BUMPER SYSTEMS-An Introduction

Design FactorsTo meet OEMs Standard on Energy absorption .Manufacturability.Cost.Weight.Re-cyclability of materials (advantage for Steel).Bumper Systems in Common use Metal face-bar.Plastic fascia and reinforcing beam.Plastic fascia, reinforcing beam and mechanical energy absorbers.Plastic fascia, reinforcing beam and foam or honeycomb energy absorber.Plastic fascia, reinforcing beam, foam, and mechanical energy absorbers.

Metal face-barSingle metallic bumper that decorates the front or rear end of a vehicle and acts as the primary energy absorber in a collision.

Cross-section of Metal face-bar is shown below :

Plastic fascia and reinforcing beam Plastic fascia and a reinforcing beam that is fastened directly to the vehicle frame. Primarily used for rear bumper systems in passenger cars as the crash requirements are less severe (i.e less need for mechanical energy absorbers and foam).

Plastic fascia, reinforcing beam and Energy Absorption Systems Most common type of bumper system in North America.

Used on both front and rear bumper systems.

Reinforcing beam always absorbs a significant amount of energy while additional energy can be absorbed by Mechanical energy absorbers, Foam or Honeycomb or both.

Bumper ComponentsFascia.Energy absorbers.Face-bar.Reinforcing beam.

1) FasciaDesign must be aerodynamic to control the flow of the air around the car and the amount of air entering the engine compartment.Design must be aesthetically pleasing to the consumer.Easy to manufacture and light in weight.Styled with many curves and ridges to distinguish vehicles from competing models.

Bumper of Nissan TeanaBumper of Renault Velastis

Energy absorbersDesigned to absorb a portion of the kinetic energy from a vehicle collision.Very effective in a low speed impact, where the bumper springs back to its original position.Types include Foam, Honeycomb and Mechanical devices.Most front bumper systems use mechanical energy absorbers due to higher energy absorption requirements.Foam energy absorber are capable of absorbing several times the energy absorbed by mechanical energy absorbers.Foam Front Impact Absorber

Face-barStamped from steel with plastic or stainless steel trim to dress them up.After stamping, steel face-bars are chrome plated or painted for appearance and corrosion protection reasons.Higher strength steels are being investigated for face-bars to reduce the thickness and weight.Chevrolet Front Bumper Face BarReinforcing beamHelp to absorb the kinetic energy from collision and provide protection to the rest of the vehicle.Design considerations for reinforcing beams include strength, manufacturability, weight, re-cyclability and cost.Roll formed beams are the most common but hot stamped beams have the lowest average mass of all steel bumper systems and are becoming more popular as a result.Zinc coating on these products provides excellent corrosion protection.Most common cross section for roll formed beams is B-section and similarly for hot stamped beams are box and hat sections.Volkswagen Jetta hot stamped bumper beam

Types of bumper beamsProduced by cold stamping, hot forming or roll forming processes.Tensile strength of cold stamped and roll formed beams ranges from 900-1500 MPa (130-218 ksi).Tensile strength of hot stamped beams, after heating and quenching, ranges from 1200-1400 MPa (174-203 ksi).Protected from corrosion by zinc coatings, aluminum coatings or electro-coatings.Ford Taurus/Mercury Sable roll formed bumper beam1) Steel Reinforcing Beams

Cold stamped from low-carbon and high-strength steels.Tensile strengths from 350-500 MPa (50-72 ksi) and an elastic modulus of 207,000 MPa (30,000 ksi).Either chrome plated or painted for corrosion protection.Ford F150 Pick-up cold stamped bumper beam2) Steel Face-bars3) Plastic Reinforcing BeamsTwo types of plastic beams glass reinforced plastic or un-reinforced plastic.Examples of glass reinforced plastic beams Polypropylene - (compression molded), Unsaturated polyester - (compression molded) and Polyurethane - (reaction injection molded).Examples of un-reinforced plastic beams Polycarbonate/Poly-Butylene - (injection or blow molded), Polyethylene - (blow molded) and Polypropylene - (blow molded).Tensile strengths up to 275 MPa (40 ksi) and flexural moduli up to 15,000 MPa (2,200 ksi).

Made by stretch or press forming (mostly from 6000 and 7000 Aluminum series).After forming and heat treating, the beams have tensile strengths up to 550 MPa (80 ksi) and an elastic modulus of 69,000 MPa (10,000 ksi).3) Aluminum Reinforcing BeamsCOMMON REINFORCING BEAM CROSS SECTIONS

TESTS CONDUCTED ON BUMPER BY NISSAN (As Per NDS)STATICDURABILITYCOATINGTESTS CONDUCTED ON BUMPERSTATICCOATINGDURABILITYRigidity Test1) Vibration Test2) Thermal Cycle Test3) Chemical Resistance Test4) Weather ability Test5) Ball Drop Impact Test6) Scratch Resistance Test7) Graining Scratch TestCoating Requirements

Rigidity TestA load shall be applied to the top, the front (rear), the side, bottom and the lower surface (apron) of the part using a device as shown on the right. Test temperature: 20 5C.Static TestsDurability Tests1) Vibration TestThe part shall be vibrated in 1) the vertical direction, 2) the lateral direction and 3) the longitudinal direction subsequently.

Frequency: 30 Hz, Acceleration: 29.4 m/s2, Test cycles: 1062) Thermal Cycle TestMount the test pieces as installed in the vehicle on the fixtures, place the fixtures in the temperature controlled chamber or the temperature and humidity controlled chamber and conduct the specified high heat test for the specified time.After heating for the specified time, check the test pieces as per EVALUATION ITEMS at the test temperature. If not possible check within 3 minutes after taken out of the chamber.At the completion of assessment in step (2), allow the test pieces to stand for more than 30 minutes at room temperature.Test Procedure - NES M0132, Method-2, Class- 1

Test ConditionsNote : 90C for Class A, 80C for Class B is to be used.Check again EVALUATION ITEMS.After that, place the test piece in sequence in the constant temperature controlled or temperature and humidity controlled chambers set to the specified heat cycle condition and allow it to stand for the specified time respectively.At the completion of the specified thermal test cycles, allow the test pieces to stand for more than 30 minutes at room temperature, than check items as per EVALUATION ITEMS.Evaluation ItemsNormal operation refers to:(a) hitting with hand, pushing or pulling by hand, scratching with fingernails.(b) kicking lightly by foot, placing objects on the part, or pushing.(c) leaning or sitting on it.

NES M0132, Method-2, Class- 13) Chemical Resistance Test(1) Place 0.3 to 0.5 ml of the chemical, with a syringe, onto the surface of the test piece. Expose the test piece to the chemical at the specified temperature for the time specified in Table below.(2) Wipe the surface of the test piece using a new piece of gauze. (3) Applicable only to uncoated area.Evaluate the test piece for abnormalities listed below.Dissolving (5) Blooming (9) Softening (13) Uneven surfaces (17) Deformation(2) Cloudiness (6) Sticky surfaces (10) Hardening (14) Breakage(3) Stains (7) Contamination (11) Swelling (15) Cracking (4) Discoloration (8) Glossiness (12) Thinning (16) ShrinkageNES M0133, Method-3

P.S

Room temperature conditions: The test room shall be maintained at the standard temperature and humidity conditions as per JIS Z-8703 (Standard atmospheric conditions for testing) Class 5 (Temperature: 205C) and Class 20 (Relative Humidity: 6520%), respectively.

Standard conditions: The temperature and humidity shall be as per JIS Z-8703 (Standard atmospheric conditions for testing) Class 2 (Temperature: 202C) and Class 2 (Relative Humidity: 652%), respectively.Room temperature and Maximum temperaturesTest MethodTest Conditions : 24 HrRemarks : Drip volume 0.3 to 0.5 m4) Weather-ability Testi) Sunshine Weather-O-Meter TestSunshine Weather-O-Meter: 2,000 h, Black panel temperature 63 3C with water spraying.Applicable only to the PP material with no coating.NES M0135, Method-2, Class-1

Test Equipment Specification and Conditions

Equipmenti). Light source Lamp consists of formed arc between carbon electrodes in open air. Or, radiation reaches to test sample through filter. Specification of light source and filter shall conform to Table 2.ii). Testing tankThe testing tank is equipped with a frame for mounting of the test piece and which rotates around the light source, a fan device for temperature control, and a device for program control of the test cycle.iii). Relative humidity regulating deviceThe relative humidity of the air which flows over the test piece is measured by a device which is mounted in such a way that it is shielded from the light of the test tank's internal lamp.iv). Spray deviceDeionized water of 6 to 8 pH and 105 cm is used for the spray.Ion exchange, reverse osmosis processing, and the like shall be used to achieve the required water quality.v). Test piece holderEither an open-type frame which exposes the rear surface of the test piece or an item which lines the test piece shall be used as the test piece holder. Said holder shall be manufactured from an alloy of aluminum, stainless steel, or some other metal which does not oxidize.Test Piece should conform to the said dimensions.Unit mm

Operationsi) Preparation of the test piecesThe sample name, test start and proposed finish dates, the control number, and any other requiredinformation shall be indicated on the rear of each test piece in such a way that they will not be removed during testing.ii) Test piece mountingThe test pieces shall be placed in holders in such a way that they are not subjected to stress.iii) Exposure to the light sourceBefore the test piece holder is assembled to the tester, it shall be confirmed that said tester can operate in accordance with the required conditions as set forth in Table above, and these conditions shall be maintained during exposure. Further, when the test sample rack is a straight type (inclined types excluded), in order to ensure that all samples are exposed for the same duration, in principle, switch the positions of the test samples once a week.iv) Measurement of the degree of radiation exposureThe radiant flux density meter shall be mounted in such a way that the irradiance of the test piece's exposed surface can be indicated. Generally, exposure times shall be determined based on the selected wavelength range and shall be indicated in units of spectral radiant energy per unit surface area of the exposed surface (W/m2).v) Removal of test piecesAfter the required period of time, the test pieces shall be removed and evaluation shall be carried out in accordance with 7.5.ii) Natural exposure Test24 months in Okinawa.Consult with Nissan design section in charge whether it is necessary to conduct the natural exposure test.

5) Ball Drop Impact TestNES M0134 VR0-2 (Method-2)TEST CONDITIONS

Applicable Location : Front part of vehicle.Applicable Parts Examples : Front bumper, Front spoiler, Front mudguard, Rear mudguard, Fillet protector, Inner fender hood, Hood.Temperature : Room temperature or (-302C) (-402C)Weight : Nominal (535g)Drop Height (cm) : 100 50 (Extremely Cold Regions (-40 2), Other (-30 2))TEST PROCEDURE

(1) Mount the test piece on the stand in vehicle position that is in a position similar to the actual condition asshown in below Figure. Position the cushioning material. Test conditions on the weakest portion of the test piece obtained from impact test on various points yielded from previous tests in advance.Allow the steel ball to free fall and impact the test piece. Determine the strength guideline for the position and perform the specified test.

(2) For the low temperature falling ball impact test, in principle, place the test piece in the low temperaturechamber and let it stand for a predetermined time, and then perform a test. However, after its removalfrom the chamber, the impact test shall be performed within 30 seconds.

Test set-up for Ball Drop Impact Test.RESULT :Record the drop height in cm as the measured value of impact strength. The impact location shall also be recorded.Record the temperature and humidity of the test location.

Note : Drop height is the distance from the bottom of the steel ball to the top of the test piece, and ifcushioning material is to be used, it will be the top of the cushioning material.

FMVSS Bumper Regulation Standards Examples for Your Reference