Inhomogeneous Deformation Behavior Research Articles

On the effect of deformation conditions on the metal flow behavior during upsetting process using finite element simulation DEFORM 3D software

AbstractThe study reports on the metal flow behaviour during upsetting or forging using the finite element method. Forging simulation studied the metal flow behaviour of a laboratory-sized specimen and a cylindrical engine connecting rod specimen of AISI 52100 high-chromium steel specified in the software database. The focus was to study the effect of deformation conditions (temperature and die velocity) on metal flow behaviour during forging. The simulation results showed heterogeneous metal flow behaviour during forging. Hence, this indicates that effective flow stress and flow strain, particle flow velocity, effective strain rate, damage and temperature distribution exhibited inhomogeneous deformation behaviour. As the temperature increased, the forging load decreased, thus a decrease in deformation resistance. The simulation of the engine connecting rod further confirmed inhomogeneous deformation during forging. Damage coefficient results show that the crack pin end had a higher damage probability during forging. This study clearly showed that finite element simulation can predict metal flow behaviour during the forging of AISI 52100 steel. The study output provides a basis for analysing and optimising most industrial metal forming processes using a numerical simulation approach. Hence, this method is effective in predicting flow behaviour.

Inhomogeneous deformation behavior and recrystallization mechanism of Mg-Gd-Y-Zn-Zr alloy containing only intragranular lamellar LPSO phase

Inhomogeneous plastic deformation and recrystallization behavior of Mg-Gd-Y-Zn-Zr alloy containing only intragranular lamellar long-period stacking ordered (LPSO) phase were investigated by isothermal compression experiments at the temperatures of 350–450 °C, and the strain rates of 0.001 ∼ 10 s−1. Results showed that Mg-Gd-Y-Zn-Zr alloys with varying degrees of bimodal structures were obtained after compression. The lamellar LPSO phase directions in residual coarse grains were aligned in the radial direction (RD). Dynamic recrystallization (DRX) grains induced at grain boundaries, kinked bands, and lamellar shearing regions during compression synergistically promoted coarse grain refinement. Moreover, the condition of high temperature and medium strain rate (450 °C-0.1 s−1) contributed to the uniform extension of "mantle layers" of fine DRX grains. In contrast, the condition of medium temperature and high strain rate (400 °C-10 s−1) could accelerate the deflection of CD-directed (compression direction) LPSO lamellae and the formation of local high-energy regions, facilitating the generation of recrystallization band. In addition, a high strain rate (400 °C-10 s−1) is more conducive to the formation of a heavily bimodal structure than a high temperature (450 °C-0.1 s−1). Only a larger spacing of LPSO lamellae (∼1.4 μm) could meet the spatial requirements of recrystallization. Further analysis revealed that the continuous dynamic recrystallization (CDRX) mechanism characterized by the expansion of "mantle layers" and nucleation along kinked boundaries and lamellar shearing regions was the primary grain refinement mechanism. The discontinuous dynamic recrystallization (DDRX) mechanism only exhibited a limited role due to the inhibition of the highly dense lamellar LPSO phase on grain boundaries bulging. After compression, the orientation of residual coarse grains gradually deviated toward the CD. While the recrystallization with limited proportion and random orientation cannot significantly weaken the basal texture.

A study on micro‐mechanical deformation behaviour of heat‐treated 20MnMoNi55 steel

AbstractSeveral heat treatment procedures are designed considering critical temperatures of phase transformation evaluated through dilatometric testing of 20MnMoNi55 steel to transform low carbon bainitic as‐received material into ferrite‐martensite dual‐phase steels consisting of varied martensite fractions. A thorough metallographic study correlated with the micro‐hardness of constituent phases ensures morphological characteristics along with its fractional variations in as‐received and dual‐phase steels. The impact of fractional variation in constituent phases on the uniaxial monotonic deformation characteristics of dual‐phase steels has been observed with a correlation study between experimental tensile and finite element simulated results. Therefore, a physical‐based model with a 2‐dimensional representative volume element has been established, addressing actual morphological characteristics obtained from metallographic studies. Moreover, the constitutive flow behaviours of ferrite and martensite are also derived from the dislocation‐based hardening model to address the actual deformation phenomenon. Finally, an inhomogeneous deformation behaviour among constituent phases and localization of plastic strain in ferrite matrix has been observed with von‐Mises stress, and equivalent plastic strain distribution through finite element simulated results. This phenomenon is again confirmed with kernel average misorientation mapping and geometrically necessary dislocation density evaluation through electron backscattered diffraction of tensile samples subjected to different degrees of plastic strain.

Island-Matrix Inhomogeneous Deformation Behavior, Formation of Deformation Band, and BUT Forming of DP Steel

Islands-Matrix-Dual-phase (I-M-DP) steel is received a great deal attention for better concern with the emissivity, fuel consumption and passengers safety. A number of deformation plasticity issues are yet to be fully understood. Complex deformation stages for various stain is predicted as the natural outfall of the plastic strain localization caused by the ill-assorted deformation between the martensite-island phase and the ferritic-matrix phase. Modeling is carried out both in macro level by bending under tension (BUT) for different roller radius/sheet thickness ratios to acquire strain and stress state deformation and micro scale by Representative Volume Element (RVE) according to element position. It can relate both the 2D, 3D micro and macro scale finite element based BUT model’s result of flow behavior. Systematically strain based severe deformation pattern arises from outfall of plastic strain localization and von Mises stress distribution in island-matrix steels are investigated on the microstructure by finite element method for ill-assorted deformation between phases.

On the inhomogeneous deformation behavior of magnesium alloy beam subjected to bending

Magnesium (Mg) alloys have attracted worldwide attention as potential lightweight structural materials. However, it is still a big challenge to manufacture or process Mg alloys that have good formability and endure high strength. This mainly stems from the lack of understanding the anisotropic mechanical behavior of Mg alloys subjected to inhomogeneous deformation which exists inevitably in various material processing routes. In this respect, the current work seeks to explore and understand the bending behavior of Mg alloy. Mechanical response and microstructure development were experimentally characterized by performing four-point bending tests, with the use of the in-situ digital-image-correlation (DIC) and ex-situ electro backscattered diffraction (EBSD) measurements. Meanwhile, a crystal plasticity-based approach was proposed and used to illustrate the characteristic deformation behavior under four-point bending. The inhomogeneous and anisotropic nature of the mechanical response of Mg alloys under bending is successfully captured by the proposed approach in terms of the moment-curvature relation, the deformed cross-sectional shape of the beam, the developed textures at different regions of the beam, the spatial distribution of the stress and strain components, and the twin volume fraction. The insight of the slip/twinning mechanisms underlying the bending behavior of Mg alloy beam offers a novel way for designing/tuning gradient twinning structures that might lead to the optimized properties of Mg alloys.

Deformation behaviour of micro-milled cp-titanium specimens under tensile loading

Abstract The functionality of components can be improved by surface modifications such as micro-milling. The micro-milled structures (notches) can cause changes in the mechanical properties of the components. To be able to predict or prevent component failure, the influence of these micro-milled notches on the deformation behaviour of commercially pure titanium under tensile loading is investigated. Quasistatic tensile tests show that the tensile strength is increased by deeper notches and the fracture elongation of the specimens decreases. Metallographic analyses and nanoindentation tests of systematically interrupted tensile tests at different strain rates show the development of the plastic deformation and the inhomogeneous deformation behaviour of the material.

The role of nano-scale elastic heterogeneity in mechanical and tribological behaviors of a Cu–Zr based metallic glass thin film

Despite its significance in fundamentally understanding mechanical behaviors of metallic glasses, the effect of elastic heterogeneity on plastic deformation and thereby nanotribological behavior of metallic glass thin films (MGTFs) remains an open question. By a combination of nano-scratch, nano-DMA and nanoindentation tests, we have investigated in the present work the room-temperature inhomogeneous plastic deformation behavior and nanotribological properties of Cu–Zr based MGTFs obtained by magnetron sputtering with different substrate temperatures. It is revealed that while the studied MGTF experiences a moderate rise of both hardness and Young's modulus with the elevating substrate temperature from 300 K to 473 K, its wear resistance significantly increases during the nano-scratch under a ramping load. More interestingly, through systematically studying the serration dynamics during the nano-scratch for MGTFs with different thermal history, we found that the increase of critical length scale for shear banding, which is well accompanied by the reduction of nano-scale elastic heterogeneity, tends to make shear banding more difficult in the amorphous structure, and thus enhance the wear resistance of the tested MGTFs. The current findings may provide a useful guidance to develop MGTFs with a superior mechanical and tribological properties via tuning their nanoscale elastic heterogeneity.

Modeling of material deformation behavior in micro-forming under consideration of individual grain heterogeneity

Abstract This study aims to develop a model to characterize the inhomogeneous material deformation behavior in micro-forming. First, the influence of individual grain heterogeneity on the deformation behavior of CuZn20 foils was investigated via tensile and micro-hardness tests. The results showed that different from thick sheets, the hardening behavior of grains in the deformation area of thin foils is not uniform. The flow stress of thin foils actually only reflects the average hardening behavior of several easy-deformation-grains, which is the reason that thinner foils own smaller flow stress. Then, a composite modeling method under consideration of individual grain heterogeneity was developed, where the effects of grain orientation and shape are quantitatively represented by the method of flow stress classification and Voronoi tessellation, respectively. This model provides an accurate and effective method to analyze the influence of individual grain heterogeneity on the deformation behavior of the micro-sized material.

The test on the inhomogeneous strain field and creep rupture behavior of the weld joint at elevated temperature by digital image correlation method

The digital image correlation (DIC) method was applied for monitoring the short and long term inhomogeneous deformation and rupture behavior of the weld joint at elevated temperature. In order to prevent the surface oxidation of the metal during the long time exposure at elevated temperature and offer a series of stable surface patterns for the DIC sensing, the thin metallic coating was introduced. Then the strain field and rupture of the weld joint were tested successfully not only during the short term tensile test but also the long term creep test. The results showed a good performance on distinguishing the deformation differences at local zone of the weld joint. Especially, the three-stage creep behavior of the local zones could be measured simultaneously, even though the weakest zone controlling the creep rupture, which is helpful to study the creep rupture behavior of the weld joint and develop the creep life evaluation method or the creep failure monitoring technology. Also the limitations of this method were discussed briefly.

Size effects affected uniaxial tensile properties and formability in rubber pad microforming process of pure nickel thin sheets

The size effects on plastic deformation behaviors of metal thin sheets have a profound impact on the development of microforming process. In this study, the deformation and forming behaviors of pure nickel thin sheets with t/d < 2 (thickness t /average grain size d) were demonstrated by micro tensile tests and rubber pad forming tests. The flow stress decreased evidently and the relationship between true stress and d−0.5 deviated from the Hall-Patch relationship when t/d <1.2 and the surface layer model is no longer applicable. Based on Hollomon equation, a new constitutive equation considering the effect of t/d was established to predict both the ductility and strength in micro tension of thin sheets. The experimental and calculated data matched well. The fracture mechanism and deformation behavior changed significantly when t/d < 1.2 based on the fracture characteristics and morphologies. The experimental results of rubber pad forming tests of microchannel indicated that the thickness thinning and surface roughening behaviors became more severe when t/d < 1.2 owing to strongly localized and inhomogeneous deformation behaviors. Local severe deformation easily occurs at the position where there is only one grain across the thickness direction. And the micro-part is likely to fracture at this location, which should be avoided as much as possible in the manufacturing process.

Inhomogeneous deformation behaviors of oblique hole-flanging parts during electromagnetic forming

The electromagnetic flanging of oblique hole-flanging parts is characterized by inhomogeneous deformation, which is closely related to the final forming quality of workpieces. In this work, the inhomogeneous deformation behaviors of a workpiece formed by electromagnetic flanging, whereby an initial blank made of annealed 2219 aluminum alloy with a circular precut hole is formed into an oblique hole-flanging part, are investigated and the influence mechanism is revealed by conducting numerical simulation. A comparison of the forming process for three typical radial deformation regions along the circumferential directions of 0°, 90°, and 180° is made. The results show that during the electromagnetic forming (EMF) of the oblique hole-flanging parts, the deformation region along Path 90° deforms fastest and impacts the die first at the maximum velocity. The deformation region along Path 180° impacts earlier than that along Path 0°. The resulting flanging angle of the workpiece is lower than the target flanging angle with a maximum deviation of approximately 4.8°, and the forming height distributes as a wavy pattern along the circumference. In the EMF of oblique hole-flanging parts, the direct influence factors responsible for the inhomogeneous deformation behaviors of the workpiece include the deformation requirement, area of the deformation region, and electromagnetic force. The inhomogeneous deformation behaviors are essentially due to the uneven deformation requirement. The area of the deformation region is the most important factor influencing the inhomogeneous deformation behaviors, with the electromagnetic force having a significant influence as well. Based on the findings, process parameters can be optimized to control the inhomogeneous deformation behaviors and to realize the precision EMF for nonaxisymmetrical, irregular parts.

Analysis of inhomogeneous deformation behavior of high-strength steels

Analysis of inhomogeneous deformation behavior of high-strength steels

Optimizing the mechanical properties of friction stir welded dissimilar joint of AM60 and AZ31 alloys by controlling deformation behavior

The special microstructure distribution of the friction stir welded (FSW) Mg alloys joints is usually responsible for the non-uniform deformation and poor mechanical properties. Hence, it was possible to improve the joint mechanical properties by modifying the microstructure. In the present study, two kinds of AM60/AZ31 Mg alloys dissimilar FSW joints with different microstructure were obtained using different rotation rates (800 rpm and 1600 rpm). The results of mechanical tests showed that the tensile strength and elongation of the joint at 1600 rpm were 13.5% and 115% higher than those at 800 rpm, respectively. The microstructure observation indicated that the grain size of various zones in the joint at 1600 rpm was obviously larger than that at 800 rpm, especially at the AM60 side. However, there was no obvious difference in the texture distribution of the two welds. In addition, microstructure observation after fracture showed that there were more twins in AM60 side of the joint with coarse grains. These coarse grains promoted the activation of basal slip and twinning in the regions far away from the nugget zone (NZ) interface. This weakened the strain localization of the joint to some extent. Meanwhile, the coarse grain joint had lower concentration degree of the strain and dislocation near the NZ boundary compared with the fine grain joint. These factors led to better mechanical properties of the joint with coarse grains. This work could provide some guidelines for improving the inhomogeneous deformation behavior of dissimilar Mg alloys FSW joints.

Deformation-based joining for high-strength Ti-3Al-2.5V tubular fittings based on internal roller swaging

Deformation-based joining presents efficient, reliable and environmentally friendly advantages widely applying in the pipeline system. Internal roller swaging (IRS), one of deformation-based joining ways, is an inner expanding spinning process with characteristics of sheet-bulk forming, and it has the potential to fabricate high-strength tubular joining components with better high-pressure resistance and sealing performance. Taking a high-strength Ti-3Al-2.5V titanium alloy (TA) tube as the case material, this study combines explicit and implicit finite element (FE) modeling with experimental validating to explore the deformation mechanisms of the IRS process. By using the digital image correlation method (DICM) based uniaxial tension, the contractile strain ratio (CSR) of the TA tube was obtained to describe its anisotropy. By analyzing the mechanism of IRS, the motion equations of three rollers were deduced in the forming process, and a simplified 3D FE model for the IRS process was developed. Based on the FE simulation and analysis, the inhomogeneous flow deformation behaviors of TA tube in the IRS process were investigated by subdividing the deformation areas of the tube. Then, the material flow features of TA tube in the IRS process were explored by analyzing the axial displacements of the tube and observing its flow localization by means of optical microscope. Finally, the forming quality of the tubular joining components can be accurately designed and controlled by revealing the relationship between the swaging depth and the axial elongation and the relationship between the swaging depth and the contact shear stress. It is concluded that this incremental deformation-based joining process has obvious superiority to fabricate high-strength TA tubular joining components, and their reliability can be effectively enhanced by accurately controlling the swaging depth.

Plastic deformation behavior of a nickel-based superalloy on the mesoscopic scale

Nickel-based superalloys have become the key materials of micro-parts depending on excellent mechanical properties at high temperatures. The plastic deformation behavior is difficult to predict due to the occurrence of size effect on the mesoscopic scale. In this paper, the effect of specimen diameter to grain size ratio (D/d) on the flow stress and inhomogeneous plastic deformation behavior in compression of nickel-based superalloy cylindrical specimens was investigated on the mesoscopic scale. The results showed that when D/d is less than 9.7, the flow stress increases with the grain size. Aiming at this phenomenon, a flow stress size effect model considering compressive strain partitioning was established. The calculated flow stress values agree well with the experimental values, thus revealing the effect of D/d on the flow stress in compression of nickel-base superalloy on the mesoscopic scale. The inhomogeneous plastic deformation during compression deformation increases with the grain size. The end surface profiles evolve from a regular circular shape to an irregular shape with the grain size. The surface folding phenomenon occurs only in partially compressed specimen with a few grains across the diameter. Crystal plasticity finite-element (CPFE) simulation of compression deformation on the mesoscopic scale real-time displayed the evolution of microstructure. The study of this paper has important guiding significance for understanding the influence of D/d on the compression deformation behavior of nickel-based superalloy on the mesoscopic scale.

Inhomogeneous deformation and recrystallization behavior of through-thickness tantalum sheet under one-cycle clock-rolling

Effects of low clock rolling passes on through-thickness deformation and recrystallization behavior of the Ta sheet have been investigated. The clock-rolled samples with one cycle (8 passes) were systematically examined under different thickness layers. X-ray diffraction (XRD) and X-ray diffraction line profile analysis (XLPA) showed that the extremely inhomogeneous texture evolution generated and the bulk stored energy existed in the through-thickness clock-rolled Ta sheet after 8 passes. The electron backscatter diffraction (EBSD) results revealed the misorientation of the grains in the deformed samples, indicating that grain subdivision in the surface and center layer was more serious than that in the quarter layer. High intensities misorientation indicates the presence of microshear bands in the surface and center layer. During annealing, the difference of the stored energy and the fragmentation of deformation microstructure along the thickness led to a heterogeneous driving force for the nucleation of the grains, resulting in subsequent different recrystallization rate in the different regions of the sample.

Double tricrystal nucleation behavior in Pb-free BGA solder joints

The orientations of tin grains in a solder joint have a significant influence on its inhomogeneous deformation behavior under thermomechanical fatigue (TMF). In this paper, the tin orientations in as-solidified BGA joints were observed in detail by electron backscattering diffraction (EBSD). Double twinning of tin in the process of solidification was observed in the Sn-based solder joints. Although the morphologies of these twinned microstructures differed (beachball or intertwined), four orientations of tin grains, with each twin grain sharing a corporate [100] or [010] axis, were observed and analyzed in these systems. The results showed that the difference in orientation between the two groups of double tricrystals was in the range of 80° to 90°. The accurate misorientations were calculated to be 79.1°, 82.9° and 86.5°, corresponding to 57.2° and 62.8°. In a joint comprising 9 grains, there were 3 groups of double tricrystals. A joint comprising two grains, involving 55–65° tricrystal misorientations and a corporate [100] rotation axis, was practically a tricrystal. The joints exhibiting 4–9 grains with misorientations close to 60° (with a [100] or [010] axis) and 85° were composed of 1–3 groups of double tricrystals.

Inhomogeneous Warm Deformation Behavior and Its Effect on the Deformability of an Fe-6.5PctSi Alloy with Ce Doping

The inhomogeneous deformation behavior generated by deformability differences between soft and hard phases is a critical factor that influences the deformation and processability of materials. For Fe-6.5pctSi alloys with coexisting disordered and ordered phases, this work studied warm (300 °C to 500 °C) tensile deformation property differences and mechanisms for non-Ce-doped and 0.02 wt pct Ce-doped alloys. The warm deformation behavior was analyzed according to the stress and strain partitioning of the two-phase alloy by establishing a two-phase (A2 disordered phase + B2/D03 ordered phase) system model based on the structural characteristics of the alloy. The results show that the plastic deformation is mainly attributed to the A2 disordered phase, and the existence of a hard and ordered phase leads to local and inhomogeneous deformation behavior, which decreases the uniform plastic elongation and deformability of the alloy. Ce doping improves the warm deformation homogeneity and deformability by reducing the size and amount of the B2 ordered phase, which improves the warm rolling deformation and increases subsequent cold rolling deformability. Cold rolling with a total thickness reduction greater than 63 pct was achieved after the Ce-doped hot-rolled specimen with a 2 mm thickness was warm rolled to an 82.5 pct reduction, and the warm-rolled and cold-rolled sheets had good surface integrity and no obvious cracking.

In Situ Local Measurement of Austenite Mechanical Stability and Transformation Behavior in Third-Generation Advanced High-Strength Steels

Austenite mechanical stability, i.e., retained austenite volume fraction (RAVF) variation with strain, and transformation behavior were investigated for two third-generation advanced high-strength steels (3GAHSS) under quasi-static uniaxial tension: a 1200 grade, two-phase medium Mn (10 wt pct) TRIP steel, and a 980 grade, three-phase TRIP steel produced with a quenching and partitioning heat treatment. The medium Mn (10 wt pct) TRIP steel deforms inhomogeneously via propagative instabilities (Luders and Portevin Le Châtelier-like bands), while the 980 grade TRIP steel deforms homogenously up to necking. The dramatically different deformation behaviors of these steels required the development of a new in situ experimental technique that couples volumetric synchrotron X-ray diffraction measurement of RAVF with surface strain measurement using stereo digital image correlation over the beam impingement area. Measurement results with the new technique are compared to those from a more conventional approach wherein strains are measured over the entire gage region, while RAVF measurement is the same as that in the new technique. A determination is made as to the appropriateness of the different measurement techniques in measuring the transformation behaviors for steels with homogeneous and inhomogeneous deformation behaviors. Extension of the new in situ technique to the measurement of austenite transformation under different deformation modes and to higher strain rates is discussed.

A finite element simulation on inhomogeneous tensile deformation behaviour due to interaction between damage and TRIP effect in SUS304

A finite element simulation on inhomogeneous tensile deformation behaviour due to interaction between damage and TRIP effect in SUS304