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.

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 Laboratory and Numerical Analysis of Steel Cold-Formed Sigma Beams Retrofitted by Bonded CFRP Tapes—Extended Research

Materials ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 4960
Author(s):  
Ilona Szewczak ◽  
Katarzyna Rzeszut ◽  
Patryk Rozylo ◽  
Malgorzata Snela
Keyword(s):  
Laboratory Tests ◽  
Numerical Models ◽  
Main Idea ◽  
Steel Beams ◽  
Bottom Flange ◽  
Large Rotation ◽  
Thin Walled Structures ◽  
Four Point Bending ◽  
Thin Walled ◽  
The Impact

The presented research is a part of a broader study of strengthening methods closely associated with cold-formed sigma steel beams with tapes made of Carbon Fiber Reinforcement Polymer/Plastic (CFRP). The presented results are a continuation and extension of the tests described in previous work by the authors and refer to high-slenderness thin-walled steel sigma beams subjected to a significant large rotation. The main idea of this expanded study was to identify the effectiveness of CFRP tapes with respect to different locations, namely at a bottom-tensioned or upper-compressed flange. Six beams with a cross-section of an Σ140 × 70 × 2.5 profile by “Blachy Pruszyński” and made of S350GD steel with a span of L = 270 cm were tested in the four-point bending scheme. Two beams, taken as reference, were tested without reinforcement. The remaining beams were reinforced with the use of a 50-mm wide and 1.2-mm thick Sika CarboDur S512 CFRP tape, with two beams reinforced by placing the tape on the upper flange and two with tape located on the bottom flange. The CFRP tape was bonded directly to the beams (by SikaDur®-30 adhesive). Laboratory tests were aimed at determining the impact of the use of composite tapes on the limitation of displacements and deformations of thin-walled structures. In order to perform a precise measurement of displacement, which is, in the case of beams subjected to large rotations, a very difficult issue in itself, the Tritop system and two coupled lenses of the Aramis system were used. Electrofusion strain gauges were used to measure the deformation. In the next step, numerical models of the analyzed beams were developed in the Abaqus program. Good compliance of the results of laboratory tests and numerical analyses was achieved. The obtained results confirm the beneficial effect of the use of tapes (CFRP) on the reduction in displacements and deformations of steel cold-formed elements.

scholarly journals Fem and Experimental Analysis of Thin-Walled Composite Elements Under Compression

2017 ◽  
Vol 22 (2) ◽  
pp. 393-402 ◽  
Author(s):  
P. Różyło ◽  
P. Wysmulski ◽  
K. Falkowicz
Keyword(s):  
Numerical Analysis ◽  
Cross Section ◽  
Numerical Models ◽  
Fem Analysis ◽  
Geometrical Parameters ◽  
Loss Of Stability ◽  
Composite Columns ◽  
Thin Walled Structures ◽  
Operating Stability ◽  
Thin Walled

Abstract Thin-walled steel elements in the form of openwork columns with variable geometrical parameters of holes were studied. The samples of thin-walled composite columns were modelled numerically. They were subjected to axial compression to examine their behavior in the critical and post-critical state. The numerical models were articulately supported on the upper and lower edges of the cross-section of the profiles. The numerical analysis was conducted only with respect to the non-linear stability of the structure. The FEM analysis was performed until the material achieved its yield stress. This was done to force the loss of stability by the structures. The numerical analysis was performed using the ABAQUS® software. The numerical analysis was performed only for the elastic range to ensure the operating stability of the tested thin-walled structures.

scholarly journals CREEP OF REINFORCED CONCRETE THIN-WALLED STRUCTURES TAKING INTO ACCOUNT REVERSE DEFORMATIONS

2020 ◽  
Vol 6 (159) ◽  
pp. 113-117
Author(s):  
O. Chuprynin ◽  
N. Sereda ◽  
A. Garbuz
Keyword(s):  
Reinforced Concrete ◽  
Material Properties ◽  
Concrete Structures ◽  
Design Stage ◽  
Reinforced Concrete Structures ◽  
Nonlinear Creep ◽  
Structural Elements ◽  
Thin Walled Structures ◽  
Proposed Model ◽  
Thin Walled

One of the main tasks, which is solved at the design stage of the reinforced concrete element, is the analysis of the stress-strain state, as well as the determination of the service life. The article is devoted to modeling of nonlinear creep of reinforced concrete structural elements taking into account damages and return of the creep. The high priority of the research topic is substantiated, the purpose and objectives are formulated. A combination of a plastic model with fracture mechanics is proposed to simulate the behavior of concrete in accordance with its characteristics, including not only stress and deformation, but also the degradation of its stiffness. The resulting equations of state correspond to the law reverse deformations. The finite element method is used to solve the boundary value problem. For the sake of numerical modeling of thin-walled structures, the use of special shell elements is proposed. The mathematical formulation of the problem of creep of reinforced concrete structural elements taking into account anisotropy of material properties and creep deformations and return of the creep is presented. Creep problems of thin-walled structural elements were solved with the help of developed software. Analyzed the deformation of reinforced concrete panel of cylinder. The analysis of the results allows us to judge the effectiveness of the proposed model as a whole. The equation of state reflects the anisotropy of the material properties and takes into account the damage, which allows for a reliable assessment of the strength, stiffness and durability of reinforced concrete structures. Conclusions about the adequacy of the analysis of reliability and durability of reinforced concrete structures using the proposed model.

scholarly journals Numerical Models of the Connection of Thin-Walled Z-Profile Roof Purlins

Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6573
Author(s):  
Přemysl Pařenica ◽  
Petr Lehner ◽  
Jiří Brožovský ◽  
Martin Krejsa
Keyword(s):  
Cross Section ◽  
Numerical Models ◽  
Element Model ◽  
Cross Sectional ◽  
Physical Test ◽  
Thin Walled Structures ◽  
Practical Design ◽  
Thin Walled ◽  
Bolt Connection ◽  
Experimental Preparation

High thin-walled purlins of Z cross-section are important elements in steel wide-span structures. Their behaviour is influenced by many variables that need to be examined for every specific case. Their practical design thus requires extended knowledge of their behaviour for the possible configurations and dimensions. Numerical analysis verified by experimental investigation can thus enrich such knowledge. Numerical models have the advantage of repeatability and the ability to offer parametric changes. The parametric study presented shows a detailed description of a finite element model of thin-walled cross-sectional roof purlins connected to other roof elements. Models include various approaches to modelling bolt connection. Two schemes of purlins, with and without cleats, are presented. The results of different approaches in numerical modelling are compared with the results of a physical test on a real structure. The article shows a significant agreement in the case of specific approaches and points out the differences with others. The results can be helpful in terms of how to approach the modelling of thin-walled structures and the effective approach to experimental preparation.

A Process Map for Consistent Build Conditions in the Solid Freeform Fabrication of Thin-Walled Structures

2000 ◽  
Vol 123 (4) ◽  
pp. 615-622 ◽  
Author(s):  
Aditad Vasinonta ◽  
Jack L. Beuth ◽  
Michelle L. Griffith
Keyword(s):  
Solid Freeform Fabrication ◽  
Numerical Models ◽  
Thermal Control ◽  
Process Map ◽  
Freeform Fabrication ◽  
Thin Walled Structures ◽  
Melt Pool ◽  
Material Deposition ◽  
Thin Walled ◽  
Net Shaping

In solid freeform fabrication (SFF) processes involving thermal deposition, thermal control of the process is critical for obtaining consistent build conditions and in limiting residual stress-induced warping of parts. In this research, a nondimensionalized plot (termed a process map) is developed from numerical models of laser-based material deposition of thin-walled structures. This process map quantifies the effects of changes in wall height, laser power, deposition speed and part preheating on melt pool length, which is an essential process parameter to control in order to obtain consistent build conditions. The principal application of this work is to the Laser Engineered Net Shaping (LENS) process under development at Sandia Laboratories; however, the general approach and a subset of the presented results are applicable to any SFF process involving a moving heat source. Procedures are detailed for using the process map to predict melt pool length and predictions are compared against experimentally measured melt pool lengths for stainless steel deposition in the LENS process.

Nonlinear Response of C/C Composite Laminated Panels with Temperature Gradients under Guassian Pressure Waves

2013 ◽  
Vol 470 ◽  
pp. 1062-1068 ◽  
Author(s):  
Yun Dong Sha ◽  
Xiao Bo Jie ◽  
Lin Zhu
Keyword(s):  
Thermal Protection ◽  
Element Model ◽  
Carbon Composite ◽  
Temperature Gradients ◽  
System Response ◽  
Equivalent Linearization ◽  
Total System ◽  
Thin Walled Structures ◽  
Thin Walled ◽  
High Level

Carbon-Carbon composite material is widely used as the thermal protection systems (TPS) of hypersonic vehicles for its special mechanical and heat-proof capabilities. The thin-walled structures with this kind of materials would exhibit large displacement response under high-level acoustic loads. Usually, the external heating is non-uniform. In the paper, a finite element model for analyzing nonlinear random dynamic behaviors of Carbon-Carbon composite panels with temperature gradients under Guassian sound excitation is founded. The total system response is decomposed into the time-independent component and the time-dependent component, using the equivalent linearization technique. Numerical results include root mean square (RMS) values of maximum deflections, time histories and power spectrum densities (PSD) of the deflection response. The results obtained in this paper can contribute to the thorough understanding of thermo-acoustic response of composite thin-walled structures.

Dynamics Modeling and Analysis of Thin-Walled Aerospace Structures for Fixture Design in Multiaxis Milling

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Mouhab Meshreki ◽  
József Kövecses ◽  
Helmi Attia ◽  
Nejah Tounsi
Keyword(s):  
Dynamic Response ◽  
Dynamic Models ◽  
Analytical Description ◽  
Cutting Parameters ◽  
Computational Time ◽  
Model Parameters ◽  
Fixture Design ◽  
Dynamics Modeling ◽  
Aerospace Structures ◽  
Thin Walled

Milling of thin-walled aerospace structures is a critical process due to the high flexibility of the workpiece. Current practices in the fixture design and the choice of cutting parameters rely solely on conservative guidelines and the designer’s experience. This is a result of the lack of computationally efficient dynamic models to represent the dynamic response of the workpiece during machining, and the interaction between the workpiece, fixture and the cutting forces. This paper presents a novel dynamic formulation of typical thin-walled pockets encountered in aerospace structures. It is based on an analytical description of a five-sided pocket using a plate model. An off-line calibration of the model parameters, using global and local optimization, is performed in order to match the dynamic response of the pocket structure. The developed simplified model is based on Rayleigh’s energy method. Various pocket shapes are examined under different loading conditions and compared to finite element (FE) predictions and experimental results. In both cases, the results obtained by the developed model are in excellent agreement. This proposed approach resulted in one to two orders of magnitude reduction in computational time when compared to FE models, with a prediction error less than 10%.

scholarly journals Advanced Structural and Technological Method of Reducing Distortion in Thin-Walled Welded Structures

Materials ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 504
Author(s):  
Piotr Horajski ◽  
Lukasz Bohdal ◽  
Leon Kukielka ◽  
Radoslaw Patyk ◽  
Pawel Kaldunski ◽  
...  
Keyword(s):  
Stress State ◽  
Numerical Models ◽  
Joint Stiffness ◽  
Welding Process ◽  
Technological Changes ◽  
The Finite Element Method ◽  
Gas Tungsten Arc ◽  
Thin Walled Structures ◽  
Thin Walled ◽  
Residual Stresses And Strains

The article presents an innovative method of reducing welding distortions of thin-walled structures by introducing structural and technological changes. The accuracy of the method was demonstrated on the example of welding the stub pipes to the outer surface of a thin-walled tank with large dimensions, made of steel 1.4301 with a wall thickness of 1.5 × 10−3 (m). During traditional Gas Tungsten Arc Welding (GTAW), distortions of the base are formed, the flatness deviation of which was 11.9 × 10−3 (m) and exceeded the permissible standards. As a result of structural and technological changes, not only does the joint stiffness increase, but also a favorable stress state is introduced in the flange, which reduces the local welding stresses. Numerical models were developed using the finite element method (FEM), which were used to analyze the residual stresses and strains pre-welding, in extruded flanges, in transient, and post-welding. The results of the calculations for various flanges heights show that there is a limit height h = 9.2 × 10−3 (m), above which flange cracks during extrusion. A function for calculating the flange height was developed due to the required stress state. The results of numerical calculations were verified experimentally on a designed and built test stand for extrusion the flange. The results of experimental research confirmed the results of numerical simulations. For further tests, bases with a flange h = 6 × 10−3 (m) were used, to which a stub pipe was welded using the GTAW method. After the welding process, the distortion of the base was measured with the ATOS III scanner (GOM a Zeiss company, Oberkochen, Germany). It has been shown that the developed methodology is correct, and the introduced structural and technological changes result in a favorable reduction of welding stresses and a reduction in the flatness deviation of the base in the welded joint to 0.39 × 10−3 (m), which meets the requirements of the standards.

Individual Stiffness of 3D Space Frame Thin Walled Structural Joint Considering Local Buckling Effect

2014 ◽  
Vol 554 ◽  
pp. 411-415 ◽  
Author(s):  
Mohd Shukri Yob ◽  
Shuhaimi Mansor ◽  
Razali Sulaiman
Keyword(s):  
Research Work ◽  
Local Buckling ◽  
Weight Ratio ◽  
Space Frame ◽  
Thin Walled Structures ◽  
3D Space ◽  
Vehicle Structure ◽  
Cross Member ◽  
Thin Walled ◽  
The Individual

Thin walled beams are widely used to build vehicle structure. Thin walled structure offers high stiffness-to-weight ratio to the vehicle for better handling and fuel consumption. Despite these advantages, thin walled structures will expose to the buckling and joint flexibility effects. For a vehicle structure, 3D space frame is used a lot in designing vehicle structure. However, the stiffness of thin joint is difficult to predict accurately by numerical and analytical model due to buckling effect and the complexity of the joint. The essence of this research work is to determine individual stiffness of 3D space frame members using reduction member method. By knowing the individual stiffness of all members, the stiffness of 3D space frame can be predicted easily. This study will help design engineer to optimize vehicle structure with more efficient way rather than trial and error approach. As a case study, structure around bulkhead area which consists of A pillar, sidesill and cross member will be analyzed.

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