Subsequent Plastic Research Articles

Effect of microstructure evolution on Lüders strain and tensile properties in an intercritical annealing medium-Mn steel

The influence of microstructural characteristics on Luders strain and mechanical properties was explored by means of altering thermo-mechanical circumstances in an intercritical annealing (IA) medium-Mn Fe-11Mn-0.09C-0.25Si (wt.%) steel. By IA of cold-rolled samples with severe plastic deformation, exclusively equiaxed dual phases were obtained because of active recovery and recrystallization. The equiaxed austenite ( $$\upgamma_{\text E}$$ ) with a larger size and inadequate chemical concentration was more readily transformed into martensite, and subsequent transformation-induced plasticity (TRIP) effect was triggered actively at relatively higher IA temperature, lessening localized deformation. In addition, grown-in dislocations were prone to multiply and migrate around a broad mean free path for coarser equiaxed ferrite ( $$\upalpha_{\text E}$$ ) due to weakening dynamic recovery; therefore, it was the ensuing increased mobility of dislocations instead of reserving plentiful initial dislocation density that facilitated the propagation velocity of Luders bands and the accumulation of work hardening. In contrast, the bimodal-grained microstructure with lath-like and equiaxed austenite ( $$\upgamma_{\text L} + \upgamma_{\text E}$$ ) satisfactorily contributed to a smaller yield point elongation (YPE) without compromise of comprehensive mechanical properties on the grounds that austenitic gradient stability gave rise to discontinuous but sustainable TRIP effect and incremental work hardening. Hence, Luders strain is closely related to the absence of work hardening in the region which yields locally. It follows that the decreased stability of retained austenite, favorable mobility of dislocations and the bimodal-grained structure all prominently make up for the insufficiency of work hardening, thereof resulting in a limited YPE.

AN UNUSUAL PRESENTATION OF CHRONIC COUGH: PLASTIC BRONCHITIS AND CHYLOPTYSIS

SESSION TITLE: Fellows Cardiothoracic Surgery Posters SESSION TYPE: Fellow Case Report Posters PRESENTED ON: October 18-21, 2020 INTRODUCTION: Plastic bronchitis and chyloptysis are rare medical conditions characterized by expectoration of bronchial cast and production of white milky sputum rich in chyle, respectively. Plastic bronchitis is associated with congenital heart disease in children and lymphatic system disease in adults. CASE PRESENTATION: A 49-year-old Hispanic female with no past medical history presented with dyspnea and right-sided pleuritic chest pain during her first pregnancy 27 years ago. Initial evaluation, work up and imaging studies revealed right-sided chylothorax requiring chest tube placement, thoracotomy with decortication, and thoracic duct ligation. One month later, cisterna chyli ligation and right lower lobe wedge resection were performed. Right lower lobe biopsy results disclosed chronic interstitial pneumonitis and focal foreign body reaction. During follow up patient reported resolution of symptoms. In May 2019, the patient presented to our institution with four-month history of dyspnea, dry cough, and expectoration episodes of a thick, white-red, cord-like material accompanied by viscous milky white sputum. The patient’s symptoms progressively worsened where she developed a choking sensation at night and in supine position. Chest CT scan show small areas of ground glass airspace opacity in the dependent portions of bilateral lungs with concentric thickening of the right pleura. Bronchoscopy was performed and was notable for milky-white secretions with abundant pale and slightly red, stranded bronchial casts lodged within the left lower lobe anterior segment. Bronchial lavage and aspiration specimen sent for oil red stain showed macrophages with lipid droplets. These findings were consistent with the clinical impression of chyloptysis producing subsequent plastic bronchitis. Cytology was negative for malignancy. Patient completed course of broad spectrum antibiotics and steroids with partial improvement in her condition. She currently is under evaluation for embolization and/or invasive approach. DISCUSSION: This case addresses a 49-year-old female who presented with milky-white sputum and cough. Bronchoscopy showed milky-white secretions and bronchial cast, bronchial lavage was positive for oil red stain which confirms chyloptysis causing plastic bronchitis. She completed a course of antibiotics and steroids with partial improvement in her condition. Now is under evaluation for embolization and/or invasive approach. CONCLUSIONS: This case illustrates an unusual presentation of chronic cough and chyloptysis, confirmed by bronchoscopy. Plastic bronchitis and chyloptysis rare medical conditions that should be suspected after obtaining thorough history and physical exam, high index of suspicion is fundamental for the recognition and treatment of this rare entity. Reference #1: Itkin M, Mccormack FX, Dori Y. Diagnosis and Treatment of Lymphatic Plastic Bronchitis in Adults Using Advanced Lymphatic Imaging and Percutaneous Embolization. Annals of the American Thoracic Society. 2016;13(10):1689-1696. Reference #2: Lim KG, Rosenow EC, Staats BS, Morgenthaler TI. Chyloptysis in Adults: Presentation, Recognition, and Differential Diagnosis. Chest. 2004; 125:336-304. Reference #3: Stoddart A, Dincer HE, Iber C, Tomic R, Bhargava M. Chyloptysis causing plastic bronchitis. Respiratory Medicine Case Reports. 2014; 13:4-6. DISCLOSURES: No relevant relationships by Michael Cruz, source=Web Response No relevant relationships by Ricardo Fernandez, source=Web Response No relevant relationships by Giovanni Veloz Irizarry, source=Web Response

HPT production of large bulk skutterudites

This paper documents that consolidation and subsequent severe plastic deformation of commercial skutterudite powders via high pressure torsion (HPT) serves for an easy, fast, cheap and sustainable production method for excellent n-type skutterudite bulks, (Sm,Mm)0.15Co4Sb12, with high ZT values. Large cylindrical samples with 30 mm in diameter and 8 mm thickness (∼55 g) were successfully prepared in one step. These large samples enabled for the first time to (i) study the influence of shear strain on the micro-structural, thermoelectric and mechanical properties by analysing specimens cut from various positions of the HPT disks and (ii) to evaluate these properties orientation sensitive. These investigations were supported by electron probe microanalyses, transmission electron microscopy as well as XPD full profile analyses, XPS, Raman and Hall measurements. Whilst the orientation dependence on the electrical and thermal conductivity is found to be rather weak, the applied shear strain has a pronounced influence, as with increasing strains the thermal conductivity was reduced to the targeted levels. This beneficial effect, however, is accompanied by a massive increase of the electrical resistivity. ZT values turned out to be rather homogeneous over the entire sample with ZT∼1.3 at 850 K.

Evolution of Brittle Structures in Plagioclase‐Rich Rocks at High‐Pressure and High‐Temperature Conditions—Linking Laboratory Results to Field Observations

AbstractPlagioclase‐rich granulites exposed on the Lofoten archipelago, Northern Norway, display strain localization in pseudotachylytes as well as ductile shear zones that formed under similar high‐pressure and high‐temperature conditions. Pseudotachylytes or pseudotachylyte networks reveal no or very little hydration, whereas ductile shear zones reveal significant hydration. We combine these observations from the field with experimental results to characterize the structural evolution of brittle faults in plagioclase‐rich rocks at conditions of the lower continental crust. We performed a series of deformation experiments on intact granulite samples prepared from a natural granulite sample at 2.5 GPa confining pressure, a strain rate of 5 × 10−5 s−1, and temperatures of 700°C and 900°C to total strains of ~7–8% and ~33–36%. Samples were either deformed “as‐is” or with ~1 wt.% H2O added. Striking similarities between the experimental and natural microstructures suggest that the transformation of precursory brittle structures into ductile shear zones at eclogite‐facies conditions is most effective in samples deformed with added water triggering reaction and subsequent plastic deformation of the products along the faults and in the adjacent wall‐rock.

Fully biodegradable film to boost rainfed maize (Zea mays L.) production in semiarid Kenya: An environmentally friendly perspective

Abstract Conventional polyethylene plastic film mulching has been widely used, but its subsequent plastic residue pollution received widespread concern. Fully biodegradable film mulching is viewed as a potential substitution solution, however, it is generally thought not to be efficient as conventional plastic film mulching in field productivity and economic harvest. A two-year field experiment using a newly produced fully biodegradable film was conducted in semiarid Kenya in 2016 and 2017 respectively. Five treatments were designed as: 1) ridge-furrow mulching (RFM) with transparent plastic film (RFMT), 2) RFM with fully biodegradable film (RFMD), 3) RFM with black plastic film (RFMB), 4) RFM with grass straw (RFMG) and 5) traditional flat planting without mulching (FP) as CK. We found that RFMD achieved the similar evaporation-restricted, yield-increased and water-saving effectiveness as RFMT and RFMB did across two growing seasons. The RFMD lowered evaporation by 58.1 mm, while increasing grain yield by 70.16 %, above-ground biomass by 77.7 % and water use efficiency (in reference to grain yield) (WUEG) by 131.8 % in comparison with CK respectively. Furthermore, RFMD increased net economic income by 49.8 % in 2016 and 42.0 % in 2017 respectively relative to CK, as RFMT and RFMB did. It is noted that the degradable film used in this experiment is a non-polyethylene material and still can be maintained for 60 days in a fine physical state. Also, average soil temperature was significantly elevated by 1.6 °C in 2016 and 1.8 °C in 2017 in RFMD respectively, in comparison with CK, which was beneficial to crop growth and grain filling particularly in relatively cool long rainy season. Considering residual film pollution, the biodegradable film showed reliable advantages in environmental friendliness and field productivity. Therefore, it might be a promising farming solution to boost rainfed maize production and environmental sustainability in east African Plateau.

Plastic deformation mechanism transition of Ti/Ni nanolaminate with pre-existing crack: Molecular dynamics study* *Project supported by the National Natural Science Foundation of China (Grant No. 11572259), the Program for International Cooperation and Exchanges of Shaanxi Province, China (Grant No. 2016KW-049), the Natural Science Foundation of Shaanxi Province, China (Grant No. 2019JQ-827), and the Scientific Research Program Funded by Shaanxi Provincial

Tensile behaviors of Ti/Ni nanolaminate with model-I crack are investigated by molecular dynamics simulations. The Ti/Ni nanolaminates with center crack either in Ti layer or in Ni layer under different loading directions are utilized to systematically study the mechanical performance of the cracked material. The results indicate that pre-existing crack dramatically changes the plastic deformation mechanism of the Ti/Ni nanolaminate. Unlike the initial plastic deformation originating from the interface or weak Ti layer of the crack-free samples, the plastic behavior of cracked Ti/Ni nanolaminate first occurs at the crack tip due to the local stress concentration. Subsequent plastic deformation is dominated by the interaction between the crack and interface. The Ti/Ni interface not only impedes the movement of the initial plastic deformation carriers (dislocation, slip band, and deformation twinning) from the crack tip, but also promotes the movement of interfacial dislocations in the tension process. Microstructure evolution analysis further confirms that the plastic deformation mechanism transition is ascribed to the orientation-dependent tensile behavior at the crack tip, which is intrinsically attributed to the anisotropy of the certain crystal structure and loading direction of the cracked Ti/Ni nanolaminate. In addition, by analyzing the effects of different plastic deformation carriers on crack propagation in specific crystal, it can be discovered that the interfacial dislocations moving towards the crack tip can further promote the crack growth.

Fatigue and Corrosion Behavior of Solid-State Recycled Aluminum Alloy EN AW 6082

In this research, a solid-state recycling process of aluminum was performed. It consisted of aluminum EN AW 6082 alloy machining chip cold precompaction and hot extrusion followed by a combination of equal channel angular pressing (ECAP) and heat treatment. The main aim of this paper is to determine the fatigue and corrosion behavior of the recycled specimens. In order to determine the recycled specimen fracture mode after fatigue testing, fractography analysis was performed. The corrosion behavior of all specimens was investigated in 0.5 M NaCl solution using open circuit potential measurements, polarization and electrochemical impedance spectroscopy (EIS) methods. It was found that the corrosion resistance of the tested specimens is similar for reference and as-extruded recycled specimens, while it is increased for those which were additionally processed with equal channel angular pressing and heat treatment. Namely, the corrosion current decreased in the same order, while the polarization resistance increased. Impedance measurements have shown that the subsequent plastic deformation and heat treatment of recycled specimens facilitated passivation of tested materials and improved surface film properties, which is confirmed with scanning electron microscopy and energy-dispersive x-ray spectroscopy. Fatigue life was similar for recycled and reference specimens for the selected stress levels. However, fractography showed that multiple cracks appeared inside the recycled specimens which caused different crack propagation mechanisms compared with reference specimens.

Finite element analysis on the effect of martensitic transformation and plastic deformation on the stress concentration factor in a thin notched superelastic NiTi ribbon

The severe nonlinear behavior caused by the martensitic transformation (MT) and subsequent plastic deformation (PD) of detwinned martensite leads to a complex local stress redistribution at the location of stress risers of superelastic shape memory alloy (SMA) components. Nevertheless, in the literature, the simple linear elastic fracture mechanics (LEFM) equations are widely used in the evaluation of the fracture response of superelastic components which has resulted in obvious conflicts between the conclusions regarding the effect of MT on the fracture parameters, i.e. stress intensity factor (SIF) and material toughness. Furthermore, the linear elasticity method is frequently used in the literature to calculate the stress intensity range ([Formula: see text]) when the fatigue crack growth rate dependence on [Formula: see text] ([Formula: see text]) is being evaluated. Moreover, the PD followed by MT is poorly considered in the fracture mechanics of SMAs. This paper presents a numerical investigation on the role of both MT and PD, as well as the notch acuity, on the evolution of notch-tip stresses and strains and stress concentration factor ([Formula: see text]) upon the incremental application of the macroscopic tensile load on a thin NiTi notched superelastic ribbon, to mimic the effects of MT and PD on the SIF of superelastic parts. It is revealed that MT results in drastic deviations of the notch-tip stress, as well as the stress concentration factor ([Formula: see text]), from that obtained in LEFM. Due to the heterogeneous evolution of MT, the trend of the deviations is not regular and unique upon monotonic external loading. Accordingly, the results represent the ineffectiveness of the LEFM method in the evolution of the stress concentration factor (hence, the SIF) and toughness in monotonic loading, as well as the stress intensity range ([Formula: see text]) under fatigue loading in SMA components.

INDENTATION SIZE EFFECT IN HIGH PRESSURE TORSION PROCESSED HIGH ENTROPY ALLOY

High entropy alloy HfNbTaTiZr in as cast conditions and after high pressure torsion straining was characterized by nanoindentation. The length-scale dependent material response (indentation size effect) was characterized by indentation at various indentation depths. Hardness dependence on the characteristic length (depth of penetration) indicated decomposition of disordered high entropy alloy in the as cast sample, which probably occurred during slow cooling after casting. Subsequent severe plastic deformation by high pressure torsion led on the other hand to the short-range disorder of (originally partially decomposed as cast) structure. Further hardening was generated during high pressure torsion by the mechanisms of grain refinement and increasing dislocation density.

Application of Phagotherapy in the Treatment of Burn Patients (Review).

Treatment of patients with a burn injury is a complex process involving multicomponent multidirectional intensive therapy of the majority of organs and systems damaged by thermal effects on the skin, alternating with repeated surgical interventions aimed at removing nonviable tissues with subsequent plastic closure of wound defects. After the recovery from the burn shock, local infectious complications are considered to be the leading problem that decelerates the process of recovery and is the main cause of lethal outcomes. Since the skin integrity is broken, microorganisms penetrate readily into the internal environment of the human organism resulting in a septic state with multiple organ failure. A widespread and often uncontrollable use of antibacterial drugs in medical practice has led to the emergence of multiple drug resistance (MDR) in microorganisms.Introduction of drugs made on the basis of bacteriophages into practice is presently becoming increasingly important. This is confirmed by the growing interest in this field of pharmacology, the development of special programs aimed at studying the processes of phage and bacterial cell interaction.This review presents the main types of bacteria pertaining to MDR pathogens, principles of their classification, and the risk factors for infecting patients. The mechanisms of the selective action of phage particles on a bacterial cell and the possibility of using phage therapy in the treatment of burn injury (experimental and clinical data) based on the analysis of foreign literature are demonstrated as well as new positive properties of phages related to the changes in the macroorganism immune status caused by the interaction with bacteriophage particles.

CaMKII inhibitor 1 (CaMK2N1) mRNA is upregulated following LTP induction in hippocampal slices.

CaMK2N1 and CaMK2N2 (also known as CaMKIINα and β) are endogenous inhibitors of calcium/calmodulin-dependent kinase II (CaMKII), an enzyme critical for memory and long-term potentiation (LTP), a form of synaptic plasticity thought to underlie learning. CaMK2N1/2 mRNAs are rapidly and differentially upregulated in the hippocampus and amygdala after acquisition or retrieval of fear memory. Moreover, CaMK2N2 protein levels increase after contextual fear conditioning. Therefore, it was proposed that CaMK2N1/2 genes (Camk2n1/2) could be immediate-early genes transcribed promptly (30-60min) after training. As a first approach to explore a role in synaptic plasticity, we assessed a possible regulation of Camk2n1/2 during the expression phase of LTP in hippocampal CA3-CA1 connections in rat brain slices. Quantitative PCR revealed that Camk2n1, but not Camk2n2, is upregulated 60min after LTP induction by Schaffer collaterals high-frequency stimulation. We observed a graded, significant positive correlation between the magnitude of LTP and Camk2n1 change in individual slices, suggesting a coordinated regulation of these properties. If mRNA increment actually resulted in the protein upregulation in plasticity-relevant subcellular locations, CaMK2N1 may be involved in CaMKII fine-tuning during LTP maintenance or in the regulation of subsequent plasticity events (metaplasticity).

Mechanically-induced martensite transformation of NiTiFe shape memory alloy subjected to plane strain compression

Abstract Based on the channel die compression, NiTiFe shape memory alloy (SMA) was subjected to plane strain compression. Mechanically-induced martensite transformation, nanocrystalline and amorphous phase can be observed in the case of large plastic strain. Mechanically-induced martensite transformation is obviously different from the conventional stress-induced martensite transformation. The former generally occurs after dislocation slip, whereas the latter arises prior to dislocation slip. The occurrence of B19’ martensite phase contributes to accommodating subsequent plastic deformation of NiTiFe SMA. Mechanically-induced B19’ martensite is partially stabilized due to the existence of local high stress field and consequently it is unable to be reverted to B2 austenite phase during unloading.

Acute ischaemic stroke alters the brain's preference for distinct dynamic connectivity states.

Acute ischaemic stroke disturbs healthy brain organization, prompting subsequent plasticity and reorganization to compensate for the loss of specialized neural tissue and function. Static resting state functional MRI studies have already furthered our understanding of cerebral reorganization by estimating stroke-induced changes in network connectivity aggregated over the duration of several minutes. In this study, we used dynamic resting state functional MRI analyses to increase temporal resolution to seconds and explore transient configurations of motor network connectivity in acute stroke. To this end, we collected resting state functional MRI data of 31 patients with acute ischaemic stroke and 17 age-matched healthy control subjects. Stroke patients presented with moderate to severe hand motor deficits. By estimating dynamic functional connectivity within a sliding window framework, we identified three distinct connectivity configurations of motor-related networks. Motor networks were organized into three regional domains, i.e. a cortical, subcortical and cerebellar domain. The dynamic connectivity patterns of stroke patients diverged from those of healthy controls depending on the severity of the initial motor impairment. Moderately affected patients (n = 18) spent significantly more time in a weakly connected configuration that was characterized by low levels of connectivity, both locally as well as between distant regions. In contrast, severely affected patients (n = 13) showed a significant preference for transitions into a spatially segregated connectivity configuration. This configuration featured particularly high levels of local connectivity within the three regional domains as well as anti-correlated connectivity between distant networks across domains. A third connectivity configuration represented an intermediate connectivity pattern compared to the preceding two, and predominantly encompassed decreased interhemispheric connectivity between cortical motor networks independent of individual deficit severity. Alterations within this third configuration thus closely resembled previously reported ones originating from static resting state functional MRI studies post-stroke. In summary, acute ischaemic stroke not only prompted changes in connectivity between distinct networks, but it also caused characteristic changes in temporal properties of large-scale network interactions depending on the severity of the individual deficit. These findings offer new vistas on the dynamic neural mechanisms underlying acute neurological symptoms, cortical reorganization and treatment effects in stroke patients.

Multiple damage mechanisms facilitated by planar dislocation glide in a commercial-grade precipitation-strengthened Fe–Ni–Cr-based steel

The present study addresses the damage evolution mechanism in precipitation-strengthened Fe–Ni–Cr-based steel (SUH 660) at ambient temperature in air. Specifically, damage quantification and associated microstructure characterization were performed. The damage initiation sites were inclusion and grain boundaries impinging dislocation slip. The early stage of damage evolution was observed before necking of the specimen. Subsequent plastic straining caused damage growth along slip planes and coalescence of damage via localized shear in ligaments between damages, for which the behavior was associated with the planar character of the slip. The damage evolution behavior observed in the post-mortem specimen was consistent with fractographic characteristics.

The variation and visualisation of elastic anisotropy in rock-forming minerals

Abstract. All minerals behave elastically; elasticity is a rheological property that controls their ability to support stress, strain, and pressure; controls the nature of acoustic wave propagation; and influences subsequent plastic (i.e. permanent non-reversible) deformation. All minerals are intrinsically anisotropic in their elastic properties – that is, they have directional variations that are related to the configuration of the crystal lattice. This means that the commonly used mechanical elastic properties that relate elastic stress to elastic strain, including Young's modulus (E), Poisson's ratio (ν), shear modulus (G) and linear compressibility (β), are dependent on crystallographic direction. In this paper, we explore the ranges of anisotropy of E, ν, G and β in 86 rock-forming minerals, using previously published data, and show that the range is much wider than commonly assumed. We also explore how these variations (the directionality and the magnitude) are important for fundamental processes in the solid earth, including deformation (mechanical) twinning, coherent phase transformations and brittle failure. We present a new open-source software package (AnisoVis, written in MATLAB), which we use to calculate and visualise directional variations in elastic properties of rock-forming minerals. Following previous work in the fields of chemistry and materials science, we demonstrate that by visualising the variations in elasticity, we discover previously unreported properties of rock-forming minerals. For example, we show previously unreported directions of negative Poisson's ratio and negative linear compressibility, and we show that the existence of these features is more widespread (i.e. present in many more minerals) than previously thought. We illustrate the consequences of intrinsic elastic anisotropy for the elastic normal and shear strains within α-quartz single crystal under different applied stress fields; the role of elastic anisotropy on Dauphiné twinning and the α–β phase transformations in quartz; and stress distributions around voids of different shapes in talc, lizardite, albite, and sanidine. In addition to our specific examples, elastic anisotropy in rock-forming minerals, to the degree that we describe, has significant consequences for seismic (acoustic) anisotropy, for the focal mechanisms of earthquakes in anisotropic source regions (e.g. subducting slabs), for a range of brittle and ductile deformation mechanisms in minerals, and for geobarometry using mineral inclusions.

Stability of twins in Mg alloys – A short review

In this article, the stability of twins, especially {10–12} twins, in Mg alloys was critically reviewed. In the last decade, pre-twinning is considered to be an effective method for adjusting the microstructure and properties of wrought Mg alloys. Especially, formation of twin-texture can remarkably improve formability of rolled Mg alloys. However, the stability of {10–12} twins determines the effect of this method. Previous work revealed that initial {10–12} twins may either grow or shrink under further deformation, and may be removed by static recrystallization under thermal effect. It is considered that improving the stability of twin structure could enhance the contribution of twin-texture on subsequent plastic formability. Based on this background, stress stability and thermal stability of {10–12} twin structure were summarized and reviewed in this article. Finally, a few critical scientific problems in this research field were pointed out.

Neurogranin Regulates Metaplasticity.

Long-term potentiation (LTP) and long-term depression (LTD) are two major forms of synaptic plasticity that are widely accepted as cellular mechanisms involved in learning and memory. Metaplasticity is a process whereby modifications in synaptic processes shift the threshold for subsequent plasticity. While metaplasticity has been functionally observed, its molecular basis is not well understood. Here, we report that neurogranin (Ng) regulates metaplasticity by shifting the threshold toward potentiation, i.e., increasing Ng in hippocampal neurons lowers the threshold for LTP and augments the threshold for LTD. We also show that Ng does not change the ultrastructural localization of calmodulin (CaM)-dependent protein Kinase II (CaMKII) or calcineurin, critical enzymes for the induction of LTP and LTD, respectively. Interestingly, while CaMKII concentrates close to the plasma membrane, calcineurin concentrates away from the plasma membrane. These data, along with the previous observation showing Ng targets CaM closer to the plasma membrane, suggesting that shifting the localization of CaM within the dendritic spines and closer to the plasma membrane, where there is more CaMKII, may be favoring the activation of CaMKII vs. that of calcineurin. Thus, the regulation of CaM localization/targeting within dendritic spines by Ng may provide a mechanistic basis for the regulation of metaplasticity.

The effect of boundary or interface on stress-induced martensitic transformation in a Fe-Ni alloy

The boundary effect on mechanical stability of metastable austenite (γ) in the Fe-Ni steels is characterized using a combination of nanoindentation and transmission electron microscopy (TEM). When load (P) - penetration depth (h) is converted to a P/h versus h plot in a nanoindentation-induced loading curve, the result of metastable γ exhibits double stages; martensitic transformation in stage I, and subsequent plastic deformation with dislocation glide in the transformed martensite (α') in stage II. The two quantitative parameters associated with transformation behavior can be obtained from the P/h versus h plot: (i) the slope a of the plot in stage I, which proportionally increases as the nanohardness and corresponds to resistance to martensitic transformation, and (ii) the critical load Pt that corresponds to the transition from stage I to II, namely the end of martensitic transformation. Both slope a in stage I and Pt become lower for the γ/α' interface, γ/γ grain boundary, and γ grain interior, in turn. Furthermore, the plots of slope a in stage I and Pt as a function of distance from the γ/γ grain boundary DGB show that both parameters decrease with increasing DGB. TEM observations of microstructures in the vicinity of the γ/γ grain boundary show that transformed α' is only observed in the indented γ grain and no transformation occurs in the adjacent γ grain. These results indicate that martensitic transformation is significantly retarded by boundaries, and retardation presumably depends on the character of boundaries due to a constraint against volume expansion of the transformation from γ to α'.

Role of Carbon Black for Enhancing the Mechanical Properties of Short Aramid Fiber Reinforced Ethylene-Acrylic Rubber

Composites based on ethylene-acrylic rubber and 1 mm short aramid fibers (AF) were developed by varying the fiber content from 3 to 40 phr. At 10 phr short fiber loading, the tensile modulus (10 % modulus) of the neat matrix was around 11 times increased. However, its breaking elongation was decreased from 408 to 58 %. This drastic reduction in the breaking elongation even at a 10 phr fiber loading leads to a brittle failure with inferior toughness. The tensile-fractured surface of the fiber-filled composite showed an intact matrix with no plastic deformation during fiber pulled-out. To solve this problem, carbon black (CB) was used as a toughening agent. Surprisingly, the addition of 20 phr CB onto a 10 phr AF-filled composite enhanced its 10 % modulus in the longitudinal direction by 70 % and also enhanced its breaking elongation from 58 to 351 %. From the morphological analysis, it has been presumed that the addition of CB enhanced the friction between the fiber and the matrix at a very low strain and also facilitate the matrix for a plastic deformation at a higher strain. This enhanced friction between the fiber and the matrix is considered as the improved low strain modulus and the subsequent plastic deformation at a higher strain is responsible for the improved toughness.

Repeatability and agreement between methods for determining the Atterberg limits of fine‐grained soils

AbstractThe Atterberg limits (plastic limit [PL] and liquid limit [LL]) of fine‐grained soils are important for civil engineering and agronomic applications. Several methodologies exist to determine the PL and LL, each with associated merits and shortcomings. The reproducibility and uncertainties associated with the various methods have not been evaluated for different samples that differ in terms of clay mineralogy and geologic origin. The objectives were to (i) assess the repeatability of two methods each for determining the PL (thread rolling and rolling device) and LL (Casagrande cup and drop cone penetrometer), and compare the subsequent plasticity indexes for 30 samples from 10 countries; and (ii) evaluate the effect of particle size (2 mm and 425 µm) on the plastic and liquid limits for 28 Venezuelan samples. For the PL, the repeatability (estimated as the repeatability coefficient, RC, among replications) for the thread rolling and rolling device methods was similar (2.28 and 2.39%, respectively). For the LL, the drop cone method was 16% more repeatable than the Casagrande cup method. There was a strong correlation between the two respective methods for PL (r2 = 0.98) and LL (r2 = 0.99). For samples that have LL < 45, the LL from the Casagrande cup was slightly higher than LL from the drop cone, and vice versa for samples with LL > 45%. No significant differences were observed between PL measured on <2‐mm or <425‐µm samples; for samples with LL < 35% the two particle sizes gave similar values. There were however larger discrepancies between the two particle sizes for samples with LL > 36%.