Tensile, compression and flexural alternating load tests

Bridging the gap between compressed hydrogen testing and room air testing to verify the strength of additively manufactured and hydrogen-exposed flexure hinges

Abstract
Flexure hinges are important connections between stationary and moving assemblies in (opto-)mechatronic applications. These joints are subjected to stresses during bending. The challenge was to create a safe basis for the design of the flexure hinges in a hydrogen atmosphere, for which, as per DIN 50142, flexural fatigue tests (under the environmental parameter) were carried out and statistically evaluated in accordance with DIN 50100. It turned out that the environmental parameter, i.e. an atmosphere of pure gaseous hydrogen in the flexural fatigue test, is difficult to prepare economically. The idea now was to cost-effectively test the nickel-based alloy "Inconel 718" (produced both additively and conventionally) in tensile compressive fatigue tests under gaseous, pure hydrogen. In order to assess the transferability of tensile compressive fatigue tests to flexural fatigue tests and to quantify them at best, reference tests for both types of stress were conducted in ambient air at room temperature. In this way, the transfer factor between both types of stress could be determined and subsequently the influence of the hydrogen on the bending stress on the investigated alloy could be quantified. The results are promising with regard, for example, to the evaluation of the influence of molecular hydrogen on service life. Click here for the technical paper.

Authors 
Timo Möller, Johannes Mayer; Carl Zeiss SMT GmbH; Oberkochen
Arnd Nitschke, Stefan Zickler; MPA Universität Stuttgart; Stuttgart
Christoph Hauck, Stefan Auernhammer; MBFZ toolcraft GmbH; Georgensgmünd