Thermophysical and thermomechanical characterization

© Photo S.K.U.B./Fraunhofer IWM

Thermophysical characterization

The modern equipment and procedures in the Fraunhofer IWM thermophysical and thermomechanical labs enable us to determine temperature dependent material properties. These properties provide the essential basis for evaluating the effects of thermal loads on components. This substantiated data is necessary for FE- simulation in order to optimize production processes, contour accuracy and energy usage. We determine the following parameters:

Heat capacity

Thermal expansion

Thermal Diffusivity

Heat conductivity

Melting point / Solidus and Liquidus temperature

Phase transformation

Softening point (for example, glass Transition)

Magnetic transformation

Latent heat / reaction enthalpy

Shrinkage (for example, during the sintering process)

More about thermophysical characterization

Thermomechanical material testing

Combined tensile and compression testing (also at high temperatures and velocity)

TTT diagrams (Time-Temperature-Transformation)

Welding simulations and replication of heat treatment and quenching processes

Thermomechanical material treatments for virtually all loads and/or temperatures

More about thermomechanical material testing
 
Our approach to material testing enables simulation and interpretation of production processes, more detailed damage analysis, the development and qualification of new alloys and the optimization of material combinations. Our clients often need us to answer the following questions:

What influence does temperature have upon component geometry?

What is the heat conductivity of a given material?

In which ways does a thermal production process alter a component's shape?

What is the optimal heat treatment for a component that warps?

How to avoid warpage by welding?

Specifically for glass and polymer: how high is the glass transition temperature?
 
The thermophysical and thermomechanical material characterization that we offer is of specific benefit to manufacturers who work with metals, ceramics, synthetic materials, polymers and glass, as well as for process steps which include shaping, heat treatments, welding, warm forming and cold forming.

Our measurement results provide the reliable data necessary for simulations and help clients to optimize their processes while minimizing energy requirements.

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© Photo Fraunhofer IWM

Thermophysical characterization

Specific heat capacity using Differential Scanning Calorimetry (DSC)

Measurements from room temperature (RT) to 1600 °C with heat rates between 0.01 to 50 K/min

Determination of melting and transformation temperatures

Quantitative determination of exothermal and endothermal reactions

Measurements in various gas atmospheres and in vacuum

Typical specimen sizes of solids: Ø 5x0.5 mm

Differential Scanning Calorimeter (DSC)

Temperature range from room temperature (RT) to 1650 °C

Cp measurements from room temperature (RT) to 1500 °C

Vacuum 10-4 mbar 

© Photo Fraunhofer IWM

DSC measuring principle

A sample pan and a reference pan are placed on a platinum disk. When the furnace is heated, both pans consume energy and heat up, but the heat flow from each pan into its platinum disk takes place at different rates. This heat flow difference is measured by thermocouples in a differential set-up. Changes in the DSC signal allow for the analysis of the heat capacity as well as melting, phase transformations, evaporation, and other reactions within the material.

© Photo Fraunhofer IWM

Thermal expansion using thermomechanical analysis (TMA)

Measurements from room temperature (RT) to 1550 °C with heat rates between 0.1 und 50 K/min

Determination of thermal expansion coefficient and phase transformations

Measurements in various gas atmospheres and in vacuum

Typical specimen sizes: Ø 4-6 mm, 5-25 mm length; similar specimen sizes for sheet materials

Thermomechanical Analyzer (TMA)

Temperature range from room temperature (RT) to 1550 °C

Maximum specimen length 30 mm

Measuring range ± 2.5 mm

Force range 0.001 N to ± 3 N

Vacuum < 10-4 mbar

Specimen holder system constructed of Al2O3 

© Photo Fraunhofer IWM

TMA measuring principles

When using a thermomechanical analyzer, a specimen is attached to a rod and clamped with one end in a conductive displacement transducer. With this set up, changes in length can be measured while the specimen is heated in the surrounding oven. From the temperature dependent change in length Δl(T), the technical coefficient of linear expansion α is calculated:

Additionally, volumetric phase transformation, shrinkage and sinter processes can all be measured in the TMA.

© Photo Fraunhofer IWM

Thermal diffusivity and heat conductivity using Laser Flash Analysis (LFA)

Thermal diffusivity measurements ranging from 0.01 to 1000 mm2/s and from room temperature (RT) to 2000 °C with heating rates from 0.1 to 50 K/min

Measurements in various gas atmospheres and in vacuum

Measurements of round specimens with diameters of 6 mm, 10 mm or 12.6 mm; square specimens 10x10 mm

Specimen thickness is dependent upon expected heat conductivity

 

Laser Flash Apparatus (LFA)

Temperature range: room temperature (RT) to 2000 °C

Laser power 25 J/Puls (adjustable power and pulse duration)

Contactless measurement of temperature increase with IR Detector

Measurement range: 0.01 mm2/s to 1000 mm2/s (thermal diffusivity) corresponding measurement range: 0.1 W/mK to 2000 W/mK (thermal conductivity)

Specimen dimensions: Ø 6 mm to 12.6 mm or square 10x10 mm

Specimen holder: Al2O3, graphite

Atmosphere: Ar dynamic

High vacuum tight up to 10-5 mbar 

© Photo Fraunhofer IWM

LFA measurement principles

This measuring technique uses a laser as a heat source. The front of the sample is heated by a short laser pulse, and the heat is conducted through the specimen. An infrared detector measures the temperature increase as a function of time on the specimen’s backside. From this temperature profile and the specimen’s size the thermal diffusivity a(T) is computed. The heat conductivity of the sample material can be determined by using temperature dependent density from DIL and thermal capacity from DSC:

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© Photo Felizitas Gemetz/Fraunhofer IWM

Thermomechanical testing machine "Gleeble 3150"

© Photo Fraunhofer IWM

Copper specimen with extensometer being tested in the Gleeble

© Photo Fraunhofer IWM

Round specimen with attached diatometer and extensometer

Thermomechanical material testing

Thermomechanical testing of metal materials using the »Gleeble 3150«

Heating rate to 8000 K/s and max. cooling rate up to approximately 2500 K/s

Loading at force and stroke control

Measurements possible in various gas atmospheres and in vacuum

Thermomechanical material treatment at various temperature cycles with or without superimposed tensile or compression loads

Replication of heat treatment processes including quenching processes

Determination of TTT (Time Temperature Transformation) diagrams

Determination of TTA (Time Temperature Austenitising) diagrams

Replication and simulation of specific microstructures

Determiniation of static, dynamic, mechanical and thermomechanical behavior of heat treated specimens 

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Additional services

Specimen manufacturing in the Fraunhofer IWM workshop

Microstrucural analysis with light microscope or Scanning Electron Microscope (SEM)

Microstructure evaluation in the Fraunhofer IWM metallography

Hardness measurements (single indents or hardness distribution)

Chemical analysis using the glow discharge optical emission spectrometer (GDOES) with depth profiling

Volumetric phase analysis using X-Ray diffractometry

Residual stress analysis using an x-ray diffractometry or the hole drilling method

High resolution phase, texture, precipitation and surface analysis using SEM, EDX and EBSD

Testing of thermal shock behavior for metals, ceramics and glass

Measurements of hydrogen content in metals

Deliberate controlled loading of metal material with hydrogen and determination of hydrogen diffusion constants

Numerical simulations of the effects of forming processes on components

Numerical simulations of component behavior under thermal and mechanical loads

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Further Information