Slight Decrease In Mechanical Properties Research Articles

Design of Heterogeneous Lamella Microstructure of 316L Austenitic Stainless Steel and Effect of Aging on Its Mechanical Behavior and Corrosion Properties

316L austenitic stainless steel (ASS) with a heterogeneous structure exhibits favorable mechanical properties at room temperature, promising excellent application potential. However, the thermal stability of 316L ASS with heterogeneous lamella structure (HLS) has not been adequately addressed yet. Herein, an HLS of 316L ASS is fabricated through 78% cold rolling followed by annealing at 750 °C for 13 min. The detailed investigation focuses on the influence of microstructure evolution on the mechanical properties and corrosion resistance of the alloy after aging at temperatures ranging from 350 to 550 °C for 100 h. The results show that a notable quantity of residual martensite persists even after annealing at high temperatures for a brief duration. The dislocation density of the test steel is reduced after long‐term aging treatment, and the residual martensite is further reversed into austenite during aging. In addition, the aging treatment also promotes further growth of nanocrystalline/ultrafine‐grained, which weakens the heterogeneous characteristics of HLS 316L ASS, resulting in a slight decrease in mechanical properties. However, the decrease in defect density and the enhancement of recrystallization degree are beneficial for eliminating most of the corrosion‐sensitive areas in the cold‐deformed structure, thereby improving the corrosion resistance.

Investigation of Microstructures and Tensile Properties of 316L Stainless Steel Fabricated via Laser Powder Bed Fusion.

In this study, a thorough investigation of the microstructures and tensile properties of 316L stainless steel fabricated via laser powder bed fusion (L-PBF) was done. 316L stainless steel specimens with two different thicknesses of 1.5 mm and 4.0 mm fabricated under similar conditions were utilized. Microstructural characterization was performed using optical microscopy (OM) and scanning electron microscopy (SEM) equipped with electron backscatter diffraction (EBSD). Melt pools and cellular structures were observed using OM, whereas EBSD was utilized to obtain the grain size, grain boundary characteristics, and crystallographic texture. The 1.5 mm thick sample demonstrated a yield strength (YS) of 538.42 MPa, ultimate tensile strength (UTS) of 606.47 MPa, and elongation to failure of 69.88%, whereas the 4.0 mm thick sample had a YS of 551.21 MPa, UTS of 619.58 MPa, and elongation to failure of 73.66%. These results demonstrated a slight decrease in mechanical properties with decreasing thickness, with a 2.4% reduction in YS, 2.1% reduction in UTS, and 5.8% reduction in elongation to failure. In addition to other microstructural features, the cellular structures were observed to be the major contributors to the high mechanical properties. Using the inverse pole figure (IPF) maps, both thicknesses depicted a crystallographic texture of {001} <101> in their as-built state. However, when subjected to tensile loads, texture transitions to {111} <001> and {111} <011> were observed for the 1.5 mm and 4.0 mm samples, respectively. Additionally, EBSD analysis revealed the pre-existence of high-density dislocation networks and a high fraction of low-angle grain boundaries. Interestingly, twinning was observed, suggesting that the plastic deformation occurred through dislocation gliding and deformation twinning.

Recent Developments of Nano Flame Retardants for Unsaturated Polyester Resin.

For many years, efforts have been made to reduce the flammability of unsaturated polyester resins (UPRs), which are often used in the rail, shipbuilding, and construction industries. Without modification, they often fail to meet fire safety standards. Despite a rich history of flame retardants (FRs) applied to UPRs, researchers seek new solutions that will provide lower flammability and smoke density, as well as attaining a lower environmental impact from the composites. The objective of the study is to highlight the most important recent research on promising nano FRs in order to promote their further development. Mechanisms of action of several groups of nano FRs, such as clay-based, carbon-based, transition metal compounds, layered double hydroxides, polyhedral oligomeric silsesquioxanes, and others, including bio-based, have been studied. Particular emphasis has been laid on nano FRs applied to UPRs, and their influences on thermal stability, flammability, and mechanical properties. Moreover, the environmental impact and toxicity of nano FRs have been discussed. Results have proved that nano FRs applied at low loadings may significantly improve thermal stability, with a simultaneous increase or only a slight decrease in mechanical properties. However, attention on related environmental issues has highlighted the necessity of carefully selecting novel nano FRs.

Microstructure, mechanical properties and thermal stability of Al2O3/Al2O3 ceramic matrix composites obtained from submicron-sized powers

Improvement in thermal stability is especially important for the oxide/oxide composites, which are widely applied at high temperatures. Herein, the continuous alumina fiber reinforced alumina matrix (Al2O3/Al2O3) composites were fabricated at 1200–1400 °C using Al2O3 powders with a mean size of 0.6 μm. The Al2O3/Al2O3 composite fabricated at 1300 °C achieved a high flexural strength of 392.9 ± 20.1 MPa and a high interlaminar shear strength of 20.6 ± 1.0 MPa. After exposure at 1000 °C for 100 h and 1400 °C for 10 min, the 1300 °C fabricated Al2O3/Al2O3 composite showed no significant reduction in mechanical properties. A slight decrease in mechanical properties was observed after aging at 1200 °C for 100 h. The high strength retention after the heat treatment benefited from the coarse Al2O3 powders, which could not be easily sintered at high temperatures. This work can expand the selection of the Al2O3/Al2O3 composites for potential applications at service temperatures as high as 1400 °C for a short term.

Maraging steel powder recycling effect on the tensile and fatigue behavior of parts produced through the laser powder bed fusion (L-PBF) process

Additive manufacturing (AM) has advanced the manufacturing industry and has been employed in a wide range of industrial applications, including aerospace, automotive, medical, and die-casting equipment. To ensure the cost-effectiveness of the AM process, unfused powder must be recycled even if its characteristics may change after each cycle, making essential the validation of powder quality and component mechanical performances. Despite the research published to date, predicting the mechanical performance of printed parts issued from reused powder remains challenging since it is dependent on many AM process variables. Until now, no research has looked at the impact of powder recycling on the fatigue behavior of maraging steel components. This study investigates the impact of maraging steel powder reuse on powder characteristics, as well as on the tensile and fatigue properties of printed components. Our results indicate that the powder particle size distribution increased after eight powder reuses, particle morphology showed the presence of aggregates, broken particles, and shattered and deformed particles, while powder apparent density remained constant. Powder reusing had no significant impact on the surface roughness of as-built specimens. Although there was a slight decrease in mechanical properties over reuse cycles, tensile and fatigue performance remained globally stable, while the standard deviation of fatigue stress became narrower after eight cycles. Finally, fractography revealed that the fatigue fracture surfaces of components manufactured from an eight-time recycled powder have more fusion defects and carbon inclusions than the parts made from virgin powder.

"OPTIMIZATION OF ENZYMATIC DESIZING AND SCOURING OF COTTON FABRIC BY RESPONSE SURFACE METHODOLOGY"

"The study aimed to estimate the influence of temperature, time, and ultrasound application during desizing and scouring of cotton with -amylase and pectinase, respectively, on the weight loss, breaking force and color difference between raw and bio-scoured cotton, to obtain purified and hydrophilic cotton, with a simultaneous slight decrease in mechanical properties. Under the optimal conditions, determined by the application of Response Surface Methodology (time – 30 min, temperature – 59.4 °C, with ultrasound treatment), a weight loss of 4.97%, color difference of 3.86, and a breaking force of 730.22N were obtained. The bio-scoured cotton fabric was also characterized in terms of electrokinetic and sorption properties, chemical composition and morphology of the cotton surface by zeta-potential measurement, wicking and contact angle determination, FTIR and SEM characterization, respectively. The developed enzymatic scouring process leads to obtaining purified, whiter and hydrophilic cotton, with slight changes in mechanical properties, which makes bio-scoured cotton fabric suitable for further wet processing."

Structures and properties of polyimide fibers prepared via gel spinning induced by chemical imidization

A series of 3,3′,4,4′-biphenyldianhydride (BPDA)/p-phenylene diamine (PDA) polyimide (PI) fibers were prepared through a novel gel spinning method induced by chemical imidization. The effects of draft ratios, solvent content and thermal treatment temperature on the aggregation structure and properties of PI fibers in the gel spinning were systematically investigated by experiment and molecular dynamics (MD) simulation. The mechanical properties of the fibers are significantly improved with increasing draft ratio due to the development of the molecular orientation along the fiber direction during large-ratio drafting process. The MD simulation results indicate that the nascent gel fiber with more solvent content has larger interchain space and weaker interchain interaction and molecular chains tend to be arranged along the drafting direction. The highly oriented PI fibers are completely imidized after thermal treatment at 320 °C, reaching the optimum tensile strength of 1.43 GPa and modulus of 121 GPa. The surface and internal defects of the highly oriented PI fiber gradually increased with increasing the thermal treatment temperature, resulting in a slight decrease in mechanical properties. In a word, the fiber orientation is carried out before the thermal imidization in the gel spinning process, which can greatly increase fiber draft ratio and reduce the subsequent thermal treatment temperature and energy consumption.

Characterization of Ecofriendly Poly (Vinyl Alcohol) and Green Banana Peel Filler (GBPF) Reinforced Bio-Films

With an intention to replace the synthetic non-biodegradable films in packaging applications, the polyvinyl alcohol (PVA) blended with green banana peel filler (GBPF), the biodegradable films were prepared by solution casting method with varying the concentrations of GBPF (5–25 wt%) in PVA matrix. The bio films were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermo gravimetric analysis, transmissibility, FESEM, tensile test, film solubility and water absorption, water vapour transmission (WVT), soil burial test. Based on results obtained, the changes evidenced in the FTIR spectrum of this PVA/GBPF biofilms suggest that strong hydrogen bonding is taking place due to interfacial exchanges of GBPF in PVA matrix. The XRD results showed that crystallinity of bio films are greater than PVA. Thermo gravimetric analyses predicted that PVA/GBPF bio films are thermally stable up to 300 °C. The light is 45% for transmittance in the visible light region for the PVA/GBPF (25 wt%) bio film. The FESEM micrographs of biofilms palpable that formation of good physical interaction and compatibility between polymer matrix and GBPF up to 20 wt% of GBPF in PVA Matrix. FESEM results also confirmed that higher loading of GBPF (25 wt%) in PVA matrix, observed voids and agglomerations in film surface. The PVA/GBPF bio films with 20% of GBPF gave the highest tensile strength and young’s modulus 44.5 MPa and 66.7 GPA respectively compared to other samples. The elongation at break decreases with increases the GBPF in PVA Matrix up to 20 wt%.The slight decrease in mechanical properties perceived due to higher loading of GBPF (25 wt%) with PVA matrix. The solubility, water absorption and WVT of the PVA/GBPF bio films increased upon increasing the GBPF content. The biodegradation test results discovered that he highest weight loss at 42.3% (25 wt% of GBPF) probably due to the hydrophilic nature of GBPF in PVA matrix. On the whole, the present investigation confirmed that the PVA/GBPF bio films potential for possible utilization in active packaging applications attributable to its better mechanical, thermal, optical, water absorption and biodegradation properties.

Infl uence of Na+-montmorillonite modifi ed with acrylamide on the structure and properties of polypropylene

Sodium form montmorillonite was obtained from natural clay from the Gerpegezh deposit (Kabardino-Balkarian Republic, Russia). A procedure has been developed for modifying the sodium form of montmorillonite using acrylamide. The structure of the organoclay was confi rmed by IR spectroscopy. Composites based on polypropylene and modifi ed montmorillonite are obtained by melt mixing on a twin-screw extruder from JiangsuXindaScience &amp; Technology. The structure of the obtained composites was investigated using X-ray diff raction analysis and scanning electron microscopy. The results of testing the obtained composites, which were used to evaluate the physical and mechanical properties, are presented: the melt fl ow index, impact strength according to Izod, modulus of elasticity, ultimate strength and elongation at break. ICompared to unfi lled polypropylene, polymer composites with 3 wt.% organoclay are shown to increase: impact strength by 31.61% (without notch) and 12.8% (with notch of 5 mm); modulus of elasticity in bending by 8.3%; tensile modulus by 10,3%. When polypropylene is fi lled with 5 wt.% organoclay, the composites show increased: impact strength by 12.60% (without notch) and by 10.52% (with an notch of 5 mm); the modulus of elasticity in bending and tension are the same as in the previous case. A further increase in the content of organoclay to 7 wt.% leads to a slight decrease in mechanical properties. Acrylamide can be used as a modifi er of organic clay; it is easily accessible and cheap, used in large-scale production. The resulting composites can be used as structural materials.

Mechanical properties, microstructure and grain orientation of hot pressed WB2 ceramics with Co as a sintering additive

Abstract Tungsten diboride (WB 2 ) ceramics were hot pressed using Co as a sintering additive at relatively low temperatures ( 2 ceramics. With the addition of Co into the WB 2 matrix, the densification of WB 2 ceramic could be achieved with a high relative density of 92.144% at a temperature of 1500 °C. The sample also exhibited excellent mechanical properties with the flexural strength of 512.7 ± 43.5 MPa, Vickers hardness of 22.4 ± 1.0 GPa and fracture toughness of 4.9 ± 0.3 MPa m 1/2 . The effects of sintering temperature and Co content on the densification, mechanical properties and microstructure development of the ceramic composites were systematically investigated. It suggested that the samples demonstrated a dramatic improvement and then a slight decrease in mechanical properties with the increasing temperature. Additionally, the mechanical properties of the samples decreased gradually with the increase in the mass fraction of Co. Based on the XRD and EDS analysis, Co reacts with WB 2 to form binary and ternary phases during the sintering process, contributing to the densification to a large extent. Besides, the formation of Co 2 B and W 3 CoB 3 also strengthened the binding force at grain boundaries, resulting in the high strength of the samples. Crack propagation path evolved from tortuous to straight with the increasing Co addition, indicating the fracture toughness of the samples decreased gradually. Additionally, the fracture behaviours and toughening mechanisms of the Co-doped WB 2 ceramic composites were also discussed. It is noteworthy that the hot pressed composites exhibited an anisotropy structure to some extent, and the growth and alignment mechanism of hexagonal WB 2 grains was illustrated in this paper.

Microstructural and mechanical property evolutions of shape memory polyurethane during a thermodynamic cycle

ABSTRACTTo better understand the shape memory behaviors of synthesized shape memory polyurethane (SMPU) sealant with a tailored transition temperature (Tt) for concrete pavement joints, the thermal and dynamic mechanical properties of SMPU were first characterized to determine the shape memory switching temperature of SMPU. Then the microstructural and mechanical property evolutions of SMPU in the original, programmed, and recovered states during a five‐step thermodynamic cycle were discussed, respectively. The results indicate that the tailored Tt of prepared SMPU can be used as the shape memory switching temperature to match its working temperature. Further, the programming causes the phase separation in SMPU, leading to an obvious anisotropy. The SMPU has satisfactory shape memory performance. The orientation of molecular chains in soft segments is confirmed along the stretching direction. The oriented molecular chains can restore to the naturally curled state during the free recovery. Finally, the programming improves the mechanical properties of SMPU. The recovered SMPU shows a slight decrease in mechanical properties because of the partially impaired crystal structures and broken molecular segments during the programming and recovery. It is concluded that the synthesized SMPU with the specially tailored Tt is suitable to use as a sealant of concrete pavement joints. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45703.

Development of high radiation-resistant glass fiber reinforced plastics with cyanate-based resin for superconducting magnet systems

Glass fiber reinforced plastics (GFRPs) with cyanate ester resin/epoxy resin, bismaleimide resin/epoxy resin, and bismaleimide-triazine resin as matrices were developed for the superconducting magnet systems used in high intensity accelerators. The radiation resistance of these GFRPs was evaluated based on their gas evolution and changes in their mechanical properties after gamma-ray irradiation with dose of 100MGy in vacuum at ambient temperature. After irradiation, a small amount of gas was evolved from all of the GFRPs, and a slight decrease in mechanical properties was observed compared with the conventional epoxy resin-GFRP, G10. Among the GFRPs, the smallest amount of gas (6×10−5mol/g) was evolved from the GFRP with the bismaleimide-triazine resin, which also retained more than 88% of its flexural strength after 100 MGy irradiation; this GFRP is thus considered the most promising material for superconducting magnet systems.

Styrene-Butadiene Rubber/Graphene Nanocomposites: Effect of Co-Milling with Cyclic Butylene-Terephthalate

Graphene nanoplatelets (GnP) reinforced styrene-butadiene rubber (SBR) nanocomposites were produced by two different methods. For reference purpose carbon black (CB) reinforced formulations served. In the first method the components were mixed on a two roll open mill directly. In the second method, GnP was subjected to milling in an attritor mill together with cyclic butylene-terephthalate oligomer (CBT) powder prior to the mixing on two roll mill. Samples were cured in a hot press. The rubber sheets were characterized by tensile and tear tests, and their fracture surfaces inspected in scanning electron microscopy (SEM). Results showed that GnP outperformed CB with respect to reinforcing effect. Previous co-milling of GnP with CBT caused a slight decrease in mechanical properties. SEM images proved, that the co-milling process did not affect significantly the dispersion of GnP, its particles were shredded into smaller pieces, which caused the slight decrease in the mechanical properties.

Fabrication of chelating diethylenetriaminated pan micro and nano fibers for heavy metal removal

In this study, commercial acrylic fibers were modified with diethylenetriamine to prepare metal chelating fibers. The effects of process parameters on the efficiency of the reaction were investigated. FTIR spectroscopy and TGA analysis were used to confirm the chemical changes made to the fibers during the reaction. The ability of the modified fibers for removal of Pb (II), Cu (II) and Ce (IV) ions from aqueous media was determined. The modified fibers showed a slight decrease in mechanical properties compared to raw ones. Furthermore, the acrylic micro fibers were electrospun to nanofibers and the ability of modified nanofibers for the adsorption of the metal ions was studied.

Sintering and Mechanical Properties of AISI M2 High-Speed Steel Powder Molded at Low Pressures

Low compaction pressures of powders result in low die wear, less power consumption and high production rate. The present study aims to investigate compaction, vacuum sintering, and mechanical behavior of AISI M2 high speed steel (HSS) powder cold molded at relatively low pressures (98–392 Mpa). It was found that sintered density rised with compaction pressure, time, and temperature. Full density was achieved in the specimens compacted at 392 Mpa and sintered for 60 min at temperatures between 1250 and 1260°C. Hardness and transverse rupture strength increased to ∼36 HRC and ∼1700 MPa with rising density. The fully dense samples exhibited a slight decrease in mechanical properties with increasing temperature owing to M6C carbide coarsening. X-ray diffraction indicated that M6C (major carbide phase) content in the alloy increased drastically as a result of sintering. It was demonstrated that compaction at a low pressure of 392 MPa could yield high mechanical properties (∼65 HRC and ∼2000 Mpa) in the heat-treated M2 HSS alloy.

Acrylic bone cements

Acrylic bone cements are in extensive use in joint replacement surgery. They are weight bearing and load transferring in the bone-cement-prosthesis complex and therefore, inter alia, their mechanical properties are deemed to be crucial for the overall outcome. In spite of adequate preclinical test results according to the current specifications (ISO, ASTM), cements with inferior clinical results have appeared on the market. The aim of this study was to investigate whether it is possible to predict the long term clinical performance of acrylic bone cement on the basis of mechanical in vitro testing. We performed in vitro quasistatic testing of cement after aging in different media and at different temperatures for up to 5 years. Dynamic creep testing and testing of retrieved cement were also performed. Testing under dry conditions, as required in current standards, always gave higher values for mechanical properties than did storage and testing under more physiological conditions. We could demonstrate a continuous increase in mechanical properties when testing in air, while testing in water resulted in a slight decrease in mechanical properties after 1 week and then levelled out. Palacos bone cement showed a higher creep than CMW3G and the retrieved Boneloc specimens showed a higher creep than retrieved Palacos. The strength of a bone cement develops more slowly than the apparent high initial setting rate indicates and there are changes in mechanical properties over a period of five years. The effect of water absorption is important for the physical properties but the mechanical changes caused by physical aging are still present after immersion in water. The established standards are in need of more clinically relevant test methods and their associated requirements need better definition. We recommend that testing of bone cements should be performed after extended aging under simulated physiological conditions. Simple quasistatic and dynamic creep tests seem unable to predict clinical performance of acrylic bone cements when the products under test are chemically very similar. However, such testing might be clinically relevant if the cements exhibit substantial differences.

Effect of Carbon Nanofiber Heat Treatment on Physical Properties of Polymeric Nanocomposites—Part I

The definition of a nanocomposite material has broadened significantly to encompass a large variety of systems made of dissimilar components and mixed at the nanometer scale. The properties of nanocomposite materials also depend on the morphology, crystallinity, and interfacial characteristics of the individual constituents. In the current work, vapor-grown carbon nanofibers were subjected to varying heat-treatment temperatures. The strength of adhesion between the nanofiber and an epoxy (thermoset) matrix was characterized by the flexural strength and modulus. Heat treatment to 1800C∘demonstrated maximum improvement in mechanical properties over that of the neat resin, while heat-treatment to higher temperatures demonstrated a slight decrease in mechanical properties likely due to the elimination of potential bonding sites caused by the elimination of the truncated edges of the graphene layers. Both the electrical and thermal properties of the resulting nanocomposites increased in conjunction with the increasing heat-treatment temperature.

Novel polyimides withp-nitrophenyl pendant groups. Synthesis and characterization

Polyimides derived from a new dianhydride with p-nitrophenyl pendant groups have been synthesized and their properties compared with those of a reference series, without side groups. The polymers were obtained by combination of the novel monomer with aromatic diamines, in a two-step procedure that involved the synthesis of poly(amic acid) or poly(amic silyl ester) intermediates and the cyclization of them to polyimides by thermal treatment. The introduction of the polar nitro groups caused significant increase of the Tgs. On the contrary, the thermal stability was reduced because of the breakdown of CAr—NO2 linkages around 400oC. A slight decrease in mechanical properties was observed, due to the bulkiness of the side groups, that also produced an important decrease in the strength of the β relaxation, as determined by dynamic mechanical analysis. The solubility of the current polyimides in organic solvents was as poor as that of the parent unsubstituted polymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3377–3384, 1999