wiley & Sons, Ltd.

Medicamentos para o tratamento da osteoporose: revisão

Osteoporosis is characterized by low bone mass with micro architectural deterioration of bone tissue leading to enhance bone fragility, thus increasing the susceptibility to fracture. Osteoporosis is an important public health problem leading to an increased risk of developing spontaneous and traumatic fractures. In India osteoporotic fractures occur more commonly in both sexes, and may occur at a younger age than in the western countries. Although exact numbers are not available, based on available data and clinical experience, 36 million Indians may be affected by osteoporosis by 2013. This would be associated with enormous costs and considerable consumption of health resources. Pharmacological therapies that effectively reduce the number of fractures by improving bone mass are now available widely in markets. At present most drugs available in the markets decrease bone loss by inhibiting bone resorption, but the upcoming therapies may increase bone mass by directly increasing bone mass as is the case of parathyroid hormone. Current treatment alternatives include bisphosphonates, calcitonin, selective estrogen receptor modulators and inhibitors of RANK pathway but sufficient calcium and vitamin D are a prerequisite. Newer osteoclast targeted agents like cathepsin K and c-src kinase are under clinical development. The therapies which target osteoblasts include the agents acting through the Wnt-β catenin signaling pathway like Dkk-1 inhibitors and sclerostin antagonists. To further improve pharmacological interventions and therapeutical choices in this field, improvement of knowledge is very necessary

A spectral finite element with embedded delamination for modeling of wave scattering in composite beams

A spectral finite element for modeling of wave scattering in laminated composite beam with embedded delamination is proposed. The method uses fast Fourier transform (FFT) for transformation of the temporal variables into frequency dependent variables and conventional node-based finite element (FE) approach for spatial discretization in frequency domain. The base-laminates and the sub-laminates are treated as structural waveguides, which form the internal spectral elements. The region of delamination is modeled by assuming constant cross-sectional rotation. Equilibrium at the interfaces between the base-laminate and the sub-laminates is imposed using efficient matrix methodology. The internal element nodes are finally condensed to form a single equivalent beam element with embedded delamination and is called damaged spectral element. Only three quantities need to be specified for automated construction of the proposed element. These are the local coordinates of one of the delamination tips and delamination length. The main advantage is the easy insertion of delamination in finite element model and efficient correlation of measured waveforms in structural health monitoring applications. Response predicted by the proposed model has been compared with 2D FE analysis and fairly matching results are found. Sensitivity studies due to parametric variation in delaminated configuration are performed. Methodologies to identify locations and extent of delaminations for structural diagnostics are also highlighted.

Identification of delamination in composite beams using spectral estimation and a genetic algorithm

An efficient strategy for identification of delamination in composite beams and connected structures is presented. A spectral finite-element model consisting of a damaged spectral element is used for model-based prediction of the damaged structural response in the frequency domain. A genetic algorithm (GA) specially tailored for damage identification is derived and is integrated with finite-element code for automation. For best application of the GA, sensitivities of various objective functions with respect to delamination parameters are studied and important conclusions are presented. Model-based simulations of increasing complexity illustrate some of the attractive features of the strategy in terms of accuracy as well as computational cost. This shows the possibility of using such strategies for the development of smart structural health monitoring softwares and systems.

Quasi-static and dynamic strain sensing using carbon nanotube/epoxy nanocomposite thin films

Thin films are developed by dispersing carbon black nanoparticles and carbon nanotubes (CNTs) in an epoxy polymer. The films show a large variation in electrical resistance when subjected to quasi-static and dynamic mechanical loading. This phenomenon is attributed to the change in the band-gap of the CNTs due to the applied strain, and also to the change in the volume fraction of the constituent phases in the percolation network. Under quasi-static loading, the films show a nonlinear response. This nonlinearity in the response of the films is primarily attributed to the pre-yield softening of the epoxy polymer. The electrical resistance of the films is found to be strongly dependent on the magnitude and frequency of the applied dynamic strain, induced by a piezoelectric substrate. Interestingly, the resistance variation is found to be a linear function of frequency and dynamic strain. Samples with a small concentration of just 0.57% of CNT show a sensitivity as high as 2.5% MPa-1 for static mechanical loading. A mathematical model based on Bruggemans effective medium theory is developed to better understand the experimental results. Dynamic mechanical loading experiments reveal a sensitivity as high as 0.007% Hz(-1) at a constant small-amplitude vibration and up to 0.13%/mu-strain at 0-500 Hz vibration. Potential applications of such thin films include highly sensitive strain sensors, accelerometers, artificial neural networks, artificial skin and polymer electronics.

Descrição de um novo método de ooforectomia em ratas

Rats are currently the most used laboratory animals to investigate osteoporosis. We report an efficient method of ovariectomy and compared this method with the two other operative methods of ovariectomy (i.e., midline dorsal skin incision and double dorsolateral approach, which are used commonly for inducing experimental osteoporosis. Female Wistar rats, 12 weeks old, were divided into three groups. Ovariectomy was preceded by a single midline dorsal skin incision, 3 cm long, in the group A; double dorsolateral incisions, approximately 1 cm long, in the group B; and a single ventral transverse incision of 0.4-0.6 cm at the middle abdominal region in the group C. Animals in groups A, B, and C had a mean weight of 258.12 ± 0.54 g, 255.78 ± 0.42 g, and 254.55 ± 1.69 g, respectively. There were significant differences in the duration (in minutes) of surgery in the groups B (9.65 ± 0.86) and C (7.55 ± 0.11, P < 0.001) when compared to the group A (15.52 ± 0.30) and in the group B (P < 0.01) when compared to the group C. Wound healing time (in days) for groups B (9.22 ± 0.67) and C (8.01 ± 0.93) was significantly shorter than that for group A (11.58 ± 1.2, P < 0.001), with the wound healing time for group C being slightly shorter than that for group B. The surgery, as conducted in the group C, was technically easier, less time consuming and showed less wound healing duration.

Energy harvesting using ionic electro-active polymer thin films with Ag-based electrodes

In this paper we employ the phenomenon of bending deformation induced transport of cations via the polymer chains in the thickness direction of an electro-active polymer (EAP)-metal composite thin film for mechanical energy harvesting. While EAPs have been applied in the past in actuators and artificial muscles, promising applications of such materials in hydrodynamic and vibratory energy harvesting are reported in this paper. For this, functionalization of EAPs with metal electrodes is the key factor in improving the energy harvesting efficiency. Unlike Pt-based electrodes, Ag-based electrodes have been deposited on an EAP membrane made of Nafion. The developed ionic metal polymer composite (IPMC) membrane is subjected to a dynamic bending load, hydrodynamically, and evaluated for the voltage generated against an external electrical load. An increase of a few orders of magnitude has been observed in the harvested energy density and power density in air, deionized water and in electrolyte solutions with varying concentrations of sodium chloride (NaCl) as compared to Pt-based IPMC performances reported in the published literature. This will have potential applications in hydrodynamic and residual environmental energy harvesting to power sensors and actuators based on micro-andn nano-electro-mechanical systems (MEMS and NEMS) for biomedical,maerospace and oceanic applications.

Coupled effect of size, strain rate, and temperature on the shape memory of a pentagonal Cu nanowire

A body-centered pentagonal nanobridge structure with lattice constants c = 2.35 and a = 2.53 A has been observed under high strain rate tensile loading on an initially constrained [Formula: see text] Cu nanowire at various temperatures. Extensive molecular dynamics (MD) simulations have been performed using the embedded atom method (EAM) for cross-sectional dimensions ranging from 0.723 x 0.723 to 2.169 x 2.169 nm(2), temperature ranging from 10 to 600 K, and strain rates of 10(9)-10(7) s(-1). Formations of such pentagonal nanowire are observed for a temperature range 200-600 K for particular cross-sectional dimensions and strain rates. A large inelastic deformation of approximately 50% is obtained under both isothermal loading and adiabatic loading. With very high degree of repeatability of such pentagonal nanowire formation, the present findings indicate that the interesting stability property and high strength of elongated nanowires have various potential applications in nanomechanical and nanoelectronic devices. Further, we demonstrate a novel thermomechanical unloading mechanism by which it is possible to impart recovery from a pentagonal nanowire following a hysteresis loop: [Formula: see text].