Life expectancy predictions via microstructure-based models

Assessment of Materials, Lifetime Concepts

We assess the influence of microstructures, internal stresses and damage on component functionality and life expectancy. We are particularly interested in linking specific analyses and experiments to advanced material models and in understanding the demands placed on our clients’ components. Our work is focused on modeling cyclical thermomechanical loads and on identifying the degradation mechanisms involved in corrosion, stress corrosion cracking and hydrogen embrittlement. In acute cases of damage, we can carry out surveys for our clients.

 

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Influence of hydrogen on metals

Degradation of materials in molten salts 

 

Services

Simulation, identification and assessment of the microstructures and internal stresses related to manufacturing and loading

Investigations into material degradation through corrosion, stress corrosion cracking and hydrogen embrittlement

Identification of damage mechanisms associated with cyclical thermomechanical loads

Mechanism-based material models for time and temperature related plasticity and damage

Software for calculating life expectancy using finite elements programs

Damage analysis, identification of technical liability, surveys, development of new testing techniques

Construction of test rigs

Microstructure, Residual Stresses


We investigate the effect of manufacturing processes and operational loads on the microstructure and the internal stress in materials and components. A particular focus lies on the identification of the ...

Lifetime Concepts, Thermomechanics

Motor components, aircraft turbines, power station and plant components are all subject to high thermal and mechanical loads. It often takes numerous expensive and time-consuming laboratory and field tests ...

© Photo Fraunhofer IWM

Influence of hydrogen on metals

Hydrogen reduces the ductility and durability of many metals – this is generally referred to as hydrogen embrittlement. The Fraunhofer IWM helps its clients with the selection and qualification of materials and manufacturing techniques, with assessments of operating life and, in the event of failure, with the identification of the causes of component failure. Our staff has many years of experience in the investigation and explanation of hydrogen embrittlement mechanisms and in the simulation of the underlying diffusion processes. We have experimental equipment with which to place specific hydrogen loads on materials (also with simultaneous mechanical and thermal loads), to determine hydrogen content, to characterize microstructures and to identify properties relevant to strength. 

Hydrogen can enter a material via different processes: either via charging with gaseous hydrogen or via electrochemical processes (e.g. corrosion or galvanic coating). The choice of materials is limited if one wishes to maintain the same level of strength-related properties without the aspect of susceptibility to hydrogen embrittlement. The problem of hydrogen embrittlement is becoming increasingly important in the transport and energy sectors as hydrogen is seen as one of the most important energy sources for the future. The development of new technologies for the manufacture, distribution and use of hydrogen as an energy source necessitates the qualification of existing and new materials for these applications.

© Photo Fraunhofer IWM

Tensile testing machine with adapted cathode hydrogen charge.

Focus

Measurement of hydrogen diffusion constants and the determination of traps in metals

Assessment of the effect of alloy composition on hydrogen embrittlement; microstructure analysis, fractography, mechanical in-situ experiments

Establishment of design guidelines and operating life assessments for metal components used in a hydrogen environment

Atomistic simulation of hydrogen bond energies within the crystal lattice, assessment of various traps

FE modeling of diffusion and local enrichment of hydrogen during welding and heat Treatment

Damage analyses to identify component failure due to hydrogen

Risk and life cycle assessment

© Photo Fraunhofer IWM

Degradation of materials in molten salts

Molten salts have been widely used in the industry. Some examples are molten chloride salt mixtures as baths for alloying surface treatments and fluoride salts as solvents. More recently molten nitrate and nitrite mixtures hav been becoming more attractive due to their application as heat transfer fluid (HTF) and thermal storage for the power industry.

Driven by the long-term need of utilization of fluctuating regenerative  energy resources Fraunhofer IWM invests in the development of methods for assessment and qualification of materials to be used in the molten salt environment of  high temperature storage systems of solar power plants (TES Thermal Energy Storage, CSP concentrated solar power plants). These activities are included in the Fraunhofer project  Supergrid  (Project management: Fraunhofer Institute for Solar Energy Systems ISE), which comprises additional aspects of integration fluctuating regenerative  energy resources into a trans-European power grid (DESERTEC).

For the cost-efficient optimisation and reliability of high temperature storage and piping systems, there is a need of comprehensive material characterization and assessment. In the field of heat exchangers the appearance of complex and cyclic thermal-mechanical stresses under the chemical influence of the molten salts can cause a critical degradation of the material resulting in failure of the system.

 

Services

Fraunhofer IWM has qualified and experienced staff (physicists, engineers and chemists) for the study of the degradation mechanisms, the material selection and optimisation, the development of protective systems and the evaluation life time prediction methods. Moreover Fraunhofer IWM is currently working on the design and building of new testing facilities for the mechanical characterization of materials exposed to molten salt environments at high temperature. These facilities include:

© Photo Fraunhofer IWM

Design of the corrosion chamber for mechanical testing in molten salts.

Study of the chemical stability of molten salts at high temperature

Static corrosion tests to evaluate the corrosion rates and identify the degradation mechanisms

CERT-Test (Slow strain rate test) to quantify the changes in structural and mechanical behaviour of the material induced by the corrosive environment

Fatigue of samples under the influence of the molten salt

Thermal cycling test of samples immersed in molten salts

Development and characterization of protective coatings

Comprehensive microstructure and surface analyse by means of optical and electron microscopy, element analysis, EBSD (Electron backscatter diffraction) and X-Ray diffraction (analysis of phases and internal stresses)

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