Tire Background & Tire Failure Evaluations

Transcription

1 Tire Background & Tire Failure Evaluations Brian A. Darr, P.E.

2 Overview 1. Background 2. Why Brief tire history 3. Tire Construction - Bias vs. Radial 4. How to read a tire sidewall 5. Steps to a tread and belt separation 6. Why tread and belt separations take place

3 Speaker Bio BSME 1996, The Ohio State University ~5.5 years experience at tire company Design, develop, test and manufacture tires ~6.5 years experience at OEM R&D Department Tire project leader for all N.A. developed vehicles Visited tire manufacturing plants and test sites around the world ~ 6 years as a Forensic Engineer Vehicle accident reconstruction Tire failure analysis Inspected 1000 s of tires Testified and qualified as tire expert in Federal courts P.E. certification in numerous states

4 A Short History of Pneumatic Tires The Pneumatic tire was invented by Dr. Thompson cir.1840 s. Used on toy carts and wagons for his daughter. Rubber Curing Invented Mr. Goodyear-1840 s Tire Reinvented by Mr. Dunlop cir.1880 s. First large-scale use on bicycles. First used on motor vehicle in 1895 by the Michelin Brothers. Beaded tires with drop center rims-cir First modern radial tire patented in 1947 and produced in 1948 by Michelin.

5 A Short History, cont.-other Notable Developments Dual Tire Mounts-cir.1920 s Michelin Tubeless tires (butyl)-1930 s-1950 s BFG and Esso. Traction Tread Rubbers-1950 s Dunlop Halobutyl Rubber Innerliner s s onward. Antidegradent s-1950 s onward. Non-Wicking Cables-1970 s Wedges and Cushions-1960 s-michelin Nylon Cap Plies-1960 s-pirelli - Michelin developed first radial tire in 1948, came to USA in 1970 s - In Early 1980 s, all cars sold in USA came with radial tires

6 Bias vs. Radial construction - Bias construction refers to direction of ply: Bias ply = cross ply - Modern radial tires typically have at least 12 different rubber compounds and 6 structural components

7 Tire Construction larger view

8 Bias vs. Radial construction benefits - Radial benefits include: - Larger footprint = better traction, handling, tread wear. - Less rigid carcass = better ride comfort and NVH properties - Reduced Rolling National resistance Association = better fuel of economy Subrogation Professionals

9 Tire vs. Tyre Why the difference? - Tire = American English - Tyre = English from Great Britain

10 Tire Sidewall markings and meaning UTQGS - Many markings National the sidewall Association of a tire of Subrogation Professionals

11 Tire Pressures on the Tire sidewall Maximum inflation pressures 1. Standard load tires 1. 36, 44 or 51 psi 2. Extra load or reinforced tires or 50 psi - What pressure to set your tires on your vehicle??

12 Tire Placard

13 Tire Sidewall markings and meaning - Most tires have National 2 body Association plies,2 steel of belts Subrogation and 1 nylon Professionals ply in tread area

14 Tire Sidewall markings and meaning - P-metric and Euro metric are most popular passenger car tire sizing in USA - Light truck metric National and high Association flotation are of most Subrogation popular light Professionals truck tire sizing

15 Tire Sidewall markings and meaning Example Tires may look the same but without the same description/option code (middle 4 digits of DOT) National they are Association not. of Subrogation Professionals

16 Tire Sidewall markings and meaning Z rated tires - Common speed symbols for passenger car tires are T, H and V - Inflation pressure listed on tire sidewall is Maximum tire inflation pressure - Vehicle tire placard should always be used to set vehicle tire pressure.

17 Tire Sidewall markings and meaning Uniform Tire Quality Grading (UTQG) - Recommend B or better temperature grade and A or better traction - Treadwear grade National is marketing Association tool and of not Subrogation completely Professionals accurate

18 Types of Claimed Automotive Failures Brake Failure Steering / Suspension Failure Wheel / Stud Failures Tire Failures Unexpected Acceleration Oil / Fuel Contamination Water Induction Into Engine Non or Unexpected Air Bag Deployment Non-Functioning Seatbelts

19 Why Tread-Belt Separations? The belt edge is the area where stiff meets flexible. This creates a stress concentration. The rubber between the belts at the edge sees two major stresses-shear and tension. The shear comes from the movement of the belt wires due to panographing, most of which occurs at the beginning of the footprint. The tension comes from the centrifugal forces. Proper countermeasures control separations. These countermeasures have been developed and proven over 60 years but involve some expensive materials. The tread-belt sep is probably the most dangerous failure mode of a tire.

20 The Design Goal Of a Tire is To Wear Out Before the Tire Structure Fails

21 The Tread-Belt Sep.-Macro View The Tire Tread-Belt Separation is a Fatigue Failure and progresses in three distinct steps like most other materials. This is the same terminology as for metal fatigue failures. Step 1-The initial Stage-The tire is used for many miles and years. A good tire will wear out during this stage with out progressing to step two. Good tires last six or more years. Defective tires can start failing after one year or less. Step 2-The Crack Initiation and Propagation Stage- A crack forms at the edge of the number two belt and grows around the tire and the across the tire. This stage typically lasts miles. Some aged spare tires last only 20 miles after being put on the vehicle. This failure is characterized by chafe and polish, bare cable and the crescent shaped zone. In a small number of cases there may be rapid wear. Step 3-The Catastrophic Failure-The Tread and outer belt physically separate from the tire. This stage lasts typically about feet and the perturbations to vehicle stability cause the accident. The tire caused noise,vibration and drag during the separation and loss of friction with the road after the tread and outer belt leave the carcass.

22 Macro View-Step 3

23 Tread-Belt Separations-The Micro View Separations start at the edge of the top belt. This is the beginning of step two- the crack initiation and propagation stage. Separations start usually at an anomaly-either at the end of the wire or some defect. Separations grow around the end of the wires and cables forming a cylindrical cracks. This has been called socketing Cracks link up to big cracks that proceed around the tire forming chafe and polish or bare wires.

24 Tire cross section showing belt cables

25 Step 2: Crack Initiation & Propagation

26 Manufacturing Defects Poor Adhesion-rubber to rubber Poor Adhesion-rubber to wire Poor Component placement Poor Curing Poor aging properties Foreign Material Others (100 s)

27 Rubber to Rubber Adhesion Defect Pattern Marks

28 Rubber embrittlement due to aging

29 Chafe And Polish on the Tread and Outer Belt The cylindrical cracks link up and progress around the tire circumference. This leaves the characteristic chafe and polish between the belt edges at the edge.

30 Close Up of Chafe and Polish on the Tread Piece Edge of Number Two Belt

31 Chafe and Polish on the Tread-Belt Piece

32 Chafe and Polish on the Carcass The separation usually progresses completely around the tire on one or both shoulders.

33 Close Up of Chafe and Polish on The Carcass This effect is comparable to beach marks in metal fatigue failures.

34 Belt Endurance Test This test shows the growth of the crescent shaped zone in the lab.

35 The Crescent Shaped Zone (CSZ) Forms When the Separation Starts Progressing Laterally Across The Tire

36 The Two Failures Every failure (in history) starts small and grows. Every separation failure has two completely different failures. The first separation failure occurs during Step two and is a slow, progressive fatigue failure over hundreds of miles. It produces the chafe and polish and the crescent shaped zone The second separation occurs in the rapid tearing in step three. It is an overstress failure and occurs over milliseconds and produces the herringbone pattern. This failure occurs mainly in the center of the tread belt.

37 Herringbone Pattern This pattern results from the final tearing of the tread and belt piece from the carcass. This occurs during the catastrophic phase.

38 The Tire Shoulder- Where the Action Is The shoulder contains most of the separation countermeasures. It is where the separation initiates.

39 Cut Tire Analysis - Separation Initiation

40 CTA-Separation Progression

41 Localized fast treadwear

42 Cross section with internal separations

43 Tread separations

44 Why Tread-Belt Separations? The belt edge is the area where stiff meets flexible. This creates a stress concentration. The rubber between the belts at the edge sees two major stresses-shear and tension. The shear comes from the movement of the belt wires due to panographing, most of which occurs at the beginning of the footprint. The tension comes from the centrifugal forces. Proper countermeasures control separations. These countermeasures have been developed and proven over 60 years but involve some expensive materials. The tread-belt sep is probably the most dangerous failure mode of a tire.

45 Radial Tire Separation Countermeasures Belt Offset Belt Cushion Belt Wedge or Belt Edge Gum Strip Nylon Cap Ply The Undertread or Insulator Anti Aging-The Inner-liner Anti-Aging-The Skim Stock Rubber Good Adhesion Between Parts Other

46 Tire Construction larger view

47 Other types of Tire Failures Running Underinflated Improper Vulcanization

48 Bead out condition

49 Tire Puncture & Repair Puncture Bad Patch

50 Typical Impact Failures

51 Sidewall punchout

52 Misuse and abuse Sidewall cut Tread cut

53 Summary 1. Brief tire history 2. Tire Construction - Bias vs. Radial 3. How to read a tire sidewall 4. Steps to a tread and belt separation 5. Why tread and belt separations take place

54 May all scrap tires end up this cool

55 Michelin man inspiration

56 Thank You Brian A. Darr P.E.