Vibration and buckling analyses of laminated panels with and without cutouts under compressive and tensile edge loads

T. Rajanna,Sauvik Banerjee,Yogesh M. Desai,D.L. Prabhakara 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.21 No.1

In this study, the influence of centrally placed circular and square cutouts on vibration and buckling characteristics of different ply-oriented laminated panels under the action of compressive and/or tensile types of nonuniform in-plane edge loads are investigated. The panels are inspected under the action of uniaxial compression, uniaxial tension and biaxial, compression-tension, loading configurations. Furthermore, the effects of different degrees of edge restraints and panel aspect ratios are also addressed in this work. Towards this, a nine-node heterosis plate element has been adopted which includes the effect of shear deformation and rotary inertia. According to the results, the tensile buckling loads are higher than that of compressive buckling loads. However, the tensile buckling load continuously reduces with the increased cutout sizes irrespective of ply-orientations. This is also true for compressive buckling loads except for some particular ply-orientations with higher sized cutouts.

Estimation of Fixity Factors of Bolted Joints in a Steel Frame Structure Using a Vibration-based Health Monitoring Technique

Joy Pal,Sauvik Banerjee,Sanjay Chikermane,Pradipta Banerji 한국강구조학회 2017 International Journal of Steel Structures Vol.17 No.2

Framed steel structures frequently have bolted connections to ensure semi-rigid joints that have a significant amount of energy dissipation incorporated in them, to avoid failure of connections and members under cyclic loading, such as wind and earthquake loading. One problem is that due to cyclic action, these bolts may loosen, and compromise subsequent behavior of the structure. A vibration-based health monitoring technique for quantification of the level of loosening of bolted joints in a steel plane frame structure is presented here, to provide a basis for evaluation of the structure state. A numerical model of a plane frame is considered with rotational springs representing semi-rigid joints. A fixity factor is defined in terms of rotational spring stiffness and is considered as a measure of level of loosening of bolts with zero representing fully loose and one representing fully tight condition. Experimental strain time histories are collected and transformed into frequency domain using Fourier transform. A shape co-relation is defined using frequency data obtained from the damaged and the undamaged structures. Using the frequency spectra and shape correlation, an objective function (OF) is developed and minimized by the particle swarm optimization to estimate the fixity factor. It is found that the technique estimates higher value of reduction of the fixity factor in the damaged location, but shows some considerable value at the other springs also. Therefore, the technique is improved using heuristics by identifying probable damage locations prior to applying model updation, in order to estimate the damage severity more accurately. Considering fixity factors at the identified locations as variables, model updating is done for estimation of fixity factors. The improved results clearly indicate actual damage locations and fixity factors for different levels of bolt loosening, and is found satisfactory for possible future application of the technique to multistory framed structures.

Oral and maxillofacial injuries in children: a retrospective study

Santanu Mukhopadhyay,Sauvik Galui,Raju Biswas,Subrata Saha,Subir Sarkar 대한구강악안면외과학회 2020 대한구강악안면외과학회지 Vol.46 No.3

Objectives: The purpose of this retrospective epidemiological study was to determine the etiology and pattern of maxillofacial injuries in a pediatric population. Materials and Methods: Data for pediatric maxillofacial trauma patients aged 12 years and younger who were registered at the Department of Pediatric and Preventive Dentistry, Dr. R. Ahmed Dental College and Hospital, Kolkata, India, were reviewed and examined. Patients who were treated between October 2016 and September 2018 were analyzed according to age, sex, cause of injury, frequency and site of facial fractures, and soft tissue injuries. The chi-square tests were carried out for statistical analyses with a significance level of 5%. Results: Of 232 patients with a mean age of 6.77±3.25 years, there were 134 males (57.8%) and 98 females (42.2%). The overall male to female ratio was 1.39:1. The most common causes of injuries were falls (56.5%) and motor vehicle accidents (16.8%). Incidence of falls decreased significantly with age (P<0.001). Dentoalveolar injuries (61.6%) and soft tissue injuries (57.3%) were more common than facial fractures (42.7%). Mandibular fractures (82.8%) were the most common facial fractures, and perioral or lip injuries were the most prevalent injuries in our patient population. There was a positive association between facial fractures and soft tissue injury (P<0.01) (odds ratio 0.26; confidence interval 0.15-0.46). Conclusion: Falls were the leading cause of maxillofacial trauma in our sample of children, and the most common site of fractures was the mandible.

Research Advances on Tension Buckling Behaviour of Aerospace Structures: A Review

Datta, Prosun Kumar,Biswas, Sauvik The Korean Society for Aeronautical and Space Scie 2011 International Journal of Aeronautical and Space Sc Vol.12 No.1

This paper reviews most of the research done in the field of tensile buckling characteristics pertaining to aerospace structural elements with special attention to local buckling and parametric excitation due to periodic loading on plate and shell elements. The concepts of buckling in aerospace structures appear as the result of the application of a global compressive applied load or shear load. A less usual situation is the case, in which a global tensile stress creates buckling instability and the formation of complex spatial buckling pattern. In contrast to the case of a pure compression or shear load, here the applied macroscopic load has no compressive component and is thus globally stabilizing. The instability stems from a local compressive stress induced by the presence of a defect, such as a crack or a hole, due to partial or non-uniform applied load at the far end. This is referred to as tensile buckling. This paper discusses all aspects of tensile buckling, theoretical and experimental. Its far reaching applications causing local instability in aerospace structural components are discussed. The important effects on dynamic stability behaviour under locally induced periodic compression have been identified and influences of various parameters are discussed. Experimental results on simple and combination resonance characteristics on plate structures due to tensile buckling effects are elaborated.

Optimum arrangement of stiffener on the buckling behaviour of stiffened composite panels with reinforced elliptical cutouts subjected to non-uniform edge load

Akshay Prakash Kalgutkar,Sauvik Banerjee,T. Rajanna 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.42 No.4

Cutouts in the beams or plates are often unavoidable due to inspection, maintenance, ventilation, structural aesthetics purpose, and sometimes to lighten the structures. Therefore, there will be a substantial reduction in the strength of the structure due to the introduction of the cutouts. However, these cutouts can be reinforced with the different patterns of ribs (stiffener) to enhance the strength of the structure. The present study highlights the influence of the elliptical cutout reinforced with a different pattern of ribs on the stability performance of such stiffened composite panels subjected to non-uniform edge loads by employing the Finite element (FE) technique. In the present formulation, a 9-noded heterosis element is used to model the skin, and a 3-noded isoparametric beam element is used to simulate the rib that is attached around a cutout in different patterns. The displacement compatibility condition is employed between the plate and stiffener, and arbitrary orientations are taken care by introducing respective transformation matrices. The effect of shear deformation and rotary inertia are incorporated in the formulation. A new mesh configuration is developed to house the attached ribs around an elliptical cutout with different patterns. Initially, a study is performed on the panels with different stiffener schemes for various ply orientations and for different stiffener depth to width ratios (ds/bs) to determine an optimal stiffener configuration. Further, various parametric studies are conducted on an obtained optimal stiffened panel to understand the effect of cutout size, cutout orientation, panel aspect ratio, and boundary conditions. Finally, from the analysis, it can be observed that the arrangement of the stiffener attached to a panel has a major impact on the buckling capacity of the stiffened panel. The stiffener’s depth to width ratio also significantly influences the buckling characteristic.

Research Advances on Tension Buckling Behaviour of Aerospace Structures : A Review

Prosun Kumar Datta,Sauvik Biswas 한국항공우주학회 2011 International Journal of Aeronautical and Space Sc Vol.12 No.1

This paper reviews most of the research done in the field of tensile buckling characteristics pertaining to aerospace structural elements with special attention to local buckling and parametric excitation due to periodic loading on plate and shell elements. The concepts of buckling in aerospace structures appear as the result of the application of a global compressive applied load or shear load. A less usual situation is the case, in which a global tensile stress creates buckling instability and the formation of complex spatial buckling pattern. In contrast to the case of a pure compression or shear load, here the applied macroscopic load has no compressive component and is thus globally stabilizing. The instability stems from a local compressive stress induced by the presence of a defect, such as a crack or a hole, due to partial or non-uniform applied load at the far end. This is referred to as tensile buckling. This paper discusses all aspects of tensile buckling, theoretical and experimental. Its far reaching applications causing local instability in aerospace structural components are discussed. The important effects on dynamic stability behaviour under locally induced periodic compression have been identified and influences of various parameters are discussed. Experimental results on simple and combination resonance characteristics on plate structures due to tensile buckling effects are elaborated.