Tensile Plastic Research Articles

A theoretical evaluation method for mechanical sealing integrity of cementing sheath

The sealing integrity of cement sheath directly affects the service life of oil and gas wells, and plays an important role in oil well operation and production. In this paper, the evaluation of sealing integrity of cement sheath was divided into two parts: the integrity of formation and cement sheath, and the integrity of cement sheath and casing. Based on the convergence-constraint theory, the effect of convergence stress generated by formation on cement slurry during the hardening process was considered. And the evaluation method for casing-cement-formation sealing integrity was established. In addition, a quantitative relationship between compressive strength of cement sheath and formation characteristic parameters was proposed to determine the cement-formation sealing integrity. Besides, the integrity evaluation method of casing-cement-formation combination was verified by tensile strength, compressive strength and plastic zone of cement. The field application analysis showed that this method is valid to predict the cement failure. During the cementing operation, the integrity of casing-cement-formation interface can be controlled by adjusting the properties of the cement sheath.

Effect of strain rate on tensile behavior in amorphous fibers by an in-situ video extensometer system

Understanding the relationship between strain rate and deformation behavior in micro-sized amorphous alloys is key to optimizing mechanical properties for emerging flexible skin smart sensors and engineering applications. The tensile behavior of Co68.15Fe4.35Si12.25B15.25 amorphous fiber was investigated over a wide range of strain rate of 5 × 10−5 s−1–1 × 10−1 s−1 at room temperature (RT) by an in-situ video extensometer system. Higher shear strain rate resulted in a hardening effect, thereby facilitating enhanced fracture strength. In contrast, tensile plasticity increased with decreasing strain rate. In comparison, to analyze the strain rate sensitivity, tensile behaviors of Fe75Si10B15 amorphous fiber over different strain rates were also observed. Fracture strength and tensile plasticity were found to be insensitive to strain rate. Pronounced tensile plasticity of up to 1% was observed for Co-rich amorphous fiber at strain rates ≤1.0 × 10−4 s−1, which is attributed to the balance between the generation rate and extinction rate of free volume. The critical shear offset had a significant impact on the plastic deformation of amorphous fibers. A predictive relationship was established between tensile plasticity and measured critical shear offset for Co-rich fiber.

Influence of aging treatment on microstructure and properties of a novel spray formed powder metallurgy superalloy FGH100L

A novel nickel-based superalloy, designated as FGH100L, was prepared by spray forming, hot isostatic pressing and isothermal forging. Following this, the billets were subjected to different heat treatments including sub-solvus and super-solvus solution heat treatments. The microstructure stability and mechanical properties of the alloy during the long-term aging treatment at 760 °C were studied. During the aging treatment, the grain size did not change significantly in both of the sub-solvus and super-solvus alloys, but the recrystallization around the coarse grain boundaries occurred in the former. When the sub-solvus alloy was aged for 500h, some secondary γ′ precipitates coarsened and split at a critical size into doublet or octet of cubes and there were two sizes of tertiary γ′ precipitates. With the aging time extending from 1000h to 2000h, secondary γ′ precipitates continued to coarsen and split, but tertiary γ′ precipitates grew uniformly. When the super-solvus alloy was aged from 500h to 2000h, only tertiary γ′ precipitates with uniform size were seen and they tended to coarsen at approximately the same rate. After aging for 2000h, the carbides in sub-solvus and super-solvus alloys are mainly M23C6, which can improve grain boundary strength. For the sub-solvus alloy, with the extension of aging time, both the room temperature and high temperature tensile strength originally decreased, then increased, and finally decreased again. Meanwhile the room temperature plasticity decreased gradually, while the high temperature tensile plasticity increased first and then decreased. Compared with the super-solvus alloy, the sub-solvus alloy after long term aging exhibited superior high temperature tensile properties. Cutting γ′ precipitates by stacking faults and forming a continuous stacking fault by increasing the width of the stacking faults is another deformation mechanism of the sub-solvus alloy. In the super-solvus alloy there are still a large number of dislocations accumulating between γ′ precipitates, but only a small amount of superdislocations cutting γ′ precipitates.

Designing new work-hardenable ductile Ti-based multilayered bulk metallic glass composites with ex-situ and in-situ hybrid strategy

To overcome the trade-off between the devisable microstructure and the excellent tensile ductility of bulk metallic glass composites (BMGCs), a novel ex-situ and in-situ hybrid strategy is successfully proposed to design a series of the work-hardenable ductile Ti-based multilayered BMGCs (ML-BMGCs). The as-prepared ML-BMGCs, consisting of α-phases, β-phases and amorphous phases, exhibit a controllable multilayered structure of the Ti layers and the amorphous layers with alternative distribution. The size and volume fraction of the crystalline phases are tuned by Nb microalloying. It is found that the ML-BMGCs possess a suitable size and volume fraction of the crystalline phases when Nb microalloying content are 5% (at.) or 8% (at.), and they obtain an optimum combination of the specific strength of 243 MPa g kg­1 or 216 MPa g kg−1, and tensile plasticity of 4.33%±0.1% or 5.10%±0.1%. The deformation mechanism of the as-prepared ML-BMGCs during tension is also revealed. The ex-situ Ti layers and in-situ dendrites together effectively serve as absorbers to suppress the propagation of shear bands and multiply shear bands. And the deformation of ex-situ α-Ti phases by dislocation slip and the transformation from in-situ metastable β-Ti phase to orthorhombic α"-Ti during tension impart significant work-hardening capability to the ML-BMGCs. The present study provides a guidance of developing novel high-performance BMGCs with a controllable microstructure.

Superior strength-ductility combination of a Co-rich CoCrNiAlTi high-entropy alloy at room and cryogenic temperatures

In the present study, a Co-rich CoCrNi-AlTi high-entropy alloy was designed and fabricated by hot forging and 700 °C for 8 h annealing process. The microstructure of the resultant alloy was composed of three multicomponent-phases with the face-centered cubic (FCC) structure, hexagonal close-packed (HCP) structure and L12 structure, respectively. The alloy exhibited a remarkable combination of tensile yield strength (gigapascal scale) and plasticity (uniform strain over 30%) at both room and cryogenic temperatures. The cooperative operation of multiple mechanisms consisting of refined-grain strengthening, second-phase strengthening, precipitation strengthening, stacking faults and phase-transformation toughening was suggested to be responsible for the excellent mechanical response.

A high-strength Co–Fe–Ta–B metallic-glass phase enabled tensile plasticity in Co–Fe–Ta–B–O oxide glass matrix nanocomposites

Oxide glasses are intrinsically brittle at room temperature when loaded under tension. In this study, a high-strength CoFe-based metallic glass was used as a strengthening phase to make a Co–Fe–Ta–B–O oxide glass become stronger and ductile in tension. The developed metallic-glass-reinforced oxide glass matrix nanocomposite possessed a supra-nanometer-sized dual-phase structure. Owing to the dispersion strengthening effects, the nanocomposite showed a tensile strength σb of ∼2.7 GPa, about 29% higher than that of the single-phase oxide glass. Meanwhile, its tensile plasticity εp was enhanced from zero to ∼2.7%. The continuous glass/glass interfaces of the dual-phase mixture are thought to enable the tensile plasticity in the nanocomposite. Our results provide an approach to effectively enhance both the strength and tensile ductility of intrinsically brittle oxide glasses.

Dislocation-Evolution Based Comprehensive Phenomenological Model for Continuum-Scale Description of Stress–Strain and Work-Hardening Behavior

Bridging continuum-scale description of uniaxial tensile plastic stress–strain behavior with adjacent mesoscale deformation models is important and, hence, requires identification of appropriate physical processes and the associated parameters. In this work, a comprehensive phenomenological model (CPM) for true stress–true strain behavior of a polycrystalline material in the plastic regime was developed based on the postulation of physical processes, viz. dislocation nucleation, multiplication, and annihilation, satisfying the statistical perception of dislocation evolution during deformation. Incorporation of these processes through intricate formulations using physical parameters, such as dislocation density, dynamic mean-free-path (MFP), fixed MFP etc. demonstrated a precise fit of a uniform tensile plastic flow curve and of its spin-off work-hardening (WH) behavior, simultaneously. Variation in the calculated parameters for different stress–strain responses of different alloy systems and the sensitivity analyses helped in appreciating the discrete modular nature of the model. Precise fits in both plastic stress–strain and WH responses using the same set of coefficients ensured the CPM to be reliable in simulating realistic uniaxial stress–strain plots from the physical parameters for various alloys. The model advances the understanding of phenomenological modeling especially in terms of incorporation of the dislocation nucleation mechanism in the evolution process, ensuing explicit expression for dislocation evolution with strain and grain size dependence. The present approach is deemed appropriate for linking the length scales in the multiscale description of deformation.

Comparison of different titanium alloys welded by Yb:YAG fibre laser for thin sheet applications used for T-ducts in bleed air systems

Research in aerospace applications includes the replacement of well-known materials by newly developed alloys or by new manufacturing methods for the existing materials. In the frame of TiB-Air project funded by the German Federal Ministry for Economic Affairs and Energy (BMWi) the development of a process chain consisting of deep drawing at elevated temperatures, chemical milling, contour machining by laser cutting and laser beam welding to produce pneumatic T-ducts used in bleed air systems is in focus. This production process of sheet metal parts could lower costs in terms of the process itself and the used materials: low alloyed Ti-alloys. Commercially pure titanium alloy (cp-Ti) is commonly used for these structures because of its balanced mechanical properties regarding tensile strength, yield strength, plastic strain and fatigue strength as well as good resistance against corrosion and oxidation. The possibility to substitute cp-Ti by low-alloyed Ti-alloys is examined in this work, by the comparison of two different low alloyed Ti-alloys, namely KS1.2ASN and Ti XT, with a cp-Ti alloy (Grade 4). Mechanical properties of the base materials, their weldability and the mechanical assessment of the laser beam welded butt joints in terms of static, cyclic and fracture mechanical behaviour is compared for sheet materials, with a thickness of 0.9 mm. Defect-free welding according to EN13919 acceptance criteria B was possible for all three alloys, no porosity problems occurred. The low strength alloy KS1.2ASN exhibited mechanical anisotropy between longitudinal direction and transverse direction in the tensile test, welded specimens of this alloy broke in the base material. Due to the tensile properties, both weld and base material of KS1.2ASN showed the least values for the fatigue strength and endurance limit strength. Ti XT and Grade 4 showed similar mechanical anisotropy and fractured in the base material, too. Fatigue strength of Ti XT is below Grade 4, but for the 50%-percentile the endurance limit strength is equal. Fracture mechanical testing showed that KS1.2ASN is a very promising alloy in the welded condition.

Coupling numerical model of hydraulic fracturing seepage in soft coal based on elastoplastic damage

In order to guide the field application of hydraulic fracturing of soft coal in coal mine, based on the elastic-plastic damage theory, the coupling numerical model of soft coal hydraulic fracturing seepage was studied. The porosity strain relationship equation, permeability strain relationship equation, the relationship between permeability and volume plastic tensile strain and volume plastic shear strain of coal and rock mass are derived, and the plastic correction equation and softening parameters are defined. The stress coupling equation and yield criterion are programmed and embedded into the finite difference software FLAC3D for numerical solution. The numerical simulation shows that the numerical calculation model of soft coal hydraulic fracturing conforms to the actual law, and the field fracturing radius investigation experiment is consistent with the numerical simulation results.

Novel α + β Type Ti-Fe-Cu Alloys Containing Sn with Pertinent Mechanical Properties

Rising demand for bone implants has led to the focus on future alternatives of alloys with better biocompatibility and mechanical strength. Thus, this research is dedicated to the synthesis and investigation of new compositions for low-alloyed Ti-based compounds, which conjoin relatively acceptable mechanical properties and low elastic moduli. In this regard, the structural and mechanical properties of α + β Ti-Fe-Cu-Sn alloys are described in the present paper. The alloys were fabricated by arc-melting and tilt-casting techniques which followed subsequent thermo-mechanical treatment aided by dual-axial forging and rolling procedures. The effect of the concentrations of the alloying elements, and other parameters, such as regimes of rolling and dual-axial forging operation, on the microstructure and mechanical properties were thoroughly investigated. The Ti94Fe1Cu1Sn4 alloy with the most promising mechanical properties was subjected to thermo-mechanical treatment. After a single rolling procedure at 750 °C, the alloy exhibited tensile strength and tensile plasticity of 1300 MPa and 6%, respectively, with an elastic modulus of 70 GPa. Such good tensile mechanical properties are explained by the optimal volume fraction balance between α and β phases and the texture alignment obtained, providing superior alternatives in comparison to pure α- titanium alloys.

Deformation Behavior and Dynamic Recrystallization of Ti–22Al–25Nb Alloy at 750–990 °C

Ti–22Al–25Nb is a representative of Ti2AlNb alloys with excellent comprehensive properties, which has great application prospects in the aerospace field. Herein, high‐temperature tensile plastic deformation behavior and dynamic recrystallization process of Ti–22Al–25Nb alloy are researched during 750–990 °C. From 750 to 870 °C, plasticity is gradually improved with temperature increasing, and the fracture mode is crack aggregation. From 900 to 930 °C, the content of B2 phase increases and plasticity is significantly improved because crack along the grain is suppressed by combined precipitation of three phases B2 + O + α2 at grain boundaries with large areas. From 960 to 990 °C, the alloy is mainly composed of B2 phase and has best plastic deformation performance. Fully dynamic recrystallization of B2 phase happens at 990 °C. Texture strength is strengthened by intense plastic deformation, but it is weakened by dynamic recrystallization subsequently.

A steel property optimization model based on the XGBoost algorithm and improved PSO

Exploring the relationships between the properties of steels and their compositions and manufacturing parameters is extremely crucial and indispensable to understanding the science of materials, and subsequently developing new materials. Tensile strength and plasticity, as two important properties of steels, are key to the improvement and optimization of the mechanical properties of steels. In the present paper, we propose an optimization model combining XGBoost algorithm with improved PSO to address the continuous multivariable optimization problem. The main goal is to determine the mapping functions between the tensile strength and plasticity and their influencing factors, based on a diversity of machine learning models such as Linear Regression, SVM, XGBoost, etc. After evaluating the performance these models, we then select the XGBoost model with highest accuracy as the mapping function, which has not been done in previous studies. Moreover, the determined mapping function serves as the fitness value of particle swarm optimization, after which the tensile strength and plasticity optimization with many variables is realized. Finally, the experimental results are analyzed theoretically, and proven to be effective and reliable.

Guidance on the Use of Existing ASTM Polymer Testing Standards for ABS Parts Fabricated Using FFF

Abstract When evaluating the static mechanical performance of fused filament fabrication (FFF) polymers, researchers have conducted tensile testing using ASTM D3039, Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials, and ASTM D638, Standard Test Method for Tensile Properties of Plastics. The choice of ASTM D638 versus ASTM D3039 test specimen geometry is usually based on the perceived susceptibility of the ASTM D638 test specimens to failure within the fillet radius. ASTM polymer and plastic tensile test standards define criteria for acceptably tested specimens as requiring failure inside the narrow length (i.e., ASTM D638) or outside of the grips (i.e., ASTM D3039) for the results to be considered acceptable. There has been limited published research regarding the selection of an ASTM test specimen geometry for FFF polymer materials. This study provides evidence-based guidance through the comparison of the mechanical performance and failure acceptance rates of ASTM D3039 and ASTM D638 test specimen geometries, fabricated using FFF acrylonitrile butadiene styrene. The purpose of this study is to provide guidance on the use of existing ASTM polymer testing standards for additively manufactured polymers. Results indicate there is an inherent benefit to using ASTM D3039 over ASTM D638 Type I and Type IV test specimens for tensile testing. ASTM D3039 test specimens provide the most consistent failure within the test specimen’s gage length, which is attributed to the rectangular design of the test specimen. Results also indicated that, like traditionally manufactured polymer composites, there will be differences in the tensile test results (e.g., ultimate tensile strength, elastic modulus) based on the different cross-sectional areas of the test specimen geometries.

Economical Si-Bearing, Nearly Ni-Free 19Cr TRIP-Aided Duplex Stainless Steels with Better High-Temperature Oxidation Resistance

A novel series of Si-bearing, nearly Ni-free economical TRIP-aided duplex stainless steels (DSSs) 19Cr-5.5Mn-0.3Ni-0.2N-xSi (x = 0.5-2.5) have been prepared to investigate effect of silicon on microstructure, tensile mechanical property and high-temperature oxidation behavior. The results have shown that the designed economical alloys have a balanced ferrite/austenite dual-phase structure after suitable solution treatment. Volume of ferrite phase increases with an increase in silicon content. Ferrite deforms by dislocation slip during tensile plastic deformation process at room temperature. However, transformation-induced plasticity effect dominates deformation mode of metastable austenite phase. The designed DSS with 1.5 wt.% Si content exhibits good combination of tensile mechanical properties, exceeding 50% in elongation and 800 MPa in ultimate tensile strength, with a sequential γ → e-martensite → α′-martensite transformation in deformed austenite phase. High-temperature oxidation resistance of DSSs could be enhanced with an increase in silicon content at 1100 °C in air due to the formation of compact and continuous Cr- and Si-rich oxide film in the inner oxide film layer.

The Role of Microstructure on Tensile Plastic Behavior of Ductile Iron GJS 400 Produced through Different Cooling Rates, Part I: Microstructure

A series of samples made of ductile iron GJS 400 was cast with different cooling rates, and their microstructural features were investigated. Quantitative metallography analyses compliant with ASTM E2567-16a and ASTM E112-13 standards were performed in order to describe graphite nodules and ferritic grains. The occurrence of pearlite was associated to segregations described through Energy Dispersive X-ray Spectroscopy (EDS) analyses. Results were related to cooling rates, which were simulated through MAGMASOFT software. This microstructural characterization, which provides the basis for the description and modeling of the tensile properties of GJS 400 alloy, subject of a second part of this investigation, highlights that higher cooling rates refines microstructural features, such as graphite nodule count and average ferritic grain size.

Effect of laser power on gradient microstructure of low-alloy steel built by laser melting deposition

In this paper low-alloy steel samples were fabricated by laser melting deposition at different laser power of 1500 W, 2000 W and 2500 W. The results show that the microstructure is gradient with a mixture of lower bainite and martensite on surface and tempered martensite in interior of each sample, and the morphology of microstructure both on surface and in interior develop with change of laser power, the develop of microstructures result in difference in mechanical properties. The hardness, ultimate tensile strength and plasticity of both surface and interior of the samples were studied, as well as the depth of the surface layer. This paper provides a reference for the evolution and control of gradient microstructure of LMD low-alloy samples.

Effect of large-size carbides on the anisotropy of mechanical properties in 11Cr-3Co-3W martensitic heat-resistant steel for turbine high temperature blades in ultra-supercritical power plants

9–12%Cr martensitic heat-resistant steels (MHRS) are the key materials for making ultra supercritical (USC) unites turbine blades. In this study, the anisotropy of mechanical properties in Cr-Co-W-type MHRS 1Cr11Co3W3NiMoVNbNB is discussed. The samples were prepared for impact and tensile tests. By utilizing characterization techniques, such as OM, FESEM, TEM, and EDS, steel sample fracture surfaces and the microvoids as well as the microstructure-anisotropy mechanical properties relationship were thoroughly investigated. It was pointed out that a strong anisotropy of mechanical properties was observed as much lower impact toughness and tensile plasticity in transverse direction in the steel sample after a heat treatment process. The anisotropy was mainly due to the large-size directionally distributed M23C6-type and M6C-type carbides. Large-size directionally distributed carbides lead to anisotropy of mechanical properties mainly by promoting the formation of microcracks and the propagation of cracks in transverse specimens. For transverse impact specimens, the propagation of microvoids is promoted to banded brittle cracks by large-size directionally distributed carbides. These banded brittle cracks become the pre-cracks of matrix and markedly decrease the toughness. For transverse tensile specimens, the propagation of microvoids is promoted to shallow chain-distributed dimples by large-size directionally distributed carbides, which markedly decrease the plasticity.

Plastic deformation mechanism of MWCNTs/AZ91D nanocomposites with high ductility at room temperature

1.0 wt% MWCNTs/AZ91D magnesium matrix nanocomposites were prepared by metal mold gravity casting process assisted by high-intensity ultrasonic dispersion, and the ductility was further improved by T4 solid solution treatment. The tensile test results at room temperature revealed that the tensile strength and elongation of 1.0 wt% MWCNTs/AZ91D nanocomposites after T4 solid solution treatment reached up to 281.7 MPa and 15.4%, respectively. The ductility of magnesium matrix nanocomposites was significantly improved by the addition of Multiwalled carbon nanotubes (MWCNTs) and T4 solid solution treatment. SEM and TEM were used to observe the microstructure of 1.0 wt% MWCNTs/AZ91D-T4 nanocomposites after the tensile plastic deformation at room temperature. A considerable number of slip bands and twins were found in the microstructure of the nanocomposites. High strain zones were formed around MWCNTs during the tensile process at room temperature. A large number of dislocations and stacking faults were generated in the high strain zones, which could be used as the origin of slip bands and twins, so MWCNTs can promote slip and twining. MWCNTs can further activate non-basal slip and cross slip, and improve the ductility of 1.0 wt% MWCNTs/AZ91D-T4 nanocomposites.

Microcrack initiation behavior around film cooling holes in a Ni-based single crystal: In situ observation and crystal plastic analysis

The microcrack initiation behavior around the film cooling holes (FCHs) of a Ni-based single crystal was investigated by in situ tensile experiments and crystal plasticity simulations, in which the hardening effect was considered. The effect of FCHs on the tensile strength and plasticity localization was determined according to experimental results. Multisource microcracks that initiated along the slip bands around the FCHs and the kink shear bands were observed. The macrocrack path characterized the features of instantaneous and crystallographic fractures, as confirmed by the fracture surface morphology. The slip bands along which the crack initiated were determined by identifying the activation type of the octahedral slip family using the crystal plasticity finite element method (CPFEM). The simulation results were found to be in excellent agreement with the experimental results. Plastic deformation mainly occurred around the FCHs where the dominant slip systems were activated, which were defined as the dominant slip sectors in this study. The resolved shear stress (RSS) induced microcracks around the FCHs along the (-11-1) [011], (-1-11) [011], (1-1-1) [0–11], and (111) [0–11] slip bands in the dominant slip sectors.

Oxide shell layer influences on size-dependent tensile and compressive mechanical properties of iron nanowires: A ReaxFF molecular dynamics study

The systematic understanding of an overall deformation mechanism of metallic iron (Fe) nanowires (NWs) with the pre-existing oxide shell layer (Fe/FexOy) under various mechanical loading conditions is of critical importance for their various applications. Herein, we perform molecular dynamics simulations using ReaxFF reactive interatomic potential to systematically investigate the effect of the pre-existing oxide shell layer on the underlying intrinsic mechanical deformation mechanism and related mechanical properties of metallic [001]-oriented Fe NWs under both uniaxial tension and compressive loading. Three different diameters of the NWs are investigated to elucidate the size effect. The Fe NWs with the preoxide shell layer possess unique and intriguing mechanical properties and deformation mechanisms. In particular, the oxide shell layer with the combined effect of the diameter and the applied uniaxial loading mode dictates the strength and the overall stress-strain behaviors of the NWs. Interestingly, the oxide-coated NWs clearly exhibit the diameter-dependent elastic deformation intrinsic mechanism and related properties as compared to the pristine counterparts. Specifically, the pre-existing oxide shell layer expedites the onset of tensile plasticity by drastically reducing the tensile yield stress and significantly decreasing the tensile elastic limit. Contrary to the tensile loading, the presence of the oxide shell layer reduces or increases the compressive yield stress of the pristine Fe NW with respect to its diameter. However, the pre-existing oxide shell layer leads to a significantly delayed onset of compressive plasticity, that is, a significant increase in the compressive elastic limit.