Gewindeverbindungen örtlich II

Local evaluation of the fatigue strength of threaded connections II
FKM 2014
Issue number 322
Project no. 297

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Abstract:
This paper deals with the fatigue strength design of threaded connections
based on the local concept. Investigations are carried out on a bolt-
nut connection M16x100 (34CrNiMo6), a nozzle clamping nut connection
(34CrNiMo6) and a steel-aluminum connection (EN AW-6082 T6). The
calculated service lives are compared with experimental results.
In addition to the well-known
Chaboche model, the Döring material model is used to calculate the local stress-strain curves for the FE calculation and description
of the cyclic plasticity effects. The damage parameter PJ is used for the service life assessment (cracking)
according to the local concept.
Very good agreement between the test results and the calculation was found for the
bolt-nut connection. For the other connections, both
an overestimation and an underestimation of the calculated service life can be determined. Furthermore,
it was shown that the positive influence of an overload on the fatigue strength
of the screw-nut connection cannot be calculated. In addition, the
investigations show that the torsional stresses introduced by tightening are low
and therefore do not need to be taken into account in the service life assessment. Furthermore,
the investigations show that a design with a low mean load can also be carried out on
the basis of the concept according to Schneider [1].
The evaluation of the crack propagation is carried out using various models. In addition to the common
fracture mechanics models from the FKM guideline [2], a special stress intensity factor
solution was determined using an FE calculation for the bolt-nut connection
.
A simplified estimation of the fatigue strength for threaded connections was developed.
Here, the service life assessment for highly stressed connections is based
on an elastic FE calculation. The local elastic-plastic component behavior
is described using an extended approximation method. In an additional
step, the medium stress relaxation, which has a particularly strong effect at low load ratios
, can be taken into account. This means that a design is also possible without complex
transient calculations and relaxation tests.
The aim of the research project was achieved.