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Investigating Elastomeric Materials

In this study we investigated elastomeric materials based on natural rubber used in the manufacture of rubber and rubber-metal vibration isolators. Basic anti-vibration properties were identified and stability over time was predicted. To achieve the objectives, tests were conducted on a mechanical oscilloscope Yerzley AYO-IV.

According to the research (Figure 1), we observed that replacement of the active carbon black N220 with high structural properties on the active carbon black К-354 and P-234 with a low index of structural in the ratio 1: 1 leads to a slight increase in such parameters as static and dynamic modules, hysteresis loss, and also to reduction of the coefficient of elasticity and vibration isolation.

Figure 1. Physical and mechanical properties of the elastomeric material based on natural rubber
Figure 1. Physical and mechanical properties of the elastomeric material based on natural rubber

To predict the stability of the main anti-vibration characteristics of the test material we were applied accelerated aging method according to GOST (Russian National Standard ) – 9.707 and method of prediction changes of properties during thermal aging according to GOST (Russian National Standard ) – 9.713.

According the results of the research we were constructed the graphics of combined curves (Figures 2, 3 and 4).

Picture 2 – Graph of the dependence of the logarithmic decrement of the elastomeric material from time
Figure 2. Dependence of the logarithmic decrement of the elastomeric material from time
Figure 3. Dependence of the static modulus of elastomeric material from time
Figure 3. Dependence of the static modulus of elastomeric material from time
Figure 4. Graph of the dependence of the hysteresis of the elastomeric material from time
Figure 4. Dependence of the hysteresis of the elastomeric material from time

The replacement of the active carbon black К-354 and P-234 on the active carbon black N220 in the elastomeric material based on natural rubber led to an increase in the stability of anti-vibration characteristics in the first years of using. However, lately no significant difference was observed.

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Contributed by: Maxim Myslivets and Elizabeth Burdakova, Russia

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Optimum Carbon Black Level for Maximum Impact Energy in Rubber

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Contributed by: Dr. Sujitkumar Dutta

Not all rubber compositions are the same. It turns out that there is an optimum level of carbon black for maximum energy absorption capacity. One of our clients ran a series of tests on their Advanced Yerzley Oscillograph (AYO-IV) for Natural Rubber and Chloroprene Rubber at five different levels of carbon black. Their results show a definite maximum impact energy absorption level at 75 parts per hundred of rubber (PHR).

Impact Energy Graph for Carbon Black Level

Dynamic parameter tests are quick and easy on our Advanced Yerzley Oscillograph, taking just two to five seconds with results evaluated instantaneously.

From a single test cycle, we determine:

  • Hysteresis
  • Natural frequency
  • Static and dynamic moduli
  • Tangent of delta and other parameters

The Advanced Yerzley Oscillograph (AYO-IV) satisfies the requirements of ASTM D945-12 and can be viewed here.

 

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Vibration Isolation and the Yerzley Oscillograph

Impact energy absorption and hysteresis are important parameters that predict vibration isolation characteristics of rubber compounds. The rubber used in vibration isolators should have an optimum amount of fillers (carbon black) to maximize energy absorption. The work by Dr. Sujit K. Datta of IRM Corp. of India shows that there is an optimum level of carbon black filler beyond which energy absorption characteristics are degraded. As illustrated below, at 75 Parts per Hundred parts of Rubber (PHR) energy absorption is maximized; whereas, the hysteresis plot flattens out after 75 PHR.

These results were obtained by using an Advanced Yerzley Oscillograph.

hysteresis impactimpact energy image

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Using Yerzley Oscillograph in Vibration Isolation

If you are working in vibration isolation with rubber pads and similar materials, you will find AYO-IV to be a versatile instrument. It allows you to estimate the natural frequency of your system as well as the static and dynamic spring constants and the amount of damping you can expect. By manipulating the location and number of weights, AYO-IV can be used to simulate the vibration isolation environment and determine the range of expected natural frequencies, spring constants, and damping. Figure 1 shows the results of a typical AYO-IV run.

Typical AYO-IV Analysis Results
Figure 1: Typical AYO-IV Analysis Results

Static spring constant (units lb./in) of a rubber pad can be defined as:

(Static Modulus) * Area / Height

Similarly, dynamic spring constant of a rubber pad is:

(Dynamic Modulus) * Area / Height

We use the parameters for “hard rubber B” as measured by AYO-IV and displayed in Figure 1. Let’s say we have a 6000 lb. machine to be isolated by three rubber pads. Let’s assume that we place these pads such that each pad carries roughly 1/3 of the weight; thus, each pad carries 2000 lbs. Let’s say we are going to use round pads that are 1 inch thick with a diameter of 4 inches. Area = 12.566 in2.

Static Spring Constant = 1387.6 lb./in2 * 12.566 in2 / 1 in. = 17,437 lb./in

Static Deflection = 2000 / 17437 = 0.115 in.

Interestingly, this is the same static deflection that was observed in the AYO-IV test shown in Figure 1.

The natural frequency of the spring-mass system is given by:

vibration_equation

Where “fn” is cycles/sec. K is (lb/in), g is the acceleration of gravity 386in/sec. sq and W is the weight in lb.

In this case, we use the Dynamic Spring Constant Kd = 2665*12.566/1 => 33,488 lb/in.

The calculated natural frequency is: 12.795 cycles/sec. We can reduce the natural frequency by increasing the height and/or reducing the area of our pads.

Controlling the natural frequency is not the only means of vibration isolation; the other is damping. Damping is the dissipation of energy. In the case of elastomeric materials, energy is dissipated by internal friction by a mechanism known as “hysteretic damping”. Yerzley Hysteresis, among the results, is a measure of this property.

Dyn_Parameters_Compression_Test_Results
Figure 2: Dynamic Parameters Compression Test Results
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Testing Rubber Sheet Material

SheetRubberWe can’t always press a proper test specimen. In order to test rubber sheet material with AYO-IV, you can use a layered approach. Get a 3/4″ hole punch. As seen in the image, punch out enough round plugs so the total thickness is close to 1/2 inch. The idea is to put enough round plugs on top of each other to reach a height of approximately 1/2 inch. During AYO-IV setup, enter the actual height. In this case, the area is the same as a standard specimen: 3/4 inch. Thus, the area is the same as the standard specimen. Please note that this approach is not approved by ASTM D945; however, it is useful for comparing different sheet materials.
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