FKM guideline

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The FKM guideline "Computational strength verification of machine components " , in practice often just called the FKM guideline , is a guideline issued by the Forschungskuratorium Maschinenbau eV (FKM), which provides a general method for calculating the strength of components in mechanical engineering .

history

The FKM guideline was created in the component strength working group with funding from the Mechanical Engineering Research Board and the working group of industrial research associations "Otto von Guericke" under the leadership of IMA Materials Research and Application Technology GmbH. It was first issued in 1994. The current 6th edition was published in September 2012. The guideline is always published in book form by the VDMA publishing house.

The guideline was developed on the basis of former TGL standards, the earlier guideline VDI 2226, regulations of DIN 18800, the IIW recommendations and the Eurocode 3 and further developed to reflect the latest state of knowledge.

scope of application

The FKM guideline

  • can be used in mechanical engineering and related areas of industry,
  • enables the computational proof of strength for rod-shaped, flat and volume-shaped components taking into account all relevant influences,
  • describes the static and the fatigue strength verification, the latter depending on the load characteristics as a fatigue, time or operational strength verification,
  • applies to steel, including stainless steel, at component temperatures from −40 ° C to 500 ° C,
  • applies to cast iron material at component temperatures from −25 ° C to 500 ° C,
  • applies to aluminum material at component temperatures from −25 ° C to 200 ° C,
  • Can be used for components that are manufactured with or without machining or by welding,
  • allows the evaluation of nominal stresses as well as local, elastically determined stresses, which are obtained by means of elasticity-theoretical solutions, finite element or boundary element calculations or from measurements.

The guideline is a uniformly structured calculation algorithm for all applications, consisting of instructions, formulas, tables and figures. Textual explanations are given when they appear necessary for safe use. The calculation process is supplemented by examples for better understanding.

Since the 4th edition in 2002, the mathematical proof of strength has also been possible for components made of aluminum materials. With reservation, because the available results were subject to large scatter or were not investigated in sufficient detail.

The FKM guideline is contained in 3 books. The first book "Computational Strength Verification for Machine Components" deals with the static strength verification and the fatigue strength verification. The second book "Fracture Mechanical Strength Proof" deals with components in which defects (e.g. individual cracks) have been found during manufacture and these have to be proven in terms of strength. In order to be able to include the non-linear material deformation behavior, the 3rd book "Guideline non-linear" has been available since the beginning of 2019. Like Book 1, this also describes a static and a fatigue strength verification. By taking into account elastic-plastic material behavior, the statically permissible limit load can in some cases be significantly increased compared to Book 1. A mechanism-oriented estimate of the crack life is used for the proof of fatigue strength.

Concepts

Color display of the cyclical degree of utilization

Depending on the component shape, the nominal stress concept (for rod-shaped components) or the local stress concept (for all other components) is used for verification. A static strength verification and a fatigue strength verification must be created for both concepts. A static degree of utilization and a so-called cyclical degree of utilization are determined in the evidence. Both must be less than 1.

It does happen that components have a static degree of utilization less than 1, but a cyclical degree of utilization greater than 1, or vice versa. In both cases, the proof of strength would not be provided. A proof of fatigue strength always requires the proof of static strength.

Line welds are detected at the seam transition cross-section and at the weld root and are also assessed with a static and a cyclic degree of utilization.

Influencing variables

  • Stresses with associated mean values, amplitudes and collective forms
  • Material strength parameters taking into account the technological size factor and temperatures
  • Design parameters, determined from plastic support numbers, notch action numbers, roughness and surface layer factors
  • Safety factors
  • Anisotropy factor
  • Residual stress factor in welds

Computing programs

As mentioned above, the FKM guideline is a structured calculation algorithm, which is why it can be implemented in a computer program. An extended option is the coupling with finite element programs. The time-consuming determination of the stresses and stress gradients is done by the computer program and contour plots of the degree of utilization can be generated for complete assemblies. In addition to components, other solutions can also evaluate weld seams according to the FKM guideline based on the FEM shell or solid results.

Web links

Individual evidence

  1. ^ Research Board of Mechanical Engineering: Computational proof of strength for machine components, 6th revised edition . VDMA-Verlag, 2012, ISBN 978-3-8163-0605-4 .
  2. ↑ Durability Inspector, example of strength verification coupled with FEM ( Memento from July 26, 2014 in the Internet Archive ) (PDF) Retrieved on February 6, 2019.
  3. ↑ S-Life FKM - software for the FKM strength verification from FEM results , accessed on June 29, 2011.
  4. ↑ winLIFE - software for the FKM strength verification with and without FEM results . Accessed on June 29, 2011.
  5. ↑ WIAM fatique RIFEST - software for strength verifications according to the FKM guideline . Accessed on April 2, 2015.
  6. ↑ FKMmadeEasy: the software for the FKM guideline. EinockAKADEMIE, accessed on July 5, 2019 (German).
  7. ↑ A-Struct, verification software for a guided verification based on FE results , accessed on February 6, 2020.
  8. ↑ AutoFENA 3D - The program for the automated FKM verification in HyperWorks , accessed on September 27, 2012.
  9. ↑ LIMIT - software for standardized evaluation of FE results, etc. a. according to the FKM guideline , accessed on March 28, 2020.