Fatigue Assessment

Simulation is just the first step

An essential part of the structural design is the qualified assessment of fatigue live and durability of structure based on FEA results. DESIGNTEC as partner of MAGNA POWERTRAIN – ENGINEERING CENTER STEYR GmbH & Co KG, the developer of software for fatigue analysis FEMFAT, offers wide range of services which help you to compute and asses fatigue damage of your structures or products in accordance with applicable norms and industrial standards.

Applications of Fatigue Assessment

Proportionally Loaded Components with Constant Load Cycles

Suitable for situations where the structure is subjected to a constant cycle or sequences of non-constant load cycles and the orientation of the principal stresses and strains does not change during the load cycle (proportional loading). The loading situation is typically defined by upper and lower stress states plus one optional constant stress state. The load spectrum can be defined to consider a sequence of non-constant load cycles. The life- or safety factor analysis can be performed using stress- or strain-life models.

Multiaxially Loaded Components

Strength analyses on components with multiple axis loading (directions of principle stresses may change permanently) on the basis of load-time histories from transient FE-analysis (transient based definition) or from multibody simulation / measurement signals (channel based definition). The resulting performance of the structure can be evaluated in term of damage values, endurance safety factors, static safety factors or life time.

Random Response Fatigue

Method designed for fatigue life analysis of multiaxially stochastically loded structures. Analysis is performed completely in the frequency domain, where the loads are defined as power spectral densities (PSDs). The prediction of fatigue life in the frequency domain is more realistic and efficient than time-domain analysis for many applications with random loading such as wind/wave loads, turbulence or shaker tests.

Thermo-Mechanical Fatigue

Applicable to situations where combined thermal and mechanical loading occurs, typically cylinder heads, turbochargers or turbine blades. For the fatigue analysis we use FEMFAT heat module which employs the Sehitoglu Method for the thermo-mechanical low-cycle fatigue. This method takes into account three relevant damage mechanisms – mechanical, environmental and creep damage.

Welds

For the fatigue analysis of weld we use FEMFAT weld – a FEMFAT module for assessment of dynamically stressed welds. Analysis of shell, solid and mixed shell-solud welds models can be used. The performance of welds can be evaluated in terms of damage/life or endurance safety factors.

Spot Welds

Fatigue analysis of spot-joints (welds, rivets) in thin sheets based on FEMFAT module SPOT. Both force- or stress-based methods can be used for fatigue assessment.

Methods and Technology

DESIGNTEC offers comprehensive spectrum of fatigue analyses based on technology and methods implemented into software for CAE based fatigue analysis FEMFAT:

• High-Cycle Fatigue (Stress-Life model),
• Low-Cycle Fatigue (Strain-Life model),
• Critical plane and stress computation,
• Rainflow counting,
• Neuber rule (elasto-plastic stresses based on a linear elastic FE analysis),
• Miner rule (damage summation),
• Safety factor analysis,
• Material generation (the creation of a new material based on the definition of a material class and certain material parameters in tension).

We can consider many interacting fatigue influences in the analyses:

• Notch influence (by relative stress gradient)
• Mean stress influence
• Influence of surface roughness
• Technological parameter influence
• Tempering condition
• Technological surface treatment (Shot peening, Rolling, Carburizing, Nitriding, Carbonitriding, Induction hardening, Flame hardening)
• Temperature influence
• Statistical influence
• Forging influence (technological factor)
• Cast microstructure

Material Models and Material Properties

The material properties for material models we defined based on

• industrial standards (German FKM guideline, EC3),
• comprehensive FEMFAT material database with over 500 material data sets,
• FEMFAT material generator,
• custom values from your material tests.