318 research outputs found
Influence of Milled Glass Fiber Fillers on Mode I & Mode II Interlaminar Fracture Toughness of Epoxy Resin for Fabrication of Glass/Epoxy Composites
No full textThe present work is focused on improving mode I and mode II delamination resistance of glass/epoxy composite laminates (50 wt.% of glass fibers) with milled glass fibers, added in various amounts (2.5, 5, 7.5 and 10% of the epoxy weight). Including fillers in the interlayer enhances the delamination resistance by providing a bridging effect, therefore demanding additional energy to initiate the crack in the interlaminar domain, which results in turn in enhanced fracture toughness. The maximal increase of mode I and mode II fracture toughness and of flexural strength was obtained by the addition of 5% milled glass fiber. The mechanism observed suggests that crack propagation is stabilized even leading to its arrest/deflection, as a considerable amount of milled glass fiber filler was oriented transverse to the crack path. In contrast, at higher filler loading, tendency towards stress concentration grows due to local agglomeration and improper dispersion of excess fillers in inter/intralaminar resin channel, causing poor adhesion to the matrix, which leads to reduction in fracture toughness, strength and strain to failure. Fractured surfaces analyzed using scanning electron microscopy (SEM) revealed a number of mechanisms, such as crack deflection, individual debonding and filler/matrix interlocking, all contributing in various ways to improve fracture toughness
Quasi-static indentation behavior of GFRP with milled glass fiber filler monitored by acoustic emission
No full textThis paper aims at investigating the influence of the addition of milled glass fibers upon quasi-static indentation (QSI) properties of glass/epoxy composite laminates. The QSI behavior was experimentally studied by evaluating indentation force, residual dent depth, energy absorbed and size of the damaged area for different indentation depths. Following the QSI tests, the filler-loaded glass/epoxy samples were subjected to three-point bending tests in order to measure residual flexural strength, and the results were compared with the baseline glass/epoxy samples. Both tests were performed with online acoustic emission monitoring in order to observe damage progression and characterize different fracture mechanisms associated with loading. The results show that the filler-loaded laminates exhibit a substantial improvement in the peak force and contact stiffness, with a reduced permanent damage both in terms of depth and of area, in comparison with the baseline ones. It is found that the filler presence offers greater stiffness and higher energy dissipation through toughening mechanisms such as filler debonding/pullout and filler bridging/interlocking
Damage characterization of stiffened glass-epoxy laminates under tensile loading with acoustic emission monitoring
No full textThe design of composite components in the aerospace industry often includes structural discontinuities, such as cutouts, for functional requirements like ventilation, tunnel passage, maintenance and repair. The presence of cutout holes leads to complicated stress concentrations with a substantial reduction in structural stability and strength of the resulting composites. It is known that reinforcing with additional material at the cutout zones can extend the damage tolerance of a structure, therefore maintaining structural integrity and load carrying capacity. This study focuses on the experimental investigation of the tensile behavior and failure characteristics of stiffened glass/epoxy composite laminates, with cutouts, under acoustic emission monitoring. The progressive failure mechanisms of laminates with cutouts and the potential benefits of additionally dropped reinforcements are evaluated under tensile loading. The additional reinforcements were provided in either a step-like or as a simultaneous drop-off sequence between adjacent continuous plies. Results showed that adding ply drop reinforcements at the location of the cutout hole improves the stiffness, strength, and also prolongs the life of the composite laminates. It is also observed that step-like ply drop arrangements performed more effectively than simultaneously dropped configurations. The location and extent of damage identified by microscopic images correlated well with the acoustic emission results
Compression after impact strength of repaired GFRP composite laminates under repeated impact loading
No full textDuring their service life, composite materials are prone to damage, which compromises their structural
performance significantly. In this study, glass/epoxy composite specimens fabricated using hand layup
method and further cured in a compression molding machine were cut from the laminates and subjected
to low velocity impact damage in order to investigate the effects of repair. The impacted laminates were
repaired by removing the damage area with a circular cutout and filled with a chopped short Kevlar/
epoxy: the efficiency of the repair procedure and toughness of the repaired laminates were examined
by repeated impacts on the repaired site. The residual strength of the post impacted repaired laminates
is investigated by the conduction of compression after impact (CAI) loading with acoustic emission
monitoring (AE) technique. The structural performance of both repaired and unrepaired laminates are
compared and discussed
Residual strength estimation and damage characterization by acoustic emission of drilled thermally conditioned fiberglass laminates
No full textStructural components of composite materials in aerospace industries are assembled using fasteners, installed by performing cutting processes, such as drilling, on the material. In composites, this is considered particularly critical, because delamination due to mechanical stresses and fiber/resin pullout may be facilitated during cutting, so that the structural integrity of composite laminates may be affected. Acoustic emission (AE) technique is employed to monitor the failure modes and damage mechanism of drilled composite materials, while in an attempt to improve the strength of the composites, thermal conditioning has been applied. This paper investigates the residual performance of drilled unidirectional glass fiber reinforced plastic (GFRP) laminates subjected to various thermal conditioning methods. Thermally treated laminates underwent three-point flexural tests under AE monitoring to compare their residual strength with the untreated ones. The results clearly show that the thermal conditioning could be used as an effective method for minimizing delamination in GFRPs
Differentials in Maternal and Child Health Care in Tamil Nadu
No full textThe present paper examines the rural urban differentials and the factors influencing net change in maternal and child healthcare MCH indicators during the National Family Health Survey NFHS 4 2015 16 and NFHS 3 2005 06 . The National Family Health Survey NFHS collected data from 28,820 ever married women in the age group of 15 49 and 5,317 men age 15 54 NFHS 4 and 5,919 women age 15 49 and 5,696 men age 15 54 NFHS 3 and this paper analyses these data. This paper describes about the trends in MCH indicators by residence, early childhood mortality rates, immunization and anemic status of women and children by using bivariate analysis and chi square test. The analysis reveals that there is a progress in MCH indicators and also there exist negative performance of certain indicators. Overall, there exits rural urban differentials in MCH achievements though government have introduced many government health programs like National Rural Health Mission NRHM , NUHM and NHM etc., The government have to take steps to reduce rural urban differentials in achieving MCH goals and to reduce early childhood mortality rates. V. Saravanakumar | Dr. C. Sivapragasam | Dr. S. Ravichandran "Differentials in Maternal and Child Health Care in Tamil Nadu" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-2 | Issue-3 , April 2018, URL: https://www.ijtsrd.com/papers/ijtsrd12790.pd
Establishment of diagnostic reference levels in computed tomography for select procedures in Pudhuchery, India
No full textComputed tomography (CT) scanner under operating conditions has become a major source of human exposure to diagnostic X-rays. In this context, weighed CT dose index (CTDI w ), volumetric CT dose index (CTDI v ), and dose length product (DLP) are important parameter to assess procedures in CT imaging as surrogate dose quantities for patient dose optimization. The current work aims to estimate the existing dose level of CT scanner for head, chest, and abdomen procedures in Pudhuchery in south India and establish dose reference level (DRL) for the region. The study was carried out for six CT scanners in six different radiology departments using 100 mm long pencil ionization chamber and polymethylmethacrylate (PMMA) phantom. From each CT scanner, data pertaining to patient and machine details were collected for 50 head, 50 chest, and 50 abdomen procedures performed over a period of 1 year. The experimental work was carried out using the machine operating parameters used during the procedures. Initially, dose received in the phantom at the center and periphery was measured by five point method. Using these values CTDI w , CTDI v , and DLP were calculated. The DRL is established based on the third quartile value of CTDI v and DLP which is 32 mGy and 925 mGy.cm for head, 12 mGy and 456 mGy.cm for chest, and 16 mGy and 482 mGy.cm for abdomen procedures. These values are well below European Commission Dose Reference Level (EC DRL) and comparable with the third quartile value reported for Tamil Nadu region in India. The present study is the first of its kind to determine the DRL for scanners operating in the Pudhuchery region. Similar studies in other regions of India are necessary in order to establish a National Dose Reference Level
RETRACTED: Feasibility Studies on Compressive Strength of Ground Coal Ash Geopolymer Mortar
No full textPAPER RETRACTED May 10, 2016, by the general editor of Periodica Polytechnica, because of plagiarism. Plagiarized paper: V Revathi, R Saravanakumar and J Thaarrini, Effect of Molar Ratio of SiO2/Na2O, Na2SiO3/NaOH Ratio and Curing Mode on the Compressive Strength of Ground Bottom Ash Geopolymer Mortar. International Journal of Earth Science and Engineering, August 2014, pp. 1511-1516
EDS microanalysis of blast furnace slag grains in aged concrete
No full textThe chemistry of ground granulated blast furnace slag (GGBFS) is one of the main factors affecting its reactivity. Knowing the composition of GGBFS used in aged concrete may help understand its past performance and estimate remaining service life. It is well known that GGBFS generally react slower than cement clinker. This thesis proposes that partially hydrated GGBFS grains found in aged concrete could be used to determine its chemical composition. The feasibility of using standard-based energy dispersive X-ray spectroscopy (EDS) microanalysis, along with electron imaging, as a tool for quantitative measurement of the chemical composition of GGBFS grains in cement/concrete is explored in this research. X-ray spectra collected from minerals or glasses of known composition are known as standards for quantitative EDS microanalysis. This study initially examined the performance of mineral and slag standards to quantify X-ray spectra obtained from GGBFS-cement paste specimens of known composition. Parameters such as GGBFS properties, experimental conditions, and microanalysis methodologies that affect the EDS quantitative total and accuracy were elaborated. Then, the same standards were used to quantify the unknown composition of GGBFS used in seven concrete specimens collected in the Netherlands representing different service life, which revealed the variation in GGBFS chemistry over the years. Finally, as a supplementary study, the variation in significant hydration products formed due to variation in GGBFS composition in a cement-GGBFS system was predicted using thermodynamic modelling with GEMS. Altogether, it was concluded that standard-based EDS is a solid tool to characterize the chemical composition of GGBFS used in aged concrete.Civil Engineerin
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