Increase In Tensile Strength Research Articles

Enhancing Thermal and Mechanical Properties of Soft PVC Composites With Phosphorylated Boron Nitride

ABSTRACTIn the present study, hexagonal boron nitride (h‐BN) nanosheets were first functionalized with hydroxyl groups (h‐BN‐OH), and then phosphonic acid groups were grafted onto the h‐BN surface (BNP) using aminotris(methylenephosphonic acid) (ATMP) through a condensation reaction. The BNP was then incorporated into a polyvinyl chloride (PVC) matrix to prepare PVC/BNP composites. Thermogravimetric analysis showed an increase in thermal stability, with BNP/PVC composites exhibiting greater resistance to degradation at elevated temperatures. The addition of BNP improved the dispersion and interfacial adhesion within the PVC matrix, as confirmed by Scanning Electron Microscopy (SEM). Furthermore, the PVC/BNP composites exhibited a 22.5% increase in tensile strength (21.2 MPa) and an 82% improvement in elongation at break (464%) compared to pristine PVC composites, which showed a tensile strength of 17.3 MPa and an elongation at break of 255%. Moreover, the addition of BNP notably improved the thermal conductivity from 0.18 to 1.50 W/m K as the BNP content increased from BNP‐0 to BNP‐4. These improvements in thermal stability and mechanical strength, as well as excellent migration resistance, make BNP/PVC composites highly promising for advanced applications.

Multi-functional bio-based DOPO derivative for enhanced flame retardancy and mechanical strength in epoxy resin

Sustainable flame retardants are crucial to address environmental concerns and meet the demands of high-performance materials. A novel bio-based flame retardant (ANDD) with multiple reactive groups was synthesized using a one-pot method. ANDD served as a co-curing agent for 4,4′-diaminodiphenylmethane (DDM) in the cross-linking of EP. Differential scanning calorimetry (DSC) revealed that ANDD accelerates the curing process of bisphenol A diglycidyl ether (DGEBA). Thermogravimetric analysis indicated that incorporating ANDD lowered the T5% and Tmax values of the EP/ANDD composites, while enhancing residual char at high temperatures due to its carbon-forming capability. The EP/ANDD composites exhibited improved flame retardancy, with a limiting oxygen index (LOI) of 33.6 % at a 5 wt% ANDD loading (P content of 0.372 %), achieving a V-0 rating in UL-94. Cone calorimetry showed that, compared to pure EP, EP/ANDD-5 reduced the peak heat release rate (pHRR) by 41.7 % and total smoke production (TSP) by 24.4 %, outperforming EP/DOPO with equivalent phosphorus content. This enhanced flame retardancy is attributed to the char layer’s protective role in the condensed phase and radical quenching in the gas phase. Additionally, EP/ANDD-3 demonstrated a 13.8 % increase in tensile strength and a 20.8 % increase in tensile modulus compared to pure EP. This study indicates that ANDD, as a bio-based flame retardant with multiple reactive groups, presents a promising pathway for the development of high-performance functional thermoset materials.

Evaluating the properties of starch/chitosan films with the incorporation of various nanoclays for use in food packaging.

This study evaluates the properties of starch/chitosan films (SCF) produced via the casting method, incorporating 40% (w/w) plasticizers (glycerol and sorbitol) and various concentrations (0, 3, 5, and 10% (w/w)) of nanoclays (Cloisite 20A, Cloisite 30B, and K-10). The effects of each nanofiller on the films were thoroughly investigated. Films containing nanoclays exhibited reduced water solubility and enhanced thermal stability compared to films without nanofillers. A higher nanoclay concentration (10% (w/w)) led to a reduction in the solubility of the starch/chitosan films, with a decrease of approximately 15% relative to the SCF sample. Incorporating the three types of nanoclays improved tensile strength at break, particularly in samples with 3% and 5% (w/w) nanoclay content, achieving an approximate 68% increase in tensile strength at break compared to the SCF sample. Atomic Force Microscopy (AFM) analysis revealed that increasing nanofiller content significantly heightened surface roughness. Films incorporating Cloisite 30B demonstrated lower surface roughness than those with Cloisite 20A and K-10 nanoclays, especially at concentrations of 3% and 5% (w/w), with a reduction of approximately 40%. X-ray diffraction (XRD) analysis indicated superior interaction in films containing Cloisite 20A and 30B, while films with 10% (w/w) K-10 exhibited a diffraction peak at 8.88°, suggesting inadequate incorporation. These findings align with the AFM analysis results for this film. Consequently, the integration of nanoclays improves the properties of starch/chitosan films, with formulations utilizing 20A and 30B nanoclays at 3% and 5% (w/w) showing the most promising potential for future applications in food packaging.

Improved properties of wire arc directed energy deposited thin-walled Al-6Mg-0.3Sc component via laser shock peening

ABSTRACT Heat treatment free aluminum alloys have been developed for wire arc directed energy deposition (DED) large thin-walled components, but their further performance enhancement methods remain unexplored. In this study, laser shock peening (LSP) treatment was performed on wire arc DED Al-6Mg-0.3Sc components. The results show that LSP creates a gradient microstructure with submicro-grains near the surface. The effects of LSP on defects were quantified by quasi-in-situ CT, demonstrating a reduction in porosity by over 68% together with decreased size. Simultaneously, tensile strength increases by 39.5% to 295.8 ± 6.4 MPa with only a marginal loss of elongation, as compared to the as-deposited (AD) state. This was due to the accumulation of dislocations and continuous dynamic recrystallization lead to grain refinement, as well as the appearance of a triple heterogeneous microstructure. Therefore, this study offers a novel solution for manufacturing of high-performance heat treatment free large thin-walled components.

Improving Stability and Mechanical Strength of Electrospun Chitosan-Polycaprolactone Scaffolds Using Genipin Cross-linking for Biomedical Applications.

Electrospun nanofiber scaffolds have become vital in biomedical applications due to their high surface area and tunable properties. Chitosan (CS) is widely used, but its rapid degradation limits its effectiveness. This study addresses this limitation by blending CS with polycaprolactone (PCL) and applying genipin cross-linking to enhance its stability and mechanical properties. Scanning electron microscopy indicated a uniform morphology of the electrospun fibers, and further, the crystallinity of the scaffolds before and after cross-linking is verified. Fourier-transform infrared spectroscopy is used to analyze the chemical structure, identifying the presence of trifluoroacetic acid residues in the as-spun fibers. These residues are successfully eliminated through neutralization and cross-linking, which are critical for enhancing stability and cell viability in in-vitro studies. Mechanical testing revealed that cross-linked CS+PCL scaffolds exhibit a 350% increase in tensile strength compared to pure CS, and zeta potential reaches the favorable for cell development -26.27mV. The cytotoxicity assay results with murine NIH 3T3 fibroblast cells indicate the suitability of CS+PCL scaffolds for targeted tissue engineering and wound healing. This work establishes the potential for fine-tuning scaffold properties to create stable, functional, and biocompatible substrates for extended biomedical use.

Stress-strain properties of microwave-irradiated polymer composite based on PDI-3A rubber

The stress diagram of polymer composite material based on PDI-3A rubber filled with thermally expanded graphite or potassium chloride before and after microwave treatment for 300, 600, 900 and 1200 s has been studied. A twofold increase in tensile strength and deformability was found after microwave treatment for 300 c and testing at 223 K. With increasing the test temperature or microwave treatment time, a marked decrease in the deformation and tensile strength characteristics of the obtained composites was observed.

Performance research and structure optimization of quartz-covered alumina high-strength wear-resistant yarn

Improved abrasion resistance and shear performance of alumina fiber yarns is crucial to the weaving process. Herein, a series of novel SiO2@Al2O3 single-layer and double-layer covered yarns were prepared by winding 48 tex quartz yarn on the outer layer of 120–600 tex alumina yarn with wrapping twist of 50–500 twists/m. Wear resistance, shear force, and tensile fracture properties of the covered yarn were tested and analyzed. Wrapping twist ranges from 50 to 400 twists/m, with increased wrapping twist improving the SiO2@Al2O3 covered yarn's breaking strength, shear force, and wear resistance. As wrapping twist ranges from 400 to 500 twists/m, uneven winding and wear of quartz yarn weaken the breaking strength, wear resistance, and shear properties of SiO2@Al2O3 covered yarn. SiO2@Al2O3 double-layer covered yarn exhibits superior shear force, wear resistance, and tensile breaking strength compared with its single-layer counterpart. In comparison with the initial alumina yarn, wear resistance of SiO2@Al2O3 covered yarn improves by 50%, whereas the maximum shear strength and tensile breaking strength increase by 125% and 15%, respectively. High-strength, wear-resistant SiO2@Al2O3 covered yarn is suitable for alumina fabrics and braid structures, and is expected to be widely used in aerospace and the high-temperature insulation industry.

Experimental research of the tensile strength of concrete reinforced with basalt fiber

Non-metallic composite fittings are increasingly used in modern construction due to their high mechanical characteristics, corrosion resistance, durability in concrete and aggressive external environments, and other properties. At the sametime, usually, non-metallic composite reinforcement is used in the form of rods with the main supporting element in the form of basalt, glass, aramid or roving made of other materials, which is thin fibers with a diameter of 7...20 mm.The specified roving, as an element of reinforcement of concrete structures, will be used in the form of fiber to a much lesser extent, although it is a real alternative to traditional steel fiber with all the advantages of fiber reinforcement, to which corrosion resistance is also added. The limited number of experimental explains the current situation andtheoretical studies of non-metallic fiber reinforcement, in particular, tensile strength, which is one of the main advantages of fiber reinforcement of concrete.This article presents the results of experimental studies of the tensile strength of concrete reinforced with fiber from basalt roving with a diameter of 16 μm and a length of 24 mm, which included bending tensile tests of three series of concrete samples with a strength class of compression, respectively, C20/25, C25/30, C30/35 and percentage of fiber reinforcement within 2.0...8%.As a result of the conducted research, it was established that the fiber reinforcement from the baseboard roving leads to an increase in the axial tensile strength of concrete. At the same time, the most intensive increase in tensile strength took place when the percentage of reinforcement was increased in the range of 2.0...4.0%. With a further increase in the percentage of reinforcement in the range of 6.0...8.0%, this growth stopped, which indicates that fiber reinforcement in the range of 2.0...4.0% is the most effective, regardless of the class of concrete in terms of compressive strength.Other things being equal, the increase in axial tensile strength of concrete with an increase in the percentage of fiber reinforcement within the limits of 2.0...8.0% is 15...20% compared to concrete without reinforcement.

Improving the Impact Resistance and Post-Impact Tensile Fatigue Damage Tolerance of Carbon Fiber Reinforced Epoxy Composites by Embedding the Carbon Nanoparticles in Matrix.

The effect of dispersing multiwalled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) in the matrix on the low-velocity impact resistance and post-impact residual tensile strength of the carbon fiber reinforced epoxy composite laminates has been experimentally analyzed in this study. The composite specimens with the matrix reinforced by different nanoparticle types and various nanoparticle concentrations (0.1, 0.3, and 0.5 wt.%) were prepared and impacted. The post-impact tensile quasi-static and fatigue tests were performed on the specimens with different configurations to study the influence of aforementioned factors on the impact resistance and damage tolerance. Experimental results show that adding nanoparticles in the matrix increases the maximum impact force, reduces the damage area, and alleviates the dent depth of the laminates remarkedly. Moreover, the improvement in these impact resistances increases with the applied nanoparticle concentrations. The nano-modified composite laminates present higher post-impact static strength and longer fatigue life than the specimens with a neat epoxy matrix. Furthermore, both the post-impact static tensile strength and fatigue life increase with the applied nanoparticle concentrations. The damage areas measured using infrared thermography were found to increase linearly with the applied fatigue cycles for all the studied specimens with various configurations. The damage area growth rates of nano-modified composite laminates decrease significantly as the applied nanoparticle concentrations increase. The MWCNTs present better performance than GNPs in improving post-impact static strength and extending the residual fatigue life, however the effect of applied nanoparticle type on the fatigue damage growth rate is slight.

Lignin Particle Size Affects the Properties of PLA Composites Prepared by In Situ Ring-Opening Polymerization.

The present work focuses on the synthesis and characterization of biobased lignin-poly(lactic) acid (PLA) composites. Organosolv lignin, extracted from beechwood, was used as a filler at 0.5, 1.0, and 2.5 wt% loadings, with ultrasonication reducing the lignin particle size to ~700 nm. The PLA-lignin composites were prepared via in situ ring-opening polymerization (ROP) of L-lactide in the presence of lignin. This method ensured uniform lignin dispersion in the PLA matrix due to grafting of PLA chains onto lignin particles, preventing aggregation. Strong polymer-filler interactions were confirmed through spectroscopic analysis (FTIR and XPS) and their effects on static and dynamic glass transitions (DSC). These interactions enhanced mechanical properties, including a two-fold increase in tensile strength and elongation at 1 wt% lignin. Crystallization was suppressed due to shorter PLA chains, and a 15% drop in dynamical fragility was observed via Broadband Dielectric Spectroscopy (BDS). Antioxidant activity improved significantly, with PLA-2.5% ultrasonicated organosolv lignin reducing DPPH• content to 7% after 8 h, while UV-blocking capability increased with lignin content.

Experimental Investigation into the Influence of Filament Layer Arrangement on the Tensile Strength of FFF-Manufactured Components

One major disadvantage of fused filament fabricated components (FFF) is its well-known anisotropy, which results from the layer-wise adding of material, and that it is not always possible to avoid loading in the layer build-up direction. In particular, components that are exposed to multi-axial load conditions must manage with reduced tensile strength in the build-up direction. This work is therefore concerned with improving the tensile strength transverse to the layering by changing the layer structure without directly changing the material itself. Therefore, the print-defining G-Code was modified to change the arrangement between the layers. The effectiveness of this method was investigated by means of tensile tests using thermoplastic samples made of Acrylonitrile Styrene Acrylate (ASA), Poly Cyclohexylenedimethylene Terephthalate Glycol (PCTG), Poly Ethylene Terephthalate Glycol (PETG) and Poly Lactic Acid (PLA) for layer thicknesses of 0.16 mm and 0.28 mm. The results show that the G-Code modification generally resulted in an increase in tensile strength. For PETG, an improvement of 25% was achieved.

The Effect of Cotton Fiber Characteristics Tested by Uster H.V.I on Yarn Properties

In this study, the effects of cotton fiber characteristics, tested by Uster High VolumeInstruments (HVI) on the tenacity, elongation, unevenness, imperfection index (IPI) and hairiness values of the combed ring spinning yarns, were investigated in detail. Based on the experiments, it was found that an increase in fiber tensile strength and elongation leads to an increase in the specific tensile strength and elongation of the yarn; an increase in short fiber content and neps fiber materials leads to an increase in the unevenness, IPI of the yarn; an increase in the fiber length leads to a decrease the hairiness values of the yarn, etc. Information concerning the relative contribution of fiber characteristics to yarn properties is one of the important targets for the spinner to choose cottons that are best suited to the manufacture of specific end product.

Compatibilizer Efficiency in Enhancing Marine Plastic Waste Valorization Through Simulated Recycled Plastic Blends.

This study investigated the optimal combination of compatibilizers and stabilizers to enhance the value of marine environment plastic (MEP). The composition of the plastics was analysed, and a simulated recycled plastic blend (sMEP) was prepared based on a simplified composition of actual MEP. Different concentrations of three commercial compatibilizers (C1, C2 and C3) were tested to improve tensile strength. The tensile tests indicated that the blend compatibilized with 10 wt.% C3 (polypropylene grafted with maleic anhydride) exhibited the highest increase in tensile strength. This optimal compatibilization was then combined with two commercial stabilizers and applied to a simulated MEP blend. Scanning electron microscopy images showed that all blends had a continuous polyethylene phase with dispersed poly(ethylene terephthalate) (PET) and polypropylene (PP) droplets. The simulated blend with 10 wt.% C3 exhibited a reduced PET droplet size in the dispersed phase. Differential scanning calorimetry results revealed a decrease in polyethylene crystallinity and an increase in PP crystallinity. The improved properties of the blend were attributed to the effectiveness of the C3 compatibilizer in enhancing the interface between the PP and PET phases. An effective formulation was developed to valorise marine-sourced plastics by leveraging existing scientific knowledge and accessible commercial additives. Applying this enhanced formulation to real MEP not only demonstrated its effectiveness, but also highlighted a practical approach for reducing plastic pollution and supporting circular economy principles, contributing to environmental conservation efforts.

Orientation control of magnetically functionalized graphene oxide nanohybrids in unsaturated polyester resin with enhanced mechanical, thermal, and fire safety performance

AbstractBoth the distribution and orientation of 2D graphene nanomaterials in polymer matrices can significantly affect the performance of polymer composites. Still, preparing high‐performance graphene polymer nanocomposites with a controlled distribution state is challenging. In this work, magnetically functionalized graphene oxide (MFGO), a ternary nanohybrid, was prepared using a facile method. The resulting MFGO nanofillers were incorporated into unsaturated polyester resin (UPR) with the assistance of an external magnetic field to achieve oriented alignment in the UPR matrix. Attributing to the uniform dispersion as well as the magnetic field‐induced orientation of MFGO in UPR, the oriented UPR/MFGO (UPR/OMFGO) nanocomposites demonstrated much‐improved mechanical and thermal properties, as the oriented UPR/MFGO2.0 (UPR/OMFGO2.0) achieved a notable increase in tensile strength to 46.71 MPa and storage modulus to 1.24 GPa. Moreover, the peak heat release rate (PHRR) and peak smoke production release (PSPR) of UPR/OMFGO2.0 nanocomposite were reduced by 34.0% and 33.6%, respectively, as compared with the neat UPR. In addition, SEM, FTIR, and Raman spectroscopy were employed to investigate the char residues of UPR samples, and a possible mechanism for the improved fire safety performance of the UPR/OMFGO nanocomposites was proposed. This work provides a promising strategy to design high‐performance UPR nanocomposites.Highlights Magnetically functionalized graphene oxide (MFGO) nanohybrids were successfully synthesized. MFGO nanohybrids were well dispersed and orderly arranged in UPR under a magnetic field. The well‐oriented MFGO significantly improved the mechanical and thermal properties of UPR. The mechanism for the enhanced fire safety performance of UPR nanocomposites was elaborated.

Incorporating a poly-ε-caprolactone scaffold in a stapled small intestinal anastomosis with induced ischemia significantly increased anastomotic tensile strength. An experimental study in pigs

Objective Anastomotic leakage is a severe complication with multifactorial aetiology, including impaired tissue oxygenation, infection, inflammation, and anastomotic tension. Reinforcement with poly-ε-caprolactone (PCL) scaffold incorporated in a stapled intestinal anastomosis has demonstrated a significant increase in the anastomotic tensile strength. This study aimed to investigate whether incorporation of the scaffold would influence tensile strength with induced ischemia compared to normal blood perfusion. Methods Eighteen pigs were randomly allocated into an intervention group with a induced relative reduction in blood perfusion to 30% at the anastomotic area and a control group with normal perfusion controlled by quantitative fluorescence angiography. Each pig recieved two stapled small intestinal anastomoses, one with a PCL scaffold incorporated and one without. On postoperative day five, the anastomoses were subjected to a maximal tensile strength test (MATS) and a histopathological analysis. Tensile strength was measured at three events: when a serosal tear became visible (MATS-1), at transmural rupture (MATS-2), and at maximum load before the load-strain curve dropped (MATS-3). Results In the intervention group, MATS-1 was significantly higher in scaffold-reinforced anastomoses compared to controls (7.9 ± 4.2N and 4.4 ± 2.5N, p < 0.02). The same tendency was found for MATS-2 and MATS-3, with statistically significant differences after adjusting for adhesion grade (p < 0.05). Histological analysis revealed no significant differences in wound healing between groups. Conclusion Incorporating a PCL scaffold in a stapled small intestinal anastomosis with induced ischemia improved anastomotic tensile strength.

Mechanical and tribological properties of AA2024 reinforced Al2O3 and ZrO2 hybrid composite

Abstract Hybrid Metal Matrix Composite (HMMC) alloys are a very attractive material for excellent mechanical and tribological performance, and their properties can be easily customized by varying reinforcement types and amounts. This research investigated the mechanical and tribological properties of an Aluminium Alloy (AA) 2024 reinforced with 2 wt% Al2O3 and (2, 4, 6) wt% ZrO2 hybrid composites. The presence and distribution of reinforcements in the stir-casted samples were confirmed by SEM, EDS, and elemental mapping. The tribological tests were conducted on a pin-on-disc under dry and wet conditions using Taguchi’s L9 orthogonal array. The SAE 20w40 oil and SAE 20w40 oil mixed with TiO2 nano additive are lubricants. The hardness and tensile strength increase linearly with the addition of a single and continue to increase with multiple reinforcements. The HMMC exhibits a maximum hardness and tensile strength of 107 BHN and 209.281 MPa, respectively. The experimental results show that the dry condition’s wear rate is much higher than that of the composites lubricated with SAE 20w40, especially SAE 20w40 with TiO2 nano additive. Compared to the base material, AA2024 reinforced with 2 wt% of Al2O3 and 6 wt% of ZrO2 exhibited an enhanced wear resistance of 0.0002353 mm3/min and COF of 0.118 with nano lubricant which is 40% and 21% higher than base lubricant.

Influence of layering variation with addition of bio-fillers on mechanical and thermal performances of hybrid polyester composites

The extensive application of composites reinforced with synthetic or natural fibers and bio-fillers represents a recent advanced trend in research. This research seeks to assess the optimal ratio of wood dust (WD) and fish scale powder (FSP) for forming a hybrid filler mix to reinforce Palmyra Palm leaf stalk (P)/Glass (G) polyester laminate, aiming to improve its mechanical and thermal properties. The ideal ratio is identified by evaluating the mechanical properties of various weight fraction combinations of WD and FSP filler in polyester. The test results showed that the optimal filler hybridization ratio is 5 wt.% WD and 10 wt.% FSP. Hybrid laminates are then produced by combining equal layers of glass and palm leaf stalk fiber in different stacking configurations, incorporating an optimal mixture of hybrid fillers. The experimental findings revealed that, the inclusion of an optimal blend of WD and FSP filler results in improvements in mechanical properties, with a 51.93% increase in tensile strength, a 36.27% boost in flexural strength, a 20.48% rise in impact resistance, and a 10.08% enhancement in micro-hardness. Additionally, the findings revealed that the laminate with GPPG stacking order shows the highest mechanical properties compared to other stacking sequences. To further examine the thermal degradation and various failure mechanisms, Thermo-gravimetric analysis (TGA) and fractography study using a Scanning Electron Microscope (SEM) are conducted.

Reinforcement of graphene nanoplatelets on water uptake and thermomechanical behaviour of epoxy adhesive subjected to water ageing conditions

Abstract Adhesive joints are frequently utilized due to their lightweight nature and minimal damage to the substrates. However, their application is constrained by a lack of reliable performance under moist conditions. This study assesses the impact of incorporating varying concentrations (0.25–0.75 wt%) of graphene nanoplatelets (GNPs) on moisture uptake, dynamic thermal properties, and tensile behaviour of engineered epoxy adhesives when subjected to water for periods of up to 8 weeks. The objective of this study is to ascertain the optimal concentration from the standpoint of degradation in the thermomechanical performance of the epoxy resulting from water ageing. The addition of GNP results in a 45% reduction in the diffusion coefficient of the 0.25 wt% GNP-modified epoxy relative to the unmodified epoxy. The reduced absorption of water by the GNP-reinforced adhesive results in diminished thermomechanical degradation, particularly during the initial immersion period (less than 14 days). The loss modulus exhibits an increase of up to 21% in comparison with the unmodified epoxy. The reduction in tensile strength of the modified epoxy is 53% less than that of the unmodified epoxy following 14 days of water ageing. Under the same water ageing conditions for 14 days, the epoxy modified with 0.25 wt% GNP exhibited a 75% increase in tensile strength compared to the unmodified epoxy. This work may facilitate the GNP application in epoxy adhesive joints, thereby enhancing their durability under high humidity conditions.

Investigation of Mechanical Properties and Color Changes of 3D-Printed Parts with Different Infill Ratios and Colors After Aging.

Since their inception, plastics have become indispensable materials. However, plastics used for extended periods in industrial applications are prone to aging, which negatively impacts their material behavior and performance. To ensure the long-term usability of these materials, they must be tested in real-time, in-service environments to assess degradation. In practice, however, accelerated aging techniques are commonly employed to avoid time loss. Over time, various indicators of degradation in plastics emerge, such as changes in molecular weight, cracking, and mechanical properties like strain at break and impact strength. Among these, color deterioration or change is a critical factor that helps evaluate the service life of these materials. Considering the increasing use of plastics in 3D printing today, and the growing focus on strength over aesthetics in these applications, it is particularly useful to evaluate aging in plastics based on the relationship between color and strength. The wide application of 3D printing in various industries necessitates understanding material properties under aging conditions. This study examines the effects of aging on the mechanical behavior of polylactic acid (PLA) with three different colors (yellow, orange, and red) and three different infill ratios (20%, 60%, and 100%). The samples underwent an accelerated aging process of 432 h, which included 8 h of UV radiation, 15 min of water spraying, followed by 3 h and 45 min with the UV lamps turned off. Tensile tests, bending tests, hardness measurements, and color evaluations were conducted on the samples, linking the color changes after aging with the materials' mechanical properties. The results show that after aging, yellow samples with a 100% infill ratio exhibited a 6.9% increase in tensile strength (44.50 MPa to 47.58 MPa). Orange samples with a 100% infill ratio were less affected by aging, while red samples experienced a decrease in tensile strength across all infill ratios. Regarding bending force, increases were observed in the orange, yellow, and red samples by 10.37%, 25.05%, and 8.87%, respectively. This study underscores the importance of color selection when designing 3D-printed materials for long-term applications.

The tensile behaviour of paper under high loading rates

This work deals with the strain-rate dependent characterization of paper under uniaxial tension at high strain-rates. Experiments were performed involving a Split Hopkinson bar for high strain-rate testing, comparing the results with conventional quasi-static tests. Tests were conducted in a strain-rate range between 0.0083 and 212 s−1, which is equivalent to testing velocities between 0.0003 and roughly 13.6 m/s. For the first time the change in tensile behaviour of paper is comprehensively characterized and modelled, using the Cowper-Symonds model for strain-rate hardening. The experimental tests showed that the tensile strength as well as the initial stiffness were gradually increasing with increasing strain-rate. The increase in tensile strength between the lowest and the highest strain-rate was 58% on average whereas the mean increase in stiffness between these two strain-rates was almost 115%. Regarding the fracture strain, it was observed that it significantly decreases with increasing strain-rate. While the average fracture strain of the quasi-static tests was at roughly 6% it was close to 3% for the dynamic tests. In case of the Split Hopkinson bar tests, high-speed videos of the samples were made to determine their elongation via target tracking and digital image correlation (DIC). We found that strain localization, which is a highly relevant mechanism for quasi-static tensile failure, is likely related to short term plastic creep of the material as strain localization nearly entirely disappears at high loading rates of paper.