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					 A Damage-Mechanics Based
Approach to Structural Design
    of ITER Components
      S. Sharafat1, N. Ghoniem1,
      R. Odette2, and E. Diegele3
            1UCLA, 2UCSB, 3FZK




          US-ITER TBM Meeting
                 UCLA
             Nov. 3-5, 2003
              OUTLINE

1. Integrated Dynamic Fusion Material
   Property Digital Data-base

2. Structural Design Approach for Novel
   Components

3. VISTA: Virtual International Structural
          Test Assembly
Integrated Fusion Material
    Digital Data-Base
    WEB-DATABASE for Accelerated Materials Design
              Interactive Web Data Base
                                              THEORY &                ACCELERATED
   DATA          CORRELATIONS               SIMULATION &               DESIGN OF
                                            EXPERIMENTS
                                                                       MATERIALS


                                          III. DESIGN
                                                a. Constitutive Eq.
                                                b. Damage Function
                                                c. FEM

          II. MODELS:
                 a. Parameterization of attributes,
                 b. Piece-wise polynomial fits, and
                 c. Physical description.



I. MATERIAL PROPERTIES
     a. material data,
     b. process information,
     c. statistical
        parameters.                  WEB-Digital Database
Material Data Base for Accelerated Materials Design

                   Al-Foam: Example of Accelerated Materials Design
                         Interactive Web Data Base
                                                         THEORY &               ACCELERATED
        DATA                CORRELATIONS               SIMULATION &              DESIGN OF
                                                       EXPERIMENTS
                                                                                 MATERIALS




 KNOWN:                    KNOWN:                FEM to Determine Effects:
 •   Thermal k             •   Rule of mixture   •    Bubble density         Identify Process Parameters
 •   Bubble Density            k(P)              •    Size distribution            to optimize
 •   Size Distribution                           •    Statistical process    •     Thermal k, vs.
 •   Process (blowing)                                variations             •     Young’s Modulus


                                                                                              Modify Bubble
                                                                                                    Blowing
                                                                                                    Process




         Al-Foam solid model:
               - Bubble size r = 1 – 5 um
               - Gaussian Distribution
               - 5% Porosity
                      APPROACH
   Use Relational Database Management Systems (RDBMS) combined
    with the Internet to develop a database backed Web site.


   Develop a DYNAMIC Web site to eliminate the cost of updating and
    archiving STATIC pages.


   Provide features for Content and Collaboration Management (CCM) by
    the Fusion Materials Community:
          Community members upload data onto the web site instead of a
           centralized web meister




The Dynamic RDBMS backed Web site is functional (testing phase)
Fusion Materials Digital Database Web-Site:
                                                3. Mouse Rollover Shows
                                                Data Point Value




1. Choose                                                          5. View Author’s
Material                                                           Comments




                                      4. Retrieve
                                      PDF File
                                                                          2. Select
                                                                          Property
Structural Design Approach for
      Novel Components
  Structural Design Objectives
• The objective of every structural design is to
  develop a structure that is able to perform its
  functions while meeting the constraints of safety
  and cost.

• An important element in this process is the
  specification of maximum permissible failure
  modes that are relevant to the structure.

• Structure reliability (complement of the maximum
  permissible failure) depends foremost on the
  consequence of the type of failure.
Structure Failure Consequences
               Inconvenience   Interference   Suspension of   Loss of Mission,   Total Loss of
                                   with         Operation      Compromise          Structure
   Level of                     Operation                        Structural
 Consequence                                                      Integrity



   MINOR


 MODERATE


  SERIOUS


  CRITICAL


CATASTROPHIC
          Structure Reliability
• Reliability-based design criteria are usually
  “calibrated” to existing structures (of the same
  class) having a history of successful service.

• However, novel ITER structures clearly exceed
  the scope of existing design standards 
  “calibration exercise” is not feasible.

• Structure reliabilities need to be derived from
  more fundamental considerations.
   Derivation of                                Define System
 Target Reliability                             Define performance requirements
                                                Identify failure modes

for ITER Structure

Develop / Include:            Identify system failure                Identify structural categories
                               consequences                           Define limit states
“Damage Functions”

              Analytical/FEM
              Existing
               structure codes
               (IISDC*)                Select component             Identify intermediate
              Scientific               reliability                   failure consequences

               considerations
              Engineering
               judgment

                                                          Derive sub-system
                                                           and component
*ITER Interim Structural Design Criteria                   reliabilities in each
                                                           relevant limit state
                                                                              after Bhattacharya B., et al.
VISTA: Virtual International
 Structural Test Assembly
  VISTA: Virtual International Structural Test
                   Assembly

• VISTA is an International Project currently including EU and
  the US:
    – UCLA, UCSB, FZK, ANL, …

• Goal:
    – Provide a methodology and physical basis to evaluate failure paths
      to establish structural integrity assessment methods.
        • Include 3-D geometric realization
        • Include interaction of different sources of loading and damage.

• Approach:
    – Combine wide range of models including:
        •   Constitutive and damage laws,
        •   Finite Element models,
        •   Geometrical configurations and
        •   Loading conditions.

• Perform “virtual experiments” over a wide range of conditions, to
  evaluate a range of potential interactions and failure paths.
VISTA: Virtual International Structural Test
                 Assembly

• VISTA is based on a general Damage Mechanics
  methodology for identifying primary limit states of
  structures.

• VISTA accounts for large scale 3-D geometric effects
  by FE-modeling of the entire 3-D radial-toroidal
  Reactor Sector

• VISTA aims at identifying, both tangible and intangible
  damage pathways
          VISTA: Hierarchical Approach
1. Hierarchical FEM:
        Full Geometry
         3-D Models              Boundary
                               Conditions for     2-D Fracture
                                2-D Models      and Plastic Flow
                                                  Localization


3-D Concept:



                 3-D FW/B Detail



                                                          2D Detailed
                                                          Failure
                                                          Analysis:
                                                          Fracture and
                                                          Plastic Flow
        VISTA: Hierarchical Approach
2. Hierarchical Material Models:
    – Constitutive laws of plasticity, visco-plasticity, creep, swelling or other
      subcategories are based on Multi-Scale integration of materials theory,
        models, simulations and experiment.

                                           Particle Mechanics:
                                                 overall properties
                                                 s = f(e,t)
 Model:
                                                 k = f(t), etc.
     creep
     swelling
     deformation
     sintering, etc.                                                                 FEM:
                                                                             3-D Geometric
                       MULT-ISCALE      MODELING                                   Effects




3. Hierarchical FEM :
         – VISTA plans to represent the hierarchical multi-physics involving the
           interactions of thermo-hydraulics, thermal, electro-magnetic, thermo-
           mechanical, and structural aspects of the function of a component structure.
               Importance of
             Damage Mechanics

Between 1985 and 1995 a total of 32 Containment pressure
 boundary degradations were reported (Naus et al., 1996)

• Corrosion resulted in 50% loss of local thickness in 18 NPPs*.

• Other effects leading to structural deterioration included:
          – Fatigue, including crack initiation and propagation to fracture
          – Elevated temperature creep
          – Irradiation effects.

• Physics of these damage processes are reasonably understood.



                                                            *NPP: Nuclear Power Plant
 Continuum Damage Mechanics

• Continuum damage mechanics (CDM)* relates the effects
  of microstructural defects (voids, discontinuities,
  inhomogeneities) to measured macroscopic quantities
  (stiffness, Poisson's ratio, etc.)

• Essential CDM assumption:
      • Damage growth is a volume-wide degradation of microstructure

• CDM is useful in modeling accumulation of damage in a
  material PRIOR to formation of a detectable defect

• With the formation of a macroscopic defect, the essential
  CDM assumption breaks down.  DAMAGE MECHANICS

                    *Lemaitre J., “How to use damage mechanics,” Nucl. Engr. & Des. 80(1984)233-245
              VISTA: Damage Mechanics
DAMAGE MECHANICS:

    Typical Thermo-
       Mechanical                 Irradiation Effects:
         Effects:                     Synergistic Effects                 FEM – Based
  • Ductile                           of Microstructure                  Structural Aging
    deformation                       Changes and                             Model:
  • Creep damage                      Loads
  • Fatigue damage



• Use Mechanistic Models (“Damage Functions”) of structural deterioration
  for time-dependent structural analysis of:
          –   Ductile deformation damage as a function of plastic strain (uniaxial)
          –   Creep damage as a function of time
          –   Fatigue damage as a function of number of cycles
          –   Irradiation damage as a function of time

• Take into account loading and strength uncertainties
                                                                       *NPP: Nuclear Power Plant
VISTA Damage-Mechanics Approach

 I. Damage Mechanics:
 • Develop “damage-functions” for
             (i) ductile deformation,
             (ii) creep,
             (iii) fatigue,
             (iv) irradiation effects, based on damage mechanics
 • Develop a FEM- based Structural Aging Model using these
   “damage functions.”

 II. Large-Scale 3-D Geometric Features:
 • Develop entire FULL 3-Dimensional FW/Blanket segment
 • Include support structure, ducts, and sub-component interfaces
Example of a Needed Analysis of a HCPBB
 A comprehensive thermo-mechanical FEM analysis of a Helium-Cooled
   Pebble Bed Blanket at steady state operation would include:

      – Solid modeling of the entire 3-D radial–toroidal TBM box including the TBM-
        housing, ITER support structure, etc.

      – Thermal stresses caused by the temperature gradients in the TBM and TBM
        support structure (both radial and toroidal T-variations)

      – Mechanical loads due to coolant pressure in normal operating conditions

      – Mechanical loads due to TBM component gravitational loads

      – Mechanical loads due to accidental over-pressurization of the TBM box

      – Stresses caused by a central plasma disruption (I=20 MA0 in 20 ms)

      – Radiation-induced dimensional changes of breeder and multiplier (He and
        neutron damage (damage-functions).
VISTA: Example of Damage Model for Pebble-
         Bed/Structure Interaction
 Developing Damage-Model for Modeling Interaction between Breeder Pebble
   Bed and Structure:

          – The interface shear tests of soil-structure shows that the failure of a rough soil–
            structure interface is accompanied with strong strain-softening and normal
            dilatancy during shearing*.

          – A damage model needs to be developed to characterize such behavior of a rough
            interface with nine parameters.

          – The DAMAGE-MODEL (relation matrix between stress and strain increments in
            the interface) has to be derived and the damage model has to be incorporated into
            a FEM program.

          – Such a damage model should capture the interface behavior, such as hardening,
            softening, and shear dilatancy.




*Liming Hu and Jia Liu Pu, “Application of damage model for soil–structure interface,” Computers and Geotechnics 30 (2003)
165–183
                 SUMMARY
• First Phase of an Internet-Based Dynamic Fusion
  Material Digital Database is nearing completion.

• Structural Design Reliability of Novel Components
  need to be derived from fundamental
  considerations based on Damage-Mechanics.

• VISTA: a Damage-Mechanics based full-scale 3-D
  geometric FEM approach is under development to
  identify component failure pathways.
                          References:

Bhattacharya B., et al., “Developing target reliability for novel structures: the case of the
Mobile Offshore Base,” Marine Structures 14(2001)


Allen DE., “Criteria for design safety factors and quality assurance expenditure.”
Proceedings of the Third International Conference on Structural Safety and Reliability,
Trondheim, Norway, 1981. p. 667-78.


Lemaitre J., “How to use damage mechanics,” Nucl. Engr. & Des. 80(1984)233-245

Naus, D. J., et al., “Aging of the containment pressure boundary in light water reactor
plants,” Proc. Water Reactor Safety Information Meeting, Rockville, MD, October 1996.


Liming Hu and Jia Liu Pu, “Application of damage model for soil–structure interface,”
Computers and Geotechnics 30 (2003) 165–183

				
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