Permanent Set Research Articles

Reduction of limonite ore from South Sulawesi with additive Na2SO4 using carbon monoxide

ABSTRACT This study utilised a selective reduction method to generate ferronickel from limonitic ore, followed by a magnetic separation stage. The research explored the kinetics and the influence of time and temperature on nickel content and recovery. Sodium sulfate was incorporated as an additive, and carbon monoxide (CO) gas served as the reductant in a vertical tube furnace. Magnetic separation employed a permanent magnet set at 500 G. Reduction took place at temperatures of 900°C, 1000°C, and 1100°C, with varying durations from 30 min to 180 min. Optimal recovery and nickel grade were achieved at 1100°C for 180 min, reaching 70.07% and 8.49%, respectively. Increasing the reduction temperature and time correlated with enhanced recovery and nickel grade.

High rubber elasticity and thermal conductivity in plasticized polyvinyl chloride film with flame retardancy and smoke suppression properties

AbstractFor hydrogenated nitrile‐butadiene rubber (HNBR) modified polyvinyl chloride (PVC), magnesium hydroxide and antimony trioxide are frequently employed as flame retardants. Fume silica is thought to be useful reinforced agent for rubber as well as efficient flame retardant for polymer‐based composites. The plasticized PVC and HNBR blend in this work were combined with three fillers mentioned above to create rubber‐plastic composites that performed well overall, with a notable improvement in combustion. The limiting oxygen index of the composites increased from 23.7% to 33.8% with no droplets falling during combustion, the smoke density rating decreased from 23.8% to 7.9%, and the maximum smoke density dropped from 95.5% to 15.5%. The cone calorimetry test findings revealed that the three fillers simultaneously prevented the emission of smoke and heat from combustion. High thermal conductivity is typically linked to excellent flame retardancy. The thermal conductivity of composites rose from 0.193 to 0.583 W m−1 K−1 with the addition of fillers. Furthermore, the low glass transition temperature and permanent set of improved composites reflect its softness and rubber elasticity. Thermogravimetric analysis was used to examine the thermal stability of the composites in nitrogen and air, and the results indicated the addition of fillers improved the thermal stability.

Pathways to social integration among homeless-experienced adults with serious mental illness: a qualitative perspective

BackgroundSocial integration (i.e., reciprocal interactions with peers and community members) is a notable challenge for many homeless-experienced adults with serious mental illness (SMI). In this study, we examine a range of housing services offered to homeless-experienced adults with SMI and identify the impacts of supportive services on participants’ social integration outcomes, with the goal of improving services in transitional and permanent housing settings for homeless-experienced adults with SMI.MethodsThrough semi-structured interviews with homeless-experienced adults with SMI (n = 30), we examine the impacts of housing and service settings on participants’ social integration. Participants received services in a variety of housing settings, including transitional housing with congregate/shared living (n = 10), transitional housing with individual quarters (n = 10), and permanent supportive housing (n = 10).ResultsParticipants expressed caution in developing social relationships, as these could pose barriers to recovery goals (e.g., substance use recovery). For many, social integration was secondary to mental and physical health and/or housing stability goals. Individual quarters gave individuals a place of respite and a sense of control regarding when and with whom they socialized. Meeting recovery goals was strongly related to connecting to and receiving a range of supportive services; interviews suggest that proximity to services was critical for engagement in these resources.ConclusionsPrograms serving homeless experienced adults with SMI should seek to understand how individuals conceptualize social integration, and how social relationships can either support or hinder participants’ recovery journey.

Multiscale experimental characterization and physical-based constitutive modeling of silicone adhesive

Silicone adhesive has been widely used in assembly glass curtain walls which leads to its mechanical behaviors under heavy investigation. Due to its complexity, the microstructure of silicone adhesive stays unclear. A detailed description of microstructures of silicone adhesive is the basis to obtain an in-depth understanding of its mechanical behavior and the related mechanisms. In this work, series of multiscale experiments, uniaxial tension, uniaxial compression, simple shear and scanning electron microscopy (SEM) observation, were conducted to characterize mechanical behaviors and microstructure features of silicone adhesive. Stress-strain curves obtained through macroscale experiments were presented. Morphology and dispersion of filler clusters in silicone adhesive were analyzed using Gaussian mixed models. A modification of molecular chain spatial distribution was made to non-affine network model to consider anisotropic damage evolution of polymer matrix. A simplified term was further introduced to account for load-bearing capacity of filler clusters based on fractal theory where fractal dimensions of clusters work as a connection between microscale and macroscale. The modified model was further extended to describe Mullins effect combined with network alteration theory. The results of model validation and comparison demonstrated that due to the consideration of polymer chain anisotropic evolution and filler cluster microscopic features, the proposed model can predict the mechanical behavior of silicone adhesive under different loading conditions as well as the stress softening and permanent set of Mullins effect more accurately.

Predicting Temperature-Dependent Aging Effects and Permanent Set of Vacuum Sealing Systems in Semiconductor Manufacturing Processes

Predicting Temperature-Dependent Aging Effects and Permanent Set of Vacuum Sealing Systems in Semiconductor Manufacturing Processes

The future of interactive information radiators for knowledge workers

Abstract Information Radiators (IRs) provide context-specific pieces of information in a semi-public place where a group of people can see it while working or passing-by. They can simplify information sharing “out-of-the-box”, foster awareness and socialization, create serendipity and enhance collaboration. Recent sociotechnical developments such as the establishment of permanent hybrid work settings as well as advances in the area of Human Computer Interaction (HCI) such as the emergence of Augmented Reality (AR) and Virtual Reality (VR) are likely to impact how IRs are being used – or even challenge their usefulness. In this article we discuss those developments and their possible implications for the design and use of IRs in the context of knowledge work in the next decades. We argue that IRs will probably remain an important part of future office environments providing awareness, supporting serendipity and building a situated social place for matchmaking as well as informal communication. Using new display and interaction technologies (such as AR) they might even grow in importance by enabling fluid work scenarios.

Double Cross‐Linked Polyisobutylene‐Based Polyurethane (xPIB‐PU) I: Synthesis, Processing, and Properties

AbstractThis publication concerns the synthesis of a novel class of hybrid thermoset/thermoplastic elastomers, i.e., double cross‐linked polyisobutylene‐based polyurethanes (xPIB‐PUs), together with their processing and some key properties. These materials are designed to exhibit a combination of properties for indwelling medical applications, specifically for heart valve prostheses. The chemical cross‐links are introduced by well‐defined 3‐arm PIB stars fitted with HO‐end groups of molecular weights (MWs) of Mn = 3081 and 9000 g mole−1 and narrow MW dispersities (<1.3). Processibility of xPIB‐PU containing 70 wt% PIB (for biocompatibility and calcification resistance) is achieved by driving the syntheses to high conversions (>97%) close to but still below the gel point and completing the cross‐linking in heated molds. The processibility period (minutes) is controlled by controlling the MW of the cross‐linking agent in the 3081 to 9000 g mole−1 range. Blends of 3‐arm stars and linear bifunctional PIBs can also control the processibility period. The creep resistance of xPIB‐PU is significantly improved (from 13.2% to 5.5%) relative to physically cross‐linked PIB‐PU. xPIB‐PUs exhibit negligible permanent set (1–2%), and high Young's modulus (41 MPa). The stress/strain properties of xPIB‐PUs are also investigated. The data clearly show the contribution of two modes of cross‐linking.

Comparison of methods for enhancing gold recovery from double refractory concentrates using the technology of autoclave oxidation

The study aims to investigate the most efficient method for significant minimization of the impact of organic carbon on gold recovery from double refractory raw materials. We tested three double refractory gold-sulfide concentrates from different deposits with the content of gold from 23.5 to 40.9 g/t and total carbon from 1.2 to 9.5 wt %. Thermal treatment was carried out in a tubular rotary furnace that provided permanent temperature setting and rotation speed in the reactor. The initial concentrate was grinded as pulp in a Fritsch planetary mono mill Pulverisette 6. Autoclave oxidation was performed in Premex and Büchi titanium autoclaves. The technology of autoclave oxidation with the addition of a secondary oxidizer was found to be the most efficient, since it can increase gold recovery up to 97%. Another technology – hightemperature autoclave oxidation – also proved high performance; however, a significant increase in the residence time of the material in the autoclave (up to 120 min) at elevated temperatures is required to achieve this performance. According to the results, thermal treatment in general can provide a small increase in gold recovery (up to 4%). Due to this, it can be used as an additional processing with other methods analyzed in this article rather than as a self-sufficient technological solution. The studies revealed that the preliminary thermal treatment of concentrates entering autoclave oxidation shows a positive effect; high-temperature autoclave oxidation of concentrates with different carbon content provides high gold recovery for high-carbon concentrates; the use of a secondary oxidizer (in the form of nitric acid) also benefits the gold recovery. The high efficiency of the technology for concentrates with different carbon content allows us to recommend it for further research.

Dubliners: The Story of A City in Paralysis

The city's image acquired special prominence in many literary works related to modernist literature. In these works, the writers used the city details simultaneously to serve as symbols and references to the themes and issues that can appear in the works. This fact is especially actual in the case of James Joyce's Dublin - the permanent setting of most works by this great Irish modernist. It is worth noting that Joyce took the steps forward to discuss his city with the bright and dark sides. Dubliners, the collection of short stories, belonged to this type of modernist literature focused on the city. James Joyce wrote this collection in the early period of his writing career, and its title highlighted the significance of Dublin – as a city and its people. In each story of the collection, the capital of Ireland was not a mere setting but a unifying factor to portray a complete and comprehensive image of the collection. In every story, Joyce presented a single issue or a merged collection of obstacles found in Dublin and affected the people. In general, Joyce represented the capital city as the center of paralysis, affecting its citizens despite their age. This paper examined the prominence and symbolic meaning of the city in the text. Joyce demonstrated detailed descriptions while mapping his city. For instance, the writer presented the characters while meandering around Dublin's different types of streets. These incidents offered symbolic importance that the people of Dublin moved in circular routs in vain attempts to break the different layers of circles imposed over them at that time. Implicitly, this reference demonstrated the inability of the people of Dublin (the Dubliners) to escape the physical, cultural, political, and religious paralysis. Joyce's portrayal of paralysis in his collection mirrored the entire country of Ireland's broader social and political context during that time. Ireland was undergoing significant changes, yet it seemed imprisoned in inertia and stagnation. The characters and their stories served as microcosms to reflect the broader and extensive social condition, highlighting the challenges faced by the Irish people in breaking free from the paralysis that held them back without tangible outcomes.

Damage-Induced Softening of the Sclera: A Pseudo-Elastic Modeling Approach

Abstract The biomechanical properties of the sclera such as the stiffness, anisotropic behavior, and nonlinear stress–strain relationship have been extensively investigated for the pathogenesis study of ocular diseases. Even so, scarce mechanical investigations have been conducted on the damage in the sclera when subjected to large and repetitive deformations. Hence, the aim of this study is to quantify microstructural damage of the posterior and anterior sclera, through mechanical testing and model fitting. We performed uniaxial mechanical tests on scleral strips dissected from African green monkeys. Samples were subjected to strain-driven cycles of 5%, 10%, 15%, and 20% to evaluate the damage behavior commonly known as the Mullins effect. Experimental results showed qualitative changes in the stress–stretch curves when higher loading cycles were applied. A pseudo-elastic model accurately captured the curve trends across all tested samples, as indicated by a coefficient of determination above 0.96 and a subsequent finite element analysis (FEA) validation. Damage evolution and resultant permanent set demonstrated that considerable microstructural failure was attainable even at small strain levels and that the inherent plasticity had a similar contribution to stress-softening as the Mullins effect. Computed material and damage properties are expected to provide a broader understanding of the underlying mechanisms of ocular diseases and the development of more effective approaches for their treatment.

A constitutive modeling approach to simulate time‐dependent phenomena in rubber‐like materials

AbstractIndustrial rubber materials and similar rubber‐like materials exhibit complex mechanical behavior including nonlinear stress‐strain behavior up to large strains, hysteresis, Mullins effect, permanent set, as well as time‐dependent effects, like relaxation and rate dependency. The modeling of all these phenomena is a challenging task. One constitutive model that is capable to capture many effects in the large strain regime is the so‐called model of rubber phenomenology (MORPH). However, it is not able to capture any of the mentioned time‐dependent phenomena. Thus, this contribution deals with the extension of this model to simulate relaxation and rate dependency of rubber‐like materials. Thereby, a basic modeling approach is proposed, where only a slight change in the original system of tensorial equations is necessary. This approach is further extended by applying not only a constant relaxation time, but also loading history‐depended relaxation properties. For numerical simulations, a time discretization has to be applied to the constitutive equations, which is briefly shown. Finally, the extended MORPH model is applied to two different materials: an industrial rubber material and a polyurethane based adhesive. In both cases, the extended MORPH model is adjusted to uniaxial tension test data by parameter identification procedures. It will be shown that basic time‐dependent phenomena of rubber‐like materials can be captured well with the proposed extensions.

Improved Dual Network Model for Aging of Rubber Composites under Set Strains.

A new model is presented to predict rubber behavior during chemical aging at fixed strains. The model is validated using a carbon black-filled nitrile butadiene rubber aged in air at 125 °C. The model improves upon Tobolsky's dual network theory, designed for unfilled elastomers undergoing conventional aging but which has also often been used in rubber composites undergoing more complex aging scenarios. This work explores the shortcomings of the original model and demonstrates how the new model overcomes them. The model was validated using uniaxial tensile samples aged at 125 °C for 24-72 h at strains from 0-30%. The permanent set was measured, and the samples were tested on an Instron uniaxial test machine after aging. The cross-link density was estimated by equilibrium swelling. Results show that the new model more accurately models the stress-strain behavior to higher strains and provides more reliable estimates of chain scission and cross-linking after aging.

In situ observation of crystal reorientation in polygranular graphite by synchrotron X-ray diffraction and neutron imaging

The capacity of polygranular graphite to accommodate strain is important to its use within structural components. This study has used in situ neutron and synchrotron X-ray experiments to demonstrate that reorientation of crystal domains accompanies the accommodation of applied mechanical strain in unirradiated Gilsocarbon (GCMB/IM24) graphite. Orientation changes were observed using 3D X-ray Diffraction, and local changes in neutron scattering were also observed with energy-resolved Bragg-edge neutron imaging. In both cases, this behaviour at the crystal level was partially recovered when the load was removed. This study provides new evidence for crystal deformation mechanisms that contribute to polycrystalline graphite's elastic non-linearity and the development of permanent set, which may also explain the effects of fast neutron irradiation on graphite elastic behaviour.

A general model for anisotropic pseudo-elasticity and viscoelasticity at finite strains

Given the growing demand for simulating anisotropic material behavior at finite strains, constitutive modeling is in a challenging position to combine descriptive capabilities for several inelastic phenomena with the numerical feasibility for real-world applications. In this article, we develop a material model capable of reproducing anisotropy, viscoelasticity, stress softening, and permanent set by merging several pre-existing frameworks. Each constitutive effect is discussed separately in terms of its thermodynamics and mechanical interpretation and successively built on top of each other. Here, the pseudo-elastic approach to permanent set occupies a special place, with a novel discussion of its applicability to generic deformations. We show that the formulation does not lead to physical behavior in general, but can be constrained in such a way to produce appropriate stress predictions in an average sense. Examples of the stress response in several different deformation modes are visualized throughout. The capabilities and possible shortcomings of the formulation are highlighted and at the end a simple numerical algorithm for stress computation is presented.

Extending the theory of pseudo-elasticity to capture the permanent set and the induced anisotropy in the Mullins effect

A new modelling framework is proposed to predict the inelastic features in elastomers’ mechanical behaviour such as the Mullins effect, the permanent set and the induced anisotropy. While based on the pseudo-elasticity theory, our model departs from the classical theory on three counts: (i) a separable damage parameter Ω, separable in the principal stretches, is devised and incorporated to facilitate capturing the induced anisotropy; (ii) the damage variable is directly incorporated into the hyperelastic strain energy function to capture the permanent set, and (iii) a specific functional form for the damage parameter is considered, conducive to modelling the foregoing behaviours. The devised framework is then specialised using a recently proposed strain energy function W and is validated against various experimental datasets ranging from filled natural and silicon rubbers, to synthetic rubbers and hydrogels. It is shown that the proposed model favourably captures the inelastic behaviours of interest exhibited by the specimens, and the devised modelling framework facilitates obtaining those favourable fits via a reduced number of model parameters compared with the existing theories in the literature. The proposed framework may also be used directly in conjunction with other strain energy functions for a versatile modelling of the Mullins effect in the finite deformation of rubber-like materials.

Sample coverage estimation, rarefaction, and extrapolation based on sample-based abundance data.

Sample coverage, the proportion of individuals that belong to observed species in a sample, is a metric used to measure the completeness of a sample. Rather than using equal sample sizes, equal sample coverage has become a widely accepted standard for comparing diversity across multiple assemblages, resulting in a more accurate representation of the true relationship between the richness of the assemblages. In practice, sample-based abundance data are the most frequently used data type for evaluating species diversity. In sample-based abundance data, the sampling unit (e.g., a plot, net, trap, or transect) is randomly selected from the target area, and the number of individuals for each species observed in the sampled unit is recorded. In this case, the individuals in the sample are no longer randomly and independently sampled, and the Good-Turing estimators of abundance-based sample coverage in reference, rarefied, and extrapolated samples may be severely biased when individuals present a highly spatially aggregated pattern. Here, I derive a novel estimator of abundance-based sample coverage based on the Good-Turing frequency formula. Additionally, a new analytical approach is introduced for enabling smooth coverage-based rarefaction and extrapolation to compare richness among assemblages. The near unbiasedness of the proposed estimator and a less biased richness ratio achieved using the newly developed coverage-based standardizing approach are demonstrated by analyzing three ForestGEO permanent forest plot data sets.

P35: Characterization and Comparison of Thermoplastic Material Performance Using Pressure-Volume Relationships

Purpose: Characterizing mechanical performance of finished materials can be challenging due to geometric constraints and the effects of downstream processing on raw material behavior. The following describes a more sensitive test method to accurately characterize the performance of a thin polymeric sheet material. Methods: Two different polymers, Thermoplastic Polyurethane, TPU, and Thermoplastic Elastomer, TPE, were selected for characterization. Each was molded and assembled into a manifold. Both polymers were under a constant pressure load over time, as a control and measurement technique. Fluid was injected incrementally into the assembly and the resulting injectate volume was measured by mass difference up to a limit volume to understand material behavior post processing. Results: The plotted pressure-volume relationships were distinct between TPU and TPE at two time intervals, as shown in Figure 1. A reduced pressure response to the same volume at test repetition demonstrated that both materials showed permanent set over time. Volume offset between sample runs illustrated reduced mechanical performance over time due to material creep. Conclusion: The pressure-volume testing method successfully characterized performance of the materials over time to discriminate the material set properties between two thin polymeric sheet material, which could not be detected for a finished component using traditional tensile test methods. This repeated method can be used during material selection in various applications for materials with a manufactured finished component, especially for the medical device industry where polymers are carefully chosen and designed for a specific function.

Effect of triethylene glycol bis(3‐tert‐butyl‐4‐hydroxy‐5‐methylphenyl)propionate on structure and mechanical properties of nitrile butadiene rubber/clay nanocomposites

AbstractClay modification by organic ammonium salts has been widely introduced in rubber/clay nanocomposites, but it is inapplicable in the polar rubbers to achieve high performance due to bad dispersion and poor compatibility. In this work, gel‐compounding method was utilized to prepare nitrile butadiene rubber (NBR)/clay nanocomposite, and then a hindered phenol antioxidant, triethylene glycol bis(3‐tert‐butyl‐4‐hydroxy‐5‐methylphenyl)propionate (AO‐245) with various contents, was mechanically blended to enhance the interactions in the nanocomposites. The elongation at break increases while the Shore A hardness, permanent set and stress at 100% or 300% strain decrease by adding AO‐245 into the nanocomposites. By adding only 5 phr AO‐245 in the nanocomposite, the tensile strength and elongation at break increased from 18.3 MPa and 521% to 20.5 MPa and 646%, respectively, which resulted from the repeated destruction/construction of the hydrogen bonds between AO‐245 and NBR. At high AO‐245 content, both clay networks and AO‐245 aggregate networks coexist in the nanocomposite, and the excess AO‐245 in the NBR matrix can form a separated phase leading to a new internal friction peak.

Improved strength, creep resistance and recyclability of polyisoprene vitrimers by bottom-up construction of inhomogeneous network

Vitrimer elastomers bring huge chance to solve the recycling problem of conventional rubbers. However, their application is extremely limited by their lack of creep resistance. Although the crosslinking density can significantly affect the relaxation behavior of dynamic covalent networks, but limited by the tradeoff between mechanical strength and creep resistant properties. Here, we introduce inhomogeneous dynamic covalent network with regions of different crosslinking densities, in which the low crosslinking density mainly contribute to the creep resistance and the high crosslinking density contribute to the mechanical strength. In detail, block copolymers with polymyrcene and polyisoprene blocks and its control sample polyisoprene were prepared and epoxidized. The polymyrcene block is a double bond-rich block compared to polyisoprene block, which will become an epoxy group-rich block after epoxidation and a high cross-link density phase region after crosslinking with a dicarboxylic acid agent. Therefore, the cross-linked block copolymer will have an inhomogeneous dynamic covalent network, which were confirmed by the Multi-quantum (MQ) NMR tests, AFM images and tanδ measurement. And the heterogeneous structure becomes more obvious with the increased length of polymyrcene block. WAXD results show that cross-linked block copolymers have lower strain-induced crystallization onset strain and higher crystallinity, making them far stronger and tougher. In addition, block copolymer samples demonstrate lower creep and lower permanent set due to slow relaxation of the low crosslinking density regions. The recycling efficiencies of mechanical strength of block copolymer samples were higher than that of homopolymer. This work provides a useful approach for improving the mechanical properties and dimensional stability of vitrimer elastomers simultaneously.

A novel approach to evaluate the mechanical responses of elastin-like bioresorbable poly(glycolide-co-caprolactone) (PGCL) suture

Poly(glycolide-co-caprolactone) (PGCL) has become a novice to the bioresorbable suture owing to the synergistic properties taken from the homo-polyglycolide (PGA) and polycaprolactone (PCL) such as excellent bioresorption and flexibility. In addition to under conventional monotonic loading, the understanding of mechanical responses of PGCL copolymers under complex loading conditions such as cyclic and stress relaxation is crucial for its application as a surgical suture. Consequently, the present work focuses on evaluating the mechanical responses of PGCL sutures under monotonic, cyclic, and stress relaxation loading conditions. Under monotonic loading, the stress-strain behavior of the PGCL suture was found to be non-linear with noticeable strain-rate dependence. Under cyclic loading, inelastic responses including stress-softening, hysteresis and permanent set were observed. During cyclic loading, both stress-softening and hysteresis were found to increase with the maximum strain. In multi-step stress relaxation, the PGCL sutures were observed to exhibit a strong viscoelastic response. In an attempt to describe the relationship between the stress-relaxation and strain-induced crystallization (SIC) occurring during the loading and relaxation processes, a schematic illustration of the conformational change of polymer chains in PGCL sutures was proposed in this work. Results showed that SIC was dependent on the strain level as well as the loading and relaxation durations. The inelastic phenomena observed in PGCL sutures can be thus correlated to the combined effect of stress relaxation and SIC.