scholarly journals Modeling and Verification of Creep Strain and Exhaustion in a Welded Steam Mixer

2009 ◽  
Vol 131 (6) ◽  
Author(s):  
Stefan Holmström ◽  
Juhani Rantala ◽  
Anssi Laukkanen ◽  
Kari Kolari ◽  
Heikki Keinänen ◽  
...  
Keyword(s):  
Creep Strain ◽  
Three Dimensional ◽  
Creep Damage ◽  
Tertiary Creep ◽  
Dimensional Structure ◽  
Rigid Plastic ◽  
Element Analysis ◽  
Filtering Technique ◽  
Long Term Behavior ◽  
Creep Regime

Structures operating in the creep regime will consume their creep life at a greater rate in locations where the stress state is aggravated by triaxiality constraints. Many structures, such as the welded steam mixer studied here, also have multiple material zones differing in microstructure and material properties. The three-dimensional structure as such, in addition to interacting material zones, is a great challenge for finite element analysis (FEA), even to accurately pinpoint the critical locations where damage will be found. The studied steam mixer, made of 10CrMo 9-10 steel (P22), has after 100,000 h of service developed severe creep damage in several saddle point positions adjacent to nozzle welds. FE-simulation of long term behavior of this structure has been performed taking developing triaxiality constraints, material zones, and primary to tertiary creep regimes into account. The creep strain rate formulation is based on the logistic creep strain prediction model implemented to ABAQUS, including primary, secondary, and tertiary creep. The results are presented using a filtering technique utilizing the formulation of rigid plastic deformation for describing and quantifying the developing “creep exhaustion.”

scholarly journals Modeling and Verification of Creep Strain and Exhaustion in a Welded Steam Mixer

2008 ◽  
Author(s):  
Stefan Holmstro¨m ◽  
Anssi Laukkanen ◽  
Juhani Rantala ◽  
Kari Kolari ◽  
Heikki Keina¨nen ◽  
...  
Keyword(s):  
Creep Strain ◽  
Creep Damage ◽  
Tertiary Creep ◽  
Dimensional Structure ◽  
Rigid Plastic ◽  
Element Analysis ◽  
3 Dimensional ◽  
Filtering Technique ◽  
Creep Regime

Structures operating in the creep regime will consume their creep life at a greater rate in locations where the stress state is aggravated by triaxiality constraints. Many structures, such as the welded steam mixer studied here, also have multiple material zones differing in microstructure and material properties. The 3-dimensional structure as such in addition to interacting material zones is a great challenge for finite element analysis (FEA), even to accurately pinpoint the critical locations where damage will be found. The studied steam mixer, made of 10CrMo 9-10 steel (P22), has after 100 000 hours of service developed severe creep damage in the several saddle point positions adjacent to nozzle welds. FE-simulation of long term behaviour of this structure has been performed taking developing triaxiality constraints, material zones and primary to tertiary creep regimes into account. The creep strain rate formulation is based on the logistic creep strain prediction (LCSP) model implemented to ABAQUS, including primary, secondary and tertiary creep. The results are presented using a filtering technique utilising the formulation of rigid plastic deformation for describing and quantifying the developing “creep exhaustion”.

Analyses of Full-Scale Tank Car Shell Impact Tests

2007 ◽  
Author(s):  
Y. H. Tang ◽  
H. Yu ◽  
J. E. Gordon ◽  
M. Priante ◽  
D. Y. Jeong ◽  
...  
Keyword(s):  
Finite Element ◽  
Test Data ◽  
Three Dimensional ◽  
Full Scale ◽  
Collision Dynamics ◽  
Dynamics Modeling ◽  
Dynamics Model ◽  
Rigid Plastic ◽  
Element Analysis ◽  
Closed Form Solutions

This paper describes analyses of a railroad tank car impacted at its side by a ram car with a rigid punch. This generalized collision, referred to as a shell impact, is examined using nonlinear (i.e., elastic-plastic) finite element analysis (FEA) and three-dimensional (3-D) collision dynamics modeling. Moreover, the analysis results are compared to full-scale test data to validate the models. Commercial software packages are used to carry out the nonlinear FEA (ABAQUS and LS-DYNA) and the 3-D collision dynamics analysis (ADAMS). Model results from the two finite element codes are compared to verify the analysis methodology. Results from static, nonlinear FEA are compared to closed-form solutions based on rigid-plastic collapse for additional verification of the analysis. Results from dynamic, nonlinear FEA are compared to data obtained from full-scale tests to validate the analysis. The collision dynamics model is calibrated using test data. While the nonlinear FEA requires high computational times, the collision dynamics model calculates gross behavior of the colliding cars in times that are several orders of magnitude less than the FEA models.

Auxetic deformation of the weft-knitted Miura-ori fold

2019 ◽  
Vol 90 (5-6) ◽  
pp. 617-630
Author(s):  
Kun Luan ◽  
Andre West ◽  
Emiel DenHartog ◽  
Marian McCord
Keyword(s):  
Deformation Mechanism ◽  
Poisson’S Ratio ◽  
Three Dimensional ◽  
Poisson's Ratio ◽  
Dimensional Structure ◽  
Damping Capacity ◽  
Analysis Model ◽  
Element Analysis ◽  
Specific Direction ◽  
Application Fields

Negative Poisson’s ratio (NPR) material with unique geometry is rare in nature and has an auxetic response under strain in a specific direction. With this unique property, this type of material is significantly promising in many specific application fields. The curling structure commonly exists in knitted products due to the unbalanced force inside a knit loop. Thus, knitted fabric is an ideal candidate to mimic natural NPR materials, since it possesses such an inherent curly configuration and the flexibility to design and process. In this work, a weft-knitted Miura-ori fold (WMF) fabric was produced that creates a self-folding three-dimensional structure with NPR performance. Also, a finite element analysis model was developed to simulate the structural auxetic response to understand the deformation mechanism of hierarchical thread-based auxetic fabrics. The simulated strain–force curves of four WMF fabrics quantitatively agree with our experimental results. The auxetic morphologies, Poisson’s ratio and damping capacity were discussed, revealing the deformation mechanism of the WMF fabrics. This study thus provides a fundamental framework for mechanical-stimulating textiles. The developed NPR knitted fabrics have a high potential to be employed in areas of tissue engineering, such as artificial blood vessels and artificial folding mucosa.

Modeling the Temperature-Dependence of Tertiary Creep Damage of a Directionally Solidified Ni-Base Superalloy

2009 ◽  
Author(s):  
Calvin M. Stewart ◽  
Erik A. Hogan ◽  
Ali P. Gordon
Keyword(s):  
Experimental Data ◽  
Gas Turbine ◽  
Creep Damage ◽  
Time Estimation ◽  
General Purpose ◽  
Tertiary Creep ◽  
Secondary Creep ◽  
Directionally Solidified ◽  
Estimation Model ◽  
Element Analysis

Directionally solidified (DS) Ni-base superalloys have become a commonly used material in gas turbine components. Controlled solidification during the material manufacturing process leads to a special alignment of the grain boundaries within the material. This alignment results in different material properties dependent on the orientation of the material. When used in gas turbine applications the direction of the first principle stress experienced by a component is aligned with the enhanced grain orientation leading to enhanced impact strength, high temperature creep and fatigue resistance, and improve corrosion resistance compared to off axis orientations. Of particular importance is the creep response of these DS materials. In the current study, the classical Kachanov-Rabotnov model for tertiary creep damage is implemented in a general-purpose finite element analysis (FEA) software. Creep deformation and rupture experiments are conducted on samples from a representative DS Ni-base superalloys tested at temperatures between 649 and 982°C and two orientations (longitudinally- and transversely-oriented). The secondary creep constants are analytically determined from available experimental data in literature. The simulated annealing optimization routine is utilized to determine the tertiary creep constants. Using regression analysis the creep constants are characterized for temperature and stress-dependence. A rupture time estimation model derived from the Kachanov-Rabotnov model is then parametrically exercised and compared with available experimental data.

scholarly journals On the Relationship between Creep Strain and Permeability of Granite: Experiment and Model Investigation

Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2859 ◽  
Author(s):  
Haiyang Yi ◽  
Hongwei Zhou ◽  
Rui Wang ◽  
Di Liu ◽  
Jingyang Ding
Keyword(s):  
Creep Strain ◽  
Three Dimensional ◽  
Creep Damage ◽  
Creep Model ◽  
Permeability Evolution ◽  
Experiment Data ◽  
Permeability Model ◽  
Design Work ◽  
High Level ◽  
The Relationship

Granite is regarded as a good option of host rock for high-level radioactive waste (HLW) repositories. Despite of its creep strain is small, the creep damage of which, especially that in the accelerated creep stage, increase its permeability significantly. To investigate the relationship between the creep strain and permeability evolution in granite, the present paper conducted a set of creep-seepage experiments associated with acoustic emission (AE) technology. The analysis in terms of the evolution of creep strain and permeability, characters of AE hits, mechanism of creep strain and that of permeability convince us that, the permeability evolution of granite is related to the volumetric dilation and microcracks connectivity. According to this relationship, a three-dimensional damage-based creep model was deduced from a one-dimensional fractal derivative-based model, and a permeability evolution model was proposed as well in this paper. The experiment data suggest nonnegligible influence of creep damage on the permeability of granite, therefore this influence should be taken into consideration of the design work of HLW repositories. The calculated results of the proposed models match well the experiment data, suggesting good capability of the models in approaching the creep and hydraulic performance of granite. In addition, the permeability model is friendly in parameter identification due to its simple mathematic formulation.

The Influence of Creep Strain Rate on Creep Damage Formation in Austenitic Stainless Steel

2018 ◽  
Author(s):  
Edward Hares ◽  
Mahmoud Mostafavi ◽  
Richard Bradford ◽  
Chris Truman
Keyword(s):  
Stainless Steel ◽  
Stress Relaxation ◽  
Creep Strain ◽  
Stress Triaxiality ◽  
Creep Damage ◽  
Operating Conditions ◽  
Element Analysis ◽  
Creep Ductility ◽  
User Subroutine ◽  
Lower Test

Motivated by the need to more accurately account for real, in-service, operating conditions, this paper aims to investigate whether creep strain accumulated at different strain rates is equally damaging. Previous research has suggested that creep strain is more damaging when accumulated more slowly in creep of notched bars. The research presented here seeks to address this question by considering the accumulation of creep strain during stress relaxation of notched bars. Repeat stress relaxation tests with varying dwell lengths were conducted so that the relative damaging effects of the early, rapid accumulation and later, slow accumulation of creep strains could be compared. Another aim was to determine how a lower test temperature affects this creep strain accumulation. In repeat relaxation tests the load is reestablished repeatedly after relaxation dwells of equal duration, until rupture of the specimen occurs. The material used was an ex-service powerplant stainless steel Type 316H. Notched bar specimens were used to introduce stress triaxiality at the notch tip to imitate the multiaxial loads plant components are subjected to during in-service operation. The stresses and strains in the specimens were then assessed using finite element analysis; a user subroutine was implemented so the onset and propagation of creep damage could be simulated throughout the specimens’ creep life. The research found that the material in question had a lower creep ductility at 515°C than at 550°C. The research also showed that creep strain accumulated rapidly at the start of a dwell is significantly less damaging than creep strain accumulated more slowly towards the end of the dwell.

Optimization of anvil design for ensuring dimensional precision of forged round billet without forging defects by three-dimensional rigid-plastic finite element analysis

2005 ◽  
Vol 219 (5) ◽  
pp. 461-475 ◽  
Author(s):  
K Tamura ◽  
M Akiyama ◽  
J Tajima
Keyword(s):  
Finite Element ◽  
Three Dimensional ◽  
Work Piece ◽  
Finite Element Analyses ◽  
Rigid Plastic ◽  
Element Analysis ◽  
Round Billet ◽  
Dimensional Precision ◽  
Number Of Passes ◽  
Final Round

Focusing upon finding an optimum anvil design of the spiral forging stage for manufacturing a round billet to good dimensional precision directly from an octagonal work-piece without forging defects, three-dimensional rigid-plastic finite element analyses have been carried out. By analysis and laboratory experiment, the mechanism through which overlapping defects are caused in spiral forging has been quantitatively clarified and a new parameter to predict overlapping defect generation proposed. By making use of the parameter, an anvil design of the entrance side has been proposed to prevent overlapping defects. Moreover, the whole geometry of the anvil has been optimized in order to ensure dimensional precision of the final round billet. As a result, a fundamental scheme to optimize anvil design for manufacturing a round billet directly from an octagonal workpiece has been established and the total number of passes was successfully reduced in the production line.

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