Thermal Analysis in the Automotive Industry
On Demand Webinar

Thermal Analysis in the Automotive Industry

On Demand Webinar

"Thermal Analysis in the Automotive Industry" presents techniques used to assess automotive parts

Thermal Analysis in the Automotive Industry
Thermal Analysis in the Automotive Industry

Thermal analysis methods are important for analyzing materials used in the automotive industry. The methods can be used for quality control, failure analysis as well as for the development of advanced, high performance materials. In this industry, knowledge of temperature-dependent material properties is very important.
The four main techniques, DSC, TGA, TMA, and DMA are ideal for meeting the analysis requirements of this industry.

In this Webinar, we will show how thermal analysis is used in the automotive industry and present some typical examples of samples measured by DSC, TGA, TMA, or DMA.

51:19 min
English

The Webinar covers the following topics:

  • Introduction
  • Typical questions
  • Thermal analysis
  • Instruments and applications
    - DSC
    - TGA
    - TMA
    - DMA
  • Summary

In the webinar titled "Thermal Analysis in the Automotive Industry", we describe a number of interesting application examples that demonstrate the use of thermal analysis techniques in the automotive industry

Thermal analysis in the automotive industry

Due to the wide range of materials used in automotive industries, virtually all thermal analysis techniques can be used in quality control, and for research and development. For example, with adhesives, parameters such as gelation and the curing time as function of temperature are important for optimizing the performance of products.

Elastomers are not only used for tires but also as sealing materials for windows or for hoses and tubes. However, the automotive industry is by far the most important market for elastomers. The main properties investigated are the glass transition, composition, expansion, the modulus, and damping behavior.

The use of composites in the automotive sector continues to grow. The primary reason for using composites instead of metals is to reduce weight and so improve fuel economy. Here again, the glass transition, composition, modulus, expansion, and damping behavior are important properties.

Thermal analysis techniques and their applications

The most important effects that can be analyzed by DSC are the glass transition, melting, crystallization behavior, reaction enthalpies and kinetics, and the influence of fillers.

For TGA, the main applications are content analysis and thermal stability.

TMA is normally used to study the expansion or shrinkage of materials.

DMA is the best method for characterizing the frequency-, force-, and amplitude-dependent mechanical behavior of materials.

Thermal Analysis in the Automotive Industry

Slide 0: Thermal Analysis in the Automotive Industry

Ladies and Gentlemen,

Welcome to the METTLER TOLEDO webinar on “Thermal Analysis in the Automotive Industry”.

During the course of the webinar, I would like to describe a number of interesting application examples that demonstrate the use of thermal analysis techniques in the automotive industry. These have mainly to do with the measurement and testing of physical properties.

Typical examples include the identification of polymers by their glass transition temperature, crystallization and melting processes, compositional analysis and decomposition behavior, and the determination of mechanical parameters such as the coefficient of thermal expansion or the modulus.

 

Slide 1: Contents

This slide lists the main topics I want to cover in the seminar.

 

I would like to begin with some comments about important effects and properties that can be investigated by thermal analysis in the automotive industry. I will then discuss the techniques used to measure them.

The techniques include:

Differential Scanning Calorimetry, or DSC,

Thermogravimetric Analysis, or TGA,

Thermomechanical Analysis, or TMA,

and Dynamic Mechanical Analysis, or DMA.

 

I will then present several applications that illustrate the use of these techniques in the automotive industry.

Finally, I want to summarize the different thermal analysis techniques and their applications and list a number of useful references for further information and reading.

 

Slide 2: Introduction

Some typical questions that arise in connection with the manufacture of cars, trains, trucks or engines are:

 

How do you ensure material properties meet your specifications?

            In the automotive industry, many parts are produced by third-party suppliers. As a manufacturer, you have to ensure that the properties of the parts meet your specifications, for example, with regard to composition, temperature of use, expansion coefficients, damping properties, or safety aspects. These characteristic properties can very often be tested and verified by thermal analysis.

 

Do you need to develop new materials?

            Currently, an important issue in the automotive industry is the development of carbon-reinforced composites and the techniques needed to bond such materials together, or to bond them with other materials such as metals or other polymeric materials. Here again, thermal analysis techniques offer significant advantages.

 

Slide 3: Introduction

The slide shows typical components and materials that can be found in different parts of a motor vehicle. These include almost all the currently used materials such as polymers, metals, and ceramics.

For example, the interior of a car is nowadays mostly made of different thermoplastic materials. The use of thermoplastics has greatly increased over the last few decades in the automotive industry. Thermoplastics offer good mechanical properties, corrosion resistance, design flexibility, and high performance at low cost. They also reduce fuel costs by reducing the weight of vehicles.

Car bumpers are almost exclusively made of reinforced thermoplastic olefins. They should have a very low coefficient of thermal expansion, long-term stability against UV and weathering, and exhibit high damping performance. These properties are influenced by the composition of the material, the degree of cure, and the type and orientation of the filler.

 

Slide 4: Example

Quality control is very important to ensure that materials meet their specifications.

 

This example illustrates the investigation of two semicrystalline thermoplastic seals. In practical use, one material was found to be good and the other unsatisfactory.

The diagram shows DSC heating curves of the two materials; one curve is labeled “Bad” and the other “Good”. The “Bad” seal failed when the temperature reached about 150 degrees Celsius, whereas the “Good” seal performed satisfactorily.

DSC analysis revealed distinct differences between the two materials. The “Bad” material exhibited a glass transition at about 145 degrees that was immediately followed by a crystallization process. In contrast, the “Good” material showed just the glass transition at about 155 degrees and no signs of crystallization.

During crystallization, the material shrinks. This is the reason why the “Bad” seal failed. The different behavior shown by the two seals is due to differences in the processing conditions - the bad seal had been cooled too quickly. As a result of this, the material did not have enough time to crystallize completely. On heating, crystallization continued immediately after the glass transition.

 

Slide 5: Applications

Due to the wide range of materials used in automotive industries, virtually all thermal analysis techniques can be used in quality control, and for research and development.

This is illustrated in the slide, which shows the different types of materials that are investigated and the corresponding applications.

For example, with adhesives, parameters such as gelation and the curing time as function of temperature are important for optimizing the performance of products.

 

Elastomers are not only used for tires but also as sealing materials for windows or for hoses and tubes. However, the automotive industry is by far the most important market for elastomers. The main properties investigated are the glass transition, composition, expansion, the modulus, and damping behavior.

 

The use of composites in the automotive sector continues to grow. The primary reason for using composites instead of metals is to reduce weight and so improve fuel economy. Here again, the glass transition, composition, modulus, expansion, and damping behavior are important properties.

 

Slide 6: Thermal analysis

So what do we mean by Thermal analysis?

According to the International Confederation for Thermal Analysis, ICTAC, thermal analysis is:

“A group of techniques in which a physical property of a substance is measured as a function of temperature whilst the substance is subjected to a controlled temperature program”.

The schematic diagram on the right shows a simple linear temperature program.

The lower half of the diagram illustrates the processes that a material undergoes when it is heated and the characteristic properties involved, for example, physical properties such as the heat capacity, expansion coefficient, or modulus. Fully or partially amorphous materials undergo a glass transition. Crystalline or semi-crystalline materials melt. If the sample is exposed to air or oxygen, it will start to oxidize and finally decompose at higher temperatures. We use thermal analysis techniques to investigate these effects.

 

Slide 7: Thermal Analysis

The slide shows the most important techniques used in thermal analysis, namely:

 

Differential Scanning Calorimetry, or DSC. This is the most widely used thermal analysis technique. The picture shows a DSC sensor with a crucible containing a sample (colored red), and a reference crucible.

 

Thermogravimetric Analysis, or TGA. This technique measures the mass of the sample as a function of temperature using a highly sensitive electronic balance.

 

Thermomechanical Analysis, or TMA, is used to measure dimensional changes of a sample. The picture shows the sample support with a sample (colored red) and the quartz probe.

 

and finally

Dynamic Mechanical Analysis, or DMA, which provides information on mechanical properties. The picture shows one of the different types of sample-clamping assemblies.

 

I will explain these techniques in more detail in the following slides and describe some application examples.

 

Slide 8: Differential Scanning Calorimetry (DSC)

Let’s begin with DSC. This technique allows us to determine the energy absorbed or released by a sample as it is heated or cooled. There are several different types of DSC instruments:

The standard METTLER TOLEDO DSC 1 instrument measures from minus one hundred and fifty degrees Celsius to plus seven hundred degrees Celsius at heating rates of up to three hundred Kelvin per minute. The samples are normally measured in small crucibles made of aluminum, alumina or other materials, using one to twenty milligrams of sample material.

 

The METTLER TOLEDO Flash DSC 1 expands the maximum heating rate to two million four hundred thousand Kelvin per minute (2,400,000 K/min) and the cooling rate to two hundred and forty thousand Kelvin per minute (240,000 K/min). To achieve this, the Flash DSC 1 uses very small samples weighing about one hundred nanograms (100 ng) and no sample crucibles - the sample is in direct contact with the chip-sensor. The ultra-fast heating and cooling rates allow industrial process conditions to be simulated in which materials undergo extremely rapidly cooling.

 

Another powerful DSC technique is high-pressure DSC or HPDSC for short. The METTLER TOLEDO HP DSC 1 can analyze samples under inert-gas- or reactive-gas-atmospheres at pressures of up to one hundred bar or ten mega-pascals. This suppresses undesired vaporization of samples or enables the stability of samples to be studied at increased oxygen pressures.

 

The schematic curve on the left shows a typical DSC measurement curve of a semi-crystalline polymer. Exothermic effects point in the upward direction and endothermic effects downward. The different effects are numbered next to the curve:

One, is the initial deflection or start-up transient of the DSC;

Two, is the baseline where no thermal effects occur;

Three, is a glass transition with enthalpy relaxation;

Four, is cold crystallization;

Five, is melting of the crystalline fraction; and finally

Six, is exothermic oxidative decomposition.

 

Slide 9: Differential Scanning Calorimetry (DSC)

The table on the left of the slide summarizes the main analytical applications of DSC in the automotive field.

 

DSC is used to investigate events and processes such as glass transitions, melting, crystallization, chemical reactions, and thermal stability in which a change in enthalpy occurs.

The information obtained can be used to identify polymers, investigate the working range of materials, and for compositional analysis. The method can be employed in quality control and for the analysis of raw materials, additives, and fillers, as well as to characterize vulcanization and other types of reactions.

DSC curves also contain information about the thermal history of a sample. The stability of materials can be determined using the oxidation induction time or OIT method. Other important applications include the investigation of the curing kinetics of reactive systems, and the influence of stabilizers, plasticizers or other additives. Most of the events involved are related to enthalpy changes that occur when the temperature is increased or decreased.

The picture on the right of the slide shows a view of an open DSC furnace with sample and reference crucibles. The standard crucibles are made of aluminum.

METTLER TOLEDO has also developed versatile optical techniques that allow you to observe changes that occur in a sample while it is heated or cooled. The techniques include DSC-Microscopy and DSC-Chemiluminescence.

The Photocalorimetry Option is used in combination with the DSC and allows you to study the effect of light-curing on network formation in materials.

 

Slide 10: Application 1: DSC                  Glass transition, melting, crystallization

The slide shows an example of polymer “fingerprinting”.

The diagram displays the glass transition, melting and crystallization curves of several different commonly used polymers. Curves like this allow you to identify polymers and to compare different batches of the same material. Glass transitions and melting peaks are the properties usually measured.

The temperatures at which the glass transition and melting occur define the usable temperature range of manufactured parts and are also used to identify polymers.

Quantitatively, a melting peak is characterized by its peak temperature and the enthalpy of melting. The normalized enthalpy of melting of a sample can also be used to quantify its crystallinity if suitable reference materials or reference values are available.

Glass transitions are characterized by a step-like change in the heat flow. In the first heating run, the transition is often accompanied by a peak related to enthalpy relaxation. An example of this can be seen in the DSC curve of PET. Large enthalpy relaxation peaks only appear in the first heating run.

Crystallization is normally measured by cooling the sample from the melt. The DSC curves of two PBT samples illustrate the fact that additives - in this case, carbon black, which is used as a colorant and UV stabilizer - can affect crystallization behavior.

 

Slide 11: Application 2: DSC                              OIT of engine oils

The long-term stability of materials such as paints, lacquers, oils, thermoplastics can be characterized by measuring the oxidation induction time, or OIT for short.

Several standard test methods define how OIT measurements should be performed. The basic procedure is to expose the sample to oxygen at a temperature specific for the material. The OIT is the time it takes until oxidation begins, that is the onset of oxidation. This is detected as an increase in the exothermic heat flow signal.

Since the isothermal measurement temperature is usually far above the temperature at which the material is normally used, OIT experiments are known as accelerated aging tests. The method is frequently used to compare the influence of stabilizers on the stability of a material.

The OIT test is performed isothermally, typically between 150 and 250 °C, in an oxygen atmosphere. Modern materials with anti-oxidative additives are designed to withstand higher temperature and longer exposure times than common materials.

OIT measurements can also be performed in a high-pressure DSC instrument. In this case, pressure acts as an additional accelerator. The oxygen pressure also influences the measured OIT. This is illustrated in the slide.

In the experiment shown, two different engine oils, A and B, were measured at various pressures. Some of the original OIT measurements are shown on the right of the diagram. The curves often exhibit a peak or a shoulder before the main oxidation process occurs. This effect is due to the stabilizer. The inset diagram on the left summarizes the influence of oxygen pressure on the OIT times.

 

Slide 12: Application 3: DSC                              Curing of an Adhesive

Adhesives are being increasingly used in the automotive industry for joining materials together, and are replacing conventional techniques such as welding, riveting, or bolting. To ensure reliable bonding, the crosslinking reaction process of the adhesive has to be carefully investigated.

The example shows the results obtained from the DSC measurement of the exothermic curing process of a cold-setting adhesive. The initial DSC curves are displayed in the upper left diagram. The samples were measured at three different heating rates. This is necessary in order to evaluate the reaction kinetics using the Model Free Kinetics software program. Each temperature program consisted of a heating step, followed by an isothermal segment. The kinetics program was then used to calculate the conversion-dependent activation energy curve shown in the lower left diagram. The activation energy curve allows curing times to be predicted for different isothermal temperatures.

Examples of this are shown by the curves on the right for temperatures of 15, 25 and 35 degrees Celsius. Most epoxy-based adhesives are already hard at 80 percent conversion. The time to reach this value at 25 degrees can be read off from the curve and is about 7.5 minutes. This was confirmed by performing an isothermal measurement at this temperature and is shown by the dashed red curve. The predicted and measured curves show very good agreement.

 

Slide 13: Application 4: DSC                              Composite by TOPEM

Reinforced thermosets such as carbon-fiber-reinforced epoxy resins are often not cured to their maximum possible extent because of the risk of decomposition.

This means that on heating in the DSC, the glass transition of the cured material often cannot be detected because the effect will be overlapped by the peak due to the postcuring reaction or by the change in the curve due to the beginning of decomposition. In this case, the use of a temperature-modulated DSC technique such as TOPEM is recommended.

This is illustrated in the slide. The top curve shows the result of a conventional DSC experiment. The peak due to postcuring and the beginning of the decomposition reaction can be clearly identified. However, there is no indication of a glass transition.

Using TOPEM, the total heat flow curve is identical to the heat flow curve of the conventional DSC measurement. TOPEM in addition, provides so-called reversing and non-reversing heat flow curves. Reversing phenomena such as the glass transition can only be separated from non-reversing phenomena by modulated DSC techniques. In this example, the glass transition of the sample at about 217 degrees Celsius can be clearly seen in the reversing heat flow curve. The maximum temperature of use for this particular material corresponds to the onset temperature which is about 180 degrees.

 

Slide 14: TGA/DSC

Now let’s turn our attention to thermogravimetric analysis, or TGA.

In this technique, the mass of a sample is continuously measured as it is heated in a defined atmosphere. We simply put a few milligrams of the sample into a crucible, heat it, and continuously record the mass change. This allows us to obtain information about the composition of the sample.

The schematic curve on the left shows a typical TGA measurement curve of a polymer. The different effects are numbered next to the curve and explained in the table. These are:

One: heating begins, and volatile components such as moisture and solvent residues vaporize;

Two: decomposition of the polymer;

Three: the atmosphere is switched from nitrogen to air;

Four: carbon black burns.

Five:  a residue consisting of ash, fillers, glass fibers, etc remains behind.   

 

The METTLER TOLEDO TGA/DSC 1 instrument can also simultaneously measure heat flow and thereby detect effects that involve heat exchange.

 

Slide 15: Thermogravimetric Analysis (TGA)

The table on the left of the slide summarizes the main analytical applications of TGA for automotive materials. TGA is used to investigate processes such as vaporization or decomposition. It allows you to measure thermal stability, the kinetics of reactions, and reaction stoichiometry.

 

The combination of TGA with a mass spectrometer or with a Fourier-transform-infrared-spectrometer allows you to analyze gaseous compounds evolved from a sample. This provides information about the nature and composition of the sample.

 

The picture on the right shows a view of the open furnace of a TGA/DSC instrument, and in particular the sample holder with positions for the sample and reference crucibles. The standard crucibles are made of alumina.

 

Slide 16: Application 1: TGA/DSC                       Decomposition of a rubber blend

The first TGA application example shows the analysis of a NR/SBR rubber blend used for the manufacture of tires.

The upper curve displays the mass loss curve, and the lower curve the DTG curve. The DTG curve is the first derivative of the TGA curve and displays the mass loss step as a peak. This makes it easier to determine the limits for a TGA step and helps to improve the evaluation. In this case, the DTG curve was used to set the limits for the overlapping effects of vaporization and decomposition.

The sample was first heated to six hundred degrees under inert conditions. In this temperature range, volatile components such as plasticizers, oils, moisture, or solvent residues vaporized. The polymers then pyrolyzed in two distinct steps, which can be attributed to the pyrolysis of NR and then SBR.

At six hundred and twenty degrees, the atmosphere was switched from nitrogen to air. This resulted in the combustion of the carbon black used as filler in the rubber. Finally, at eight hundred and fifty degrees, inorganic components remained behind as a residue.

Evaluation of the TGA curve yielded the following sample composition:

four-point-four percent (4.4%) volatile components,

twenty-nine-point-four percent (29.4%) NR

twenty-three-point-eight percent (23.8%) SBR,

and thirty-nine-point-five percent (39.5%) carbon black,

and a residue, mainly zinc oxide, of about three percent (3%).

 

Slide 17: Application 2: TGA                               Polymer with flame retardant

The slide shows the analysis of polypropylene with and without a flame retardant. Polypropylene is a thermoplastic that is chemically resistant and almost completely impermeable to water. It is mainly used for car bumpers, fuel tanks, cable insulation, battery boxes and carpet fibers.

 

Since polymers are usually combustible, high demands are put on fire prevention for safety reasons. The addition of combinations of different chemicals used as fire or flame retardants allows an adequate degree of protection to be achieved.

Typical fire retardants are aluminum and magnesium hydroxides, and brominated and phosphorus compounds:

The metal hydroxides form water on decomposition and produce a large cooling effect.

Brominated fire retardants inhibit free-radical chain-reactions during combustion and form volatile hydrogen bromide, HBr, which helps to dilute the combustion gases.

Phosphorus-containing fire retardants reduce the local oxygen content through oxidation and promote the formation of a non-flammable, carbon-like crust.

 

In this example, the two samples were measured in the temperature range 35 to 650 degrees Celsius at a heating rate of 10 Kelvin per minute using an air flow rate of 50 milli-liters per minute (50 mL/min). The polypropylene sample without the flame retardant exhibits a single mass loss step starting at about 250 degrees. This corresponds to the pyrolysis of polypropylene. The polypropylene sample with the flame retardant shows two distinct steps between 300 and 450 degrees. The first step up to 350 degrees corresponds to the decomposition of the flame retardant, while the second step corresponds to the decomposition of polypropylene.

Important information about the mechanism and the effect of fire retardants can be obtained by TGA. This is particularly useful for material development.

 

Slide 18: Application 3: TGA/FTIR                                   Sealing ring by TGA-FTIR          

The METTLER TOLEDO TGA/DSC 1 can be interfaced with a Fourier Transform Infrared Spectrometer. The online combination of a TGA and an FTIR spectrometer enables qualitative and quantitative analysis to be simultaneously performed. As with TGA-MS, the technique allows the gaseous substances evolved to be identified and correlated with the mass-loss steps recorded by the TGA.

 

The slide shows the thermal degradation of a sealing ring. The sample was measured in the temperature range 30 to 900 degrees Celsius at a heating rate of 10 Kelvin per minute and a nitrogen flow rate of 40 milli-liters per minute (40 mL/min). The first derivative curve was used to identify the individual weight loss steps. The TGA curve consists of at least six overlapping degradation steps at about 130, 320, 460, 510, 650, and 880 degrees Celsius. The small mass loss at about 130 degrees is due to the evaporation of water. Afterwards, decomposition of the nitrile groups leads to the elimination of hydrogen cyanide, HCN. At the largest decomposition step, HCN, CO2 and cyclohexane are liberated. The elimination of CO2 at 650 and 880 degrees is the result of the decomposition of the magnesium- and calcium-carbonate inorganic fillers.

The combination of TGA and FTIR is a powerful tool that helps you understand the mechanisms and kinetics of decomposition processes.

 

Slide 19: Thermomechanical Analysis (TMA)

We now move on to thermomechanical analysis, or TMA. This technique measures the dimensional changes of a sample as it is heated or cooled.

 

The schematic curve on the left shows the typical TMA curve of a polymer measured under low force conditions. The effects are numbered next to the curve:

One, is gradual expansion below the glass transition;

Two, is the glass transition temperature at which the rate of expansion increases;

Three, is expansion above the glass transition;

Four, is softening with plastic deformation;

 

Slide 20: Thermomechanical Analysis (TMA)

The table on the left of the slide summarizes different analytical applications of TMA in the automotive field.

TMA instruments measure dimensional changes of a sample under a defined load. This information can be used to determine the coefficient of thermal expansion. Furthermore, other thermal effects such as glass transitions, melting, crystallization, curing or swelling behavior can be investigated.

 

Besides conventional TMA measurements in which the load remains constant, Dynamic Load TMA or DLTMA can also be performed. In this mode, the load applied to the sample alternates between a small and a large force. The periodically changing force compresses the sample to different extents. This technique can be used to determine Young’s modulus.

 

The picture on the right shows the typical TMA experimental setup with a ball-point probe in contact with the sample specimen resting on a flat support.

The following slides describe specific application examples.

 

Slide 21: Application 1: TMA                  TMA curves and CTE of polymers

Materials expand or contract when they are heated or cooled. This behavior is described by the coefficient of thermal expansion or CTE. It is an important criterion when designing products - otherwise, cracks and damage can occur that lead to product failure.

The slide shows TMA measurements of an SBR/BR rubber blend and a printed circuit board (PCB). The TMA curves are displayed in the main part of the diagram. The curve for the printed circuit board shows a change in slope at about 95 degrees Celsius. This corresponds to the glass transition of the material. Delamination of the PCB occurs above 330 degrees.

The TMA curve of the rubber blend also shows a change in slope at about minus sixty degrees (–60 °C). Closer inspection reveals a second change at minus ninety-seven degrees (–97 °C). These temperatures correspond to the glass transitions of the two components of the rubber blend.

The results can be seen more clearly in the small inset diagram. The curves in this diagram display the expansion coefficient as a function of temperature. In this presentation, a change in the slope in the TMA curve corresponds to a step-like change of the expansion coefficient.

The CTE curve of the rubber blend exhibits two clear steps. As can be seen in the table, the expansion coefficient of the printed circuit board changes from about 80 to 320 ppm during the glass transition.

 

Slide 22: Application 2: TMA                              Isothermal creep of SBR samples

The slide shows the creep and recovery behavior of three different samples of styrene-butadiene-rubber with different degrees of vulcanization measured at 30 degrees Celsius.

 

Creep and recovery behavior is one of the most important properties of elastomers used for sealing applications. Creep refers to the time-and-temperature-dependent deformation of a material when it is subjected to a stress over a longer period of time.

The deformation consists of three main components:

First: the almost instantaneous reversible elastic response,

Second: the slower reversible viscoelastic relaxation,

and Third: the almost constant irreversible viscous flow.

The second and third components are generally referred to as “creep”.

Creep and recovery experiments can be performed by TMA. In such an experiment, the sample is first held isothermally at a specified temperature after which a force is suddenly applied. The force is kept constant for a certain period, and then quickly removed. The strain or dimensional change is recorded as a function of time and results in a stress-strain diagram of the type shown in the slide.

In this example, the initial elastic deformation of the samples is marked by the vertical downward-pointing arrows on the left. The unvulcanized SBR0 sample shows the largest elastic deformation. The elastic deformation of the vulcanized SBR1 and SBR2 samples decreases with increasing degree of vulcanization.

The SBR0 sample also exhibits the largest irreversible deformation component. This is shown by the black arrow on the right of the diagram. Ideally, the creep recovery segment should be long enough to record the complete recovery curve. The SBR1 sample still shows a certain amount of viscous flow, whereas the SBR2 sample, which has a vulcanizing agent content of 4 parts per hundred of rubber, exhibits practically no viscous flow at all.

 

Slide 23: Application 3: TMA                                                      Foam material

A common process in the manufacture of automobiles is to fill cavities in vehicle bodies with injection-moldable materials. This increases the acoustic and safety performance of vehicles.

The materials start to foam after they have been injected into the cavities. The foam should cure when the foaming process is almost finished so that the foam remains fixed in place. TMA measurements can be used to investigate this process.

In this example, the TMA curve of a foam material is displayed in the upper diagram and the simultaneously recorded SDTA curve in the lower diagram.

About fifty milligrams (50 mg) of the material was put into a 100-microliter aluminum crucible. The sample was covered with an aluminum disk. A load of 3 milli-newtons was applied to the disk. On heating, the sample undergoes a glass transition at around 80 degrees Celsius. As a result of this, the sample flows within the crucible and its height decreases. At about 87 degrees, the liquid sample is spread uniformly in the crucible. Foaming begins slightly above 90 degrees and an increase of volume of about 60% occurs.

Above 140 degrees, some shrinkage is observed. This correlates with the curing reaction, which can be seen on the SDTA curve. The curve shows that the curing reaction begins at about 125 degrees and finishes at 175 degrees.

TMA with simultaneous SDTA allows us to observe both the foaming process and the curing reaction. The results for this material confirm that the curing reaction, as desired, only starts after the material has undergone a substantial volume expansion.

 

Slide 24: Dynamic Mechanical Analysis (DMA)

Dynamic Mechanical Analysis is used to measure the mechanical properties of a viscoelastic material as a function of time, temperature and frequency when the material is deformed under a periodic oscillating stress.

 

The schematic diagram on the left of the slide shows the results of a DMA measurement of a shock-cooled semi-crystalline polymer. The curves display the storage modulus, gee prime (G′), the loss modulus, gee double prime (G″),and the loss factor tan delta as a function of temperature.

The different effects are numbered next to the curve and explained in the table. These are:

One: secondary relaxation, observed as a peak in the tan delta and gee double prime curves; gee prime decreases slightly

Two: the glass transition, seen as a peak in the tan delta and gee double prime curves and as a decrease in the storage modulus curve;

Three: cold crystallization of the polymer. The stiffness and hence the storage modulus, gee prime (G′), increase.

Four: recrystallization accompanied by a peak in tan delta and gee double prime;

Five: melting of the crystalline fraction with a decrease in the storage and the loss moduli. After melting, the loss factor increases considerably. Gee double prime is then larger than gee prime.

 

Slide 25: Dynamic Mechanical Analysis (DMA)

The table on the left of the slide lists the main analytical applications of DMA in the automotive field.

 

In general, DMA provides information about relaxation processes such as the glass transition or secondary relaxation. Curing processes, melting, and crystallization can be also be studied by DMA. Quantitatively, DMA provides accurate data on the shear modulus and Young's modulus as a function of temperature and frequency.

The picture on the right shows a sample installed in the DMA ready for measurement in one of the bending modes.

 

Slide 26: Application 1: DMA                  Carbon-fiber-reinforced polymers

The slide shows the measurement curves of two carbon-fiber-reinforced polymers by DMA in the 3 point-bending mode.

Materials like this are frequently used in racing cars and high-end automobiles. The carbon fibers increase the stiffness and decrease the mass of components compared with materials such as metals or glass-fiber-reinforced polymers.

The upper diagram displays the storage modulus curves, eee prime, and the lower diagram the tan delta curves of two different carbon-fiber-reinforced test specimens. The continuous curves in black and red display the first heating runs of Specimens A and B. The dashed black curved is the second heating run of Specimen A.

The glass transition is characterized by a step in eee prime (E’) and a peak in tan delta. The first heating runs of Specimens A and B exhibit significantly different glass transition temperatures of about 180 and 100 degrees Celsius respectively.

The increase of the storage modulus of Specimen A in the first heating run is due to relaxation of the polymer network. The slight increase of the modulus after the glass transition is due to post-curing. This explains why the modulus value in the glassy state in the second heating run is higher. The shift of the glass transition to lower temperature in the second heating run is due to decomposition from about 280 degrees onward in the first heating run.

 

DMA is an extremely powerful technique for analyzing materials of this type and is much more economical than producing trial parts. The technique helps you select suitable materials and optimize their performance in the development process.

 

Slide 27: Application 2: DMA                  Multi-frequency analysis

The slide displays DMA shear measurement curves of a rubber sample at several different frequencies between one hertz and one thousand hertz.

The curves show that the glass transition depends on the applied frequency. At higher frequencies, the glass transition shifts to higher temperatures. The glass transition temperature determined from the maximum of the loss modulus curve, gee double prime(G″), is about minus fifty-five degrees Celsius (-55 °C) at one hertz (1 Hz), and minus forty degrees (-40 °C) at one thousand hertz (1000 Hz).

As a rule of thumb, a frequency shift of one decade corresponds to a shift in temperature of about 5 Kelvin. The mechanical behavior of a material should therefore be measured at frequencies at which it is intended to be used.

Slide 28: Summary

The table summarizes the most important events and properties that characterize materials used in automotive industry as well as the thermal analysis techniques recommended for their measurement. A red box means that the technique is strongly recommended; a blue box indicates that the technique can also be used for some applications. 

 

The most important effects that can be analyzed by DSC are the melting point, melting range and melting behavior. DSC is also used to determine the heat of fusion, the glass transition, and oxidation stability.

 

TGA measures weight changes. The main applications of TGA are content determination, thermal stability, decomposition kinetics, and the analysis of composition.

 

TMA and DMA are used to measure the mechanical behavior and properties of materials:

 

TMA is normally used to study the expansion, softening or shrinkage of materials and the glass transition.

 

DMA is used to determine the modulus and damping behavior of materials. It is the most sensitive method for measuring and characterizing glass transitions of materials.

 

Slide 29: Summary Instruments

This slide gives an overview of the temperature ranges of the METTLER TOLEDO DSC, TGA, TMA, DMA and thermo-optical analysis instruments.

 

Depending on the specific cooling accessories, DSC experiments can be performed at temperatures between minus one hundred and fifty degrees Celsius and plus seven hundred degrees.

 

TGA measurements normally begin at room temperature. The maximum possible temperature is sixteen hundred degrees.

 

TMA experiments can be performed between minus one hundred and fifty degrees and plus eleven hundred degrees.

 

DMA samples are measured in the range minus one hundred and fifty degrees to plus six hundred degrees.

 

Slide 30: For More Information

Finally, I would like to draw your attention to information about application examples that you can download from the Internet.

METTLER TOLEDO publishes articles on thermal analysis and applications from different fields twice a year in UserCom, the well-known METTLER TOLEDO technical customer magazine. Back issues can be downloaded as PDFs at www.mt.com/ta-usercoms as shown on the slide.

Our “Collected Applications” and “Thermal Analysis in Practice” handbooks contain many other examples and are recommended for further reading.

 

Slide 31: For More Information on Thermal Analysis

In addition, you can download details about webinars, application handbooks or information of a more general nature from the Internet addresses given on this slide and so ensure that you are always fully up-to-date in thermal analysis.

 

Slide 32: Thank You

This concludes my presentation on Thermal Analysis in Automotive Industry. Thank you very much for your interest and attention.

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