Abstract:
A test fixture, test apparatus, and test method utilize a radially cut tire section that is mounted and sealed to a test jig in a airtight manner such that an air chamber is formed between an innerliner surface of the radial tire section and a recessed portion of the jig body such that the tire section may be pressurized on the test jig. A test surface is provided and either the test surface or the test jig is moveable relative to the other to the other to provide a dynamic load to the radial tire sections.

Description:
[0001]     This application claims the benefit of U.S. provisional patent application Ser. No. 60/488,922, filed Jul. 21, 2003, and is hereby incorporated by reference. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to an apparatus for conducting a predictive test to determine failure due to “belt-leaves-belt” (“BLB”) separations in a tire, particularly a radial passenger automobile tire.  
       BACKGROUND OF THE ART  
       [0003]     In a “belt-leaves-belt” failure, particularly involving a steel-belted radial tire, the adjacent belts in the tire separate from each other. These tire failures may occur from a variety of problems, but regardless of the problem, it is essential that a tire manufacturer be able to effectively test tires to predict such failures.  
         [0004]     The BLB failure appears to be exemplified by a premature aging or oxidation, so it may be predicted by accelerating the aging process, by exposing the tire to increased temperature or oxygen partial pressure while exposing the tire to a dynamic vibratory input that dynamically activates the process of thermal and oxidative aging simulating dynamic road conditions.  
         [0005]     In some of the known prior art methods, a series of complete tires are tested at differing time, temperature and oxygen pressure schemes. An inherent difficulty with this methodology is that variations in the individual tires used confounds the testing methodology, resulting in unacceptable data scatter. This data scatter can be eliminated only by exposing the same tire to the differing test conditions, but this is also confounded by the destructive nature of the testing.  
         [0006]     It is therefore an object of the present invention to provide a method and device wherein each single complete tire can be used to provide a series of data points, such that individual tire-to-tire variation may be demonstrated by comparing the sets of data points generated by the given individual tires.  
       SUMMARY OF THE INVENTION  
       [0007]     This and other objects of the present invention are provided by the apparatus and method for predicting tire life relative to “belt-leaves-belt” failures as described in more detail below.  
         [0008]     In the test method of the present invention, a tire to be tested is sectioned into a plurality of identical radial wedges. The radially cut tire section is mounted on a test jig and sealed around its edges to prevent the pressurized air from leaking. The interior chamber of the mounted tire section is then “inflated” such that the interior face of the section is exposed to a higher pressure than the exterior face. This allows diffusion of gas through the tire, simulating an inflated tire. Gas pressure and particularly partial pressure of oxygen at the interior face is controlled in the jig. The exposed exterior face, that is, the tread surface, is exposed to a vibration source, especially a source vibrating at about 10 Hz, to simulate road vibration. If desired, the entire test jig is contained in a temperature controlled chamber, so that increased temperature can be utilized to simulate both operating conditions and to accelerate aging.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The present invention will be better understood when reference is made to the accompanying drawings, wherein identical parts are identified with identical reference numerals and wherein  
         [0010]      FIG. 1  shows a perspective view of a tire segment and a test jig body as used in one embodiment of the present invention  
         [0011]      FIG. 2  shows a perspective view of a tire segment mounted on a test jig as used in one embodiment of the present invention.  
         [0012]      FIG. 3  shows a side view of a first test configuration of the present invention utilizing a plurality of test surfaces and mounted tire segments in accordance with an embodiment of the present invention;  
         [0013]      FIG. 4  shows a perspective view of a variation of the first test configuration utilizing two test positions;  
         [0014]      FIG. 5  shows a side view of a third test configuration of the present invention utilizing a plurality of test surfaces and mounted tire segments in accordance with an embodiment of the present invention;  
         [0015]      FIG. 6  shows a partial front view of the third test configuration of the present invention as shown in  FIG. 5 ;  
         [0016]      FIG. 7  shows a side view of a the plurality of test surfaces showing the radial displacement of the rollers for loading the tire segments in accordance with an embodiment of the present invention;  
         [0017]      FIG. 8  shows a side view of another test configuration of the present invention; and  
         [0018]      FIGS. 9A-9D  show the sequence of tire loading and unloading in the test configuration shown in  FIG. 8 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]     The test method of the present invention proceeds from an initial assumption that a statistically significant majority of all steel-belted radial tire failures, excepting those caused by user neglect, road hazard or manufacturing anomalies, are caused by BLB failure, caused in turn by aging of the wedge and skim stocks initiated by the ever-socketing steel belt in the wedge area.  
         [0020]     Referring now to  FIG. 1 , to test a tire, a single tire is selected and sectioned into suitable circumferential sections  12 . The sidewalls are retained and the section is mounted onto the test jig  14  and sealed to prevent air loss as shown in  FIG. 2 . Two sections  12  are selected for photomicrography prior to testing. In the preferred test, the two sections  12  to be analyzed in this manner should be diametrically opposed in the tire prior to sectioning. In other words, they should be as far apart from each other in the unsectioned tire as possible, to allow the best opportunity to see tire variations. Additionally, the fundamental construction features of the tire sections  12  should be documented, such as component dimensions and placement, gauges of the inner liner, wedge and skim compounds, and stock division lines in the crown and belt regions including tread, tread base, under tread, sidewall, skim and wedge components. These sections may be used as control sections if desired, or other sections may be retained as controls.  
         [0021]     Further circumferential sections of the tire are tested in the test jig  20  as described below. These tests are conducted under a simulated inflation, with simulated dynamic vibration, similar tire loads and loading frequency (for example, 1000 pounds and 5 Hz) for various time and temperature combinations. Air permeation rate through the tire section  12  can be measured during the test.  
         [0022]     After the testing, the segments  12  will have rubber specimens extracted from the area between the belts. These specimens will be tested to fully characterize them. Tests that would typically be conducted would include: physical properties, for a Ahagon plot; dynamic properties (E″, E′ and tan delta); sulfidic crosslink densities (S P , S D  and S M ); mini or micro DeMattia (for crack growth); antidegradant content (depletion rate); air permeation rate (rate of oxidation); and peel adhesion at both 23 C and 100 C. These tests are itemized for illustrative purposes and additional tests can of course be performed.  
         [0023]     Diffusion dependent oxidation, that is, oxidation due to the natural diffusion of oxygen through the tire, is the primary cause of the aging and failure of wedge and the skim stocks. The diffusion rate and the directly related degradation rate are influenced by tire geometry and components. Factors known to be influential include inner liner formulation and gauge and cumulative mechanical flexing.  
         [0024]     This testing protocol provides replication as a primary advantage. Prior art methodologies that utilize a series of tires clearly show that differences between tires may be greater than the differences induced in the testing, so the test results are not readily observed. There are several advantages inherent in the simultaneous testing of segments from a single tire. First, tire to tire variations are eliminated. These may include differences in tire builders, difference in curing pressure, and differences in gauges and age of compounds and components. Even day to day variations of a single tire builder can be introduced as a confounding factor when more than one tire is used. Changes in the linkages of sulfur are modified because of oxygen absorption in the tire. While the use of a single tire does not remove variations within a single tire, these variations are effectively recognized by the use of a larger number of segments, rendering outlying samples more obvious.  
         [0025]     The economics of using a single tire is also important. By allowing many specimens to be extracted from a single tire, the test jig  14  of the present invention allows the use of experimental designs and other statistical studies. These include factorial or composite designs with replication, Weibull studies and Arrhenius aging studies.  
         [0026]     A yet further advantage of the present invention method is that the results would be expected to provide more realistic parameters for finite element analysis studies, which, if permitted, provide even more economical testing through computer simulations. This is particularly useful in determining aerobic/anaerobic aging in a given tire brand.  
       EXAMPLE 1  
       [0027]     ANAEROBIC AGING—In one test, 5-inch circumferential sections were oven-aged prior to preparing test dumbbells. The aging, therefore, is primarily anaerobic and have been exposed to very little oxygen and not at all to an oxygen partial pressure differential across the thickness of the tire section. Thirteen different time and temperature combinations were tested for each tire; the time exposure varying from 0 hrs to 504 hrs and the temperature exposure varying from 60 C to 100 C, as shown below:  
                                                                                                                   Degrees                C.   Time Hours   0   8   48   96   144   168   336   504                    60               X       X   X   X       80               X   X   X   X       100    X   X   X   X       X                  
 
 This test varied from an Ahagon aging protocol because the Ahagon test prepares the dumbbells prior to aging and exposes the specimens to more oxygen. The data collected from testing tires from five different tire manufacturers shows a general scatter when log elongation is plotted against log modulus, although manufacturer differences are detectable, as noted in Graph 1 below: 
         
 
       EXAMPLE 2  
       [0029]     AEROBIC AGING—In this test, dumbbell test samples were prepared from the wedge sections prior to aging. The aging, therefore, was an Ahagon aging, where the dumbbells are exposed to circulating air during aging. Thirteen different time and temperature combinations were tested for each tire; the time exposure varying from 0 hrs to 16 hrs (a 32 fold reduction in time range) and the temperature exposure varying from 60 C to 100 C, as shown in the table below:  
                                                                                                 Degrees C.   Time hours   0   2   4   6   8   10   16                                60               X       X   X       80               X   X   X   X       100    X   X   X   X       X                  
 
 The data collected from testing tires from three different tire manufacturers shows a general scatter when log elongation is plotted against log modulus, although manufacturer differences are detectable. The greater linearity of the results is shown in Graph 2 below: 
         
 
       EXAMPLE 3 A  
       [0031]     In this test, the intent is to provide a realistic “in service” oxygen degradation using the test devices of the present invention, to overcome the perceived weaknesses of the oxygen starved anaerobic method and the excessive oxygen exposure of the Ahagon aging testing. In this example, the intent is to age the tire sections under a 30 psig air pressure applied to the interior face, while applying dynamic vibration. Thirteen different time and temperature combinations were tested for each tire; the time exposure varying from 0 hrs to 504 hrs and the temperature exposure varying from 60 C to 100 C, in the same manner shown in Example 1. In this test, the differences in tire constructions that cause stress and strain in the wedge region due to sidewall deflections are not considered. In the preferred embodiment of the test device  10  for this example, as shown in  FIG. 3 , a plurality of tire sections  12  are provided and each tire section  12  is constrained between a pair of cylindrical plates  14 , with the tread exposed to a dynamic vibration imposed by a test surface  16  in the form of a beam or the like. The test surface  120  is moved vertically to provide a load force F at a predetermined frequency as required by the testing. The entire test fixture is housed within a temperature controlled oven  110 .  FIG. 3  shows a four position configuration while  FIG. 4  shows a similar two position configuration, however the present invention is not intended to be limited to any number of test stations.  
       EXAMPLE 3B  
       [0032]     In this test, a saddle-shaped jig  14 ′ is provided as shown-in  FIGS. 1 and 2 , wherein the jig  14 ′ is shown with and without a mounted tire section  12 ′. In this test, the preferred test specimen is a ⅙ section of a tire circumference, however, the invention is not intended to be limited to such a length. The jig allows the test section  12 ′ to be supported as if a complete tire was present, while providing a sealed air chamber for pressurizing the tire and to expose the tread surface to dynamic vibration, particularly at 10 Hz. Seven different time and temperature combinations were tested for each tire; the time exposure varying from 0 hrs to 168 hrs and the temperature exposure varying from 70 C to 90 C, as shown below:  
                                                                                 Degrees C.   Time hours   0   16   48   96   168                                70           X   X   X       90   X   X   X   X                  
 
         [0033]     In this test, the differences in tire constructions that cause stress and strain in the wedge region due to sidewall deflections are not considered. In the preferred embodiment of the test device  10 ′ for this example, the test jigs can be mounted for exposure on a rotating wheel device that applies the dynamic vibration, as shown in  FIGS. 5-7 .  
         [0034]     Referring now to  FIG. 5 , a plurality of radial tire segments  12 ′ are mounted on test jigs  14 ′ and are sealed and pressurized, then mounted on a fixture  16 ′. A plurality of test surfaces  20 ′ in the form of rolls  20 ′ are shown spaced about a central axis  22 . The rolls  20 ′ rotate about axis  22  and engage the stationary tire segments  12 ′. The roll  20 ′ rotates about its roll axis  24  across the footprint of the tire segment  12 ′. The roll  20 ′ applies a load force F to the tire segment  12 ′. The rolls  20 ′ may translate radially inward and outward to apply the appropriate force F as required by the testing as shown in  FIG. 7 .  
         [0035]     An alternate rolling type of test is also provided by the test configuration  10 ″ as shown in  FIGS. 8-9D .  FIG. 8  shows a side view similar to that of  FIG. 5  except that the test surface  20 ″ is a single drum  20 ″ instead of multiple rollers  20 ′. The large drum  20 ″ having a radius Z provides less curvature and better simulates the flat road surface. Drum  20 ″ also comprises at least one radial arc portion  40  having a thickness Y, attached thereto and equally spaced about the drum  20 ″. The tire sections  12 ″ are mounted upon a test jig  14 ″ that is pivotal about a central axis  42  of the tire section. As with the previous embodiment, the mounted tire sections  12 ″ are sealed to the jig  14 ″ and pressurized. The tire sections  12 ″ are biased to one side by a biasing means  44  such as a spring or the like and held in a starting position by a stop means  46  (both shown for simplicity on only one station but existing on each station). The operation of the test apparatus  10 ″ is best shown in  FIGS. 9A-9D . In  FIG. 9A , the tire section  12 ″ is held in position and the drum  20 ″ rotates until an arc portion  40  engages the tire section at a touchdown portion TD. The rotating drum  20 ″ causes the engaged tire section  12 ″ to pivot until the full tire footprint is engaged as best shown in  FIG. 9B . The drum  20 ″ continues to rotate and the tire section  12 ″ continues to pivot until the tire section  12 ″ disengages the arc portion  40  at the take off portion TO representing the end of the tire footprint as shown in  FIG. 9C . The radius Z of the drum is a distance X away from the tire section  12 ″ so that the drum  20 ″ does not engage the tire section  12 ″ when the arc portion  40  passes the tire section  12 ″. As shown in  FIG. 9D , the biasing means  44  is now free to move the tire section  12 ″ back against stop means  46  and to its original start position until it is once again engaged by the next arc portion  40 . The distances X and Z are predetermined to provide the appropriate test load and deflection of the tire section at the point of full footprint shown in  FIG. 9B . Although shown with only four stations, it is contemplated that six to twelve tire sections may be utilized about the circumference of the drum  20 ″ and the radius of the drum may be any size and is not intended to be limited herein.  
         [0036]     It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed and reasonable equivalents thereof.