In recent years, the use of Stereo lithography (SL) to produce end-use parts has
increased rapidly. However, only limited applications have been considered as
there are several problems that impede the conversion of Stereolithography to be
used as a mainstream manufacturing process. One of the major problems is the
instability of the SL parts post-build when subjected to environmental factors.
This research included long-term material testing to investigate the effects of
ageing, humidity and temperature on the mechanical properties of the SL parts.
This work was carried out at a temperature range of -40°C to +lOO°C over
differing ageing and humidity conditions (dry (lO%RH), controlled (SO%RH) and
wet (lOO%RH». The results indicated that the main degradation factor was
humidity. It was therefore selected for further investigation in this research. This
is the most comprehensive analysis and characterisation of materials data yet
compiled for additively manufactured materials.
Stereolithography materials tested have been shown to significantly degrade over
time when subjected to a high level of relative humidity. Therefore, it was the
primary aim of this research to identify the mechanism of hygroscopic
degradation of Epoxy-based SL materials. This was achieved using various
techniques including mechanical tests, Differential Scanning Calorimetry (DSC)
and Attenuated Total Reflectance (ATR).
Modelling of water penetration into SL Epoxy-based parts was undertaken and the
type of diffusion was found to be anomalous (non-Fickian). Therefore a dualFickian
model was developed to identify the diffusion coefficients of the
investigated materials. Additional equations were developed to model the profiles
of moisture concentration and Young's Modulus within a specimen and to predict
the stiffuess of an SL material at a certain age. The methodology that has been
developed in this work can now be further used to predict the mechanical
properties of any future Epoxy-based SL material providing the diffusion
coefficient(s) of the material are known.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.
Innovative Manufacturing Research Centres (IMRC) I Engineering and Physical
Sciences Research Council (EPSRC), 3D Systems and Huntsman