Resin Hardener Research Articles

Experimental characterization of multiscale solidification in thermoset CFRP during gelation for flow and stress modeling

Two types of flow mechanisms consisting of unidirectionally arrayed fibers and uncured thermoset resin exist in prepreg materials. These mechanisms are percolation flow where resin flows out of the gaps between fibers, and shear flow where resin and fibers flow together. Based on our previous study, we assumed that percolation flow is controlled by the rheology of the matrix resin, whereas shear flow is controlled by the rheology of prepreg. Based on this assumption, we experimentally evaluated the ‘multiscale’ solidification (solidification of matrix resin and that of prepreg) process using dynamic mechanical analysis during gelation. The solidification of matrix resin was examined by observing the development of loss angle, which provides a continuous description of the solidification process. On the other hand, the solidification of prepreg was characterized by analyzing the relationship between the shear storage modulus of prepreg and that of the matrix resin. Finally, we examined the difference in the solidification process between prepreg and matrix resin during gelation.

Exploring Microgravity Liquid Printing Based on Resin Solidification for Outer Space Applications

Space traveling, extra-planetary exploration and even colonization requires to replicate our capabilities of manufacturing under non-entirely known environments and conditions. With the recent, yet always present, interest on colonizing spaces like the Moon or even Mars, space-based Additive Manufacturing (AM) has been considered for enabling space inhabitants to build their own tools. However, the same manufacturing techniques that are commonly used on Earth are not entirely applicable in space, especially during the considerably long traveling stage. Thus, several works have reported the study of how AM could be used in microgravity or near-zero g conditions by using the International Space Station as a laboratory. Unfortunately, the costs for doing such experiments are prohibitive, which is why experimentation in microgravity conditions on Earth is promising. In this paper, we explore the possibility of applying light-sensitive resin under Microgravity conditions using a Drop Tower facility and we propose a microgravity liquid printing technique. Our preliminary experiments focused on studying movement and extrusion velocities, extrusion nozzle diameter, UV light power, extrusion, and solidification times. The experimental runs (one catapult launch and four drops) let us find promising, although not entirely conclusive, data and practices to be considered in future works using this methodology. As expected, there is a similarity to liquid extrusion on Earth given that the initial shape and speed of extrusion influences the liquid material. Our findings also suggest that an initial contact point would help to increase the contact force due to surface tension and that the extrusion and solidification times are less than 5 seconds, which implies faster printing processes than in earth gravity conditions because the microgravity provides us less layer mixing during extrusion. The hardware, material and Microgravity drop tests used confirm the feasibility of this technique and they become an initial step for this printing process and liquid materials.

Orientation of flake pigments in injection-molded polymer: Numerical simulation and its application to appearance prediction

A particle-level simulation of flake pigment orientation in injection molding was proposed to predict appearance defects caused by disturbed flake orientations. The effects of fountain flow and resin solidification were considered in order to reproduce the formation process for the orientation near the product surface, which has a large impact on the product appearance. In addition, an efficient method using a reverse-time calculation to predict the orientation in a surface layer was developed. The proposed method was verified by applying it to two types of center-gated disks, with different numbers of obstacles consisting of a hole and a thin-walled area, which were injection molded using polypropylene and aluminum flakes. For both disks, the proposed simulation reasonably predicted the location of the flow line defects generated downstream of the obstacles. We also performed an X-ray micro-computed tomography analysis to reveal the characteristic orientation distribution in the flow line.

Interfaces in reinforced epoxy resins: from molecular scale understanding towards mechanical properties

ContextWe report on atomic level of detail analyses of polymer composite models featuring epoxy resin interfaces to silica, iron oxide, and cellulose layers. Using “reactive” molecular dynamics simulations to explore epoxy network formation, resin hardening is investigated in an unprejudiced manner. This allows the detailed characterization of salt-bridges and hydrogen bonds at the interfaces. Moreover, our sandwich-type composite systems are subjected to tensile testing along the interface normal. To elucidate the role of relaxation processes, we contrast (i) direct dissociation of the epoxy-metal oxide/cellulose contact layer, (ii) constant strain-rate molecular dynamics studies featuring (visco-)elastic deformation and bond rupture of the epoxy resin, and (iii) extrapolated relaxation dynamics mimicking quasi-static conditions. While the fracture mechanism is clearly identified as interface dissociation of the composite constituents, we still find damaging of the nearby polymer phase. The observed plastic deformation and local cavitation are rationalized from the comparably large stress required for the dissociation of salt-bridges, hydrogen bonds, and van der Waals contacts. Indeed, the delamination of the contact layers of epoxy resins with slabs of silica, magnetite, and cellulose call for a maximum stress of 33, 26, and 21 MPa, respectively, as compared to 84 MPa required for bulk epoxy yielding.MethodsMolecular dynamics simulations using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code were augmented by a Monte Carlo–type procedure to probe epoxy bond formation (Macromolecules 53(22): 9698–9705). The underlying interaction models are split into conventional Generalized Amber Force Fields (GAFF) for non-reacting moieties and a recently developed reactive molecular mechanics potential enabling epoxy bond formation and cleavage (ACS Polymers Au 1(3): 165–174).

Modeling and static modal analysis of lathe bed using conventional and composite materials using FEM

The bed has a significant impact on a machine tool's performance. The Bed of the Machine Tool has to be appropriately robust to absorb all vibrations and rigid enough to avoid deflections under different cutting forces transferred over the tool-post and carriage to the Lathe Bed. In general, the various permanent and moveable Lathe parts are supported by the Lathe bed. Typically, cast iron or mild steel are used to make lathe beds. When dealing with really large machinery, the bed may be constructed from two or more segments that are connected together to achieve the appropriate length. Large and robust, the lathe bed has a large ability to absorb machine vibrations during machining.This paper summaries, static structural and mode forms analysis are done on the lathe bed under maximum load circumstances. By incorporating ribs and reducing volume where loads and deflection are less caused, these simulated outcomes are utilized to lighten the lathe bed without sacrificing its structural integrity and dampening ability. As an alternative material, FEA analysis of a modified lathe bed is conducted using CAST IRON, MILD STEEL, and CFRP, this is a blend of epoxy resin hardener and granite. The efficiency of both materials is compared with regard to generated stresses, deformation, and weight reduction. CATIAV5 Modeling software was used to create lathe bed CAD Models. ANSYS 16.2 was used to generate the FE Model. ANSYS is used to perform the analysis. The observations are calculated and presented as contour plots to analyse the impact of reduced weight on the machine bed's structural strength prior to and after weight reduction, and decisions on the ideal design are made.

Determination of the slip resistance of interspersed synthetic resin flooring with a convolutional neural network

The ramp slip test is a reliable and widely used method to evaluate the slip resistance of interspersed synthetic resin floors, common in industrial and parking areas. Following EN 16165 and using a ramp with varying inclinations, the floor R-class can be determined. This test can, however, only be performed in a laboratory, and not on-site. Here, we propose a method to determine the floor R-class from its surface topography, which can easily be measured on-site. In this study, floors of various slip resistances were prepared following the conventional method of spreading quartz sand onto a liquid resin. The interspersed surface creates a 3-dimensional topography, which is characteristic for the anti-slip properties. After the resin hardening, the R-class was measured and, in parallel, a convolutional neural network was developed and trained with the numerous photographs taken from the specimen surfaces. The used convolutional neural network classifies 95% of the surfaces into the correct R-class. This result makes it possible, for the first time, to determine the R-class slip resistance on-site with a high probability of correctness.

Study on a new cementitious material waterborne modified epoxy resin under sealed conditions for oil and gas wells

Given the poor environmental performance of epoxy resin for oil and gas wells and the lack of research on curing and durability in well conditions, a waterborne modified epoxy resin was synthesized, and then combining with the matched viscosity regulator, curing agent and coagulant, a new cementitious material waterborne modified epoxy resin system was developed for oil and gas wells. The new cementitious material was evaluated by means of macroscopicandmicrocosmictests. The effects of curing conditions and hydrophilic monomer ratio on the solidification of waterborne resin and the long-term durability of resin under well conditions were discussed. Research shows that the safe construction and effective curing of resin under sealed conditions can be realized by adequately controlling the proportion of hydrophilic groups and selecting appropriate regulators. This also ensures that the system is cleanable, safe, and environmentally friendly. This resin system enables effective control of thickening time in the temperature range of 30 to 110 °C. After curing, compared with traditional oil well cement, its compressive strength increased by 81.1 %, Young 's modulus decreased by 62.5 % and Poisson 's ratio increased by 131.6 %. It can significantly improve the mechanical properties of oil well cement stone by film forming, filling, and optimizing pore structure. In addition, microscopic studies have shown that the sealing conditions of wells will seriously affect the curing and crosslinking of traditional waterborne epoxy resins due to the inability of water to volatilize, and it is inappropriate for oil and gas wells to adopt an epoxy resin system cured by volatilization mechanism. The durability of resin after curing under well conditions mainly depends on its glass transition temperature.

Molecular Dynamics Study of Cured ED-20 Epoxy Resin for Predicting the Glass Transition Temperature and Relationship with Structure Features.

A structural model of ED-20 epoxy resin cured by triethylenetetramine was constructed using a molecular dynamics (MD) simulation method. In order to model the epoxy resin hardening, we modified a typical stepwise protocol introducing cross-links between the amino groups and epoxide carbon atoms that allowed us to reproduce experimentally observed glass transition temperature at the value of 360-364 K. The set of MD trajectories of the final molecular-mechanical model can be useful for analysis of alterations in structural and physical properties of the epoxy resin depending on scaleable parameters. The relationships among qualitative alterations in macromolecular structure, the glass transition temperature, and the number of imposed cross-links were elucidated. Analysis of intermolecular interactions between the largest macromolecules and other molecules of a system made it possible to observe the features of the transition from glassy to the viscoelastic state of the studied polymer during the temperature rise.

Electrically-assisted void reduction for synergistic improvement in strength and toughness of fiber-reinforced composites

In the pursuit of designing fiber-reinforced composites with synergistic increased strength and toughness, a novel electric field-driven resin infiltration method is proposed. Specifically, during epoxy resin solidification, the void content of the composites is effectively reduced by 77.1%, from 2.14% to 0.49%, and the tensile strength, interlaminar shear strength, and interlaminar fracture toughness of the composites increase from 539.9 MPa to 748.7 MPa (equivalent to 38.7%), from 40.9 MPa to 57.3 MPa (equivalent to 40.1%) and from 2.1 kJ/m2 to 3.0 kJ/m2 (equivalent to 42.9%) under the applied electric field, respectively. The improvement of the mechanical properties is primarily ascribed to the fact that the electric field-induced Maxwell force drives the liquid resin to flow into intra-tows and inter-tows, thereby improving the wettability of the resin to the fiber tows and correspondingly reducing the void content of the composite, which is supported by the finite element simulation of the rheological behavior of the resin. Interestingly, the application of an electric field can reduce the curing temperature of the composites by nearly 10 °C compared to the baseline composites, while maintaining the same mechanical properties. Therefore, it is an economical, and promising approach to fabricating composites with excellent mechanical properties.

Shrinkage stress of thermal cured epoxy resin reduced by addition of functional hollow microspheres

The shrinkage stress of thermal cured epoxy resin developed during curing process can cause low film adhesion strength, low dimensional accuracy and even coating films warping which severely reduce service lifetime of the coating. Therefore, there is growing interest in developing effective means to reduce the shrinkage stress. In this paper, we report the use of hollow microspheres prepared from Pickering emulsion droplets in the thermal cured epoxy resin formulations and the shrinkage stress due to resin solidification is monitored in real time to reveal the effect of hollow microspheres upon shrinkage stress of the resin. Epoxy group functionalized silica nanoparticles from the Stöber method are used as Pickering emulsion stabilizer and the emulsion droplets are polymerized to obtain hollow microspheres with controllable mechanical properties and surface morphologies. Due to the reactivity of the hollow microspheres, they can be incorporated into the epoxy resin coatings and the shrinkage stress is thus reduced with the addition of hollow microspheres. It is revealed that the shrinkage stress is reduced from 195.79 kPa to 140. 40 kPa with the addition of 12 wt% hollow microspheres and polydisperse hollow microspheres are more effective in shrinkage stress reduction. As the modulus of the hollow microspheres is reduced and elasticity is increased, the shrinkage stress of the coating film is also reduced from 181. 37 kPa to 157.42 kPa which is not achieved by hollow glass microspheres. The hollow microspheres are well dispersed in the resin matrices which doesn't undermine the basic mechanical properties of the coating such as adhesion and surface hardness.

Immersion Corrosion Tests to Evaluate Polyaspartic Coatings on Steel

In this study, a waterproof polyaspartic coating used for concrete structures was modified into an anti-corrosion coating system to prevent steel assets from corroding. A micaceous iron oxide barrier, a zinc phosphate corrosion inhibitor and a novel resin hardener were added to the polyaspartic coating. Its corrosion performance was assessed through immersion corrosion tests in 3.5% NaCl solutions at room temperature (RT) and 35 °C for 30 days. The surface finish of the steel samples was milled and blasted (SA 2.5). The coating was applied directly to the metal substrate. The average thickness of the coating was 220 ±10 µm. The experimental results confirmed the successful enhancement of the control coating on steel that was previously applied to concrete by adding a zinc phosphate corrosion inhibitor and micaceous iron oxide barrier. However, defects in the coating and rust on the substrate of the control coating were hindered by applying the developed coating.

Elaboration of geopolymer package derived from uncalcined phosphate sludge and its solidification performance on nuclear grade resins loaded with 134Cs.

Nuclear-grade Spent Organic Resin (SOR) contains high concentrations of radioactive nuclides and metal contaminants, while phosphate sludge contains high amount of fine clayey particles and CO32-, both posing a major threat to the biosphere. In this study, a novel geopolymer package (GP) was proposed to directly solidify SOR loaded with 134Cs by incorporating uncalcined phosphate sludge (UPS) as feedstocks, activated by NaOH/KOH. The results showed that alkali-mixed reagents-activated GP is more advantageous in terms of chemical stability and mechanical properties than NaOH-activated GP, recording compressive strength values greater than the waste acceptance criteria and OPC. The 28-day compressive strength of solidified packages can exceed 31 MPa at the highest amount of 42 wt% UPS. The addition of NaF powder into the solidified packages generates more hybrid type gels, which are more conducive to partial dissolution and bonding UPS particles, thereby producing stable and stronger GP. Leaching results of solidified GP in presence of up to 13 wt% SORs showed that only 0.15 % of total 134Cs was leached, even under aggressive solutions. Solidification mechanism revealed that activation of UPS-MK blend forms N,K-A-S-H, (N,K,C)-A-S-H/C-S-H gels coexisting with unreacted particles, thereby solidify/stabilize metal contaminants and Cs+ by a synergetic immobilization action of hydration products via substitution and encapsulation. This study provides a promising paradigm for effective solidification of nuclear-grade resins and synergetic harmless treatment of industrial/phosphate mine solid wastes.

Characterization of biobased epoxy resins to manufacture eco‐composites showing recycling properties

AbstractThe present study details the composite fabrication, characterization, and full recyclability of the biobased polymer resins with flax fiber as the reinforcement. Two different biobased resins are selected by varying the resin hardener combination and curing parameters for the comparison. The optimum parameters for the composite preparation are finalized by evaluating the neat resin's mechanical and glass transition temperature (Tg) values. According to the results obtained, a biobased epoxy resin cured by a cleavable hardener displayed the highest Tg (i.e., 93.5°C) upon a two‐step cure cycle, guaranteeing full recyclability. Subsequently, eco‐composite flat panels are manufactured using the selected formulation reinforced with commercial flax‐based fabric. These panel's flexural strength, modulus, and interlaminar shear strength are measured after each curing step. The recyclability yield of the composite is tested, through a specific chemical process, demonstrating the possibility of separating and recovering both the constituent fibers and resin from the composite panels.

Metakaolin-Reinforced Sulfoaluminate-Cement-Solidified Wasteforms of Spent Radioactive Resins—Optimization by a Mixture Design

Cement solidification is a main technique for radioactive waste treatment to reduce its risk to the environment and human health. However, this method underperforms when dealing with spent radioactive ion-exchange resin, taking much space, and costing much money for final disposal. In this work, simulated spent radioactive resin was solidified using a metakaolin-reinforced sulfoaluminate cement system, which was optimized by a mixture design based on the effects of components and parameters, and the durability of solidified wasteforms was assessed in terms of strength and Cs(I) leaching. Solidified by an optimized formula of 40 wt.% spent resin, 55.8 wt.% sulfoaluminate cement, 2.2 wt.% metakaolin, and 2 wt.% water reducer, the resin loading in wasteforms reached 64% and the compressive strength 13.7 MPa. The dominant mineral phases of hydration products were ettringite crystalline of acicular and columnar morphology, with small amounts of scattered amorphous clusters of aluminum gels and C–S–H gels. Metakaolin, a source of aluminum, promoted the growth of ettringite, which facilitated (1) the encapsulation of resin beads with high strengths, even in acidic environments or during frequent freezing-thawing, and (2) the retention of Cs(I), with a 42 day leaching rate of 2.3 × 10−4 cm/day. This work offers a technical justification for spent resin solidification in the metakaolin-reinforced sulfoaluminate cement system, which is an applicational solution for the efficient treatment of radioactive waste.

Effect of Two Different Experimental Mixing Ratios on Selective Physical, Antibacterial and Tissue Compatibility Properties of Two Commonly Used Endodontic Root Canal Sealers—An In-Vitro and In-Vivo Study

Many root canal sealers have been launched in the last decade, with a lot of interest renewed in calcium hydroxide [Ca(OH)2], especially its long term intra-canal medication effect. This study aims to introduce two novel experimental composition percentage of calcium hydroxide and epoxy resin based root canal sealers (RCS) material and observe the effect of such formulations in term of working time (WT), setting time (ST), radiopacity, histopathological reactions and antibacterial effects. Four different formulations were formed with first two being experimental while remaining two being pure forms. Each formulation was assigned to a group (Gp) [Gp1 (Base: Epoxy resin 48%, Calcium Hydroxide 39%, Barium sulfate 13%; Catalyst: epoxy resin hardener; Gp2 (Base: Epoxy resin 37%, Calcium Hydroxide 46%, Barium sulfate 17%; Catalyst: epoxy resin hardener; Gp 3 (Pure Resin based RCSs); Gp4 (Calcium hydroxide base cement)]. Physical properties like WT, ST and radiopacity were measured using different tests [WT—Penetration test; ST—surface loss of gloss; radiopacity—fluorescent viewer and bone densometer]. Histopathological reactions were evaluated using 60 healthy rabbits, by injecting subcutaneously (2 sites). Scarified tissue was removed after 3, 14 and 28 days and the inflammatory response was evaluated. Antimicrobial effects were tested by deriving ten microbial samples from randomly selected patients with acute pulpitis followed by culturing. Physical properties were associated with the composition and the percentage of calcium hydroxide. Resin RCS showed the severe inflammatory reaction while the experimental formulation showed mild—moderate inflammatory reaction. One of the experimental formula exhibited the highest antibacterial action against all microorganisms tested.

INFLUENCE OF THERMOSETTING MODIFIERS ON THE PROPERTIES OF BITUMEN FOR THEIR APPLICATION AT THE ARRANGEMENT OF EPOXY ASPHALT PAVEMENTS ON ROAD BRIDGES

One of the mechanisms of the destruction of asphalt concrete pavement layers on bridges, especially with an orthotropic slab, is a large final deformation, which negatively affects the long-term operational performance of the entire bridge structure. Modification of the asphalt concrete mixture with epoxy components can be very relevant to eliminate the final deformation due to their thermoreactive nature. In this review, epoxy resin and its hardener are considered as the dominant component of the epoxy-asphalt concrete composite system, and based on the results of studies on determining the effect of temperature on the rate of hardening of epoxy resin, on the results of the selection of a binder for the production of epoxy-asphalt concrete mixtures and establishing the viability of an epoxy binder with different contents of epoxy components in bitumen, this article discusses the methods and mechanism of its hardening. The research mentioned in this description is also very useful from a practical point of view, because thanks to the obtained results of determining the viscosity of epoxy-asphalt concrete, depending on the amount of epoxy components in its composition, it is possible to determine the permissible time for its arrangement, taking into account possible features. With the aim of using epoxy-asphalt concrete coatings on road bridges and thanks to the conducted studies, the influence of the introduction of epoxy components as thermosetting modifiers on the properties of bitumen was determined. The research methodology and the obtained results of already conducted research will allow to determine the possibility of using certain components for the preparation of epoxy-asphalt concrete mixtures and their viability. It will make it possible to make an optimal selection of the mixture, taking into account the variation of temperatures and the content of epoxy components. Key words: epoxy asphalt concrete, epoxy resin, coating on bridges, bitumen modification, bitumen properties, viability of modified bitumen.

Stabilization of ferric arsenate sludge with ZVI intensive corrosion and enhancement of long-term arsenic immobilization via resin encapsulation

In this study, a novel stabilization/solidification (S/S) method, achieved by mechanochemically activated zero-valent iron (ZVI) intensive corrosion and resin encapsulation, was investigated for arsenic sludge disposal. The results showed that arsenic stabilization was enhanced by intensive corrosion process, with arsenic leaching concentration decreasing from 128.75 mg/L to 0.35 mg/L after stabilization treatment under optimized conditions. The residual state arsenic was increased from 96.32 wt% to 99.13 wt% after stabilization. The subsequent resin encapsulation solidification scheme has a significant effect on the low arsenic leachability of the stabilized sludge. The arsenic concentration of resin solidification matrix was 0.47 mg/L, which was significantly lower than that of cement solidification matrix (1.77 mg/L), as a control group. It also can be seen that resin curing showed much lower cumulative release rate (0.009 wt%) than cement curing (0.54 wt%) at the end of leaching test, under a 60-day long-term leaching test, indicating that resin curing has higher long-term arsenic stability. Resin curing can maintain the structure of the stabilized As-Fe phase by resin encapsulation, while the traditional cement curing would destroy the original stable As-Fe phase, and produce unstable As-Ca phase, resulting in the risk of arsenic pollution. Moreover, the matrix based on ZVI intensive corrosion and resin encapsulation scheme has great advantages in low compatibilization ratio and resistance to pH impact.

Investigation of the Impact of Micro-Structuring on the Bonding Performance of Beechwood (Fagus Sylvatica L.)

Although glueing softwood is well mastered by the industry, predicting and controlling bond quality for hardwood is still challenging after years of research. Parameters such as the adhesive type, resin–hardener ratio, and the penetration behaviour of the wood are determinants for the bond quality. The aim of this work was to assess to what extent the glueing behaviour of beechwood can be improved by using structural planing. The different surfacing methods were characterised by their roughness. The bond strength of the micro-structured surfaces was determined according to EN 302-1, and the delamination resistance was tested as indicated by EN 302-2 for type I adhesives. Micro-structured surfaces were compared with different surfaces (generated by surfacing methods such as dull/sharp planing and sanding). In dry test conditions, all surfacing methods gave satisfying results. In the wet stage, the bond strength on the finer micro-structured surface slightly outperformed the coarse structure surface. For the delamination resistance, a clear improvement could be observed for melamine-formaldehyde-bonded specimens since, when using the recommended amount of adhesive, micro-structured surfaces fulfilled the requirements. Nevertheless, structural planing cannot lead to a reduction in the applied grammage since no sample with a smaller amount fulfilled EN 302-2 requirements even by observing the recommended closed assembly waiting time. Adhesion area enlargement of the micro-structuring is minor. The good delamination performance without waiting time (CAT) is not caused by surface enlargement, since finer micro-structured surface with negligible area increase and delivered even better delamination resistance. Subsurface analysis should be carried out to thoroughly investigate this phenomenon.

An experimental investigation on bearing behavior and failure mechanism of bolted composite interference-fit joints under thermal effects

This paper reports an experimental investigation on bearing behavior and failure mechanism of single-lap bolted composite interference-fit joints under thermal effects. To achieve this target, testing temperatures ranged from −25 to 110 ℃ were designed to simulate thermal service environments. The unidirectional composite lamina was tested longitudinally and transversely to figure out potential change of material properties induced by thermal loading. The residual effects of stacking sequence, interference-fit size and tightening torque on bearing strength and stiffness of composite joints after exposed to thermal conditions were evaluated. Microscopic studies applying X-ray technique on damage areas to monitor damage evolution were conducted to comprehend the thermal failure mechanism. The results evidence that the bearing performance of composite joints was slightly enhanced by low temperature due to cold hardening of matrix resin but greatly weakened by high temperature owing to the combined effects of heat softening of resin, residual stress relaxation and thermal expansion of joint components. Tightening torque to enhance bearing performance is the most beneficial at room temperature, whereas the interference-fit remains the dominant influence at sub-freezing environments. In conclusion, thermal loading plays an important role in bolted composite interference-fit joints. It is an unneglectable factor that would enlarge damage area, alter failure mode and should be understood thoroughly.

Multiphysics Modeling and Experiments of Grayscale Photopolymerization With Application to Microlens Fabrication

Abstract A phenomenological model of a single-shot grayscale photopolymerization process is developed and used within a virtual process planning framework for microlens fabrication. Along with previous research, the kinetic relations describing the solidification of UV-curable resin are derived based on the underlying chemical reactions involved in free radical photopolymerization. As enhancements to the state-of-the-art, our multiphysics model includes a recently proposed super-Gaussian description of the light field, as well as the photobleaching effect due to the live reduction in photoinitiator concentration during UV illumination. In addition, heat generation and thermal strains due to the exothermic chemical reactions, and chemical shrinkage due to polymerization and cross-linking of monomers are considered. The model is numerically implemented via finite element method in comsol multiphysics software. Using a simulation-based virtual process planning framework, customized microlenses are fabricated with an in-house grayscale lithography experimental setup for digital micromirror device (DMD)-based volumetric additive manufacturing. Simulation and experimental results show that after the end of exposure, the temperature quickly rises by the advancement of exothermic chemical reactions and reaches a maximum rise of 100 K in a few seconds, followed by a slow cooling and recovery of thermal strains. It is observed that chemical and thermal shrinkages can compromise the dimensional accuracy of the final part near the resin–substrate interface due to the strong adhesion of the solidified part to the rigid substrate that prevents material shrinkage in the vicinity of the rigid substrate.