Flexural Properties Research Articles

Study on the polymerization shrinkage and mechanical-physical properties of dental resin composite modified by polyurethane dimechacrylate and glass flake fillers: Short title: Aging resistance for dental resin composites with low shrinkage

ObjectivesWe intend to explore the polymerization shrinkage and mechanical-physical properties of the dental resin composite modified by polyurethane oligomer PU-MA and glass flakes fillers, and provide some experimental information for developing new dental materials. MethodsBased on Bis-GMA/TEGDMA, the new dental resin composite was hand fabricated by combining PU-MA with different content (65 wt% ∼ 75 wt%) of glass flakes/Si-Al-borosilicate glass mixed fillers. The kinetics of polymerization shrinkage was investigated by using an experimental set-up based on laser triangulation. The mechanical-physical properties of specimens after 60 days water immersion and 5000 times thermo-cycles were measured by three-point bending test and micro vickers hardness tester. Data were submitted to one-way ANOVA/LSD-test (α = 0.05). Independent sample T test was used to analyze the data before and after aging. Two-way ANOVA was adopted to analyze the effect of composition and aging condition on the mechanical-physical properties (α = 0.05). ResultsPU-PG-75% performs lower volume shrinkage (1.35 %). As the increase of filler content, the water sorption and solubility increased and the depth of cure decreased significantly (P < 0.05). After aging, the flexural strength, elasticity modulus and vickers hardness of commercial products dropped obviously and PU-PG-75wt% was relatively stable. Conclusions20 wt% PU-MA could decrease the volume shrinkage of dental resin composite effectively. 60 days water immersion and 5000 times thermal cycles simultaneously resulted in a significant reduction in the flexural properties for experimental materials. PU-PG-75% may have the potential to be taken as a low shrinkage dental resin composite with good mechanical properties. Clinical SignificanceThis new synthesized composite could perform low polymerization shrinkage and better mechanical resistance, which may provide a new idea for improving the lifespan of direct restoration.

Development of Kagome-based functionally graded beams optimized for flexural loadings

This study is concerned with the development of an innovative beam geometry based on a tessellation of Kagome unit cells and the improvement of its geometry with the aim of increasing its flexural properties. This aspect was achieved by generating a functionally graded metamaterial structure based on a novel approach that considers the well-established analytical beam theory models as the basis of for the optimization of the structural parameters of the unit cells at an individual level. The starting premise is that the optimal strut thickness variation with the height of the beam will cause the material to yield uniformly in the critical cross-section. Preliminary studies were conducted in order to numerically determine the variation of the stiffness and the strength of the Kagome structure with the thickness of its struts. Considering the equivalent stress distribution during bending in the critical cross-section, an optimal variation of the stiffness with the height of the beam was evaluated. Based on these results, different values for the strut diameter were imposed at corresponding coordinates relative to the neutral axis, assuring a continuous transition across the height of the beam. The flexural properties of the developed functionally graded structure were evaluated using finite element analyses and determined superior characteristics when compared with the data obtained from simulations performed on an uniform Kagome beam with of the same mass. The investigated structures were manufactured through stereolithography and subjected to three-point bending tests, the results being in agreement with the numerical data, thus validating the design.

Effect of Dispersing Agents on the Electrical and Mechanical Performance of GNPs Filled Epoxy Nanocomposite

In this work, graphene nanoplatelets (GNPs) filled epoxy nanocomposites with the addition of different dispersing agents were fabricated using a method combines mechanical mixing and tip sonication. The loading of GNPs used is 0.8 vol% determined previously as the amount required to achieve the percolation threshold to conduct electricity. Three dispersing agents were used in this work: Sodium dodecyl sulphate (SDS), ethanol and Phenyl glycidyl ether (PGE), with loadings varying from 2 vol% to 10 vol%. The incorporation of dispersing agent enhanced the electrical bulk conductivity of GNPs filled nanocomposites. The mechanical performance (flexural properties and fracture toughness) of the nanocomposite were evaluated and compared. The optimum loading of SDS to obtain the highest flexural strength and fracture toughness is 2 vol%, where further increases will deteriorate the performance of nanocomposites. On the other hand, the optimum loading of ethanol and PGE are 4 vol%. The fracture toughness of GNPs filled nanocomposites improved with the addition of 2 vol% SDS and deteriorated with increasing loadings of SDS up to 10 vol%. By incorporating 4 vol% of ethanol, the optimum fracture toughness of the nanocomposite is achieved. Fracture toughness is then dropped with further increases in ethanol. The addition of PGE caused deterioration in fracture toughness of GNPs filled epoxy nanocomposite.

Semi-Alicyclic Thermoplastic Polyimide Matrixes Based on Hydrogenated Pyromellitic Dianhydride and Asymmetrical 3,4′-Oxydianiline with Good Thermal Stability and Improved Optical Transparency

Thermoplastic polyimide (PI) matrixes, including PI-a (cc-34ODA) and PI-b (ct-34ODA) were prepared via the hot-pressing procedures of the resins derived from the 3,4′-oxydianiline (34ODA) and two alicyclic dianhydrides of 1S,2R,4S,5R-hydrogenated pyromellitic dianhydride (ccHPMDA) and 1R,2S,4S,5R-hydrogenated pyromellitic dianhydride (ctHPMDA), respectively. The resins exhibited thermoplastic features with good formability at higher temperatures. The afforded semi-alicyclic PI sheets exhibited enhanced properties in comparison to commercially available, wholly aromatic thermoplastic PIs, such as PI-ref1, which are derived from 3,3′,4,4′-oxydiphthalic anhydride (ODPA) and 4,4′-oxydianiline (44ODA), as well as PI-ref2, which is based on pyromellitic dianhydride (PMDA) and 4,4′-bis(3-aminophenoxy)biphenyl (mBAPB). In addition, the developed PI sheets exhibited high heat deflection temperatures (HDT) of 267.4 °C for PI-a and 268.6 °C for PI-b. There values were significantly higher when compared with those of PI-ref1 (Ratem® YS20, HDT: 239.0 °C), PI-ref2 (Aurum® PL450C, HDT: 238.0 °C), PI-ref3 (Ultem® 1000, HDT: 206.0 °C), PI-ref4 (Therplim® TO65, HDT: 180.0 °C), and PI-ref5 based on phthalic anhydride-terminated fluorinated PIs (HDT: 215.0 °C). In terms of mechanical properties, the current PI sheets showed superior flexural properties among the polymers with the flexural strength of 189.0 ± 11.7 MPa (PI-a) and 200.5 ± 4.2 MPa (PI-b), respectively. In addition, the PI sheets exhibited comparable compression properties, inferior impact strength, and tensile properties compared with the referenced PI counterparts. Basically, the PI-b sheet showed better comprehensive properties than those of the stereoisomeric PI-a analog.

Characterization of the thermomechanical and aging behaviour of PAEK and CF/PAEK composites under long-term high-temperatures

The growing use of poly(aryl ether ketone) (PAEK) polymers reinforced with carbon fiber (CF) aims to meet the increasing demand for thermoplastic composites in applications that require excellent mechanical properties and thermal stability at higher temperatures. This study investigated the physicochemical properties of PAEK and CF/PAEK composites under long-term high-temperature exposure (150 °C, 200 °C and 250 °C) for durations of 15, 30, and 45 days, aiming to elucidate the durability mechanisms and enhance understanding of their performance. Specifically, the changes in the flexural properties and dynamic thermo-mechanical properties of the materials were evaluated after long-term high-temperature treatment. The results indicated that both PAEK and CF/PAEK composites possess substantial potential for long-term high-temperature applications, with CF not significantly altering the fundamental high-temperature response of the PAEK matrix. Regarding durability mechanisms, at 150 °C, PAEK's amorphous region undergoes chain reorientation, while temperatures of 200 °C and 250 °C induce significant secondary crystallization, which significantly improved the high-temperature mechanical properties of these materials. Additionally, at temperatures up to 250 °C, shorter linear chain fragments form through oxidative scission in PAEK's amorphous molecular chains. This work not only enriches the existing data on the properties of PAEK and CF/PAEK composites after long-term high-temperature treatment, but also provides further insights into their durability mechanisms.

Effect of hybrid sizings on the surface morphology, mechanical behavior of basalt fibers, and fiber/epoxy composite properties

AbstractIn the present study, the basalt fibers (BFs) were treated with hybrid sizings consisting silane coupling agent (3‐Glycidoxypropyl)trimethoxysilane, and silicon dioxide nanoparticles (SNPs). Using acetone washing and heat treatment, the commercial sizing previously on the BFs was removed. Next, the fibers were dip‐coated, and silanes condensed on the surface of the fibers. Fiber samples were characterized using thermogravimetric analysis (TGA), atomic force microscopy (AFM), X‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The test findings demonstrate that acetone extraction was an effective way to remove sizings. The AFM analysis and SEM micrographs demonstrate that SNP and silane particles were dispersed uniformly across the fiber surface. The single fiber tensile testing results indicated that the deposition of hybrid sizings enhanced the fibers strength. Because of the better adhesion between the fiber and epoxy, the hybrid sizings also improved the flexural strength by 22.28% and the interlaminar shear strength by 20.75%.Highlights Hybrid sizings (silanes and nano‐particles) on the basalt fiber surface. Characterization of the sizings and understanding of surface morphology. Hybrid sizings resulted in better tensile strength. Failure mechanisms of the fibers were observed using fractography. The effect of hybrid sizing on ILSS and flexural properties was observed.

Effect of toughening agent and flame‐retardant additives on the recycled polypropylene/oil palm empty fruit bunch laminated composites

AbstractThe increasing awareness of the environmental problems caused by the use of plastics has led to a demand for sustainable materials. The concept of turning waste into wealth has been considered in the study where the waste materials are value‐added into new composite materials that are recyclable, durable, and fire‐resistant. This effort aims to meet global environmental goals and the demand for high‐performance and sustainable building materials. The purpose of this current study is to develop laminated composites based on the combination of recycled plastic and oil palm empty fruit bunch (OPEFB). The addition of various loading of ammonium polyphosphate (APP) and 6 wt% of ethylene vinyl acetate (EVA) in the formulation was considered to enhance the performance of the composite laminates. The rPP and additives were compounded using a two‐roll mill. Then the rPP sheet and OPEFB were laminated using compression molding techniques. Results showed that rPP with addition of 30 wt% APP and 6 wt% EVA exhibited the highest thermal stability and the lowest melt flow index (MFI) value compared to other samples. Composites with 20 wt% APP and 6 wt% EVA showed 56% increase in flexural properties and 33% increase in impact strength compared to that of rPP/OPEFB composite sample without EVA. Addition of 30 wt% in recycled PP and OPEFB demonstrated self‐extinguished properties when exposed to fire compared to other samples. These findings indicated that rPP/OPEFB laminated composites with the addition of APP and EVA have a potential to be used in applications that require good strength and fire performance. The use of rPP/OPEFB composites with addition of APP and EVA has a potential to reduce virgin plastic consumption and agriculture material waste and establishing an environmentally friendly material for construction sector.Highlights Additives included in recycled PP enhance its thermal stability and reduce MFI. Recycled PP with OPEFB composite self‐extinguished at 30 wt% APP. The highest flexural strength is shown by composite laminates with 20 wt% APP and 6 wt% EVA. rPP/OPEFB laminates are ideal for building materials.

Hygrothermal aging and durability prediction of 3D-printed hybrid fiber composites with continuous carbon/Kevlar-fiber and short carbon-fiber

Hybrid Fiber Reinforced Polymers (HFRP) have excellent mechanical properties. However, preparation with 3D-printing technology is prone to hydrothermal aging compared to conventional method. Currently, complex hygrothermal aging and degradation mechanisms of 3D-printed HFRP are still unclear. Thus, hygrothermal aging and durability prediction of 3D-printed HFRP with continuous carbon/Kevlar-fiber and short carbon-fiber are studied, which considers four typical stacking sequences. All experimental samples are manufactured by Fused Deposition Modeling (FDM) 3D-printing. The artificial accelerate aging testing is conducted on samples at different times, and then flexural testing is adopted to evaluate the residual mechanical properties and failure modes. The results show that the stacking sequence significantly influences the moisture absorption behaviors, and [OC4O2K4]S absorbed more moisture than [OK4O2C4]S. During the aging process, the flexural properties of the 3D-printed HFRP first decrease rapidly and then keep stable. Among them, [OK4O2C4]S have the fastest degradation but possessed the highest residual strength. OC8O4K8O possess the slowest degradation but have a lower residual strength. The morphologies and micro failure modes/mechanisms are analyzed to explain the significant mechanical degradation. Finally, the Arrhenius relationship is adopted to accurately predict and analyze the degradation evolution process of specimens. This work offers a novel perspective on the hygrothermal aging and durability of 3D-printed HFRP.

Upcycling end-of-life carbon fiber in high-performance CFRP composites by the material extrusion additive manufacturing process

Each year, a significant amount of waste is produced from carbon fiber polymer composites at the end of its lifecycle due to extensive use across various applications. Utilizing regenerative carbon fiber as a feedstock material offers a promising and sustainable approach to additive manufacturing based on materials. This study proposes the additive manufacturing of recycled carbon fiber with a polyamide-12 polymer composite. Filaments of recycled carbon fiber-reinforced polyamide-12 (rCF-PA12) with different recycled carbon fiber contents (0%, 10%, and 15% by weight) in the polyamide-12 matrix are developed. These filaments are utilized for 3D printing of specimens by using various infill density parameters (80% and 100%) on a fused deposition modeling 3D printer. The study examined how the fiber content and infill densities influenced the flexural performance of the printed specimens. Notably, the part containing 15 wt% recycled carbon fiber (rCF) composites showed a significant improvement in flexural performance due to enhanced interface bonding and effective fiber alignment. The results indicated that reinforcing the printed part with 10% and 15 wt% recycled carbon fiber (rCF) improved the flexural properties by 49.86% and 91.75%, respectively, compared to the unreinforced printed part under the same infill density and printing parameters. The investigation demonstrates that the additive manufacturing-based technique presents a potential approach to use carbon fiber-reinforced polymers waste and manufacture high-performance engineering, economic, and environmentally friendly industrial applications with the complicated design using different polymer matrices.

Simulation and mechanical testing of 3D printing shin guard composite materials

ABSTRACT This study critically examines the composite material's mechanical properties and performance for 3D-printed shin guards. It contains a thermoplastic polymer matrix with short carbon fibre reinforcement. Shin guard stress and deformation under impact loading were modelled using FEA models. The composite material was 3D-printed and tested for tensile, flexural, and impact properties. The entire cycle of FEA models and careful mechanical testing allows for the development and evaluation of new composite materials and designs. The finite element analysis, such as maximum von Mises stress, is 2890.5 MPa. The carbon fibre-reinforced composite's mechanical properties, including tensile strength, flexural strength, and impact resistance, showed a considerable improvement over those of the unreinforced polymer. The solid design could be heavier and less adaptable than the pattern. Compared to unreinforced polymers, carbon fibre improves strength, stiffness, and impact resistance for the 3D-printed composite. This result thus proves that 3D-printed carbon fibre-reinforced composites could make superior sports protective equipment like shin guards. The FEA calculations and extensive mechanical testing provide a dependable framework for creating and testing these new composite materials and systems.

Thermal analysis, flexural mechanical properties and FTIR analysis of an HDPE matrix composite reinforced with alumina and silicon carbide

This research developed an HDPE composite reinforced with Al2O3 and 1% SiC in the proportions of pure HDPE, 40 %, 50 % and 60 % of ceramic load. The mechanical flexural test showed results of sMAX 19.09 ± 2.89 MPa and E 1806 ± 400 MPa for the A60 group and concluded that with ceramic loadings above 60 % contribute to crystallization in the regions around the particles. TGA analysis showed initial degradation at 409 °C and final degradation between 499 and 504 °C, with a residue in pure HDPE of 0.46%. The DSC curves showed an endothermic peak at 132 °C and crystallization around 119 °C, and the crystallinity of the HDPE was 95.29 %, and the analyses showed a decrease in the enthalpy of fusion and crystallization with increasing ceramic loading due to the decrease in the polymer fraction in the composite. DMA analysis showed that temperatures above the Tg of the crystalline phases were the mechanism that contributed most to the storage modulus. FTIR analysis showed several interactions in different bands between the 3 compounds in the composite.

Turning Discarded Agricultural Remnants and Poultry Waste into Usable Hybrid Polymer Matrix Reinforcements: An Experimental Study

The primary objective of the present study was to transform discarded agricultural remnants and poultry waste into value-added materials. Rice straw and chicken feathers are disposed of after their primary consumption into landfills or are incinerated, causing pollution and environmental threats. In this study, epoxy composites were fabricated using different volume proportions (5–45%) of these raw and alkali-treated remnants, and their mechanical strength was tested. The flexural strength of the rice straw composites and chicken feather composites initially decreased with the addition of fibers from 5 to 35 vol% and then the values increased when the fiber content was more than 35 vol%. The chicken feather composites showed increased impact strength with fiber addition. Alkali treatment of the rice straw resulted in improved flexural and impact strengths of the composites due to the removal of the waxy layer on the fiber surface, which was observed in the FTIR studies. Alkali treatment of the chicken feathers did not produce any significant change in the flexural strength of the composites, but their impact strength increased with fiber addition. Hybrid composites fabricated using rice straw and chicken feathers exhibited enhanced flexural and impact strength properties both with and without the alkali treatment, corroborating the synergistic effect of these fibers. SEM analysis of the fractured samples showed noteworthy interfacial adhesion between the fibers and matrix. This study presents a better method for converting these disposable materials into value-added usable materials and increasing their life cycle in the circular economy.

Post impact flexural behavior investigation of hybrid foam-core sandwich composites at extreme Arctic temperature

This study explores the post-impact bending behavior and failure mechanisms in hybrid sandwich composites made of Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP). Flexural tests conducted at both ambient room temperature and low temperature Arctic conditions reveal a significant enhancement in flexural performance when GFRP layer is incorporated on the outer side of the hybrid composite. The investigation utilizes images from testing to elucidate damage modes, including fiber and matrix cracking in the composite facesheet, as well as core shearing and debonding in the Polyvinyl Chloride (PVC) foam core. Residual flexural properties are notably influenced by stacking sequence, facesheet compressive properties, pre-existing impact damage and temperature conditions. Analytical predictions, validated experimentally, highlight the effect of stacking sequence, low temperature, and impact energy on flexural collapse modes, with competing failure modes such as indentation and core shear. Collapse maps indicate that room temperature specimens predominantly collapse through indentation, while diverse collapse mechanisms emerge due to facesheet thickness, rigidity, and degraded tensile strength. The study aims to provide fundamental insights for future composite designs tailored for Arctic applications.

Development of engineered polymeric reinforced cementitious composite (EPRC) using nature-inspired hollow architectures: Flexural experimental and numerical evaluations

This study explores the integration of nature-inspired architectural designs into Mechanics of Materials (MoM)-based reinforcement layouts for reinforced cementitious composites (RCs). While traditional MoM layouts focus on longitudinal rebars for tensile strength, this study aims to enhance the flexural properties of RCs by incorporating nature-inspired elements like hollow tubes found in plant stems. The research utilizes both experimental and numerical methods to evaluate the flexural performance of engineered polymeric reinforced cementitious composites (EPRCs) with integrated nature-inspired motifs. A numerical model, based on the material properties of reinforcing elements and the cementitious matrix, was developed to simulate the flexural performance of EPRCs reinforced with both solid and hollow bars, including MoM-based solid and hollow rebars. The model's predictions were validated through experimental testing of 3D-printed MoM-based solid and hollow rebars under three-point bending conditions. The results demonstrated that EPRCs reinforced with hollow rebars exhibited significantly improved flexural properties compared to those with solid rebars. Specifically, the hollow-reinforced samples achieved an average modulus of rupture of 8.68 MPa, toughness of 11.76 N m, and mid-point deflection of 1.99 mm, representing increases of 34 %, 55 %, and 93 %, respectively, over their solid counterparts. These enhancements are attributed to improved shear reinforcement and bond strength despite the reduced moment of inertia of the hollow rebars. The study provides valuable insights for optimizing the mechanical properties of RCs in civil engineering applications through the incorporation of nature-inspired architectural designs.

Flexural properties and optimisation of hybrid composites reinforced by carbon, glass and flax fibres

This paper presents a study on the flexural properties of hybrid composites (HC) reinforced by carbon, glass, and flax fibres, utilising Finite Element Analysis (FEA). Possible optimal layups are identified through the application of design rules, and regression-based models are developed to predict flexural strength. With the developed models, multi-objective optimisation is done to minimise the cost and weight subjected to a given minimum required flexural strength. By integrating numerical simulation, regression analysis, and optimisation techniques, this research offers a practical approach to the design and fabrication of HC with enhanced mechanical performance and cost-efficiency.

Effects of Postmanufacture Conditioning on the Mechanical and Hygroscopic Properties of Extrusion Printed Wood–Sodium Silicate Composites

Abstract Additive manufacturing of wood–sodium silicate composites could aid in mitigating the carbon footprint of the building and construction industry. However, the effect of postmanufacture conditioning on the mechanical and physical properties of additively manufactured wood–sodium silicate composites is not well understood. This study investigated eight different postmanufacture drying processes, including: ambient indoor and outdoor conditions, oven-drying at two different temperatures, microwave drying, alcohol-induced dehydration using ethanol and denatured alcohol, and desiccant drying. Each postmanufacture conditioning treatment was assessed in terms of total moisture extraction and moisture extraction rate as well as the flexural strength, flexural stiffness, and hardness of the wood–sodium silicate samples after drying. In addition, the water absorption and volumetric swelling properties of the additively manufactured wood–sodium silicate samples were assessed via water submersion tests. The postmanufacture conditioning treatments were found to significantly affect the mechanical and physical properties of the samples. A universal ranking system was established based on cumulative rankings of each evaluated characteristic. Samples dried in ambient outdoor conditions achieved the best overall ranking and had the smallest carbon footprint. However, ovendried samples had the best flexural properties. Future studies investigating hybrid approaches in which composites are sequentially subjected to different drying methods will likely provide the most desirable mechanical and physical properties of wood–sodium silicate composites.

Trio/hybrid fiber effect on the geopolymer reinforced concrete for flexural and shear behavior

AbstractGeopolymer concrete (GC) is an innovative and sustainable type of composite resulting from the chemical reaction between waste materials containing and alkaline activators. The researchers have been focused to reduction of the greenhouse‐gas release, especially during the production of cement. Although numerous studies have been conducted on alkali‐activated cement or GC at the material level, there is limited research in the literature on the structural performance of reinforced GC members. The aim of this study is to investigate the effect of fiber combination on the shear and flexural performance of RC beams with maximum and minimum reinforcement ratio. To investigate the shear and flexural behavior of GC beam, four‐point and three‐point tests were performed on 12 GC with hybrid fibers, 4 GC with trio fibers, and 2 GC fiber‐free as references beams. The test parameters were the combination of fibers (steel, glass, carbon, and basalt), the longitudinal reinforcement ratio, and loading type. The key test results include the load‐deflection behavior, characteristics of the cracks, the effect of fiber type on the shear and flexural performance, ductility and stiffness properties, microstructure, the strain in the concrete, and the bars and code predictions. The test results showed that as expected, reducing the longitudinal reinforcement ratio decreased the strength, but the decrease in strength was tolerated by using different types of fibers. The use of trio fibers in beams under bending increased the strength capacity, considerably. Finally, the capacity prediction performance of current codes, that is, GB50010, EuroCode‐2, TS500, and ACI318, were also examined, and the calculations resulted that the current code equations had a percentage error of approximately 25% and 82% on average for flexural and shear, respectively, although EuroCode‐2 equations performed slightly better.

Characterisation of the Mechanical Properties of Natural Fibre Polypropylene Composites Manufactured with Automated Tape Placement

The integration of natural fibre thermoplastic composites, particularly those combining flax fibres with polypropylene, offers a promising alternative to traditional synthetic composites, emphasising sustainability in composite materials. This study investigates the mechanical properties of flax/polypropylene composites manufactured using flashlamp automated tape placement and press consolidation, individually and in combination. Tensile, compression, three-point bending, and double cantilever beam tests are utilised for comparing these manufacturing processes and the mechanical performance of the resulting composites. The microstructure of the tapes is investigated using cross-sectional microscopy, and the thermophysical behaviour is analysed utilising thermogravimetric analysis and differential scanning calorimetry. The temperature during placement is monitored using an infrared camera, and the pressure is mapped with pressure-sensitive films. The natural fibre tapes show a good aptitude for being manufactured with automated tape placement. The tensile performance of tapes manufactured with automated tape placement is close to that of press consolidated samples. Compression, flexural properties, and the mode I fracture toughness critical energy release rate all benefit from a second consolidation step.

Recycled Low Density Polyethylene Reinforced with Deverra tortuosa Vegetable Fibers

In this work, natural fibers extracted from the medicinal aromatic plant Deverra tortuosa, with different sizes (S1 = 2 mm and S2 = 500 μm), were incorporated into recycled low density polyethylene (rLDPE) to produce sustainable biocomposites. Compounding was performed with different fiber concentrations (0 to 30% wt.) via twin-screw extrusion followed by injection molding. Based on the samples obtained, a comprehensive series of characterization was conducted, encompassing morphological and mechanical (flexural, tensile, hardness, and impact) properties. Additionally, thermal properties were assessed via differential scanning calorimetry (DSC), while Fourier transform infrared spectroscopy (FTIR) was used to elucidate potential chemical interactions and changes with processing. Across the range of conditions investigated, substantial improvements were observed in the rLDPE properties, in particular for the tensile modulus (23% for S1 and 104% for S2), flexural modulus (47% for S1 and 61% for S2), and flexural strength (31% for S1 and 65% for S2). Nevertheless, the tensile strength decreased (15% for S1 and 46% for S2) due to poor fiber–matrix interfacial adhesion. These preliminary results can be used for further development in sustainable packaging materials.

Towards gradient design of TPMS lattices and laser powder bed fusion processing– Role of laser strategies and lattice thickness

The ability to manufacture complex design geometries via Additive Manufacturing (AM) has led to a rapid growth in advancing the design methods, fabrication, and application of Triply Periodic Minimal Surface (TPMS) lattices with minimal surface topologies. Due to its zero-mean curvature, TPMS lattices can be additively manufactured without any sacrificial support structures and offer both design and manufacturing engineers, unprecedented control over the local physical properties (surface area, relative density, etc.) and local mechanical properties (flexural strength, Young’s modulus, etc.). TPMS lattices are of high interest for a wide range of applications such as biomedical implants, energy absorption, and surface fluidic applications such as heat exchangers, and energy storage. Recent advancements in functionally graded TPMS lattice design by varying local lattice geometry has shown to result in different mechanical performance. However, there have been limited studies in understanding the functional grading of AM process conditions (e.g., Laser-Powder Bed Fusion in this study) and lattice sheet thickness to better map the design-processing conditions-properties. The goal of this study is to achieve similar mechanical properties in TPMS sheet lattices with two different TPMS sheet thicknesses by varying laser processing conditions (e.g., contour and hatch conditions in this study). Quasi-static tensile testing of solid samples with corresponding AM conditions and 3-point bending tests of TPMS lattices were performed in accordance with ASTM E8 and ASTM E290, respectively. It was observed that the flexural properties of the 0.75 mm and 0.25 mm TPMS lattices are similar and exhibit different properties with different scan strategies and speed variations under contour-only and hatch-only laser scanning strategies. Also, the 0.75 mm TPMS sheet lattices exhibited 79 % higher flexural stiffness than the 0.25 mm sheet lattices. It was also observed that this observed trend was reversed in the case of tensile properties. Findings from this study can provide new directions towards achieving gradient TPMS lattice designs with varying local mechanical performance by grading the laser scanning strategies to achieve desired mechanical properties and surface topologies.