Optimal Shape Design Under Elastic-Plastic Behavior Based on Reference Volume Method

2011 ◽  
Author(s):  
R. Adibi-Asl
Keyword(s):  
Elastic Modulus ◽  
Optimum Shape ◽  
Shape Design ◽  
Plastic Behavior ◽  
Element Analysis ◽  
Adjustment Procedure ◽  
Linear Elastic ◽  
Reference Volume ◽  
Overlap Joint ◽  
Volume Method

The main objective of this paper is to determine the regions in a component or structure that directly participate in inelastic action (reference volume) using a new robust simplified method, namely the Elastic Modulus Adjustment Procedure (EMAP). The proposed method is based on iterative linear elastic finite element analysis that is implemented by modifying the local elastic modulus of the material at each subsequent iteration. The application of reference volume on optimum shape design is demonstrated through some practical examples including thick-walled cylinder, shank-head component and overlap joint weld. The results show that the reference volume concept can be used to optimize the shape of a body with respect to load carrying capacity and fatigue strength.

Limit Load Analysis of Cracked Components Using the Reference Volume Method

2006 ◽  
Vol 129 (3) ◽  
pp. 391-399 ◽  
Author(s):  
R. Adibi-Asl ◽  
R. Seshadri
Keyword(s):  
Elastic Modulus ◽  
Three Dimensional ◽  
Local Limit ◽  
Limit Load ◽  
Multiple Cracks ◽  
Element Analysis ◽  
Limit Loads ◽  
Integrity Assessment ◽  
Reference Volume ◽  
Volume Method

Cracks and flaws occur in mechanical components and structures, and can lead to catastrophic failures. Therefore, integrity assessment of components with defects is carried out. This paper describes the Elastic Modulus Adjustment Procedures (EMAP) employed herein to determine the limit load of components with cracks or crack-like flaw. On the basis of linear elastic Finite Element Analysis (FEA), by specifying spatial variations in the elastic modulus, numerous sets of statically admissible and kinematically admissible distributions can be generated, to obtain lower and upper bounds limit loads. Due to the expected local plastic collapse, the reference volume concept is applied to identify the kinematically active and dead zones in the component. The Reference Volume Method is shown to yield a more accurate prediction of local limit loads. The limit load values are then compared with results obtained from inelastic FEA. The procedures are applied to a practical component with crack in order to verify their effectiveness in analyzing crack geometries. The analysis is then directed to geometries containing multiple cracks and three-dimensional defect in pressurized components.

Comparison of Elastic and Plastic Reference Volume Approaches

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
P. S. Reddy Gudimetla ◽  
Munaswamy Katna
Keyword(s):  
Limit Load ◽  
Nonlinear Finite Element ◽  
Empirical Methods ◽  
Element Analysis ◽  
Volume Correction ◽  
Adjustment Procedure ◽  
Reference Volume ◽  
Tangent Method ◽  
Proper Estimation ◽  
Volume Method

For finding out reliable limit load multipliers in pressure vessel components or structures using simplified limit load methods, proper estimation of reference volume is important. In this paper, two empirical methods namely elastic reference volume method (ERVM) and plastic reference volume method (PRVM) for reference volume correction are presented and compared. These reference volume correction concepts are used in combination with mα-tangent method and elastic modulus adjustment procedure to achieve converged limit load multiplier solution. These multipliers are compared with nonlinear finite element analysis results and are found to be lower bounded. Elastic reference volume method is the simplest method for reference volume correction when compared to plastic reference volume method.

Limit Load Analysis of Cracked Components Using the Reference Volume Method

2006 ◽  
Author(s):  
R. Adibi-Asl ◽  
R. Seshadri
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Elastic Modulus ◽  
Limit Load ◽  
Multiple Cracks ◽  
Element Analysis ◽  
Limit Loads ◽  
Integrity Assessment ◽  
Reference Volume ◽  
Volume Method

Cracks and flaws occur in mechanical components and structures, and can lead to catastrophic failures. Therefore, integrity assessment of components with defects is carried out. This paper describes the Elastic Modulus Adjustment Procedures (EMAP) employed herein to determine the limit load of components with cracks or crack-like flaw. On the basis of linear elastic Finite Element Analysis (FEA), by specifying spatial variations in the elastic modulus, numerous set of statically admissible and kinematically admissible distributions can be generated, to obtain lower and upper bounds limit loads. Due to the expected local plastic collapse, the reference volume concept is applied to identify the kinematically active and dead zones in the component. The Reference Volume Method is shown to yield a more accurate prediction of local limit loads. The limit load values are then compared with results obtained from inelastic finite element analysis. The procedures are applied to some practical components with cracks in order to verify their effectiveness in analyzing crack geometries. The analysis is then directed to geometries containing multiple cracks and three-dimensional defect in pressurized components.

Elastic Modulus Adjustment Improved Convergement Schemes Using Variable Local Constraints

2005 ◽  
Author(s):  
R. Adibi-Asl ◽  
Ihab F. Z. Fanous ◽  
R. Seshadri
Keyword(s):  
Finite Element Analysis ◽  
Elastic Modulus ◽  
Simple Procedure ◽  
Upper Bounds ◽  
Lower And Upper Bounds ◽  
Element Analysis ◽  
Local Constraints ◽  
Limit Loads ◽  
Linear Elastic ◽  
Degree Of Convergence

Elastic modulus adjustment procedures (EMAP) have been employed to determine limit loads of pressure components. On the basis of linear elastic Finite Element Analysis (FEA) with non-hardening elastic properties, i.e., by specifying spatial variations in the elastic modulus, numerous set of statically admissible and kinematically admissible distributions can be generated, and both lower and upper bounds on limit loads can be obtained. Some methods such as the classical, r-node and mα methods provide limit loads on the basis of partly-converged distributions, whereas the accuracy of linear matching procedures rely on fully converged distributions. In this paper, a criterion for establishing the degree of convergence of EMAP is developed, and a simple procedure for achieving improved convergence is described. The procedure is applied to some practical pressure component configurations.

Local Limit-Load Analysis Using the mβ Method

2006 ◽  
Vol 129 (2) ◽  
pp. 296-305 ◽  
Author(s):  
R. Adibi-Asl ◽  
R. Seshadri
Keyword(s):  
Lower Bound ◽  
Upper Bound ◽  
Local Limit ◽  
Limit Load ◽  
Element Analysis ◽  
Limit Loads ◽  
Linear Elastic ◽  
Reference Volume ◽  
Component Design ◽  
Load Analysis

Several upper-bound limit-load multipliers based on elastic modulus adjustment procedures converge to the lowest upper-bound value after several linear elastic iterations. However, pressure component design requires the use of lower-bound multipliers. Local limit loads are obtained in this paper by invoking the concept of “reference volume” in conjunction with the mβ multiplier method. The lower-bound limit loads obtained compare well to inelastic finite element analysis results for several pressure component configurations.

Comparison Study of Various Buckling and Ultimate Strength Assessment Methodologies for Stiffened Panels in Offshore Structures

2010 ◽  
Author(s):  
Xiaozhi Wang ◽  
Haihong Sun ◽  
Xiaohong Wang ◽  
Zhinong Wang ◽  
Anil Thayamballi
Keyword(s):  
Ultimate Strength ◽  
Offshore Structures ◽  
Design Analysis ◽  
Plastic Behavior ◽  
Comparison Study ◽  
Element Analysis ◽  
Strength Assessment ◽  
Stiffened Panels ◽  
Linear Elastic ◽  
Local Strength

Strength of offshore structures including FPSOs consists broadly of three aspects which are global intact and damaged strength, and local strength. Any of these strength aspects can be assessed by either prescriptive rule or finite element analysis (FEA). While many considerations relate to behavior in the linear elastic regime, the buckling and ultimate strength of both structural components (plate and stiffened panels) and structural systems can involve material and geometric nonlinearity behavior beyond the elastic region. With the development of computers and robust methods for nonlinear FEA, there has been a tremendous increase in the number of studies of structures under plastic or elasto-plastic behavior. However, even with today’s computers and software, nonlinear FEA of offshore structures remains complex and is not routinely applied in design analysis. Considerable effort therefore continues to be devoted to the development of simplified methods for rapid structural assessment and design analysis, instead of lengthy and complex nonlinear FEA. In this paper, various bucking and ultimate strength methodologies for plate and stiffener panels are first introduced. Each method is then compared with collected test data for buckling and ultimate strength of plate panels and stiffeners. Finally, conclusions are summarized based on the comparison study.

The Elastic Modulus Adjustment Procedure (EMAP) for Shakedown

2008 ◽  
Author(s):  
R. Adibi-Asl ◽  
W. Reinhardt
Keyword(s):  
Elastic Modulus ◽  
Elastic Moduli ◽  
Time History ◽  
Structure Model ◽  
Stress Distributions ◽  
Element Analysis ◽  
Shakedown Analysis ◽  
Adjustment Procedure ◽  
Linear Finite Element ◽  
History Analysis

A simple and systematic procedure is proposed for shakedown analysis using combination of linear and non-linear finite element analysis (FEA). The method can identify the boundary between the shakedown and ratcheting domains directly does not require a time history analysis (non-cyclic). The proposed method is based on elastic modulus adjustment procedure (EMAP) and non-cyclic elastic-plastic FEA. The aim of EMAP is to generate statically admissible stress distributions and kinematically admissible strain distributions. By modifying the local elastic moduli it is possible to obtain an inelastic-like stress redistribution. The method is first demonstrated with a two-bar structure model based on analytical routine. The analysis is then applied to some typical shakedown problems including the “classical Bree problem” and the “bi-material cylinder”.

Use of Limit Load Analysis for Design of Pressure Vessel Cover

2012 ◽  
Author(s):  
Rahul Jain
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Pressure Vessel ◽  
Limit Load ◽  
Plastic Limit ◽  
Element Analysis ◽  
Linear Elastic ◽  
Reference Volume ◽  
Plastic Limit Load ◽  
Load Analysis

This paper explores the use of limit load analysis methods for the design of a pressure vessel manway cover as per the ASME boiler and pressure vessel code guidelines. The results of elastic and limit load finite element analysis are discussed for the design. The concept of reference volume consideration along with linear elastic finite element analysis to determine the lower bound limit load has been explored and the results are compared with the non-linear elastic-plastic limit load analysis.

Reference Volume Consideration in the mα-Tangent Method Based Linear Elastic Analysis

2011 ◽  
Author(s):  
R. Adibi-Asl ◽  
M. M. Hossain ◽  
S. L. Mahmood ◽  
P. S. R. Gudimetla ◽  
R. Seshadri
Keyword(s):  
Finite Element ◽  
Rapid Determination ◽  
Limit Load ◽  
Elastic Analysis ◽  
Element Analysis ◽  
Limit Loads ◽  
Linear Elastic ◽  
Reference Volume ◽  
Tangent Method

Limit loads for pressure components are determined on the basis of a single linear elastic finite element analysis by invoking the concept of kinematically active (reference) volume in the context of the “mα-tangent” method. The resulting technique enables rapid determination of lower bound limit load for pressure components by eliminating the kinematically inactive volume. This method is applied to a number of practical components with different percentages of inactive volume. The results are compared with the corresponding inelastic finite element results, or available analytical solutions.

scholarly journals Influence of crown and hybrid abutment ceramic materials on the stress distribution of implant-supported prosthesis

2018 ◽  
Vol 47 (3) ◽  
pp. 149-154 ◽  
Author(s):  
João Paulo Mendes TRIBST ◽  
Amanda Maria de Oliveira DAL PIVA ◽  
Alexandre Luiz Souto BORGES ◽  
Marco Antonio BOTTINO
Keyword(s):  
Elastic Modulus ◽  
Stress Distribution ◽  
Ceramic Materials ◽  
Element Analysis ◽  
Linear Elastic ◽  
Crown Structure ◽  
Fixation Screw ◽  
Cad Cam ◽  
Ceramic Blocks ◽  
Hybrid Ceramic

Abstract Introduction A new dental implant-abutment design is available with the possibility of improving aesthetic with no compromise of mechanical strength, using perforated CAD/CAM ceramic blocks. Objective This study evaluated the influence of crown and hybrid abutment ceramic materials combination on the stress distribution of external hexagon implant supported prosthesis. Method Zirconia, lithium disilicate and hybrid ceramic were evaluated, totaling 9 combinations of crown and mesostructure materials. For finite element analysis, a monolithic crown cemented over a hybrid abutment (mesostructure + titanium base) was modeled and screwed onto an external hexagon implant. Models were then exported in STEP format to analysis software, and the materials were considered isotropic, linear, elastic and homogeneous. An oblique load (30°, 300N) was applied to the central fossa bottom and the system’s fixation occurred on the bone’s base. Result For crown structure, flexible materials concentrate less stress than rigid ones. In analyzing the hybrid abutment, it presented higher stress values when it was made with zirconia combined with a hybrid ceramic crown. The stress distribution was similar regarding all combinations for the fixation screw and implant. Conclusion For external hexagon implant, the higher elastic modulus of the ceramic crowns associated with lower elastic modulus of the hybrid abutment shows a better stress distribution on the set, suggesting a promising mechanical behavior.

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