Hemendra Arya

A zigzag model for laminated composite beams

Abstract In the present work, a zigzag model for symmetric laminated beam is developed. This model uses a sine term to represent the non-linear displacement field across the thickness as compared to a third order polynomial term in conventional theories. Transverse shear stress and strain are represented by a cosine term as compared to parabolic term. This model satisfies displacement and transverse shear stress continuity at the interface. Zero transverse shear stress boundary condition at the top and bottom of the beam are also satisfied. The numerical results indicates that the present model predicts very accurate results for displacement and stresses for symmetric cross-ply laminated beam, even for small length to thickness ratio. The results are also compared with a simplified theory of same class.

Impact response and damage tolerance characteristics of glass-carbon/epoxy hybrid composite plates

Abstract Impact behaviour and post impact compressive characteristics of glass–carbon/epoxy hybrid composites with alternate stacking sequences have been investigated. Plain weave E-glass and twill weave T-300 carbon have been used as reinforcing materials. For comparison, laminates containing only-carbon and only-glass reinforcements have also been studied. Experimental studies have been carried out on instrumented drop weight impact test apparatus. Post impact compressive strength has been obtained using NASA 1142 test fixture. It is observed that hybrid composites are less notch sensitive compared to only-carbon or only-glass composites. Further, carbon-outside/glass-inside clustered hybrid configuration gives lower notch sensitivity compared to the other hybrid configurations.

Experimental Studies on Impact Behaviour of Woven Fabric Composites: Effect of Impact Parameters

Experimental studies have been presented on the impact behaviour of plain weave E-glass-epoxy laminates with different combinations of impactor mass and incident impact velocity with the same incident impact energy of 24.43 J. Four combinations of impactor mass-incident impact velocity have been considered. Impact tests have been carried out on an instrumented drop weight impact test apparatus. The unsupported area of the specimens during the impact loading was 127 mm 127 mm with clamped boundary condition. Thickness of the plate was 5 mm. Post-impact-compression testing of impacted specimens has been carried out using Compression-After-Impact test fixture as per NASA 1142 standard. It is observed that for the materials tested, damage tolerance is higher for low mass and high velocity combination as compared to high mass and low velocity combination.

A HIGHER ORDER DISPLACEMENT MODEL FOR THE PLATE ANALYSIS

A higher order displacement model for laminated composite plates is presented. The displacement model has trigonometric terms in addition to thin plate terms and contains six unknowns. The model satisfies shear stress conditions at top and bottom of the plate. Governing equations and boundary conditions are obtained using virtual work principle. The present displacement model gives simple governing equations. The model has been applied to various simply supported rectangular isotropic, orthotropic and layered plates for static and free vibration analysis. This model yields better results as compared to other higher order displacement models.

Design and Development of a Real-Time DSP and FPGA-Based Integrated GPS-INS System for Compact and Low Power Applications

Emphasis of the present work is on an elegant real-time solution for GPS/INS integration. Micro-electro mechanical system (MEMS) based inertial sensors are light but not accurate enough for inertial navigation system (INS) applications. An integrated INS/GPS system provides better accuracy compared with either INS or GPS, used individually. This paper describes an improved design and fabrication of a loosely coupled INS-GPS integrated system. The systems currently available use commercial off-the-shelf (COTS) hardware and are, therefore, not optimized for compact, single supply, and low power requirements. In the proposed system, a digital signal processor (DSP) is used for inertial navigation solution and Kalman filter computations. A field programmable gate array (FPGA) is used for creating an efficient interface of the GPS with the DSP. Direct serial interface of the GPS involve tedious processing overhead on the navigation processor. Therefore, a universal asynchronous receiver transmitter (UART) and dual port random axis memory (DPRAM) are created on the FPGA itself. This also reduces the total chip count, resulting in a compact system. The system is designed to give real time processed navigation solutions with an update rate of 100 Hz. All the details of this work are presented.

High Strain Rate Tensile Behavior of Aluminum Alloy 7075 T651 and IS 2062 Mild Steel

Investigations on the effect of strain rate on tensile properties of two materials, namely, aluminum alloy 7075 T651 and IS 2062 mild steel, are presented. Experimental studies were carried out on tensile split Hopkinson pressure bar (SHPB) apparatus in the strain rate range of 54–164/s. Uncertainty analysis for the experimental results is presented. Johnson–Cook material constitutive model was applied to predict the tensile yield strength of the tested materials at different strain rates. It is observed that the tensile yield strength is enhanced compared with that at quasi-static loading. During tensile SHPB testing of the specimens, it was observed that the peak force obtained from the strain gauge mounted on the transmitter bar is lower than the peak force obtained from the strain gauge mounted on the incident bar. An explanation to this is provided based on the increase in dislocation density and necking in the tested specimens during high strain rate loading and the consequent stress wave attenuation as it propagates within the specimen. The fracture behavior and effect of high strain rate testing on microstructure changes are examined. The peak force obtained based on strain gauge mounted on the transmitter bar is lower than the peak force obtained based on strain gauge mounted on the incident bar. There is an increase in tensile yield strength at high strain rate loading compared with that at quasi-static loading for both materials. The enhancement is more for IS 2062 mild steel than that for aluminum alloy 7075 T651. In the range of parameters considered, the strength enhancement factor was up to 1.3 for aluminum alloy 7075 T651 and it was up to 1.8 for IS 2062 mild steel. Generally, there was a good match between the experimental values and the Johnson–Cook model predictions.

Extended Kalman Filter based loosely coupled INS/GPS integration scheme using FPGA and DSP

GPS provides an accurate position and velocity information but with a slower update rate, whereas INS provides position, velocity and attitude information with a higher update rate. However, INS alone cannot provide proper solutions due to the increasing error characteristics of the accelerometer and gyros of the inertial sensor. To get an accurate navigation solution, it is necessary to integrate INS with GPS. This paper discusses integration of INS/GPS systems using Extended Kalman Filter (EKF). TMS320vc33 floating point DSP is used for INS and EKF computations. A FPGA (Field Programmable Gate Array) based GPS data acquisition system and Dual Port RAM (DPRAM) have been designed and used for the presented architecture.

Layer-by-Layer Analysis of a Simply Supported Thick Flexible Sandwich Beam

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Precision targeting in guided munition using infrared sensor and millimeter wave radar

Abstract. Conventional munitions are not guided with sensors and therefore miss the target, particularly if the target is mobile. The miss distance of these munitions can be decreased by incorporating sensors to detect the target and guide the munition during flight. This paper is concerned with a precision guided munition equipped with an infrared (IR) sensor and a millimeter wave radar (MmW). Three-dimensional flight of the munition and its pitch and yaw motion models are developed and simulated. The forward and lateral motion of a target tank on the ground is modeled as two independent second-order Gauss–Markov processes. To estimate the target location on the ground and the line-of-sight (LOS) rate to intercept it, an extended Kalman filter is composed whose state vector consists of cascaded state vectors of missile dynamics and target dynamics. The LOS angle measurement from the IR seeker is by centroiding the target image in 40 Hz. The centroid estimation of the images in the focal plane is at a frequency of 10 Hz. Every 10 Hz, centroids of four consecutive images are averaged, yielding a time-averaged centroid, implying some measurement delay. The miss distance achieved by including image processing delays is 1.45 m.