Gangadhara B Prusty

Free and forced vibration analysis using improved third-order shear deformation theory for functionally graded plates under high temperature loading

An improved third-order shear deformation theory is employed to investigate free and forced vibration responses of functionally graded plates. A power law distribution is used to describe the variation of material compositions across the plate thickness. The governing equations for vibration analysis obtained using an energy approach are then solved using the Ritz method. Two types of solutions, temperature independent and dependent material properties, are considered. Many effects of the volume fraction index, temperature, material pairs, thickness, plate aspect ratio, etc., which have significant impact on dynamic behaviour of the plates, are considered in the numerical illustrations of free and forced vibration results. At high temperatures, it is observed that the maximum deflections of the functionally graded plates subjected to the dynamic loading increase with the increase of frequency ratio and temperature.

Can More Become Less? Effects of an Intensive Assessment Environment on Students' Learning Performance.

Online interactive systems offer the beguiling prospect of an improved environment for learning at minimum extra cost. We have developed online interactive tutorials that adapt the learning environment to the current learning status of each individual student. These Adaptive Tutorials (ATs) modify the tasks given to each student according to their previous responses. Feedback, assessment and remediation are also adapted. Over a three-year period we progressively blended ATs into notoriously challenging courses in introductory Engineering Mechanics. We assessed the impact of this initiative by reviewing three lines of data: (i) the built-in diagnostics of the system, (ii) changes in student grades from year-to-year and (iii) supplementary surveys. Generally, students liked the new blended system and grades improved. Detailed analysis revealed nuances in the measures of student learning, such as differences between high-performing and low-performing students. With these insights we are able to further adapt the system to meet the learning needs of our students.

Thermal sensitivity and relaxation of carbon fibre-foam sandwich composites with fibre optic sensors

The increasing use of sandwich composites for structural applications brings with it a need to establish a reliable inspection and monitoring method to ensure structural integrity and safe operation throughout the service life. Since optical fibre-based photonic sensing technologies are increasingly common for structural health monitoring of composite structures, selection of optical fibre Bragg grating sensors could be one possible choice for this purpose. In this paper, performance characterisation of sandwich composite with embedded silica fibre Bragg grating sensor is reported. Experimental tests were performed on a carbon fibre foam core sandwich composite embedded with a silica fibre Bragg grating sensor to extract the structural health monitoring parameters such as strain and temperature. The current study found that sandwich composite exhibits foam relaxation; however, its impact on strain measurement is negligible. Another important finding from the theoretical and the experimental thermal modelling was that although the constituent components of the sandwich composite have entirely different thermal expansion coefficients, its effect on the embedded fibre sensor can be minimal if the sensors are embedded between the face sheets. These results can initiate further research in this area and can lead to the development of state-of-the art structural health monitoring techniques for sandwich composite structures.

Fibre optic acoustic emission sensor system for hydrogen induced cold crack monitoring in welding applications

A fibre optic acoustic emission method to monitor hydrogen induced cold crack activities during welding is presented in this paper. A high sensitivity fiber Bragg grating (FBG) based acoustic emission (AE) measurement system is developed to monitor the cold crack induced AE events during a titanium aluminide alloy welding using gas tungsten arc welding method Frequency ranges of the AE where cold cracking occurs in the metal also has been evaluated. The measured frequency components of the AE events were within 270 kHz. The results of this feasibility study shows the potential of FBG based AE detection method to accurately predict the defects in welding, which will improve the quality of the final weld product in applications where higher welding standards are required.

Optical fiber Bragg grating sensors for process monitoring in advanced composites

The potential for increased productivity offered by automated tape placement method has opened up a wider range of applications as well as new markets for lightweight, fiber-reinforced composite materials in various industries. However, different flaws such as voids or delaminations may still occur during or after layup. In the experimental work presented in this paper, glass fiber/HDPE laminates with embedded fiber Bragg gratings (FBGs) are fabricated using automated tape placement method and the lay-up process conditions are monitored by FBG sensors. The results indicate that embedded FBGs can be reliably used for on-line monitoring of lay-up process and ensure the quality of final product.

Fibre Bragg grating sensing technology for the evaluation of physical properties of dental resin composites

The characterization of the physical properties of dental resin composites is fraught with difficulties relating to significant intra and inter test parameter variabilities and is relatively time consuming and expensive. The main aim of this study was to evaluate whether optical fibre Brag grating (FBG) sensing system may become a viable tool to study dental material characteristics. Of particular focus was the potential for the system to demonstrate a multi parameter all-in-one feature. A miniature FBG was embedded in six different dental resin composites and employed as a sensor to evaluate linear polymerization shrinkage, thermal expansion and water sorption. This study demonstrates how optical fibre technology can provide simple and reliable methods of measuring the critical physical properties of dental composites. In addition due to the embedding and preservation of the sensor within the samples multiple parameters can be tested for with the same sample.

Evaluation of the physical properties of dental resin composites using optical fiber sensing technology

OBJECTIVES The characterization of the physical properties of dental resin composites is fraught with difficulties relating to significant intra and inter test parameter variabilities and is relatively time consuming and expensive. The main aim of this study was to evaluate whether optical fiber Bragg grating (FBG) sensing system may become a viable tool to study dental material characteristics. Of particular focus was the potential for the system to demonstrate a multi parameter all-in-one feature. METHODS A miniature FBG was embedded in six different dental resin composites and employed as a sensor to evaluate linear polymerization shrinkage, thermal expansion and water sorption. Six commercially available dental composites with different filler types and volume are evaluated. The tests are repeated with three sets of samples. The curing characteristics and residual strain gradient exhibited by the cured dental composites were also observed and commented. RESULTS Among the studied samples, SDR shows lowest polymerization shrinkage, while Beautifil FO3 shows the highest. The results also show clear distinction between particle filler type and fiber reinforcement based composites in their polymerization shrinkage properties. The agreement of the results with existing literatures show that FBG based system provides accurate results. Polymerization shrinkage rate of the samples are also obtained. Thermal expansion of the composites are measured using the FBG sensing method for the first time and is correlated with resin type, volume, filler type and glass transition temperature. The water sorption characteristics of the dental composite are also successfully measured using the FBG sensing method. The high level of repeatability and the low standard deviations shown in the results indicate good reliability with the use of FBG sensors. SIGNIFICANCE This study demonstrates how optical fiber technology can provide simple and reliable methods of measuring the critical physical properties of dental composites. In addition due to the embedding and preservation of the sensor within the samples multiple parameters can be tested for with the same sample. These features are expected to greatly assist material science researchers in dentistry as well as other biomedical fields. Of some interest the phenomenon of stress relaxation of dental composite at higher temperature was observed.

Carbon fibre-foam sandwich composite laminate embedded with fiber Bragg grating sensors

Carbon fibre-foam sandwich composite with embedded FBGs are fabricated and dynamic load testing and temperature studies were carried out. It was found from the tests that, the embedded FBG can measure the strain inside a sandwich composite, but a gauge factor is required to measure the absolute strain experienced inside the composite. The temperature sensitivity of the embedded FBG is found to be close to that of the free space sensitivity of the FBG, concluding that the thermal expansion of the carbon fibre-foam composite is minimal and has negligible effect on the embedded grating. The effect of the foam relaxation is also studied and it is found that foam relaxation can contribute to a strain error of ±16 με in strain measurements during the observed time period in this study. The results presented in this paper points to a direction that, embedded FBGs can be reliably used for strain measurement in sandwich composites and is less impacted by the thermal expansion of the composite laminate which is an advantage compared to other types of composite laminates. Further studies are required to estimate the FBG gauge factor for strain measurements and also to quantify the foam relaxation error based on an applied load.