Fatigue strength of unwelded components


FKM stands for mathematical proof of strength of machine components. The guideline was based on former TGL standards, the earlier guideline VDI 2226 and other sources and further developed to the new level of knowledge. The guideline is a calculation algorithm consisting of instructions, formulas and tables. Represents a general method for calculating the strength of components in mechanical engineering.

Area of application of the FKM guideline:

  1. In mechanical engineering and related fields.
  2. Mathematical proof for rod-shaped, flat-shaped and volume-shaped components.
  3. Static proof and proof of fatigue.
  4. Verification with nominal stresses or local stresses.
  5. Can be used for components with or without machining or can also be made by welding.

There are 4 calculation tools on our site, that are based on the FKM guideline :

  • Static strength of (un-)welded components
  • Fatigue strength of (un-)welded components
Fatigue strength of unwelded components

Stress characteristics

Stresses: alternating

Main stress amplitudes
Main stress 1 σ1,a,i [MPa]
σ2,a,i [MPa]
σ3,a,i [MPa]
Associated mean stresses
Mean stress 1 σ1,m,i 0 [MPa]
Mean stress 2 σ2,m,i 0 [MPa]
Mean stress 3 σ3,m,i 0 [MPa]
Material characteristics
Tensile strenght Rm - [MPa]
Temperature factor1 KT,D 1 [-]
Technological size factor2 Kd,m 1 [-]
Material change resistance for tensile pressure σW,zd - [MPa]
Construction characteristics
Surface hardening: none
Construction factor3 KWK,σ 1 [-]
Plastic support number4 npl 1 [-]
Component strength
Proof of fatigue strength
Material change resistance σWK - [MPa]
Mean stress factor5 KAK 1 [-]
Fatigue strength factor6 KBK,σ 1 [-]
Amplitude of the component fatigue strength σBK - [MPa]
Safety factors
Safety factors: applied conservatively
Safety factor7 j 1.4 [-]
cyclical degree of utilization aBK,σ1 - [%]
cyclical degree of utilization aBK,σ2 - [%]
cyclical degree of utilization aBK,σ3 - [%]
cyclical comparative degree of utilization8 aBK,σv - [%]
Notes on the factors
  1. Temperature factor: This takes into account the influence of increased temperatures on the strength of the material.
  2. Technological size factor: This takes into account an influence of the component size on the strength of the material.
  3. Construction factor: This includes an influence of component properties such as surface roughness, surface hardening, notch effect on component strength
  4. Plastic support number: This takes into account plastic bearing reserves, which allow a higher load on the component.
  5. Mean stress factor: This takes into account the influence of residual and medium stresses. With a medium voltage in the train area, the value of 1 can no longer be conservative
  6. Durability factor: takes into account the load on the load spectrum and the required number of cycles. Here fatigue strength and NO fatigue strength proof
  7. Safety factor: This takes into account the influence of the consequences of damage and the frequency of inspections
  8. Comparative degree of utilization: it is conservatively assumed that all stress amplitudes reinforce each other
KONSCHA Simulation GmbH assumes no liability for the correctness, completeness, functionality and topicality of the collection of formulas, calculation programs or their results. The use of the content of the website is at the user's own risk. Liability claims are fundamentally excluded. We are grateful for any information about any errors or improvements.