Tensile Deformation Behavior Research Articles

Molecular dynamics simulation of tensile deformation behavior of single-crystal Fe–Cr–Al before and after irradiation

Molecular dynamics simulation of tensile deformation behavior of single-crystal Fe–Cr–Al before and after irradiation

Hot tensile deformation behavior and a fracture damage model of the wrought Mg–Gd−Y–Zn–Zr alloy

The hot deformation behavior of the wrought Mg–Gd−Y–Zn–Zr alloy was studied by uniaxial tensile tests conducted at various temperatures (350–500 °C) and strain rates (0.1–0.0001s−1). Furthermore, the effects of the deformation parameter on the true stress−strain curves, microstructure, fracture characteristics, and fracture mechanisms were discussed, and a damage model for predicting fracture strain was established. The results are as follows. The increasing temperature or the decreasing strain rate reduce the peak stress and increase the fracture strain, except for 500 °C/0.0001s−1. The increasing in the fracture strain is attributed to the easier activation of multi−slip, the smaller size of broken 14H−LPSO during deformation, the higher fraction of fine grain generated by DRX. The β phase around the grain boundary will gradually disappear with the decrease of strain rate at high temperature (450 °C and 500 °C), which will cause DRXed−grain coarsening. Especially the alloy deformed at 500 °C/0.0001s−1, the grains are significantly coarsened. Thus, the fracture strain of the alloy deformed at 500 °C/0.0001s−1 is not greater than that of the alloy deformed at 500 °C/0.001s−1. The fracture morphology changes from the coexistence of cleavage surfaces and dimple to dimple with increasing deformation temperature and decreasing strain rate. In addition, the fracture damage predicted using the fracture damage model agreed well with the experimental results, with a maximum relative error of only 8.8%.

An atomistic study of the newly-developed single-phase refractory high entropy alloy of TiZrVMo: Defect accumulation and evolution under tensile deformation

For the very first time, novel refractory high entropy alloys (RHEAs) of the Ti-Zr-V-Mo system with a single bcc solid solution structure have been predicted and confirmed by molecular dynamics, resulting in twelve new compositions with a single bcc structure here. For the equiatomic RHEA of TiZrVMo specifically, the tensile deformation behavior and underlying mechanism were studied by molecular dynamic simulations. Except for the dislocation toughening and stacking fault formation, the simulation revealed that the bcc to fcc and hcp phase transformation occurred during the plastic deformation of the RHEA, which was also reversible after the tensile failure. This work provides a solid theoretical reference for the composition design and ductility understanding for the development of RHEAs in practical applications.

Tensile Behavior, Constitutive Model, and Deformation Mechanisms of MarBN Steel at Various Temperatures and Strain Rates.

To reduce harmful gas emission and improve the operational efficiency, advanced ultra-supercritical power plants put forward higher requirements on the high temperature mechanical properties of applied materials. In this paper, the tensile behavior and deformation mechanisms of MarBN steel are discussed at different strain rates (5 × 10-3 s-1, 5 × 10-4 s-1, and 5 × 10-5 s-1) under room temperature and 630 °C. The results show that the tensile behavior of the alloy is dependent on temperature and strain rate, which derived from the balance between the average dislocation velocity and dislocation density. Furthermore, observed dynamic recrystallized grains under severe deformation reveal the existence of dynamic recovery at 630 °C, which increases the elongation compared to room temperature. Finally, three typical constitutive equations are used to quantitatively describe the tensile deformation behavior of MarBN steel under different strain rates and temperatures. Meanwhile, the constitutive model of flow stress for MarBN steel is developed based on the hyperbolic sine law.

Response Features of Silk Warp Yarns during Weaving

ABSTRACT Raw, undegummed organzine, and degummed organzine mulberry warp silk yarns were subjected to cyclic loading on tensile testing instrument by simulating the conditions of the loom during weaving. Minimum and maximum load for these cyclic loading were designated based on the theoretical base tension on the warp yarns and maximum tension at beat-up process. The speed of cyclic loading was attuned to match with the speed of the conventional power loom. The stress-strain curves of the yarns were analyzed and the deformation behavior was investigated with respect to yield point, maximum load, elongation, and energy. The response of silk warp yarn to fatigue developed during weaving due to its tensile deformation behavior was studied at the fabric formation stage. All the three warp yarns exhibited significant deformation during weaving. Cyclic loading had resulted in modification of the tensile deformation characteristics of the three different types of mulberry silk yarns and the deformations in the hookean region signified the phenomenon of strain hardening.

Effect of fiber alignment on mechanical properties of chopped graphite fiber-reinforced copper-matrix composites: Designing fiber alignment in various stress conditions

Carbon-reinforced copper-matrix composites must provide improved mechanical properties if used as a structural part of machinery. However, little research has been conducted on the effect of the alignment of graphite fibers (GFs) with a high aspect ratio on the mechanical properties of composites. In this work, the effects of the alignment and volume fraction of GFs on the mechanical properties of GF/Cu composites subjected to tensile and compressive loading were analyzed and compared. The yield strength was highest when the composite with a GF volume fraction of 5% was subjected to compressive loading in the through-plane direction. The yield strength during tensile deformation was higher in the in-plane direction than in the through-plane direction. However, during compression testing, the yield strength was higher in the through-plane direction. Thus, the effects of the alignment and volume fraction of GFs on the tensile and compressive deformation behaviors of GF/Cu composites were revealed. These results are expected to provide a practical guide for optimizing the mechanical properties of GF/Cu composites subjected to various stress conditions as materials for the structural parts of machinery.

Tensile properties and deformation behavior of an extra-low interstitial fine-grained powder metallurgy near alpha titanium alloy by recycling coarse pre-alloyed powder

An extra-low interstitial near alpha alloy Ti−3Al−2Zr−2Mo (wt%) was fabricated by hydrogenation and thermomechanical consolidation (TMC) of the coarse and spherical pre-alloyed powder with particle sizes of 60 to 270 μm. The coarse powder is a byproduct of pre-alloyed powder produced for selective laser and electron beam additive manufacturing. The TMC process involves powder compaction, fast sintering, in-situ dehydrogenation and an immediate hot extrusion to form a fully dense and fine-grained martensitic microstructure. Further dehydrogenation in vaccum at 700 °C converted the martensitic microstructure into an interwoven α/β microstructure which exhibited an improved yield strength, apparent necking and premature cracking at grain boundary α (αGB) ribbons. A further annealing of 880 °C/1 h/AC led to the formation of a fine-grained α/βt composite structure, which achieved an enhance ultimate tensile strength of 835 MPa and excellent tensile ductility of 16.0%. Analysis of the deformation behavior of the alloy in different states revealed that the α/βt composite structures brought about an enhanced strain hardening capability by heterogeneous deformation effect of hard βt and soft α-laths, which inhibited the formation of microcracks and consequently improved the coordinated deformation.

Homogenization of TiVTaNb refractory high-entropy alloy

Homogenization of refractory high entropy alloys (RHEAs) usually requires very high annealing temperatures and long periods due to the high melting temperature of alloying elements and the sluggish diffusion effects. TiVTaNb is a typical RHEA with excellent mechanical properties. The present work takes TiVTaNb as a model alloy and shows the influence of cold-deformation, annealing temperature, and annealing time on its homogenization microstructure. The optimal process parameters are determined as cold deformation of 80% thickness reduction, followed by annealing at 1250 °C for 48 h. The tensile deformation behavior of the homogenized alloy is then studied based on quasi-in situ tensile testing, showing a tensile strength of 766 MPa. The tensile deformation is accompanied by grain rotation, meanwhile, a large number of geometrically necessary dislocations piles-up at the grain boundaries.

Stress partitioning in harmonic structure materials at the early stages of tensile loading studied in situ by synchrotron X-ray diffraction

In situ X-ray diffraction was employed to gain insight into the tensile deformation behavior of harmonic structure (HS) nickel. HS consists of a continuous network of fine grains encompassing islands of coarse grains. With the aid of a newly developed separation algorithm, the X-ray diffraction signals from coarse and fine grains were analyzed separately. Using line profile analysis, the evolution of local stresses and microstrains in the respective grain fractions were examined. Several stages were identified during yielding and the onset of plastic deformation in HS nickel. The mechanical behavior of the individual fractions was related to the macroscopic behavior of the HS and compared to that of homogeneous counterparts with similar average grain sizes as the grain fractions. The analysis reveals that the stress partitions between the grain fractions and that the plastic deformation of coarse grains within the HS are constrained by the network of fine grains.

Deformation behavior at cryogenic temperature in extruded Mg–Al–Zn alloy

ABSTRACT The effect of grain size on tensile deformation behaviors at room- and cryogenic-temperatures was examined using extruded Mg–Al–Zn (AZ31) alloys with different average grain sizes of 3.7, 14.0, and 38.7 μm. The mechanical properties were influenced by the grain size as well as the testing temperature. Strength increased with a finer grained structure and a lower testing temperature. Regarding the elongation-to-failure in tension, all the alloys tested at cryogenic-temperature exhibited about half the values of those at room-temperature. Deformed microstructural observations revealed that deformation twins formed in the alloys with coarse- and meso-grained structures, but decreased with grain refinement. The reduction of twin formation at both room- and cryogenic-temperatures is due to enhancement of grain boundary plasticity. Contrary to our expectation, it is interesting to note that grain boundary compatibility contributes to activation of non-basal dislocation slips, irrespective of testing temperatures. In addition, dislocation slips lead to occurrence of strain hardening after yielding even at 77 K.

Deformation behavior and strengthening mechanism of CuTa/CuTa amorphous/amorphous nanomultilayers

The tensile deformation behaviors of Cu80Ta20/Cu20Ta80 amorphous/amorphous nanomultilayers (AANMs) are investigated using molecular dynamics simulation. The tensile strength of the AANMs shows that the AANMs with reduced layer thickness from 160.0 Å to 26.7 Å demonstrate the Hall-Petch relationship because of the obstruction of interface to the shear band movement, while the specimens with more reduced layer thickness from 26.7 Å to 10.0 Å manifest the inverse Hall-Petch effect due to the direct interaction of the shear transformation zones. Additionally, the tensile strength of AANMs increases with increasing the strain rate and decreasing the temperature. The deformation mechanism reveals that multiple shear bands cross the amorphous/amorphous interfaces and interact with each other, which leads to enhanced ductility of the specimen with a small layer thickness. However, the shear bands locally focus on soft amorphous layers for AANMs with great layer thicknesses, causing shear softening and sample damage.

Quasi-superplasticity in the AlCoNiV medium entropy alloy with Heusler L21 precipitates

The high-temperature tensile deformation behaviors of the recrystallization annealed Al7(CoNiV)93 medium entropy alloy with a duplex hierarchical microstructure of face-centered cubic (fcc) and ordered body-centered cubic L21 Heusler-type grains were investigated. The alloy showed a remarkably high tensile strength of ∼1.1 GPa and good ductility of ∼17% at 923 K due to a good strain hardening capacity of 60 MPa. At 1073 K, the highest fracture elongation of ∼270% was displayed at a strain rate of 10−3 s−1. The strain rate sensitivity was estimated to be about 0.32, which is typical of alloys that show this quasi-superplastic elongation. The activation energy was also estimated to be ∼421 kJ/mol. With deformation at 1073 K at a strain rate of 10−3 s−1, the duplex microstructure transformed into a refined triplex fcc-L21-σ equiaxed microstructure. The development of the triplex equiaxed microstructure resulted from dynamic recrystallization (DRX), which assisted in the maximum superplastic-like elongation of 270%. The inability of the alloy to access true superplasticity was attributed to immense cavitation due to the high amount of the brittle σ phase, which served as de-cohesion sites for the early fracture of the sample. However, the observed quasi-superplasticity could still be useful in superplastic forming operations.

Tensile Deformation Behavior of Rotary Friction Welded Joint of Steels 32G2 and 40KhN

Tensile Deformation Behavior of Rotary Friction Welded Joint of Steels 32G2 and 40KhN

Tensile Deformation Behavior of Steel 20Kh3 After Quenching and Tempering

Tensile Deformation Behavior of Steel 20Kh3 After Quenching and Tempering

Analysis of hot tensile behaviour and prediction of thermal stresses during processing of AZ31 magnesium alloy

The use of magnesium alloys is rapidly increasing in automotive and aerospace industries. Accurate constitutive modelling of material at high temperature is a key input for numerical simulation of manufacturing processes. In the present work, hot tensile deformation behaviour of AZ31 alloy was studied by performing uniaxial tensile tests in the temperature range of 250°C–450°C and strain rates ranging from 0.1 to 0.001 s−1. The flow stress behaviour of AZ31 alloy was modelled using two rate-dependent inelastic models, viz. Garafalo law and extended Ludwik law. Various constants in these models were predicted as a function of strain rate and temperature. These rate dependent laws were integrated using Finite Element (FE) based algorithms for thermo-mechanical simulation. Evolution of thermal stresses in solid state quenching and static casting of AZ31 alloys were studied. Results reveal that both material models accurately predict the evolution of thermal stresses for high temperature quenching and casting processes.

High-Speed Tensile Deformation Behavior of a Metastable 18Cr–6Ni–0.2N–0.1C Steel

High-Speed Tensile Deformation Behavior of a Metastable 18Cr–6Ni–0.2N–0.1C Steel

A Variable-Order Fractional Constitutive Model to Characterize the Rate-Dependent Mechanical Behavior of Soft Materials

Building an accurate constitutive model for soft materials is essential for better understanding its rate-dependent deformation characteristics and improving the design of soft material devices. To establish a concise constitutive model with few parameters and clear physical meaning, a variable-order fractional model is proposed to accurately describe and predict the rate-dependent mechanical behavior of soft materials. In this work, the discrete variable-order fractional operator enables the predicted stress response to be entirely consistent with the whole stress history and the fractional order’s path-dependent values. The proposed model is further implemented in a numerical form and applied to predict several typical soft materials’ tensile and compressive deformation behavior. Our research indicates that the proposed variable-order fractional constitutive model is capable of predicting the nonlinear rate-dependent mechanical behavior of soft materials with high accuracy and more convinced reliability in comparison with the existing fractional models, where the fractional order contains a constant initial order to depict the initial elastic response and a linear variable-order function to account for the strain hardening behavior after acrossing the yield point.

Achieving High Tensile Strength of Heat-Resistant Ni-Fe-Based Alloy by Controlling Microstructure Stability for Power Plant Application

A new, wrought Ni-Fe-based alloy with excellent creep rupture life has been developed for 700 °C-class advanced ultra-supercritical (A-USC) steam turbine rotor application. In this study, its tensile deformation behaviors and related microstructure evolution were investigated. Tensile tests were carried out at room temperature, 700 °C, and 750 °C. The results show that the Ni-Fe-based alloy has excellent yield strength at 700 °C, which is higher than that of some other Ni-based/Ni-Fe-based alloys. The fracture surface characteristics indicate trans-granular and intergranular fracture modes at room temperature, 700 °C, and 750 °C. However, the intergranular fraction mode became dominant above 700 °C. Dynamic recrystallization occurred at 700 °C and 750 °C with increasing average misorientation angles. The volume fraction of the γ′ precipitate was around 20%, and the average size of the γ′ precipitates was around 30 μm, which had no noticeable change after the tensile tests. The predominant deformation mechanisms were planar slip at room temperature, bypassing of the γ′ precipitates by the Orowan mechanism, and dislocation shearing at 700 °C and 750 °C. The tensile properties, fracture characteristics, and deformation mechanisms have been well-correlated. The results are helpful in providing experimental evidence for the development and optimization of high-temperature alloys for 700 °C-class A-USC applications.

Development of a textile structure for multi-directional auxetic deformation

Previous studies of auxetic composites reinforced with woven fiber structures focused on unidirectional tension or compression. Multiple fibers are often required to play different roles in the structure, making it difficult to fully exploit the advantages of auxetic materials in real-world applications. Here, a single fiber-composed textile structure that can be stretched in various directions to produce auxetic behavior was developed. The single-layer structure was successfully fabricated using a three-dimensional (3D) printing method and evaluated by finite element analysis (FEA). The tensile deformation behavior of the 3D structure was simulated, and Poisson’s ratio (PR) values of the single-layer and 3D structures were obtained. There was good agreement between the FEA and experimental results, and the proposed structure can exhibit auxetic behavior when stretched in three orthogonal directions. With tensile displacements of 4 mm in the X and Z directions, the 3D structure was able to achieve maximum negative Poisson's ratio (NPR) values of −0.26 and −0.43, respectively. In particular, the diameter ratio of the fibers in each direction is an influential factor in terms of the degree of auxetic deformation of the textile. Thus, the results of this study could inform the development of novel multi-directional auxetic textile composites.

Tensile Deformation Behavior and Dynamic Recrystallization of TA15 Alloy over a Wide Temperature Range

TA15 is a near‐α titanium alloy that is used extensively in the manufacturing of high‐temperature structural components and has important applications in the aerospace field. Herein, the tensile deformation behavior of a TA15 alloy with equiaxed α grains is investigated over a wide temperature range of 25–900 °C. Based on the microstructural observations and tensile testing results, the deformation behavior of the TA15 alloy is classified into four stages: 1) deformation strengthening stage at 25–550 °C; 2) α‐phase softening stage at 600–650 °C; 3) phase transition softening stage at 700–800 °C; and 4) dynamic recrystallization stage at 850–900 °C. The α→β phase transition occurs predominantly between equiaxed α grains, and the increase in β‐phase content results in further enhancement of alloy plasticity. Dynamic recrystallization occurs first at the edge of the equiaxed α grains and gradually extends into the grain interior. The size of the dimples on the fracture surface increases gradually as the temperature increases, and a large shearing and splitting area is observed at 600 °C due to α‐phase softening.