Article

Failure analysis of tire tread separations

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Abstract

In-service catastrophic radial tire failure is often a separation of the tread and outer steel belt from the tire casing and inner steel belt. These separations generally occur in the field at high temperature and high speed. This paper presents a catalog of surface characteristics that define the various types of rubber cracking that takes place during a tire belt-leaving-belt separation. A mechanism that explains the generation of the rapid tearing surface is used to detail the variation found in forensic examinations.

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... He found that penny-shaped cracks initiated in rubber at the free ends of the cords when a cord rubber composite was subjected to cyclic loading conditions [1]. R.W. Smith and J.W. Daws studied crack initiation at the edges of steel belt plies in automobile tires [2,3]. Here, the steel belt plies were from the same cut type as the nylon cord belt plies found on some aircraft tires. ...
Article
Two-sized radial tires from a famous brand have been installed on Airbus planes. Several times, tread throw failures have occurred with these types of tires. Laboratory observations showed that these two-sized tires feature two cut-type belt plies (belt plies with cut cord ends lined at either edge). These are the 7th and 8th belt plies and, on all failed tires, separation occurred at the cut cord ends of the 7th belt plies. Because the cut cord ends of the 7th and 8th belt plies were not chemically pre-treated after the fabric ply was cut to get belt ply strips, the adhesion strength between the rubber and the cut cord ends decreased significantly. This means that micro-cracks initiated easily around the cut cord ends of the 7th and 8th belt plies. Due to the structural effect of these two-sized tires, there was uneven wear on their treads with the third ribs having the maximum amount of remaining thickness. Uneven tread wear resulted in a higher load at the third ribs. This generated higher temperatures around the edge of the 7th belt ply at the later stages of one life cycle. The higher temperatures decreased the strength of the local rubber and sped up the rubber's aging process. The higher loads experienced around the edges of the 7th belt ply and transferred from the third rib, and the decreased mechanical properties of the rubber at that location (due to higher temperatures), ultimately sped up micro-crack formation and expansion at the cut cord ends of the 7th belt ply. This finally led to premature tire failure. The tire manufacturer is currently taking measures to modify the structure of these two-sized tires in order to avoid uneven wear and hopefully prevent such failures in the future.
... "Tire failure analysis is often focused on the mechanism of the separation of the tread and outer steel belt from the tire casing and inner steel belt. The analyst must determine the point of origin of the separation from the appearance of the fracture surfaces" (Daws, 2003). ...
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Trucking fleets and owners of commercial vehicles utilize both new and retread tires on their vehicles in the United States. Retread tires are used primarily for the cost advantage they provide over a similar new tire. Despite the advantages that retreaded tires may bring, public perception is that retread tires are less safe than new tires as evidenced by the amount of tire debris frequently found on the sides of U.S. Interstate highways. During summer 2007, the University of Michigan Transportation Research Institute (UMTRI) under a subcontract from Virginia Tech Transportation Institute (VTTI) collected and studied truck tire debris and discarded tire casings from five sites in the United States. A random sample (totaling 1,496 items) of the tire debris/casings collected was analyzed to determine the probable cause of failure and its original equipment or retread status. This report presents the methodology and results from this investigation into the underlying causes of truck tire failures and gives an overview of the crash safety problem associated with heavy-truck tire failures. Also, background information on the manufacture of a truck tire, the truck tire retread industry, tire failure modes, industry stakeholder perspectives, an overview of other previous tire debris studies, conclusions, and recommendations for topics for further research are given. National Highway Traffic Safety, Administration Office of Applied Vehicle Safety Research http://deepblue.lib.umich.edu/bitstream/2027.42/61517/1/102117.pdf
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Tire sometimes suffer catastrophic failure during travel of highways, resulting in a scatter of tire fragments along the pavement and berms. A large member of these fragments, including partial and whole tires, were collected and examined microscopically. The goal was to determine what sort of evidence might be "read" from these fragments via the optical stereo microscope using examinations of 7x to 60x. It was found that these fragments contain a wealth of well preserved information. Rubber tear lines and other fracture topographies are readable, allowing the failure analyst to determine directions of fracture/tear propagation which make it possible to postulate modes of separation. The features of torn surfaces that are normally encountered in laboratory testing are modified in tire failures due to the presence of adjoining compounds, complex shapes, and nonrubber components. Guidelines have been established to account for these complicating variables. A concept of "direction anisotropy" aids the analyst in understanding product failure surfeces. Additional items surveyed in this post mortem study were the condition at wire belt ends and indications of wire corrosion.
Fractography of Tire Tread Separations,” presented at the 163rd Technical Conference
  • J W Daws