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1

A parametric study of higher-mode natural frequencies of composite stiffened cylindrical shell with cut-out

Chaudhuri Puja Basu, Sahoo Sarmila, Mitra Anirban

Engineering Transactions

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2023

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Vol. 71, iss. 1

81--109

EN

A finite element-based dynamic study of cut-out borne composite cylindrical shells reinforced with stiffeners is conducted. Isoparametric shell element with eight nodes and beam element with three nodes are used to study the mode-frequency behavior of shells with varied edge conditions. Anti-symmetric angle-ply laminates of two, four and ten layers with varying lamination angles are considered. Ten-layer laminates are investigated further as they exhibit better performance in fundamental frequency than two and four-layer laminates. The reduced integration method is adopted to find the shell element’s stiffness and mass matrices and the subspace iteration method is used for the eigenvalue solution of free vibration formulation. Natural frequencies for the first five modes are considered. The effects of fiber orientation angle (θ), degree of orthotropy (E11/E22), and width/thickness ratio (b/h) on the natural frequency are determined through numerical studies. It is revealed that vibration behavior strongly depends on both the number and arrangement of boundary constraints.

2

Influence of Composite Lay-Up on the Stability of Channel-Section Profiles Weakened by Cut-Outs – A Numerical Investigation

Falkowicz Katarzyna, Valvo Paolo Sebastiano

Advances in Science and Technology. Research Journal

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2023

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Vol. 17, no 1

108--115

EN

This paper presents a numerical study on the stability of composite channel-section profiles weakened by cut-outs. Profiles were made from carbon fibre-reinforced polymer (CFRP) laminates and subjected to compression load. Numerical analysis carried out in the Abaqus software allowed us to determine the value of the buckling load and the corresponding buckling form. Four different laminate lay-ups were chosen to study their effects on the buckling behaviour of the profiles. Obtained results help identify the best laminate lay-up to get the highest critical buckling load for perforated columns. The performed analysis shows that [45/-45/90/0]s and [90/-45/45/0]s composite lay-ups have the greatest impact on the buckling load. Moreover, the introduced perforation caused a change in the buckling form and a decrease in the critical load value.

3

Numerical investigations of stress concentration in reinforcement steel structure by composite overlays

Szybiński Bogdan, Wygoda Mateusz

Journal of KONES

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2019

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Vol. 26, No. 4

249--256

EN

The stress concentration observed in the vicinity of cut-outs and holes in structural elements significantly influences the fatigue endurance of machines subjected to cyclic loads. Numerous studies have been made so far to improve this situation and increase the structure lifetime. Several design recommendations have also been worked out to avoid the problem of premature failure. The proposed article illustrates the influence of the composite overlays applied around the cut-outs made in flat steel constructional elements subjected to axial tension. The detailed study concerns the reinforcement made from the FRP (fibre reinforcement polymer) composite applied around the notches. Two types of composite materials were used, namely: TVR 380 M12/R-glass (glass fibres embedded in epoxy resin matrix) and AS4D/9310 (carbon fibres embedded in epoxy resin matrix). In the first step, the detailed numerical studies (finite element analysis) were performed for the steel samples (with no overlays added) with cut-outs made in the form of circle, square and triangle hole (the last two with rounded corners). The results of these studies were compared with the existing analytical solutions with respect to the stress concentration factors (SCF) estimation. The relatively good conformity was observed when using dense meshes of finite elements placed around the void vicinity. In the next step, the composite overlays were applied around cut-outs and their influence on the stress concentration was investigated. The influence of the fibre orientation, numbers of layers, sizes of the composite overlay used were considered. It was proved that the application of composite overlays evidently decreases the stress concentration around the notches.

4

Characteristics of vibrating composite stiffened hypars with cut-out at different modes

Sahoo Sarmila

Engineering Transactions

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2019

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Vol. 67, iss. 1

75--99

EN

Vibration characteristics of laminated composite stiffened hypar (hyperbolic paraboloid shell bounded by straight edges) with cut-out are analysed in terms of natural frequency and mode shapes. A finite element code is developed for the purpose by combining an eight noded curved shell element with a three noded curved beam element for stiffener. Finite element formulation is based on first order shear deformation theory and includes the effect of cross curvature. The isoparametric shell element used in the present model consists of eight nodes with five degrees of freedom per node while beam element has four degrees of freedom per node. The code is validated by solving benchmark problems available in the literature and comparing the results. The generalised Eigen value solution is chosen for the un-damped free vibration analysis. New results are presented for first five modes of natural frequency by varying boundary conditions, ply orientation and curvature of the shell. The results furnished here may be readily used by practicing engineers dealing with stiffened composite hypars with cut-outs.

5

Wpływ czynników środowiskowych i oddziaływania gazu na funkcjonowanie reduktorów średniego ciśnienia

Wiśniowicz A.

Nafta-Gaz

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2013

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R. 69, nr 6

463--467

PL

W artykule omówiono zagadnienia związane z reduktorami średniego ciśnienia. Przedstawiono wyniki badań dziesięciu reduktorów średniego ciśnienia po różnych okresach eksploatacji, wynoszących od 13 do 25 lat, pochodzących z rejonu Polski południowej. Przedstawiono także wyniki ankiety dotyczącej nadzoru nad reduktorami. Rezultaty pracy wskazują na konieczność prowadzenia nadzoru nad reduktorami. W wyniku niniejszej pracy sugeruje się wymianę reduktora po 10-letnim okresie jego eksploatacji.

EN

In the article, presented are the issues related to medium-pressure regulators. Results of research on ten medium-pressure regulators at different periods of life, ranging from 13 to 25 years, from the region of Southern Poland are presented. The results of a survey on the supervision of regulators are presented as well. Our results point to the need for supervision of regulators. The results of this work suggests the replacement of regulators after every 10 years of their operation.

6

Analytical and Experimental Studies of Stability of Cylindrical Shells with a Cut-Out

Stasiewicz P.

Mechanics and Mechanical Engineering

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2013

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Vol. 17, nr 2

167--176

EN

Thin-walled structure, by its nature, is subjected to loss of stability. In addition, the shell has a cutout, which reduces the critical load. The aim of this study is to determine critical stress of the shell under pure bending. The goal was achieved in two ways: experimentally and analytically. Experimental studies were carried out on a specially designed test bench with the use of a resistive strain gauge. In the analytical solution the form of buckled shell was assumed, and then Bubnov-Galerkin method was applied.

7

Stability analysis of multilayered composite shells with cut-outs

Sabik A., Kreja I.

Archives of Civil and Mechanical Engineering

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2011

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Vol. 11, no 1

195-207

EN

A numerical stability analysis of an axially compressed multilayered composite shell is presented. The authors examine how the stability performance of a panel can be influenced by a centrally located square cut-out. The computations are performed within FEM computer program NX-Nastran (ver. 6.0). The stability is investigated by means of a linearized buckling analysis as well as of a non-linear large deformations incremental analysis. To get more insight into the performance of the layered structure, the failure index according to Tsai-Wu criterion is monitored in the study.

PL

W pracy analizowana jest stateczność ściskanej osiowo kompozytowej powłoki warstwowej. Badany jest wpływ usytuowanego centralnie w powłoce otworu kwadratowego na stateczność konstrukcji. Obliczenia wykonano w programie NX-Nastran (wersja 6.0). Poziom obciążeń krytycznych wyznaczony został w rozwiązaniu liniowym (liniowy problem własny) oraz na drodze analizy przyrostowej z uwzględnieniem dużych przemieszczeń (statyka nieliniowa). Dodatkowo analizowano wytężenie konstrukcji wykorzystując kryterium Tsai-Wu. Z analizy rezultatów wynika, że wraz z pojawieniem się otworu i wzrostem jego wymiarów obniża się poziom obciążeń krytycznych oraz maleje zakres liniowej odpowiedzi konstrukcji. Ponadto obserwowany jest znaczny wzrost wskaźników wytężenia w obszarach koncentracji naprężeń.

8

Elastic stability of square stiffened plates with cutouts under biaxial loading

Srivastava A. K. L., Datta P. K.

International Journal of Applied Mechanics and Engineering

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2006

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Vol. 11, no 2

421-433

EN

A finite element method for the buckling loads on a longitudinally square stiffened plate with square cutouts is investigated under various combinations of biaxial loading at the plate boundary. The forces are assumed to act in the plane of the undeformed middle surface of the plate. The characteristic equations for the natural frequencies, buckling loads and their corresponding mode shapes are obtained from the equation of motion. The buckling load parameter for various modes of the stiffened plate with square cutouts subjected to in-plane biaxial loads, has been determined for various edge conditions. Numerical results are presented for a range of hole to plate size from 0 to 0.8. In the structural modeling, the plate and the stiffeners are treated as separate elements where the compatibility between these two types of elements is maintained. The present approach is more flexible than any other finite element modeling in that the mesh division is independent of the location of the stiffeners.