Papers by Keyword: Tensile Deformation

Abstract: Aluminum-Iron-Silicon (Al-Fe-Si) alloys are extremely applied in many specific industries, such as aerospace and automobiles. Their atomic concentration influences the mechanical behavior of the investigated τ_4-Al₃Fe₂Si and τ_12-Al₃FeSi₂ phases. The uniaxial-tensile deformation is used to compare their structural evolution under the same conditions.Atomic displacement and mechanical behavior have an interest in the elastic and plastic areas. Stress-Strain responses and Radial Distribution Function (RDF) are required. Further, atomic simulations using molecular dynamics demonstrate the change occurs. Its process is carried out at a strain rate of 21×10¹⁰ s^-1 using the NPT (isothermal-isobaric) with roughly 20 700 atoms at a pressure of 10⁵ Pa. Furthermore, using a Nosée Hoover thermostat at the temperature of 300 k is decisive.The Modified Embedded Atoms Method (MEAM) is the applied potential between Al, Fe, and Si atoms. The elastic modulus and single pair atomic correlation before and after straining are increased by this method. The atomic correlations are shown in short- and long-range order and the τ₁₂-Al₃Fe₂Si phase illustrates stronger properties compared to τ_4-Al₃Fe₂Si phase. Our results underscore an important variation associated with the change of iron and silicon concentration. More specifics are covered in the selection paper.

Abstract: Low-density medium-manganese steels offer a vast development prospect for industrial application due to their outstanding combination of mechanical properties and density reduction. The microstructural evolution following tensile deformation of cold-rolled and annealed Fe-10Mn-10Al-0.7C steels was investigated by means of SEM and TEM microstructure analysis and XRD measurements. Annealing in the range of 700-1100 °C led to an austenite-ferrite dual-phase microstructure that was characterized by tensile strength of 700-1100 MPa and elongation of 6-34%. κ-carbides were observed in steels annealed at relatively low temperatures (700-850 °C). The steel exhibited the optimum combination of tensile strength of 930 MPa and elongation of 34% after annealing at 900 °C for 0.5 h. The stacking fault energy was estimated to be 69mJ/m2 considering the difference between average constituent and practical constituent of austenite caused by the high ferrite fraction. The deformed microstructures of the austenite exhibited the typical planer glide characteristics in sequence of dislocation array, Taylor lattice, Taylor lattice domain and microband. And the wavy glide occurs in ferrite was manifested by tangled dislocation and dislocation cells.

Abstract: Nanostructured Cu-Ag alloys with bimodal grain size distribution were prepared and their tensile deformation behaviors were studied. The alloys were processed by hot isostatic pressing of blends of nanoand micrometer-sized powder particles. The microstructure of the alloys consisted of nanograins with an average grain size of 40 nm and coarse-grains with an average grain size of 30 um. The bimodal structured alloy exhibited high tensile strengths 522 MPa and a large plastic strain to failure approximately 30%. Simultaneously, Their tensile stress-strain curves displayed a long work-hardening region, and their tensile ductility increased with increasing coarse-grained volume fraction. The high strength primarily results from the contribution of nanograins, while the enhanced ductility may be attributed to the improved strain hardening capability by the presence of coarse grains.

Abstract: Fe-based shape memory alloy (Fe-SMA) shows a shape memory effect (SME) governed by forward and reverse stress-induced martensitic transformation (SIMT). Fe-SMA has been applied to joints and dampers utilized at various strain rates. To utilize Fe-SMA better, it is necessary to understand the mechanical properties in a wide range of strain rate. In previous study, the results of a tensile test at various strain rates show a rate-sensitivity, however, the mechanism of rate-sensitive tensile deformation behavior is still unclear. Thus, a numerical simulation using a transformation kinetics model is needed to clarify the mechanism. Some transformation kinetics models have been proposed, however, the rate sensitivity cannot be included. In this study, the rate sensitivity of volume fraction martensite is considered into the transformation kinetics model as an improvement of the past-proposed model. The numerical simulation of the uniaxial tensile test at various strain rates is performed to reproduce transformation behavior of the martensite phase. Then, the model is validated by comparing to the experimental results. Afterwards, the mechanism of rate-sensitive tensile deformation behavior of Fe-SMA is discussed.

Abstract: Fe-based shape memory alloy (Fe-SMA) shows the smaller shape memory effect (SME) compared with the widely-used NiTi alloy. However, because its production cost is much lower than the NiTi alloy, Fe-SMA is challenged to be applied in civil engineering fields such as vibration absorbers and joints. A key of the SME is stress-induced martensitic transformation. Thus, it is important to evaluate an amount of martensite, which can control such excellent performance of Fe-SMA, for increasing a reliability of the Fe-SMA. However, until now, it is quite hard to find studies to evaluate the amount of martensite in Fe-SMA experimentally during deformation at various strain rates, especially during high speed deformation. Instead of the evaluation, it is convenient to capture change in volume resistivity, which has a correlation with the amount of martensite, at various strain rates. In the past, the volume fraction of α’ martensite is evaluated by using a resistance measurement based on the four point-probes method. The advantages of the method are quite simple and relatively high precision, however, its disadvantages are a requirement of strictly-precise reference resistor and power supply, and it is easily affected from noise. In this study, at first, a circuit of Kelvin double bridge with a higher precision is assembled. Then, the rate sensitivity of volume resistivity in Fe-28Mn-6Si-5Cr alloy, which is a kind of Fe-SMA, is experimentally estimated by using the assembled circuit of Kelvin double bridge during tensile testing at various strain rates.

Abstract: The paper presents results of in-situ neutron diffraction experiments aimed on monitoring the phase evolution and load distribution in transformation induced plasticity (TRIP) steel when subjected to tensile loading. Tensile deformation behaviour of two TRIP-assisted multiphase steel with slightly different microstructures resulted from different thermo-mechanical treatments applied was investigated by in-situ neutron diffraction. The steel with lower retained austenite volume fraction (f^γ=0.04) and higher volume fraction of needle-like bainite in the α-matrix exhibits higher yield stress (sample B, 600MPa) but considerably lower elongation in comparison to the steel with higher austenite volume fraction (f^γ=0.08), granular bainite and ferrite matrix (sample A, 500 MPa). The neutron diffraction results showed that the applied tensile load is redistributed at the yielding point in a way that the retained austenite bears a significantly larger load than the α-matrix during the TRIP steel deformation. Steel sample with higher volume fraction of retained austenite and less strong ferrite matrix proved to be a better TRIP steel with respect to strength, ductility and the side effect of the strain induced austenite-martensite transformation. The transforming retained austenite in time of loading provides potential for higher ductility of experimental TRIP steel but at the same time acts as a reinforcement phase during the further plastic deformation.TRIP steel, austenite conditioning, austenite transformation, structure, retained austenite, tensile deformation, neutron diffraction, load partitioning, mechanical properties.

Abstract: The dynamic strain aging (DSA) behavior of SA508-III steel was evaluated through tensile tests with different strain rates from 10^-4 to 10^-1s^-1 at 350°C. The OM, SEM and TEM were carried out to observe the microstructures and fracture morphologies of the steel. The results show that the serrated flows appear in the stress-strain curves when the strain rate is between 10^-3~10^-2s^-1, indicating that DSA occurs. Under the strain rate range, the tensile strength increases and the elongation and the reduction of area decrease. However, the fracture surface of the steel after tensile tests is still ductile. DSA in SA508-III steel at the strain rates from10^-3 to 10^-2s^-1 is mainly caused by the interaction between the internal solute atoms and dislocations, which leads to the dislocations multiplication and the formation of sub-grain boundaries and dislocation cell structure.

Abstract: A highly deformable composite composed of a network of electrically-conductive entangled carbon nanotubes embedded in elastic polyurethane for sensing tensile deformation by changes in strain has been prepared. The testing has shown that the composite can be extended as by much as 400 % during which the electrical resistance increases more than 270 times. The high strain sensing can be attributed to the network cracking upon extension. To understand the cracking mechanism and explain the resistance change, the structural changes of networks made of pristine carbon nanotubes (as well as functionalized multi-walled) were examined. The microscopic observation of crack formation and resistance change of the networks correlates well with the amount of cracking.

Abstract: Serrated flow has been observed in AZ81 alloy during tensile deformation. The observed static strain ageing effect and negative strain rate sensitivity suggest that the serrated flow is due to interaction between dislocations and solute atoms, know as dynamic strain ageing (DSA). The Portevin-Le Chatelier effect is observed at temperatures between 150oC~200oC and 125oC~200oC. In the microstructure of deformed samples dislocations and twins is observed. It is suggested that the occurrence of the dynamic strain aging is associated with interactions between solute atoms and dislocations.

Abstract: Microstructural features and tensile behaviors of an AZ31 alloy with Nd and La additions were investigated with elongation-to-failure tensile tests at constant temperatures of 300 °C, 350 °C, 400 °C, and 450 °C, and constant strain rates of 10^-2 s^-1 and 10^-3 s^-1. Experimental data show that the material exhibits tensile ductilities of over 100% at 450 °C, featured by long steady state deformation. Microstructure studies show that annealed coarse grains were remained in the gauge region after the tensile tests, and the dominate deformation mechanism was dislocation creep, other than dynamic recrystallization or grain boundary sliding. Cavity evolution near fracture end caused premature failure of the material, although fine grains developed through dynamic recrystallization.