Crack propagation considering complex stresses

Fracture Mechanics, Structural Integrity

© Fraunhofer IWM
© Fraunhofer IWM
© Fraunhofer IWM

We provide proof for safety, fitness of purpose and endurance of complex and highly stressed components by the use of modern fracture mechanics concepts. On this basis we develop solutions for improved component safety, optimized component design or inspection intervals together with our customers.

For the design and assessment of safety-relevant components fracture mechanics methodologies are state-of-the-art. In the presence of crack-like defects (detected or postulated), the methods of fracture mechanics provide information about the fitness of purpose of components, the remaining service life and the safety regarding an uncontrolled crack growth. Well-founded decisions about commissioning, lifetime extension, periodic inspections or the exchange of a component can be provided on this basis.

Typical industrial areas for the application of fracture mechanics are:

Aerospace

Plant construction

Pressure vessels and piping systems of power plants

Gas and steam turbines

Pipelines

Railway vehicles

Steel structures, i.e. for crane and bridge construction

Welded components

 
We support our customers with our competencies in material testing, numerical simulation, analytical failure assessment and failure analysis related to fracture mechanics questions. Together with our customers we develop solutions for the assessment of the safety and the remaining service lifetime of machines and plants, the extension of their service lifetime, the determination of inspection intervals, the design optimization and a safety-related material selection. Moreover, we offer support for the preparation of expert reports and represent investigation results in front of technical regulatory authorities. 

 

Services

 

Our portfolio ranges from materials characterization to safety evaluation and lifetime assessment of components with defects.
 
Experimental determination of fracture mechanics parameters:

Fracture toughness, crack resistance curves, fatigue crack growth curves

Crack resistance tests in a temperature range of about -196 °C to 600 °C in compliance with test standards such as ASTM E399, E1820, E1921, E647

Non-standardized tests under custom specified conditions or with non-standard specimen geometries
 
Stress analyses:

Of specimens and components with cracks or other defects

Under complex thermo-mechanical constraints

Using state-of-the-art and advanced material models

With consideration of elastic-plastic deformation, creep and progressing damage

Under static and cyclic loading

Considering welding stresses

 
Fracture mechanics assessment:

In accordance with specific standards such as R6, SINTAP, FITNET, BS 7910, API 579 or FKM guideline

Using special software, for example, IWM VERB or ERWIN

Including custom-specific software implementation (component and crack geometry, stress conditions, material properties)

Using deterministic and probabilistic methods


Furthermore, we develop advanced solutions and evaluation concepts and consistently implement them into our calculation programs and the FKM guideline "Fracture mechanics strength assessment" co-developed by us (FKM = Forschungskuratorium Maschinenbau). Companies all over the world use the failure assessment software IWM VERB to solve fracture-mechanical problems. The optimization and the development of the software is performed in a close cooperation with our customers. Additionally, we provide training courses in fracture mechanics methods.

Contact us! Together we'll find a customized solution for the challenges you face.

How to work with the Fraunhofer IWM

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© Fraunhofer IWM

IWM Verb

 

IWM Verb is a software tool for the assessment of components containing crack-like defects. [more]

 

 

 

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Selection of measurement and equipment highlights

 

Equipment to perform fracture mechanical tests (i.e. ASTM E399, E1820, E1921 and E647) over large force and temperature ranges

Determination of strains by use of clip-gauges or digital image correlation (DIC) for areal strain measurements

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Topics

 

Structural integrity of pressurized structures: advanced non-linear methodology

 

Fracture mechanics assessment according to the concept of the Failure Assessment Diagram FAD requires precise calculation methods for the determination of fracture mechanics load parameters and also experimental and numerical validation of the assessment concept. The FAD concept as a part of different technical codes was mainly validated for ferritic steels.

 

Fatigue crack growth inside railway axles

 

If a crack is detected in a cyclic loaded component or its presence cannot be excluded by non-destructive testing, the remaining lifetime of this component can be estimated by the use of the fracture mechanics method. This occurs during the assessment or the dimensioning of railway axles of vehicles in service and newly designed vehicles.

 

Fatigue and fracture mechanics assessment of weld joints

 

By combining cyclic plasticity models, numerical welding process simulation, fatigue and fracture mechanics models the lifetime of a welded component can be described realistically. In the following example welding residual stresses and their stabilized state were determined by fatigue tests. In corresponding experiments (Fraunhofer LBF) a significant difference between the crack-initiation- and fracture-Wöhler-curves was found...

 

Publications regarding Fracture Mechanics, Structural Integrity


Contributions to newspapers, books and conferences as well as dissertations and project reports...