Richtlinie Nichtlinear 2nd Edition 2025
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This product will be released on 1 February 2026
Richtlinie Nichtlinear 2nd Edition 2025
Content language: German
About the content:
2nd edition 2025
200 pages
The FKM guideline Nonlinear represents a standard for the mathematical verification of strength with elastic-plastic material behavior. The first edition was published in 2019 and was initially limited to uniaxial and multiaxial proportional stresses for fatigue strength verification, and thus severely restricted in terms of its applicability to real-world problems.
This led to various IGF research projects in which extensions to the guideline were pursued. Expanded to include the findings from these projects, the second edition is now available, which can also be used to verify multiaxial non-proportional stresses. In addition to various adjustments, fundamental extensions have been made with regard to weld seams and components with surface layers.
This second edition has been completely revised, so that a list of all changes is not manageable. During the revision, attention was paid to homogenizing the symbols. For example, the safety factors are now designated by γ in both the static and fatigue strength verification.
The following significant changes have been made:
• Addition of general information regarding the application of this guideline through the information provided in Chapter 1.
• Static strength verification:
– Removal of the partial safety factor jm for tensile strength or the failure criterion of fracture, as the characteristic value of tensile strength does not play a role in static strength verification.
– Specification of the requirement for determining the quasi-static characteristic values for the failure limit curve and the stress-strain curve: Both must be determined experimentally in tensile tests on samples from the material in the component. This eliminates the need to apply the technological scale factor in the plastic portion of the stress-strain curve.
– Inclusion of statistical validation of the quasi-static characteristic values before the failure limit curve is calculated.
• Fatigue strength verification:
– Independent of the damage parameter used:
∗ The calculation procedure has been fundamentally revised and restructured by extending the verification to include the following aspects:
· Steel components with surface layers
· Welded steel components
· Multi-axial non-proportional stresses and the resulting requirements.
However, the calculation procedure familiar from the 1st edition is essentially still included.
∗ Removal of the classification of safety levels for safety factors depending on redundancy.
∗ Inclusion of hardness as an alternative material parameter for the mathematical determination of cyclic stress-strain curves and damage parameter Wöhler curves for steel.
∗ Inclusion of the material groups cast iron (GJL, GJS, ADI, GJM) and cast aluminum with the restriction that only average service lives can be calculated for these.
∗ Simplification of the equation for the mathematical determination of the cyclic hardening exponent K′ without changing the accuracy of the estimate.
∗ Extension of the steel material group to include the highest-strength steels from Rm = 1,500MPa by adjusting the mathematical determination of the damage parameter Wöhler curve for the material.
∗ Specification of the experimental determination of fatigue strength for the material.
∗ Division of the steel material group into the subgroups case-hardened steel, stainless steel, and forged steel on the one hand, and other steel on the other hand, for the mathematical determination of the fatigue strength for the material, analogous to [1].
∗ Inclusion of the non-proportionality index fnp for evaluating the strength of the non-proportionality of the stress tensor.
∗ Inclusion of the multiaxiality index m to characterize the stress state with regard to the composition of normal and shear stresses.
∗ Extension of the sign-affected comparative stress: Depending on the shear fatigue strength factor of the material, the strain energy hypothesis,
the normal stress hypothesis, or a linear combination of both is now used. The sign rule has been adjusted to ensure compatibility with scaled normal stress (in conjunction with PRAM).
∗ Inclusion of a notch approximation method for components with a boundary layer.
∗ Inclusion of a method for considering residual stresses in proportional external loads.
∗ Consideration of the multiaxiality index m in the calculation of the damage parameter. This eliminates the previously necessary double verification for the case of pure torsion (multiaxiality index h = 0).
∗ Inclusion of the factor Katm for verification points below the component surface.
∗ Inclusion of a new concept for taking surface roughness into account as a function of notch sharpness.
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∗ Reformulation of the RainflowHCM algorithm for simulating local stresses and strains with the option of considering residual stresses.
– Damage parameter PRAM (or P):
∗ Inclusion of the representative load vector ⃗L
∗ for simplified description of a non-proportional stress state for use in the support effect concept.
∗ Introduction of a critical section plane method in conjunction with scaled normal stresses for handling non-proportional stresses.
∗ Consideration of non-proportional hardening.
∗ Consideration of the factor Knp in the damage parameter Wöhler curve for the component to lower the Wöhler curve in the case of non-proportional stresses.
∗ Introduction of the Miner-Haibach method instead of Miner-elementary for damage accumulation.
– Damage parameter Z:
∗ Reformulation with damage parameter Z instead of PRAJ.
∗ Reference to the calculation algorithm from [7] for non-proportional stresses.
In addition:
• The examples have been fundamentally revised in line with the extensions to the calculation algorithms.
• Standard values for tensile strength for use in fatigue strength verification have been included in Section 5.4.
Productinfo
| Productnumber | 9783816307754 |
|---|---|
| EAN | 9783816307754 |
| Authors | FKM |
| Language of Content | DE |
