B. Gangadhara Prusty

Analysis of stiffened shell for ships and ocean structures by finite element method

Static analysis of stiffened shells has been carried out using an eight-noded isoparametric element for the shell and a three-noded curved beam element for the stiffener. A same displacement function is used for the shell and the stiffener elements. A modified technique has been followed to analyse the shell, which is an improvement over the degenerated shell concept. The stiffness matrix of the curved beam element is generated irrespective of its position and orientation within the shell element. The stiffness matrix of the stiffener is then transferred to all the nodes of the shell element. Numerical examples of stiffened shells with concentric and eccentric stiffeners have been analysed and the results presented together with those available in published literature.

Progressive Failure Analysis of Laminated Unstiffened and Stiffened Composite Panels

Progressive failure analysis of laminated unstiffened and stiffened composite panels has been carried out in the present investigation. The laminated panels under transverse static loadings in the linear elastic range have been investigated using the finite element method. In the finite element analysis of stiffened panels, eight-noded isoparametric quadratic elements in association with the three-noded curved beam elements have been considered and the first-order shear deformation theory is utilized. An iterative method has been adopted using the various failure theories to predict the first-ply failure load. After the first-ply failure, the stiffness of the failed lamina has been totally discarded from the laminate and the remaining laminae were considered for further analysis. The progressive failure analysis using the Tsai-Wu failure criterion has been implemented into a general-purpose finite element code to predict the failure loading from the initial to the final stage.

Linear static analysis of composite hat-stiffened laminated shells using finite elements

Analysis of composite stiffened panels used in aerospace, ship and other engineering structures by the method of finite elements has been presented. The formulation presented is based on the concept of equal displacements at the shell-stiffener interface. An eight-noded isoparametric shell element is used in association with three-noded curved beam element for the formulation of the stiffened panel element. First-order shear deformation theory is used in the present study. The stiffness matrix of the stiffener is computed first irrespective of its position within the plate/shell element. The stiffness matrix so computed for the stiffener is then transferred to that of the plate/shell element nodes depending on its position and orientation within the element before assembling the element stiffness matrix. A generalised formulation for the hat-shaped stiffener is presented. The investigation is restricted to linear static analysis of composite stiffened panels and parametric studies have been made to study the various aspects of laminated composite shell with open and closed shaped stiffeners.

Intrinsic High-Sensitivity Sensors Based on Etched Single-Mode Polymer Optical Fibers

The significance of etched single-mode polymer optical fibers and their potential for the development of high-sensitivity sensors are presented. A polymethyl methacrylate-based single-mode polymer optical fiber is etched to various diameters and it is observed that etching can lead to change in the material properties of the fiber, such as Youngs modulus and thermal expansion coefficient. This can play a vital role in improving the intrinsic sensing capabilities of sensors based on etched polymer optical fiber. To demonstrate that the modified material properties of the etched polymer fiber can enhance its intrinsic sensing capabilities, sensing characteristics of etched polymer fiber Bragg gratings for strain, temperature, and pressure are obtained. From the results, it is confirmed that the sensors based on etched polymer fibers exhibit high intrinsic sensitivity compared with un-etched ones. The potential of developing a sensing system for simultaneous measurement of strain and temperature is also demonstrated.

Experimental and theoretical investigations on stiffened and unstiffened composite panels under uniform transverse loading

An experimental investigation on fibre-reinforced stiffened and unstiffened panels under transverse uniform pressure has been carried out. The deflections and strains measured inside the laminate are compared with a finite element analysis. The effect of one or two stiffeners within the panel is small since the stiffener fail at small loads. In contrary to this, the effect of a different lay-up is big, because the angle-ply panels [+45°/−45°]2 carried higher loads than the cross-ply panels [0°/90°]2. The failure of the panels near the centre of the long edge at the clamping is correctly predicted by the FEA. In addition, calculated and predicted stresses are close to each other.

Numerical investigations of the mechanical properties of a braided non-vascular stent design using finite element method.

This paper discusses various issues relating to the mechanical properties of a braided non-vascular stent made of a Ni–Ti alloy. The design of the stent is a major factor which determines its reliability after implantation into a stenosed non-vascular cavity. This paper presents the effect of the main structural parameters on the mechanical properties of braided stents. A parametric analysis of a commercial stent model is developed using the commercial finite element code ANSYS. As a consequence of the analytical results that the pitch of wire has a greater effect than other structural parameters, a new design of a variable pitch stent is presented to improve mechanical properties of these braided stents. The effect of structural parameters on mechanical properties is compared for both stent models: constant and variable pitches. When the pitches of the left and right quarters of the stent are 50% larger and 100% larger than that of the central portion, respectively, the radial stiffness in the central portion increases by 10% and 38.8%, while the radial stiffness at the end portions decreases by 128% and 164.7%, the axial elongation by 25.6% and 56.6% and the bending deflection by 3.96% and 10.15%. It has been demonstrated by finite element analysis that the variable pitch stent can better meet the clinical requirements.

Hybrid structure of white layer in high carbon steel – Formation mechanism and its properties

This study identifies for the first time, the hybrid structure of the white layer in high carbon steel and describes its formation mechanism and properties. The so-called ‘white layer’ in steel forms during high strain rate deformation and appears featureless under optical microscopy. While many researchers have investigated the formation of the white layer, there has been no definitive study, nor is there sufficient evidence to fully explain the formation, structure and properties of the layer. In this study, the formation, morphology and mechanical properties of the white layer was determined following impact testing, using a combination of optical and SE- microscopy, HR-EBSD, TKD and TEM as well as nano-indentation hardness measurements and FE modelling. The phase transformation and recrystallization within and near the white layer was also investigated. The microstructure of the steel in the white layer consisted of nano-sized grains of martensite. A very thin layer of austenite with nano sized grains was identified within the white layer by HR-EBSD techniques, the presence of which is attributed to a thermally-induced reverse phase transformation. Overall, the combination of phase transformations, strain hardening and grain refinement led to a hybrid structure and an increase in hardness of the white layer.

Study of magnetorheological fluids towards smart energy absorption of composite structures for crashworthiness.

ABSTRACT A study of magnetorheological fluids energy absorption capability towards development of composite retrofit technologies for aged helicopters is presented in this article. Design parameters that influence the performance of magnetorheological dampers were identified and evaluated based on the damping force as a measure of compatibility to energy absorption. Tensile, compression, and cyclic loading tests were also conducted experimentally to validate the numerical investigation. An extensive parametric study conveyed that the piston head radius plays a major role in achieving higher damping force. The fundamental behaviors and results of the damping force in the numerical studies were also in a good agreement with the experimental results. The novel parametric numerical analysis framework validated in this article will allow for efficient design and optimization of future dampers. Received 2 August 2013 Accepted 9 January 2015

Characterization of process-induced defects in automated fiber placement manufacturing of composites using fiber Bragg grating sensors

With the increasing use of automated fiber placement method for manufacturing highly precise bespoke composite components in the aerospace industry, the level of manufacturing defects within the laminate structure needs to be monitored and minimized for structural integrity. One of the main common defects in automated fiber placement process is misalignment between the tape paths in successive courses which leads to non-integrity of laminate and consequently significant reduction in mechanical strength of the laminate. Therefore, it is necessary to find an appropriate inspection method to monitor and identify these processing defects at the earlier stages of manufacturing. Since optical fiber Bragg grating sensors are being increasingly utilized for structural health monitoring in composite materials and as they were successfully implemented by Oromiehie et al. in their earlier work for on-line lay-up process monitoring, the same methodology is once again tried for identifying the misalignment defects in automated fiber placement process. The experiments are carried out on glass-fiber/nylon laminate with embedded fiber Bragg gratings for the automated tape placement method. The defects due to misalignment are identified by the fiber Bragg grating sensors through their reflected wavelength changes during the automated manufacturing process. The analysis of results indicates that the fiber Bragg grating sensors can be reliably implemented for on-line defect monitoring during the automated fiber placement process to ensure the quality of final product and maintain the expected design life.

In-situ simultaneous measurement of strain and temperature in automated fiber placement (AFP) using optical fiber Bragg grating (FBG) sensors

Abstract There has been a tremendous growth of utilizing automated fiber placement (AFP) to manufacture highly precise components and large structures like fuselage panels and wing skins for high-end applications in aircrafts and next generation of spacecrafts. Consequently, in-situ identification of potential defects and strain level within the laminates is critical to ensure the quality and integrity of the final product. In this study, optical fiber Bragg grating sensors (FBGs) have been implemented as an on-line monitoring technique for simultaneous measurement of strain and temperature in AFP. In addition, it is also shown that, the embedded FBG sensors can remain within the laminate for continuous health monitoring after manufacturing process toward the identification of crack induced acoustic emissions.