Take You Behind the Scenes of Thermal Mechanical Analysis - Thermomechanical Analyzer

1 Introduction

In real life and production, when we study a certain material, we often need to measure its physical properties in relation to temperature to better understand the characteristics of the material. Therefore, various thermal analysis techniques are commonly used for related measurements, such as thermogravimetric analysis (TG), derivative thermogravimetric analysis (DTG), and differential scanning calorimetry (DSC). Among them, thermomechanical analysis is a technique for measuring the relationship between the deformation of a material and functions such as temperature and time. It is mainly used to measure parameters like the coefficient of expansion and phase transition temperature of materials and is widely applied in many fields of life. The instrument used for this measurement is called a thermomechanical analyzer (TMA). Next, we will provide a detailed introduction to the thermomechanical analyzer.

2 Classification of Thermomechanical Analyzers

The method of conducting mechanical measurements on a sample during heating is called thermomechanical analysis. Based on the measurement content, thermomechanical methods can be divided into two types: static and dynamic.

2.1Dynamic Thermomechanical Analysis (DMA)

Dynamic thermomechanical analysis (DMA) is a method for measuring the modulus and mechanical damping of materials under oscillatory load as the temperature changes, under programmed temperature control. It is commonly used to measure the relationship between the mechanical properties of viscoelastic materials and time, temperature, or frequency. The sample undergoes deformation under the influence of periodically varying (sinusoidal) mechanical stress. This method is particularly sensitive and practical for measuring the movement of molecular structural units, especially at low temperatures. The instrument used for this measurement is called a dynamic thermomechanical analyzer, as shown in Figure 1.

Figure 1: Dynamic Thermomechanical Analyzer (DMA)

2.2 Static Thermomechanical Analysis (TMA)

Static thermomechanical analysis (TMA) is a technique for measuring the deformation of a material under non-oscillatory load as the temperature changes, under programmed temperature control. When the load is zero, the relationship between the size change of the material and temperature is measured, which is also known as the dilatometry method. These two functions are often realized on the same instrument, differing only in the shape of the probe and the load applied. The instrument used for this measurement is called a static thermomechanical analyzer, as shown in Figure 2.

Figure 2: Thermomechanical Analyzer (TMA)

Since the mechanical properties of various materials change with temperature, thermomechanical analysis is crucial for studying and measuring the application temperature range, processing conditions, and mechanical properties of materials. Compared to TMA (static thermomechanical analyzers), DMA (dynamic thermomechanical analyzers) can determine the dynamic mechanical properties of viscoelastic materials under different frequencies, temperatures, and loads. However, DMA is less commonly used in China, with only a few universities and research institutions capable of conducting DMA testing. TMA is more commonly used for analysis and research.

3 Basic Principles and Composition of Thermomechanical Analyzers

3.1 Basic Principles of Thermomechanical Analyzers

As one of the major types of thermal analysis techniques, the basic principle of thermomechanical analyzers is similar to that of dilatometry analyzers, which measure the size changes of solids and liquids with temperature. Mainly, under programmed temperature control, the internal linear variable differential transformer (LVDT) of the instrument measures the size changes of materials caused by heat and mechanical loads. This obtains measurements of expansion, stretching, compression, and bending under different load conditions (such as pressure or tension). The operating modes, test probes, and working fixtures of thermomechanical analyzers are highly flexible and can provide sensitive signals. The probe in the instrument is supported by a cantilever beam and a coil spring mounted on it. A motor applies a load to the sample. When the sample length (i.e., the relative position of the sample tube and the probe) changes, the differential transformer detects this change. The temperature, stress, and strain data are collected by the central processor of the thermomechanical analyzer and sent to the workstation for data analysis.

3.2 Composition of Thermomechanical Analyzers

Thermomechanical analyzers are mainly composed of the frame, indenter, loading device, heating device, cooling device, deformation measuring device, recording device, and temperature program control device. The main parameters of each component are as follows:

1. Frame: Rigid structure that does not deform in the axial direction within the test temperature range.
2. Indenter: Diameter of 4.0 mm and length of 10 mm.
3. Loading Device: Can apply a pressure of 0.4 MPa to the sample through the rod and indenter.
4. Heating Device: Program control system with a temperature control rate of 1.2 °C/min and a temperature control accuracy of 0.5 °C.
5. Cooling Device: Minimum temperature of -150 °C.
6. Deformation Measuring Device: The probe outputs an electrical signal of 1 μV for every 1 μm displacement.

4 Features of Thermomechanical Analyzers

Thermomechanical analyzers have outstanding performance, making them ideal tools for scientific research, teaching, and quality control. The instrument has many features, as detailed below:

Wide working temperature range: -150 to 1500 °C, with self-protection function during melting. Superimposed sinusoidal load: Forms DMA mode (0.001-1 Hz) to measure the dynamic mechanical properties of materials.

1. High precision loading motor: Ensures accurate experimental results.
2. Stress and strain control technology.
3. High-resolution function: Uses Step Temp mode.
4. Wide measurement range: Maximum load: 0.01-6 N.
5. Equipped with an automatic liquid nitrogen cooling system.
6. Large-volume thermogravimetric analysis (TGA) function.
7. Capability to perform measurements while immersed in liquid.
8. Constant/linear load mode: Measures the dynamic mechanical properties of materials.
9. Controlled conversion rate technology (CRTA): Controls the material's strain.
10. Background subtraction.
11. Automatic sample size reading.
12. Capability to perform measurements under different humidity conditions.

5 Functions and Applications of Thermomechanical Analyzers

5.1 Functions of Thermomechanical Analyzers

Thermomechanical analyzers are widely used in various fields, including plastics, rubber, films, fibers, coatings, ceramics, glass, metals, and composite materials. The instrument can be used to measure and study the following properties of materials:

1. Linear expansion and shrinkage properties.
2. Glass transition temperature.
3. Puncture properties.
4. Stretching and shrinkage of films and fibers.
5. Thermal properties analysis of thermoplastic materials.
6. Phase transitions.
7. Softening temperature.
8. Molecular recrystallization effects.
9. Stress-strain relationships.
10. Curing properties of thermosetting materials.

5.2 Applications of Thermomechanical Analyzers

Dynamic thermomechanical analyzers are mainly used to measure the relationship between the mechanical properties of viscoelastic materials and time, temperature, or frequency. They are also widely used in various fields.

It is well known that non-aqueous reactive polymer materials are new anti-seepage repair and support materials, characterized by light weight, early strength, high toughness, durability, and environmental friendliness. They are currently widely used in flood control and repair projects for basic engineering facilities. In practical engineering applications, polymer materials are often subjected to dynamic loads, and their viscoelastic properties are crucial for analyzing the dynamic response of polymer composite structures. Researchers such as Li Jia and Chen Shuo first applied dynamic thermomechanical analysis technology to study the dynamic viscoelastic properties of non-aqueous reactive polymer materials. As shown in Figures 4 and 5, during the corresponding amplitude test process of non-aqueous reactive polymer grouting materials, the amplitude test results of the temperature spectrum and frequency spectrum can be obtained.

Figure 3: DMA amplitude test (temperature spectrum)

Figure 4: DMA amplitude test (frequency spectrum)

References

[1] Li Jia, Chen Shuo, Zhang Jingwei, Wang Julong. Dynamic Viscoelastic Test Study of Non-Aqueous Reactive Polymer Materials Based on Dynamic Thermomechanical Analysis [J]. Journal of Building Materials, 2019.