425 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
Defensing Confidentiality During Complete Packet Inspection On A Middlebox
No full textIn Internet to encrypt traffic, HTTPS provides secure and private data communication between clients and servers. Network operators often deploy middleboxes to perform deep packet inspection DPI to detect attacks using techniques ranging from simple keyword matching to more advanced machine learning and data mining analysis. But this approach cannot protect users' private information from a service provider who deploys middleboxes. SPABox, a middlebox based system that supports both keyword based and data analysis based DPI functions over encrypted traffic. SPABox preserves privacy by using a novel protocol with a limited connection setup overhead. In this paper to further improve the performance, we are working on the network performance requirements. K. Geetharani | K. Kowsalya | A. M. SenthilKumar | M. S. Vijaykumar | M. Saravanakumar "Defensing Confidentiality During Complete Packet Inspection On A Middlebox" 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/ijtsrd10725.pd
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
Finite-Time Passivity-Based Stability Criteria for Delayed Discrete-Time Neural Networks via New Weighted Summation Inequalities
No full textIn this paper, we study the problem of finite-time stability and passivity criteria for discrete-time neural networks (DNNs) with variable delays. The main objective is how to effectively evaluate the finite-time passivity conditions for NNs. To achieve this, some new weighted summation inequalities are proposed for application to a finite-sum term appearing in the forward difference of a novel Lyapunov-Krasovskii functional, which helps to ensure that the considered delayed DNN is passive. The derived passivity criteria are presented in terms of linear matrix inequalities. A numerical example is given to illustrate the effectiveness of the proposed results
Robust Stabilization of Delayed Neural Networks: Dissipativity-Learning Approach
No full textThis paper examines the robust stabilization problem of continuous-time delayed neural networks via the dissipativity-learning approach. A new learning algorithm is established to guarantee the asymptotic stability as well as the (Q, S, R)-alpha-dissipativity of the considered neural networks. The developed result encompasses some existing results, such as H-infinity and passivity performances, in a unified framework. With the introduction of a Lyapunov-Krasovskii functional together with the Legendre polynomial, a novel delay-dependent linear matrix inequality (LMI) condition and a learning algorithm for robust stabilization are presented. Demonstrative examples are given to show the usefulness of the established learning algorithm
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
Comparison of Clinical and Radiographic Success of Three Obturation Materials in Primary Teeth: A Randomized Controlled Clinical Trial
No full textAIM :
To evaluate and compare the clinical and radiographic success of zinc oxide eugenol, metapex and endoflas as obturating materials in pulpectomy of primary teeth at 3 and 6 months follow up.
METHODOLOGY :
A total of 60 carious primary molars with clinical signs and symptoms indicative of irreversible pulpitis were selected from 36 children, aged 4 to 9 years and free from any systemic disease who visited the outpatient ward of Department of Pedodontics, KSRIDSR, Tiruchengode
between January 2015 till April, 2015. The teeth were selected on specific inclusion and exclusion criteria randomly divided into three groups A, B and C. The pulpectomy procedure was performed under rubber dam isolation after administration of local anaesthesia. The selected
teeth were randomly obturated with zinc oxide eugenol in group A, metapex in group B and zinc
oxide eugenol and endoflas as Group C. Post operative radiographs were taken immediately after
obturation. All obturated teeth received an entrance restoration, followed by preformed stainless
steel crown. The teeth were evaluated at 3 and 6 months respectively using clinical and
radiographic criteria cited by Gupta and Das (2011). Clinical and radiographic success was
scored by two well-trained pediatric dentists. Inter examiner reliability was correlated by using
Cohen’s Kappa coefficient (k = 0.8).
STATISTICS: Statistical analysis was done using SPSS version 17.0 (Chicago: SPSS Inc)
with statistical significance set at p _ 0.05. Chi square test was employed for the statistical
analysis.
RESULTS AND CONCLUSION : Zinc oxide eugenol had 100 % overall success rate, followed by endoflas with 98.6% and metapex with 92.1%. Intergroup comparison of overall success was statistically significant (p = 0.0027). Both zinc oxide eugenol and endoflas showed 100% clinical
success rate at 3 and 6 months interval. Metapex showed 100 % clinical success at the 3rd month,
but it declined to 89.4 % in the 6th month follow up. Similary, inter group comparisons of clinical
success between the three groups was highly statistically significant at the 6th month interval (p <
0.001). Intra group comparison of radiographic success was highly statistically significant for
metapex (p < 0.001) and statistically significant for the endoflas (p = 0.045). Inter group comparison between the three groups was statistically significant at the 3rd and 6th month interval
with p = 0.004 and p < 0.001 respectively
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