automotive safety inside the cabin, and materials o be used

this ppt describes about interior safety and materials to be used in manufacturing of automobile

1. UNIT -3 SAFETY EQUIPMENTS 29/07/24 1 AUTOMOTIVE SAFETY Mr. Ramkumar N P Assistant Professor Department of Mechanical Engineering FET-JAIN Deemed to be University

2. Content Seat belt Regulations Automatic seat belt tightener system Collapsible steering column Tiltable steering wheel Air bag Electronic system for activating air bags Bumper design for safety

3. Seat belt A seat belt, called as safety belt, is a safety harness designed to secure the occupant of a vehicle against harmful movement that may result from a collision or a sudden stop. As part of an overall automobile passive safety system, seat belts are intended to reduce injuries by stopping the wearer from hitting hard interior elements of the vehicle, or other passengers (the so-called second impact), are in the correct position for the airbag to deploy and prevent the passenger from being thrown from the vehicle. Seat belts also absorb energy by being designed to stretch during an impact, so that there is less speed differential between the passenger's body and their vehicle interior, and also to spread the loading of impact on the passengers’ body. Seat belts minimise injuries during accidents. Seat belts are woven narrow fabric made from nylon filament yarns or high tensile polyester filament yarn. The load specification is an important criterion for usage in vehicles.

4. Passenger Restraint Systems Automatic seat belt (manual systems) Three-point seat belt with retractor mechanism ("automatic seat belt") represents a good compromise between effective safety, ease of buckling, comfort and cost. When a specific vehicle-deceleration value is reached, a built-in, quick-response interlock inhibits the seat-belt roller. Three point seat belt Inertia-reel seat-belt system Seat belt, Ratchet wheel, Inertia-reel shaft, Pendulum, Pawl (in locked position).

5. The final, so-called 'third impact' after a passenger's body hits the car interior, airbag or seat belts, is that of the internal organs hitting the ribcage or skull. The force of this impact is the mechanism through which car crashes cause disabling or life threatening injury. The sequence of energy dissipating and speed reducing technologies - crumple zone - seat belt - airbags - padded interior, are designed to work together as system, to reduce the force of this final impact A typical seatbelt consists of a  lap belt , which rests over pelvis, and a  shoulder belt , which extends across chest. The two belt sections are tightly secured to the frame of the car in order to hold passengers in their seats. The seatbelt webbing is made of more flexible material than the dashboard or windshield. It stretches a little bit, which means the stop isn't quite so abrupt. The seatbelt shouldn't give more than a little, however, or you might bang into the steering wheel or side window. Safe seatbelts will only let you shift forward slightly.

6. Types of seat belts Lap seat belt Three points seatbelt Five point Seat

7. Lap: Adjustable strap that goes over the waist. Used frequently in older cars, now uncommon except in some rear middle seats. Passenger’s aircraft seats also use lap seat belts to prevent injuries. Adjustable strap that goes over the shoulder. Used mainly in the 1960s, but of limited benefit because it is very easy to slip out of in a collision.

8. How effective are lap seat belts? Lap belts are  63 percent effective  and lap/shoulder belts are 73 percent effective . Belts are so effective in low speed vehicles because they eliminate the risk of ejection, a big problem for unrestrained occupants in these vehicles. Seat belts dramatically reduce risk of death and serious injury. ... Seat belts  prevent drivers and passengers from being ejected during a crash . People not wearing a seat belt are 30 times more likely to be ejected from a vehicle during a crash

9. Three-point seat belt: Similar to the lap and shoulder, but one single continuous length of webbing. Both three-point and lap-and-sash belts help spread out the energy of the moving body in a collision over the chest, pelvis, and shoulders. Volvo introduced the first production three-point belt in 1959. The first car with three point belt was a Volvo PV 544 that was delivered to a dealer in Kristian stad on August 13, 1959.

10. One such invention was the Three-Point Seat Belt invented by Nils Bohlin , a Swedish Mechanical Engineer who developed it while he worked at the Volvo Car Corporation.

11. The three point belt was developed by Nils Bohlin who earlier had worked on ejection seats. Until the 1980s, three-point belts were commonly available only in the front seats of cars; the back seats had only lap belts or diagonal belts. passenger safety regulations in nearly all developed countries requiring that all seats in a vehicle be equipped with three-point belts. Since September 1, 2007, all new cars sold in the U.S. require a lap and shoulder belt in the center rear.

12. By 1968, the Three-Point System was made a mandatory requirement in American cars and began to be adopted by cars all over the globe. Nils Bohlin went on to develop more safety mechanisms and features, improving the previous ones until his retirement in 1985. He died in 2002 and an article by Volvo estimated that in the past four decades the Three-Point Seat Belt had saved over one million lives. Nils Bohlin was posthumously added in the National Inventors Hall of Fame and is even today praised for such an important invention.

13. Five Point Seat Belt

14. Seat-belt Tightener Systems Seat-belt tightener 1 From sensor 2 Firing pellet 3 Solid propellant 4 Tensioning cable 5 Cylinder 6 Piston 7 Seat belt Represents a further development and improvement of the three-point automatic seat-belt systems. By reducing seat-belt slack, they eliminate excessive forward passenger movement in serious accidents. This in turn reduces the differential speed between the vehicle and passengers, and thus also reduces the corresponding forces acting on the passengers. Integrated belt-force limiters ensure that controlled give of the belt takes place after it has been tightened, so as to prevent potential overloading in the chest area.

15. Concept of Seat belt working – 3D animation

16. Seat belts and seat-belt tighteners Occupant protection systems with belt tighteners and front airbags , 1 Belt tightener , 2 Front airbag for passenger, 3 Front airbag for driver, 4 ECU

17. Function: The function of seat belts is to restrain the occupants of a vehicle in their seats when the vehicle hits an obstacle. Seat-belt tighteners improve the restraining characteristics of a three- point inertia-reel belt and increase the protection against injury. In the event of a frontal impact, they pull the seat belts tighter against the body and thus hold the upper body as closely as possible against the seat backrest. This prevents excessive forward displacement of the occupants caused by mass inertia.

18. Operating concept: In a frontal impact with a solid obstacle at a speed of 50 km/h, the seat belts must absorb a level of energy comparable to the kinetic energy of a person in free fall from the 4th floor of a building. Because of the belt slack, the belt stretch and the delayed effect of the belt retractor, three-point inertia-reel belts provide only limited protection in frontal impacts with solid obstacles at speeds of over 40 km/h because they can no longer safely prevent the head and body from impacting against the steering wheel or the instrument panel. An occupant experiences extensive forward displacement without restraint systems. Shoulder-belt tightener 1. Ignition cable, 2 Firing elements, 3 Propellant charge, 4 Piston, 5 Cylinder, 6 Metal cables, 7 Belt reel, 8 Belt strap.

19. In an impact, the shoulder belt tightener compensates for the belt slack and by retracting and tightening the belt strap. At an impact speed of 50 km/h, this system achieves its full effect within the first 20 m/s of the impact; and thus supports the airbag which needs approx. 40 m/s to inflate completely. The occupant continues to move forward slightly until making contact with the deflating airbag and in this manner is protected from injury. A prerequisite for optimum protection is that the occupants' forward movement away from their seats remains minimal as they decelerate along with the vehicle. This is achieved by triggering the belt tighteners immediately upon initial impact to ensure that safe restraint of the occupants in the front seats starts as soon as possible. The explosive pressure acts on a piston, which turns the belt reel via a steel cable in such a way that the belt rests tightly against the body.

20. Variants: In addition to the above-mentioned shoulder-belt tighteners for retracting the belt reel, there are variants which pull the belt buckle back (buckle tighteners ) and thus simultaneously tighten the shoulder and lap belts. The restraining effect and the protection afforded against occupants sliding forward beneath the lap belt are improved still further by buckle tighteners . The tightening process in these two systems takes place in the same period of time as for shoulder-belt tighteners . In the case of a mechanical tightener , a mechanical or electrical sensor releases a pre tensioned spring, which pulls the belt buckle back. The sole advantage of these systems is that they are cheaper.

21. Seat Belt Tightening System In a typical seatbelt system, the belt webbing is connected to a retractor mechanism . The central element in the retractor is a spool, which is attached to one end of the webbing. Inside the retractor, a spring applies a rotation force, or torque , to the spool. This works to rotate the spool so it winds up any loose webbing When we pull the webbing out, the spool rotates counter-clockwise, which turns the attached spring in the same direction. Effectively, the rotating spool works to untwist the spring. The spring wants to return to its original shape, so it resists this twisting motion. If we release the webbing, the spring will tighten up, rotating the spool clockwise until there is no more slack in the belt.

22. The retractor has a locking mechanism that stops the spool from rotating when the car is involved in a collision. There are two sorts of locking systems in common use today: systems triggered by the car's movement systems triggered by the belt's movement The first system locks the spool when the car rapidly decelerates (when it hits something). The diagram below shows the simplest version of this design The central operating element in this mechanism is a weighted pendulum. When the car comes to a sudden stop, the inertia causes the pendulum to swing forward. The pawl on the other end of the pendulum catch hold of a toothed ratchet gear attached to the spool. With the pawl gripping one of its teeth, the gear can't rotate counter-clockwise, and neither can the connected spool. When the webbing loosens again after the crash, the gear rotates clockwise and the pawl disengages

23. The second kind of system locks the spool when something jerks the belt webbing. The activating force in most designs is the speed of the spool rotation. The diagram shows a common configuration. The central operating element in this design is a centrifugal clutch -a weighted pivoting lever mounted to the rotating spool. When the spool spins slowly, the lever doesn't pivot at all. A spring keeps it in position. But when something yanks the webbing, spinning the spool more quickly, centrifugal force drives the weighted end of the lever outward. The extended lever pushes a cam piece mounted to the retractor housing. The cam is connected to a pivoting pawl by a sliding pin. As the cam shifts to the left, the pin moves along a groove in the pawl. This pulls the pawl into the spinning ratchet gear attached to the spool. The pawl locks into the gear's teeth, preventing counter-clockwise rotation.

24. The idea of a pretensioner is to tighten up any slack in the belt webbing in the event of a crash. Whereas the conventional locking mechanism in a retractor keeps the belt from extending any farther, the pretensioner actually  pulls in on the belt . This force helps move the passenger into the optimum crash position in his or her seat. Pretensioners normally work together with conventional locking mechanisms, not in place of them. There are a number of different pretensioner systems on the market. Some pretensioners pull the entire retractor mechanism backward and some rotate the spool itself. The processor monitors mechanical or electronic motion sensors that respond to the sudden deceleration of an impact. When an impact is detected, the processor activates the pretensioner and then the air bag.

25. Some pretensioners are built around  electric motors  or  solenoids , but the most popular designs today use  pyrotechnics  to pull in the belt webbing. The diagram below shows a representative model. The central element in this pretensioner is a chamber of combustible gas. Inside the chamber, there is a smaller chamber with explosive  igniter  material. This smaller chamber is outfitted with two electrodes, which are wired to the central processor. When the processor detects a collision, it immediately applies an electrical current across the electrodes. The spark from the electrodes ignites the igniter material, which combusts to ignite the gas in the chamber. The burning gas generates a great deal of outward pressure. The pressure pushes on a  piston  resting in the chamber, driving it upward at high speed.

26. Torsion Bars as Load Limiters More advanced load limiters rely on a  torsion bar  in the retractor mechanism. A torsion bar is just a length of metal material that will  twist  when enough force is applied to it. In a load limiter, the torsion bar is secured to the locking mechanism on one end and the rotating spool on the other. In a less severe accident, the torsion bar will hold its shape, and the spool will lock along with the locking mechanism. But when a great deal of force is applied to the webbing (and therefore the spool), the torsion bar will twist slightly. This allows the webbing to extend a little bit farther.

27. Law on Use of Seatbelt: CENTRAL MOTOR VEHICLES RULES 1989 As per the provisions of sub-rule (3) of Rule 138 of the Central Motor Vehicle Rules, 1989 'in a motor vehicle, in which seat-belts have been provided under sub-rule (1) or sub-rule (1A) of rule 125 or rule 125A, as the case may be, It shall be ensured that the driver, and the person seated in the front seat or the persons occupying front facing rear seats, as the case may be, wear the seat belts while the vehicle is in motion. Rule 125 (1) requires the manufacturer of every motor vehicle other than motor cycles and three wheelers of engine capacity not exceeding 500 cc, shall equip every such vehicle with a seat belt for the driver and for the person occupying the front seat. Rule 125 (1A) requires the manufacturer of every motor vehicle that is used for carriage of passengers and their luggage and comprising no more than 8 seats in addition to the driver's seat, shall equip it with a seat belt for a person occupying the front facing rear seat.

28. Collapsible Steering Column The collapsible  steering  column is a type of advanced steering column. It is a part of the  passive safety system  in cars. Most passenger vehicles commonly employ the collapsible version instead of the regular steering column. It is also known as ‘Energy absorbing steering column’. Engineers invented it to reduce the risk of injuries occurring to the driver in case of frontal impacts. The function of a typical steering column is to transfer the motion of steering wheel to ground wheels of the vehicle. It does this through the steering  gearbox  and respective linkages. The earlier generation of vehicles used a solid shaft in the steering column. Even though it served the purpose well, it had a drawback in terms of a safety threat.

29. Based on the several studies on this collapse. In case such a vehicle confronts a severe frontal impact, then the solid rod of steering column hurts the head and rib cage of the driver. Thus, it elevates the severity of injuries. This is the main reason why automotive engineers invented the collapsible-steering columns. They protect the drivers from possible injuries.

30. Constructional details of Collapsible Steering column (Courtesy: Team Chevelle ) Working of Collapsible Steering Column From the structural point of view, the collapsible column has a ‘tube within a tube’ type of structure. It consists of hollow tubes of steel fitted into each other with the help of a special bearing and sealing. When the vehicle meets a frontal impact of a sever intensity, this tube structure collapses and absorbs the energy of impact. Thus, it considerably reduces the risk of damage to the driver’s body.

31. Collapsible Steering Column -3D animation

32. Nowadays, Most manufacturers offer  Collapsible steering-columns  for passenger vehicles as a standard fitment.

33. Tiltable steering wheel Assignment on Tilt steering wheels  allow drivers to adjust the steering wheel height with an up and down motion . Depending on the design, the pivot may be slightly forward which allows for greater movement with less tilt Assignment on Adjustable Steering Wheels

34. About Good Steering System It is a key interface between the Driver and Vehicle It must be light, compact and smooth to run It must also provide the perfect feel of the road surface and help the driver to turn in the straight-ahead position easily and steadily with no hassle. It should have right ergonomic design to make the driver to get comfort driving at all road conditions It should safe guard/ not injure the driver and passenger during the collision

35. Driver Defined Steering System Driver-defined goals are those which are a direct result of driver feedback. This means the driver needs to feel confident in the car and its handling at all times, and this directly relates to the design of the steering system. The driver is given a large amount of their road information from the forces in the steering wheel, and so the force path between the wheels and the steering wheel must be sufficient enough that any outside interference is limited. A few goals defined by the driver are shown below: - Steering wheel must have 110° to each side to guarantee maximum wheel turn without the driver removing their hands from the wheel - The force required to steer must equal to or less than the steering force - The steering column must utilize two universal joints to provide consistent feedback from the road - The steering rack must be mounted at the ends to reduce compliance in the system. Recentering of the steering / wheels

36. Steering system - conceptualized

37. Parallel Steering Ackerman’s Steering

38. Tiltable Steering Wheel and adjustable steering Column

39. Steering Column Universal Joints: Properties of U-Joints Unless the steering wheel axis is directly aligned with the pinion axis of the steering rack, some sort of mechanical joint is needed to angle the rotational force along a new axis. The conventional method of transferring force through such an angle is by the use of either a single universal joint (or u-joint for short), double universal joint, or two universal joints. The difference between the later two methods are where they are constrained, resulting in separate output axis locations. Universal joints must be mounted properly to function: the rotational shafts must be constrained radially, but free to rotate, therefore calling for a bearing.

40. Preference of two universal joints configuration . First , due to driver preferences, the more vertical steering wheel angle requires a greater angle between the upper steering axis and the steering pinion axis, which can only be satisfied with two universal joints. Secondly, a double universal joint requires a rotational constraint much higher up the steering axis. Using the two universal joints allows for the attachment point between the lower u-joint, allows the steering rack to act as the radial constraint, and provides optimal feedback from the road through the steering column. The actual steering wheel placement will require two of these universal joints, which benefits the design by providing a greater range for the steering wheel angle, but at the same time adds weight and complexity to the system. However, because the steering rack will be closer to the driver than previous years, it requires a greater angle range to avoid a steering wheel that is mounted too flat. The most important benefit of using two u-joints is that the second u-joint counteracts any negative effects which the first one might have with driver feel.

41. Air Bags The purpose of an airbag is to reduce injury by either cushioning the occupants contact with the interior of the vehicle or preventing contact completely. An airbag is a large nylon bag which inflates and deflates very rapidly in the event of a severe crash.  The driver’s airbag is housed in the centre pad of the steering wheel, and the passenger’s airbag, where fitted, in the upper left of the dash. Other airbags could also be found in the lower dash, seats, seatbelts, roof pillars and roof structures. Airbags (frontal airbags, side bags, window bags) serve to prevent or reduce the impact of the occupant against interior vehicle components (steering wheel, instrument panel, doors, windows, roof pillars).

42. Airbag Systems 1 Belt tightener 2 Front airbag for passenger 3 Front airbag for driver 4 ECU

43. How airbags work The airbag’s deployment is controlled by sensors that detect the occurrence and severity of a crash. When the airbag controller determines that the airbag should be deployed, the system triggers an inflator unit that burns chemicals very rapidly to produce large volumes of inert gas to inflate the bag. As the bag inflates, it splits open the covers on the wheel / dash / pillar / seat etc , as it emerges.  In the case of a front airbag, as the occupant’s head and upper body moves forward and strikes the inflated bag, the bag starts deflating through vent holes in its base to cushion the decelerating head’s forward movement.

44. The whole process of inflating and deflating occurs within about 100 milliseconds - about the same time as the blink-of-an-eye.  The process is so fast that the occupant is often unaware that the airbag has deployed. Side and curtain airbags are sometimes slightly slower to deflate as the types of crash they are designed to protect against are different to frontal impacts. In the process of deploying, considerable smoke, dust and noise is produced. This is normal. 

45. When do they deploy? For the driver or passenger airbags to deploy in a crash, all the following minimum criteria must be met: The vehicle must be travelling at more than about 25km/h.  The angle of impact is within around thirty degrees either side of the car’s centre line (around 60 degrees in total).  The deceleration forces produced are at least equal to those produced when the car collides head-on with an immovable barrier at approximately 25km/h.  Note: Front airbags will not be deployed in the event of a side or rear end collision or in a rollover as they would provide no additional protection. 

46. Other types of airbags Dual stage airbags are a smarter generation of airbags that optimise the level of airbag deployment to suit the severity of the crash.  Knee bags are fitted to some cars to protect lower limbs from injuries caused by impact with dash panels. Some manufacturers provide seatbelt airbags to reduce seatbelt induced injuries

47. Air Bags, Electronic System for activating air bags: Function: The function of front airbags is to protect the driver and the front passenger against head and chest injuries in a vehicle impact with a solid obstacle at speeds of up to 60 km/h. In a frontal impact between two vehicles, the front airbags afford protection at relative speeds of up to 100 km/h.

48. A belt tightener alone cannot prevent the head from hitting the steering wheel in response to severe impact. In order to fulfill this function, depending on the installation location, vehicle type and structure-deformation response, airbag shave different filling capacities and pressure build-up sequences adapted to the specific vehicle conditions. In a few vehicle types, front airbags also operate in conjunction with "inflatable knee pads", which safeguard the "ride down benefit", i.e. the speed decrease of the occupants together with the speed decrease of the passenger cell. This ensures the rotational forward motion of the upper body and head which is actually needed for optimal airbag protection, and is of particular benefit in countries where seat- belt usage is not mandatory.

49. Concept of Airbag Working – 3D Animation

50. Soon Hetrick came up with a prototype and in 1952 was granted the first patent for what would become the predecessor to the airbag. The original idea of using compressed air turned out to be not workable because the air cylinder itself represented a risk. Furthermore, at the time, car manufacturers were more interested in enticing customers with huge engines and tail fins than airbags. But as the slaughter on highways continued unabated, carmakers realized that something had to be done.  They began to install seat belts, but most drivers didn’t use them.  Air bags began to be seriously considered but how could they be inflated safely within a few milliseconds of impact without using compressed gases? The answer would be found in a fascinating chemical called sodium azide , 2NaN3. When this substance is ignited by a spark it releases nitrogen gas which can instantly inflate an airbag.  2NaN 3 => fire => Na + 3N 2

51. The problem, however, is that the reaction also forms sodium metal which reacts with moisture to generate sodium hydroxide, a highly corrosive substance. A burst airbag could wreak havoc. Chemical ingenuity, however, came to the fore.  If potassium nitrate and silicon dioxide were also included with the sodium azide , the only products that would form in addition to nitrogen would be potassium silicate and sodium silicate. Both of these are inert, harmless substances further problem that needs to be addressed is Sodium azide is more toxic than cyanide.  If sodium azide is released it can react with water to form hydrazoic acid which is not only toxic but is highly explosive.  Sodium azide can also react with metals such as copper or lead form explosive copper or lead azides .  Addition of calcium sulphate Recently technology is addition of Guanidine Nitrate Sodium azide

52. Impact detection: Optimal occupant protection against the effects of frontal, offset, oblique or pole impact is obtained through the precisely coordinated interplay of electrically fired pyrotechnical front airbags and seat-belt tighteners . To maximize the effect of both protective devices, they are activated with optimized time response by a common ECU (triggering unit) installed in the passenger cell. The ECU's deceleration calculations are based on data from one or two electronic acceleration sensors used to monitor the decelerative forces that accompany an impact.

53. The impact must also be analyzed. A hammer blow in the workshop, gentle pushing, driving over a curbstone or a pothole should not trigger the airbag. With this end in mind, the sensor signals are processed in digital analysis algorithms whose sensitivity parameters have been optimized with the aid of crash-data simulations. Depending on the impact type, the first trigger threshold is reached within 5...60 ms. the acceleration characteristics, which are influenced for instance by the vehicle equipment and the body's deformation performance, are different for each vehicle. They determine the setting parameters which are of crucial importance for the sensitivity in the analysis algorithm (computing process) and, in the end, for airbag and belt- tightener firing.

54. Depending on the vehicle-manufacturer's production concept, the trigger parameters and the extent of vehicle equipment can also be programmed into the ECU at the end of the assembly line ("end-of-line programming" or " EoL programming"). In order to prevent injuries caused by airbags or fatalities to "out-of-position" occupants or to small children in Re board child seats, it is essential that the front airbags are triggered and inflated in accordance with the particular situations. The following improvement measures are available for this purpose 1. Deactivation switches. These switches can be used to deactivate the driver or passenger airbag. The airbag function states are indicated by special lamps.

55. In the India, where there have been approx. 130 fatalities caused by airbags, attempts are being made to reduce aggressive inflation by introducing "depowered airbags". These are airbags whose gas-inflator power has been reduced by 20...30 %, which itself reduces the inflation speed, the inflation severity and the risk of injury to "out-of-position" occupants. "Depowered airbags" can thus be depressed more easily by large and heavy occupants, i.e. they have a reduced energy-absorption capacity. It is therefore essential above all with regard to the possibility of severe frontal impacts for the occupants to fasten their seatbelts. "Intelligent airbag systems". The introduction of improved sensing functions and control options for the airbag inflation process, with the accompanying improvement of the protective effect, is intended to result in a step-by-step reduction in the risk of injury.

56. Components: Acceleration sensors: Acceleration sensors for impact detection are integrated directly in the ECU (belt tightener , front airbag)and mounted at selected points on the left and right body sides (side airbag) or in the vehicle's front-end deformation area (upfront sensors for "intelligent airbag systems"). The precision of these sensors is crucial in saving lives. They are generally surface-micromechanical sensors consisting of fixed and moving finger structures and spring pins. A special process is used to incorporate the "spring/mass system" on the surface of a silicon wafer. Since the sensors only have low working capacitance (≈1 pF), it is necessary to accommodate the evaluation electronics in the same housing so as to avoid stray-capacitance and other forms of interference.

57. Gas inflators: The pyrotechnical propellant charges of the gas inflators for generating the airbag inflation gas (mainly nitrogen) and for actuating belt tighteners are activated by an electrically operated f iring element. The gas inflator in question inflates the airbag with nitrogen. The driver's airbag integrated in the steering-wheel hub (volume 35...67 l) or the passenger airbag installed in the glove box (70...150 l) is inflated approx. 30 ms after firing.

58. Bumper design for safety Bumper is a component front and rear projecting portion for a car. Looking at today's complex designs of car bumpers, it is hard to believe that in the very beginning they served only as a subtle decoration of the vehicle, providing no protection at the time of a collision. As early as 1910, car manufacturers began using strips of steel attached to the rear and front of the vehicle. Vehicles at the time were developing minimal speeds, and the bumper was only to prevent costly repairs to the car in the event of a possible contact with an obstacle. In addition to sheet steel, many bumpers are manufactured using fiber- reinforced plastics and aluminum sections.

59. As the automotive industry grew, these designs became heavier and more decorative to take the shape of a "slimmed down" chrome piece in the 1960s. The first plastic bumpers were introduced in the late 1960s and early 1970s by the General Motors brand. They were to absorb the energy of a low-speed collision and not be permanently damaged in the process. Today, modern bumpers are integrated into the body of the car and conceal many different functions. Their primary task is to ensure safety – not only for vehicle passengers, but especially for pedestrians

60. CAR BUMPER – NOT JUST PLASTIC Modern car bumpers must have a properly resilient design that acts like a shock absorber in a moment of impact. Their main element is a steel structural section, the so-called bumper beam. This reinforcement is mounted horizontally on the front and rear panel of a car and carries the heaviest load during a crash. It is covered from the outside with a flexible EPP foam bumper padding. In the event of an accident, the bumper padding dissipates kinetic energy and reduces noise, even during everyday driving. This element is usually given a profiled shape that corresponds to the geometry of the outermost part of the bumper, which is injection moulded cover made of thermoplastic materials such as polypropylene (PP) or polycarbonate (PC). Nowadays, various electronic elements such as parking sensors, reversing camera, fog lights, and sometimes additional air intakes are additionally built into the bumper's construction.

61. SAFETY BUMPER – FUNCTIONS The primary function of a car bumper is to offset the effects of a possible collision, both for passengers and pedestrians. Designers and manufacturers in the automotive industry are constantly looking for the right design and material solutions to balance stiffness and flexibility with hardness and strength. Generally, the stronger and tougher the bumper design, the better it protects the structure of the car; however, it can be dangerous to the other vehicle and pedestrians. Considering the fact that most often bumpers break during high-speed crashes, they serve little protective function for the vehicle passengers in such situations. The main crash force is taken up by the reinforced frame and the control crush zones, while the bumper is only the first barrier during contact. However, this initial dampening is to give the airbags time to deploy.

62. A car bumper nowadays mainly serves as protection in case of low-speed collisions. Though, the shape and curvature of the car's front panel and the design of the bonnet are primarily intended to minimise pedestrian injuries in the event of a collision Plastics have become the preferred materials for external impact strips, trim, skirts and spoilers, and particularly for those components whose purpose is to improve the aerodynamic characteristics of the vehicle. Criteria used in the selection of the proper material are flexibility, high-temperature shape retention, and coefficient of linear expansion, notched-bar toughness, resistance to scratches, and resistance to chemicals, surface quality and paint ability.

63. Bumpers 1. Shock-absorber system, 2 Energy-absorbing PUR-foam systems

64. Material for Bumpers The most important role in terms of pedestrian safety is played by the flexible bumper padding, which acts as a shock absorber. In this area, foam materials are often used. Although alternative materials are being sought, these are still niche solutions. Research has been conducted, for example, on a bumper made of oak cork, which was to be designed especially for cars with a high bonnet, or a crash absorber with special rotors to dissipate kinetic energy. So far, EPP foam has proven to be the best material for bumper padding. This material combines high mechanical strength with high elasticity to effectively dampen impact energy while being the most pedestrian friendly.

65. The wide range of possibilities offered by the foamed polypropylene EPP processed in Knauf Industries' plants allow for easy adaptation of all the properties of foam damping elements, bumper paddings and grille covers made of it – from its low weight to its mechanical strength and elasticity, to its noise damping and even thermal insulation properties. EPP does not crumble or disintegrate on impact, but deforms in the short term and immediately returns to its original shape. Thanks to modern software and 3D visualization techniques it is possible to work out the best solution of shock absorbing elements, which will fully meet the requirements of a given project, both in terms of use and aesthetics