Functionally Graded Materials: controlling the polymer curing

Abstract

FGMs (Functionally Graded Materials) have gradients of mechanical properties depending on the position. FGMs are inspired in nature and recognised due to their superiority and application flexibility. Exceptional materials capable of combining harder and softer zones. Exhibiting high performance tensile properties either for fracture stress strength or enlargement capability. FGMs merge in one material counter properties to lighten stress concentrations, as it is continuously seen in human tissues and organs. Which allows them to withstand dissimilar quotidian activities such as running or jumping. [19] FGMs has kickstarted thanks to the growth of 3D printing techniques of high quality as SLA (Stereolithography). The rise of SLA techniques has drastically reduced their cost improving the investigation possibilities and subsequent cost-effective application. The 3D printing machine used for this study is based on SLA, offering an outstanding dimensioning reliability and repeatability by printing layers from 50 to 100 microns. Once the pieces are printed, they go through a post-curing process to change their tensile behaviour in distinct areas. The aim of the study is to stablish the independent variables of the aforementioned process that alter the tensile behaviour of the selected photopolymer. Various patterns and curing conditions are evaluated looking for stablishing hypothesis of how the manifold elements changed influence the tensile behaviour. With the aim of outlining the parameters of relevance, of the patterning and curing procedures. The application of patterns varying the curing conditions ushers in tailoring the properties of FGMs. Analytical tools used are Force-Displacement curves provided by the Universal Testing Machine and Digital Image Correlation software. By means of Force-Displacement charts pieces differently cured or without curing can be characterized obtaining tensile properties of the material depending on curing conditions without pattern effect. Pattern designs are proposed and masking procedure selected. Then, pieces cured following a pattern are analysed through Force-Displacement charts supported by DIC (Digital Image Correlation) software engine in order that local properties of strain can be measured. For the purpose of studying the mixed-properties of the pattern’s proposal, the tensile test is taken pictures of. Frames are latter analysed using DICE (Digital Image Correlation Engine) tool. DICE is an opensource software for stereocorrelation of images that had never been used in the department. With the aim of getting empirical knowledge of the tool capabilities and limitations. As well as, stablishing a proper method for the characterization of mixed-properties test specimens suitable to be repeated in the future, either for further research extensions or for applying the proven knowledge. To achieve the aim some challenges have to be overcome. Speckle painting is a hand-operated job necessary to the successive DIC analysis. Speckles painted by an airbrush create a pattern that is deformed with the test specimen which permits the DIC tool to correlate each frame with the ensuing one. Carrying out the research the following learning has been acquired or trained: test specimen design and evaluation according to standard; handling 3D printing software for SLA machines; pattern design and evaluation for FGMs; fundamental characterization of materials; getting expertise in DIC tools configuration; characterization and analysis of strain by means of DIC frames; and analysis of materials tensile behaviour.