Mechanical Reliability

Experimental and numerical investigation on the influence of support effects on the fatigue strength of pre-stressed bolted joints subjected to bending load


In many applications in industrial field, bolted joints are often subjected to a combination of axial and bending loads, which cause a combined loading in the thread base and in the head-shaft transition, e.g. multi-axial stress state and support effects due to stress gradients. These local effects are not considered in the current design of bolted joints. However, experimental analyses from the literature show that support effects due to bending stress can lead to higher local endurable stresses. A more reliable estimation of the fatigue strength of bolted joints under bending load by taking into account the support effects would allow the use of smaller bolts, which would have a great potential for lightweight design.


The aim of the project is the development of an assessment method to take into account the support effects on the fatigue strength of pre-stressed bolted joints under bending stress condition.


First, tests on unnotched specimens are carried out to determine the material behavior under cyclic load condition, providing the input values for the numerical investigation. Based on the FE analysis, geometry and load parameters are defined for the test set-ups that reproduce the axial, bending and combined loading cases. The experimental results are compared with the results obtained with the numerical simulations to derive a design method, which takes into account the support effects. The analysis is carried out using stress and strain-based evaluation criteria. The investigation is performed on different bolt diameters in order to make it possible to transfer the results to various bolted joints.

Picture: Fachgebiet SAM

Information about the project

Research facilities:

  • Technical University Darmstadt, State Material Testing Lab Darmstadt (MPA) and the Institute for Material Science (IfW)
  • Technical University Darmstadt, Research group System Reliability, Adaptive Structures, and Machine Acoustics (SAM)

AiF-Project, IGF-Nr. 20821
DSV – German Association of Fastener Producers
Duration: 30 months


M.Sc. Elena De Tomaso
Tel: +49 6151 705 8458