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SMC 4133 AUTOMOTIVE STRUCTURES

SMC 4133 AUTOMOTIVE STRUCTURES. DESIGN FOR CRASHWORTHINESS. The main function of the body structure is to protect occupants in a collision There are many standard crash tests and performance levels For the USA, these standards are contained in Federal Motor Vehicle Safety

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SMC 4133 AUTOMOTIVE STRUCTURES

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  1. SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR CRASHWORTHINESS • The main function of the body structure is to protect occupants in a collision • There are many standard crash tests and performance levels • For the USA, these standards are contained in Federal Motor Vehicle Safety • Standards (FMVSS) • They are FMVSS 208 (front), 214 (side), 301 (rear) and 216 (roof) All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.

  2. SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR CRASHWORTHINESS • The insurance industry & consumer groups have their own test standard to • evaluate vehicles beyond government standards • For instance, the New Car Assessment Program (NCAP) • It is based on the probability of injury; measured with a star rating where • the five stars indicate lower probability of injury and vice-versa All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.

  3. SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR CRASHWORTHINESS FRONT BARRIER • Is a condition of a moving vehicle crashes onto a rigid barrier at a front end • Let’s model the frontal impact with a point mass t = 0 t = 0, dx/dt = V0 t = 0, x = 0 dx/dt = 0 Resulting behavior of the point mass model The crush efficiency factor is used to consider non-uniform crash force properties All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.

  4. SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR CRASHWORTHINESS Example 1 Consider a vehicle of mass 1580kg impacting a rigid barrier at 55 km/h and average crush load of 300 kN. Calculate crash acceleration, deformation and time. Acceleration = -300000/1580 = 189.87 m/s^2 = -19.4g time = 1580 x 55/(3.6 x 300000) = 0.0805s Deformation = -300000 x (0.0805^2)/(2 x 1580) + (55/3.6) x 0.0805 = 0.614m All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.

  5. SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR CRASHWORTHINESS The crush efficiency factor is used to consider non-uniform crash force properties • When crush factor approaching 1, it • indicates the lower the head injury • When designing the collapsed structure • of the motor compartment, it is desirable • to have a square wave shape All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.

  6. SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR CRASHWORTHINESS Procedure for establishing Front body structural requirements: Maximum allowable cabin decelerations based on occupant injury Consistent structural efficiency and crush space Average and maximum allowable crush forces Total crush forces to be used in the structural elements Crush force: 10% - hood & fender 20% - lower cradle 50% - mid-rail 20% - top of fender The front end elements are sized to ensure that the cabin zone won’t be intruded All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.

  7. SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR CRASHWORTHINESS Example 2 a) Determine the required crush space. The structure will be 80% efficient and the allowable maximum deceleration is 20g. The impact speed is 48km/h. b) Compute the average total crush force with a vehicle mass of 1200kg and impact speed of 35 km/h. Solution: a) Crush space = (48/3.6)^2/(2*20*9.81*0.8) = 0.57m b) Crush force = 0.5*1200*(48/3.6)^2/0.57 = 187N All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.

  8. SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR CRASHWORTHINESS Beam section can be determined Beam sizing • A thin-walled square section is subjected to an axial compressive load • As the compressive load is gradually increased, the elastic buckling load • is reached and the walls buckle • As the load increases further and past the ultimate load, the walls section cripple • and the load drops All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.

  9. SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR CRASHWORTHINESS Example 3 Each of motor compartment side rail must generate 25% of the crush force F=300kN. A 100mm square section is used. Find the required thickness for yield stress of 207 MPa. Solution: Pm = 0.25*300000 = 75000N Pm = 386*t^1.86*100^0.14*207^0.57 = 75000 t^1.86 = 4.88 t = 2.34mm All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.

  10. SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR CRASHWORTHINESS • Motor compartment packaging typically • require flange location & section shapes All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.

  11. SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR CRASHWORTHINESS Limit load analysis • Is the ultimate load-carrying ability for the structure • Is used to determine the failure load that cause to initiation of permanent • deformation Plastic hinge model All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.

  12. SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR CRASHWORTHINESS Model with small deflection All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.

  13. SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR CRASHWORTHINESS Vehicle pitch during impact • Some vehicles rotate/pitch upon crash with a fixed barrier • It can increase the possibility of neck injuries • To reduce pitching, crushable beam is introduced All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.

  14. SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR CRASHWORTHINESS Example 4 Fup = 100000* 100/(400) = 25kN All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.

  15. SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR CRASHWORTHINESS • Side impact • Plays an important role in sizing vehicle structure • FMVSS requires a minimum injury performance while NCAP uses star scale • The injury criterion is TTI index where the larger values indicate a more severe injury • TTI < 57 in desirable All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.

  16. SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR CRASHWORTHINESS Kinematic and load path analysis Acceleration & time Final velocity Distance traveled All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.

  17. SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR CRASHWORTHINESS Side – impact model Time at which the occupant hit the door All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.

  18. SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR CRASHWORTHINESS Rear impact - To minimize fuel system from leakage Final speed Final speed Work of deformation Equivalent impact velocity Average rear crush force All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.

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