Temperature Dependence Of Tensile Properties Research Articles

Atomistic simulation of temperature dependence of tensile properties and estimation of DBTT of Cu–Ag core–shell nanowires

An atomistic model of Cu-Ag core–shell nanowire using molecular dynamics is proposed. The simulation model was utilized for the evolution of temperature dependent (in the range of 10–500 K) tensile behavior and the identification of ductile-to-brittle transition temperature (DBTT) of single-crystal Cu-Ag core–shell nanowire. The evolution of defects such as point defects, dislocations, and stacking faults, arising from tensile deformation in the mentioned temperature rage were analyzed. The Wigner-Seitz Defect analysis, Dislocation analysis, and Common Neighbor analysis methods were implemented in this study to estimate the various defects concentration in the nanowire. The study identified that Cu-Ag core–shell (core diameter = 4 nm and shell thickness = 1 nm nanowire) exhibits DBTT somewhere in the temperature between 25 K to 30 K. The modulus of elasticity found to be increasing from 19.7 TPa at 10 K to 23.7 TPa at 30 K (within brittle regime), followed by a steep fall to 14.9 TPa at 500 K where fracture seems to be in ductile mode. The observed mechanical properties of the nanowire are discussed in the article in view of the dislocation and stacking faults generation in the core–shell nanostructures.

Behaviors of water molecules in polyvinyl alcohol gel amid stretch and temperature changes: A molecular dynamics study

Mechanical performance of polyvinyl alcohol (PVA) gel features temperature dependence, which is closely related to the behaviors of water molecules at the microscale. In this study, we use molecular dynamics simulation to study the effect of temperature on hydrogen bonding and tensile properties of PVA gel. By analyzing the states of water molecules in the polymer network, we reveal the mechanism behind the temperature dependence of tensile properties of PVA gel. Based on a method that classifies water into different states, we find that there are 3 states of water in PVA gel, including non-freezing water, freezing water, and free water. It is shown that the conversion of water molecules from bonded to free states is a critical behavior for the decline of tensile properties of PVA gel at elevated temperatures. Furthermore, we investigate the changes of hydrogen bond contents in PVA gel at different temperatures. The analyses show that increasing temperature decreases the content of hydrogen bonds between solvent water molecules and polymer chains, which destabilizes the cross-linking points and weakens the integrity of the gel, thereby degrading the mechanical properties of PVA gel. The mechanism behind the temperature dependence is revealed in this work.

Achieving high tensile strength-ductility synergy of a fully-lamellar structured near alpha titanium alloy at extra-low temperatures

The previous study has indicated that a near alpha titanium alloy of an equiaxed microstructure could hardly exhibit a desirable ductility at 20 K. This study aimed at achieving a promising balance of superhigh strength and excellent ductility of a Ti−3Al−3Mo−3Zr (wt%) alloy in cryogenic temperature field. Temperature dependence of tensile properties and deformation behavior was investigated systematically. It was found that the ultimate tensile strength (UTS) and elongation-to-fracture (EI) jumped from 730 MPa and 19.0% at 298 K to 1300 MPa and 23.0% at 77 K, respectively. Ultrahigh UTS up to 1600 MPa and an acceptable EI of 13.5% were achieved at 20 K. The ultrahigh UTS at 77 and 20 K was considered to be attributed to the sharp increase of CRSS of slip and the Hall-Petch effect of {101̅2}< 101̅1̅> twinning. The enhanced ductility at 77 K was owing to the improved strain hardening ability from large-scale twinning and prismatic and basal slips. Besides, a serrated plastic flow took place at 20 K, which was essentially because the intermittent start of twinning brought about alternate stress jump and cliff-like drop. A fully-lamellar microstructure is suggested to synchronously enhance the strength and ductility of a near-alpha titanium alloy at extra-low temperatures.

Temperature dependence of tensile properties and deformation behaviors of nickel-base superalloy M951G

Tensile behaviors of M951G alloy have been studied from 20°C to 1100°C. It shows that the higher W and Hf additions enhance the tensile strength of M951G alloy greatly compared to M951 alloy from RT to 800°C, which has been analyzed from the points of deformation microstructures, the strong effect of solid solution strengthening and precipitation strengthening in detail. The continuous stacking faults present in the microstructures at low temperatures, which have a significant influence on work hardening and rarely been reported in the traditional casting superalloy previously. The primary deformation mechanisms include shearing of the γ′ precipitates by a/2〈110〉 dislocations below 600°C and by-passing of γ′ precipitates by a/2〈110〉 matrix dislocations above 900°C. At intermediate temperatures, it shows a transition from shearing to by-passing. At last, the relationship between tensile properties and microstructures has been reasonably explained.

Characterization of high temperature tensile and creep–fatigue properties of Alloy 800H for intermediate heat exchanger components of (V)HTRs

Alloy 800H is considered as a candidate material for intermediate heat exchanger (IHX) components of (very) high temperature reactors (V)HTRs. Qualification of the this alloy for the aforementioned nuclear applications requires understanding of its high temperature tensile, low-cycle fatigue behavior and creep–fatigue interactions because the IHX components suffer from combined creep–fatigue loadings resulting from thermally induced strain cycles associated with start-up and shutdown cycles. To this end, in this paper, the tensile properties of the Alloy 800H base and tungsten inert gas (TIG) welded materials are studied at three different temperatures, room temperature 21, 700 and 800°C. Low cycle fatigue (LCF) behavior of the base material is investigated at 800°C with no-hold time (no-HT) and hold time (HT) to study creep–fatigue interactions. The tensile test results showed substantial differences between the strength and ductility properties of the base and weld materials at all 3 temperatures, however, the trends in temperature dependence of tensile properties are similar for both base and weld materials. LCF studies with no-HT and HT showed a strong influence of HT on the low cycle fatigue life of this alloy illustrating the substantial influence of creep mechanisms at 800°C. Finally, cumulative values of creep versus fatigue damage fractions are plotted in a creep–fatigue interaction diagram and these results are discussed with respect to the existing bi-linear damage summation curve for Alloy 800H in ASME Code Case N-47 in order to understand the synergetic effects of both the damage mechanisms.

Effect of Manganese on Microstructure and Mechanical Properties of Cast High Alloyed CrMnNi‐N Steels

The effect of the manganese content (0–11%) on the transformation temperatures, the mechanical properties and microstructure development of five highly alloyed 14Cr–XMn–6Ni cast stainless steels with 0.1% nitrogen was studied. The examinations reveal that the Ms, As, and Af temperatures decrease with increasing manganese contents. As a result of low austenite stability, room temperature austenitic‐martensitic as‐cast microstructure was formed at manganese contents between 0 and 3%. At manganese levels of 6% and higher a fully austenitic as‐cast microstructure was observed. The temperature dependence of tensile properties in alloys was explained on the basis of varying contributions to the strength and ductility of deformation‐induced martensite and twin formation mechanisms. All investigated cast steel alloys achieved yield strengths above 200 MPa at room temperature. The increased proof stress is caused by solid solution strengthening due to the addition of nitrogen and manganese as well as phase hardening by as‐quenched martensite.

Temperature Dependence of Tensile Properties and Fracture Behavior of Welded Joints of Titanium Matrix Composites in Gas Tungsten Arc Welding

Temperature Dependence of Tensile Properties and Fracture Behavior of Welded Joints of Titanium Matrix Composites in Gas Tungsten Arc Welding

Temperature dependence of tensile properties and fracture behavior of as rolled TiB/Ti composite sheet

In this paper, the tensile properties and fracture behavior of 7.5vol% TiB/Ti composite sheet were studied in the temperature range RT–900°C. The results show that the TiB/Ti composite sheet exhibits much higher ultimate strength in RT to 700°C temperature range compared to matrix alloy sheet while a comparable strength at temperature above 700°C. The ductility of the composite is much lower than that of the matrix alloy at all temperatures. The strengthening mechanism of the composite and strengthening effect of TiB varying with temperature are investigated. In addition, the softening behavior of the composite with the increasing temperature is discussed. Fractograph characteristic of the composite reveals that fracture of TiB whiskers followed by the ductile failure of the matrix is the main failure mechanism of the composite below 700°C while interfacial debonding dominates the fracture mechanism of the composite sheet above 700°C.

Effects of strain rate and temperature on tensile properties of CPVC pipe material

In this study, crosshead speed and temperature dependence of tensile properties of CPVC pipe material is investigated. Standard ASTM tensile specimens are used. Temperatures ranging from –10 to 70°C and three crosshead speeds (5, 50 and 500 mm min-1) are considered in the testing programme. The tensile test results showed that a reduction in temperature and an increase in crosshead speed have favoured brittle fracture. The yield stress and elastic modulus decreased logarithmically with decreasing crosshead speed and linearly with increasing temperature. The strain rate–temperature superposition held for both yield stress and modulus of elasticity and master curves were developed for both properties using a temperature based shift factor. A single power law relationship is developed between the shear strength and the shear modulus for all temperatures and strain rates. The value of fracture strain remained almost constant with crosshead speed at 50°C and below. At 70°C however, an enhancement of fracture strain occurred with increasing crosshead speed between 5 and 50 mm min-1 then stabilised with further increasing crosshead speed.

Mechanical Behavior of Oxide Dispersion Strengthened Steels Irradiated in JOYO

Oxide dispersion strengthened (ODS) steels, which are candidate materials for water-cooled solid breeder blankets, were fabricated with several manufacturing parameters, and then irradiated in the experimental fast reactor JOYO to evaluate their irradiation behavior. Engineering stress strain curves of ODS steels irradiated at 673 K exhibited superior material response, i.e., increased tensile strength due to irradiation hardening and no loss of total elongation. Also, their temperature dependence of tensile properties indicated that degradation of the tensile properties at elevated temperature, which is closely related to phase stability during irradiation, could be avoided due to optimal combination of manufacturing parameters, such as chemical composition, types of inert gas during mechanical alloying, heat-treatment temperature and initial phases of the matrix.

Brittle-to-ductile transition temperature and its strain rate sensitivity in a two-phase titanium aluminide with near lamellar microstructure

The temperature dependence of tensile properties of a two-phase titanium aluminide with nearly lamellar microstructure has been investigated and brittle-to-ductile transition (BDT) temperatures (TBDS) have been determined under different strain rates from 10−5 to 10−1 s−1. It is found that TBD rises with the increase of strain rate. From the positive strain rate sensitivity of TBD, the apparent activation energy of BDT is determined to be 324 kJ/mol by means of Zener-Hollomon factor. The determined activation energy approximates to the activation energies of self-diffusion of Ti atoms, and inter-diffusion of Ti and Al atoms in TiAl phase. The approximation, fractography analysis and theoretical calculation using the Nabarro Model add up to the speculation that the BDT of the alloy is controlled by dislocation climbing.

Brittle‐to‐ductile transition temperature and its controlling mechanism in ti‐47Al‐2Mn‐2Nb alloy†

Brittle‐to‐ductile transition (BDT) temperature (TBD) has been evaluated according to temperature dependence of tensile properties under different strain rates from 10‐5 to 10‐1 s‐1 in a two‐phase Ti‐47Al‐2Mn‐2Nb alloy with near lamellar microstructure. Tensile fractography was observed using a scanning electron microscope while deformation substructures were investigated using a transmission electron microscope. It was found that TBD, when defined as the temperature corresponding to 7.5% elongation, increases from 1023K to more than 1373K, the strain rate increases from 10‐5 to 10‐1 s‐1. Based on the strain rate dependence of TBD (and using the Zener‐Hollomon factor) an apparent activation energy of 324kJ/mol was obtained, which is approximate to the self‐ and inter‐diffusion activation energies in the y‐TiAl phase. Transgranular fracture and dimple fracture were found to dominate in fracture surfaces below and above TBd, respectively. Furthermore, the most popular 1/2<110] ordinary dislocations were found to begin to climb around TBD. All this evidence, as well as a theoretical calculation using the Nabarro Model, add up to a conclusion that the BDT of the alloy is controlled by dislocation climbing.

Cladding metallurgy and fracture behavior during reactivity-initiated accidents at high burnup

High-burnup fuel failure during a reactivity-initiated accident has been a subject of safety-related concern. Because of wide variations in cladding metallurgical and simulation test conditions, it has been difficult to understand the complex failure behavior observed in tests in the SPERT, NSRR and CABRI reactors. In this paper, we propose a failure model that is based on temperature-sensitive tensile properties and fracture toughness. The model assumes that dynamic fracture toughness and high-strain-rate tensile properties of high-burnup cladding are sensitive to temperature and exhibit ductile–brittle transition phenomena similar to those of bcc alloys. Significant effects of temperature and shape of the pulse are predicted when a simulated test is conducted near the cladding material's ductile–brittle transition temperature. Temperature dependence of tensile properties and fracture toughness is, in turn, sensitive to cladding microstructural characteristics such as density, distribution and orientation of hydrides; distribution of oxygen in the metallic phase; and irradiation-induced damage. Because all of these characteristics are strongly influenced by corrosion, the key parameters that influence susceptibility to failure are oxide layer thickness and hydriding behavior. Therefore, high-burnup fuel failure is predicted to be more sensitive to local cladding corrosion (e.g. grid span location) than to fuel burnup.

The Effects of Strain Rate and Minor Baron Addition on Brittle-to-Ductile Transition Temperature in Gamma TiAl Alloy

ABSTRACTBrittle-to-ductile transition (BDT) temperature (TBD) was evaluated according to temperature dependence of tensile properties under different strain rates from 10−5to 10−1s−1in two-phase Ti-47Al-2Mn-2Nb and Ti-47A1–2Mn-2Nb-0.8 TiB2alloys with nearly lamellar microstructure. Based on the strain rate dependence of the determined TBD values, apparent BDT activation energies were determined using Zener-Hollomon factor. Tensile fracture surfaces were observed using a scanning electron microscope while deformation substructures were investigated by transmission electron microscopy. It was found that the BDTT of both alloys increased sharply with the strain rate and that the minor addition of 0.8 vol% TiB2reduced TBD by about 100K at the same strain rate. The TiB2addition also decreases the apparent BDT activation energy from 324 to 256 kJ/mol. Both of these values approximate to self- or inter-diffusion of Ti and Al atoms in TiAl phase. Transgranular fracture and dimple fracture were found dominant in fracture surfaces below and above TBD, respectively. The most common 1/2&lt;110] ordinary dislocations were found to begin climb at mound TBD. All this evidence, as well as a theoretical calculation using the Nabarro Model, add up to a conclusion that the BDT is controlled by dislocation climb in both alloys.

オーステナイト系ステンレス鋼単結晶の作製とその諸特性

The single crystal austenitic stainless steels Type 316L and 304L were grown in order to improve the resistance to stress corrosion cracking (SCC) using a unidirectional solidification method which can provide the large size single crystals. The mechanical properties and the chemical properties were examined. The orientation and temperature dependence of tensile properties of the single crystals were measured. The yield stress of the single crystal steels are lower than those of the conventional polycrystal steels because of the grain boundary strength cannot be expected in the single crystal steels. The tensile properties of the single crystal austenitic stainless steel Type 316L depend strongly on the orientation. The tensile strength in 〈111〉 orientation are about 200 MPa higher than those in the 〈100〉 and 〈110〉 orientations. The microstructure of the single crystal consists of a mixture of the continuous γ-austenitic single crystal matrix and the δ-ferrite phase so that the effects of the γ⁄δ boundaries on the chemical properties were studied. The effects of the δ-ferrite phases and the γ⁄δ boundaries on the resistance to SCC were examined by the creviced bent beam test (CBB test). No crack is observed in all the CBB test specimens of the single crystals, even at the γ⁄δ boundaries. The behavior of the radiation induced segregation (RIS) at the γ⁄δ boundaries in the single crystal austenitic stainless steel Type 316L was evaluated by the electron irradiation test in the high voltage electron microscope (HVEM). The depletion of oversized solute chromium at the γ⁄δ boundary in the single crystal austenitic stainless steel Type 316L is remarkably lower than that at the grain boundary in the polycrystalline-type 316L.

Temperature Dependence of the Tensile Behavior of Cast and Extruded Al&amp;ndash;7Si&amp;ndash;0.3Mg Alloys in 213&amp;ndash;673 K

The temperature dependence of tensile properties of an A356 cast alloy is studied. The solution-treated, natural aged and peak aged specimens of the A356 cast alloy have been tensile tested in the temperature range of 213-673 K at the strain rate of 5.7 x 10 -4 s -1 . The data are also compared with that of extruded A356 specimens, in which more uniform silicon particles distribution is achieved. Independent of the particle distribution, both the cast alloy and the extruded alloy show a similar temperature dependence of tensile properties, implying that the tensile properties of the cast alloy are mainly determined by the precipitation of Mg 2 Si. At temperatures below about 573 K, the yield stress of the solution-treated cast specimens increases, while that of the peak aged specimens decreases gradually with increasing temperature. The yield stress of the natural aged specimens is nearly temperature independent. Corresponding to the high yield stress regime, the elongation of the solution-treated and natural aged specimens decreases drastically. At higher temperature at which dissolution of Mg 2 Si occurs, softening and recovery of the ductility are observed in all the specimens. On the temperature regime of about 223-373 K, the solution-treated specimens exhibit the Portevin-LeChatelier effect which is dependent on the concentration of vacancies and solute atoms. Since both vacancies and solute atoms are depleted during aging, the flow instability is absent in all aged specimens.

Ａｌ‐Ｌｉ‐Ｍｇ合金の極低温における機械的性質の温度依存性

Temperature dependence of tensile properties and fracture morphorogy were investigated in the temperature range from 7 to 293K for the as-quenched and peak-aged specimens of Al-2 mass%Li-0, 1, 2 mass%Mg alloys. The increase in the proof stress with decreasing temperature in the as-quenched specimens was explained in terms of the short-range interactions between dislocations and the solute atoms, whereas the small temperature dependence of the proof stress in the peak-aged specimens was explained in terms of the long range interactions between dislocations and δ'-Al3Li precipitates. Constant tensile strength at very low temperatures (<-40K) was due to the grain boundary fracture. The increase in both the elongation to fracture and toughness defined as the work done for fracture with decreasing temperature to about 20K was attributed to the increasing difficultes of cross slip of dislocations as temperature decreased for an Al-Li binary alloy. The decrease in both the properties with decreasing temperature was due to both the acceleration of intergranular fracture and the increase in strain hardening with decreasing temperature. Magnesium addition to Al-Li alloys enhanced both the intergranular fracture and strain hardening, which resulted in the decrease in elongation and toughness with decreasing temperature.

Temperature dependence of tensile properties of composites consisting of carbon fiber tow in thermosetting polymers

Temperature dependence of tensile properties of composites consisting of carbon fiber tow in thermosetting polymers

Elevated Temperature Tensile Properties of Weld-Deposited Austenitic Stainless Steels

Trend curves describing the temperature dependence of tensile properties have been formulated for several weld-deposited austenitic stainless steels and also for wrought Type 304. Ratios of elevated-temperature properties to room-temperature properties were fitted to polynomial expressions in temperature by regression analysis. Represented in the study were eleven weldments, four weld processes, and five weld metal alloys. Trend curves were established for 308/308L, CRE 308, and 16-8-2 compositions as well as for all the weld metal data. The results showed that the degree of correlation between predicted and observed properties was dependent upon variations in weld process and parameters but that the ratio trend curve approach yielded a useful degree of correlation of the elevated-temperature properties even without considering all the complex features of the weld-deposited materials.