Fraunhofer Institute for Mechanics of Materials IWM
Fraunhofer Institute for Mechanics of Materials IWM
© Achim Käflein/Fraunhofer IWM

Identifying the internal structure of materials

© Achim Käflein/Fraunhofer IWM

Material and component characterization

To reach solutions for improving the reliability and useful life of materials and components, it is necessary to gain knowledge of the internal structure of those materials. Scientists at the Fraunhofer IWM investigate the reactions of materials and components to mechanical, thermal, chemo-mechanical and tribological loading and clarify their deformation and failure mechanisms. The necessary material parameters are obtained and evaluated in correlation to the microstructure and to structure-altering processes on all size scales. On this basis the Fraunhofer IWM offers materials development as well as process and technique development services.

The institute’s core competence of material and component characterization is derived from its capacity to develop and apply complex testing and analysis methods that go beyond standard procedures and which are thus able to meet the demands of a wide spectrum of simulation approaches tailored to the type and quality of the test data. The basis of this is on the one hand the availability of mechanical testing techniques for a very wide spectrum of temperature, environment and force ranges and load speeds, and on the other hand, expertise in both the selection of characterization methods appropriate to the material and application as well as in the evaluation of damage development. Component testing takes into account locally varying material properties. Additionally, fracture mechanics evaluations and damage analyses are performed.

Salient features of the scope of services include the capturing and evaluation of multiaxial stress conditions, locally obtaining parameters through micro-testing techniques and structure analysis, and expertise in the field of crack propagation, which may for example be used in the development of innovative separation processes. The portfolio is complemented by a range of high-resolution residual stress analysis techniques plus thermo-physical and thermo-mechanical characterization

 

How to work with the Fraunhofer IWM

Possibilities for measurement and analysis


Experts at the Fraunhofer IWM work with the most up-to-date equipment available and develop special testing systems and experimental setups for individual customer queries.
The scientists working at the institute can obtain a large number of material and component properties using a variety of measurement and analysis methods.

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Static and cyclic material and component characterization

 

  • Static strength, multiaxiality parameters, vibration resistance, fracture toughness, crack growth, torsional stiffness, tested using servo hydraulic, electrodynamic and electromechanical testing machines:
    • Tension, compression, shear
    • Test forces from 10 mN to 8 MN
    • Test chambers from 100 to 2500 K
    • 2D and 3D strain measurement using grayscale correlation (ARAMIS)
    • Experiments performed on the basis of force or strain
    • Single-step tests; variable-amplitude tests
    • Various methods for measuring crack length, including ASTM 1820, ASTM 1921, ASTM 647
  • Fretting fatigue using a module for application of simultaneous combined longitudinal and transverse forces
  • Component strength evaluation in a stretching field with servo hydraulic (63 kN and 25 kN) cylinders and torsion cylinders up to 4 kNm
  • Module of elasticity, storage module and loss module obtained via dynamic mechanical analysis (18 mN to 500 N)
  • Natural frequencies, modal analysis, vibration testing and shock testing with climate-controlled shaker unit:
    • Sine force approx. 10 kN, random force approx. 10 kN, frequency up to 4000 Hz
    • Max. oscillation speed (sinusoidal) 1.8 m/s (dependent on test mass), oscillation displacement approx. 51 mm
    • Max. acceleration for sine/random 100 g/40 g (dependent on test mass)
  • Strain rate dependence measurement on high-speed tensile test machine (100 kN up to 20 m/s, 500 kN up to 10 m/s); drop rate testers and notch impact test rigs
  • Evaluation of creep behavior on temperate, climate-controlled test rigs

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Thermo-mechanical material and component characterization


Determination of fatigue life, yield point, tensile strength, elasticity modulus and crack growth using mechanical and/or servo hydraulic testing machines:

  • From -180°C to >1000°C
  • Isothermal or anisothermal (heating and cooling rates up to approx. 10°C/s)
  • Heating, inductive or in furnace
  • Controlled by strain or by tension
  • Typically cylindrical probes with diameter 5-10 mm
  • Hot tension tests to determine yield point, e.g. at 0.2% plastic strain
  • Modulus of elasticity obtained using resonance method by matching with stress-strain curve in linear range
  • Fatigue crack growth with typically a corner crack probe, diameter 8x8 mm in measurement range

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Micromechanical material and component characterization

 

  • Determination of modulus of elasticity, vibration resistance and sample natural frequency using microtension instruments:
    • Room temperature to 200 °C
    • Microsamples made in-house using customer’s material; sample thicknesses 10 to 400 µm, base material can be thicker
    • Test frequency 1200 Hz
  • Characterization using a resonant microfatigue testing unit:
    • Test frequency 1200 Hz through defined sample natural frequency/geometry, which is adjustable
    • Measurement of sample natural frequency, which changes as fatiguing progresses; detection of first damage well before initiation of cracks
  • Measurement of position, displacement and stretching using cameras, microscopes and scanning electron microscopes:
    • Optical strain measurement with digital image correlation for samples with characteristic surface (with features in the form of grayscale transitions)

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Thermo-physical material properties

 

  • Determination of specific heat capacity and quantitative determination of exothermic and endothermic reactions using dynamic differential scanning calorimeter, DSC:
    • Room temperature to 1600 °C with heating rates between 0.01 and 50 K/min
    • Determination of transformation temperatures
    • Quantitative determination of exothermic and endothermic reactions
    • Tests performed in various gas atmospheres and in vacuum
    • Typical sample size for solid bodies: 5 x 1.2 mm
  • Measurement of thermal expansion in length and coefficient of linear expansion, phase transformations and transformation temperatures, also of temperature-dependent density changes, using thermo-mechanical analyzer:
    • Room temperature to 1600 °C with heating rates between 0.1 and 20 K/min
    • Tests performed in various gas atmospheres and in vacuum
    • Typical sample size: Diameter 3-6 mm, length 10-25 mm; similar dimensions for plates
  • Analysis of thermal conductivity with laser-flash apparatus LFA:
    • Range of 0.01-1000 mm2/s and from room temperature to 2000 °C with heating rates between 0.1 and 50 K/min
    • Tests performed in various gas atmospheres and in vacuum
    • Sample dimensions for round samples 6, 10 and 12.7 mm diameter; for rectangular samples, max. 10 x 10 mm
    • Sample thickness to vary with the expected thermal conductivity
  • Determination of thermo-mechanical properties of metals using a Gleeble 3150 testing unit in gas atmospheres and in high vacuum:
    • Heating rate up to 8000 K/s and max. cooling approx. 2500 K/s
    • Application of stresses under regulation of force, strain and path
    • Tests performed in various gas atmospheres and in high vacuum
    • Load range 44 kN tensile/compression
    • Temperature range from room temperature to melting point
    • Tensile and compression tests with simultaneous thermal stress
    • Weld simulation and creation of various material conditions
  • Capturing of component geometries using a 3D laser scanner for optical scanning and sampling of components:
    • Focal distance 130 mm
    • Precision: approx. 25 µm
    • Evaluation software enables direct comparison between scan and CAD part and much more
    • Scan can be exported in all common CAD formats

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Chemo-mechanical material and component characterization – high vacuum

 

  • Determination of hydrogen and oxygen content using a suitable analyzer:
    • Hot extraction of carrier gases in inorganic materials
    • Sensitivity: 0.1-1000 ppm
  • Measurement of hydrogen content, determination of binding energies of hydrogen events; distinction of hydrogen trapped with different strengths using hot extraction analyzer for diffusible hydrogen and with thermal desorption spectroscopy:
    • Infrared oven up to 900°C; wire-wound tube oven up to 1100°C
    • Measurement range: 0.05-1000 ppm, resolution: 0.01 ppm
  • Determination of diffusion coefficients and kinetic constants of hydrogen events (trap and release relate) using permeation test rig:
    • Testing to DIN EN ISO 17081
    • Temperature control of samples
  • Analysis of mechanical properties during hydrogen embrittlement and of the mechanical behavior of coated samples using tensile, notch tensile, fatigue and crack propagation tests on servo-mechanical testing machines:
    • Stress corrosion cracking tests: CERT (or SSRT) tests: Tensile tests with slow strain rate, e.g. after ASTM G 129
    • Fluid media, molten salts up to 600°C, oxidizing atmosphere up to 900°C
    • Exposure tests in fluid/gaseous media (molten salts up to 1100°C)

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Metallography (clarification of microstructure)

 

  • Analysis of chemical composition using GDOES depth profile spectrometer:
    • Chemical composition of metals
    • Depth profiles possible up to approx. 100 µm
    • Calibrated for Fe and Ni-based materials
  • Measurement of nanoindentation hardness using a nano indenter:
    • Hardness measurement to DIN EN ISO14577
    • Creep loads adjustable up to 60 s
    • Force range 0.4 - 1000 mN
    • Measurable hardness range 0.001-120,000 N/mm²
    • Vickers or ball indentation
    • Automatically traveling measurement table for recording hardness mappings
  • Hardness measurement:
    • Hardening methods as per Vickers, Brinell, Knoop, Rockwell, Shore A
    • Manual or automatic (for hardness mappings or hardness curves)
    • All common load ranges, including as per DIN6507, 4545, 6506 or as per ASTM E384, E92, E384, E10
  • Analysis of local chemical composition using EDX, EDAX:
    • Measurement of local chemical composition
    • Elements with atomic number 6 or more (carbon) can be measured
    • Carbon is not quantifiable
    • Resolution dependent on sample material (approx. 1 µm)
    • Measurement of chemical composition at defined points, along lines or using element mappings
    • Particle and pore analyses (volume fraction, size distributions, form factors) using optical microscopes and an image processing system
  • Determination of crystal and grain orientation, texture, grain deformation; imaging of orientation maps by electron backscatter diffraction (EBSD):
    • Can be coupled to EDX
    • Angular precision approx. 1°

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Radiographic residual stress measurements

 

  • Determination of residual stresses, texture, depth profiles and phase analysis (in particular residual austenite) using stationary x-ray diffractometers:
    • Metals, ceramics, various phases
    • Depth profiles through electrolytic erosion
    • Lateral resolution up to 100µm
  • Residual stress measurements using mobile x-ray diffractometers:
    • Metals, ceramics, various phases
    • Large samples and at the customer’s site
    • Depth profiles can be obtained at the customer’s site by electrolytic erosion using a mobile instrument
    • Lateral resolution up to 300µm
  • Residual stress mapping on measurement tracks in the case of complicated surface geometry using a robot diffractometer:
    • Metals, ceramics, various phases
    • Lateral resolution up to 300µm can be obtained
    • Automated measurements at multiple measurement points of large components where surface geometry is complex
  • Determination of residual stress depth profiles using hole-drilling devices:
    • Residual stress depth profiles with depths from approx. 0.04 mm to approx. 1 mm
    • Not nondestructive since a small hole is drilled in the material
    • Hardness of material up to 55 HRC (greater hardnesses on request)
    • Measurements can be made on the surface using radiographic techniques
    • Measurements can be made at the customer’s site and on large components
  • Measurement of residual stress depth profiles via the ring core method:
    • Residual stress depth profiles for depths up to 5 mm
    • Hardness of material up to 55 HRC
    • Not nondestructive since a circumferential groove is milled into the material
    • Measurements can be made on the surface using radiographic techniques
    • Measurements can be made at the customer’s site and on large components

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Characterization of granulates and their behavior during processing

 

  • Flow properties examined with hopper outflow experiment
  • Angle of repose measured with repose angle analyzer
  • Fill level measurement
  • Compaction behavior, wall friction using matrix fitted with instruments
  • Sinter shrinkage using load dilatometer

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