Presentation documenting tests performed to demonstrate shape and load measurement using fiber optic strain sensors (FOSS

Bakalyar, John A.

NASA Technical Reports Server

NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  
Fiber-­‐Op)c	  Strain	  Sensing	  	  (FOSS)	  
Shape	  and	  Load	  Measurement	  
Demonstra2on	  Tests	  
John	  Bakalyar	  
NASA	  DFRC	  –	  Aerostructures	  (RS)	  Branch	  	  
9	  May	  2011	  
https://ntrs.nasa.gov/search.jsp?R=20110014495 2019-08-30T16:28:28+00:00Z
NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  
Technology	  Overview	  
•  Fiber-­‐op)c	  strain	  sensing	  (FOSS)	  allows	  nearly	  con)nuous	  strain	  
measurements	  
–  Measurements	  every	  half	  inch	  
–  Hundreds	  of	  measurements	  per	  channel	  
–  Flight-­‐capable	  system	  
•  FOSS	  oﬀers	  several	  notable	  advantages	  to	  foil	  strain	  gages:	  
–  Lightweight	  sensor	  package	  (no	  copper	  leadwires)	  
–  Immune	  to	  EMI/radio-­‐frequency	  interference	  and	  radia)on	  
–  Fibers	  can	  be	  embedded	  within	  a	  composite	  part	  
•  Strain	  values	  can	  be	  used	  to	  calculate	  structural	  deﬂec)ons	  and	  loads*	  
–  Based	  on	  classical	  beam	  and	  basic	  bending	  equa)ons	  	  
–  Structure	  discre)zed	  into	  many	  span-­‐wise	  analysis	  sta)on	  
*PATENT	  NOTICE	  
The	  structural	  shape	  and	  load	  predic)on	  methods	  described	  in	  this	  technical	  paper	  (or	  presenta)on)	  are	  protected	  under	  U.	  
S.	  Patent	  No.	  7,520,176,	  issued	  April	  21,	  2009,	  and	  U.	  S.	  Patent	  No.	  7,715,994,	  issued	  May	  11,	  2010.	  
Therefore	  those	  interested	  in	  using	  the	  method	  should	  contact	  the	  NASA	  Innova)ve	  Partnership	  Program	  Oﬃce	  at	  NASA	  
Dryden	  Flight	  Research	  Center	  for	  more	  informa)on.	  	  
NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  
Technology	  Progression	  
•  Deﬂec)on	  and	  load	  equa)ons	  had	  been	  analy)cally	  veriﬁed	  
–  Ques)ons	  remained	  about	  prac)cal	  implementa)on	  
•  The	  capability	  is	  desired	  in	  order	  to	  improve	  aircrac	  design	  
–  Real-­‐)me	  shape	  and	  load	  measurement	  during	  ﬂight	  enable:	  
•  Eﬃcient,	  lightweight	  design	  
•  Maneuver/gust	  load	  allevia)on	  
•  Structural	  feedback	  to	  control	  system	  
•  Structural	  health	  monitoring	  and	  damage	  detec)on	  
–  Upcoming	  opportunity	  to	  test	  the	  technology	  on	  NASA	  F/A-­‐18	  
–  Beneﬁts	  across	  speed	  regimes	  
Theory	   Flying	  Laboratory	  Valida2on	  
Enabling	  New	  Designs	  
NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  
Test	  Setup	  
•  4	  Interchangeable	  Test	  Ar)cles	  
–  Planform	  shapes	  of	  wings	  
–  Aluminum	  plate	  (.190”	  thick)	  
Rectangular	  Plate	  Test	  Ar)cle	  
Tapered	  Plate	  Test	  Ar)cle	  
Swept	  Plate	  Test	  Ar)cle	  
Open	  Plate	  Test	  Ar)cle	  
NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  
Summary	  of	  Tests	  
•  Mul)ple	  load	  cases	  applied	  to	  
each	  test	  ar)cle	  
–  Uniform	  loading	  
–  Tip-­‐	  and	  root-­‐biased	  loading	  
–  Leading	  and	  trailing	  edge	  loading	  
–  Single-­‐point	  loading	  
•  Data	  
–  FOSS	  (ﬁber	  op)c	  strain	  sensor)	  
•  input	  to	  equa)ons	  
–  Conven)onal	  strain	  gages	  
–  Photogrammetry	  
•  Displacement	  to	  verify	  results	  
–  Load	  	  
•  calibrated	  weights	  
NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  
Deﬂec)on	  Calcula)on	  
NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  
Determina)on	  of	  Wing	  Deﬂec)on	  
Deﬂec2on	  of	  a	  Single	  Fiber:	  	  
Slope:	  Typically the first 
station is at the root: 
NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  
Deﬂec)on	  Results	  
Swept	  Plate	  Test	  Ar)cle	   Tapered	  Plate	  Test	  Ar)cle	  
NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  
Uniform	  Load	  Case	  Results	  
1.9%	  (.
138”)	  
• 	  	  1800	  microstrain	  at	  root	  
Swept	  Plate	  Test	  Ar)cle	  
Span	  (in)	  
D
eﬂ
ec
)o
n	  
(in
)	  
0.6%	  (.
040”)	  
Span	  (in)	  
D
eﬂ
ec
)o
n	  
(in
)	  
Tapered	  Plate	  Test	  Ar)cle	  
• 	  	  1620	  microstrain	  at	  root	  
•  Equal	  load	  applied	  to	  each	  of	  12	  load	  points	  
•  Deﬂec)on	  measured	  along	  middle	  ﬁber	  
NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  
Trailing	  Edge	  Load	  Case	  Results	  
• 	  	  1880	  microstrain	  at	  root	  
Swept	  Plate	  Test	  Ar)cle	  
Span	  (in)	  
D
eﬂ
ec
)o
n	  
(in
)	  
Span	  (in)	  
D
eﬂ
ec
)o
n	  
(in
)	  
Tapered	  Plate	  Test	  Ar)cle	  
• 	  	  1650	  microstrain	  at	  root	  
•  Load	  applied	  to	  points	  along	  trailing	  edge	  
•  Deﬂec)on	  measured	  along	  middle	  ﬁber	  
0.2%	  (.
013”)	  
0.7%	  (.
042”)	  
NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  
Angle	  of	  Twist	  
•  Angle	  measurement	  requires	  diﬀerence	  between	  two	  similar	  
deﬂec)on	  values	  
–  Small	  error	  in	  deﬂec)ons	  equates	  to	  large	  error	  in	  angle	  of	  twist	  
•  Tapered	  Plate	  
–  Leading	  Edge:	  	  
•  Calculated:	  2.78	  degrees	  
•  Photogrammetry:	  1.43	  degrees	  
–  Uniform:	  
•  Calculated:	  1.63	  degrees	  
•  Photogrammetry:	  0.25	  degrees	  
NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  
Load	  Calcula)on	  
NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  
Load	  Calcula)on	  Process	  
•  Bending	  moment	  calculated	  at	  each	  analysis	  sta)on	  
•  Cross-­‐sec)onal	  proper)es	  calculated	  by	  applying	  known	  load	  
–  EI/c	  term	  backed	  out	  at	  each	  evalua)on	  sta)on	  
•  With	  proper)es	  known,	  strain	  can	  be	  directly	  related	  to	  
bending	  moment	  
  Get properties at 
each station  
Calculate moment  
at each station 
Known moment 
Unknown moment 
NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  
Swept	  Plate	  Load	  Results	  
NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  
Swept	  Plate	  Load	  
Cross-­‐sec)onal	  proper)es	  calculated	  using	  ‘Uniform	  A’	  load	  case	  
Uniform	  B	  Load	  Case	   Single	  Point	  Load	  Case	  
NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  
Swept	  Plate	  Load	  (cont.)	  
Cross-­‐sec)onal	  proper)es	  calculated	  using	  ‘Uniform	  A’	  load	  case	  
Tip-­‐Biased	  Load	  Case	   Leading	  Edge	  Load	  Case	  
NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  
Shape	  and	  Load	  Calcula)on	  Conclusions	  
•  Deﬂec)on	  calcula)ons	  are	  accurate	  	  (within	  ~5%)	  
–  Diﬀerent	  test	  ar)cles	  
–  Diﬀerent	  load	  cases	  
–  Diﬀerent	  load	  magnitudes	  
•  Load	  results	  will	  be	  improved	  
–  Least-­‐squares	  method	  
•  Developing	  methods	  to	  further	  use	  FOSS	  measurements	  
–  Angle-­‐of-­‐twist	  	  
–  Improved	  deﬂec)on	  and	  load	  
–  Torque	  
NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  
Shape	  Measurement	  –	  Future	  Tes)ng	  
•  Working	  to	  create	  new	  method	  for	  determining	  wing	  twist	  
–  New	  ﬁber	  rou)ng	  being	  explored	  
–  Measure	  en)re	  strain	  state	  (εxx,	  εyy,	  and	  γxy)	  
–  Map/spline	  strain	  components	  to	  get	  strain	  ﬁelds	  over	  test	  ar)cle	  
–  Integrate	  to	  determine	  deﬂec)ons	  
∫∫	  
NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  
Future	  Tes)ng	  (con)nued)	  
•  Fiber	  rou)ng	  ground	  tests	  
–  Will	  test	  new	  ﬁber	  rou)ng	  methods	  
–  Aimed	  at	  twist	  measurement	  and	  more	  accurate	  deﬂec)on	  
–  More	  complex	  load	  cases	  
•  NASA	  F/A-­‐18	  N853	  
–  Fiber	  will	  be	  installed	  on	  wings	  
–  Ground	  tests	  will	  be	  performed	  
–  FOSS	  data	  will	  be	  sent	  through	  control	  system	  and	  telemetered	  	  
•  Mul)-­‐U)lity	  Technology	  Testbed	  (MUTT)	  	  
–  Unique	  opportunity	  to	  use	  system	  
•  Ground	  tests	  
•  Flight	  tests	  
–  Very	  ﬂexible	  wings	  
–  Versa)le	  ﬂight	  control	  system	  
NASA	  DRYDEN	  FLIGHT	  RESEARCH	  CENTER	  


Fiber-Optic Strain Sensing (FOSS): Shape and Load Measurement Demonstration Tests

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