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ASTM D945-16 and the AYO-IV Yerzley mechanical oscillograph can improve rubber compounding and molding operations.

Increasing demands in the automotive industry are driving evolution in vibration isolation elements. The rubber industry is challenged to keep up with the speed of developments and multiplying design variables. To meet the dynamic characteristics that the automotive engineers have foreseen (ref. 1), the compounding department should develop suitable formulations, produce test samples and test on an AYO-IV Yerzley mechanical oscillograph (ref. 2). This process saves time and reduces the cost of labor and energy, and improves the efficiency of product development overall.

The original Yerzley mechanical oscillograph was developed to study dynamic properties of polychloroprene for the evaluation of these characteristics in applications such as vibration absorbers (ref. 2).

The AYO-IV is a well-proven testing machine for dynamic properties of rubber, based on free oscillation (simple harmonic motion) at the low end of the frequency spectrum (nominally up to 15 Hz). It has been serving the global rubber industry successfully for over half a century.

The AYO-IV (figures 1 and 2) (table 1) yields the natural frequency of a given specimen within seconds. It is the most reliable testing equipment to assist compounding and production engineers in a rubber factory (ref. 3). Impact energy absorption and hysteresis are critical parameters to predict how the energy absorption will occur in vibration isolation end-products. Dr. Sujitkumar Datta reported a study showing that extremely high concentration of fillers in rubber, such as carbon black, actually decreases the energy absorption features of the rubber; hence, it is best to work at optimum levels such as 75 phr (ref. 4).

Most importantly, the AYO-IV's design parameters are accurate, resulting in reliable and reproducible outputs. Its standard deviation, also known as the measurement of uncertainty, is low (tables 2 and 3). It is a rugged, durable workhorse that does not need a clean-room environment and employs user-friendly software for use by operators with any level of technical background.

A study completed by Cihan Cengiz of Tekno Kaucuk, Turkey, has reaffirmed the repeatability, reproducibility and accuracy of the AYO-IV (tables 2 and 3).

The standard deviation figures that the AYO-IV outputs are low, proving its dependability, repeatability and accuracy. The AYO-IV is a unique and well-utilized rubber testing machine; it has helped compounding and molding/finishing rubber technicians for decades. It is a fact that keeping the shape factor as the primary parameter, the AYO-IV software now allows the operator to utilize noncylindrical cross-sections as the specimen under investigation (ref. 5).

Is the Yerzley measuring the natural frequency of the HNBR? Can this be seen in the DMA?

This study was designed to consider the natural frequency of the rubber (ref. 6). When the weight drops on the AYO-IV Yerzley mechanical oscillograph, it is possible that the rubber determines the frequency of the decaying oscillation. This could well be the natural resonant frequency of the rubber. This is significant if a rubber is used for dynamic properties, for example in a vibration damping application. These damping rubbers can be used in car engine mounts to prevent engine vibrations from affecting automobile passengers.

The normal way of assessing the damping behavior of rubbers is to use dynamic testing. This can be on a small scale with a DMA (dynamic mechanical analyzer) such as the TA ARES, or on a large scale with an electric or servo hydraulic oscillating tester.

One common study is to look at the hysteresis behavior across several decades of frequency in a frequency sweep, perhaps in a logarithmic sequence 0.1,0.2,0.5,1,2,5,10, 20 Hz. This will typically characterize the G' elastic stored modulus, the G" viscous loss modulus, and the ratio between them, tan delta (G"/G'), also known as the tangent of the phase advance of stress before strain.

These machines force the rubber to oscillate at the desired frequency. A large frequency sweep may miss a sharp frequency resonance peak if the measured frequencies are far apart. So the aim of the ARES testing was to perform a 'high resolution' frequency sweep across a narrow frequency range, rather than the more usual two or three decades of frequency. Would a high resolution frequency sweep measure a resonance in the rubber at the same frequency as the AYO-IV?

To study this relationship, three compounds were developed (HNBR A, HNBR B and HNBR C), and each compound was tested in compression on the AYO-IV. Results are shown in table 4 and figures 3-5. These same samples were also tested on the TA ARES, and the results were plotted as tan delta versus frequency. A typical graph (figure 6) represents the HNBR C compound with low (top) and high (bottom) normal forces.

The data showed an oddity (figure 6) in the smooth trend of results versus frequency, which was of the same order of magnitude as the AYO-IV. The results did change with the normal force applied to the rubber compound. The preliminary study suggests that the AYO-IV can measure the resonant frequency of the rubber that could be missed by normal frequency sweep testing. The top curve (figure 6) is obtained when less normal force was applied (the specimen was fairly free from normal forces), and the bottom curve represents more normal force being applied (over-damped conditions of the specimen, does not yield the resonant frequency). The hump seen on the top curve is the oddity, which roughly matches the natural frequency obtained on the AYO-IV. This is important to any rubber application where the dynamic behavior of the moving rubber is part of the performance of the system.

The engineers designing rubber goods now have a tool that compounders can use. The compounders can make many experimental compounds, and evaluate each one within a few minutes (including set-up, triplicate measurement and demounting). The AYO-IV is particularly helpful for companies that need dynamic property evaluation. The AYO-IV Yerzley offers time efficient measurement of conventional stiffness and tan delta information, as well as the uniqueness of measuring the natural frequency of the rubber. And the AYO-IV Yerzley is not an expensive machine.

The ARES search for a resonance phenomenon in the forced frequency high resolution testing suggests that the Yerzley technology does indeed measure a feature of the rubber.

Conclusion

The suggested procedure for establishing a common reference between compounding and product molding is as follows:

* The compounders' formulation is vulcanized in a standard sample mold. The resulting sample is tested in an AYO-IV machine at the compounders' sites. Of particular importance is dynamic modulus, natural frequency, tangent of delta and phase angle.

* At the product molding site, the finished product might be tested on a testing machine other than the AYO-IV to obtain the same fundamental parameters and correlate them to the parameters from the AYO-IV. The correlation would be a simple ratio. Users' results indicate that the AYO-IV is very repeatable and exhibits very low standard deviations. Therefore, one can depend on the AYO-IV results to determine how to modify the compound in the desired direction.

* Once these correlation factors are established with repeated use, it may be possible to hit the desired product characteristics by testing at the compounding site only.

* The natural frequency of rubber is indeed measured on the AYO-IV. It should be noted that the natural frequency measured under forced conditions is going to be influenced by the "forced" nature of the frequency sweep tests.

by Ismail Saltuk and Nuri Akgerman, Tavdi Company; Chris Stevens, NGS Group; and Cihan Cengiz, Tekno Kaucuk

References

(1.) ASTM D-945-16 test method.

(2.) Felix L. Yerzley, "The evaluation of rubber and rubber-like compositions as vibration absorbers," Industrial and Engineering Chemistry, Vol. 9, No. 8, August 15, 1937, p. 392.

(3.) Nuri Akgerman and Ismail Saltuk, "Natural frequency in seconds: The modern Yerzley oscillograph (AYO-IV)," Rubber World, January 2017, p. 28.

(4.) Sujitkumar Datta, "Optimum Carbon Black Level for Maximum Impact Energy in Rubber," blog.

(5.) Nuri Akgerman and Ismail Saltuk, "Yerzley oscillograph revisited," Rubber Technology Conference, June 2011, Cleveland, OH.

(6.) Chris Stevens, NSG Group, "Flexible composite rubber reinforced by glass cord for automotive applications," and "Rubber and others," Composite Materials with Rubber, Rubber in Engineering Group, Institute of Materials, Minerals and Mining, December 11, 2015.

Caption: Figure 1--AYO-IV Yerzley mechanical oscillograph with a laptop to test rubber samples within seconds as per ASTM D945-16

Caption: Figure 2--typical compression graph of AYO-IV Yerzley oscillograph

Caption: Figure 3--frequency versus compression strain of rubber compounds (A, B, C)

Caption: Figure 4--dynamic modulus versus compression strain of rubber compounds (A, B, C)

Caption: Figure 5--tan delta versus compression strain of rubber compounds (A, B, C)

Caption: Figure 6--ARES DMA frequency sweep for HNBR C rubber with the oddity at the same order of magnitude as the AYO-IV
Table 1--typical output of an AYO-IV Yerzley compression test

Dynamic parameters compression test results
Machine ID: AYO-IV s/n: 131200C

Material layered rubber HNBR-A
Test ID:                                                1001
Operator:                                               Nuri
Test date:                                          10/22/14
Test time:                                          13:59:55
Specimen height                                 0.575 inches

Specimen area                            0.442 square inches
Sampling rate                          100.00 samples/second
Test duration                                           3.00
Weights forward                                         9.00
Weights middle                                          0.00
Weights rear                                            0.00
Yerzley resilience                            63.005 percent
Resilience-SAE J16                            72.854 percent
Yerzley hysteresis                            36.995 percent
Point modulus                       1116.152 lb./square inch
Frequency                                4.255 cycles/second
Dynamic modulus                     1646.485 lb./square inch
Moment of inertia                   0.37770 slug square foot
Impact energy                     39.415 in.- lb./cubic inch
  or absorbed energy per milspec ZZ-R-768B
Tangent of delta                                      0.1479
Final deflection                              16.119 percent

Table 2--AYO-IV Yerzley shear tests of
rubber specimens per ASTM D945-16

                                           Yerzley shear

                          Yerzley    Resilience      Point
                       resilience        SAEJ16    modulus

1/1                        86.071        89.093      0.548
1/2                        86.581        89.230      0.448
1/3                        86.868        89.537      0.478
1/4                        86.724        89.622      0.432
1/5                        83.783        89.703      0.638
Average                    86.605        89.437      0.509
Range                       0.797         0.610      0.207
Standard deviation          0.317         0.263      0.085

2/1                        82.890        86.885      0.359
2/2                        84.092        87.283      0.345
2/3                        84.331        87.279      0.337
2/4                        84.467        87.541      0.326
2/5                        84.581        87.378      0.359
Average                    84.072        87.273      0.345
Range                       1.691         0.656      0.033
Standard deviation          0.686         0.242      0.014

3/1                        85.872        89.544      0.440
3/2                        86.790        89.367      0.395
3/3                        86.704        89.356      0.401
3/4                        86.929        89.493      0.421
3/5                        87.190        89.707      0.011
Average                    86.697        89.493      0.333
Range                       1.318         0.351      0.429
Standard deviation          0.497         0.144      0.181

4/1                        85.938        89.160      0.433
4/2                        86.816        89.453      0.413
4/3                        86.633        89.074      0.442
4/4                        86.689        89.160      0.429
4/5                        86.848        89.407      0.541
Average                    86.585        89.251      0.452
Range                       0.910         0.379      0.128
Standard deviation          0.372         0.168      0.051

Average                    85.990        88.864      0.410
Range                       2.625         2.220      0.175
Standard deviation          0.939         0.738      0.071

                       Dynamic       Tan        [delta]
                       modulus     delta    ([degrees])

1/1                      0.597    0.0687          3.930
1/2                      0.595    0.0681          3.896
1/3                      0.597    0.0650          3.719
1/4                      0.596    0.0638          3.651
1/5                      0.594    0.0635          3.633
Average                  0.596     0.066          3.766
Range                    0.003     0.005          0.297
Standard deviation       0.001     0.002          0.139

2/1                      0.510    0.0811          4.637
2/2                      0.512    0.0802          4.585
2/3                      0.512    0.0808          4.619
2/4                      0.511    0.0775          4.432
2/5                      0.511    0.0789          4.511
Average                  0.511     0.080          4.557
Range                    0.002     0.004          0.205
Standard deviation       0.001     0.001          0.085

3/1                      0.579    0.0641          3.668
3/2                      0.577    0.0668          3.822
3/3                      0.579    0.0678          3.879
3/4                      0.579    0.0661          3.782
3/5                      0.579    0.0648          3.708
Average                  0.579     0.066          3.771
Range                    0.002     0.004          0.211
Standard deviation       0.001     0.001          0.085

4/1                      0.600    0.0671          3.839
4/2                      0.597    0.0649          3.713
4/3                      0.601    0.0683          3.907
4/4                      0.599    0.0679          3.884
4/5                      0.600    0.0651          3.725
Average                  0.599     0.067          3.814
Range                    0.003     0.003          0.194
Standard deviation       0.001     0.002          0.090

Average                  0.571     0.070         3.9771
Range                    0.088     0.014         0.7911
Standard deviation       0.031     0.005         0.2771

Table 3--AYO-IV Yerzley compression tests of
rubber specimens per ASTM D945-16

                                    Yerzley compression

                        Yerzley    Resilience      Point
                     resilience        SAEJ16    modulus

1/1                      85.705        90.024      2.627
1/2                      85.631        90.191      2.556
1/3                      85.616        90.274      2.634
1/4                      85.859        90.057      2.347
1/5                      85.647        90.118      2.367
Average                  85.692        90.133      2.506
Range                     0.243         0.250      0.287
Standard deviation        0.099         0.101      0.140

2/1                      84.923        89.343      2.479
2/2                      84.811        89.346      2.589
2/3                      85.079        89.392      2.447
2/4                      84.959        89.401      2.433
2/5                      83.983        89.194      2.480
Average                  84.751        89.335      2.486
Range                     1.096         0.207      0.156
Standard deviation        0.440         0.083      0.061

3/1                      86.154        90.651      2.575
3/2                      86.847        90.952      2.395
3/3                      86.975        90.907      2.521
3/4                      86.784        90.877      2.654
3/5                          --            --         --
Average                  86.690        90.847      2.536
Range                     0.821         0.301      0.259
Standard deviation        0.366         0.134      0.109

4                        85.516        90.161      2.492
5                        85.755        90.765      2.631
6                        85.949        91.174      2.578
7                        85.599        90.570      2.596
8                        85.981        90.656      2.570
Average                  85.760        90.665      2.573
Range                     0.465         1.013      0.139
Standard deviation        0.206         0.365      0.051

Average                  85.742        90.455      2.549
Range                     1.939         1.839      0.145
Standard deviation        0.542         0.569      0.053

                     Dynamic       Tan      [delta]
                     modulus     delta    ([degrees])

1/1                    4.576    0.0507        2.902
1/2                    4.630    0.0490        2.805
1/3                    4.626    0.0485        2.777
1/4                    4.616    0.0499        2.857
1/5                    4.629    0.0493        2.822
Average                4.615     0.049        2.833
Range                  0.054     0.002        0.126
Standard deviation     0.023     0.001        0.049

2/1                    4.516    0.0548        3.137
2/2                    4.484    0.0545        3.120
2/3                    4.502    0.0541        3.097
2/4                    4.508    0.0547        3.131
2/5                    4.466    0.0565        3.234
Average                4.495     0.055        3.144
Range                  0.050     0.002        0.137
Standard deviation     0.020     0.001        0.053

3/1                    4.657    0.0477        2.731
3/2                    4.681    0.0461        2.639
3/3                    4.694    0.0460        2.634
3/4                    4.681    0.0466        2.668
3/5                       --        --           --
Average                4.678     0.047        2.668
Range                  0.037     0.002        0.097
Standard deviation     0.015     0.001        0.045

4                      4.545    0.0514        2.942
5                      4.640    0.0461        2.639
6                      4.665    0.0431        2.468
7                      4.583    0.0470        2.691
8                      4.653    0.0483        2.765
Average                4.617     0.047        2.701
Range                  0.120     0.008        0.474
Standard deviation     0.051     0.003        0.174

Average                4.609     0.048       2.7691
Range                  0.183     0.012       0.6761
Standard deviation     0.064     0.004       0.2061

Table 4--AYO-IV Yerzley compression test
results of rubber compounds A, B, C

                                Dynamic
HNBR A   Strain    Frequency    modulus     MPa    Tan delta
         16.12%        4.255       1646    11.3       0.1479
         16.93%        4.348       1719    11.8       0.1478
         16.07%        4.255       1646    11.3       0.1481
         10.21%            5       1524    10.5       0.1489

                                Dynamic
HNBR B   Strain    Frequency    modulus     MPa    Tan delta
          8.75%        6.667       5565    38.2       0.1739
          8.65%        6.667       5565    38.2        0.167
          8.83%        6.452       5212    35.8       0.1657
          7.01%        7.407       3995    27.4       0.1509

                                Dynamic
HNBR C   Strain    Frequency    modulus     MPa    Tan delta
         10.19%         6.25       5476    37.6       0.1662
         10.25%        6.452       5835    40.1       0.1664
         10.14%         6.25       5476    37.6       0.1686
          9.50%         6.25       4837    33.2       0.1769
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Author:Saltuk, Ismail; Akgerman, Nuri; Stevens, Chris; Cengiz, Cihan
Publication:Rubber World
Date:Jan 1, 2019
Words:2841
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