To read the full version of this content please select one of the options below:

Fatigue behaviour of laser-sintered PA12 specimens under four-point rotating bending

Javier Munguia (School of Mechanical and Systems Engineering, Newcastle University, Newcastle upon Tyne, UK)
Kenny Dalgarno (School of Mechanical and Systems Engineering, Newcastle University, Newcastle upon Tyne, UK)

Rapid Prototyping Journal

ISSN: 1355-2546

Article publication date: 10 June 2014

652

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

Related articles