Small Debris Impact Simulation with MSC.Dytran Part II

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Small Debris Impact Simulation with MSC.Dytran
Part II

• Klaus O. Schwarzmeier,
• Carlos E. Chaves, Franco Olmi
• Embraer S/A
• André de Jesus, Eduardo Araújo, Paul Buis
• MSC.Software Corporation

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Presentation Contents

• Introduction
• Background
• Strain Rate
• Sphere Flexibility
• Failure Model
• Plate x Solid Model
• General Conclusions

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Introduction

• Embraer Empresa Brasileira de Aeronáutica S.A.
  
• It is one of the worlds leading designer and
  manufacturer of aircraft for regional
  airlines,defense and corporate use
• Founded in 1969
• Based in São José dos Campos, 50 miles from São
  Paulo - Brazil
• Plant area 2.51 million sq.ft
• More than 5,300 aircraft producedand sold in
  over 30 years

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Introduction

• Embraer Empresa Brasileira de Aeronáutica S.A.

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Background

• Previous work (MSC Aerospace 1999)

• Steel spheres impacting Al-2024-T3 panels with
  1.6 and 3.2 mm thickness

• Experimental results compared with numerical
  results from dynamic analysis with MSC.Dytran

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Background

• MSC.Dytran Models Characteristics

• Lagrangian shell elements (CQUAD4)
• Impacting sphere initially simulated as a rigid
  ellipsoid.
• Constitutive model Johnson-Cook (YLDJC)

• Failure model element maximum plastic strain
  failure (FAILMPS)

• Material properties obtained from MSC.Mvision
  database
• Previous analysis all parameters in the
  Johnson-Cook relation as well as the value of
  FAILMPS assumed as constants

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Background

• Discrepancy between
• analytical and
• experimental results
• (sphere velocities)
• from the previous work
• is shown in the figure

• This work Influence of parameters used as input
  for the constitutive equation and failure model,
  as well as the modeling characteristics, will be
  addressed
• Parameters assumed as material constants in the
  previous work (regardless of the dynamic
  condition) will be analyzed in detail

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Strain Rate

• Assuming that actual material stress-strain
  behavior could differ significantly from the data
  available, a sensitivity analysis for the strain
  rate parameter C was carried out

• Results for 1.6 mm thickness plate shown in the
  figure
• Value of C available in the MSC.Mvision database
  is 0.015

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Strain Rate

• In order to have close agreement with the
  experimental results for the range of velocities
  analysed, C value of must change more than one
  order
• Conversely, small changes in C will imply in
  small changes in the final velocity
• CONCLUSION strain rate parameter does not exert
  a major influence in analysis results

Sphere Flexibility

• Influence of the sphere flexibility and friction
  between sphere and plate considered
• Small reduction in the final velocity due to
  friction observed
• This trend seems to be correct only when initial
  velocities are smaller

CONCLUSION sphere flexibility and friction
between sphere and plate do not explain the
discrepancies between analytical and experimental
results
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Failure Model

• Present results showed that the failure
  parameter (FAILMPS) plays a key role in
  numerical analysis
• Starting with FAILMPS 0.18 (static result for
  Al 2024-T3), a series of analyses with varying
  values for this parameter were carried out
• Results of these analyses for both plates shown
  in figures below

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Failure Model

• CONCLUSIONS
• 1. Value of FAILMPS
• Previous work FAILMPS assumed as fixed and
  equals to 0.18
• FAILMPS may change significantly, according to
  the impact velocity and plate thickness
  (geometry)
• This work failure index changes, and can be
  significantly higher than the one obtained from
  static tests
• MSC.Mvision database failure index FAILMPS
  0.5 supplied for Al 2024-T3
• This may correspond to some specific dynamic
  condition, but will not necessarily cover the
  impact conditions evaluated in this work

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Failure Model

• CONCLUSIONS (cont.)
• 2. Stress Triaxiality
• Sphere penetrating in a plate stress state is
  clearly bi-axial
• It is apparent that a failure parameter based on
  the effective plastic strain may not be suitable
  for the dynamic conditions analyzed
• Desirable to find a correlation between some
  triaxiality parameter and the strain rate, such
  that a more adequate failure model can be
  implemented (for example, by means of an external
  subroutine in MSC.Dytran)
• 3. Failure Modes
• According to the plate thickness, two distinct
  failure modes observed
• These failure mechanisms are associated to the
  triaxial strain state due to plate thickness, and
  can be interpreted only by means of a more
  appropriate failure criterion

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Failure Model

• LEFT impact energy 750 J, thickness 1.6 mm
• bulge formation and tearing (petaling)
• RIGHT impact energy 1500 J, thickness 3.2
  mm
• precipitated plug formation, followed by a plug
  removal

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Solid x Plate Model

• Possibility to run the analysis with solid
  elements also investigated.
• CHEXA elements along the thickness direction.
• Plate with thickness 1.6 mm modeled with 12
  layers
• Plate with thickness 3.2 mm modeled with 24
  layers
• Material properties same as in the previous
  work, C0.015, FAILMPS 0.18

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Solid x Plate Model

• In general, plots show decrease in final
  velocity for model with solid elements,
  expressing some ability of solid elements to
  absorb energy during the impact (or to take into
  account the strain variations along the plate
  thickness direction)
• This trend is opposite to the experimental
  results for the 3.2 mm thickness plate
• CONCLUSION solid elements do not to reproduce
  appropriately experimental results when compared
  to the shell elements
• Computational effort in a NT workstation with
  512 Mb of RAM memory and one processor, models
  with shell elements typically run in about 20
  minutes, while models with solid elements last
  about 20 hours
• Obviously 2D model is much more economic and
  should always be used when there are time or CPU
  constraints

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General Conclusions

• PRESENT STUDY brings some important concepts
  that were not taken into account previously
• Influence of the parameters of material
  constitutive equation is not relevant when
  compared to the failure index (FAILMPS)
• Sphere flexibility and friction also do not
  imply in significant losses of energy
• Failure index (FAILMPS) can change considerably
  according to strain rate, and values higher than
  the one obtained by static tests can be
  considered
• Failure mechanism quite complex, and a
  parameter based on an equivalent plastic strain
  will not describe this mechanism completely.
  There are also stress triaxiality issues that
  must be considered. The complete understanding of
  this parameter requires further studies
• Solid elements do not result in a major
  improvement in the analysis results, but imply
  in a significant increase in the CPU time for the
  analysis