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Firestone Tire Failure Analysis
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This report is an assessment of what is presently understood about the recent Firestone ATX and AT tire problems. It provides an overview of factors related to tire failures of the type observed. Example computations are presented that indicate the relative importance of a selection of variables on crack tip driving forces. An assessment of experimental data collected by Bridgestone/Firestone laboratories and an independent testing lab on returned tires is also given. The report concludes with summary observations based upon more detailed statements made within the body of the report. The problem of belt separation is understood to be the propagation of a fatigue crack in the bulk of the rubber separating the two steel belts of the tire, not at the interface between the steel and the rubber. The important factors for this type of failure are the capacity of the material to resist the propagation of the crack and the forces that are driving the crack forward. An understanding of the problem is complicated by the fact that there are no well established criteria for in-service tire failures against which tire components are designed. Secondly, analytical techniques for predicting failures such as belt separations are only today becoming technically feasible. Thus while one can and does perform many standard laboratory tests on tires and their components it is not clear how these are related to in-service failures. A survey of material properties from returned tires shows that materials from tires in southern climates have reduced ductility (extensibility) and higher sti#ness. These observations are interestingly independent of service condition. Further, the capacity of the belt skim rubber to resist catastrophic fracture is markedly reduced for tires that were manufactu...
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... In addition, research on tire durability has been ongoing since the mid-1990s because of incidents of broken and damaged layers of tire belts as described in Fig. 1. In a research paper which analyzed the damaged layers of tire belts put forth by Sanjay Govindjee, he applied an approach of fracture mechanical life evaluation to fatigue lifespan evaluation by inserting cracks into belt layers of a tire model in a 3D image [1]. ...
... (3). 1 2 10% ...
... In this formula, values of reference m and A were used to evaluate fatigue crack growth life [1]. ...
Tire belt separation failure is occurred by internal cracks generated in #1 and #2 belt layers and by its growth. And belt failure seriously affects tire endurance. Therefore, to improve the tire endurance, it is necessary to analyze tire crack growth behavior and predict fatigue life. Generally, the prediction of tire endurance is performed by the experimental method using tire test machine. But it takes much cost and time to perform experiment. In this paper, to predict tire fatigue life, we applied deterministic fracture mechanics approach, based on finite element analysis. Also, probabilistic analysis method based on statistics using Monte Carlo simulation is presented. Above mentioned two methods include a global-local finite element analysis to provide the detail necessary to model explicitly an internal crack and calculate the J-integral for tire life prediction.
... A tire is comprised of rubber and various reinforcements, and it is the only part of an automobile that contacts the ground. Tire durability has always been an issue because the failure of a tire puts the occupants in danger [1,2]. Many researchers have made a great effort to improve tire durability, and they also have focused on assessing tire durability accurately. ...
... However, it is not easy to obtain an exact tearing energy of a tire specimen because the lower half is easily peeled off due to high bending stiffness of the specimen. In tire industry a conventional peel test method where a belt is pulled while one end of the lower part is held by a grip as shown in Fig. 1a is used [2,16]. However, the crack does not usually propagate at a constant rate, especially when the bending stiffness of the upper half is different from that of the lower half, causing the peel force to oscillate as shown in Fig. 1b. ...
... When it is exposed to high temperature, its fatigue life decreases significantly [17,23]. A tire experiences a high temperature especially around the belt edge due to heat built up by hysteresis [2,24,25]. The high temperature condition was considered in two different stages; before the test and during the test. ...
Crack growth plays an important role in the durability of tires, and it is necessary to evaluate the characteristics of crack growth and tearing energy accurately. Since a crack around the belt edge is subjected mainly to interlaminar shear deformation, a Mode III fatigue test method was developed. In addition, a peel test method was developed to assess the tearing energy. Based on the fatigue and peel test results, the effects of heat aging, temperature and belt stiffness were analyzed.
... In contrast, tire durability simulations have traditionally been abbreviated to a single operating condition [3][4][5][6][7][8][9][10][11]. This simplification reduces analysis complexity and cost while still providing a form of relative guidance, but it gets in the way of matching up simulation results with regulatory test results. ...
Tire speed ratings derive from regulatory testing in which tire structural integrity is validated over a series of steps with successively increasing speed. For the FMVSS 139 high-speed standard, there are four half-hour duration speed steps at 80, 140, 150, and 160 kph. Speed ratings from Q through Y may be attained through the UN ECE R30 regulation high-speed testing. For either protocol, a tire must demonstrate the ability to operate without crack development at high speed for a specified period. After the test, “there shall be no evidence of tread, sidewall, ply, cord, inner liner, belt or bead separation, chunking, broken cords, cracking, or open splices.” A workflow for simulating regulatory high-speed durability performance has been developed based upon (1) recent improvements to the Abaqus steady-state transport formulation that now permit converged solutions to be obtained at high speed (including after the development of standing waves in the tire) and (2) Endurica DT self-heating and incremental fatigue simulations that account for thermal effects and for damage accumulation occurring due to a schedule of load cases. The self-heating calculation features the Kraus model and accurately captures viscoelastic loss modulus dependence on strain amplitude and temperature. For each step of the high-speed procedure, steady-state structural and thermal solutions are first computed. The deformation history in the presence of standing waves is shown to require rainflow counting due to the occurrence of multiple load cycles per tire revolution. Crack growth is finally integrated for each potential critical plane through each step of the test until failure is indicated. Standing waves at high speed induce significant self-heating and damage, rapidly limiting high-speed performance. The temperature dependence of self-heating and strength properties also plays a major role in limiting high-speed durability. The simulations were executed on both a flat surface and on the regulation specified 1.7 m diameter road wheel. As expected, durability testing on the road wheel is more severe, and the beneficial effect of a nylon overwrap is predicted.
... This is evident, as shown for example in the evolution of tire warranties over the last few decades; see Fig. 1. Developers are responsible to design against the eventuality of crack development in each of the various components of a tire [1,2]. The task requires knowledge of the stress-strain and fatigue behaviors of each compound in the tire, analysis of the loads carried by each tire component, and calculation of the damaging effects of operation under load. ...
Tire developers are responsible for designing against the possibility of crack development in each of the various components of a tire. The task requires knowledge of the fatigue behavior of each compound in the tire, as well as adequate accounting for the multiaxial stresses carried by tire materials. The analysis is illustrated here using the Endurica CL fatigue solver for the case of a 1200R20 TBR tire operating at 837 kPa under loads ranging from 66 to 170% of rated load. The fatigue behavior of the tire’s materials is described from a fracture mechanical viewpoint, with care taken to specify each of the several phenomena (crack growth rate, crack precursor size, strain crystallization, fatigue threshold) that govern. The analysis of crack development is made by considering how many cycles are required to grow cracks of various potential orientations at each element of the model. The most critical plane is then identified as the plane with the shortest fatigue life. We consider each component of the tire and show that where cracks develop from precursors intrinsic to the rubber compound (sidewall, tread grooves, innerliner) the critical plane analysis provides a comprehensive view of the failure mechanics. For cases where a crack develops near a stress singularity (i.e., belt-edge separation), the critical plane analysis remains advantageous for design guidance, particularly relative to analysis approaches based upon scalar invariant theories (i.e., strain energy density) that neglect to account for crack closure effects.
... Tire durability due to large local loading, stiffness discontinuities, and production flaws is frequently related to the fracture of tire components such as belt edge separation, ply turn-up separation, or lug cracking in radial truck tire [1][4]. An influence factor on fracture and fatigue behaviors of the tire component is the key to improve durability and assess lifetime of the radial truck tire [5]. Bead area separation in passenger tires has been fairly uncommon since the middle to late 1990s. ...
... Even though these methodologies have existed for some time their direct application to the spinning tire in the open peer reviewed literature is amazingly scarce. In this paper we review an extension of Steinmann's method (Steinmann, 2000 andSteinmann et al., 2001) for finite deformation elasticity to the case of an elastic spinning tire in steady rotation as was done recently in Govindjee, 2001b. Standard stress analysis in a steady spinning frame of reference emanates from the early work of Lynch, 1969 andOden andLin, 1986 were apparently the first to give a complete detailed presentation of a suitable method in finite deformation; see also Le Tallec andRahier, 1994 andMihalic, 1998. ...
The recent well publicized failures of the Firestone ATX tire has brought to light the poor state of research into the basic physical causes of such failures and the poor state of research into analytic methods suitable for analyzing such failures. The essence of problems of this nature lies in the finite deformation fatigue fracture of elastomers at large strains. The definition of failure criteria is further complicated by the issue of material aging. The computational problem itself is rather demanding due to the truly 3-D nature of the tire system under load. In particular, the computation of the failure forces (the singular energy momentum tractions) is rather challenging due to the spinning reference state normally utilized in tire analysis. In this paper we present a suitable numerical formulation for computing energy release rates in cracked tires and apply this to the question of the effect of varying inter-belt ply gauges. It is found that the energy release rates increase in the example tire for an increasing inter-belt gauge which seems to be in contradiction to the typical field experience of longer life for larger gauges. The contradiction however can be explained through a size effect argument related to the process zone around the crack-tip which causes the critical energy release rate to increase with gauge at a rate faster than the available energy release rate.
... A more rigorous physical basis is given for considerations founding on fracture mechanics. After the Firestone tire failure (see Govindjee [4] for further details), a significant amount of attention has been drawn to fracture investigations of tires. Investigations using traditional fracture mechanical methods like the J-integral (Rice [16]) or the material force approach (Braun [2]) yield the energy release rate for an evaluation of fracture sensitivity. ...
The contribution has its focus on several aspects of the description of tire features through finite ele-ment modeling. It is starting with the formulation of rubber material properties. Material characteristics, which have to be taken into account depending on the focus of analysis, are introduced. Geometrical nonlinearities, i.e. large strain, nonlinear elasticity, softening, inelastic and dissipative features are of importance and influence certain tire properties. An important simulation feature is the steady state rolling framework. In this case, the finite element discretization is fixed in space and the material is considered as flowing through the mesh. This approach is computationally very efficient and repre-sents the real loading conditions of the tire. During the design process, various structural aspects need to be investigated in order to obtain an optimal product. Tire mechanical properties which are in the reach of current computing facilities are shown.
... pressure and temperature) in order to provide timely alerts to drivers in an effort increase overall road safety. As a result of the Ford-Firestone tire failure controversy [41], TPMSs represent the first federally mandated in-vehicle wireless sensor network [42]. In our study, a variety of the most common TPMS sensors were backward engineered in order to discover the protocols used to send messages. ...
... It is hard to fi nd a single causative agent for the tire failures. There is the lack of established criteria for different types of tire failures (Govindjee, 2001). Modern radial tires seldom fail and even fewer cause crashes. ...
Automotive forensic examination is the systematical analyses of failed automotive components in the pursuit of and the identification of the cause(s) or root cause(s) of the physical damage or other disablement done to vehicle by collision. It comprises a combination of science, experience and some art by using the laws of physics, mathematics, engineering, etc. mixed with the expert's real-world automotive component background and expertise in the design, testing, development, manufacturing and maintenance. Automotive wheel systems are often blamed for causing accidents, but their complete and catastrophic failure is rare. Automotive forensic experts are asked to determine the most likely events that led up to and caused the given product to fail. These findings are often asked to fulfill specific time and cost constrains. This paper offers a systematic approach to forensic engineering investigation applied in the post-collision condition of automotive braking, steering and suspension, wheels and tyres.
A global-local finite element modeling technique is employed in this paper to predict the fatigue life of radial truck tires. This paper assumes that a flaw exists inside the tire, in the local model. The local model uses an FEM fracture analysis in conjunction with a global-local technique in ABAQUS. A 3D finite element local model calculates the energy release rate at the belt edge. Using the analysis of the local model, a study of the energy release rate is performed in the crack region and used to determine the crack growth rate analysis. The result considers how different driving conditions contribute to the detrimental effects of belt separation in truck tire failure. The calculation of the total mileage on four sizes of radial truck tires has performed on the belt edge separation. The effect of the change of belt width design on the fatigue lifetime of tire belt separation is discussed.
Direct chemical investigation of the degradation of polymeric networks is usually impracticable owing to the experimental difficulty of insolubility and to the fact that reaction at only a small proportion of network units is sufficient to cause marked alteration of network structure. Resort has, therefore, to be made to the measurement of physical changes brought about by the chemical reactions. Change of tension at constant extension is a useful measure for this purpose, since statistical elasticity theory predicts a direct proportionality between the tension and the number of chains supporting the stress. The present purpose is: (1) to describe a stress relaxometer possessing certain advantages over previous models; (2) to report on the stress relaxation of peroxide-crosslinked rubber, which can be considered from a chemical viewpoint to be the simplest possible rubber network; (3) to point out some complications in the relaxation behavior of sulfur vulcanizates, and (4) to interpret the shapes of stress relaxation curves.
It is nearly a century since Hofmann and Spiller made the first recorded experimental observations linking oxygen with substantial changes in polyisoprenoid hydrocarbons. In the first sixty-odd years following this work technological progress was slow, but certain characteristic features of the oxidation reaction were observed. It was firmly established that oxygen played an important role in the deterioration of rubber and rubber products with the passage of time, and the accelerating effects of exposure to light or to elevated temperatures were realized. Within a short additional period a very nearly complete solution to the problems of oxygen aging was obtained with the discovery of efficient vulcanization methods and of effective antioxidants. These discoveries made possible the transition of rubber from a relatively expensive, short-lived material of commerce to its present position of a high-volume, low-cost, essential ingredient of our everyday life. Since that period technological progress has consisted in steady refinements of these important discoveries. During these years many observations necessary for understanding the chemistry of the oxidation process were accumulated, but it was necessary to wait for two fundamental developments in order to obtain a complete explanation of the reactions occurring during the reaction of rubber with oxygen. These were, first, a clear realization of the high molecular character of the rubber hydrocarbon and the effect of this on its macroscopic properties, and-second, the work on oxidation of low molecular weight olefins which forms the basis for inferring the nature of steps in the oxidation of rubber inaccessible because of experimental difficulties. Since both of these developments have been made it is quite probable that we shall know in complete detail the reaction sequence in rubber oxidation before the centennial of Hofmann's paper is reached.
The author presents a continuum mechanical description of steady crack propagation in a linearly viscoelastic solid. The analysis is exact within the realm of linear viscoelasticity theory. Particular attention is paid in this study to the fracture of crosslinked polymer above the glass transition temperature. The presentation consists of seven sections. Following the introduction the author describes first the mechanical characterization of the polyurethane. In the third section some background on the mechanical degradation of material at the microscopic size scale is presented. The fourth section deals with two possible criteria for crack propagation. The displacements are documented in the fifth section on the viscoelastic-boundary-value problem. The sixth section deals with a comparison of the two hypothetical failure criteria with each other and with the experimental data documented in the second section. The paper is accompanied by a panel discussion.
Measurements of cutting resistance have been made for a crosslinked styrene-butadiene copolymer over a wide range of cutting speeds and temperatures. A characteristic fracture energy was determined using the procedure of Lake and Yeoh. A lower limit, about 150 J/m2, was obtained at low cutting speeds. This value is significantly higher than the threshold tear strength, about 30 J/m2, due to roughness of the blade tip. The tear resistance increased dramatically as the test temperature was lowered, by a factor of over 1000X, whereas the cutting resistance remained largely unchanged over a considerable temperature range. Much of the enhanced tear resistance at low temperatures is therefore attributed to increasing roughness of the tear tip, the intrinsic strength remaining approximately constant. As the tear strength followed a WLF temperature dependence closely, roughening of the tear tip is associated with viscoelastic effects. Higher cutting resistance was shown by a sulfur vulcanizate, but carbon black had no additional effect. Variations in tensile strength with rate of elongation and temperature are discussed in terms of tearing from an initial edge flaw.
Vulcanization kinetics for a SBR compound was studied by using both curemeter and DSC methods by a kinetic approach. A simplified but realistic model reaction scheme was used to simulate both inductionn and curing periods simultaneously. Model parameters were extracted from isothermal curemeter experiments. The model predicion demonstrated a good agreement with isothermal curemeter data over a temperature range of 120°C to 180°C. The variaition of equilibrium modulus with temperautre, observed from cure curves, can also be predicted. However, DSC experiments showed a different reaction behavior in the curing period as compared to model calculaitons. This was explained by the assumption that the reaction heat observed in DSC is due to all possible esothermal reacitons, and the formation of crosslinks is only a part of these reacitons. Hence the curemeter can provide a good indicaiton of crosslink formation while DSC displays the entire reaciton heat released during the vulcanizaiton process. The kinetic approach allows one to incorporate vulcanizaion kinetics into the practical siumlaiton of reactive processing operations.