R.M.V. Pidaparti

Free vibration and flutter of damaged composite panels

A finite element method is investigated for studying the free vibration and supersonic flutter analysis of arbitrary damaged composite panels. The finite element method employs a 48 degrees of freedom (DOF) general plate element and uses the classical lamination theory, microstructural continuum damage theory and linearized piston theory. Two different damage models were investigated. Finite element results are obtained to illustrate the effect of damage on the eigenvalues and flutter boundaries. The results obtained indicate that between the two models considered, damage model 1 has a strong influence on both free vibration and flutter boundaries.

Design simulation of twisted cord-rubber structure using ProE/ANSYS

Abstract A three-dimensional model of a twisted cord embedded in rubber matrix was investigated to estimate the interface stresses. CAD model of the twisted cord geometry through blended feature was carried out using Pro/ENGINEER software. Twisted cord model representative of a typical cord was developed and analyzed for a realistic analysis of cords used in cord–rubber structure. Finite element analysis was performed on the models under axial, and combined axial and lateral loading using the ANSYS software. A circular cord with surrounding rubber model was also analyzed and the results obtained were validated with other studies that exist in the literature. The stresses and deformations obtained from the finite element analysis are shown for various cases illustrating the effects of twist, rubber modulus, and non-circular cord.

Stiffness characteristics of twisted cords for cord-rubber composites

Abstract A finite element model is presented to predict the stiffness characteristics of twisted cords by treating them as structures and considering the stiffness couplings due to extension-bending-torsional deformations. The axial, bending, and torsional stiffnesses are calculated for both the aramid-cord and steel-cord, and compared to an approximate expression with good agreement where applicable. To illustrate the stiffness behavior, all the three stiffnesses are presented with variations in the number of twists per unit length, the surrounding rubber modulus and the thickness. The stiffness couplings among the extension, bending, and twisting deformations are presented for aramid-cords with varying number of twists per unit length and rubber thickness. The results illustrate that stiffness characteristics are strongly dependent upon the number of twists per unit length, type of cord, surrounding rubber layer thickness and modulus. The stiffness coupling presented illustrate the mechanisms of load transfer, which are important for understanding failure mechanisms of cords, and cord-rubber composites.

Smooth Muscle Tissue Response to Applied Vibration Following Extreme Isotonic Shortening

The objectives of the present study are to investigate the response of a tracheal smooth muscle tissue to an applied longitudinal vibration following isotonic shortening, and, using experimental data, to simulate the mechanical response through a non-linear finite element analysis. The response of an activated smooth muscle tissue to forced length oscillations at 33Hz for 1 second was obtained. The response in terms of stiffness change and hysteresis was estimated from the experimental data. A finite element simulation was carried out to simulate the vibratory response under experimental conditions. The results obtained indicate that the approach and the vibratory response obtained may be useful for describing the cross-bridge deattachements within the cells as well as connective tissue connections characteristics of tracheal smooth muscle tissue.Copyright

Fracture and material degradation properties of cortical bone under accelerated stress

The fracture stress and material property degradation of bovine cortical bone specimens were investigated experimentally under accelerated cyclic tensile stress testing. The fracture stress of a typical specimen was found from a static tensile test, and the cyclic loading/unloading was calculated as a percentage of this fracture stress. The results of accelerated cyclic stress tests were compared to monotonically increased static tests to determine if loading/unloading has an effect on the damage mechanism in bone. It was found that fracture stress of the bone increases due to accelerated stress cycling whereas the modulus decreases in a logarithmic fashion with increasing cyclic stress.

Flutter analysis of cantilevered curved composite panels

Abstract A 48 degrees of freedom (dof) doubly curved quadrilateral thin shell finite element is used for studying the supersonic flutter of cantilevered curved composite panels. The composite material behavior is included using classical lamination theory and supersonic aerodynamic behavior is included using linearized piston theory. To reduce the number of dof of the finite element aeroelastic system, a normal mode approach is adopted. Results are presented to illustrate the behavior of flutter characteristics for composite curved cylindrical panels. The effects of fiber orientation and flow angle on the flutter characteristics are presented for selected examples. The accuracy, efficiency, and applicability of the present finite element method is demonstrated by illustrative examples with some results comparing well with the available alternate solutions in the literature.

Effect of Off-Axis Cell Orientation in Smooth Muscle Tissue

The cell alignment in a smooth muscle tissue plays a significant role in determining its mechanical properties. In addition to shortening strain, the off-axis cell orientation θ also modify the shear stress relationship significantly. A simulation model based on finite element analysis is developed to study the effect of stresses of tracheal smooth muscle tissue when its cells are orientated off-axially. Results obtained indicate that the maximum shear stress values of tracheal smooth muscle tissue at 45% strain are 2.5 times the values at 20% strain for all three off-axis orientation values θ = 15°, 30° and 45°.Copyright

Un modèle de gauchissement pour les plaques piézo-électriques

ABSTRACT A warping theory for the piezoelectric composite plates is presented using a previously developed model for laminated composite plates. The warping theory takes into account the effects of non linear distribution of the displacements through the thickness and also the transverse shear deformation. The results from the present theory are compared to the low-order theory of Mindlin and exact solutions available in the literature. Examples of a one layer and two layer composite plates were presented to illustrate the thickness effects on displacements, stresses and electric potential. The results obtained indicate that warping theory gives more realistic predictions as compared to lower order theories of piezoelectric composite plates.