Limited Plastic Deformation Research Articles

The deformation mechanism of low symmetric Ti–Pt intermetallic compounds containing high density of planar defects

Intermetallic compounds typically exhibit limited plastic deformation capacity due to challenges in activating dislocation slip and deformation twinning, coupled with a lack of alternative deformation mechanisms. Ti–Pt alloys are a prevalent type of intermetallic compound utilized in high-temperature shape memory alloys and as materials for energy applications in electric fields. However, they often exhibit poor deformation capability. Here, we prepared a low-symmetry intermetallic phase, Ti4Pt3, which demonstrates significant plastic deformation capability. This phase features a high density of parallel planar defects, resulting in an exceptionally large lattice periodicity perpendicular to these defects. Through in-situ scanning electron microscope compression tests, we observed substantial plastic deformation in this new phase. Analysis of the deformed Ti4Pt3 phase revealed that the dense planar defects create uniformly distributed sites of internal stress concentration, enabling a rapid increase in back stress within crystals. This phenomenon leads to notable lattice rotation and localized order-disorder transitions, both crucial mechanisms facilitating plastic deformation and enhancing deformation capacity. Our research underscores the potential of leveraging structural asymmetry to enable unconventional deformation mechanisms, thereby enhancing the plasticity of intermetallic materials.

Influence of nanofiller surface treatment on mechanical properties of pyrolyzed ceramic nanocomposites

The brittleness and limited plastic deformation of ceramics restrict their applications. In this work, the effects of pristine (CNTP), functionalized (CNTOH, CNTCOOH) and silanized MWCNTs on the mechanical properties of Silicon Carbide obtained by pyrolyzing polycarbosilane SMP-10 were studied. Functionalization with 3-glycidoxypropyltrimethoxy was analyzed through dispersion stability, zeta potential, and EDS analyses, revealing increased silicon content and colloidal stability in silanized MWCNTs. However, silanized MWCNTs led to reduced mechanical properties in composites, while untreated MWCNTs (CNTP, CNTOH, CNTCOOH), showed a substantial increase in modulus by 74.2 %, 86.9 %, and 30.5 %, respectively. The observed enhancement in mechanical properties exceeded the outcomes predicted by the rule of mixtures, suggesting notable morphological changes induced by MWCNTs. Potential underlying factors including toughening mechanisms and changes in porosity were evaluated and discussed in depth. Composites with untreated MWCNTs showed nearly a two-fold increase in fracture toughness. This work shows a streamlined approach for the development of ceramic nanocomposites (CNCs), achieving significant improvement in mechanical properties through pyrolysis, surpassing traditional methods reliant on densification processes. These findings demonstrate the substantial potential of CNCs, enhancing their suitability for advanced engineering applications.

Study on microstructure and mechanical properties of Ti–Co–Ni–Nb multi-principal component alloys designed by proportionally mixing intermetallics and eutectic units

The compositions of Ti–Co–Ni–Nb multi-principal component alloys (MCAs) were designed by proportionally mixing the Ti2Co intermetallics and Ni60Nb40 eutectic unit. The Ti30Co15Ni33Nb22 alloy mainly consists of body-centered cubic (BCC) TiNi matrix phase, along with small quantities of NiNb and Ti2Ni phases. The Ti32Co16Ni31.2Nb20.8 and Ti34Co17Ni29.4Nb19.6 alloys are primarily composed of a B2 TiNi matrix phase, with small amounts of NiNb and Ti2Ni phases. The Ti30Co15Ni33Nb22 alloy exhibits high yield strength and specific yield strength, while the Ti32Co16Ni31.2Nb20.8 alloy demonstrates high fracture strength (2802 MPa) and specific fracture strength. The plastic deformation behavior of these alloys is related to the structure of the TiNi phase. The limited plastic deformation observed in the Ti30Co15Ni33Nb22 alloy is attributed to the deformation of the brittle BCC TiNi phase, whereas the significant plastic deformation observed in the Ti32Co16Ni31.2Nb20.8 and Ti34Co17Ni29.4Nb19.6 alloys is a result of the deformation of the more ductile B2 TiNi phase. This study reaffirms that the proportional mixing of intermetallics and eutectic units is an important method for designing MCAs with high strength.

Numerical analysis of the indentation of a poro-elastoplastic half space by a rigid cylinder

Poro-elasto-plastic cylindrical indentation as a means for material characterization is explored numerically in this work. When a rigid cylinder is being pressed into a semi-infinite, fully saturated poroelastic medium via step displacement loading, undrained and drained elastic constants are reflected in the responses at the early and late times, while hydraulic diffusivity is manifested in the transient behavior. Such an indentation test can therefore be used in principle to identify material parameters. For geomaterials, plastic deformation may occur due to the indentation action. How the hydromechanically coupled indentation response is affected by plastic deformation is investigated here using finite element analysis. We consider the problem to be plane strain with frictionless contact. Drucker-Prager failure criteria with and without a cap are considered. We show that if there is only limited plastic deformation, the concept of using the transient response for determining hydraulic diffusivity may be extended from poroelasticity to poro-elasto-plasticity.

Brittle‐Ductile Rheological Behavior in Subduction Zones: Effects of Strength Ratio Between Strong and Weak Phases in a Bi‐Phase System

AbstractThe brittle‐ductile rheological behavior in subduction zones is commonly proposed to explain deep transient slips. Generally observed at large scales in tectonic “mélanges”, here we show that it is also observed at the grain scale in exhumed blueschist metagabbros. In these rocks, petrologic and microstructural observations show a bi‐phase material constituted by strong microfractured magmatic pyroxene clasts located in a weak and ductile lawsonite‐rich metamorphic matrix. To constrain the mechanical conditions allowing the brittle deformation of a clast in a ductile matrix, we used two‐dimensional simple shear numerical experiments. Results show four behaviors: (a) entirely brittle; (b) brittle‐ductile with clast fracturing in a ductile matrix; (c) ductile‐dominant with limited plastic deformation at clast edges; and (d) entirely ductile. We propose that the conditions of the brittle‐ductile behavior, commonly associated with deep transient slips, are controlled by the strength ratio between the strong brittle phase and the weak ductile phase.

Impact behavior of spark plasma sintered Ti–Al–Mo/TiN composites: a finite element analysis approach using Abaqus CAE

BackgroundThe utilization of Finite Element Analysis (FEA) has emerged as a crucial methodology in the field of structural and elasticity analysis, facilitating researchers in their understanding of material responses to diverse thermal or structural loads. This study investigates the utilization of FEA to simulate the Impact characteristics of titanium composites, with specific emphasis on the Charpy impact test. The research utilizes the Abaqus Explicit software, which is widely recognized for its explicit dynamic analysis functionalities, to simulate high-speed and short-duration events such as impacts. The primary objective of this study is to examine the impact behavior of Ti–7Al–1mo/TiN composites fabricated through the spark plasma sintering technique. The impact behavior is simulated using FEA, wherein the shear failure model is utilized to replicate fracture phenomena. This paper examines the methodology employed in the FEA approach, with a particular focus on various factors including boundary conditions, explicit dynamic analysis settings, and material properties.ResultsThe outcomes and analyses involve the examination of the von Mises stress distribution, displacement magnitude, and energy behavior of the models that were tested. Reinforcement of Ti–Al–Mo ternary alloy with TiN led to a progressive increase in maximum von Mises stress, reaching a peak at 3 wt% TiN. Conversely, displacement magnitude decreased with increasing TiN content, with CP-Ti and the unreinforced alloy exhibiting the highest values. Absorbed energy also declined with higher TiN levels. While models containing 5 and 7 wt% TiN displayed limited plastic deformation before fracture, composites with ≤ 3 wt% TiN maintained acceptable ductility despite enhanced strength and stiffness.ConclusionThe FEA methodology effectively simulates the Charpy impact characteristics of Ti–7Al–1Mo/TiN composites, thereby offering significant contributions to understanding their mechanical behaviors. These findings suggest that TiN reinforcement up to 3 wt% presents a promising strategy for improving the mechanical performance of Ti–Al–Mo alloys while minimizing the trade-off in toughness. This research emphasizes the inherent trade-off between toughness and strength/stiffness, suggesting the possibility of optimizing the composition of materials to suit particular applications. This study makes a valuable contribution to the expanding field of impact behavior research, demonstrating the potential of FEA, specifically utilizing Abaqus Explicit software, for enhancing material design and evaluation.

Study of self-heating and local strain rate in polyamide-6 and short fibre glass/polyamide-6 under tension through synchronised full-field strain and temperature measurements

This paper studies thermomechanical coupling during room-temperature tensile testing of polyamide-6 (PA6) and 50 wt% short glass fibre/PA6. The tests were performed for different fibre angles (0°, 45°, 90°), moisture contents (dry, 50%RH), and strain rates (10−4, 10−2, 10−1s−1). Digital image correlation (DIC) was coupled with infrared thermography. The contribution of the local strains, strain rates and temperatures to the global mechanical behaviour was investigated throughout deformation. The initial thermoelastic response was used to estimate the coefficient of thermal expansion. In PA6, neck development caused significant self-heating at high strain rates, differently between dry and 50%RH. In glass/PA6, however, temperature rises were always small (<+3 °C) despite local strain rate peaks in the fracture zone. This was ascribed to limited plastic deformation, as confirmed by post-mortem microscopy. The full-field data can be highly valuable for the development of advanced constitutive models for both pure polymer and short fibre composite.

Coatable strain sensors for nonplanar surfaces.

Rapidly fabricating flexible and stretchable sensors on nonplanar surfaces is crucial for wearable device applications. We employed a novel fabrication method, incorporating molds and gels into electroless plating, to enable direct printing of sensors on a wide array of surfaces, from those with up to 100 μm profile heights to hydrogels with a Young's modulus of 100 kPa. This coatable strain (CS) sensor offers several potential advantages. Firstly, it is designed to circumvent the typical limitations of limited flexibility, plastic deformation, and low repeatability found in viscoelastic polymers by being directly coated onto the surface without requiring a substrate. Secondly, it potentially increases the effective contact area and signal-to-noise ratio by eliminating voids between the sensor and the surface. Finally, the CS sensor can obtain any desired patterning at room temperature in a matter of minutes, significantly reducing energy and time consumption. In this study, we demonstrated the versatility of the CS sensor by applying it to a range of substrates, showcasing its adaptability to diverse materials, surface roughness levels, and Young's modulus values. Our primary focus was on plant growth monitoring, a challenging application that showcased the sensor's efficacy on surfaces like needles, hairy leaves, and fruits. These applications, traditionally difficult for conventional polymer-based sensors, serve to illustrate the CS sensor's potential in a range of complex environmental contexts. The successful deployment of the CS sensor in these settings suggests its broader applicability in various scientific and technological fields, potentially contributing to significant developments in the area of wearable devices and beyond.

Effect of dendritic structure and secondary phases on the fatigue behavior of ERNiCrMo-3 weld metal

The effect of dendritic structure and secondary phases on the fatigue crack propagation mechanism of ERNiCrMo-3 weld metal was investigated. Element segregation in the weld metal induced severe lattice distortion in the interdendritic region, creating substantial variations in mechanical properties between the dendrite core and interdendritic region. This disparity resulted in an unstable crack propagation rate. The limited plastic deformation capacity of the interdendritic region caused a contraction in the local plastic deformation zone at the crack tip, increasing stress concentration and accelerating crack propagation. The fatigue crack in the interdendritic regions exhibited a rate of approximately 2.6 μm/cycle, surpassing the 1.5 μm/cycle observed in the dendrite cores. Meanwhile, element segregation promoted the precipitation of numerous Laves phases in the interdendritic regions. With increasing stress, micro-voids formed by broken Laves phases served as rapid channels for crack propagation. Post-weld heat treatment weakened the non-uniformity of the microstructure. The fatigue crack propagated at a rate of about 1.2 μm/cycle. Furthermore, the dissolution of Laves phases and the precipitation of γ″ enhanced the fatigue performance of the weld metal. Under equivalent stress levels, the fatigue life of post-weld heat-treated weld metal increased by approximately 1.2 times compared to that of as-welded metal.

Formation mechanism of zig-zag crack region on the shattered rim of railway wheel

Shattered rim is a century-old problem that restricts the reliability of railway wheels in service. In this paper, the formation mechanisms of the zig-zag crack region on the shattered rim of railway wheel were investigated. First, the zig-zag crack region was observed using both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and was identified as a typical region for crack propagation in giga-cycle rolling contact fatigue behavior. The zig-zag crack bands have a height range of 3–30 μm, with an average of 13.4 μm, and a width range of 0–500 μm, with an average of 184.6 μm. The size values of band height and width are close to the values of the pearlite and protoaustenitic grain size. The formation of the zig-zag morphology in the zig-zag crack region is due to the periodic deflection of the propagation path relative to the initial propagation plane, which is a result of the limited plastic deformation zone at the crack tip that extends only a few grain diameters. The grain refinement and secondary cracks in the zig-zag crack region are attributed to the large compressive and shear stresses induced by the applied rolling contact loading.

The effect of nickel-induced finite plasticity on the tribological behavior and wear resistance of Cu-Sn-Bi alloy

This article investigates the effect of nickel-induced finite plastic deformation at the friction interface of the CuSn10Bi3 bimetallic copper layer on its tribological properties. CuSn10Bi3 alloy bimetallic samples with different nickel contents were prepared by powder metallurgy, and the microstructure and Brinell hardness were observed. The tribological performances and wear behaviors under dry friction and oil-depleted lubrication conditions were evaluated and analyzed. The results show that the Ni in the copper-tin-based alloy reduces the surface porosity of the powder metallurgical samples. With the increase of Ni content from 0.5 wt% to 1.2 wt% and 2 wt%, the porosity decreased by 36%, 48.7% and 62.3%, respectively, and the hardness of the samples increased slightly. The grain size of the alloy decreases with the increased Ni content, which is attributed to the increase of twinning. Besides, the friction coefficient of Ni-containing samples was more stable and the wear under dry friction was significantly reduced, especially, the wear loss is reduced by 78.2% when the content of Ni is 2%. The wear mechanism changed from abrasive-dominated and oxidative wear to plastic deformation-dominated and furrow wear. The limited plastic deformation of the friction interface caused by the addition of 2% nickel is a new strategy for solving the problem of brittle exfoliation of wear surfaces and improving the wear resistance of Bi-containing copper alloys.

Local atomic structure studies of Zr55Cu35Al10 alloy around Tg

As a result of examining the structure of Zr55Cu35Al10 alloy around the glass transition temperature (Tg) using the classical molecular dynamics simulations, it was proven that the atomic bonds in the interconnecting zones (i-zones) became loose with the small amount of energy absorption, and it became free volumes easily when the temperature approached Tg. Instead of i-zones, when clusters were largely separated by free volume networks, the solid amorphous structure was converted into supercooled liquid state, resulting in a sharp strength reduce and the great plasticity change from a limited plastic deformation to superplasticity.

Elasto-plastic analysis and optimal design of composite integral abutment bridge extended with limited residual plastic deformation

Due to the growing significance of structural theories concerning the composite structure analysed and designed plastically, this paper introduces a new optimisation method for controlling the plastic behaviour of a full-scale composite integral abutment bridge by employing complementary strain energy of residual forces that existed within the reinforcing rebars. Composite bridges are structures made of components such as steel and concrete, which are frequent and cost-effective building methods. Thus, various objective functions were used in this work when applying optimum elasto-plastic analysing and designing the composite integrated bridge structure that was tested experimentally in the laboratory. In contrast, the plastic deformations were constrained by restricting the complementary strain energy of the residual internal forces aiming to find the maximum applied load and the minimum number of steel bars used to reinforce the concrete column part of the structure. The numerical model employed in this paper was validated and calibrated using experimental results, which were considered inside ABAQUS to produce the validated numerical model, using concrete damage plasticity (CDP) constitutive model and concrete data from laboratory testing to solve the nonlinear programming code provided by the authors. This paper presents a novel optimization method using complementary strain energy to control the plastic behaviour of a full-scale composite integral abutment bridge, with the original contribution being the incorporation of residual forces within reinforcing rebars to limit plastic deformations. Following that, a parametric investigation of the various optimisation problems revealed how models performed variously under different complementary strain energy values, which influenced the general behaviour of the structure as it transitioned from elastic to elasto-plastic to plastic; also results showed how the complementary strain energy value is connected with the amount of damaged accrued in both concrete and steel.

Bonding mechanisms and micro-mechanical properties of the interfacial transition zone (ITZ) between biochar and paste in carbon-sink cement-based composites

A better understanding of the interfacial transition zone (ITZ) in biochar-augmented carbon-negative cementitious materials can facilitate their potential applications. This study illustrated the key chemical and mechanical features of such a region in Portland cement using backscattered electron microscopy-energy dispersive X-ray analysis (BSEM-EDX), nano-indentation, and X-ray computed tomography (X-CT). It was found that a significant ‘wall effect’ was identified at the side-edge of biochar, where the degree of hydration and the porosity significantly increased. The biochar was integrated into the hardened cement matrix via a layer of Ca-rich hydration products mainly composed of AFm phases, CH and C–S–H gels. Regarding the mechanical behaviour, the biochar showed a typical viscous-elastic (VE) deformation mode at the nano/micro scale, whereas the hardened cement was a typical plastic-elastic (PE) material. Therefore, the value of the hardness of biochar was not accurate under limited plastic deformation. The distinct differences in deformation resulted in the largest residual deformation (i.e., plasticity) of the hardened cement after indentation when compared to ITZ and biochar regions, whereas the ITZ maintained a lower value due to well connection with biochar. These microstructural characteristics partially explained the higher compressive strength of biochar-cement composites than previously expected.

Effect of counter-surface chemical activity on mechanochemical removal of GaAs surface

Using atomic force microcopy, mechanochemical removal behaviors of GaAs surface slid by Al2O3, SiO2, and CeO2 micro-spherical tips were investigated in ambient environment. High-resolution transmission electron microscope characterization demonstrates that defect-free material removal was achieved on GaAs surface under the contact pressures much below the yield limit of plastic deformation, which can be ascribed to water-participated mechanochemical reactions. Further analysis indicates that the interfacial mechanochemical reactions are strongly affected by the counter-surface chemistry. Nano abrasive with low chemical activity inhibits the mechanochemical reaction via increasing the activation energy of the formation of interfacial bonding bridges, but there is no obvious difference in the mechanically weakening process of the activation energy for the rupture of Ga−As bond on the substrate.

Computational delving into conceivable thermoelectric and spintronic applications of NH4AF3 (A = Fe and Co) ferromagnets

In this investigation, the structural, mechanical, electronic, magnetic, and thermoelectric properties of fluoroperovskite NH4AF3 (A = Fe and Co) compounds were determined utilizing the WIEN2k code. The structural properties such as tolerance factor, enthalpy, and elastic stability criterion predict that the studied compounds are mechanically and thermodynamically stable. Furthermore, the mechanical properties show that NH4FeF3 is more stretchable and rigid in nature than NH4CoF3. Interestingly, both compounds exhibit the anisotropic, intermediate type of bonding effect, higher plastic deformation limit, and brittle nature. The high melting temperature of the present compounds indicates the possible usage of these compounds in high-temperature electronic applications. The electronic calculations show that NH4FeF3 and NH4CoF3 are half-metallic and ferromagnetic compounds with a combination of ionic and covalent bonds between the different atoms. The thermoelectric parameters predict that electrons are the main charge carriers for the present compound with p-type character. Our study suggests that these plausible applications of the compounds are very versatile and include heat sensors, spintronic devices, optoelectronic sensors, and magnetic tunnel junction devices.

Ultrahigh strength and shear-assisted separation of sliding nanocontacts studied in situ

The behavior of materials in sliding contact is challenging to determine since the interface is normally hidden from view. Using a custom microfabricated device, we conduct in situ, ultrahigh vacuum transmission electron microscope measurements of crystalline silver nanocontacts under combined tension and shear, permitting simultaneous observation of contact forces and contact width. While silver classically exhibits substantial sliding-induced plastic junction growth, the nanocontacts exhibit only limited plastic deformation despite high applied stresses. This difference arises from the nanocontacts’ high strength, as we find the von Mises stresses at yield points approach the ideal strength of silver. We attribute this to the nanocontacts’ nearly defect-free nature and small size. The contacts also separate unstably, with pull-off forces well below classical predictions for rupture under pure tension. This strongly indicates that shearing reduces nanoscale pull-off forces, predicted theoretically at the continuum level, but not directly observed before.

Self-Assembled Epitaxial Ferroelectric Oxide Nanospring with Super-Scalability.

Oxide nanosprings have attracted many research interests because of their anticorrosion, high-temperature tolerance, oxidation resistance, and enhanced-mechanic-response from unique helix structures, enabling various applications like nanomanipulators, nanomotors, nanoswitches, sensors, and energy harvesters. However, preparing oxide nanosprings is a challenge for their intrinsic lack of elasticity. Here, an approach for preparing self-assembled, epitaxial, ferroelectric nanosprings with built-in strain due to the lattice mismatch in freestanding La0.7 Sr0.3 MnO3 /BaTiO3 (LSMO/BTO) bilayer heterostructures is developed. It is found that these LSMO/BTO nanosprings can be extensively pulled or pushed up to their geometrical limits back and forth without breaking, exhibiting super-scalability with full recovery capability. The phase-field simulations reveal that the excellent scalability originates from the continuous ferroelastic domain structures, resulting from twisting under co-existing axial and shear strains. In addition, the oxide heterostructural springs exhibit strong resilience due to the limited plastic deformation nature and the built-in strain between the bilayers. This discovery provides an alternative way for preparing and operating functional oxide nanosprings that can be applied to various technologies.

Pure shear plastic flow and failure of titanium alloys under quasi-static and dynamic torsional loading

The pure shear responses of Ti6Al4V alloy and Ti3Al2.5V alloy, conceived for unique applications in jet engine components, are compared using Digital Image Correlation technique from quasi-static (10−3/s), medium strain rate (101/s) and high strain rates (103/s). A series of bespoke torsion tests have been performed on a screw driven mechanical system, a fast hydraulic Instron machine and a Campbell split Hopkinson torsion bar, equipped with high speed photographic equipment. Observations have provided the strain rate dependence and the relation of pure shear failure at quasi-static and high strain rates. The quasi-static shear constitutive relationships including shear modulus, yield stress and failure strain of both alloys are compared at the location of failure initiation, using a bespoke four camera system. The Ti3Al2.5V alloy presents lower shear flow stress and strain rate sensitivity with higher ductility, as opposed to the Ti6Al4V alloy with limited plastic deformation capacity. Associated with modest estimated overall temperature rise until final collapse of the specimen, both ductile Ti3Al2.5V alloy and brittle Ti6Al4V alloy fail by adiabatic shear banding at high strain rates. This is different from the void growth induced failure at medium strain rate with mild temperature rise and at quasi-isothermal condition. The present results show a general description of brittle and ductile alloys in engineering design. Likewise, this study will guide the characterization of pure shear flow and failure for current and future developed impact resistant alloys.

True Stress–True Strain Relationship up to the Plastic Deformation Limit in Ferrite–Pearlite Steel at Various Temperatures

True Stress–True Strain Relationship up to the Plastic Deformation Limit in Ferrite–Pearlite Steel at Various Temperatures