Consequences of Using the Plane Stress Assumption for Damage Calculations in Crash Analyses

2014 ◽  
Author(s):  
Carey L. Walters ◽  
Lars O. Voormeeren
Keyword(s):  
Plane Stress ◽  
Stress Triaxiality ◽  
Shell Element ◽  
Element Model ◽  
Offshore Structures ◽  
Two Dimensions ◽  
Shell Structures ◽  
Planar Case ◽  
Lode Parameter ◽  
Shell Elements

Simulation of failure in plate materials (represented as shell elements) is critical for the correct determination of crash performance of ships and offshore structures. This need has traditionally been filled with failure loci that give the failure strain in terms of stress triaxiality. In recent years, a third dimension (Lode parameter) has been introduced in the form of the Modified Mohr Coulomb failure criterion and Lode parameter adjusted Gurson-type models. This development introduces ambiguity for shell structures, in which only two dimensions are represented. The typical way of addressing this is to assume that shell structures fail in plane stress, thus reducing the problem back to 2-D. However, the assumption of plane stress is violated as soon as necking begins, causing different stress triaxialities and Lode parameters than would be expected from the planar case. More importantly, the inhomogenous necked region is then homogenized over the entire shell element. In this paper, the consequences of the through-thickness plane stress assumption are assessed through a finite element model of a plate that is subjected to a far-field stress.

Calculation of Shell Element Failure Based on the State of Stress Inside of a Neck

2015 ◽  
Author(s):  
R. C. Dragt ◽  
J. Kraus ◽  
C. L. Walters
Keyword(s):  
Three Dimensional ◽  
Shell Element ◽  
Offshore Structures ◽  
Shell Elements ◽  
Thin Walled Structures ◽  
Coulomb Failure ◽  
Correct Determination ◽  
Element Failure ◽  
The Relationship

Simulation of failure in thin-walled structures is critical for the correct determination of crash performance of ships and offshore structures. Typically, shell elements are used, but these elements are not able to adequately capture local failure, especially inside of a neck. This paper addresses these gaps by adapting the Bridgman (1952) model of a neck inside of a plate by making it three-dimensional and offering an estimate of the relationship between state parameters of a shell element and the geometry inside of a neck. Finally, recommendations are also made about how to interface this information with the Modified Mohr-Coulomb failure locus to create a practical algorithm for assessing failure in shell elements.

Quick Aeromechanical Assessment of Turbine Blades Based on Shell Element Based Models

2014 ◽  
Author(s):  
Suryarghya Chakrabarti ◽  
Letian Wang ◽  
K. M. K. Genghis Khan
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Natural Frequencies ◽  
Turbine Blades ◽  
Computation Time ◽  
Shell Element ◽  
Element Model ◽  
Shell Elements ◽  
Barrier Coating ◽  
Order Of Magnitude

A fast finite element model based tool has been developed to calculate the natural frequencies of fundamental modes of cooled gas turbine bladed disk assemblies during conceptual design. The tool uses shell elements to model the airfoil, shank, and disk, and achieves order of magnitude reduction in computation time allowing exploration of a wide design space at the preliminary design stages. The analysis includes prestress effects due to centrifugal loading and approximate temperature loading on the parts. Sensitivity studies are performed to understand the relative impact of design features such as airfoil internal geometry, bond coat, and thermal barrier coating on the system natural frequencies. Critical features are selected which need to be modeled to get an accurate natural frequency estimate. The results obtained are shown to be within 5% of the frequencies obtained from a full-fidelity finite element model. A case study performed on seven blade designs illustrates the use of this tool for quick aeromechanical assessment of a large number of designs.

A Parametric Study for Four Node Bilinear EAS Shell Elements

2010 ◽  
Vol 26 (4) ◽  
pp. 431-438
Author(s):  
Cengiz Polat
Keyword(s):  
Variational Principle ◽  
Transverse Shear ◽  
Strain Field ◽  
Shell Element ◽  
Shell Structures ◽  
Shear Locking ◽  
Shell Elements ◽  
Assumed Strain ◽  
Dependent Strain ◽  
Transverse Shear Locking

ABSTRACTA locking free formulation of 4-node bilinear shell element and its application to shell structures is demonstrated. The Enhanced Assumed Strain (EAS) method based on three-field variational principle of Hu-Washizu is used in the formulation. Transverse shear locking and membrane locking are circumvented by means of enhancing the displacement-dependent strain field with extra assumed strain field. Several benchmark shell problems are analyzed.

Mixed-dimensional coupling modeling for laser forming process

2014 ◽  
Vol 228 (16) ◽  
pp. 2950-2959
Author(s):  
Hong Shen ◽  
Jun Hu ◽  
Zhenqiang Yao
Keyword(s):  
Finite Element ◽  
Three Dimensional ◽  
Shell Element ◽  
Element Model ◽  
Thermomechanical Analysis ◽  
Coupling Method ◽  
Computational Time ◽  
Laser Forming ◽  
Forming Process ◽  
Shell Elements

Efficient laser forming modeling for industrial application is still in the developing stage and many researchers are in the process of modifying it. Conventional three-dimensional finite element models are still expensive on computational time. In this paper, a finite element model adopting a shell-solid coupling technique is developed for the thermomechanical analysis of laser forming process. In the shell-solid coupling method, an additional shell element plane is utilized to transfer heat flux and displacement from the solid elements to the shell elements. The effects of the additional interface shell element thickness on temperature distribution and final distortion are investigated. The presented shell-solid coupling method is evaluated by the results of three-dimensional simulations and experimental data.

Subregion Analysis by the SBSF Method in Commercial Finite Element Software

1993 ◽  
Author(s):  
Charles E. Knight
Keyword(s):  
Finite Element ◽  
Complex Structure ◽  
Laminated Composite ◽  
Shell Element ◽  
Element Model ◽  
Interlaminar Stresses ◽  
Layered Shell ◽  
Shell Elements ◽  
Finite Element Software ◽  
Commercial Code

Abstract It is difficult to analyze a large, complex structure in sufficient detail to obtain accurate results everywhere. One approach to this problem is simply to refine the whole structure model in the regions of interest which is obviously costly. Another approach is to identify a subregion of the structure and develop a separate refined model of the subregion. The most recent method for subregion analysis presented in the literature[1] is called the Specified Boundary Stiffness and Force (SBSF) method. While the method is relatively straight forward and efficient, none of the commercial code vendors has yet included an implementation. This paper gives a brief review of the theory behind the method and then describes its application in two commercial finite element programs. Examples of the application of this method to the problem of a plate with a center hole in tensile loading are presented using ANSYS® and CAEDS(IDEAS)®. The results compare favorably to the theoretical value and show significant improvement in accuracy over the specified boundary displacement method implemented in ANSYS. The capability of the method is also demonstrated by transfer from a 2-D global model to a 3-D subregion model in a laminated composite plate. A laminated plate with a center hole is analyzed overall by use of a layered shell element model. A subregion around the hole is then analyzed using 3-D solid elements with nodal coupling to the layered shell elements on the subregion interface. The 3-D element model provides the well-known interlaminar stresses existing at the composite edge along the hole that are not available from the shell model.

Benchmark model updating for cable stayed bridges

2021 ◽  
Author(s):  
Minghui Lai ◽  
Haiying Ma ◽  
Pingkuan Sun ◽  
José Turmo
Keyword(s):  
Model Updating ◽  
Shell Element ◽  
Element Model ◽  
Mode Shapes ◽  
Model Parameters ◽  
Fe Model ◽  
Analysis Program ◽  
Shell Elements ◽  
Benchmark Model ◽  
Cable Stayed Bridges

<p>The use of benchmark model aims to establish a model with sufficient accuracy to reflect structure performance. Its purpose is seeking differences through repeated studying on problems using common FE model. In the paper, a novel approach is proposed for the benchmark model updating of a cable stayed bridge. It is based on the interaction of numerical analysis program and FE analysis program with updating model parameters from loop iteration operation. Shell elements and beam elements are both used, and the natural vibration frequencies and mode shapes from plate-shell element model are determined. These are used to modify the parameters used in a spine-beam element model, and to simplify a complicated FE model as a benchmark model. The genetic algorithm (GA) is introduced to complete the calculation process of loop iteration. Finally, an updated benchmark model is proposed for cable stayed bridges.</p>

scholarly journals An 8-Node Shell Element for Nonlinear Analysis of Shells Using the Refined Combination of Membrane and Shear Interpolation Functions

2013 ◽  
Vol 2013 ◽  
pp. 1-16 ◽  
Author(s):  
Woo-Young Jung ◽  
Sung-Cheon Han
Keyword(s):  
Finite Element ◽  
Shear Deformation Theory ◽  
Shell Element ◽  
Element Model ◽  
Shell Elements ◽  
Numerical Examples ◽  
Plates And Shells ◽  
Shell Finite Element ◽  
Assumed Natural Strain ◽  
Interpolation Functions

An improved 8-node shell finite element applicable for the geometrically linear and nonlinear analyses of plates and shells is presented. Based on previous first-order shear deformation theory, the finite element model is further improved by the combined use of assumed natural strains and different sets of collocation points for the interpolation of the different strain components. The influence of the shell element with various conditions such as locations, number of enhanced membranes, and shear interpolation is also identified. By using assumed natural strain method with proper interpolation functions, the present shell element generates neither membrane nor shear locking behavior even when full integration is used in the formulation. Furthermore, to characterize the efficiency of these modifications of the 8-node shell finite elements, numerical studies are carried out for the geometrically linear and non-linear analysis of plates and shells. In comparison to some other shell elements, numerical examples for the methodology indicate that the modified element described locking-free behavior and better performance. More specifically, the numerical examples of annular plate presented herein show good validity, efficiency, and accuracy to the developed nonlinear shell element.

scholarly journals Corrosion of Steel Rebars in Anoxic Environments. Part II: Pit Growth Rate and Mechanical Strength

Materials ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2547
Author(s):  
Elena Garcia ◽  
Julio Torres ◽  
Nuria Rebolledo ◽  
Raul Arrabal ◽  
Javier Sanchez
Keyword(s):  
Mechanical Strength ◽  
Chloride Content ◽  
Element Model ◽  
Offshore Structures ◽  
Anoxic Environments ◽  
Electrochemical Parameters ◽  
Cathode Area ◽  
Optical Profilometer ◽  
Set Up ◽  
Corrosion Of Steel

Reinforced concrete may corrode in anoxic environments such as offshore structures. Under such conditions the reinforcement fails to passivate completely, irrespective of chloride content, and the corrosion taking place locally induces the growth of discrete pits. This study characterised such pits and simulated their growth from experimentally determined electrochemical parameters. Pit morphology was assessed with an optical profilometer. A finite element model was developed to simulate pit growth based on electrochemical parameters for different cathode areas. The model was able to predict long-term pit growth by deformed geometry set up. Simulations showed that pit growth-related corrosion tends to maximise as cathode area declines, which lower the pitting factor. The mechanical strength developed by the passive and prestressed rebar throughout its service life was also estimated. Passive rebar strength may drop by nearly 20% over 100 years, whilst in the presence of cracking from the base of the pit steel strength may decline by over 40%.

Improved Bilinear Degenerated Shell Element

2015 ◽  
Vol 12 (02) ◽  
pp. 1550004 ◽  
Author(s):  
N. V. Swamy Naidu ◽  
B. Sateesh
Keyword(s):  
Shell Element ◽  
Shell Structures ◽  
Thin Plates ◽  
Element Formulation ◽  
Rigid Body Modes ◽  
Test Requirements ◽  
Degenerated Shell Element ◽  
Deformation Modes ◽  
Torsional Rotation ◽  
Transverse Shear Strains

The development of a new four node 24 degree of freedom bilinear degenerated shell element is presented for the analysis of shell structures. The present finite element formulation considers the assumed covariant transverse shear strains to avoid the shear locking problem and the assumed covariant membrane strains, which are separated from covariant in-plane strains, to overcome the membrane locking problem. The formulation also includes the deviation of the normal torsional rotation of the mid surface in the governing equation. This element is free from serious shear and membrane locking problems and undesirable spurious kinematic deformation modes. The element is tested for rigid body modes and distorted edges to meet the patch test requirements. The versatility and accuracy of this new degenerated shell element is demonstrated by solving several numerical examples for thick and thin plates.

A New Reinforcement Measure Suited for Space Truss with No-Fire Operation

2014 ◽  
Vol 919-921 ◽  
pp. 401-405
Author(s):  
Zuo Yun Mei ◽  
Chuan Qing Liu ◽  
Xing Mi ◽  
Ping Wu
Keyword(s):  
Element Model ◽  
High Yield ◽  
Nonlinear Analyses ◽  
High Yield Strength ◽  
Shell Elements ◽  
Gas Stations ◽  
Space Truss ◽  
Reinforcement Measure ◽  
Space Trusses ◽  
Elastic Stage

A new reinforcement measure with no-fire operation is presented, which is very suitable for space trusses which are located in gas stations. A finite element model (FEM) is presented with shell elements and multipoint constraint elements. With this FEM, nonlinear analyses are carried out. Analytical results show that integral failure of reinforced pipe is caused by yielding of original pipe inside. So it is not necessary to reinforce original pipe using steel pipe bonded outside with high yield strength. With the increase of length of bonded pipe outside, loading according to elastic stage and ultimate bearing loading increase, it is clear that the length of bonded pipe outside is an important factor which influences the bearing capacity.

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