Contents
DISCLAIMER 2
EXECUTIVE SUMMARY 8
1.0. INTRODUCTION 11
2.0. METHODOLOGY 16
2.1. Michelin LTDE Test 18
2.2. Continental P-END Test 20
2.3. Oven Aging 21
2.4. Air Permeability 21
2.5. Roadwheel Testing 21
2.6. Tires Studied 21
3.0. RESULTS 29
3.1. Pearson R, Product-Moment Correlations 29
3.1.1. Shore A Hardness 29
3.1.2. Indentation Modulus 30
3.1.3. Tensile and Elongation of Skim-Coat Compound 31
3.1.4. Tensile and Elongation of Wedge Compound 32
3.1.5. Micro-DeMattia Flex Test 33
3.1.6. Crosslink Density and Distribution 33
3.1.7. Peel Adhesion 34
3.1.8. Two-Ply Laminate Fatigue Test 35
3.1.9. Shearography 36
3.1.10. Fixed Oxygen Level 37
3.2. Analysis of Variance and Linear Regression Analysis 38
3.2.1. Shore A Hardness 38
3.2.2. Indentation Modulus 39
3.2.3. Tensile and Elongation of Skim-Coat Compound 46
3.2.4. Tensile and Elongation of Wedge Compound 60
3.2.5. Micro-DeMattia Flex Test 74
3.2.6. Crosslink Density and Distribution 74
3.2.7. Peel Adhesion 75
3.2.8. Two-Ply Laminate Fatigue Test 84
3.2.9. Shearography 84
3.2.10. Fixed Oxygen Level 87
3.2.11. Oxygen Depletion During Oven Aging 89
3.2.12. Roadwheel Testing: Stepped-up Load to Structural Failure After Oven Aging 89
4.0. SUMMARY AND CONCLUSIONS 95
Appendix 1. Test Descriptions 103
Appendix 2. Indentation Modulus Profiles for the Wedge Compounds 112
Appendix 3. Indentation Modulus Profiles of Tires by Type 115
5.0. REFERENCES 146
Table 1. NHTSA Safety-Related Tire Defect and Compliance Campaigns Since 1966 13
Table 2. Tire Models Selected for Testing 16
Table 3. Test Parameters - Long-Term Durability Endurance Test 19
Table 4. Material Properties Evaluated 20
Table 5. Tires and Tests Used in Phase 2 Aging Study 22
Table 6. Terms for Strength of Correlation Used 29
Table 7. Correlations of Shore A Hardness to Time 30
Table 8. Correlations of Indentation Modulus to Time 31
Table 9. Correlations of Tensile and Elongation for Skim-Coat Compound 32
Table 10. Correlations of Tensile and Elongation for Wedge Compound 33
Table 11. Correlations of Micro-DeMattia Flex Fatigue for Wedge Compound 33
Table 12. Correlation of Crosslink Density and Distribution 34
Table 13. Correlation of Peel Adhesion for Skim and Wedge Compounds 35
Table 14. Correlation of Two-Ply Fatigue Parameters 36
Table 15. Correlation of Shearography Separation Area 37
Table 16. Correlations of Fixed Oxygen Level 37
Table 17. Terms Used in Linear Regression Model 38
Table 18. ANOVA and Linear Regression Terms for Shore A Hardness 39
Table 19. Components Measured by Indentation Modulus 41
Table 20. ANOVA and Linear Regression Terms for Indentation Modulus 41
Table 21. ANOVA and Linear Regression Terms for Modulus, Tensile, and Elongation of Skim-Coat Compound 47
Table 22. Ahagon Slopes for Skim-Coat Compound 56
Table 23. ANOVA and Linear Regression Terms for Modulus, Tensile, and Elongation of Wedge Compound 61
Table 24. Ahagon Slopes for Wedge Compound 70
Table 25. ANOVA and Regression of Micro-DeMattia Flex Fatigue for Wedge Compound 74
Table 26. ANOVA and Regression for Peel Adhesion of Skim-Coat Compound 76
Table 27. ANOVA and Regression for Peel Adhesion of Wedge Compound 80
Table 28. Linear Regression Coefficients: Shearography mm2 Separation 87
Table 29. ANOVA and Linear Regression of Percent Fixed Oxygen Level for Skim-Coat, Wedge and Innermost Tread Compounds 88
Table 30. Stepped-Up Load Roadwheel Test Conditions 90
Table 31. Material and Chemical Tests and Tire Components Studied 96
Table 32. Approximate Equivalent Average Indentation Modulus for Laboratory-Aged Tires and Tires in Phoenix Service 98
Table 33. Approximate Equivalent Average Elongation and Modulus for Laboratory-Aged Tires and Tires in Phoenix Service 99
Table 34. Approximate Equivalent Average Peel Adhesion Values for Laboratory-Aged Tires and Tires in Phoenix Service 100
Figure 1. Simplified Illustration of Rubber Degradation by Mechanical Energy, Heat Energy, and Reaction With Oxygen 17
Figure 2. Picture of Two-Ply Test Sample Post-Test 36
Figure 3. Example Micro-Indentation Modulus 40
Figure 4. Changes in Indentation Modulus for Roadwheel Tests and Phoenix Service Tires 42
Figure 5. Changes in Indentation Modulus for Oven-Aged and Phoenix Service Tires 43
Figure 6. Modulus Profile of Type B Phoenix-Retrieved Tires 44
Figure 7. Modulus@100% Strain and Ultimate Elongation for Skim-Coat Compound of Type B Tires 50
Figure 8. Modulus@100% Strain and Ultimate Elongation for Skim-Coat Compound of Type C Tires 51
Figure 9. Modulus@100% Strain and Ultimate Elongation for Skim-Coat Compound of Type D Tires 52
Figure 10. Modulus@100% Strain and Ultimate Elongation for Skim-Coat Compound of Type E Tires 53
Figure 11. Modulus@100% Strain and Ultimate Elongation for Skim-Coat Compound of Type H Tires 54
Figure 12. Modulus@100% Strain and Ultimate Elongation for Skim-Coat Compound of Type L Tires 55
Figure 13. Ahagon Plot of Skim-Coat Compound for Type B Tires 57
Figure 14. Ahagon Plot of Skim-Coat Compound for Type C Tires 57
Figure 15. Ahagon Plot of Skim-Coat Compound for Type D Tires 58
Figure 16. Ahagon Plot of Skim-Coat Compound for Type E Tires 58
Figure 17. Ahagon Plot of Skim-Coat Compound for Type H Tires 59
Figure 18. Ahagon Plot of Skim-Coat Compound for Type L Tires 59
Figure 19. Modulus@100% Strain and Ultimate Elongation for Wedge Compound of Type B Tires 64
Figure 20. Modulus@100% Strain and Ultimate Elongation for Wedge Compound of Type C Tires 65
Figure 21. Modulus@100% Strain and Ultimate Elongation for Wedge Compound of Type D Tires 66
Figure 22. Modulus@100% Strain and Ultimate Elongation for Wedge Compound of Type E Tires 67
Figure 23. Modulus@100% Strain and Ultimate Elongation for Wedge Compound of Type H Tires 68
Figure 24. Modulus@100% Strain and Ultimate Elongation for Wedge Compound of Type L Tires 69
Figure 25. Ahagon Plot of Skim-Coat Compound for Type B Tires 71
Figure 26. Ahagon Plot of Skim-Coat Compound for Type C Tires 71
Figure 27. Ahagon Plot of Skim-Coat Compound for Type D Tires 72
Figure 28. Ahagon Plot of Skim-Coat Compound for Type E Tires 72
Figure 29. Ahagon Plot of Skim-Coat Compound for Type H Tires 73
Figure 30. Ahagon Plot of Skim-Coat Compound for Type L Tires 73
Figure 31. Peel Adhesion Type B Tire Skim Compound After Oven-Aging, Roadwheel Testing, or Service in Phoenix 77
Figure 32. Peel Adhesion Type C Tire Skim Compound After Oven-Aging, Roadwheel Testing or Service in Phoenix 77
Figure 33. Peel Adhesion Type D Tire Skim Compound After Oven-Aging, Roadwheel Testing or Service in Phoenix 78
Figure 34. Peel Adhesion Type E Tire Skim Compound After Oven-Aging, Roadwheel Testing or Service in Phoenix 78
Figure 35. Peel Adhesion Type H Tire Skim Compound After Oven-Aging, Roadwheel Testing or Service in Phoenix 79
Figure 36. Peel Adhesion Type L Tire Skim Compound After Oven-Aging, Roadwheel Testing or Service in Phoenix 79
Figure 37. Peel Adhesion Type B Tire Wedge Compound After Oven-Aging, Roadwheel Testing or Service in Phoenix 81
Figure 38. Peel Adhesion Type C Tire Wedge Compound After Oven-Aging, Roadwheel Testing or Service in Phoenix 81
Figure 39. Peel Adhesion Type D Tire Wedge Compound After Oven-Aging, Roadwheel Testing or Service in Phoenix 82
Figure 40. Peel Adhesion Type E Tire Wedge Compound After Oven-Aging, Roadwheel Testing or Service in Phoenix 82
Figure 41. Peel Adhesion Type H Tire Wedge Compound After Oven-Aging, Roadwheel Testing or Service in Phoenix 83
Figure 42. Peel Adhesion Type L Tire Wedge Compound After Oven-Aging, Roadwheel Testing or Service in Phoenix 83
Figure 43. Bead-to-Bead Shearography Separation @ 50 mbar Vacuum Versus Age, New, and Phoenix On-Road Tires (45 New Tires, 106 Phoenix Tires) 85
Figure 44. Bead-to-Bead Shearography Separation @ 50 mbar Vacuum Versus Mileage, New, and Phoenix On-Road Tires (45 New Tires, 106 Phoenix Tires) 86
Figure 45. Percent Oxygen Content of the Fill Gas Versus Oven Aging Time 89
Figure 46. Stepped-up Load Test Failure Times: Oven-Aged Type B Tires Compared to Predicted Values for Tires With 1 to 6 Years of Service in Phoenix 92
Figure 47. Stepped-up Load Test Failure Times: Oven-Aged Type C Tires Compared to Predicted Values for Tires With 1 to 6 Years of Service in Phoenix 92
Figure 48. Stepped-up Load Test Failure Times: Oven-Aged Type D Tires Compared to Predicted Values for Tires With 1 to 6 Years of Service in Phoenix 93
Figure 49. Stepped-up Load Test Failure Times: Oven-Aged Type E Tires Compared to Predicted Values for Tires With 1 to 6 Years of Service in Phoenix 93
Figure 50. Stepped-up Load Test Failure Times: Oven-Aged Type H Tires Compared to Predicted Values for Tires With 1 to 6 Years of Service in Phoenix 94
Figure 51. Stepped-up Load Test Failure Times: Oven-Aged Type L Tires Compared to Predicted Values for Tires With 1 to 6 Years of Service in Phoenix 94