Low Deformation Levels Research Articles

Diffusion of lithium in copper current collectors of lithium metal anodes in liquid cells

Conflicting views are found in the literature on the significance of lithium diffusion into copper current collectors of lithium metal anodes. Previously published in situ Neutron Depth Profiling (NDP) measurements in a liquid cell revealed reversible Li diffusion in the current collector during electrochemical cycling, resulting in concentrations of ∼ 1 at. %. Herein, a model for these experiments is presented, in which stress in the deposit is induced by Li diffusion accompanying plating and stripping. This in turn produces stress gradients in the current collector, which together with composition gradients drive reversible grain boundary diffusion in Cu during cycling. Quantitative agreement with the NDP results is obtained for a fit diffusivity comparable to previous in situ measurements, but much larger than values from ex situ measurements using Li–Cu bilayers. Creep due to grain boundary diffusion is found to relax stress in the copper foil, resulting in low levels of stress and deformation during cycling. The results clarify the significance of Li diffusion in Cu, and also help elucidate the origin of stress in the lithium anode during cycling, which may induce interfacial instability.

New Insights Into the Active Tectonics of the Northern Canadian Cordillera From an Enhanced Earthquake Catalog

AbstractSeismic activity in the Northern Canadian Cordillera is characterized by diffuse earthquakes that extend hundreds of km northwest from the Yakutat collision zone. We use 25 months of broadband seismic data from Mackenzie Mountain Earthscope Project (MMEP), USArray Transportable Array (TA), and permanent Canadian National Seismic Network stations to present a local earthquake catalog with high sensitivity to small regional events. Deep learning techniques are adopted for both seismic phase detection and association. Event relocations are performed to provide well constrained estimates of earthquake depth distributions. Clusters of seismicity spanning the upper crust are located in the central Richardson Mountains, along the Tintina fault, and in the northeast Selwyn Basin. These clusters suggest that the core of the Richardson Anticlinorium is tectonically active and that the Tintina fault is a locus for low levels of active deformation. We interpret seismicity in the northeast Selwyn Basin as primarily occurring in the hanging wall of the Plateau thrust fault and suggest that some combination of localized duplex structures and lithological strength contrasts both within the Selwyn Basin and between abutting Paleozoic shelf sequences may be responsible for seismicity in the Mackenzie Mountain foreland.

Relation between sampling, sensitivity and precision in strain mapping using the Geometric Phase Analysis method in Scanning Transmission Electron Microscopy

The sensitivity and the precision of the Geometric Phase Analysis (GPA) method for strain characterization is a topic widely discussed in the literature and is usually difficult to quantify. Indeed, the GPA precision is intricately linked to the resolution of the strain maps defined when masking the periodic reflections in Fourier space. In this study an additional parameter, sampling, is proposed to be analyzed regarding the precision of GPA by developing the concept of a phase noise in the GPA equations. Both experimentally and theoretically, the following article demonstrates how the precision, and the sensitivity of the GPA method is improved when using a larger pixel spacing to record an electron micrograph in Scanning Transmission Electron Microscopy (STEM). The counterintuitive concept of increasing the field of view to improve the GPA precision results is an extension of the application of strain characterization methods in STEM towards low deformation levels.

Integrated multi-scale modeling of variant selection during stress-induced martensite formation in metastable β Ti-alloys

Stress-induced martensite formation is the predominant mechanism during the deformation of various functional and structural Ti- alloys. To predict the performance of these alloys, stress-induced martensite formation was modeled as a function of crystal orientation and stress state. We present an integrated micromechanical modeling approach using finite element (FE) analysis and an elastic spectral solver based on Fast Fourier Transforms (EFFT), which allows direct correlation of the available work from martensite formation under complex stress-states in an in-situ characterized microstructure. The model is applied as a virtual analogue of an experimental 3-point bending test of a metastable β Ti–10V–2Fe–3Al alloy containing 5% α. The FE model incorporates the experimental β microstructure from electron backscattering diffraction (EBSD) with anisotropic elastic behavior. The EFFT solver uses strain fields in two local regions from the FE model to predict local stresses in experimental microstructures containing β and α phases. The stress and orientation data are used to predict the available work from stress-induced α″ martensite formation of the six different α″ variants. It was found that stress and available work concentrated around the tips of lamellar α, making these regions preferred nucleation sites for α″ formation, which is in excellent agreement with the in-situ experimental observations. This suggests that the local stress conditions in the β phase play a more important role in triggering α″ formation than the compositional inhomogeneity in the β phase at α-β interfaces. Using the integrated model, the first variants forming at low levels of deformation could be confidently predicted. However, the transformation behavior at elevated levels of deformation could not be properly captured. This indicates the need of further model improvement, including Dirichlet boundary conditions for the EFFT solver and accounting for the role of plasticity induced by phase transformation.

The influence of temperature on the strain-hardening behavior of Fe-22/25/28Mn-3Al-3Si TRIP/TWIP steels

The influence of temperature and stacking fault energy (SFE) on the strain-hardening behavior and critical resolved shear stress for twinning was investigated for three Fe–22/25/28Mn–3Al–3Si wt.% transformation- and twinning-induced plasticity (TRIP/TWIP) steels. The SFEs were calculated by two different methods, density functional theory and statistical thermodynamic modeling. The dislocation structure, observed at low levels of plastic deformation, transitions from “planar” to “wavy” dislocation glide with an increase in temperature, Mn content, and/or SFE. The change in dislocation glide mechanisms from planar to wavy reduces the strain hardening rate, in part due to fewer planar obstacles and greater cross slip activity. In addition, the alloys exhibit a large decrease in strength and ductility with increasing temperature from 25 to 200 °C, attributed to a substantial reduction in the thermally activated component of the flow stress, predominate suppression of TRIP and TWIP, and a significant increase in the critical resolved shear stress for mechanical twinning. Interestingly, the increase in SFE with temperature had a rather minor influence on the critical resolved shear stress for mechanical twinning, and other temperature dependent factors which likely play a more dominant role are discussed.

Strain states and unique properties in cold-rolled TiNi shape memory alloys

Martensitic transformation (MT), strain glass transition (SGT) and the corresponding stress-strain responses in cold-rolled Ti49.2Ni50.8 shape memory alloys (SMAs) at various amounts of cold-rolling deformation are investigated. A phase diagram describing all the strain states and transitions among them is established in the temperature – deformation space. It shows a normal sharp, strong first-order B2 to B19′ MT at low deformation levels (cold-rolling thickness reduction εp < 27%), but a continuous B2 to B19′ SGT at high deformation levels (εp ≥ 27%) upon cooling. Superelasticity with small hysteresis, tunable modulus and functional-fatigue resistance properties are achieved by altering the transition behavior from MT to SGT at εp ≥ 27%. Nanodomains of single variant B19′ martensite at the atomic scale are observed by using aberration-corrected scanning transmission electron microscopy in samples with εp = 27%. Further in-situ loading synchrotron-based high energy X-ray diffraction technique shows that the quasi-linear superelasticity associated with the SGT can be attributed to stress-induced continuous growth of B19′ nanodomains. Geometrical phase analysis of high-resolution transmission electron microscopy image reveals a nanoscale network of severe lattice distortion associated with the accumulated high-density of defects at εp ≥ 27%, which is the microstructural origin of the B19′ strain glass state. This work provides a detailed explanation for the longstanding puzzle of unique quasi-linear superelastic response in plastically deformed TiNi SMAs, and may shed light on achieving novel mechanical properties through defect engineering.

Assessment of Dislocation Density by Various Techniques in Cold Rolled 1050 Aluminum Alloy

This study examines the evolution of dislocation density in cold rolled 1050 Al alloy. Various techniques such as numerical approaches, indentation techniques, X-ray diffraction line profile analysis, and electron backscattering diffraction were employed for the characterization of the deformed state. These methods allowed us to determine the nature of the evolution of the dislocation substructure during cold rolling. The investigated material was subjected to thickness reductions varying from 5% to 47%, which resulted in a continuous increase in hardness while the estimated dislocation density showed a tendency towards a less intense increase after a ~30% straining level. The numerical approaches employed, such as the Kubin–Estrin and a modified version of this model, are capable of ensuring a reasonable estimation of dislocation density at low and moderate deformation levels (~5–30%), while the discrepancy between the measured and simulated data is negligible when the material has been exposed to more severe rolling reductions.

New Insight into the development of deformation texture in face-centered cubic material

Despite a tremendous amount of research to understand the evolution of microstructural and texture changes during deformation, there is still a need for further deep insight into it. The most used deformation process underuse in industries is the rolling of material. Stacking fault energy is the most critical material property, which governs the deformation behavior. In the present study, the microstructure and texture changes of a high SFE material (pure nickel) during cold rolling was investigated. The objective is to find criteria for the change of orientation of a particular grain as rolling proceed. Pseudo-in-situ rolling was done through which the shape, orientations, and neighbors of each grain could be tracked as a function of rolling reductions. It was found that orientations of some grains remain stable after a large reduction and do not develop sub-grains within it, whereas orientations of some grains change drastically at a very low deformation level along with the evolution of a large number of sub-grains.

The effect of structure-property relationships on the formability of pigmented polyester coatings

Pre-painted metal sheet (PPM) is used in applications from domestic appliances to architectural cladding. The coating provides excellent aesthetics and corrosion protection, but must possess excellent formability to not fail due to the large strains applied during the folding and hemming processes used to produce components. Therefore it is important to understand how the coating formulation affects the free-film properties and formability of a coating system. Polyester coatings crosslinked with hexa(methoxymethyl)melamine (HMMM) with a Tg of ∼40 °C were used, pigmented with TiO2. The glass transition temperature was increased by increasing the crosslinker content (from 5% to 30%), decreasing the adipic acid content (from 24% to 12%) and decreasing the molecular weight (from Mn = 3300 g/mol to Mn = 1500 g/mol). The chemical structure of the resin had little effect on the formability of the coatings when the test temperature was normalised with respect to Tg. The formability measured using the Erichsen cupping and T-bend tests is related to the tensile properties of the free-films. The damage induced by the T-bend is greater than that by the Erichsen cupping test due to the higher applied deformation rates in T-bend tests. Increasing the apparent yield and fracture stress increases the likelihood of damage at lower deformation levels, whilst increasing the strain to failure decreases the likelihood of damage in both the T-bend and Erichsen cupping tests. The strength of these correlations reduces with an increase in T-bend level as the magnitudes of the strains applied are reduced. This work takes a holistic approach to correlate structure and tensile properties with formability in both the Erichsen cupping test and T-bend test for the first time, enabling industry to improve coating performance significantly but cost-effectively.

On energy-absorbing mechanisms and structural crashworthiness of laterally crushed thin-walled structures filled with aluminum foam and CFRP skeleton

In the present study, thin-walled tubes filled with aluminum foam and CFRP skeleton (FCFTs) are developed and manufactured based on a multiple material system. The structural crashworthiness of the proposed design is investigated under quasi-static lateral loading. Further, the aluminum tube, the foam-filled tube and the tubes filled with CFRP skeleton are also designed and tested to perform a comparative study. It is found that the FCFT-1 (the tube filled with foam and CFRP skeleton with square cells) exhibits superior SEA (specific energy absorption), which is almost five times that of the individual aluminum tube, and almost 10% higher than that of the foam-filled tube. However, FCFT-2 (the tube filled with foam and CFRP skeleton with triangular cells) provides relatively lower energy-absorbing capacity, as its aluminum tube generates several axial cracks during crushing process leading to low deformation level of the foams. Furthermore, crush simulations are conducted to better understand the energy-absorbing mechanisms of the FCFT-1. The numerical results demonstrate that the plastic deformation of the separated foams makes up the major part of the total energy absorption. Besides, the performance improvement of FCFT-1 can be partly attributed to the fact that the separated foams generate larger plastic deformation during crushing process. Apart from this, the increased interaction effects between the separated foams and the CFRP skeleton lead to a higher FE (frictional energy), which also makes a slight contribution to the performance improvement of FCFT-1. Finally, parametric studies are performed to explore the influences of design parameters on the crashworthiness characteristics of FCFT-1. It is indicated that the energy-absorbing capacity can be slightly improved by raising cell number, proportion of 45° layer or foam density. The present work is expected to provide some insights for researchers and engineers to design such structures for energy absorption applications.

Effect of compaction water content and stress ratio on permanent deformation of a subgrade lateritic soil

Permanent deformation is a potential distress that affects the functional characteristics of pavement. Subgrade soil might contribute to different levels of permanent deformation depending on traffic intensity. This paper assesses the stress ratio effects as well as compaction water content variation on permanent deformation of subgrade soil, presents some contributions to understanding the Shakedown concept in fine-grained soils and evaluates models for estimating soil plastic strain. Repeated load triaxial (RLT) tests were performed on lateritic sandy soil in order to obtain: permanent deformation and Shakedown parameters. Findings indicated a prevalence of stress ratio in permanent deformation for a specified compaction water content range (wopt ± 1.5%). However, analysis of plastic strain rates showed that permanent deformation might be more influenced by compaction water content than by stress ratio, mainly in cases where compaction water content range is wider. Furthermore, stabilization, i.e. Shakedown first phase occurrence, was achieved under all test conditions, in spite of low deformation levels. Lastly, the model adjusted in function of stress ratio and compaction water content closely represented the complexity of soil plastic strain accumulation.

Microstructure and Mechanical Properties of an Austenitic CrMnNiMoN Spring Steel Strip with a Reduced Ni Content

The article presents the mechanical properties of the austenitic stainless steel X5CrMnNiMoN16-4-4 after deformation by cold rolling and subsequent short-term tempering (deformation and partitioning (D&amp;P) treatment). Tensile strengths of 1700–900 MPa and beyond were achieved both after work hardening and in the D&amp;P-treated strip. The initial state of austenite in terms of grain size and pre-strengthening, as well as the selected cold rolling temperature significantly influenced the deformation-induced formation of α’ martensite and thus the flow and hardening behavior of the steel. The usage of two different rolling temperature regimes showed that the strength properties in the cold strip can be specifically adjusted. Lower deformation-induced martensite fractions enabled a larger thickness reduction of the strip without increasing the rolling force, while high deformation-induced martensite fractions led to strong hardening at low deformation levels. The D&amp;P-treatment permits the strength of the cold-rolled strip with a predominantly austenitic microstructure to be increased to the required level. The total elongation of such a D&amp;P strip was well over 2%. The D&amp;P treatment of the spring steel strip is a cost-effective alternative to conventional tempering treatment.

The effect of processing parameters on rapid-heating β recrystallization in inter-pass deformed Ti-6Al-4V wire-arc additive manufacturing

Relatively low levels of inter-pass deformation have been found to be very effective in refining the coarse columnar grain structures normally seen in Ti-6Al-4V components, built using wire-fed high-deposition-rate additive manufacturing processes. The most important process parameters that control the level of β recrystallization – the final grain size and micro-texture – were systematically investigated by simulating the deformation and high heating rate conditions in controlled samples, to develop the process knowledge required to optimise inter-pass deformation and obtain predictable grain sizes. Overall, it was found that the level of β-grain refinement achieved by inter-pass deformation was surprisingly insensitive to the ranges of deformation temperatures, deformation speeds, and changes to the as-deposited α + β microstructure, expected within the WAAM process window, provided a minimum plastic strain of only 14% was achieved in each added layer. Conversely, the final component grain size was shown to be strongly affected by rapid grain growth on re-heating above the β transus. The texture results obtained were consistent with previous work which suggested that, with fine AM transformation microstructures, new β-grain orientations may be produced during the α → β transformation from the development of twinning faults, induced by the prior deformation and rapid heating. In contrast, greatly increasing the starting α lamellar spacing – to be more similar to that found in a wrought material – greatly reduced the level of recrystallization and also appeared to change the recrystallization mechanism to favour new β orientations produced largely by local lattice rotation.

Detailed experimental and theoretical investigation of the thermomechanical properties of epoxy composites containing paraffin microcapsules for thermal management

AbstractMicroencapsulated phase change materials (PCMs) are being increasingly employed as functional fillers in polymer matrices for thermal management. Therefore, the effect of PCM microcapsules on the rheological, microstructural, thermal and mechanical properties of the host polymer matrices must be understood. This work concerned the preparation of epoxy polymers filled with PCM microcapsules (MC) in various concentrations and their subsequent characterization. The MC phase increases the viscosity of epoxy before curing, thereby reducing castability and hindering elimination of air bubbles. The latter was reflected in an increase in porosity for highly filled compositions, as elucidated by density measurements and microscopic investigation. SEM micrographs showed that the adhesion between the capsule shell and the epoxy matrix was not optimal. The interfacial weakness and the intrinsic low stiffness and strength of MC caused a reduction in mechanical properties, as evidenced by the Nicolais‐Narkis and Pukanszky models. On the other hand, at zero or low deformation levels, the interface presents no gaps and is able to transfer load and heat, as demonstrated by the data of elastic modulus, modeled with the Halpin‐Tsai and Lewis‐Nielsen models, and those of thermal conductivity, in excellent agreement with the Pal model. POLYM. ENG. SCI., 2020. © 2020 Society of Plastics Engineers

Mechanical Characterization of Fine-Grained Lateritic Soils for Mechanistic-Empirical Flexible Pavement Design

Abstract Fine-grained lateritic soils, which are typically found in tropical regions and have been used successfully in low-cost pavements, are often considered inadequate for the base and subbase pavement layers when the material selection is based on the California bearing ratio (CBR). When analyzed in repeated load triaxial (RLT) test equipment, which is the most frequently used device to analyze the mechanical behavior of unbound pavement materials, fine-grained lateritic soils exhibit low levels of plastic deformation. Thus, to allow more appropriate analyses of the mechanical behavior of such soils compared to traditional CBR-based analyses, resilient modulus and permanent deformation tests using RLT test equipment were performed. Then, multifactorial regression analysis of the experimental results was performed to identify the parameters of the material models that are implemented in the Brazilian mechanistic-empirical pavement design software program, MEDINA. The experimental program included material characterization in accordance with the so-called miniature, compacted, tropical (MCT) methodology that is tailored specifically to classify tropical soils. For one of the lateritic soils, two key parameters, i.e., the stress level and compaction moisture content, were varied in the RLT permanent deformation tests. An additional numerical analysis using MEDINA was conducted to evaluate the structural characteristics of flexible pavements composed of the four lateritic soils analyzed in this study. In general, the results obtained from this study indicate that lateritic soils can potentially be used as base and subbase layers in flexible pavement structures.

A study on slip activation for a coarse-grained and single crystalline CoCrNi medium entropy alloy

The new CoCrNi medium entropy alloy (MEA) has emerged to be one of the most promising systems which provide extraordinary ductility and strength at cryogenic temperatures. In this study, utilizing both polycrystalline and single crystal specimens, as well as advanced optical strain measurements, the deformation mechanisms dictating the mechanical behavior at the onset of plasticity were detected and precisely quantified. Independent of deformation temperature, the accumulation of permanent strains at the microstructural level was attributed to plastic slip at the onset of yielding and at low levels of deformation (<10%). The resolved shear stress for slip activation was measured to be 78 MPa at 298 K and between 140 MPa and 160 MPa at 77 K. These unique measurements were used to provide an estimate of the temperature dependent resolved shear stress for slip at temperatures ranging from 77 K to 575 K. In addition, strain heterogeneities at the grain-scale were measured to study the nucleation of slip at the micro-scale in polycrystalline specimens. In summary, the present study aims to quantitatively assess the accumulation of plastic strain and reveal the underlying deformation mechanisms (i.e., slip or/twinning) leading to the buildup of plastic strains at the microstructural level.

Bond evaluation of SRP strengthening system exposed to several harsh environmental conditions

Bridge retrofitting is a billion-dollar industry. Thus, finding effective and economically feasible solutions to strengthen bridges that deteriorate to extend service life until replacement is feasible is a critical global need. There are several types of fiber reinforced polymers (FRP) based repair systems available now commercially to strengthen bridge members including systems that utilize carbon, glass, and now even steel fibers. The latter is a system most often referred to as steel reinforced polymer (SRP) and is considered fairly new to the bridge industry; yet a very promising system due to its close-to-carbon fiber strength, and close-to-glass fiber price. One current research gap for SRP has been the performance of this system relative to exposure to environmental conditioning and its overall durability resilience. In this work, the SRP strengthening system used both micro-fine galvanized and micro-fine brass coated steel fibers to externally reinforce concrete prisms using the recently published American Concrete Institute (ACI) 440.9R-15 approach to evaluate FRP bond behavior. Companion dog-bone style coupon specimens were also prepared using both SRP systems to examine tensile mechanical properties of the SRP system alone. Both types of specimens were exposed to several types of harsh environments including cycles of freeze-thaw, varying temperature, and cycles of humidity. The study investigated accelerated environmental exposure in an environmental chamber as well as direct real-time weather exposure. The environmental chamber involved subjecting the specimens to freeze-thaw cycles, cycles of varying temperature, and humidity cycles. For the real-time weather exposure, the specimens were exposed to daily weather for 12 months in Rolla, Missouri, USA where the city is moderately exposed to freeze-thaw, high-range of temperature fluctuation, and wide ranging humidity levels. The results of the flexural tests conducted indicated that the bond strength between the SRP and concrete interface was reduced by harsh environment. All conditioned specimens had a mode II or mode III bond failure, while the control specimens failed in mode I. Real-time weather specimens failed at lower deformation levels with less concrete-covered substrate than those conditioned in the environmental chamber. An ACI 440 style environmental reduction factor, CE, of 0.75 is suggested for wet-environment and 0.65 for highly aggressive environment based on the work undertaken in the overall study.

Effect of heat input on the corrosion resistance of the cold worked 2304 lean duplex stainless steel GMAW welded joint

The effect of the welding GMAW, with heat input of 1.4 kJ/mm, on the microstructure and corrosion resistance of the steel UNS S32304 prior cold worked (0, 10, 30, and 30% thickness reduction) was evaluated. The welding process generated, in the weld joint, the regions: fusion zone (FZ), heat‐affected zone (HAZ), an annealed region around the HAZ, and the metal base zone (BM) deformed by cold working. Excessive ferritization and high precipitation of chromium nitrides in the HAZ were identified. The corrosion resistance of the welded joints was not significantly changed for low deformation levels by cold work (up to 30% thickness reduction). However, for 50% thickness reduction a decrease in the corrosion resistance of the welded joint was observed. The annealing of the BM around the HAZ increased its corrosion resistance, making this region immune to localized corrosion. The heat input used in this study promoted higher ferritization and precipitation of chromium nitrides, lower annealing of the base metal near the HAZ and lower corrosion resistance when compared with the higher heat input used in our previous work (about 2.5 kJ/mm).

ε-Martensite formation for low strains in a lean duplex stainless steel

Martensitic transformation induced by strain in duplex stainless steels is a good option to increase their strength and elongation. The influence of low deformation levels on the phase transformation was studied in a 2304 lean duplex stainless steel. It was demonstrated that this steel exhibited the phase transformation of austenite (γ) into epsilon (ε) and alpha (α′) martensite after cold rolling. The ε and α′ were observed in shear bands and close to the grain boundaries. The Shoji–Nishiyama relation 110γ//2110ε was observed. Hitherto, the ε formation has not been reported in the literature for this steel by cold deformation.

Advances in 6d diffraction contrast tomography

The ability to measure 3D orientation fields and to determine grain boundary character plays a key role in understanding many material science processes, including: crack formation and propagation, grain coarsening, and corrosion processes. X-ray diffraction imaging techniques offer the ability to retrieve such information in a non-destructive manner. Among them, Diffraction Contrast Tomography (DCT) is a monochromatic beam, near-field technique, that uses an extended beam and offers fast mapping of 3D sample volumes. It was previously shown that the six-dimensional extension of DCT can be applied to moderately deformed samples (⩽ 5% total strain), made from materials that exhibit low levels of elastic deformation of the unit cell (⩽ 1%). In this article, we improved over the previously proposed 6D-DCT reconstruction method, through the introduction of both a more advanced forward model and reconstruction algorithm. The results obtained with the proposed improvements are compared against the reconstructions previously published in [1], using Electron Backscatter Diffraction (EBSD) measurements as a reference. The result was a noticeably higher quality reconstruction of the grain boundary positions and local orientation fields. The achieved reconstruction quality, together with the low acquisition times, render DCT a valuable tool for the stop-motion study of polycrystalline microstructures, evolving as a function of applied strain or thermal annealing treatments, for selected materials.