DEVELOPMENT  OF  AN  INTELLIGENT  HEADREST  USING  

SMART  MATERIALS  

Ajmal  Abdu  Salam  M.Sc.  Mechanical  Engineering  with  Industrial  Management  

 Supervisor:    

Dr.  Olga  Ganilova  

AIMS  AND  OBJECTIVES  

•  To  inves;gate  the  problem  of  whiplash  and  the  latest  achievements  in  the  field  

•  To  study  the  area  of  smart  materials  •  To  develop  a  novel  design  for  an  intelligent  headrest  applying  smart  materials  

•  Evolvement  of  an  analy;cal  model  of  the  smart  headrest  

© The University of Sheffield

Whiplash  Injuries  in  an  Accident  

•  Whiplash  injury  results  from  an  rear  end  accident  in  which  the  driver  is  in  a  sta;onary  vehicle  that  is  struck  from  behind  

•  The  movement  of  the  neck  is  followed  by  massive  rebound  in  the  opposite  direc;on,  causing  bone  and  soD  ;ssue  injuries  

•  Around  570,000  whiplash  injury  claims  were  made  in  the  UK,  last  year  [ABI  2012]  

© The University of Sheffield

What is a Whiplash?

Figure  2.  ‘S’  curve  during  Whiplash  [Chiroprac)c  Health  Blog]  

Figure  1.  Mechanism  of  Whiplash  [IIHS]  

Smart  Materials  •  “A    system  or  material  which  has  built-­‐in  or  intrinsic  sensor(s),  

actuator(s)  and  control  mechanism(s)  whereby  it  is  capable  of  sensing  a  s;mulus,  responding  to  it  in  a  predetermined  

manner  and  extent,  in  a  short/appropriate  ;me,  and  rever;ng  to  its  original  state  as  soon  as  the  s;mulus  is  removed.”  

 •  Examples  -­‐  Piezo-­‐ceramics,  Piezoelectric  polymers,  Magnetostric;ve  ceramics,  Shape  memory  alloys,  Electro-­‐

rheological  fluids  and  Magneto-­‐rheological  fields  etc.  

© The University of Sheffield

Comparison  of  Mechanical  Actuators      

   

Actuator

   

Max.  ActuaPon  Strain

   

Max.  ActuaPon  

Stress  (MPa)

   

Modulus  

E  (GPa)

   

Maximum  Frequency  (s-­‐1)

   

Maximum  Power  Density  

(Wm-­‐3)

   

Density  (kgm-­‐3)

   

Efficiency

   

Low  Strain  Piezoelectric

   

5  x  10-­‐6  –  

3  x  10-­‐5

   

1-­‐3

   

90-­‐300

   

5  x  105  –  

3  x  107

   

1  x  108  –  

1  x  109

   

2600-­‐4700

   

>  0.999

   

High  Strain  Piezoelectric

   

5  x  10-­‐5  –  

2  x  10-­‐4

   

4-­‐9

   

50-­‐80

   

5  x  105  –  

2  x  107

   

9  x  107  –  

5  x  108

   

7500-­‐7800

   

0.90  –  0.99

   

Piezoelectric  Polymer

   

2  x  10-­‐4  –  

1  x  10-­‐3

   

0.5-­‐5

   

2-­‐10

   

1  x  105  –  

1  x  107

   

≈  3  x  108

   

1750-­‐1900

   

0.90  -­‐  0.95

   

SHAPE  MEMORY  ALLOY

   

7  x  10-­‐3  –  

7  x  10-­‐2

   

100-­‐700

   

30-­‐90

   

2  x  10-­‐2  –  

7  x  100

   

7  x  105  –  

1  x  108

   

6400-­‐6600

   

0.01  -­‐  0.02

© The University of Sheffield

Table  1.  Characteris;c  features  of  the  mechanical  actuators  [The  Selec)on  of  Mechanical  Actuators]  

Shape  Memory  Alloys  •  Shape  Memory  Alloys  are  alloys  of  

metals  that  have  the  ability  to  remember  their  original  shapes.  

•  The  Two  Unique  Proper;es  –    1.  One-­‐way  Effect  2.  Two-­‐way  Effect  3.  Pseudo-­‐elas;city  

•  The  Advantages  –    1.  Rela;vely  Light  Weight  2.  Easy  to  manufacture  3.  High  Force  to  Weight  Ra;o    

© The University of Sheffield

Figure  3.  One-­‐way  and  Two-­‐way  effect  of  SMA  [Issues  in  the  Design  of  Shape  Memory  Alloy  Actuators]  

Figure  4.  Pseudo  elas;city  behavior  of  SMA  [h=p://linkinghub.elsevier.com/retrieve/pii/S0045782596012327]  

NiTi  -­‐  Flexinol®  •  The  NiTi  SMA  -­‐  developed  at  the  

Naval  Ordnance  Laboratory  •  ADVANTAGES  –    1.  Large  Recoverable  Mo;on  2.  Great  Duc;lity,    3.  Excellent  Corrosion  Resistance,    4.  Stable  Transforma;on  Temperatures    5.  High  resis;vity,  resul;ng  in  Cheaper  

costs  in  cyclic  applica;ons    

Property Value

Density,   6.45  g/cm3

Specific  Heat,  cA  =  cM 837.36  J/kg/K

Latent  Heat  of  TransformaPon,  XAM 24,190.4  J/kg

Electrical  ResisPvity  

Austenite,   100  micro-­‐ohms*cm

Martensite,   80  micro-­‐ohms*cm

TransiPon  Temperatures 70  Wire 90  Wire

As 70 90

Af 90 110

Ms 65 80

Mf 45 60

Modulus  of  ElasPcity  

Martensite,  Em 28  GPa

Austenite,  EA 83  GPa

Poisson’s  raPo 0.3

Stress  Influence  Coefficients  

CA 7MPa/℃

CM 7MPa/℃

CriPcal  Shear  Stress  

Start  of  Martensite  De-­‐twinning  process  ,   114.0  MPa

End  of  Martensite  De-­‐twinning  process  ,   72.4  MPa

Upper  Plateau  Shear  Stress  ,   183  MPa

Maximum  Recoverable  Shear  Strain,   0.05

© The University of Sheffield

Table  2.  Technical  Characteris;cs  of  NiTi  Wire  [Technical  Characteris)cs  of  FLEXINOL  ®  ]  

Figure  5.    NiTi  Shape  Memory  Alloy  [http://www.pnk.com.cn/material/shape_memory_alloy.htm]  

ProtecPon  Systems  developed  by  Automobile  Companies  

10/10/13 © The University of Sheffield

•  Volvo  and  Jaguar  use  WhiPS  or  more  commonly  known  as  Whiplash  Protec;on  System.  

•  Consists  of  a  recliner  along  with  a  modified  backrest  and  a  head  restraint.    

•  Toyota  uses  WIL  or  Whiplash  Injury  Lessening  system,  which  has  no  ac;ve  parts  but  has  an  improved  geometry  and  a  soDer  seat  back  

•  This  is  a  concept  idea  and  has  not  been  implemented  yet  

 •  Grammar  AG  and  BMW  jointly  developed  ac;ve  

head  rest  systems.    •  The  forward  displacement  of  the  seat’s  head  rest  

is  ini;ated  by  a  pyrotechnical  inflator  unit,  ac;vated  when  there  is  a  rear  end  collision.    

Figure  8.  Headrest  designed  by  Grammar  AG  in  BMW  [Grammar  AG]    

Figure  7.  WIL  and  RHR  Concept  [TOYOTA.  WIL  -­‐  Whiplash  Injury  Lessening]  

Figure  6.  The  WhiPS  Seat  Mo;on  [WHIPS  –  Volvo’s  whiplash  protec)on  study]  

Design  Methodology  

•  Headrest  is  fiped  with  a  Smart  Material  Actuator  

•  One-­‐way  Shape  Memory  Effect  NiTi  used  for  the  NiTi  Spring  Actuator  

•  Actuator  will  have  a  fixed  part  and  a  movable  part  

•  All  the  components  designed  in  Solidworks  

© The University of Sheffield

Design  of  the  NiTi  Spring  Actuator  •  NiTi  Spring  Actuator  was  designed  by  

taking  the  NiTi  Wire  diameter  as  0.510mm,  keeping  a  Spring  Index  of  6.22.  The  Spring  diameter  was  calculated  to  be  3.175mm  .  

 •  A  bias  spring  of  low  s;ffness  made  of  

Titanium  provided  on  the  opposite  side  to  provide  the  required  poten;al  energy.  

 

 

© The University of Sheffield

Figure  9.  Pre-­‐ac;vated  and  Post-­‐ac;vated  NiTi  Spring  Actuators  

Pre-­‐acPvated  Smart  Headrest  •  Carefully  designed  aDer  a  study  of  

the  male  and  female  anthropometry  data.  

•  The  headrest  has  a  total  length  of  229.09mm  suitable  for  both  male  and  female.  

•  The  Design  is  just  en;tled  to  show  the  headrest  and  it’s  working  mechanism  

•  The  en;re  headrest  will  be  covered  with  foam  and  leather  when  installed  inside  the  vehicle.    

 

© The University of Sheffield

Figure  10.  Pre-­‐ac;vated  Smart  Headrest  

Post-­‐acPvated  Smart  Headrest  •  Phase  transforma;on  of  the  NiTi  

Spring  takes  place  when  the  sensor  detects  an  imminent  collision,  which  leads  to  the  contrac;on  of  the  spring  in  its  length.  

 •  Because  of  this,  the  top  part  of  

the  headrest  apached  along  with  hinges  ;lts  for  an  angle  of  22  degrees.  

 

© The University of Sheffield

Figure  11.  Post-­‐ac;vated  Smart  Headrest  

Flow-­‐chart  of  the  AcPvaPon  Mechanism  

© The University of Sheffield

ConvenPonal  Head  Rest  

© The University of Sheffield

•  During  a  rear  impact,  the  occupant’s  head  makes  a  point  contact  with  the  head  rest.  

•  This  point  contact  is  not  sufficient  enough  for  the  headrest  to  prevent  the  whiplash.  

•  The  head  thus,  rotates  to  more  than  45  degrees  leading  to  hyper-­‐extension  causing  whiplash  injury.  

Figure  12.  Contact  of  Driver  with  a  Conven;onal  Headrest  

Figure  13.  Point  Contact  of  the  Driver’s  Head  in  a  Conven;onal  Headrest  

Smart  Head  Restraint  •  In  this  case,  the  head  makes  a  contact  with  the  

head  rest  and  the  area  was  calculated  to  be  1532.30  mm2  

 

𝑚↓ℎ ∗   𝑣↓ℎ +   𝑚↓ℎ𝑟 ∗   𝑣↓ℎ𝑟 =   𝑚↓ℎ ∗   𝑣↑′ ↓ℎ +   𝑚↓ℎ𝑟 ∗   𝑣′↓ℎ𝑟     

𝑒=   𝑣↑′ ↓ℎ −   𝑣′↓ℎ𝑟   /𝑚↓ℎ        

𝐹=   𝑚↓ℎ ∗  ∆𝑣  /∆𝑡     

•  From  the  above  equa;ons,  the  force  created  by  the  head  due  to  the  contact  with  the  headrest  was  calculated  to  be  101.546  Newton  at  an  impact  speed  of  35  km/hr.  and  the  stress  as  0.662  N/mm2.   © The University of Sheffield

Figure  14.  Contact  of  Driver  with  the  Smart  Head  Restraint  

Figure  15.  Contact  Area  of  the  Driver’s  Head  with  the  Smart  Headrest  

EquaPons  –  [Engineering  Mechanics;  Dynamics  –  J.L.  Meriam,  6th  Edi)on]  

CONCLUSIONS  •  Insight  about  whiplash  injuries  due  to  rear  impact  collisions  and  the  latest  

achievements  by  the  automobile  companies  to  prevent  this  injury.  •  Insight  into  smart  materials  and  shape  memory  alloy  actuators  are  

compara;vely  beper.  

•  LimitaPon  was  observed  in  the  wire  diameter  as  it  was  limited  to  0.510mm.  •  Actua;on  Times  and  the  Force  generated  by  SMA  Spring  were  approximated  

based  on  the  researches  done  in  the  par;cular  field  

•  Smart  Head  Restraint  with  NiTi  Spring  Actuator  can  arrest  the  head  neck  moPon  before  it  goes  to  hyper-­‐extension,  thus  preven;ng  the  driver  from  suffering  the  whiplash  injury  when  compared  to  a  conven;onal  headrest.  

© The University of Sheffield

Further  Research  •  In-­‐depth  research  needs  to  be  done  on  the  ac;va;on  ;mes  of  the  phase  

transforma;ons  of  the  Ni;nol.  

•  Actua;on  force  needs  to  be  calculated  with  bundle  wires  and  larger  wire  diameters.  

•  A  Locking  Mechanism  can  be  used  in  order  to  retain  the  head  restraint  in  its  ac;vated  state.  This  can  be  either  mechanically  or  electronically  actuated.  

•  An  effec;ve  ANSYS  or  LS  –  DYNA  simula;on  of  the  head  impact  on  the  headrest  for  a  more  approximate  stress  calcula;on  on  the  driver’s  head.  

•  Valida;on  of  the  Smart  head  rest  performance  in  terms  of  Whiplash  Injury  Criterion.    

 

© The University of Sheffield

Thank You !! Any Questions?