Reduction In Tensile Strength Research Articles

In-situ study of microstructure and mechanical properties of GH3536 alloy manufactured by selective laser melting at 750 °C

Nickel-based GH3536 alloy exhibits high strength but low ductility when produced by selective laser melting (SLM), which hinders its widespread application in aerospace. This paper employed a ‘two-step’ method of heat treatment to optimize the microstructure of the SLM GH3536 alloy and investigated the mechanical properties. Tensile tests were conducted on SLM GH3536 alloy before and after heat treatment at 750 °C, using an in-situ high-temperature tensile stage. The relationship between the microstructural evolution and deformation behavior of the alloys was investigated by combining the in-situ tensile experiments and crystal plasticity finite element method (CPFEM). The results suggested that the elongation can be increased by 80% without a significant reduction in tensile strength. The improved elongation is attributed to the complete recrystallization, formation of annealed twins and serrated grain boundaries after heat treatment. The study also investigated the deformation behavior and fracture mode of the alloy before and after heat treatment. Discussion was done on the influence of the microstructure, particularly the twin and serrated grain boundaries on the alloy's plastic deformation. This study enhanced the understanding of plastic deformation of SLM GH3536 alloy and provided a valuable reference for the design and post-treatment of superalloy.

Smart and Green Packaging Made from Chitosan-based Biofilm with the Addition of Ginger Oil and Anthocyanins from Butterfly Pea Flower Extract (Clitoria Ternatea L)

A chitosan-based biofilm modified with ginger essential oil and butterfly flower extract has been made. This biofilm was tested for its potential as a raw material for smart and environmentally friendly packaging (smart and green packaging). The potential of biofilm as a packaging raw material is known from the characterization results, which include color changes at various pHs, mechanical properties, antioxidant properties, antibacterial properties, and morphological structure. The produced biofilms exhibit sensitivity to alterations in pH levels, manifesting distinct color transitions from pink and purple to green within the pH range of 1 to 12. This phenomenon arises due to adding butterfly flower extract into the biofilm, which contains anthocyanin dyes with a total concentration of 1113.3 mg/L. Adding butterfly flower extract and ginger oil contributes to an augmented biofilm thickness; however, this is accompanied by a reduction in both tensile strength and percent elongation. Concurrently, the addition of butterfly flower extract and ginger oil imparts antioxidant and antibacterial properties to the biofilm. The introduction of additional extracts enhances the antioxidant and antibacterial attributes of the biofilm. In the color and pH response assessment, the biofilm augmented with a 7.5% v/v extract exhibited a color difference value (ΔE) exceeding 5 across all assessed pH values. These findings signify the observable color variations in the biofilm due to pH fluctuations with the unaided eye. According to the outcomes of characterization and analysis, the produced biofilm holds promise as an environmentally friendly packaging solution due to its reliance on natural components and its endowed antioxidant and antibacterial properties, contributing to the prolonged preservation of packaged food items. Moreover, the biofilm demonstrates the capability to gauge the quality of food products based on their pH, which is evident through direct color alterations.

Effects of elevated temperature exposure on the mechanical properties of recycled fine aggregate concrete

ABSTRACT In this work, a compound waste material was made up of raw construction waste concrete, waste tiles, and waste bricks was mixed at a weight ratio of 6:3:1. They were ground into recycled fine aggregates (RFA). RFA substituted the local river sand in proportions of 0%, 30%, 50%, 70%, and 100% for preparing recycled fine aggregate concrete (RFAC) with varied water-to-cement ratios. It intended to explore concrete’s mechanical properties and ultrasonic pulse velocity changes before and after high temperatures (300–800°C). The loss on ignition (LOI) of concrete was simultaneously determined to compare the performance in resisting elevated temperature. Test results presented that the higher the replacement ratio of RFA, the gradually higher the reduction in the concrete splitting tensile, compressive, and residual compressive strengths and ultrasonic pulse velocity after elevated temperature exposure. A rapid reduction was especially found at the heated temperature of exceeding 440°C. Furthermore, the old cement paste adhered to the surface of the raw construction waste had a relatively higher LOI. This led to the consequence that the RFAC had an increased LOI with the increment of the RFA replacement ratio, while the LOI of RFAC dropped with the increment of the originally heated temperature.

Surface modification of poly (ethylene terephthalate) using imidazolium-based ionic liquids

Ionic liquids (ILs), with their unique characteristics, are widely known as new alternatives for solvents and catalysts used in various chemical reactions. Due to their extensive range of applications and environmental compatibility, they are suitable options for treating fibrous substrates. In this regard, this paper focuses on investigating the possibility of poly (ethylene terephthalate) surface modification via imidazolium-based ILs. Surface modification was carried out under different process conditions by varying the temperature and the catalyst. The possibility of treating samples in the IL solution for the second time was also examined. Moreover, the effect of the modification on the dyeing of polyester with disperse dye without carrier at 100 °C was studied. The samples’ wettability properties were investigated through several test methods by measuring vertical wicking height, wetting time, drop contact angle, surface resistivity and absorption of methylene blue dye. The chemical and physical changes of the modified samples were also evaluated via scanning electron microscopy images, Fourier-transform infrared spectroscopy (FTIR) spectra and mechanical tests. Results demonstrate that treatment with [BMIM]Cl and [BMIM]Br induces morphological changes on the fibre surface, creating grooves and voids. FTIR analysis and Methylene blue staining test confirm the formation of hydroxyl and carboxyl groups, enhancing the fabric's hydrophilicity and dyeability. Wettability tests reveal that increased water absorption leads to reduced electrical resistivity. Mechanical tests indicate a slight reduction in tensile strength attributed to surface roughness.

Effects of Heat Treatment on the Microstructure and Mechanical Properties of a Dual-Phase High-Entropy Alloy Fabricated via Laser Beam Power Bed Fusion.

To enhance the applicability of dual-phase high-entropy alloys (HEAs) like Fe32Cr33Ni29Al3Ti3, fabricated via laser beam power bed fusion (LB-PBF), a focus on improving their mechanical properties is essential. As part of this effort, heat treatment was explored. This study compares the microstructure and mechanical properties of the as-printed sample with those cooled in water after undergoing heat treatment at temperatures ranging from 1000 to 1200 °C for 1 h. Both pre- and post-treatment samples reveal a dual-phase microstructure comprising FCC and BCC phases. Although heat treatment led to a reduction in tensile and yield strength, it significantly increased ductility compared to the as-printed sample. This strength-ductility trade-off is related to changes in grain sizes with ultrafine grains enhancing strength and micron grains optimizing ductility, also influencing the content of FCC/BCC phases and dislocation density. In particular, the sample heat-treated at 1000 °C for 1 h and then water-cooled exhibited a better combination of strength and ductility, a yield strength of 790 MPa, and an elongation of 13%. This research offers innovative perspectives on crafting dual-phase HEA of Fe32Cr33Ni29Al3Ti3, allowing for tailorable microstructure and mechanical properties through a synergistic approach involving LB-PBF and heat treatment.

Load-Bearing Capacity of Bended FRP Reinforcement with Various Anchorage Lengths

The research builds upon the analysis of bent glass-fibre-reinforced-polymer reinforcement. The presented work focuses on examining the influence of anchor length on the overall tensile strength of bent FRP rebar. In general, to ensure secure anchoring of the reinforcement in concrete, it is necessary to determine a specific length of the straight section of the rebar beyond the bend, which prevents the reinforcement from being pulled out of the concrete. A total of 27 pieces of bent rebar were tested in the research and divided into four subgroups based on the anchor length beyond the bend. The reference value of the load-carrying capacity of the straight reinforcement was tested on four experimental samples. The research results confirmed that the reduction in tensile strength depends on the anchor length and suggest that the minimum anchorage length stated in the literature should be sufficient; exceeding it does not lead to a significant increase in the load-carrying capacity of the rebar. The research findings expand the Czech Republic’s design knowledge of FRP reinforcement and facilitate the resolution of subsequent phases of the project.

Environmentally Friendly Bleaching Process of the Cellulose Fibres Materials Using Ozone and Hydrogen Peroxide in the Gas Phase.

The paper presents the new eco-friendly method of bleaching process of the cellulose fibre materials. Cellulose materials were bleached using hydrogen peroxide (both in aqueous solution, vapours, ozone and by the combined action of gaseous hydrogen peroxide and ozone. The method using hydrogen peroxide in aqueous solution presents the standard procedure and was used as the comparison technique. The bleaching processes using gaseous oxidants were carried out in a prototype device for dry, low-temperature treatment of fibrous materials with the use of oxidising agents in the gas phase. The influence of the innovative gas-phase bleaching method on the cotton samples' properties was analysed by Scanning Electron Microscopy (SEM), evaluation of the colour and whiteness, assessment of the polymerisation degree (DP), analysis of the mechanical properties and sorption capacity as well as microbiological assessment against colonies of Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The comparison of the obtained results led to the conclusion that the bleaching processes using gas-phase agents-vaporised hydrogen peroxide, ozone or their combination-are non-invasive. The applied bleaching processes resulted in a slightly lower whiteness parameters than standard bath bleaching. After the bleaching processes with ozone and vaporised hydrogen peroxide separately, the decrease in the DP and tensile strength was similar to that observed after the bleaching with aqueous H2O2. When both processes were used together, a higher reduction in DP and tensile strength was noticed. Both oxidising agents showed a strong biocidal effect against bacteria. Gas-phase bleaching procedures, due to the lower temperature (35 °C vs. 98 °C) and minimal water consumption, have economic and environmental advantages, which allows their use in semi-industrial applications. It has been shown that the treatment of cotton fabrics using ozone and hydrogen peroxide in the gas phase allows to simultaneously obtain the bleaching and disinfection effect.

Studies on high power laser cladding Stellite 6 alloy coatings: Metallurgical quality and mechanical performances

The present study systematically investigates the effect of powder feeding rates (Vp) on the quality of Stellite 6 alloy coatings with a 20 kW fiber laser. The results demonstrate that the hot cracks in the Stellite 6 coatings can be effectively eliminated by increasing the Vp without preheating substrate or adding buffer layers. It is possible to achieve a single-track coating with a thickness of 2.34 mm, width of 20 mm and dilution rate of 17.3 % with crack-free and densely microstructure when Vp is 90 g/min. Moreover, the build rate (172 mm3/s) surpasses the maximum build rate (133 mm3/s) of low power laser cladding. The heat accumulation of multi-track and double-layer (5.6 mm) under high power laser results in the formation of ε-Co through phase transformation from part of γ-Co. Consequently, the dendrite region primarily consists of γ-Co while a small amount of ε-Co and Cr23C6 dominate in the inter-dendritic region. Although the heat accumulation effect also tends to coarsen the grains in bottom region of the coatings, leading to a slight reduction in mechanical properties, both hardness (485 HV–523 HV) and tensile strength (1131 MPa–1250 MPa) are comparable to those achieved by low power laser cladding, and the break elongation (6.9 %–8.1 %) has significantly surpassed the current level of 3 %. High power laser cladding processes may play a significant role in enhancing the effectiveness of surface modification or remanufacturing for large workpieces, such as the runner of hydroelectric generator set.

Mechanical Properties Characterization of Glass/Carbon Fiber Hybrid Multilayer Composite under Environmental Aging Condition

Metallic components in boating industry are being replaced with carbon fiber composites due to their light weight, excellent mechanical properties, and corrosion resistance. However, the carbon fiber cost has obstructed the substitution. Hybridization is suggested to merge carbon and glass fibers in cost-effective composites while maintaining the desired engineering properties. This study experimentally examines the impact of hybridization and seawater aging on the mechanical properties of glass and carbon fibers hybrid composites. A range of composites ([C]6, [CGC]s, [C]3[G]3, [GCG]s, and [G]6) are fabricated and aged in simulated seawater solution before their tensile, flexural, impact, and hardness properties are examined. The results revealed degradation in properties due to the ageing, the degree of degradation is influenced by the s hybridization configuration. The [G]6 sample shows the highest tensile strength reduction of 30% compared to 20% for the [C]6. The remaining samples exhibit reduction percentages falling between these two extremes. A similar behavior is observed in the flexural test, though the extremes values are smaller, 10.2%, and 12.5%. The impact and hardness tests showed an inverse relationship between the glass fiber content and impact strength degradation due to aging, while they exhibited a linear correlation for hardness degradation due to ageing.

Capacity assessment of uncorroded and corroded dapped‐end beams by NLFE and strut‐and‐tie based methods

AbstractThe verification of dapped‐end beams degraded by corrosion is a problem, especially for existing bridges in service. This paper proposes a nonlinear finite element (NLFE) modeling procedure and a simple strut‐and‐tie based procedure for predicting the response of dapped‐end beams subjected to chloride corrosion. Firstly, the finite element modeling strategy, based on the adoption of multilayer shell elements and the PARC_CL 2.1 crack model is described. Then, the degradation effects on concrete, rebars, and steel‐to‐concrete interaction are defined as a function of the propagation period of corrosion. In particular, the effects of corrosion on the reinforcement are modeled by applying a reduction of tensile strength that considers for both the reduction of cross‐section and the ultimate strain caused by pitting. Concrete splitting cracking due to volume expansion during rust formation is modeled by reducing the mechanical properties of concrete. Corrosion effects in steel‐to‐concrete interaction are modeled by applying a bond strength decay to the spring elements connecting corroded rebars—modeled with truss elements—and concrete multilayer shell elements. The proposed finite element procedure is used to study two scenarios based on different spatial distributions of corrosion‐prone areas. Subsequently, a simplified analytical approach based on the strut‐and‐corroded tie method—called S&CT method—is proposed and compared with the finite element outcomes. Finally, the validations of the two proposed methods are presented with respect to a corroded dapped‐end beam, showing that corrosion of rebars affects the resistance mechanisms of the dapped‐end beam, by reducing both resistance and ductility. The proposed simplified analytical S&CT method provides conservative and safe results compared to the numerical NLFE model and to experimental data.

Recycling Automotive Plastic Waste: Residual Polyvinyl Butyral (rPVB) as Solid Lubricant in Polyoxymethylene (POM) Blends

Polyoxymethylene (POM) is an engineering thermoplastic commonly used in tribological applications due to its low friction and auto-lubrication properties. To improve its performance further and broaden its applications to higher sliding speeds and loads, it is commonly reinforced with different particles, fibers, or solid lubricants. In this study, the effect of adding residual polyvinyl butyral (rPVB) from automotive windshields production lines on the tribological performance of POM during pin-on-disk wear tests at different loads (12, 15, and 18 N) and sliding speeds (0.25, 0.50, and 0.75 m/s) is investigated. It was found that rPVB acts as a solid lubricant, reducing the coefficient of friction (CoF) up to 50%. It is suggested that the formation of a protective layer of adhered material on the wear track is the mechanism behind CoF reduction. Melt flow index, Shore D hardness and elastic properties decrease linearly with rPVB content. However, the reduction in tensile strength, and thus shear strength of the blends, seems to be more significant on their CoF behavior than the reduction in hardness. No trend was found for wear resistance. Under certain sliding conditions rPVB decreased volume loss, but in other cases it increased it. It is suggested that, for the conditions analyzed in this study, adding 10 wt% of rPVB to a POM matrix results in the best balance of tribological performance, with an overall CoF reduction of 36%, and an average volume loss increase of only 1%.

Accelerated Weathering Testing (AWT) and Bacterial Biodegradation Effects on Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/Rapeseed Microfiber Biocomposites Properties.

In the context of sustainable materials, this study explores the effects of accelerated weathering testing and bacterial biodegradation on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/rapeseed microfiber biocomposites. Accelerated weathering, simulating outdoor environmental conditions, and bacterial biodegradation, representing natural degradation processes in soil, were employed to investigate the changes in the mechanical, thermal and morphological properties of these materials during its post-production life cycle. Attention was paid to the assessment of the change of structural, mechanical and calorimetric properties of alkali and N-methylmorpholine N-oxide (NMMO)-treated rapeseed microfiber (RS)-reinforced plasticized PHBV composites before and after accelerated weathering. Results revealed that accelerated weathering led to an increase in stiffness, but a reduction in tensile strength and elongation at break, of the investigated PHBV biocomposites. Additionally, during accelerated weathering, the crystallinity of PHBV biocomposites increased, especially in the presence of RS, due to both the hydrolytic degradation of the polymer matrix and the nucleating effect of the filler. It has been observed that an increase in PHBV crystallinity, determined by DSC measurements, correlates with the intensity ratio I1225/1180 obtained from FTIR-ATR data. The treatment of RS microfibers increased the biodegradation capability of the developed PHBV composites, especially in the case of chemically untreated RS. All the developed PHBV composites demonstrated faster biodegradation in comparison to neat PHBV matrix.

Durability assessment of GFRP bars embedded in UHP-ECCs subjected to an accelerated aging environment with sustained loading

Ultra high-performance engineered cementitious composites (UHP-ECCs) have garnered significant attention in the field of civil engineering primarily due to their exceptional tensile strain-hardening performance and excellent compressive strength. To further enhance their tensile strength, particularly in meeting the rigorous environmental and mechanical demands frequently encountered in marine environments, fiber-reinforced polymer (FRP) bars can be employed as the internal tensile reinforcement for UHP-ECCs (referred to as “FRP-UHP-ECC members”). While numerous studies have focused on the durability of FRP bars in concrete environments, the durability of FRP bars embedded within UHP-ECCs, especially with sustained loads, remains unexplored. Glass FRP bars are commonly utilized in civil engineering due to their cost-effectiveness and favorable mechanical properties. Therefore, this paper investigated the durability performance of GFRP bars made from three different matrix resins (i.e. epoxy, vinyl ester and polyester). These bars were centrally embedded in UHP-ECCs and subsequently immersed in alkaline solutions at elevated temperatures while under sustained loads. Their tensile properties over a specified period were evaluated after exposure. The test results revealed a larger degradation in polyester-based GFRP bars compared to vinyl ester-based and epoxy-based bars. In addition, GFRP bars with UHP-ECC covers exhibited less degradation than the bare bars, but this protective effect diminished under sustained loads. Scanning electron microscope (SEM) and X-ray computed tomography (CT) analysis demonstrated that the degradation of GFRP bars was primarily attributed to matrix hydrolysis, which led to a reduction in stress transfer efficiency between fibers, contributing to the tensile strength reduction in GFRP bars.

Precipitation and tensile behaviors of Allvac 718Plus superalloy during long-term thermal exposure

Allvac 718Plus alloy is a promising Ni-based superalloy with excellent thermal stability and mechanical properties up to 704 °C. The γ′ coarsening, σ precipitation and the resulting degraded tensile properties at room and elevated (704 °C) temperatures during long-term thermal exposure at 704 and 760 °C are systematically investigated in this work. The results showed that a higher exposure temperature and a longer exposure time significantly accelerate the γ′ coarsening and σ precipitation. The σ particles were detrimental to the alloy by acting as the preferential nucleation sites for cracks, and the reduction in tensile strengths was mainly caused by the increasing size of γ′ precipitates during thermal exposure. Furthermore, there were significant differences between the deformation mechanisms of room-temperature and elevated-temperature (760 °C) tensile tests. Concerning the deformation mechanism of γ-matrix, planar slipping dominates during tensile testing at room temperature, while the formation of stacking faults and microtwinning are primary during tensile testing at elevated temperature (760 °C). The dominant precipitation strengthening mechanism depended on the γ′ characteristics of different thermal exposure conditions and the tensile temperature. The 704 °C/100 h exposure sample shows a dislocation shearing mechanism when tested at room or elevated (760 °C) temperature. Notably, the 760 °C/1000 h exposure sample exhibits a mixed precipitation strengthening mechanism of Orowan bypassing and superlattice stacking faults shearing when tensile tested at room temperature while showing a dislocation and superlattice stacking faults shearing mechanism when tensile tested at elevated (760 °C) temperature.

Tailoring Multiple Strengthening Phases to Achieve Superior High-Temperature Strength in Cast Mg-RE-Ag Alloys.

Mg alloys with excellent high-temperature mechanical properties are urgently desired to meet the design requirements of new-generation aircraft. Herein, novel cast Mg-10Gd-2Y-0.4Zn-0.2Ca-0.5Zr-xAg alloys were designed and prepared according to the advantages of multi-component alloying. The SEM and XRD results revealed that the as-cast microstructures contained α-Mg grains, β, and Zr-containing phase. As Ag rose from 0 wt.% to 2.0 wt.%, the grain size was refined from 40.7 μm to 33.5 μm, and the β phase significantly increased. The TEM observations revealed that the nano-scaled γ' phase could be induced to precipitate in the α-Mg matrix by the addition of Ag. The stacking sequence of lamellar γ' phases is ABCA. The multiple strengthening phases, including β phase, γ' phases, and Zr-containing particles, were effectively tailored through alloying and synergistically enhanced the mechanical properties. The ultimate tensile strength increased from 154.0 ± 3.5 MPa to 231.0 ± 4.0 MPa at 548 K when Ag was added from 0 to 2.0 wt.%. Compared to the Ag-free alloy, the as-cast alloy containing 2.0 wt.% Ag exhibited a minor reduction in ultimate tensile strength (7.0 ± 4.0 MPa) from 498 K to 548 K. The excellent high-temperature performance of the newly developed Mg-RE-Ag alloy has great value in promoting the use of Mg alloys in aviation industries.

Tensile strength retention of glass fibre-reinforced stirrups subjected to aggressive solutions: effect of environmental condition, stirrup shape and stirrup diameter

The aim of this study was to examine how the tensile strength of glass fibre reinforced polymer stirrups is affected by different types of solutions, including alkaline, seawater, tap water, and acidic solutions. The study involved the production and testing of 260 stirrups in two different shapes (L and U) with diameters of 6 and 8 mm. The stirrups were immersed in different solutions for a period of 9 months at different temperatures (25, 40, and 60 °C). The findings indicated that the alkaline solution was the most aggressive environment, resulting in a maximum reduction of 92% in tensile strength after 9 months at 60 °C. Seawater and acidic solutions were the second and third most aggressive environments, causing maximum tensile strength reductions of 34 and 22% respectively, after 9 months at 60 °C. On the other hand, tap water was found to be the least aggressive environment, causing a maximum tensile strength reduction of 20% after 9 months at 60 °C. Furthermore, the study observed that the L-shaped stirrups exhibited slightly superior performance compared to the U-shaped stirrups. However, the diameter of the stirrups was found to be a negligible factor.

Heat-Treated Inconel 625 by Laser Powder Bed Fusion: Microstructure, Tensile Properties, and Residual Stress Evolution

This work investigates the impact of different heat treatments on the evolution of the microstructure, tensile properties, and residual stresses of Inconel 625 (IN625) processed by laser powder bed fusion (LPBF). Applying a heat treatment is an essential step to mitigate the high residual stresses in the components produced by LPBF and, simultaneously, to design the mechanical properties of the components. A high magnitude of residual stress can involve deformation and reduce the fatigue resistance of the components. In the current work, heat treatments performed at 600, 800, and 870 °C provided minimal modification on the dimensions of the grains but involved the formation of new phases, which increased the tensile strength. The results showed mitigation of the residual stresses at 800 and 870 °C correlated with the formation of Cr-rich M23C6 carbides and δ phases, respectively. Finally, the solution annealing at 1150 °C triggered recrystallization with the formation of sub-micrometric carbides, reducing the residual stresses. The solution annealing treatment involved an improvement of the ductility and a reduction in tensile strength. This work provides a guide to understanding the microstructure, residual stress, and mechanical properties evolution of the IN625 alloy under heat treatments.

The effect of heat input on weld-bead geometry, mechanical, phase transformation temperature, and corrosion properties of autogenous double pulse TIG welded nitinol sheets

This research aims to analyze the welding of 1 mm thick NiTinol sheets using an autogenous double pulse tungsten inert gas (DPTIG) welding process. The effect of heat input (HI) on bead geometry, microstructure, hardness, tensile strength, phase transformation temperature (PTT), and corrosion behavior was studied. The lower (111.25 J/mm), and higher (120.14 J/mm) HI produced an average grain size of 26 μm and 36 μm, respectively. The microstructure of the fusion zone (FZ) had coarser columnar grains with intermetallic phases such as Ni3Ti, and TiO2. The grain size in the FZ increased with the increase in HI. Sample P (111.25 J/mm) showed a higher hardness of 280.54 HV and tensile strength of 566 MPa due to a higher proportion of austenite phase (99.4%), the smaller grain size of 26 µm, a larger fraction of high angle grain boundary (HAGB) of 75.8%, and higher kernel average misorientation (KAM) value of 4.93. Compared to base metal (BM), sample P (111.25 J/mm), and sample S (120.14 J/mm) exhibited a reduction in tensile strength of 19.14% and 32.29%, respectively. The decline in hardness and tensile strength was attributed to the formation of intermetallic phases, a decrease in the Ti/Ni ratio, coarser grain formation, and a decrease in HAGB fraction and KAM values. The fractured tensile samples showed a mixed mode of fracture with dimples and cleavage facets. Compared to BM, Sample Q (118.05 J/mm) exhibited lesser variation in temperature hysteresis values for austenite and martensite temperatures, with a deviation of 0.4°C and 3.1°C, respectively. All the welded samples had better corrosion behavior than the BM due to a higher Ti/Ni ratio.

FDM Parameters Optimization for Improving Tensile Strength using Response Surface Methodology and Particle Swarm Optimization

Fused deposition modelling (FDM) is a popular 3D printing technique that uses a thermoplastic filament as the build material. In FDM 3D printing, tensile strength can be an issue because the layers of the object are built on top of each other, and if the layers do not adhere properly, the object can be weak and prone to breaking. Typically, this problem is caused by incorrect parameter settings. Hence, this study was then carried out to analyse and improve the printing quality in term of tensile strength of the printed part using the response surface methodology (RSM) and the particle swarm optimization (PSO) method. The effect of four input parameters such as layer height, printing speed, infill density, and print temperature was examined on the tensile strength of polylactic acid (PLA) standard samples ASTM D638-IV. The experimental design was performed using face-centred central composite designs (FCCD). The experimental data were statistically analysed to form a regression model of the tensile strength. This model was used to approximate the actual process. The optimization was performed using desirability analysis from RSM and PSO to search for the optimal parameter for maximum tensile strength. Experimental results showed that PSO outperformed RSM with a 1.52 % reduction in tensile strength. The maximum tensile strength obtained from PSO was about 39.069 MPa with the optimal process parameters of layer height of 0.30 mm, printing speed of 30.17 m/s, infill density of 79.72 %, and print temperature of 205.92 °C.

Circular production of recycled binder from fly ash-based geopolymer concrete

This paper presents an investigation into the potential of recycling fly ash - based geopolymer concrete, to produce a recycled binder for circular re – use as starting material. The aforementioned would be a significant advantage over Portland cement which is non – recyclable, owing to its irreversible hydration. The experiment conducted involved crushing and sieving old parent fly ash – based geopolymer concrete, to separate out the paste from aggregate. The paste was then pulverized using a ball – mill to produce the recycled aluminosilicate starting material, herein referred to as recycled geopolymer cement (RGPC). Fly ash was blended with 0 to 100% RGPC, then used to prepare fresh geopolymer paste and mortar mixtures activated using a binary alkali activator consisting of sodium hydroxide and sodium silicate. Samples were cast then cured at 23 or 80 °C. The various tests done were workability, setting time, compressive strength, splitting tensile strength, drying shrinkage, water absorption, and volume of permeable pores. Analytical studies were done using X – ray diffraction, scanning electron microscopy and Fourier – transform infrared spectroscopy. Results showed that incorporation of RGPC into geopolymer mixtures generally led to reduction of workability and setting time, reduction of compressive and tensile strength, along with increase in drying shrinkage. It was, however, found that up to 60% RGPC can be incorporated into geopolymer mixtures while maintaining adequate performance suitable for structural applications. Unlike Portland cement, hardened geopolymer concrete is evidently recyclable to produce a circularly re – usable binder.