Monitoring of solidification induced strains in two resins used in photofabrication

Mechanical characteristics of an Ormocomp® biocompatible hybrid photopolymer

“…It is observed that after 42 h of light curing, where a high degree of consolidation is achieved (see Section 3.2), significant shrinkage strain values, namely 17 104.7 µε (Table 1) and 14 511.9 µε (Table 2), are calculated. Furthermore, it is worth noticing that when these values were compared to the ones reported by Karalekas and Schizas (2009), they were found to be considerably higher. In that study the same Ormocomp resin, without having been exposed to vacuum treatment, was light-cured for 15 h inside the mould apparatus leading to shrinkage strains of 5226.8 µε (demoulded specimen).…”

“…(4), along with the reference values of λ B0 (z = 13) = 1300.45 nm (specimen 1) and λ B0 (z = 10) = 1299.99 nm (specimen 2), the corresponding maximum value of the resulted shrinkage strain within the photopolymerised specimens was calculated at the end of the stepwise applied UV exposure. Again, it is noted that no temperature effects exist due to the negligible effect that the exothermic reactions have during polymerisation ( T = 0) (Karalekas and Schizas, 2009). The calculated strain values are presented in Tables 1 and 2.…”

“…As a result, rectangular specimens, for compressive testing according to ASTM D695-08 standard, of 10 mm × 10 mm × 40 mm were fabricated at room temperature in a custom made aluminum mould, with its open top long surface being exposed to UV radiation. The same mould had been used in a previous research work to investigate consolidation uniformity of an acrylate-based photopolymer at selected UV-exposure times and to measure the corresponding photopolymerisation induced shrinkage strains (Karalekas and Schizas, 2009). The mould cavity was coated with a thin layer of liquid release agent in order to minimise bonding of the solidified photopolymer to its surfaces.…”

“…Two test specimens were prepared (designated as specimen 1 and specimen 2) following the exact same procedure of fabrication; that is, time of vacuum treatment for air extraction before casting, casting process, initial UV-curing, demoulding procedure and time intervals of additional UV post-curing for completion of consolidation. The followed FBG embedding process is well documented elsewhere (Karalekas and Schizas, 2009). Bragg wavelength measurements were taken before resin casting, before UV initiation, during initial solidification inside the mould and at selected time intervals of UV exposure of unconstrained specimens (demoulded) for shrinkage strain evolution and corresponding consolidation degree measurements until full cure conditions were met.…”

Note: Strain sensitivity comparison between fiber Bragg gratings inscribed on 125 and 80 micron cladding diameter fibers, case study on the solidification monitoring of a photo-curable resin

“…In the past, similar experiments on strain measurements during curing reported data concerning the use of 125 µm FBG only. [6][7][8][9][10][11] However, monitoring the strain in a curable resin during and/or after the curing process using embedded small diameter FBGs can be very useful to control the process parameters in 3D printing technology as well as to fabricate "functional" 3D objects. [11][12][13][14][15][16] The FBGs are fabricated by excimer laser exposure of bare photosensitive fibers through a phase mask, and are tested a) Electronic mail: fernando.brandi@ino.it by simultaneously recording the Bragg wavelength shift of both FBGs during UV-Vis light exposure of the resin in which the fibers are embedded.…”