Fatigue behaviour of laser-sintered PA12 specimens under four-point rotating bending
Abstract
Purpose
The purpose of this paper was twofold: first, to determine if rotating bending could be used as an effective way of determining the fatigue behaviour of laser-sintered nylon, and second, to examine whether the fatigue behaviour of laser-sintered PA12 showed any significant anisotropy.
Design/methodology/approach
Specimens were measured to obtain dimensional accuracy, density and surface roughness levels. Then, uniaxial tensile and rotating-bending fatigue tests were performed. A purpose-built test-jig has been used to subject hourglass-shaped specimens to reversed bending at two frequencies: 50 and 30 Hz. Additionally, thermal and microstructural analyses were performed to understand the underlying mechanisms of failure.
Findings
The experiments suggest PA12 specimens will fail in fatigue following the conventional fatigue mechanisms observed in previous research with ductile polymers. Although high-frequency loading caused a heat build-up in the specimen, temperatures stabilised between 20 and 30°C, suggesting that rotating-bending fatigue at frequencies of up to 50 Hz is a valid way of determining the fatigue behaviour of laser-sintered PA12 specimens. Stresses below 20 MPa led to fatigue lives above 1 million cycles. Some anisotropic behaviour was observed in the fatigue test results, with specimens made orientated with the Z axis showing the lowest fatigue lives on average, but an endurance limit of approximately 15 MPa seems to be common for all specimens regardless of their build orientation.
Practical implications
The observed endurance limit of 15 MPa did not depend significantly on the orientation at which a part was built – meaning that it may be possible to guarantee a service life for a part which does not depend on part orientation within a build. Clearly, good-quality control will also be required to ensure performance, but this has important implications for the design of laser-sintered PA12 parts for realistic service conditions.
Originality/value
To our knowledge, this is the first paper to present rotating-bending fatigue data for laser-sintered PA12 parts, and the first to identify an endurance limit which is independent of part orientation.
Keywords
Acknowledgements
This research was funded through the European Commission Framework Seven Program (grant number NMP2-SE-2009-228893) as part of the A-Footprint project www.afootprint.eu. The authors are also indebted to Peacocks Medical Group and Dr Jari Pallari for supplying test specimens and giving access to their facilities. Special thanks to the Engineering and Physical Sciences Research Council (EPSRC) and the Engineering Instrument Pool for lending the thermal imaging equipment for this research, and special thanks to Peter Anthony for the support and assistance.
Citation
Munguia, J. and Dalgarno, K. (2014), "Fatigue behaviour of laser-sintered PA12 specimens under four-point rotating bending", Rapid Prototyping Journal, Vol. 20 No. 4, pp. 291-300. https://doi.org/10.1108/RPJ-07-2012-0064
Publisher
:Emerald Group Publishing Limited
Copyright © 2014, Emerald Group Publishing Limited