Influence of Lubrication Systems on the Fatigue Strength of Bolted Joints

Abstract

The fatigue behavior of bolted joints is critical to failure for many applications due to the high notch effect. Among other parameters, the lifetime is based on the influence of the surface system, consisting of corrosion protection and lubricant. With the intention of considering the surface system in the design and dimensioning process of bolted joints, experimental investigations are carried out systematically for an exemplary selected basecoat and various lubricant systems. The basis is given by fatigue tests supported by selected methods of material analysis for the fractographic evaluation. A reproducible method to determine the crack initiation as well as the crack propagation is developed and used for the evaluation of lubricant systems. Defined damage can be reproducibly assigned on the basis of a critical frequency change rate of the resonance test machine. A high durability of the friction in the load-bearing contact (e.g., greases) reduces the stress and delays the crack initiation. Lubricants which are able to creep (e.g., oil) slow down the crack propagation and increase the lifetime, which is proved by a higher number of cycles to failure and an increased fatigue strength.

Further development of detail categories for bolt‐assemblies subjected to normal stress in steel constructions

“…For uncoated black HV bolts, the detail category 63 shows good agreement with the test results presented up to the nominal diameter M36. A specification of the lubrication condition for uncoated black bolts also appears to be reasonable [38]. Based on tests on bolts with threads rolled after heat treatment according to ISO 4014 [21] and nuts according to ISO 4032 [22] without subsequent thermal coating, it was possible to derive detail category 71 for nominal diameter M20, which is in line with the target value according to BS 7608 [12].…”

“…Further fatigue tests should be carried out on bolting assemblies with large diameter to validate the proposed adjustment of the exponent in the formula for capturing the size-effect. In addition, further investigations concerning the possible effect of the lubrication condition [38] on the fatigue strength would be useful and is planned to be performed in [35].…”

Advances in the Experimentation and Numerical Modeling of Material Joining Processes

“…In mechanical fastening, increasing durability and fatigue strength are essential for applications under repetitive loading or dynamic stress [ 29 ]. Industrially, simplifying the assembly process by designing fastening mechanisms that are user-friendly and require minimal manual effort is a crucial aspect to enhance productivity [ 30 ].…”