Content area
Purpose
This paper aims to investigate the influence of post-curing temperature, post-curing time and gamma ray irradiation dose upon the tensile and compressive mechanical properties of the medical graded vat photopolymerization parts.
Design/methodology/approach
Medical graded vat photopolymerization specimens, made from photopolymer resin, were fabricated using bottom-up vat photopolymerization machine. Tensile and compressive tests were conducted to assess the mechanical properties. The specimens were categorized into uncured and post-curing groups. Temperature post-processing and/or gamma irradiation exposure were for post-curing specimens. The post-curing parameters considered included temperature levels of 50°C, 60°C and 70°C, with 1, 2, 3 and 4 h periods. For the gamma irradiation, the exposure doses were 25, 50, 75 and 100 kGy.
Findings
Post-curing improved the mechanical properties of medical graded vat photopolymerization parts for both tensile and compressive specimens. Post-curing temperature greater than 50°C or a prolonged post-curing period of more than 1 h made insignificant changes or deterioration in mechanical properties. The optimal post-curing condition was therefore a 50°C post-curing temperature with 1 h post-curing time. Exposure to gamma ray improved the compressive mechanical properties, but deteriorated tensile mechanical properties. Higher gamma irradiation doses could decrease the mechanical properties and also make the part more brittle, especially for doses more than 25 kGy.
Originality/value
The obtained results would be beneficial to the medical device manufacturer who fabricated the invasive temporary contact personalized surgical instruments by vat photopolymerization technique. In addition, it also raised awareness in excessive gamma sterilization in the medical graded vat photopolymerization parts.
1. Introduction
Since the development of digital design and manufacturing technologies such as computer-aided design (CAD), -aided manufacturing and additive manufacturing (AM) techniques, the 3D printing (3DP) has gained more attention and has been widely applied for medical and dental purposes (Khorsandi et al., 2021; Pruksakorn et al., 2015; Melchels et al., 2010). These include use for the production of personalized implants for organ replacement (Turna et al., 2014), endoprosthesis (Pruksakorn et al., 2015), tissue engineering scaffolds (Melchels et al., 2010) and single-use surgical instruments (Hu et al., 2020). The concept of 3DP is to deposit the material to create the physical workpiece layer-by-layer. There are several systems of 3DP which can be classified into processed material forms, i.e. power-based, solid-based and liquid-based principles (Chantarapanich et al., 2013). In addition to the material extrusion, a solid-based 3DP which has been seen widespread use in medical applications, a liquid-based technology known as vat photopolymerization (VPP) is another 3DP system which has been recognized for its potential in manufacturing medical parts and instruments. This is due to its advantages in accuracy, a precise and smooth fabrication process and high mechanical strength. Also, various liquid photopolymer resins have been certified for medical use (Formlabs, 2021; Formlabs, 2016). Examples of use include orthopaedic surgical drilling/osteotomy guides (Anunmana et al., 2020; Takeyasu et al., 2013), clear orthodontic aligners (Tartaglia et al., 2021), bone tissue scaffolds (Melchels et al., 2010) and so forth.
The manufacturing principle of VPP is to solidify liquid photopolymer resin from energy dissipated from ultraviolet (UV) light source. It currently has bottom-up and top-down working concepts (Schmidleithner and Kalaskar, 2018), as shown in Figure 1. For the bottom-up concept, the build platform is upside down, and the built part is then hung above. The top-down concept is a conventional part-building principle, whereby the part is upright on the platform. In either concept, the solidification begins at the near-build platform layer, which is the bottom layer. Then, the successive build surfaces are solidified one by one until reaching the topmost layer (Chantarapanich et al., 2013). The photopolymer resin used in the VPP are those such as DSM’s Somos WaterShed (Puebla et al., 2012), Surgical Guide (Formlabs, 2021) and Dental SG (Formlabs, 2016). In addition, there is some photopolymer resin mixed with ceramic powder such as zirconia for specific dental implant applications (Li et al., 2019).
The mechanical properties of solidified photopolymer resin are considered a concern for medical purposes. Insufficient mechanical strength of VPP parts has been a problem for loading application (Karalekas and Antoniou, 2004) which may lead to clinical complications during intra-operative and post-operative stages. Various publications have reported the study results of VPP part mechanical strength for different manufacturing parameters and post-curing processes. Some of the studies revealed that a 45-degree angle on the platform build orientation results in higher tensile strength compared to other platform orientations (Cingesar et al., 2022; Shirinbayan et al., 2022; Chantarapanich et al., 2013). Also, previous reports have shown the significance of aging and pre-conditioning on the mechanical properties of VPP part (Puebla et al., 2012; Mansour et al., 2007). In addition, medical use VPP parts are required to have proper post-processing methods. This is to clear out the residue uncured monomer on and within the parts (Riccio et al., 2021; Hong et al., 2018). The post-processing method involved the use of UV curing with a certain temperature and time. Previous studies found that post-curing under UV could enhance the strength of the photopolymer resin (Ahmad et al., 2020; Bonada et al., 2017; Salmoria et al., 2005). Moreover, the temperature used during post-curing was an associated factor which made the material more brittle (Jindal et al., 2020). Although these studies showed the significant effect of temperature and post-curing time, there is still nevertheless limited information on how combinations of these two factors influence the mechanical properties of medical graded VPP parts.
The VPP parts as medical devices or implants have to be sterilized to eliminate microbes prior to clinical use. There are several techniques used for the sterilization of polymeric medical devices such as ethylene oxide gas (EO), hydrogen peroxide (H2O2), plasma sterilizer and gamma irradiation (Rogers, 2012). Among these techniques, gamma irradiation is the most suitable for invasive medical devices. Gamma irradiation sterilization uses radioactive isotopes such as cobalt-60 (60 Co), to generate the emitted gamma rays (Rogers, 2012; Wiseman et al., 2022). The emitted gamma rays penetrate through the entirety of the medical device and can eliminate the microbes on the surface as well as internal layers (Wiseman et al., 2022). Then, the sterilization technique may affect the mechanical properties. Most of the previous research paid attention to the effects of gamma radiation upon polymer mechanical properties. For example, some polymers, i.e. polylactic acid and acrylonitrile butadiene styrene, have their mechanical properties significantly decreased as they become more brittle when exposed to high gamma ray doses (Chaitat et al., 2022; West et al., 2019; Rankouhi et al., 2016). On the other hand, exposure to gamma rays in polymers, i.e. polyethylene increased the mechanical properties at low doses, but caused declines at high doses (Cota et al., 2007). Hong et al. (2018) investigated the mechanical properties of UV curable 3DP materials after gamma irradiation with various doses and specimen thicknesses. The results reported an increase in Young’s modulus and the tensile strength of specimens after gamma irradiation, whereas other mechanical properties have not yet been explored. Also, to best of the authors’ knowledge, there are no studies on the effects of gamma irradiation upon compressive mechanical properties. Then, there is still limited investigation on the effects of gamma irradiation upon medical graded VPP parts.
The trend of VPP usage for medical device manufacturing has increased sharply, especially since the onset of the COVID-19 pandemic (Longhitano et al., 2021). Many protective equipment was manufactured using VPP such as face shield (Maracaja et al., 2020), face mask (Bilalis et al., 2022) and nasopharyngeal swaps (Ford et al., 2020). This signifies the importance of VPP for current and future demand in medical applications. Besides its biological compatibilities, mechanical properties are an important concern with parts used for medical devices as well as for surgical instruments. As aforementioned, the parts fabricated by VPP are required to perform the post-processing method and sterilization process which could influence the mechanical properties of the finished parts. Hence, the aims of this study were to assess the influence of different post-curing temperatures and times as well as the influence of different gamma irradiation doses upon the tensile and compressive mechanical properties of the medical graded VPP parts. The obtained results would be beneficial to the medical device manufacturer.
2. Material and methods
The studied VPP specimens were categorized into uncured (control group) and post-curing groups. The uncured specimens were not subjected to either post-processing methods or gamma irradiation exposure. Temperature post-processing and/or gamma irradiation exposure were for post-processing specimens. The considered post-processing parameters included three temperature levels (50°C, 60°C and 70°C) with four different time periods (1, 2, 3 and 4 h). For the gamma irradiation, the exposure doses were 25, 50, 75 and 100 kGy. All specimens were made of Surgical Guide V1 (Formlabs Inc., USA) photopolymer resin, fabricated using the FormLabs Form2 AM machine (Formlabs Inc., USA). The tensile and compressive tests were performed using a Universal Testing Machine (UTM) (EMIC DL500, Instron Corp., USA, and UH-1000, Shimadzu Corp., Japan).
2.1 Photopolymer resin
The Surgical Guide V1 (Formlabs Inc., USA), which is a commercially available VPP resin, was used as a material for the study. The resin was received in a liquid form contained in a liter of plastic cartridge. The Surgical Guide V1 has a clear colour. The resin was stored in cartridge at all times in the controlled temperature room at 27°C with 35% relative humidity (RH). Based on information in the technical datasheet, the resin was evaluated in accordance with ISO 10993–1 biological evaluation of medical devices – Part 1: Evaluation and testing within a risk management process, and ISO 7405 Dentistry – Evaluation of biocompatibility of medical devices used in dentistry, and was found to be not cytotoxic according to EN ISO 10993–5 biological evaluation of medical devices – Part 5: Tests for in vitro cytotoxicity, not an irritant and a sensitizer according to EN ISO 10993–10 biological evaluation of medical devices – Part 10: Tests for skin sensitization. The mechanical properties of Surgical Guide V1 as information provided in the technical datasheet are shown in Table 1 (Formlabs, 2021).
2.2 Testing specimen fabrication
The Type IV dumbbell shape of the American Standard for Testing Materials (ASTM) D638-14 (ASTM, Standard D638, 2014) and the rectangular shape of ASTM D695-15 (ASTM, Standard D695, 2015) were the referred geometry used for the tensile and compressive tests, respectively, with the dimensions shown in Figure 2. The 3D models of tensile and compressive specimens were created in CAD software (VISI 21, Hexagon AB, Sweden) and made in STereoLithography file format (STL). The STL files of the specimen geometry were imported into PreForm 3D (Formlabs Inc., USA), a pre-processing software for the FormLabs Form2 AM machine (Formlabs Inc., USA).
In the PreForm 3D, the tensile models were on-edge with a 45-degree orientation on the platform, as previous studies presented superior mechanical properties than other orientations (Cingesar et al., 2022; Shirinbayan et al., 2022; Chantarapanich et al., 2013). For compressive models, they were oriented at a 0-degree angle on the platform. Due to the limited dimensions of the printing platform (145 × 145 mm), eight tensile specimens and eight compressive specimens could be included in one printing batch. Branching tree structure shape supports were created between each part and the platform. There was a total of 324 printing layers. The arrangement of specimens for one printing batch is shown in Figure 3.
The fabrication was performed using FormLabs Form2 AM machine (Formlabs Inc., USA), as shown in Figure 4. The manufacturing parameters were set as follows: 100 µm layer thickness (You et al., 2022), 405 nm UV laser wavelength with a maximum output of 96 mW at the print plane, 140 microns laser spot size and 35°C resin tank temperature. The printing time per batch was 4 h 42 min. After fabrication, the specimens were cleaned using isopropanol alcohol (IPA). The structure support and surplus material were removed via a flush cutter. All fabrication and material removal processes were operated in a dark room with a controlled room temperature of 26°C and RH of 55%.
2.3 Post-curing
The non-post-processing group (uncured group) was covered with aluminum foil just after fabrication to prevent exposure to light that could induce further curing. Then, the specimens were stored in a dehumidified cabinet (DrySmart DS-50C, Zhuhai Huazhiyuan Technology Co., Ltd., China PR) at 29°C with 35% RH. For the post-processing groups, the VPP specimens were post-cured in the post-curing chamber (Form Cure, Formlabs Inc., USA), as shown in Figure 5, at temperatures of 50°C, 60°C and 70°C with also four time periods of 1, 2, 3 and 4 h. In the post-curing process, 13 multi-directional LEDs with radiant power of 9.1 W and wavelength of 405 nm were used. The specimens were placed on turntables during post-curing. After post-curing, all cured specimens were also covered with aluminum foil and stored in the dehumidified cabinet (DrySmart DS-50C, Zhuhai Huazhiyuan Technology Co., Ltd., China PR). The specimen group designation of the specimens used within this study is summarized in Table 2.
2.4 Mechanical tests
Mechanical tests were used to determine the mechanical properties of fabricated VPP parts. The testing was performed under tension and compression modes using a Universal Testing Machine (UTM). The UTM used for tensile testing was EMIC DL500 (Instron Corp., USA), whereas the UTM for compression testing was UH-1000 (Shimadzu Corp., Japan), as shown in Figure 6.
For tensile testing, the ends of the tensile specimens were held by upper and lower grips. According to ASTM D638-14 (ASTM, Standard D638, 2014), the testing speed was set at 5 mm/min throughout the testing. The test was terminated once the specimens were separated. The tensile mechanical properties, i.e elastic modulus (EM), yield stress (YS), ultimate tensile stress (UTS), fracture stress (FS), %elongation at YS, %elongation at UTS and %elongation at break were collected and reported in the form of an average with standard deviation values calculated from four specimens.
The fabricated compression specimens were tested following ASTM D695-15 guidelines (ASTM, Standard D695, 2015). The specimens were placed at the center of the machine base and between the upper crosshead and machine base. The compression speed was set at 1.3 mm/min. The test was terminated once the specimens failed. The compressive mechanical properties, i.e. EM, YS and %elongation at YS were collected and reported in the form of an average with standard deviation values calculated from four specimens.
2.5 Statistical analysis
To assess the differences in mechanical properties among VPP specimens with different curing times and temperatures, the mechanical properties obtained from the tests were analysed to determine any statistically significant differences among each group using a t-test. The selected p-value threshold for the t-test was 0.05 (p-value ≤ 0.05). All analyses were performed using MS Excel.
2.6 Test for effects of gamma irradiation
To simulate the effects of medical sterilization using gamma irradiation on the mechanical properties of VPP specimens, the VPP specimens were exposed to gamma rays at various doses prior to undergoing testing of the tensile and compression properties. The specimen undergoing gamma irradiation was selected from the group presenting insignificant differences in mechanical properties compared to the greater mechanical properties group, which had a lower curing temperature and less post-curing time. The gamma irradiation generated from cobalt-60 (60 Co) was performed at the Irradiation Center, Thailand Institute of Nuclear Technology (TINT) (Public Organization), Nakhon Nayok, Thailand (Figure 7), which was registered as a Medical Device Manufacturer by the Thai Food and Drug Administration (Reg. No. 3/2560). The minimum radiation exposure dose was set at 25 kGy. This exposure dose provides a sterility assurance level (SAL) of 10−6 for medical devices and surgical instruments. The study also set exposure dose intervals of 50, 75 and 100 kGy, respectively. The gamma irradiated specimens were tested and their tensile and compression mechanical properties under identical methods were reported, as described in 2.4. The specimen group designation of the specimens used within this study is summarized in Table 3.
3. Results
The specimens become more yellowish after undergoing the post-curing process. The darker colour could be observed when prolonging the post-curing time and increasing the post-curing temperature. The gamma irradiation made the specimens’ colour even darker and less transparent. Figures 8 and 9 show the specimens’ colour for different post-curing conditions, including the appearance of specimens before and after the mechanical test. The mechanical properties for different post-curing conditions and after gamma ray exposure are reported in this section, whereas the statistical analysis results are shown in supplementary table.
3.1 Mechanical properties for different post-curing conditions
Table 4 reports the mechanical properties of the tensile specimens. Figure S1 and S2 show bar charts indicating the mechanical properties of tensile specimens post-curing, which are EM, YS, UTS, FS, %elongation at YS, %elongation at UTS and %elongation at break. Figure 10 shows the representative tensile stress-strain diagram of each specimen group. Table S1–S7 in supplementary table show p-values obtained from statistical analysis for tensile mechanical properties among non-irradiated specimens.
It can be observed that EM, YS, UTS and FS of the tensile specimens increased after being subjected to 1 h post-curing. From 2 to 4 h of post-curing, EM, YS, UTS and FS of the tensile specimens are comparable to those specimens which underwent 1 h post-curing. This was supported by statistical testing in which most of the p-values were less than 0.05 between the uncured group and 1-h post-curing group. In addition, most of the p-values among different post-curing times at the same curing temperature were above 0.05, which presented no significant difference. The specimens were also observed to present a similar magnitude for %elongation at YS for both uncured and post-curing groups, while %elongation at UTS and %elongation at break for the post-curing specimens were lower than in the uncured specimens. This indicates that the specimen becomes more brittle after post-curing.
The mechanical properties, i.e. EM, YS, UTS and FS, at 1-h post-curing time presented in decreasing trend with increasing post-curing temperature. The 50°C post-curing temperature presented the greatest mechanical properties, whereas the 70°C post-curing temperature presented the lowest mechanical properties. At 2 and 3 h post-curing time, the influence of post-curing temperature on EM revealed a significant difference (p-value < 0.05). For YS after 2 h post-curing time, the different temperatures had a significant difference in mechanical properties. At the 3-h post-curing time, the YS had insignificant differences at the different temperatures. UTS and FS presented the decreasing trend with increasing post-curing temperature. At the 4-h post-curing time, almost all mechanical properties were of a relatively similar magnitude for all post-curing temperatures. In addition, the specimen became more brittle with an increase in post-curing temperature as the %elongation at break decreased.
Table 5 reports the mechanical properties of the compressive specimens. Table S8–S10 (in supplementary table) show p-values obtained from statistical analysis for compressive mechanical properties among non-irradiated specimens. Figure S3 shows bar charts indicating the mechanical properties of compressive specimens post-curing, which are EM, YS and %elongation at YS. Figure 11 shows the representative compression stress-strain diagram of each specimen group. For compressive specimens, EM and YS increased after post-curing, while the p-values of the uncured group compared to the post-cured group were less than 0.05. Different post-curing periods and post-curing temperatures slightly affected the compressive mechanical properties for which most of the p-values among post-cured group specimens were greater than 0.05.
3.2 Mechanical properties after gamma ray irradiation
As shown in Tables 6 and 7 and Figure 12, gamma irradiation was demonstrated to have an impact upon both tensile and compressive VPP specimens. It lowered significantly EM at low gamma ray irradiation doses (25–50 kGy) compared to T50P1.
The EM and YS at high gamma ray irradiation doses (75–100 kGy) significantly improved the mechanical properties compared to the low gamma ray irradiation doses (25–50 kGy), but were insignificantly different from T50P1. This result is supported by p-value shown in Tables S11–S12. Nevertheless, YS after gamma irradiation showed a slight change, and by the values were lowered by 4.48% from the maximum compared to non-irradiated specimens (T50P1: 41.68 MPa, IR25: 39.81 MPa). Greater doses of gamma irradiation have an adverse effect on UTS, FS, %elongation at YS, %elongation at UTS and %elongation at break. Furthermore, the UTS of the specimens also became the FS after gamma radiation exposure. As %elongation at break also decreased as stated, the tensile specimens therefore became more brittle.
For compressive specimens, the gamma irradiation has a positive effect on EM while having a negative effect on YS and %elongation at YS. Doses of gamma radiation between 25 and 100 kGy have slight effects on most of the mechanical properties of compressive specimens, as shown in Table 7. This is supported by p-values shown in Table S18–S20 which are greater than 0.05. The representative stress-strain diagram of compressive specimens after exposure to 25–100 kGy gamma irradiation almost overlapped, as shown in Figure S4.
4. Discussion
Post-curing temperature and period exhibited an important role in changing the mechanical properties. After post-curing for 1 h, the mechanical properties of the tensile and compressive VPP specimens were enhanced. Compared to the uncured specimen groups, parameters such as EM of tensile specimens increased by 23.64%−34.23% (T50P1: 34.23%, T60P1: 23.64%, T70P1: 24.81%), YS of tensile specimens increased by 34.41%−41.33% (T50P1: 41.33%, T60P1: 34.31%, T70P1: 35.84%), UTS of tensile specimens increased by 21.96%−41.00% (T50P1: 41.00%, T60P1: 32.11%, T70P1: 21.96%), EM of compressive specimens increased by 18.30%−30.98% (T50P1: 18.30%, T60P1: 19.93%, T70P1: 30.98%) and YS of compressive specimens increased by 17.25%−24.34% (T50P1: 24.34%, T60P1: 17.25%, T70P1: 17.86%). The uncured specimens when subjected to temperatures for a certain time enhanced polymerization of free radicals throughout the specimens (Riccio et al., 2021; Hong et al., 2018). With the increase in the degree of polymerization, it increases the mechanical strength of the specimens.
Despite the mechanical properties’ improvement, the greater temperature and longer post-curing time could lead to over-curing that deteriorates the mechanical properties. According to the study findings, the mechanical properties of VPP specimens were reduced at higher post-curing temperatures of 60°C and 70°C, when compared to lower post-curing temperatures of 50°C. For both tensile and compressive specimens, the post-curing time of more than 1 h presented comparable or less mechanical strength compared to the 1-h post-curing time. For other liquid photopolymer resins, previous investigation has revealed a similar trend for mechanical properties after certain post-curing times, i.e., a post-curing time between 4 and 8 h has an insignificant influence on the mechanical properties of DSM’s Somos WaterShed 11120 (Chantarapanich et al., 2013).
Based on the results, both tensile and compressive mechanical properties of VPP specimens with 50°C temperature after 1 h post-curing were sufficient for enhancing the mechanical properties. Holistically, increasing the temperature or prolonging the post-curing time beyond the aforementioned values resulted in insignificant differences in improvement or even a decrease in the VPP specimens’ mechanical strength. This means that prolonging the post-curing time could lead to ineffective operation, i.e. lowering fabrication capacity. Increasing the curing temperature could also affect the electrical power energy consumption. In addition, it could make the VPP specimens more brittle, which increases the intra-operative risk of breakage for medical grade VPP medical devices when subjected to holding force.
Gamma irradiation is considered to be a reliable sterilization technique, especially for invasive and direct medical devices. The gamma rays are able to penetrate through the medical device, eliminating the micro-organisms living on reachable surfaces and through the entire volume of the medical device (Wiseman et al., 2022). The gamma irradiation affected both tensile and compressive VPP specimens. The results highlighted the improvement and deterioration of various mechanical properties of the irradiated compressive and tensile specimens, respectively. Although mechanical properties at low irradiation dose (25–50 kGy) lowered the tensile mechanical properties; however, exposure to greater than 25 kGy could make the specimens brittle and increase the intra-operative risk of breakage similar to over-post-curing. This was observed by the %elongation at break being lowered by 30.5% at maximum from non-irradiated specimens. Hence, 25 kGy is sufficient for sterilization. The value of 25 kGy also matches the minimum dose requirement for gamma sterilization on medical devices achieving SAL 10−6 (Silindir and Özer, 2009).
While the study designs of the others have paid attention to the effects of specific post-curing parameters on the mechanical properties of photo-curable resin (Ahmad et al., 2020; Jindal et al., 2020; Bonada et al., 2017; Salmoria et al., 2005), this study covered combinations of various post-curing temperatures and times, in extension to the effect on various irradiation doses, specifically on medical graded VPP parts. Although this study showed the optimal post-curing temperature and period including optimal gamma irradiation dose, it was based on a thickness of 4 mm for tensile specimens and 12.7 mm for compressive specimens. Different thicknesses of parts may also affect the mechanical properties. In addition, this method of study can also be extended to other medical grade UV photo-curable materials.
5. Conclusion
This study investigated the effects of post-curing temperature and time including gamma irradiation on the tensile and compressive mechanical properties of medical graded VPP parts made from Surgical Guide V1 photopolymer resin. The results found that post-curing improved the mechanical properties of VPP parts in the case of both tensile and compressive specimens. The post-curing temperature greater than 50°C or a prolonged post-curing period of more than 1 h revealed insignificant changes or a deterioration in mechanical properties, including becoming more brittle. Therefore, the optimal post-curing condition was a 50°C post-curing temperature with 1 h post-curing time. Gamma irradiation improved the compressive mechanical properties. Adverse effects of gamma irradiation were found for tensile mechanical properties. Higher gamma irradiation doses could decrease the VPP part strength and also make the VPP part more brittle, especially for doses more than 25 kGy. As a result, 25 kGy is considered sufficient for the dose of gamma irradiation.
Conflict of interest: The authors declare no conflict of interest.
VPP part fabrication principle
Test specimen dimension
The arrangement of specimens for one printing batch
Specimen fabrication
Test specimens in post-curing chamber
Mechanical test
Specimens in gamma ray chamber
Uncured, post-cure,and irradiated tensile test specimens: before and after mechanical test
Uncured, post-cure and irradiated compressive test specimens: before and after mechanical test
Tensile stress-strain representative curves
Compressive stress-strain representative curves
Stress-strain representative curves of non-irradiated and irradiated groups
Mechanical properties of Surgical Guide V1 after post-curing
| Mechanical properties | Value | Test method |
|---|---|---|
| Elongation | 12% | ASTM D638 |
| Flexural strength | >102 MPa | ASTM D790 |
| Flexural modulus | >2,400 MPa | ASTM D790 |
Source: Formlabs (2021)
Designation and description of the post-curing specimen groups
| Designation | Description |
|---|---|
| Uncured | VPP specimens without undergoing any post-processing |
| T50P1 | VPP specimens undergoing 50 °C post-curing temperature for 1 h, non-irradiated |
| T50P2 | VPP specimens undergoing 50 °C post-curing temperature for 2 h, non-irradiated |
| T50P3 | VPP specimens undergoing 50 °C post-curing temperature for 3 h, non-irradiated |
| T50P4 | VPP specimens undergoing 50 °C post-curing temperature for 4 h, non-irradiated |
| T60P1 | VPP specimens undergoing 60 °C post-curing temperature for 1 h, non-irradiated |
| T60P2 | VPP specimens undergoing 60 °C post-curing temperature for 2 h, non-irradiated |
| T60P3 | VPP specimens undergoing 60 °C post-curing temperature for 3 h, non-irradiated |
| T60P4 | VPP specimens undergoing 60 °C post-curing temperature for 4 h, non-irradiated |
| T70P1 | VPP specimens undergoing 70 °C post-curing temperature for 1 h, non-irradiated |
| T70P2 | VPP specimens undergoing 70 °C post-curing temperature for 2 h, non-irradiated |
| T70P3 | VPP specimens undergoing 70 °C post-curing temperature for 3 h, non-irradiated |
| T70P4 | VPP specimens undergoing 70 °C post-curing temperature for 4 h, non-irradiated |
Source: Authors’ work
Designation and description of the post-curing specimen groups
| Designation | Description |
|---|---|
| 25IR | Selected group of VPP specimens undergoing 25 kGy exposure |
| 50IR | Selected group of VPP specimens undergoing 50 kGy exposure |
| 75IR | Selected group of VPP specimens undergoing 75 kGy exposure |
| 100IR | Selected group of VPP specimens undergoing 100 kGy exposure |
Source: Authors’ work
Tensile mechanical properties of uncured specimens and specimens after different post-curing conditions (n = 4)
| Specimens | EM |
YS |
UTS |
FS |
%elongation at YS | %elongation at UTS | %elongation at break |
|---|---|---|---|---|---|---|---|
| Uncured | 1,076.02 ± 57.67 | 29.49 ± 1.58 | 54.87 ± 2.45 | 47.17 ± 3.26 | 2.94 ± 0.02 | 8.56 ± 0.25 | 16.74 ± 3.08 |
| T50P1 | 1,444.35 ± 27.55 | 41.68 ± 0.87 | 77.37 ± 1.56 | 77.08 ± 1.80 | 3.09 ± 0.02 | 8.79 ± 0.07 | 9.31 ± 0.31 |
| T50P2 | 1,446.83 ± 2.73 | 41.84 ± 0.22 | 78.80 ± 0.35 | 78.14 ± 0.35 | 3.09 ± 0.01 | 8.84 ± 0.45 | 9.37 ± 0.87 |
| T50P3 | 1,426.83 ± 11.88 | 41.16 ± 0.43 | 74.03 ± 1.72 | 74.03 ± 1.72 | 3.09 ± 0.02 | 7.64 ± 0.71 | 7.64 ± 0.71 |
| T50P4 | 1,429.35 ± 3.67 | 41.29 ± 0.28 | 75.96 ± 2.61 | 75.96 ± 2.61 | 3.09 ± 0.01 | 8.04 ± 0.91 | 8.04 ± 0.91 |
| T60P1 | 1,330.43 ± 16.34 | 39.61 ± 0.48 | 72.49 ± 3.34 | 72.49 ± 3.34 | 3.18 ± 0.01 | 6.61 ± 2.18 | 6.62 ± 2.19 |
| T60P2 | 1,352.00 ± 7.41 | 40.39 ± 0.32 | 70.12 ± 3.02 | 70.12 ± 3.02 | 3.19 ± 0.01 | 6.81 ± 0.63 | 6.81 ± 0.63 |
| T60P3 | 1,354.90 ± 19.03 | 40.51 ± 0.69 | 76.19 ± 4.39 | 76.08 ± 4.31 | 3.19 ± 0.01 | 8.59 ± 1.11 | 8.81 ± 1.41 |
| T60P4 | 1,353.68 ± 10.97 | 40.64 ± 0.25 | 74.46 ± 5.08 | 74.46 ± 5.08 | 3.20 ± 0.01 | 8.03 ± 1.24 | 8.03 ± 1.24 |
| T70P1 | 1,343.03 ± 12.73 | 40.06 ± 0.52 | 66.92 ± 4.28 | 66.92 ± 4.28 | 3.18 ± 0.01 | 6.41 ± 0.97 | 6.41 ± 0.97 |
| T70P2 | 1,380.73 ± 5.67 | 41.33 ± 0.07 | 69.33 ± 5.08 | 69.33 ± 5.08 | 3.20 ± 0.02 | 6.39 ± 0.81 | 6.39 ± 0.81 |
| T70P3 | 1,368.33 ± 14.24 | 41.09 ± 0.44 | 68.10 ± 6.01 | 68.10 ± 6.01 | 3.20 ± 0.00 | 6.37 ± 1.09 | 6.37 ± 1.09 |
| T70P4 | 1,370.68 ± 8.16 | 41.21 ± 0.26 | 75.35 ± 4.57 | 75.35 ± 4.57 | 3.21 ± 0.01 | 7.72 ± 1.08 | 7.72 ± 1.08 |
Source: Authors’ work
Compressive mechanical properties of uncured specimens and specimens after different post-curing conditions (n = 4)
| Specimens | EM |
YS |
%elongation at |
|
|---|---|---|---|---|
| Uncured | 1,404.85 ± 135.36 | 52.86 ± 2.18 | 4.01 ± 0.48 | |
| T50P1 | 1,661.95 ± 234.41 | 65.73 ± 4.80 | 4.24 ± 0.68 | |
| T50P2 | 1,766.98 ± 26.18 | 61.09 ± 1.62 | 3.66 ± 0.10 | |
| T50P3 | 1,784.80 ± 225.85 | 67.83 ± 3.25 | 4.10 ± 0.76 | |
| T50P4 | 1,793.48 ± 132.16 | 63.49 ± 3.22 | 3.76 ± 0.34 | |
| T60P1 | 1,684.90 ± 96.66 | 61.98 ± 2.47 | 3.89 ± 0.27 | |
| T60P2 | 1,784.83 ± 123.20 | 59.36 ± 2.80 | 3.53 ± 0.08 | |
| T60P3 | 1,758.08 ± 193.20 | 65.96 ± 2.40 | 4.00 ± 0.50 | |
| T60P4 | 1,790.00 ± 115.17 | 63.24 ± 2.30 | 3.75 ± 0.29 | |
| T70P1 | 1,840.20 ± 141.22 | 62.30 ± 5.93 | 3.59 ± 0.12 | |
| T70P2 | 1,674.93 ± 189.39 | 65.42 ± 1.93 | 3.41 ± 0.09 | |
| T70P3 | 1,725.78 ± 173.41 | 71.12 ± 5.79 | 4.38 ± 0.79 | |
| T70P4 | 1,811.15 ± 58.21 | 71.31 ± 3.68 | 4.14 ± 0.22 | |
Source: Authors’ work
Tensile mechanical properties of T50P1 specimens and after undergoing with different irradiation dose (n = 4)
| Specimens | EM |
YS |
UTS |
FS |
%elongation at YS | %elongation at UTS | %elongation at break |
|---|---|---|---|---|---|---|---|
| T50P1 | 1,444.35 ± 27.55 | 41.68 ± 0.87 | 77.37 ± 1.56 | 77.08 ± 1.80 | 3.09 ± 0.02 | 8.79 ± 0.07 | 9.31 ± 0.31 |
| IR25 | 1,385.28 ± 11.69 | 39.81 ± 0.55 | 76.04 ± 0.62 | 75.76 ± 0.38 | 3.08 ± 0.02 | 9.00 ± 0.43 | 9.52 ± 0.98 |
| IR50 | 1,376.60 ± 5.67 | 40.13 ± 0.38 | 74.52 ± 2.57 | 74.23 ± 2.62 | 3.12 ± 0.02 | 8.65 ± 1.01 | 9.08 ± 1.51 |
| IR75 | 1,413.73 ± 5.38 | 41.07 ± 0.46 | 73.59 ± 3.33 | 73.59 ± 3.32 | 3.11 ± 0.03 | 7.57 ± 1.15 | 7.61 ± 1.21 |
| IR100 | 1,413.93 ± 8.56 | 41.39 ± 0.34 | 69.96 ± 4.04 | 69.96 ± 4.04 | 3.13 ± 0.01 | 6.47 ± 0.60 | 6.47 ± 0.60 |
Source: Authors’ work
Compressive mechanical properties of T50P1 specimens and after undergoing with different irradiation dose (n = 4)
| Specimens | EM |
YS |
%elongation at |
|
|---|---|---|---|---|
| T50P1 | 1,661.95 ± 234.41 | 65.73 ± 4.80 | 4.24 ± 0.68 | |
| IR25 | 2,008.48 ± 72.31 | 62.02 ± 2.83 | 3.29 ± 0.13 | |
| IR50 | 1,940.00 ± 127.41 | 62.30 ± 1.37 | 3.43 ± 0.20 | |
| IR75 | 1,916.00 ± 163.98 | 62.41 ± 4.18 | 3.47 ± 0.17 | |
| IR100 | 1,946.30 ± 159.24 | 63.99 ± 2.71 | 3.51 ± 0.24 | |
Source: Authors’ work
© Emerald Publishing Limited.