Favorable Tensile Properties Research Articles

The Effects of Heat Inputs on LDSS 2101 GTAW and SMAW Weld Microstructure and Mechanical Behavior

The welding has been utilized to stabilize the phase fractions in the microstructure of lean duplex stainless steel (LDSS) to build massive mechanical structures. The influence of heat input on the microstructure, mechanical properties, and corrosion behavior of LDSS 2101 during the gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW) processes is investigated in the present work. Specifically, we compared the outcomes between low heat input (LHI) at 0.85 kJ/mm and high heat input (HHI) at 1.3 kJ/mm for both welding techniques. Throughout the welding process, ER2209 filler wire was utilized. To assess the microstructural changes in the weldments, we employed an optical microscope, a scanning electron microscope, and X-ray diffraction. The results revealed that the volume phase fraction of ferrite was significantly higher in the LHI sample of GTAW compared to HHI GTAW and all SMAW welds. LHI GTAW welds have 18.2% greater Charpy impact toughness than LHI SMAW, whereas HHI GTAW has 35.7% higher than HHI SMAW specimens. The microhardness of the LHI GTAW weldments increased (from 230 ± 3.2 to 252 ± 4.8 HV10), whereas the microhardness of the LHI SMAW weldments increased (from 227 ± 2.8 to 246 ± 5.2 HV10). GTAW exhibited a fine grain structure, showcasing favorable tensile properties and higher hardness compared to SMAW. Conversely, the SMAW welds and their heat-affected regions exhibited coarse grain structures. These findings highlight the superior performance of GTAW in terms of microstructural characteristics, and mechanical properties when working with LD SS 2101 in comparison to SMAW.

Microstructures and mechanical properties of additively manufactured T91 steel and T91/316H bimetallic components by laser powder bed fusion

Precise deposition of multiple materials by additive manufacturing (AM) has considerable potential for controlling the properties of materials. In this work, T91 martensitic steel with various process parameters was deposited on 316H steel fabricated by laser powder bed fusion (L-PBF), and the microstructure, mechanical properties, and corresponding defect formation of the T91 material were investigated based on the volumetric energy density (VED). This work studied the interface characteristics and properties of T91/316H bimetallic components with various process parameters to improve the performance of joint between martensitic and austenitic steels by AM. The presented results showed that the tensile strength and uniform elongation (UE) appeared to increase with the VED of the T91 materials. The ultimate tensile strength and UE of the T91 materials significantly decreased when the VED of the T91 materials approached 110 J, which was determined by the dramatic growth in defect number and defect size. Additionally, these bimetallic components obtained favorable tensile properties, exceeding those of the 316H sections, ascribed to solid solution strengthening at the interface. The 316H grains (γ) and the T91 grains (α) near the interface follow the K–S orientation relationship: {111}γ//{110}α, <110>γ//<111>α. The process parameters of the T91 sections obviously affected the tensile strength of these bimetallic components, as well as the molten pool morphology and mechanical properties of the 316H section near the interface.

Investigation of microstructures and high-temperature tensile behavior of heat treated GTD222 nickel-based superalloy prepared by selective laser melting

In this study, various heat treatment methods including direct aging and solution aging were performed on the selective laser melted (SLMed) GTD222 nickel-based superalloy, and the microstructures and high-temperature tensile behavior of the superalloys were systematically investigated. The results indicate that, in comparison to the as-deposited superalloy, both direct aging and solution aging lead to a significant enhancement in high-temperature strength and ductility. The directly aged superalloy exhibits a higher yield strength, while the solution-aged ones displays superior elongation. Specifically, at a tensile temperature of 760 °C, the superalloy subjected to a solution treatment at 1240 °C demonstrates the most favorable tensile properties, boasting a tensile strength of 835 MPa, an elongation rate of 6.5 %, and a reduction in area of 13 %. This study also provides a detailed discussion of the high temperature tensile behavior of the SLMed GTD222 superalloy after heat treatment.

Mechanical and Biological Evaluation of Melt-Electrowritten Polycaprolactone Scaffolds for Acetabular Labrum Restoration.

Repair or reconstruction of a degenerated or injured acetabular labrum is essential to the stability and health of the hip joint. Current methods for restoration fail to reproduce the structure and mechanical properties of the labrum. In this study, we characterized the structure and tensile mechanical properties of melt-electrowritten polycaprolactone scaffolds of varying architectures and assessed the labrum cell compatibility of selected graft candidates. Cell compatibility was assessed using immunofluorescence of the actin skeleton. First, labrum explants were co-cultured with scaffold specimen to investigate the scaffold compatibility with primary cells. Second, effects of pore size on pre-cultured seeded labrum cells were studied. Third, cell compatibility under dynamic stretching was examined. Grid-like structures showed favorable tensile properties with decreasing fibre spacing. Young's moduli ranging from 2.33 ± 0.34 to 13.36 ± 2.59 MPa were measured across all structures. Primary labrum cells were able to migrate from co-cultured labrum tissue specimens into the scaffold and grow in vitro. Incorporation of small-diameter-fibre and interfibre spacing improved cell distribution and cell spreading, whereas mechanical properties were only marginally affected. Wave-patterned constructs reproduced the non-linear elastic behaviour of native labrum tissue and, therefore, allowed for physiological cyclic tensile strain but showed decreased cell compatibility under dynamic loading. In conclusion, melt-electrowritten polycaprolactone scaffolds are promising candidates for labral grafts; however, further development is required to improve both the mechanical and biological compatibility.

Paper 02: ACL Reconstruction in Cutting and Pivoting Athletes: Soft Tissue Quadriceps Tendon Autograft vs. Bone-Patellar Tendon-Bone Autograft

Objectives:ACL reconstruction is one of the most common knee procedures performed annually in the United States. Athletes participating in cutting and pivoting sports are at high risk for ACL injury. In the general population, most graft choices including allograft, bone-patellar tendon-bone (BTB) autograft, hamstring autograft and quadriceps autograft have all been shown to excellent results following reconstruction. However, in the high-level cutting and pivoting athlete, the optimal graft for reconstruction remains controversial. Most consider BTB autograft to be the gold standard for such athletes. However, BTB autografts have drawbacks including anterior knee pain, difficulty kneeling and possible patellar fracture and patellar tendon rupture. Quadriceps autograft has increased in popularity since it offers a thicker graft with more favorable tensile properties compared to BTB and hamstring autografts. The quadriceps autograft has nearly twice the cross sectional area, higher load to failure and greater stiffness than the BTB autograft. Studies have shown equivalent outcomes when directly comparing BTB autograft vs. soft tissue quadriceps autograft in the general population. No studies have directly compared these two grafts in athletes participating in cutting and pivoting sports. We hypothesized that the quadriceps autograft would lead to similar patient outcomes, re-tear rates, return to sport and complications as BTB autografts in the cutting and pivoting athlete.Methods:A retrospective review of cutting and pivoting athletes with ACL tears treated with BTB autograft or soft tissue quadriceps autograft with at least 2 years of follow up was performed. Only athletes participating in cutting and pivoting sports were included in the study. Four sports were considered to be cutting and pivoting including soccer, football, lacrosse and basketball. The decision on which graft to use was based on the athlete’s choice after discussing the pros and cons of each graft. Exclusion criteria included those athletes with recurrent ACL tears, multiligamentous injuries, previous meniscal surgery and those requiring osteotomies. International Knee Documentation Committee Subjective Knee Evaluation (IKDC) and Lysholm knee scoring scale were used to evaluate patient reported outcomes. Through chart review, ability to return to sport, time to return to sport and complications were identified. The postoperative rehabilitation protocol for both grafts was identical.Results:There were 32 athletes in the soft tissue quadriceps autograft group and 36 in the BTB autograft group. The average age was 18.6 years for the quad group and 19.7 years for the BTB autograft group (p=0.63). Females made up 62.5% of the quadriceps group and 44.4% of the BTB group (p=0.14). The quad group was made up of 56.3% high school and 43.7% college athletes compared to 61.1% high school and 38.9% college athletes in the BTB autograft group (p=0.53). Soccer was the most common sport with 16 in the quad group and 14 in the BTB group. The rest of the quad group included 8 football players, 4 lacrosse and 4 basketball players. The remaining BTB group consisted of 12 football players, 8 lacrosse and 2 basketball players. Meniscal surgery was performed in combination with the ACL reconstruction in 17 (53.1%) of the quad group and 22 (61.1%) of the BTB autograft group (p=0.37). Average graft size was 9.5mm for the quad autograft group and 10 for the BTB autograft group. The 2-year IKDC score was 93.6 for the quad group and 95.1 for the BTB group (p=0.45). The 2 year Lysholm scores were 95.7 and 96.1 for the quad and BTB groups respectively. Return to play at the same or higher level was 90.6% in the quad group and 86.1% in the BTB autograft group (p=0.82). Time to return was also similar between the groups with 7.1 months for the quad group and 7.6 months for the BTB autograft group. There was 1 re-tear which required revision in the BTB group and no re-tears in the quad group (p=0.34). Arthrofibrosis requiring MUA and lysis of adhesions occurred in 2 quad autografts and 4 BTB autografts (p=0.49). One contralateral ACL rupture occurred in the quad autograft group and 4 in the BTB autograft group (p=0.21).Conclusions:The optimal ACL graft in high level athletes participating in cutting and pivoting sports remains in question. In our comparison of quadriceps autograft compared to BTB autograft in this athletic population, no difference in patient reported outcomes, return to sport or re-tear rates was identified. Based on these findings, quadriceps autograft is as effective as BTB autografts in cutting and pivoting athletes and should be part of the graft choice discussion with the athlete.

Effect of silicate modulus on tensile properties and microstructure of waterproof coating based on polymer and sodium silicate-activated GGBS

Abstract This paper investigated a novel and environmentally-friendly waterproof coating produced by the organic (i.e., styrene-acrylate copolymer) and inorganic (i.e., waterglass and ground granulated blast-furnace slag (GGBS)) compounds. The good cohesion of polymer and sodium silicate-activated GGBS can provide good mechanical properties, and this material also shows a better environmental benefit as no cement was used for coating. In this work, an appropriate proportion of polymer, waterglass and GGBS was given, and the effect of silicate modulus on the macro-performances and microstructures of the waterproof coating was studied. The optimal silicate modulus was 1.75, and the corresponding tensile strength and breaking elongation were 2.20 MPa and 90.48%, respectively. Furthermore, the waterproof coating also exhibited favorable tensile properties, flexibility or water impermeability after subjected to high temperature, alkali, water immersion, low temperature and high water pressure. This new waterproof coating exhibited the favorable tensile properties owing to (i) appropriate reaction rate, (ii) high degree of polymerization of C-S-H gel, (iii) high content of C-S-H gel and CaCO3 crystal, (iv) high reaction degree between emulsion and sodium silicate-activated GGBS, (v) nano-sized CaCO3 crystals and mechanical bond between the CaCO3 particles.

Facile preparation of medical segmented poly(ester-urethane) containing uniformly sized hard segments and phosphorylcholine groups for improved hemocompatibility.

In order to improve the hemocompatibility of durable medical-grade polyurethane, a novel series of segmented poly(ester-urethane)s containing uniformly sized hard segments and phosphorylcholine (PC) groups on the side chains (SPU-PCs) was prepared by a facile method. The 2-methacryloyloxyethyl phosphorylcholine (MPC) was first reacted with α-thioglycerol by Michael addition to give a diol compound (MPC-diol), then the SPU-PCs with various PC content were prepared by a one-step chain extension of the mixture of MPC-diol and poly(ε-caprolactone) diol (PCL-diol) with aliphatic diurethane diisocyanates (HBH). The chemical structures of MPC-diol and SPU-PCs were confirmed by 1H NMR and FT-IR, and the influences of PC content on the physicochemical properties of the SPU-PC films were studied. The introduction of PC groups enhanced the degree of micro-phase separation and improved the hydrolytic degradation of the films. Due to the denser hydrogen bonds formed in the uniformly sized hard segments, the films exhibited favorable tensile properties and a slow hydrolytic degradation rate. The results of water contact angle and XPS analysis indicated that the PC groups on the flexible side chains were concentrated on the surface after contact with water. The surface hemocompatibility of the films was evaluated by testing the protein adsorption and platelet adhesion, and the results revealed that the films surfaces could dramatically suppress the protein adsorption and platelet adhesion. The PC-containing polyurethane films possessed outstanding tensile properties, low degradation rate and good surface hemocompatibility, implying their great potential for use as long-term implant or blood-contacting devices.

End lateral extension path strategy for intersection in wire and arc additive manufactured 2319 aluminum alloy

Purpose Large-scale aircraft parts usually with many frame features, which consist of intersections. Profile and tensile properties of junctions in wire and arc additive manufacturing (WAAM) are significantly affected by path strategies. The purpose of this paper is to propose a novel path strategy for intersections in WAAM and compare it with commonly used ones. Design/methodology/approach Three typical intersections including T crossing (TC), square crossing (SC) and arbitrary-angle crossing (AAC) were built up with two commonly used path strategies (parallel and oscillation) and a proposed method named end lateral extension (ELE) which extends the weld track along the crossed direction. A robotic system and cold metal transfer (CMT) process were used to deposit Al-6.3Cu (2319) alloy. The profile of the bead was scanned by laser vision sensor. Tightened ratio (r), inter-layer height increment (Δh) and deviation to the fitting plane (df) are calculated based on the point cloud. Tensile tests were done for all built intersections. Findings Comparison to the commonly used path strategies, the proposed ELE method eliminated the tightened defects at the intersection, achieved a more stable inter-layer height increment (Δh) and improved the profile quality with a lower deviation to the fitting plane (df). Tensile tests show that the proposed strategy has exhibited favorable tensile properties. Originality/value In this paper, a novel path strategy named ELE is proposed, which provides a new path choice for fabricating intersections by WAAM.

Synergetic Toughening Effect of Carbon Nanotubes and β-Nucleating Agents on the Polypropylene Random Copolymer/Styrene-Ethylene-Butylene- Styrene Block Copolymer Blends.

Polypropylene random co-polymer (PPR)/styrene-ethylene-butylene-styrene (SBS) block copolymer blends with high toughness and favorable tensile properties were successfully obtained by blending with traces of multi-wall carbon nanotubes (MWCNTs) and β-nucleating agents (β-NAs). β-NAs can effectively induce the ductile β-form crystal in the PPR matrix. Although the addition of MWCNTs was reported to be only benefit for the tensile strength of PPR and relatively disadvantageous for the toughness, the obviously synergistic toughening effect in PPR/SBS blends was found when MWCNTs and β-NAs coexisted. The notched izod impact strength of PPR/30 wt % SBS blend with MWCNTs and β-NAs increased from 11.3 to 58.9 kJ/m2; more than 5-fold increment compared with pure PPR. Meanwhile, the tensile strength retention of this PPR blend is still above 72.2%. The micro-morphology indicated that the MWCNTs can act as bridges between SBS particle and PPR matrix, effectively transferring the stress and absorbing impact energy among SBS particles.

Highly stretchable strain sensor based on polyurethane substrate using hydrogen bond-assisted laminated structure for monitoring of tiny human motions

Strain sensors used as flexible and wearable electronic devices have improved prospects in the fields of artificial skin, robotics, human–machine interfaces, and healthcare. This work introduces a highly stretchable fiber-based strain sensor with a laminated structure made up of a graphene nanoplatelet layer and a carbon black/single-walled carbon nanotube synergetic conductive network layer. An ultrathin, flexible, and elastic two-layer polyurethane (PU) yarn substrate was successively deposited by a novel chemical bonding-based layered dip-coating process. These strain sensors demonstrated high stretchability (∼350%), little hysteresis, and long-term durability (over 2400 cycles) due to the favorable tensile properties of the PU substrate. The linearity of the strain sensor could reach an adjusted R-squared of 0.990 at 100% strain, which is better than most of the recently reported strain sensors. Meanwhile, the strain sensor exhibited good sensibility, rapid response, and a lower detection limit. The lower detection limit benefited from the hydrogen bond-assisted laminated structure and continuous conductive path. Finally, a series of experiments were carried out based on the special features of the PU strain sensor to show its capacity of detecting and monitoring tiny human motions.

Graphene/cyclodextrin-based nanocomposite hydrogel with enhanced strength and thermo-responsive ability

Dual crosslinked system has been proved to be an efficient method to obtain tough and high strength hydrogels. Herein, we synthesized a novel graphene oxide/p(acrylamide-co-poly(ethylene glycol) methyl ether methacrylate)/α-cyclodextrin (GO/P(AM-co-PEGMA)/CD) physical dual crosslinked hydrogel via copolymerization of AM and PEGMA in the α-CD/GO solution. The polymer main chains adsorb onto the GO surface resulting in the first crosslinked system and multiple hydrogen bonds between α-CDs that thread on the PEGMA side chains establish the second crosslinked system. The GO/P(AM-co-PEGMA)/CD hydrogel exhibits favorable tensile properties with fracture strain of 1800% and high fracture stress of 660kPa; in addition, the hydrogel can bear large compressive stress (2.7MPa) at strain of 85% without rupture. Furthermore, physical dual crosslinked system endows the GO/P(AM-co-PEGMA)/CD hydrogel with thermoplastic ability and thermo-responsive shape memory behavior. This facial one-pot method will contribute to design and application of high performance hydrogel.

Mechanically enhanced electrically conductive films from polymerization of 3,4‐ethylenedioxythiophene with wood microfibers

ABSTRACTThis study was aimed at enhancing the mechanical properties of poly(3,4‐ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT:PSS) using wood microfibers. Ultra fine friction grinding was conducted on wood particles to reduce their size to the micron scale and to induce fibrillation. Oxidative polymerization was performed on 3,4‐ethylenedioxythiophene (EDOT) monomer at seven dosages based on the content of microfibers in the formulation. The presence of PEDOT:PSS in the prepared films was verified by infrared spectroscopy and scanning electron microscopy. The composite films became stronger and stiffer as the fiber content increased. An EDOT:microfibers ratio of 33 wt % was considered the best among the seven tested levels, judging from their low sheet resistivity (340 Ω/sq.) and favorable tensile properties (38 MPa strength and 4.8 GPa stiffness). The selected films were also tested for their resistance to solvents to obtain information about their potential use in different environments. Among the tested solvents, sodium hydroxide greatly decreased the film conductivity. It also had the harshest effect on reducing the weight of the film. Findings from this study demonstrate the successful use of wood microfibers alternative to synthetic substrates and cellulose nanofiber as a supportive and reinforcing material for electrically conductive polymers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45127.

Effective design of new austenitic cast steels for ultra-high temperature automotive exhaust components through combined CALPHAD and experimental approaches

Designing engines with higher power densities to comply with ever increasing emissions and fuel economy regulations requires the development of cost-effective alloys with superior properties than existing high-performance alloys. A new class of Nb-bearing austenitic heat-resistant cast steels showed promise to withstand exhaust gas temperatures of as high as 1000°C. This paper describes the development of this new class of alloys using combined CALPHAD (CALculation of PHAse Diagrams) and experimental approaches to investigate the effect of C and N additions on the microstructure and tensile properties. Composition ranges were first established based on CALPHAD predictions to achieve the desired phases, and then four alloys of varying N/C ratios were cast and experimentally characterized to determine quantitatively the microstructure and mechanical properties. Microstructural characterization revealed that the NbC/Nb(C,N) phase transformed from “Chinese-script”, a mixed flake-blocky morphology to faceted-blocky morphology as the N/C ratio increased. The area fractions of the different phases were quantified and agreed favorably with the calculated results. Alloys with the “Chinese-script” NbC/Nb(C,N) showed favorable tensile properties at room temperature and 1000°C. Excessive δ-ferrite diminished the tensile resistance at 1000°C, while limited quantity of (Cr, Fe)23C6 did not show adverse effects.

Experimental study of friction taper plug welding for low alloy structure steel: Welding process, defects, microstructures and mechanical properties

A research investigation has been undertaken to identify the various stages and variation of welding parameters in friction taper plug welding (FTPW) process and to explore their effects on the performance and properties of the welds. According to the variation of axial force, the overall FTPW process is divided into feeding phase, pressing phase, welding phase, and forging phase. The rotating speed, welding force, and burn-off rate remain nearly constant in welding phase. However, the torque peaks in welding phase when after few seconds of welding force setting is reached. Rising the welding force would increase the peak torque, welding torque, and burn-off rate, but decrease the welding time. When improper welding parameter is used lack of bonding and incomplete filling defects would form within the weld. The microstructure of the weld metal is consist of retained austenite, pearlite, and various Widmanstätten ferrite. In heat affect zone, it is mainly of lathy upper bainite. Defect free welds exhibit favorable tensile properties of which 548.3MPa tensile strength and 27.5% elongation that equal to the base metal could be found.

Novel silica/poly(2,6-dimethyl-1,4-phenylene oxide) hybrid anion-exchange membranes for alkaline fuel cells: Effect of heat treatment

A series of silica/poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) anion exchange hybrid membranes are prepared. PPO is modified by bromination, hydroxylation and quaternization in sequence. Subsequent sol–gel reaction with monophenyl triethoxysilane (EPh) and tetraethoxysilane (TEOS), followed by heat treatment at 120–140 °C for different times, yields the hybrid membranes. Results show that the physico-chemical properties of the membranes, including ion exchange property, hydrophilicity, OH − conductivity and tensile property, can be easily controlled by adjusting the heating temperature and time. The membranes have proper conductivity (up to 0.0085 S/cm) and favorable tensile properties. The tensile strength (TS) can be higher than 20 MPa and the elongation at break ( E b) is in the range of 5.5–19.5%. Besides, the chemical stability in alkali conditions and thermal stability are comparable to those of anion-exchange membranes based on (partially) fluorinated-polymer. Hence, the hybrid membranes are suitable for potential application in alkaline fuel cells.

Successive epoxy and carbodiimide cross-linking of dermal sheep collagen

Cross-linking of dermal sheep collagen (N-DSC, T s=46°C, number of amine groups =31 (n/1000) ) with 1,4-butanediol diglycidyl ether (BDDGE) at pH 9.0 resulted in a material (BD90) with a high T s (69° C) , a decreased number of amine groups of 15 ( n/1000) and a high resistance towards collagenase and pronase degradation. Reaction of DSC with BDDGE at pH 4.5 yielded a material (BD45) with a T s of 64°C, hardly any reduction in amine groups and a lower stability towards enzymatic degradation as compared to BD90. The tensile strength of BD45 (9.2 MPa) was substantially improved as compared to N-DSC (2.4 MPa), whereas the elongation at break was reduced from 210 to 140%. BD90 had a tensile strength of 2.6 MPa and an elongation at break of only 93%. To improve the resistance to enzymes and to retain the favorable tensile properties, BD45 was post-treated with 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) in the presence of N-hydroxysuccinimide (NHS) to give BD45EN. Additional cross-linking via the formation of amide bonds took place as indicated by the T s of 81°C and the residual number of amine groups of 19 ( n/1000). BD45EN was stable during exposure to both collagenase and pronase solutions. The tensile properties (tensile strength 7.2 MPa, elongation at break 100%) were comparable to those of BD45 and glutaraldehyde treated controls (G-DSC). Acylation of the residual amine groups of BD45 with acetic acid N-hydroxysuccinimide ester (HAc-NHS) yielded BD45HAc with a large reduction in amine groups to 10 ( n/1000) and a small reduction in T s to 62°C. The stability towards enzymatic degradation was reduced, but the tensile properties were comparable to BD45.