scholarly journals Experimental Nondestructive Test for Estimation of Buckling Load on Unstiffened Cylindrical Shells Using Vibration Correlation Technique

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Kaspars Kalnins ◽  
Mariano A. Arbelo ◽  
Olgerts Ozolins ◽  
Eduards Skukis ◽  
Saullo G. P. Castro ◽  
...  
Keyword(s):  
Large Scale ◽  
Numerical Models ◽  
Cylindrical Shells ◽  
Laser Scanner ◽  
Experimental Tests ◽  
Buckling Load ◽  
Correlation Technique ◽  
Thin Walled Structures ◽  
Instability Point ◽  
Thin Walled

Nondestructive methods, to calculate the buckling load of imperfection sensitive thin-walled structures, such as large-scale aerospace structures, are one of the most important techniques for the evaluation of new structures and validation of numerical models. The vibration correlation technique (VCT) allows determining the buckling load for several types of structures without reaching the instability point, but this technique is still under development for thin-walled plates and shells. This paper presents and discusses an experimental verification of a novel approach using vibration correlation technique for the prediction of realistic buckling loads of unstiffened cylindrical shells loaded under axial compression. Four different test structures were manufactured and loaded up to buckling: two composite laminated cylindrical shells and two stainless steel cylinders. In order to characterize a relationship with the applied load, the first natural frequency of vibration and mode shape is measured during testing using a 3D laser scanner. The proposed vibration correlation technique allows one to predict the experimental buckling load with a very good approximation without actually reaching the instability point. Additional experimental tests and numerical models are currently under development to further validate the proposed approach for composite and metallic conical structures.

scholarly journals Displacement Study of a Large-Scale Freeform Timber Plate Structure Using a Total Station and a Terrestrial Laser Scanner

Sensors ◽  
2020 ◽  
Vol 20 (2) ◽  
pp. 413 ◽  
Author(s):  
Anh Chi Nguyen ◽  
Yves Weinand
Keyword(s):  
Large Scale ◽  
Numerical Models ◽  
Laser Scanner ◽  
Experimental Tests ◽  
Point Clouds ◽  
Element Model ◽  
Experimental Investigations ◽  
Bottom Surface ◽  
Terrestrial Laser Scanner ◽  
Total Station

Recent advances in timber construction have led to the realization of complex timber plate structures assembled with wood-wood connections. Although advanced numerical modelling tools have been developed to perform their structural analysis, limited experimental tests have been carried out on large-scale structures. However, experimental investigations remain necessary to better understand their mechanical behaviour and assess the numerical models developed. In this paper, static loading tests performed on timber plate shells of about 25 m span are reported. Displacements were measured at 16 target positions on the structure using a total station and on its entire bottom surface using a terrestrial laser scanner. Both methods were compared to each other and to a finite element model in which the semi-rigidity of the connections was represented by springs. Total station measurements provided more consistent results than point clouds, which nonetheless allowed the visualization of displacement fields. Results predicted by the model were found to be in good agreement with the measurements compared to a rigid model. The semi-rigid behaviour of the connections was therefore proven to be crucial to precisely predict the behaviour of the structure. Furthermore, large variations were observed between as-built and designed geometries due to the accumulation of fabrication and construction tolerances.

scholarly journals Fracture Mechanical Analysis of Thin-Walled Cylindrical Shells with Cracks

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 592
Author(s):  
Feng Yue ◽  
Ziyan Wu
Keyword(s):  
Fracture Mechanics ◽  
Tensile Stress ◽  
Failure Modes ◽  
Cylindrical Shells ◽  
Crack Tip ◽  
Mechanical Analysis ◽  
J Integral ◽  
Thin Walled Structures ◽  
Circumferential Tensile Stress ◽  
Thin Walled

The fracture mechanical behaviour of thin-walled structures with cracks is highly significant for structural strength design, safety and reliability analysis, and defect evaluation. In this study, the effects of various factors on the fracture parameters, crack initiation angles and plastic zones of thin-walled cylindrical shells with cracks are investigated. First, based on the J-integral and displacement extrapolation methods, the stress intensity factors of thin-walled cylindrical shells with circumferential cracks and compound cracks are studied using linear elastic fracture mechanics, respectively. Second, based on the theory of maximum circumferential tensile stress of compound cracks, the number of singular elements at a crack tip is varied to determine the node of the element corresponding to the maximum circumferential tensile stress, and the initiation angle for a compound crack is predicted. Third, based on the J-integral theory, the size of the plastic zone and J-integral of a thin-walled cylindrical shell with a circumferential crack are analysed, using elastic-plastic fracture mechanics. The results show that the stress in front of a crack tip does not increase after reaching the yield strength and enters the stage of plastic development, and the predicted initiation angle of an oblique crack mainly depends on its original inclination angle. The conclusions have theoretical and engineering significance for the selection of the fracture criteria and determination of the failure modes of thin-walled structures with cracks.

An efficient decomposition-condensation method for chatter prediction in milling large-scale thin-walled structures

2019 ◽  
Vol 121 ◽  
pp. 58-76 ◽  
Author(s):  
Yun Yang ◽  
Wei-Hong Zhang ◽  
Ying-Chao Ma ◽  
Min Wan ◽  
Xue-Bin Dang
Keyword(s):  
Large Scale ◽  
Condensation Method ◽  
Thin Walled Structures ◽  
Chatter Prediction ◽  
Thin Walled

scholarly journals Modeling and Experimental Validation of the VARTM Process for Thin-Walled Preforms

Polymers ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2003
Author(s):  
Da Wu ◽  
Ragnar Larsson ◽  
Mohammad S. Rouhi
Keyword(s):  
Shell Model ◽  
Computational Efficiency ◽  
Large Scale ◽  
Strongly Coupled ◽  
Thin Walled Structures ◽  
Simulation Based ◽  
Thin Walled ◽  
High Computational Efficiency ◽  
Insight Into ◽  
Vartm Process

In this paper, recent shell model is advanced towards the calibration and validation of the Vacuum-assisted Resin Transfer Molding (VARTM) process in a novel way. The model solves the nonlinear and strongly coupled resin flow and preform deformation when the 3-D flow and stress problem is simplified to a corresponding 2-D problem. In this way, the computational efficiency is enhanced dramatically, which allows for simulations of the VARTM process of large scale thin-walled structures. The main novelty is that the assumptions of the neglected through-thickness flow and the restricted preform deformation along the normal of preform surface suffice well for the thin-walled VARTM process. The model shows excellent agreement with the VARTM process experiment. With good accuracy and high computational efficiency, the shell model provides an insight into the simulation-based optimization of the VARTM process. It can be applied to either determine locations of the gate and vents or optimize process parameters to reduce the deformation.

On the timoshenko buckling load of thin walled cylindrical shells

1968 ◽  
Vol 19 (1) ◽  
pp. 459-464
Author(s):  
J. Genin
Keyword(s):  
Cylindrical Shells ◽  
Buckling Load ◽  
Thin Walled

An Experiential Optimization Design Method for Orthogonal Rib-Stiffened Thin Walled Cylindrical Shells under Axial Loading

2011 ◽  
Vol 110-116 ◽  
pp. 1773-1783
Author(s):  
Jia Mao ◽  
Yu Feng Chen ◽  
Wei Hua Zhang
Keyword(s):  
Optimization Design ◽  
Design Method ◽  
Mass Parameter ◽  
Cylindrical Shells ◽  
Reference Value ◽  
Buckling Load ◽  
Element Analysis ◽  
Buckling Loads ◽  
Load Optimization ◽  
Thin Walled

Parametric structural FEA (Finite Element Analysis) models of the orthogonal rib-stiffened thin walled cylindrical shells are established using APDL (ANSYS Parametric Design Language). An experiential optimization design method is then developed based on conclusions of series numerical analysis investigating the effects of parameters’ modification upon buckling loads and modes of the structure. The effects of single design parameter modification under both variational and fixed volume (mass) constraints upon the buckling loads and modes indicate that, only one design scheme is able to obtain maximum buckling load when deployment of the strengthening ribs and volume (mass) parameter were settled previously, and minimum mass would be obtained while this maximum buckling load equals to the required design load. Optimization calculations for aluminum alloy material and layered C/E (Carbon/Epoxy) composite material shells with three layering styles are implemented and discussed, and some useful conclusions are obtained. Method and approach developed in this paper provide certain reference value for the optimal design of such structures.

Modeling the Varying Dynamics of Thin-Walled Aerospace Structures for Fixture Design Using Genetic Algorithms

2011 ◽  
Vol 223 ◽  
pp. 652-661
Author(s):  
Mouhab Meshreki ◽  
Helmi Attia ◽  
József Kövecses
Keyword(s):  
Numerical Models ◽  
Research Work ◽  
Computational Effort ◽  
Computational Time ◽  
Fixture Design ◽  
Structural Elements ◽  
Thin Walled Structures ◽  
Thin Walled ◽  
High Flexibility ◽  
High Level

Fixture design for milling of aerospace thin-walled structures is a challenging process due to the high flexibility of the structure and the nonlinear interaction between the forces and the system dynamics. At the same time, the industry is aiming at achieving tight tolerances while maintaining a high level of productivity. Numerical models based on FEM have been developed to simulate the dynamics of thin-walled structures and the effect of the fixture layout. These models require an extensive computational effort, which makes their use for optimization very unpractical. In this research work, a new concept is introduced by using a multi-span plate with torsional and translational springs to simulate the varying dynamics of thin-walled structure during machining. A formulation, based on holonomic constraints, was developed and implemented to take into account the effect of rigid fixture supports. The developed model, which reduces the computational time by one to two orders of magnitude as compared to FE models, is used to predict the dynamic response of complex aerospace structural elements including pockets and ribs while taking into account different fixture layouts. The model predictions are validated numerically. The developed model meets the conflicting requirements of prediction accuracy and computational efficiency.

Limit States for Deepwater Flowlines and Risers: Review of the Research Activities at the Submarine Technology Laboratory/COPPE

2003 ◽  
Author(s):  
S. F. Estefen ◽  
T. A. Netto ◽  
I. P. Pasqualino
Keyword(s):  
Ultimate Strength ◽  
Large Scale ◽  
Failure Modes ◽  
Numerical Models ◽  
Experimental Tests ◽  
Limit States ◽  
Collapse Pressure ◽  
Research Activities ◽  
Structural Resistance ◽  
Buckle Arrestors

Research activities related to the limit states of flowlines and risers conducted at the Submarine Technology Laboratory / COPPE in cooperation with PETROBRAS are presented. The motivation for most of the research programs is associated with deepwater challenges arising from the rigid pipe installations at Campos Basin. Initially ultimate strength of intact pipes are investigated together with aspects related to residual strength, buckling propagation and buckle arrestors. Based on the experimental results numerical models have been correlated in order to be used to generate results for full scale steel pipes. Ultimate strength curves have been then produced as well as the analytical equation representative of these curves. Experimental tests of buckling propagation for small and large scale pipes have also been performed to obtain the bias factor for different equations proposed in the literature. Based on this study an equation for propagation pressure has been recommended. In addition, ring and cylinder buckle arrestors have been tested in order to propose an expression relating crossing over pressure with the arrestor geometries. An overview of the studies aiming at establishing the influence of the reeling method of installation on the failure modes of flowlines and steel catenary risers is presented. It is emphasized the influence of cross-section ovality and weld defect amplification due to plastic bending on collapse pressure and fatigue life, respectively. Finally, the development of a new concept of sandwich pipe for ultra deepwater, combining structural resistance and thermal insulation is discussed.

Exploring the constancy of the global buckling load after a critical geometric imperfection level in thin-walled cylindrical shells for less conservative knock-down factors

2013 ◽  
Vol 72 ◽  
pp. 76-87 ◽  
Author(s):  
Saullo G.P. Castro ◽  
Rolf Zimmermann ◽  
Mariano A. Arbelo ◽  
Richard Degenhardt
Keyword(s):  
Cylindrical Shells ◽  
Buckling Load ◽  
Geometric Imperfection ◽  
Knock Down ◽  
Global Buckling ◽  
Thin Walled
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