MASS PROPERTIES and AUTOMOTIVE CRASH SURVIVAL, Rev. A
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This presentation accompanied the delivery of SAWE Paper #3634 at the 74th SAWE International Conference held from May 18 to 21, 2015, at the Crown Plaza Hotel in Alexandria, VA, USA. The purpose of this paper was to make explicit the exact role that mass properties play in determining the automotive deceleration performance during a crash. This has a direct bearing on the survivability of a crash, which can be enhanced through thoughtful mass properties engineering.
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MASS PROPERTIES and AUTOMOTIVE CRASH SURVIVAL, Rev. A
- 1. Brian Paul Wiegand, PE 74TH SAWE International Conference on Mass Properties Engineering Alexandria, VA, 18-22 May 2015
- 2. …WAS INITIALLY CONSIDERED SOMETHING ABOUT WHICH LITTLE COULD BE DONE. A DECELERATION LEVEL GREATER THAN 18 G’s WAS THOUGHT TO BE UNAVOIDABLY FATAL. SAFETY EFFORT WAS FOCUSSED ON AVOIDING THE CRASH THROUGH BETTER BRAKES, HANDLING, LIGHTING, SPEED LIMITS, TRAFFIC LIGHTS, ROADWAY CONSTRUCTION, DRIVER EDUCATION, ETC. THE PASSIVE ASPECT OF AUTOMOTIVE CRASH SAFETY WAS IGNORED… 74th SAWE International Conference 2
- 3. …ATTITUDES BEGAN TO CHANGE IN THE 1930’s. DR. CLAIR L. STRAITH (1891- 1958), JOESEPH CHAMBERLAIN FURNAS (1906-2001), HUGH DeHAVEN (1895-1980), COL. JOHN PAUL STAPP (1910-1999), & RALPH NADER (1934-????) INVESTIGATED AND/OR AGITATED FOR GREATER AUTOMOTIVE PASSIVE CRASH SAFETY. 74th SAWE International Conference 3
- 4. …DEPENDS ON A NUMBER OF FACTORS: 1. MAGNITUDE OF DECELERATION. 2. RATE OF ONSET OF DECELERATION. 3. DURATION OF DECELERATION. 4. POSITION W.R.T. THE DECELERATION VECTOR. 5. OSCILLATION OF THE DECELERATION. 6. ANGULAR COMPONENT PRESENCE. 7. PHYSICAL CRUSH &/OR PENETRATION. 74th SAWE International Conference 4
- 5. …IS POSSIBLE FOR VERY HIGH LEVELS OF DECELERATION IF: 1. THE DURATION IS SHORT. 2. THE RATE OF ONSET LOW. 3. THE POSITION W.R.T. DECELERATION VECTOR IS FAVORABLE, WITH PROPER RESTRAINT AND SUPPORT. 4. THE DECELERATION PULSE IS SMOOTH. 5. THERE IS NO ANGULAR COMPONENT . 6. THERE IS NO BODILY CRUSH AND/OR PENETRATION. 74th SAWE International Conference 5
- 6. 74th SAWE International Conference 6
- 7. 74th SAWE International Conference 7
- 8. 74th SAWE International Conference 8
- 9. 74th SAWE International Conference 9
- 10. 74th SAWE International Conference 10 THE CONVENTIONAL >>> <<<< THE ULTIMATE
- 11. 74th SAWE International Conference 11 PACKAGING CONCEPT: PROPER RESTRAINT AND SUPPORT WITHIN AN INVIOLATE PASSENGER COMPARTMENT SURROUNDED BY SACRIFICIAL CRUSHABLE STRUCTURE.
- 12. 74th SAWE International Conference 12
- 13. 74th SAWE International Conference 13 THE FORCE “F” IS NOT CONSTANT BUT FLUXES AS THE VEHICLE STRUCTURE CRUSHES IN SPURTS:
- 14. 74th SAWE International Conference 14 THE KINETIC ENERGY AT IMPACT WILL BE DISSIPATED MAINLY AS THE WORK DONE CRUSHING THE VEHICLE STRUCTURE: EXPRESSED IN RAMP MODEL TERMS:
- 15. 74th SAWE International Conference 15 Wt = Weight of the vehicle (lb). g = Gravitational constant, “g” = 32.174 ft/s2. I1 = Rotational inertia about front axle line (lb-ft2). I2 = Rotational inertia about the crankshaft axis (lb-ft2). I3 = Rotational inertia about transmission 3rd motion axis (lb-ft2). I4 = Rotational inertia about rear axle line (lb-ft2). TR = Transmission gear ratio (dimensionless). AR = Axle gear ratio (dimensionless). RD = Dynamic rolling radius at drive wheels (ft).
- 16. 74th SAWE International Conference 16 TWO TYPES: 1- FMVSS or COMPLIANCE TESTING 2- NCAP or 5-STAR RATING TESTING NCAP TESTING IS THE MORE “RIGOROUS” (35 MPH vs. 30 MPH FIXED BARRIER CRASH, ETC.) AND MANUFACTURERS TEND TO DESIGN SO AS TO GET A HIGH NCAP 5-STAR RATING.
- 17. 74th SAWE International Conference 17 CONSISTS OF A NUMBER OF TESTS: 1) 35 MPH FRONT FIXED BARRIER CRASH 2) 38.5 MPH SIDE MOVING DEFORMABLE BARRIER CRASH 3) 20 MPH SIDE POLE CRASH 4) ROLLOVER RESISTANCE (SSF CALC + “FISHHOOK” TEST) THE 35 MPH FRONT FIXED BARRIER CRASH IS THE MOST SIGNIFICANT TEST, AND DRIVES THE DESIGN OF VEHICLE FRONT STRUCTURES
- 18. 74th SAWE International Conference 18 HEAD INJURY CRITERION (HIC): FOR FMVSS THE HIC VALUE MERELY HAS TO BE LESS THAN 1000 FOR THE 95th PERCENTILE DUMMY AND LESS THAN 700 FOR THE 5th PERCENTILE DUMMY. FOR NCAP RATING IS BASED ON BEST SCORE IN CLASS. NECK INJURY CRITERION: FOR FMVSS THIS CRITERION MERELY HAS TO BE LESS THAN 937 lb TENSION/899 lb COMPRESSION FOR THE 95th PERCENTILE DUMMY AND LESS THAN 589 lb TENSION/566 lb COMPRESSION FOR THE 5th PERCENTILE DUMMY. FOR NCAP RATING IS BASED ON BEST SCORE IN CLASS. CHEST ACCELERATION/COMPRESSION CRITERION: FOR FMVSS HAS TO BE LESS THAN 60 g’s DECELERATION OR LESS THAN 2.5 in COMPRESSION. FOR NCAP RATING IS BASED ON BEST SCORE IN CLASS.
- 19. 74th SAWE International Conference 19 PC/Mi (Passenger Car/Mini): 1,500-1,999 lb (680-906 kg). PC/L (Passenger Car/Light): 2,000-2,499 lb (907-1133 kg). PC/C (Passenger Car/Compact): 2,500-2,999 lb (1134-1360 kg). PC/Me (Passenger Car/Medium): 3,000-3,499 lb (1361-1587 kg). PC/H (Passenger Car/Heavy): 3,500 lb and up (1588 kg and up). LTV (Light Trucks, Vans): includes SUV’s.
- 20. 74th SAWE International Conference 20 Where: HIC = Head Injury Criterion (dimensionless). t1 = Time at start of interval of interest (seconds). t2 = Time at end of interval of interest (seconds). a = Resultant (total) deceleration (g’s) as per:
- 21. 74th SAWE International Conference 21 1996 Dodge Neon 2006 Honda Ridgeline
- 22. 74th SAWE International Conference 22 24.34 g’s 21.61 g’s
- 23. 74th SAWE International Conference 23 24.34 g’s 14.31 g’s
- 24. 74th SAWE International Conference 24 LIGHTER VEHICLES ARE NOW AT AN EVEN GREATER DISADVANTAGE TO HEAVIER VEHICLES IN A CRASH; THE LIGHTER VEHICLE OCCUPANTS ARE MORE LIKELY TO BE INJURED OR KILLED. THE OCCUPANTS OF ALL VEHICLES ARE MORE LIKELY TO BE INJURED OR KILLED WHEN THE CRASH IS NOT ORTHOGONAL TO A FIXED FLAT BARRIER, OR WHEN THE BARRIER IS NOT SMOOTH AND FLAT, OR WHEN THE IMPACT VELOCITY IS GREATER THAN 35 MPH.
- 25. 74th SAWE International Conference 25 MANUFACTURER’S DESIGN VEHICLES TO HAVE THE LOWEST DECELERATION POSSIBLE WITHIN THE AVAILABLE CRUSH DISTANCE (I.E., WITHOUT ENGAGING THE PASSENGER SPACE STRUCTURE). THIS MEANS THAT HEAVIER VEHICLES WILL ALWAYS HAVE SIGNIFICANTLY STIFFER FRONT STRUCTURE THAN LIGHTER VEHICLES, AND THAT ALL VEHICLES ARE NOW ONLY FIT FOR FRONT END CRASHES THAT EXACTLY DUPLICATE CRASH TEST CONDITIONS.
- 26. 74th SAWE International Conference 26 THE NCAP 5-STAR RATING SYSTEM AS IT IS NOW CONSTITUTED INSTUTIONALIZES A MINIMUM LEVEL OF SAFETY AND PENALIZES MANUFACTURES WHO WOULD AIM HIGHER. HUMAN BEINGS CAN SURVIVE FAR HIGHER “G” LOADINGS THAN THOSE RESULTING FROM PRESENT NCAP SYSTEM, AND SMALL LIGHT VEHICLES SHOULD BE ALLOWED HIGHER “G” LOADINGS WITH ATTENDENT BETTER PACKAGING SO AS TO “EVEN THE PLAYING FIELD” W.R.T. LARGER HEAVIER VEHICLES.
- 27. 74TH SAWE International Conference on Mass Properties Engineering Alexandria, VA, 18-22 May 2015 27
- 28. 74TH SAWE International Conference on Mass Properties Engineering Alexandria, VA, 18-22 May 2015 28 WHEN CRUSH DISTANCE IS EXCEEDED: g’s
- 29. 74TH SAWE International Conference on Mass Properties Engineering Alexandria, VA, 18-22 May 2015 29 SHEDDING KINETIC ENERGY (PARTS): g’s
- 30. 74TH SAWE International Conference on Mass Properties Engineering Alexandria, VA, 18-22 May 2015 30 CRASH MODELING SUMMARY: g’s
- 31. 74TH SAWE International Conference on Mass Properties Engineering Alexandria, VA, 18-22 May 2015 31 WHEN CRASHES DO NOT FOLLOW NCAP SCENARIO: g’s
- 32. 74TH SAWE International Conference on Mass Properties Engineering Alexandria, VA, 18-22 May 2015 32 RACE CAR DRIVERS ROUTINELY SURVIVE WHAT NHTSA CALLS FATAL g’s “…(Purley) survived an estimated 179.8 g’s when he decelerated from 173 km/h (108 mph) to 0 in a distance of 66 cm (26 inches)… This was the highest measured (sic) g-force ever survived by a human being…(until in 2003, Kenny Bräck's crash violence recording system measured 214 g). “David Charles Purley…(26 January 1945 – 2 July 1985) was a British racing driver… best known for his actions at the 1973 Dutch Grand Prix, where he abandoned…(his race car)…and attempted to save…fellow driver Roger Williamson, whose car was…on fire...Purley was awarded the George Medal for his courage in trying to save Williamson, who suffocated...During pre- qualifying for the 1977 British Grand Prix Purley sustained multiple bone fractures (when)…he crashed into a wall. His deceleration from 173 kph (108 mph) to 0 in a distance of 66 cm (26 in) is thought to be one of the highest G-loads in human history…He died in a plane crash in…1985.”
- 33. 74TH SAWE International Conference on Mass Properties Engineering Alexandria, VA, 18-22 May 2015 33 1948 TUCKER “TORPEDO” AFTER NEAR 100 MPH ROLLOVER AT INDY DEMONSTRATION
Editor's Notes
- MASS PROPERTIES & AUTOMOTIVE CRASH SURVIVAL IS SOMETHING THAT SHOULD CONCERN US ALL AS JUST ABOUT ALL OF US DRIVE, YET IT DOESN’T. WE JUST ACCEPT THE FACT THAT THE MATTER IS IN THE HANDS OF THE BIG AUTOMOTIVE MANUFACTURERS AND THE GOVERNMENT REGULATIORY AGENCIES AND ASSUME THAT THEY ARE DOING THE BEST JOB POSSIBLE…
- OF COURSE, AT ONE TIME CRASH SURVIVAL WAS PRETTY MUCH IGNORED COMPLETELY, SO THERE HAS BEEN SOME IMPROVEMENT…
- THAT INITIAL ATTITUDE BEGAN TO CHANGE IN THE 1930’S…
- With respect to duration we are talking milliseconds for very high deceleration levels up to around 200 g’s. A rate of onset less than 1000 g/sec is good…
- How some of those factors interrelate is illustrated in the Lovelace Chart, which conveniently relates deceleration level, duration, deceleration distance, and initial velocity all in one handy graph. It establishes the upper limits for human survivability (narrow yellow band). Hugh DeHaven is primarily responsible for the initial collecting and organizing of this sort of data. The “55 ft fall with 4 in deceleration” (145 g’s average) is one of the many cases he investigated.
- A chart of this sort is less concerned with fatality but the level of deceleration which is endurable allowing for continued function. Col. Stapp is primarily responsible for the initial collecting and organizing of this sort of data, which comes in handy for carrier landings, ejection systems, rocket launches, etc.
- Another Stapp type data graph. Note that here the rate of onset is about 1000 g’s/sec when the situation starts to become critical…
- This a sort of NASA chart which illustrates the importance of positioning w.r.t. the acceleration vector…
- RESTRAINT AND SUPPORT IS RELATED TO THE MATTER OF PROPER POSITINING W.R.T. THE DECELERATION VECTOR, THAT IS, THE MAINTAINING OF THAT POSITIONING AND THE SPREADING OUT OF DECELERATION LOADS ON THE HUMAN BODY.
- The “packaging concept” for human survival in car crashes has been around for quite awhile, and is universally accepted (not that the automotive manufacturers pay strict adherence to it). Béla Barényi (1907-1997) while working for Mercedes patented (DBP 854,157) the automotive “crumple zone” in 1951. 1963 Mercedes 230 SL body incorporated a rigid passenger cell and crumple zones at the front and rear as per the concept of Barényi. In 1966 Barényi and Hans Scherenberg created the division of auto safety into the active and passive.
- The force generated “F” causes not only a deceleration “a” but also dynamic moments about the contact point of “F dz” and “F dy” (latter not shown). This gives the height of the CG and the lateral offset of the CG w.r.t. the line of action special significance. In the fixed barrier crash test depicted note how the “F dz” moment causes the rear wheels to lose contact with the ground plane.
- THERE IS SOME RANDOM FLUX IN THE ACTUAL FORCE-CRUSH FUNCTION DUE TO THE COLUMN-LIKE NATURE OF MANY OF THE STRUCTURAL ELEMENTS. THIS FLUX IS MUCH LESS TODAY THAN YEARS AGO DUE TO THE EFFORT TAKEN TO SMOOTH OUT THE INHERENT HARSH VIBRATION TENDENCY. THE RANDOM VIBRATION FLUX OF “Fx” CREATS A VIBRATORY FLUX IN “Fz” AND “Fy” WHEN “dZ” AND “dY” ARE LARGE ENOUGH TO BE SIGNIFICANT. IF SO, THEN THERE WILL BE A FLUCUATING ACCELERATION IN THE X, Y, AND Z DIRECTIONS. NOTE THAT FOR SIMPLIFIED STUDIES THE FORCE-CRUSH FUNCTION CAN BE MODELED AS A “RAMP”, A.K.A. “PROGRESSIVE FORCE”, FUNCTION. THE AREA BOUNDED BY THE FORCE-CRUSH FUNCTION IS THE WORK ENERGY UTILIZED TO CRUSH THE STRUCTURE, AND IS EQUAL TO THE KINETIC ENERGY OF THE VEHICLE AT IMPACT.
- IN A CRASH THE DRIVETRAIN IS OFTEN QUICKLY INCAPACITATED, SO THE I2 TERM AND MAYBE THE I3 TERM MIGHT NOT CONTRIBUTE TO THE EFFECTIVE MASS IN A CRASH. ALSO THE BRAKES MIGHT BE LOCKED PRIOR THE CRASH, WHICH COULD EXCLUDE TERMS I1 AND I2. ALSO THERE IS THE UNCERTAINTY OF COMPONENTS BREAKING OFF FROM THE MAIN BODY DURING THE CRASH, AND THE POSSIBLE LOSS OF GROUND CONTACT BY THE REAR WHEELS WHICH WILL INFLUENCE HOW THE I4 ROTATIONAL ENERGY IS FED INTO THE CRASH. THIS IS WHY THE EFFECTIVE MASS IS OFTEN JUST APPROXIMATED AS THE WEIGHT MASS. THE OTHER SOURCE OF UNCERTAINTY INVOLVES ENERGY DISSIPATION IN WAYS OTHER THAN WORK CRUSHING STRUCTURE (FRICTION, VIBRATION, LIGHT, SOUND).
- FOR FRONT FIXED BARRIER CRASH COMPLIANCE TESTING DUMMY MEASUREMENTS HAVE TO BE LESS THAN CERTAIN VALUES. FOR FRONT FIXED BARRIER CRASH 5-STAR TESTING THERE IS NO PASS/FAIL; RATINGS ARE RELATIVE TO THE REST OF THE VEHICLES IN CLASS.
- THE NCAP VEHICLE CLASSES ARE EXPLICITLY WEIGHT DRIVEN FOR PASSENGER CARS, FOR LTV/SUV IT IS ASSUMED THAT WEIGHT IS PROPORTIONAL TO SIZE ALTHOUGH THIS ALLOWS FOR A CERTAIN AMOUNT OF OVERLAP WITH THE HEAVIER PASSENGER CAR CLASS.
- THE HEAD INJURY CRITERION IS THE MOST SIGNIFICANT AND COMPLICATED. HERE WE CAN SEE THE SIGNIFICANCE OF THE ACCELERATIONS IN THE LATERAL AND VERTICAL DIRECTIONS. THIS IS ONE OF THE REASONS WHY IT MAY BE BEST FOR CRASH PERFORMANCE TO HAVE THE LOWEST VERTICAL CG AND LEAST LATERALLY OFFSET CG POSSIBLE.
- THE LARGE HEAVY VEHICLE (5122 lb) IS 1.7 TIMES THE WEIGHT OF THE SMALL LIGHT VEHICLE (3011 lb, PASSENGER CAR, MEDIUM), BUT ITS AVAILABLE CRUSH DISTANCE IS ONLY 1.11 TIMES THE SMALL LIGHT. MORE IMPORTANTLY, THE FRONT END AREA RATIO IS 1.28. EVEN THOUGH BOTH VEHICLES HAVE TO BE AS “SOFT” AS POSSIBLE STRUCTURALLY TO GET THE BEST SCORE (LOWEST DECEL), THE HEAVY VEHICLE HAS TO ABSORB 70% MORE KINETIC ENERGY IN ONLY 11% MORE DISTANCE AND WITH ONLY 28% MORE AREA; THE HEAVY VEHICLE MUST HAVE A 33% STIFFER STRUCTURE (1.7/1.28) THAN THE LIGHTER VEHICLE IF THE PASSENGER SPACE IS TO BE MAINTAINED. (The volume ratio is 2.07. THE MODEL STIFFNESS RATIO IS 1.34)
- NOTE THAT THE MODEL FRT STIFFNESS RATIO IS 1.34. THE 35 MPH NCAP BARRIER TEST DECELERATIONS ARE 24.34 g’s SL and 21.61 g’s LH, WHICH ARE CLOSE.
- THE INDIVIDUAL DELTA VELOCITIES SMALL LIGHT TO LARGE HEAVY ARE 35.21 mph TO 20.70 mph (TOTALS 55.91 mph) with a closing speed of 57.9 mph (leaves 1.99 mph “unaccounted” for) AND DECELERATIONS ARE 24.34 g’s TO 14.31 g’s. THESE ARE THE MAX RESULTS POSSIBLE WITHOUT VIOLATING THE PASSENGER SPACE OF THE SMALL LIGHT VEHICLE.
- YOU COULD TAKE SOMETHING THE SIZE OF A DODGE NEON AND, WITH BETTER PACKAGING AND STIFFER STRUCTURE, MAKE IT FAR SAFER THAN AT PRESENT, BUT IT WOULD SCORE FAR LESS IN NCAP 5-STAR “SAFETY” RATING.
- In demonstration runs at Indianapolis Motor Speedway in 1948 seven Tuckers were driven around the 2 1/2-mile Indianapolis Speedway oval for two weeks at 90-95 mph average. Car #1027 had a tire blow out and rolled three times at about 95 miles per hour (153km/h) and the driver walked away with bruises. After the tire was replaced the car was re-started and driven off the track.