Solutions to improve your welding processes

Evaluation and lifetime analyses of welded joints

Welded joints: Evaluation and lifetime concepts

What we can do for you


We develop solutions which enable you to improve welding processes in your applications. Additionally, we support you in evaluating welded joints: was the welding done correctly? Did any cavities, pores or welding mistakes occur and/or was the welding incomplete? Did you create unwanted residual stresses?

During operation we evaluate a joint’s safety and life expectancy, especially for high temperature applications. We also consider the extreme environment of power plants, including aggressive atmospheres and changing temperatures. 

We rely on our broad range of know-how to answer our clients’ questions. We simulate the welding process in order to calculate the resulting structure and residual stresses. Subsequently, we develop procedures to reduce the component’s warping. We optimize post weld heat treatments to prolong the components’ working life. Using a detailed mechanical characterization under conditions similar to operation we can define weld strenght reduction factors, especially for high temperatures. Furthermore, we can determine the remaining lifetime of cracked welded joints. Our expertise is also useful in evaluating joints between different metals: our clients gain vital information and solutions for the improvement of their joining processes, thus prolonging the components’ working life.

Analyses

Evaluations

Simulations
 

© Fraunhofer IWM

Analyses


Microstructure and damage analysis: evaluation of the micro structure via light microscopy, REM, EDX, XRD, chemical analysis using GDOES, determination of local strength and strength distribution via hardness mappings and fracture analyses.

residual stress measurements in the lab and on site

hydrogen analyses: measuring of hydrogen content via heat extraction method and thermal desorption spectroscopy (TDS), determination of characteristic values for hydrogen diffusion via permeation tests

determination of degradation mechanisms

isothermal and thermocyclic endurance tests and operation-like creep-fatigue tests as well as cyclic crack growth rates on cross-weld samples, samples from a welding simulator and samples from the weld metal to:

Evaluate the life time of welded joints (determination of weld strenght reduction factors)

Evaluate the fracture growth in welded joints

Examine the influence of welding defects (such as hot cracks) on life expectancy

Examine the influence and change of residual stresses, microstructure and mechanical properties

Optical fracture tracking and strain measurement for improved evaluation of cross-weld samples

Examinations of relaxation cracks via SSRT (slow strain rate tests) and deduction of appropriate heat treatments

to top

© Fraunhofer IWM

Evaluations

 

Determination of relevant damage mechanisms

Evaluation of welding parameters under consideration of the evolved microstructure and the respective properties

Lifetime analyses

Leak-before-break and (remaining) lifetime evaluation of crack containing components and their welded joints under operation-like stress/load

to top

© Fraunhofer IWM

Simulations

 

Simulation of precipitation kinetics during the welding process, during heat treatment and during operation as well as their effect on the life time at elevated temperatures

Welding and heat treatment simulations: microstructure, hardness, residual stresses and distortions

Cold crack simulation: simulation of hydrogen diffusion during welding under consideration of microstructure, residual stresses, plastic strain and hydrogen traps

Simulation of distortion and lifetime of components (including their welded joints) under thermocyclic creep fatigue

Evaluation of the remaining lifetime of crack containing components (including their welded joints) via a lifetime prognosis tool

to top

 

Topics

 

Microstructure assessment 

 

Microstructures are responsible for the properties of raw materials and therefore for the properties of the resulting components which are produced. Microstructures are adjusted using different manufacturing steps. In use, they can change both positively and negatively. We uncover the relationships between the raw materials’ properties and those of the microstructure and use this information for optimized raw material properties and for the optimized use of raw materials - for example with...

 

Residual stress analyses

 

Our aim is to create residual stress optimized components for our clients.
To do so, we determine manufacturing and use-caused residual stresses, assess them with regard to the reliability, safety and lifetime of parts and develop recommendations and concepts for component design, raw material use and manufacturing processing.
In order to prepare requirements to use components safely and reliably, we investigate and analyze residual stresses in connection with the underlying raw...
 

 

Hydrogen embrittlement in metals

 

Atomic hydrogen is capable of significantly reducing the ductility of metals. This can cause components to fail unexpectedly. The potential risk is generally related to the diffusible portion of the hydrogen. In order to predict the effects of hydrogen on material and component behavior via numerical simulations, we determine the dependence of the hydrogen diffusion constants on mechanical stress and temperature. The effects of hydrogen on the mechanical parameters of a metal are...
 

 

Simulation of heat treatment processes

 

The heat treatment of metals is an important means of creating a favorable microstructure and residual stress within a component. A movable inductor is often used to heat up the components. The experimental optimization of the treatment parameters is time-consuming and costly, particularly for larger components such as wind turbine bearings. Thanks to our effective mapping techniques and an enhanced simulation environment, we are able to...

 

Relationship between microstructure and properties in re-melted surface

 

In many cases, the surface of a component is critical to operational behavior and can be modified in various ways. A new technique, laser re-melting of surface layers, finely polishes or adds structure to a surface. The mechanical properties in the surface layers are modified by adjusting the laser parameters. The effect of process parameters on residual stresses...

 

Damage Analysis: Metals

 

We answer questions that occur during the quality assurance phase of industrial production or due to failure during service. The scientific investigation of damage to and failures of metals and metallic components is well established within the Fraunhofer IWM. We will build an expert project team customized for your individual task, which will assess the situation and discuss the next steps with you to reach an effective solution...

 

Material characterization for thermal and mechanical loads

 

We have developed sophisticated tests with which to characterize the cast, forged and sheet metals used in components, which are subject to high thermal and mechanical loads. The testing temperatures range from -180 °C to >1000 °C, depending on the specifications. Mechanical loads can be applied monotonously or cyclically. The test results help to better understand material behavior and form the basis for the development and modification of...

 

Identification of deformation and damage mechanisms

 

Thermal and mechanical loading can lead to transcrystalline and intercrystalline cracks and creep pores forming and growing. Oxidation and corrosion processes can also damage the material and change the microstructure to such an extent that the mechanical properties are significantly altered. When developing material models and designing components, it is therefore important to understand which deformation and damage mechanisms dominate...

 

Mechanism-based models for time and temperature dependent plasticity and damage

 

Sophisticated deformation models can describe typical material phenomena such as strain hardening, creep, relaxation and strain rate effects, taking account of microstructural changes and their effects on the mechanics. The mechanism-based damage models can describe crack growth under fatigue and creep fatigue loads. The models account for material properties that change with temperature ...

Fraunhofer IWM groups that work with welded joints

Fatigue

 

Load-bearing components and structures in all industrial sectors such as automotive, vehicle, railway, aerospace, steel and bridge constructions are exposed to complex stresses...

Joining and Joints


We characterize the mechanical properties of joints and assess them in terms of their deformation and failure behavior. A particular focus of our work is joint modeling for crash simulations, as this is...

 

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...