Development of a New Model for the Varying Dynamics of Flexible Pocket-Structures During Machining

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Mouhab Meshreki ◽  
Helmi Attia ◽  
József Kövecses
Keyword(s):  
Dynamic Models ◽  
Ritz Method ◽  
Computation Time ◽  
Dynamic Effect ◽  
Dynamic Responses ◽  
Prediction Errors ◽  
Continuous Change ◽  
Thin Walled Structures ◽  
Aspect Ratios ◽  
Thin Walled

Many of the aerospace components are characterized by having pocket-shaped thin-walled structures. During milling, the varying dynamics of the workpiece due to the change of thickness affects the final part quality. Available dynamic models rely on computationally prohibitive techniques that limit their use in the aerospace industry. In this paper, a new dynamic model was developed to predict the vibrations of thin-walled pocket structures during milling while taking into account the continuous change of thickness. The model is based on representing the change of thickness of a pocket-structure with a two-directional multispan plate. For the model formulation, the Rayleigh–Ritz method is used together with multispan beam models for the trial functions in both the x- and y-directions. An extensive finite element (FE) validation of the developed model was performed for different aspect ratios of rectangular and nonrectangular pockets and various change of thickness schemes. It was shown that the proposed model can accurately capture the dynamic effect of the change of thickness with prediction errors of less than 5% and at least 20 times reduction in the computation time. Experimental validation of the models was performed through the machining of thin-walled components. The predictions of the developed models were found to be in excellent agreement with the measured dynamic responses.

A New Analytical Formulation for the Dynamics of Multipocket Thin-Walled Structures Considering the Fixture Constraints

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Mouhab Meshreki ◽  
Helmi Attia ◽  
József Kövecses
Keyword(s):  
Dynamic Response ◽  
Ritz Method ◽  
Computation Time ◽  
Unit Element ◽  
Fixture Design ◽  
Prediction Errors ◽  
Computationally Efficient ◽  
Aerospace Structures ◽  
Thin Walled Structures ◽  
Thin Walled

Milling of thin-walled aerospace structures is a critical and challenging process. Available models for the prediction of the effect of the fixture on the dynamic response of flexible workpieces are computationally demanding and fail to represent practical cases for milling of thin-walled structures. Based on the analysis of typical structural components encountered in the aerospace industry, a generalized unit-element, with the shape of an asymmetric pocket, was identified to represent the dynamic response of these components. Accordingly, a computationally efficient dynamic model was developed to predict the dynamic response of typical thin-walled aerospace structures using the Rayleigh–Ritz method. In the formulation of this model, the dynamics of a 3D pocket is represented by an equivalent 2D multispan plate taking into account the effect of deformable fixture supports. The developed model was validated numerically and experimentally for different workpiece geometries and various types of loading. This model resulted in one to two orders of magnitude reduction in computation time when compared with the finite element models, with prediction errors less than 10%. The developed model meets the conflicting requirements of prediction accuracy and computational efficiency needed for interactive fixture design.

An Integrated Approach for the Predictions of the Workpiece Vibrations During Machining of Aerospace Structure: Numerical and Experimental Validation

2012 ◽  
Author(s):  
Mouhab Meshreki ◽  
József Kövecses ◽  
Helmi Attia
Keyword(s):  
High Speed ◽  
Dynamic Models ◽  
Force Measurement ◽  
Integrated Approach ◽  
Analytical Models ◽  
Prediction Errors ◽  
Continuous Change ◽  
Element Analysis ◽  
Analytical Methodology ◽  
Thin Walled

Accurate predictions of the workpiece vibrations during high speed machining of aerospace structural components is a critical issue since it affects the accuracy of the final part. For fixture design purposes, and for force predictions, the computational efficiency of the dynamic models predicting the workpiece vibrations is a crucial factor since it affects the cycle time for the design and optimization of the fixtures. Most of the available dynamic models are based on computationally prohibitive techniques, such as finite element analysis. In this work, an integrated approach, based on recently developed semi-analytical models, is presented for the analysis of the effect of the fixture layout on the dynamics of thin-walled structures while taking into account the continuous change of thickness of the workpiece, and the effect of rigid and deformable fixture supports. The developed approach is based on plate models with holonomic constraints and finite stiffness springs. This approach, together with all the developed models and formulations are validated numerically for different workpiece geometries and various types of loading. An experimental study has been performed to validate this approach through the machining of thin-walled components. It was found that this approach led to prediction errors within 10% and more than 20 times reduction in the computation time. The challenge of filtering the effect of the dynamics of the force measurement system from the measured signals was overcome by developing a new hybrid semi-analytical methodology for accurate measurement of the machining forces.

Dynamic Response of Pre/Post Buckled Thin-Walled Structure under Thermo-Acoustic Loading

2011 ◽  
Vol 80-81 ◽  
pp. 536-541 ◽  
Author(s):  
Yun Dong Sha ◽  
Ji Yong Li ◽  
Zhi Jun Gao
Keyword(s):  
Dynamic Response ◽  
Dynamic Responses ◽  
Transverse Displacement ◽  
Response Characteristics ◽  
Thin Walled Structures ◽  
Fem Method ◽  
Operating Environments ◽  
Thin Walled ◽  
Frequency Changes ◽  
High Level

Advanced aircraft and spacecraft structures are exposed to increasingly severe operating environments, including a combination of mechanical, aerodynamic, acoustic and thermal loads. Such loading conditions can cause thin-walled structures to respond in a nonlinear fashion and exhibit complex response characteristics. This paper investigates the dynamic response of pre/post buckled thin-walled structure under high level random acoustic loading. Firstly, different orders of critical buckling temperatures and modal frequencies under alternative temperatures are obtained using Finite Element Method (FEM), and the modal frequency changes in a disorder fashion are discussed in detail. Then with coupled BEM/FEM method, the dynamic responses including transverse displacement, strain and stress of a stiffened rectangular plate under thermo-acoustic loading are simulated. By comparing the response characteristics of the plate in pre/post buckled conditions, some valuable conclusions are derived, which can be used to explain the response behaviours of thin-walled structures.

Buckling vs. Crack Growth: Numerical Simulation

2000 ◽  
Author(s):  
T. Siegmund
Keyword(s):  
Numerical Simulation ◽  
Crack Growth ◽  
Local Failure ◽  
Small Thickness ◽  
Mechanical Integrity ◽  
Thin Walled Structures ◽  
Aspect Ratios ◽  
Thin Walled

Abstract Thin walled structures are characterized by configurations that possess large aspect ratios, i.e. large in-plane dimensions and small thickness dimensions. The present work aims on investigations of the mechanical integrity of such structures thereby focusing on the competition and interaction between global failure due to buckling and local failure due to crack growth.

Frame-Monolithic Technology of Construction of Low-Rise Buildings Made of Foam Gypsum and Steel Thin-Walled Structures

2018 ◽  
Vol 762 (8) ◽  
pp. 36-39 ◽  
Author(s):  
B.G. BULATOV ◽  
◽  
R.I. SHIGAPOV ◽  
M.A. IVLEV ◽  
I.V. NEDOSEKO ◽  
...  
Keyword(s):  
Thin Walled Structures ◽  
Thin Walled

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.

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