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PT Category: Indentation | Loss and Storage
Dynamic Mechanical Analysis (DMA) Frequency Sweep on Polymer
DMA FREQUENCY SWEEP
ON POLYMER USING NANOINDENTATION
Prepared by
Duanjie Li, PhD
INTRODUCTION
IMPORTANCE OF DYNAMIC MECHANICAL ANALYSIS FREQUENCY SWEEP TEST
The changing frequency of the stress often leads to variations in the complex modulus, which is a critical mechanical property of polymers. For example, tires are subjected to cyclical high deformations when vehicles are running on the road. The frequency of the pressure and deformation changes as the car accelerates to higher speeds. Such a change can result in variation in the viscoelastic properties of the tire, which are important factors in the car performance. A reliable and repeatable test of the viscoelastic behavior of polymers at different frequencies is in need. The Nano module of the NANOVEA Mechanical Tester generates sinusoidal load by a high precision piezo actuator and directly measures the evolution of force and displacement using ultrasensitive load cell and capacitor. The combination of easy setup and high accuracy makes it an ideal tool for Dynamic Mechanical Analysis frequency sweep.
Viscoelastic materials exhibit both viscous and elastic characteristics when undergoing deformation. Long molecular chains in polymer materials contribute to their unique viscoelastic properties, i.e. a combination of the characteristics of both elastic solids and Newtonian fluids. Stress, temperature, frequency and other factors all play roles in the viscoelastic properties. Dynamic Mechanical Analysis, also known as DMA, studies the viscoelastic behavior and complex modulus of the material by applying a sinusoidal stress and measuring the change of strain.
MEASUREMENT OBJECTIVE
In this application, we study viscoelastic properties of a polished tire sample at different DMA frequencies using the Most Powerful Mechanical Tester, NANOVEA PB1000, in Nanoindentation mode.
NANOVEA
PB1000
TEST CONDITIONS
FREQUENCIES (Hz):
0.1, 1.5, 10, 20
CREEP TIME AT EACH FREQ.
50 sec
OSCILLATION VOLTAGE
0.1 V
LOADING VOLTAGE
1 V
indenter type
Spherical
Diamond | 100 μm
RESULTS & DISCUSSION
The Dynamic Mechanical Analysis frequency sweep at the maximum load allows a fast and simple measurement on the viscoelastic characteristics of the sample at different loading frequencies in one test. The phase shift and the amplitudes of the load and displacement waves at different frequencies can be used to calculate a variety of fundamental material viscoelastic properties, including Storage Modulus, Loss Modulus and Tan (δ) as summarized in the following graphs.
Frequencies of 1, 5, 10 and 20 Hz in this study, correspond to speeds of about 7, 33, 67 and 134 km per hour. As the test frequency increases from 0.1 to 20 Hz, it can be observed that both Storage Modulus and Loss Modulus progressively increase. Tan (δ) decreases from ~0.27 to 0.18 as the frequency increases from 0.1 to 1 Hz, and then it gradually increases to ~0.55 when the frequency of 20 Hz is reached. DMA frequency sweep allows measuring the trends of Storage Modulus, Loss Modulus and Tan (δ), which provide information on the movement of the monomers and cross-linking as well as the glass transition of polymers. By raising the temperature using a heating plate during the frequency sweep, a more complete picture of the nature of the molecular motion under different test conditions can be obtained.
EVOLUTION OF LOAD & DEPTH
OF THE FULL DMA FREQUENCY SWEEP
LOAD & DEPTH vs TIME AT DIFFERENT FREQUENCIES
STORAGE MODULUS
AT DIFFERENT FREQUENCIES
LOSS MODULUS
AT DIFFERENT FREQUENCIES
TAN (δ)
AT DIFFERENT FREQUENCIES
CONCLUSION
In this study, we showcased the capacity of the NANOVEA Mechanical Tester in performing the Dynamic Mechanical Analysis frequency sweep test on a tire sample. This test measures the viscoelastic properties of the tire at different frequencies of stress. The tire shows increased storage and loss modulus as the loading frequency increases from 0.1 to 20 Hz. It provides useful information on the viscoelastic behaviors of the tire running at different speeds, which is essential in improving the performance of tires for smoother and safer rides. The DMA frequency sweep test can be performed at various temperatures to mimic the realistic working environment of the tire under different weather.
In the Nano Module of the NANOVEA Mechanical Tester, the load application with the fast piezo is independent from the load measurement done by a separate high sensitivity strain gage. This gives a distinct advantage during Dynamic Mechanical Analysis since the phase between depth and load is measured directly from the data collected from the sensor. The calculation of phase is direct and does not need mathematical modeling that adds inaccuracy to the resulting loss and storage modulus. This is not the case for a coil-based system.
In conclusion, DMA measures loss and storage modulus, complex modulus and Tan (δ) as a function of contact depth, time and frequency. Optional heating stage allows determination of materials phase transition temperature during DMA. The NANOVEA Mechanical Testers provide unmatched multi-function Nano and Micro modules on a single platform. Both the Nano and Micro modules include scratch tester, hardness tester and wear tester modes, providing the widest and most user friendly range of testing available on a single module.
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Precise Localized Glass Transition with Nanoindentation DMA
Precise Localized Glass Transition with Nanoindentation DMA
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Imagine a scenario where a bulk sample is uniformly heated at a constant rate. As a bulk material heats up and approaches its melting point, it will start to lose its rigidity. If periodic indentations (hardness tests) are conducted at the same target force, the depth of each indent should be constantly increasing since the sample is becoming softer (see figure 1). This continues until the sample begins to melt. At this point, a large increase in the depth per indent will be observed. Using this concept, phase change in a material can be observed by using dynamic oscillations with a fixed force amplitude and measuring its displacement, i.e. Dynamic Mechanical Analysis (DMA).
Read about Precise Localized Glass Transition!
Stress Relaxation Measurement using Nanoindentation
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Viscoelastic Analysis of Rubber
Viscoelastic Analysis of Rubber
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Tires are subjected to cyclical high deformations when vehicles are running on the road. When exposed to harsh road conditions, the service lifetime of the tires is jeopardized by many factors, such as the wear of the thread, the heat generated by friction, rubber aging, and others.
As a result, tires usually have composite layer structures made of carbon-filled rubber, nylon cords, and steel wires, etc. In particular, the composition of rubber at different areas of the tire systems is optimized to provide different functional properties, including but not limited to wear resistant thread, cushion rubber layer, and hard rubber base layer.
A reliable and repeatable test of the viscoelastic behavior of rubber is critical in quality control and R&D of new tires, as well as evaluation of the life span of old tires. Dynamic Mechanical Analysis(DMA) during Nanoindentation is a technique of characterizing the viscoelasticity. When controlled oscillatory stress is applied, the resulting strain is measured, allowing users to determine the complex modulus of the tested materials.
Dynamic Mechanical Analysis With Nanoindentation
The quality of corks depends heavily on its mechanical and physical property. Its ability to seal wine can be identified as these important factors: flexibility, insulation, resilience, and impermeability to gas and liquids. By conducting dynamic mechanical analysis (DMA) testing, its flexibility and resilience properties can be gauged with a quantifiable method. These properties are characterized with Nanovea Mechanical Tester’s Nanoindentaion in the form of Young’s modulus, storage modulus, loss modulus, and tan delta (tan (δ)). Other data that can be gathered from DMA testing are phase shift, hardness, stress, and strain of the material.
