Impact and Shock Loading in Engineering Failure analysis

The various types of Impact , Crash Tests, Shock loading and the associated standards required to evaluate the various structures or vehicles for impact, shock and/or crashworthiness are discussed here.

1. Impact and Shock Loading Padmanabhan.K

2. 2/8/2023 2 Impact Behaviour of Plastics and Reinforced Plastics Izod Impact Charpy Impact Drop Weight Impact Low Velocity Impact Tests Repeated Impact Tests Medium and High Velocity Impact Tests Crashworthiness Tests Ballistic Impact Tests. Single Point Bird Hits .

3. Classification of impact based on velocity 3

4. (a) Charpy impact testing machine. (b) Charpy impact test specimen. (c) Izod impact test specimen. Impact Testing Impact Testing Charpy Impact Testing

5. Energy absorbed versus temperature for a steel in annealed and in quenched and tempered states. (Adapted with permission from J. C. Miguez Suarez and K. K. Chawla, Metalurgia-ABM , 34 (1978) ‏ 825.) ‏ Energy Absorbed vs. Temperature

6. Effect of temperature on the morphology of fracture surface of Charpy steel specimen. Test temperatures T a < T b < T c < T d . (a) Fully brittle fracture. (b, c) ‏ Mixed-mode fractures. (d) Fully ductile (fibrous) fracture . Temperature Effect on Fracture Appearance

7. Energy absorbed, cleavage area ,and lateral expansion as a function of temperature of testing for AISI 1018 steel (cold drawn). Charpy Testing of Steel: DBTT

8. Charpy V-notch curve for a pressure-vessel steel. Note that the NDT temperature determined by the drop-weight test corresponds to the high-toughness region of the Charpy curve. Pneumatic pressurization; material: 21/4 Cr-1 Mo steel, yield stress 590 MPa. (After W. J. Langford, Can. Met. Quart ., 19 (1980) 13.) ‏ Charpy V-notch Curve for a Pressure Vessel Steel

9. (a) Typical oscilloscope record of an instrumented Charpy impact test. (b) Schematic representation of (a). Instrumented Charpy Test

10. Drop-Weight Test Specimen

11. Impact velocity and impact force During drop weight impact, tup’s gravitational potential energy is converted to kinetic energy. Conservation of energy as a tool permits the calculation of the velocity just before it hits the surface . 12 Average impact force x distance travelled = change in kinetic energy

12. 2/8/2023 13 Impact of Epoxy-Polycarbonate Blends

13. Handling and Free Fall Drop Tests Drop Surfaces Concrete Steel Wood Sand Package or Device

14. 2/8/2023 15 Tensile Impact The tensile impact test is a unique test. It is the extensional answer to crashworthiness. Characterized by gross and fast fibre pull out and interfacial Fracture, it is very dependent on the interfacial shear stress in UD conditions !

15. 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.

16. 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.

17. 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.

18. 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.

19. 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.

20. 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.

21. 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.

22. 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.

23. Bird hits are single point impacts with out a supported loading. The Relative velocities can be very high to cause a severe damge on Engines.

24. Shock and Vibration Testing

25. 2/8/2023 27 Thermal Shock Test (JESD22 – A106B) Purpose of this test is t o determine the resistance of the part to sudden exposures of extreme changes in temperature and alternate exposures to these extremes as well as its ability to withstand cyclical stresses Here the IC packages are baked in an oven for 125 ºC/24 Hrs and the temperature is spiked to 260ºC for lead free product and 240ºC for leaded product for 5 to 10 minutes. If the baking temperature is higher than the glass transition temperature at this extreme heat the package tends to delaminate or fail. This failure or delamination can be viewed using SAM (Scanning Acoustic Microscopy)

26. Vibration and Shock

27. Vibration and Shock Sine Vibration From rotating or oscillating machinery; electric motors, wheels, engines, gears, springs. Useful for evaluating dynamic characteristics of structures, i.e resonance Random Vibration More accurately represents the true environment. Excites all frequencies Most damage occurs at fundamental frequency of electronics PCB.

28. Vibration and Shock Shock High stresses causing fracture or permanent deformation High accelerations which can cause relays to chatter, potentiometers to slip, bolts to loosen. High displacement which can cause impact between adjacent circuit boards Usually not considered a fatigue failure if shock quantity less than 1,000 cycles.

29. Selecting a Vibration Level or a Shock Pulse Which Shock Pulse should I Apply? How Many? Which Level? What is the vibration spectrum of interest? How long should I test for? Follow the Contract Specifications Create Your Test Based on Existing Specifications as Guidance Make Field Measurements

30. Shock Test Specs & Methods Automotive FORD, GM SAE J1455 Commercial Products IEC 68-2-27; -29; -31 Commercial Aviation RTCA DO 160E Section 8 Military MIL-STD-810 Systems MIL-STD-883 Circuit Cards MIL-STD-202 Components Handling Drop Classical Shock (Potholes & Crashes) Classical Shock Bump Free Fall Operational and Crash Safety Shock Sustained Shock SRS Classical Pyroshock Ballistic Shock

31. Classical Shock Pulses Advantages Easy to specify and understand shape, tolerance, mathematics Test machinery can generate pulses Accepted methods written into many specs Disadvantages Not real world pulses Does not evaluate device response to shock

32. Classical Shock Tests

33. Shock Response Spectrum Input Pulse Measured Response

34. Pyrotechnic Shock

35. Ballistic Shock

36. External factors Projectiles Bullets Trauma zone of Damage Damage tolerance Energy of Absorption 38 S . No Bullets Mass Velocity 1. .22 cal 38grams 380m/s 2 Type 2A 9mm 8grams 373m/s 3. Type 2 9mm Carbine 8grams 400m/s 4. Type IIIA ( .44 Magnum) 8.1grams 450m/s 5. Type III (Rifles) 7.62mm AK-47, SLR 9.6grams 847m/s 6. Type IV (Armor Piercing Rifle) 10.8grams 878m/s

37. Custom Shock Evaluation ASTM D3332 Damage Boundary Response to short duration pulse is a function of velocity change. Response to long duration pulse is a function of the peak acceleration and waveform. MIL-810 Fragility Test