Measurement and Control
The concept of the new “Dynamic Mechanical Yerzley Oscillograph – V” is based on the venerable “Advanced Yerzley Oscillograph – IV as per ASTM D945-16”. Both are based on weights on an oscillating beam always testing elastomers at the natural frequency of the configuration.
- AYO-IV has two possible moment arms, 5″ or 10″; whereas, DMYO-V has a variable moment arm that automatically adjusts between 4″ and 11″. The weight table is motorized, it can setup automatically at any specified strain.
- DMYO-V has a load cell in addition to a displacement transducer. Both load and displacement are measured simultaneously, enabling:
- The observation of the phase lag between Load and Displacement.
- The comparison of measured Phase Angle to the theoretically calculated (ASTM 5992) Loss Angle.
- The manual “Step Wise” hysteresis test of the AYO-IV is fully automated on the DMYO-V. The static hysteresis test is user-programmable and normally runs unattended on this test machine.
- The Dynamic Test on the DMYO-V is automated with a magnetic trigger, which enhances repeatability.
- The data processing and parameter evaluation procedures have been improved with noise elimination and data-smoothing algorithms.
- Minima and Maxima detection mechanisms use least square error curve fitting to improve accuracy. This is crucial for evaluating phase angles.
Figure 1. Point Modulus and Dynamic Modulus vs. Measured Load for NR with Shore A 40.
Figure 2. Point Modulus and Dynamic Modulus vs. Measured Load for NR with Shore A 70.
Here are some points to stress to the engineers and the technicians of the compounders, process engineers, sales engineers, and so on.
- Automotive door seals: Dynamic Modulus (low values), Dynamic/Static Ratio of moduli (low values), help to design the automotive door seals correctly for better sound-proofing and longevity.
- Engine mounts: Yerzley Resilience (low values) and Yerzley Hysteresis (higher values) as well as Impact Energy (low values), Phase angle (high values) will absorb vibration energy much more efficiently for smooth riding.
- Windshield wipers: Dynamic Modulus (low values), Dynamic/Static Ratio of moduli (low values), helps to design the wipers correctly for better and long-term wiping function. Climate change (summer & winter) should have minimal effect on the wiping function.
- Seismic Pads in construction industry: Dynamic Modulus, Impact Energy, Phase angle all have to have high values for high damping function. Natural frequency around 5 to 9 Hertz may also be useful for the design criteria.
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.
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).
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.
Contributed by: Maxim Myslivets and Elizabeth Burdakova, Russia
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).
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:
- 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.
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.
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:
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.
We 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.