Natural fiber composites are gaining popularity in various fields such as aerospace, automotive, and interior design due to their biodegradability, cost-effectiveness, and wide availability. Hybrid ...composites, which utilize both natural and synthetic fibers as reinforcement, are becoming more prevalent due to the desirable properties of each. Natural fibers possess strong damping properties and are biodegradable, while synthetic fibers have good elastic modulus. This research aimed to investigate the mechanical properties of bamboo and carbon fiber reinforced hybrid composites through tensile, flexural, and Izod tests. Hybrid composites exhibited 74.53% higher tensile strengths, 41.47% higher flexural strengths, and 182.24% higher impact strength than bamboo fiber reinforced composites. Carbon fiber reinforced composites had superior mechanical properties compared to hybrid and bamboo fiber reinforced composites, especially in terms of tensile and flexural characteristics. The study concludes that combining natural and synthetic fibers leads to composite materials with acceptable mechanical performance.
•The prediction of the onset of rupture of austenitic stainless steel during a forming process has been carried out.•The fracture behavior of AISI 304L stainless steel, tensile and Erichsen tests ...were performed.•A 3D numerical simulation via Abaqus/Standard was used.•Four ductile fracture criteria are used to predict rupture during the Erichsen test.
The present study focuses upon the numerical investigation of fracture initiation of austenitic stainless steel, AISI 304L, during a forming process leading to an expansion strain path. Hence, a combined experimental and numerical approach was tested. Monotonic tensile tests up to fracture were carried out. Load-extensometer displacement curves and a major strain distribution were measured. Numerical simulations of the tensile test up to rupture were carried out to calibrate damage parameters of several macroscopic fracture criteria.
Numerical simulations of the Erichsen test were also carried out to verify the validity of the determined parameters of the ductile fracture criteria. The numerical predictions of the strain field, the onset of fracture, and the fracture location were compared with the experimental results. The simulation results show that the Rice-Tracey or Brozzo fracture criteria are reliable predictors of the onset of fracture of AISI 304L in the Erichsen test. More precisely, the Rice-Tracey criterion is the most effective to predict the ductile fracture in this case.
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•Self-healing plant-based epoxy-ionic liquid blends were prepared.•A reversible bonding is formed between the epoxy resin and ionic liquid.•Self-healed samples retained ca. 42 % and ...53 % of their TS and EB.
In this study, self-healing in a plant-based bioepoxy resin has been reported by incorporating reversible ionic groups in the networks of epoxy resin using a simple blending process with ionic liquid. The interaction between the hydroxyl groups in epoxy resin and ionic groups in ionic liquids was reversible. Such material with reversible reactive bonds was expected to show instantaneous self-healing of minor cracks. To study the self-healing efficacy of the system, tensile and nanoindentation tests were performed. The tensile measurements reported the retention of mechanical properties after the reassembling of ionic clusters due to self-healing. It was observed that the self-healed samples retained ca. 42 % and 53 % of their tensile strength and elongation at break. Furthermore, nanoindentation repairing studies were carried out by making a nanoindentation mark on the prepared samples and measuring the needed time to undertake autonomous self-healing. Interestingly, the self-healing was initiated immediately (<3 sec) after the nanoindentation, although with scarring. The complete self-healing of the damage was observed after 48 h. Thus, the modified samples showed improved self-healing under nanoindentation test conditions. Further, studies were conducted to understand the thermal, morphological, and physical properties of the prepared blend. All these studies prove that the prepared blend is a promising material in application areas such as flexible indoor coatings.
Stress relaxation, which occurs during holding at the bottom dead center in press forming, affects press formability. Because holding at the bottom dead center is completed within several seconds, it ...is important to predict the stress relaxation behavior of the first few seconds after the start of holding. The purpose of this study is to propose a model, the material parameters of which are obtained from tensile tests, to predict the stress decreasing behavior in the early stage of stress relaxation in steel sheets. We constructed the model by modifying the Kocks-Mecking model based on the following assumptions: Stress relaxation at room temperature is due to the slip motion of dislocations, which indicates that the plastic strain rates at the start of stress relaxation are same as those in the previous tensile process. In this study, it was assumed that the change in microstructure during stress relaxation is negligible; hence material parameters remain constant during stress relaxation. The measured and predicted stress relaxation behaviors for various strain rates during the tensile process were compared. It was observed that an increase in the plastic strain rate during the tensile process accelerated stress relaxation. The proposed model was able to predict this phenomenon. However, the relative error between experimental results and the model increased as the stress relaxation progressed mainly owing to dynamic strain aging. Therefore, the proposed model is applicable in the condition when effect of dynamic strain aging is negligible.
Free-standing microtensile specimens were extracted from the substrate and the interdiffusion zone of a MCrAlY coated nickel-based single-crystal superalloy. Testing of these specimens was conducted ...at elevated temperatures, up to 1100°C under controlled atmosphere, to assess the tensile and thermal expansion properties of the interdiffusion zone materials. These properties were measured and found to lie between the properties of the substrate and those of the coating. The poor mechanical strength of the interdiffusion zone evidenced its non-load bearing contribution to the system for uniaxial creep loading at high temperature representative of service conditions. It was also shown that the fabrication process of MCrAlY coated nickel-based superalloy affects the mechanical properties of the system due to the presence of voids and non-adherent grit-blasting particles within the interdiffusion zone.
•Local tensile and thermal expansion properties of a coated system are measured.•The interdiffusion (ID.) weakens the local tensile properties of the substrate.•Voids and grit-blasting particles are highly present in the interdiffusion zone.•Voids and grit-blasting particles favor the early fracture of the ID. zone.
Gas Tungsten arc welding (GTAW) process was employed for welding of Inconel 718 with two different shielding gases, namely argon (Ar) and argon with a 5 vol% hydrogen mixture (ArH) and two fillers ...viz., ERNiCrMo-10 and ERNiCrMo-4. The effects of gas composition and filler wires on the laves phase formation were studied in detail. The results revealed that hydrogen addition through ArH shielding gas mixture resulted in better grain refinement in the welds than pure Ar. The hydrogen addition induced a steep thermal gradient in the weld, which lowered the segregation of elements like Niobium (Nb) and Molybdenum (Mo) at the interdendritic regions. The laves phase formation in Mo-rich filler addition welds was minimized due to restriction of Nb segregation by Mo at the interdendritic region. Tensile test results indicated that the strength and ductility of the joints of both autogenous and filler added welds of Ar were higher than the ArH shielded welds. In the case of filler added welds, higher Mo content filler exhibited better tensile properties in both shielding gas combinations due to solid solution strengthening of Mo. Nano-sized hydrogen assisted cracks observed in ArH autogenous welds caused a reduction of strength and ductility.
•The gas mixture of Ar (95%) plus H2 (5%) with Mo rich fillers was employed for welding of Inconel 718.•Hydrogen addition induced steep temperature gradient in weld; thus the size of the laves phase got reduced.•Autogenous weld exhibited low tensile strength due to hydrogen assisted cracking.•Molybdenum addition improves the tensile properties of welds.
Nowadays, adhesively bonded joints are frequently employed in engineering designs as they enable the manufacture of joints with great strength while remaining light. These joints used in aviation ...sectors, where lightness and reliability are important, are generally designed to join metal-metal, metal-composite and composite-composite adherends. The surface roughness of the adherends with its degree and the way the adhesive interacts with the surface are the most crucial parameters in these applications. In the current work, surface roughness and normal stress strength of nano-composite adhesive in butt joint subjected to tensile loading were investigated. DP460 liquid structural epoxy from 3 M was used as adhesive, AA2024-T3 aluminum alloy as adherend, Graphene-COOH and Carbon Nanotube-COOH as nanostructures while sandpaper and sandblasting methods were used for introducing roughness to the adherend surfaces. A two dimensional axisymmetric FE model was developed to get an insight about the joint failure. When the failure load obtained from experiments was examined, an increasing trend in maximum force values was noticed with an increase in surface roughness, but this increase in joint strength decreased when the surface roughness increased to very high values. In addition, minimum surface roughness reduces the adhesive's adhesion to the surface, thus reducing the normal stress strength of the joint. When 1 % Graphene-COOH nanostructure was added to the adhesive, the ultimate normal stress of the joints increased from 9 % to 21 %. However, when the same percentage of Carbon Nanotube-COOH was added, the increase was from 27 % to 62 %. Different normal stress values of the joints were obtained using by sanding and sandblasting methods even though the roughness resulting from the two treatments was similar.
The quenching and partitioning steels have received much attention because of the material's high strength and good ductility, which results from deformation-induced martensitic transformation. To ...investigate the strain rate and temperature dependence of martensitic transformation and flow behavior, we conducted interrupted uniaxial tension tests and X-ray diffraction. The experiments covered a wide range of strain rate and six ambient temperatures conditions, which are in accordance with conditions encountered in sheet metal forming and car crash process. Based on the martensitic phase transformation behavior and newly proposed heat balance equation, a modified transformation kinetics law was proposed to describe both the thermal effect and positive effect of strain rate on deformation-induced martensitic transformation. The new model reproduces the martensitic phase transformation behavior of quenching and partitioning sheet steels for a wide range of strain rate and temperature conditions well.
Class II malocclusion is one of the most common dental anomalies and the use of intermaxillary elastomers is the standard method in its treatment. However, orthodontic elastics cannot exert ...continuous force over a period of time due to force degradation. Our goal was to mechanically characterize the different types of elastomers during static and cyclic loads, based on uniform methodology and examine the morphological changes after loading. Ten types of latex-containing and four latex-free intermaxillary elastics were examined from six different manufacturers. To determine the mechanical characteristics of the elastomers, tensile tests, cyclical tensile fatigue tests and 24 h relaxation tests were performed, and the elastics were also subjected to scanning electron microscopy (SEM) and Raman spectroscopy. Regardless of the manufacturer, the latex-containing elastomers did not show significant differences in the percentage of elongation at break during the tensile test. Only one type of latex-containing elastomer did not tear during the 24 h cyclical fatigue test. Fatigue was confirmed by electron microscopy images, and the pulling force reduced significantly. During the force relaxation test, only one latex-free ligature was torn; the force degradation was between 7.8% and 20.3% for latex ligatures and between 29.6% and 40.1% for latex-free elastomers. The results showed that dynamic loading was more damaging to ligatures than static loading, latex-containing elastomers were more resistant than latex-free elastics, and which observation could have clinical consequences or a potential effect on patient outcome.
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