Dimensional Instability Research Articles

Characterization of Glass/Jute Hybrid Fibre Reinforced Epoxy Composite for Axial Flow Fan Blade

Traditionally axial flow fan blades were manufactured by using metal alloys, but with the increase in blade size the blades grew heavier resulting in more vibrations during its working. It is impossible to manufacture the metallic blades to close tolerances making it uneconomical. Due to this dimensional instability, the metallic impeller fan blades are instead fabricated with glass fiber reinforced plastics (GFRP). To reduce the after effects of GFRP blades on the environment necessitates the partial reinforcement of natural fibre. This paper deals with the characterization of GFRP blade material with partial Jute reinforcements i.e., glass to jute (95:5) weight percentage and estimating the properties like tensile strength, bending strength, shear strength, fracture toughness. The conventional GFRP blade material has 14 layers of glass fibers in various forms. By placing jute layer at various positions in GFRP blade material the mechanical strengths were estimated and compared with conventional one.

An effective technique for constructing wood composite with superior dimensional stability

Abstract Fast-growing wood is an abundant and low-cost material and is widely used for structural building and furniture construction. However, inferior mechanical properties and dimensional instability limit its application in advanced engineering structures. Herein, we developed a simple, effective and “green” method to transform bulk poplar into a high-performance wood composite. The wood composite was prepared by the impregnation of the itaconic acid (IA) solution acting as a grafting anchor into the wood matrix, followed by in situ polymerization of styrene upon heating to form a hydrophobic polymer within the wood scaffold. Scanning electron microscope (SEM) analysis revealed that hydrophobic polystyrene (PS) was deposited in wood cell walls and lumens, leading to a reduced water uptake and remarkably enhanced dimensional stability, as well as generally improved mechanical properties. In addition, the PS generated improvement in the thermal stability of the wood composite in comparison with that of natural wood (W).

Solid matrix-assisted printing for three-dimensional structuring of a viscoelastic medium surface

Gluconacetobacter xylinus (G. xylinus) metabolism is activated by oxygen, which makes the formation of an air-medium interface critical. Here we report solid matrix-assisted 3D printing (SMAP) of an incubation medium surface and the 3D fabrication of bacterial cellulose (BC) hydrogels by in situ biosynthesis of G. xylinus. A printing matrix of polytetrafluoroethylene (PTFE) microparticles and a hydrogel ink containing an incubation medium, bacteria, and cellulose nanofibers (CNFs) are used in the SMAP process. The hydrogel ink can be printed in the solid matrix with control over the topology and dimensional stability. Furthermore, bioactive bacteria produce BC hydrogels at the surface of the medium due to the permeability of oxygen through the PTFE microparticle layer. The flexibility of the design is verified by fabricating complex 3D structures that were not reported previously. The resulting tubular BC structures suggest future biomedical applications, such as artificial blood vessels and engineered vascular tissue scaffolding. The fabrication of a versatile free-form structure of BC has been challenged due to restricted oxygen supplies at the medium and the dimensional instability of hydrogel printing. SMAP is a solution to the problem of fabricating free-form biopolymer structures, providing both printability and design diversity.

Normal form of synchronization and resonance between vorticity waves in shear flow instability.

A minimal model of linearized two-dimensional shear instabilities can be formulated in terms of an action-at-a-distance, phase-locking resonance between two vorticity waves, which propagate counter to their local mean flow as well as counter to each other. Here we analyze the prototype of this interaction as an autonomous, nonlinear dynamical system. The wave interaction equations can be written in a generalized Hamiltonian action-angle form. The pseudoenergy serves as the Hamiltonian of the system, the action coordinates are the contribution of the vorticity waves to the wave action, and the angles are the phases of the vorticity waves. The term "generalized action angle" emphasizes that the action of each wave is generally time dependent, which allows instability. The synchronization mechanism between the wave phases depends on the cosine of their relative phase, rather than the sine as in the Kuramoto model. The unstable normal modes of the linearized dynamics correspond to the stable fixed points of the dynamical system and vice versa. Furthermore, the normal form of the wave interaction dynamics reveals a new type of inhomogeneous bifurcation: annihilation of a stable and an unstable star node yields the emergence of two neutral center fixed points of opposite circulation.

Effect of acetylation technique on mechanical behavior and durability of palm fibre vinyl-ester composites

Abstract In natural fiber reinforced polymer (NFRP) composites, there is a lack of good inter-facial adhesion between the hydrophilic cellulose fibers due to their inherent incompatibility. High water and moisture absorption of the cellulose fibres causes swelling, dimensional instability, poor mechanical properties. This work focuses on eliminating the swelling effect of the palm fiber composite by Acetylation. This acetylated palm fiber composites reduce manufacturing cost of automobile interiors, door panels, etc. The chemical treatment improved the tensile strength till 6% concentration. The ANOVA study was carried out to reveal the effects of concentration and soaking period on strength of fiber composites.

Rendering mortars with incorporation of very fine aggregates from construction and demolition waste

The intense rate of construction and demolition waste generation (CDW) over the years should boost recycling. The use of CDW as constituents of cementitious composites has been considered a feasible alternative to dumping. This paper presents a study of the behaviour of cementitious renderings incorporating very fine recycled aggregates from two types of CDW. Only particles of recycled aggregates below 0.149 mm were used as filler, hereinafter referred as recycled concrete aggregate (RCA) and mixed recycled aggregate (MRA). The incorporation’ percentages used were 0%, 10%, 15% and 20% of natural aggregates’ volume. Several tests have been carried out, in order to evaluate the mortars in terms of mechanical strength, workability, water absorption, dimensional instability and water vapour permeability. The experimental programme consisted in three consecutive phases, in which the mortars that presented the best performances were selected for a deeper analysis of their features. The test results showed that modified mortars had a better behaviour in most of tests compared with the reference mortar (with no CDW). Mortars with incorporation of 20% of RCA and 15% of MRA presented the best performance.

Water Absorption and Dimensional Stability of Heat-treated Fast-growing Hardwoods

A common problem with fast-growing hardwoods is dimensional instability that limits use of their wood. In this study, we investigated the effects of pre-drying methods, temperatures, and heating duration on the specific gravity, water absorption, and dimensional stability of three tropical fast-growing hardwoods, jabon (Neolamarckia cadamba Roxb.), sengon (Falcataria moluccana Miq.), and mangium (Acacia mangium Willd.). Wood samples were pre-dried by two methods (fan and oven at 40 °C), and heat treatments were performed at three temperatures (120, 150, and 180 °C) for two different time periods (2 and 6 hours). The specific gravity, water absorption, dimensional stability, and structural changes of the samples were evaluated. The results revealed that heat treatments slightly reduced the specific gravity of all three wood species. In addition, the heat treatments reduced water absorption and significantly improved dimensional stability of the samples. Oven pre-drying followed by heat treatment at 180 °C for 6 hours resulted in good physical improvement of jabon and sengon wood. Fan pre-drying followed by heat treatment at 180 °C for 2 hours improved the physical properties of mangium wood. The heat treatment shows a promising technique for improving the physical characteristic of fast growing hardwoods.

Everlasting Living and Breathing Gyroid 3D Network in Si@SiOx/C Nanoarchitecture for Lithium Ion Battery.

Silicon-based materials are the most promising candidates to surpass the capacity limitation of conventional graphite anode for lithium ion batteries. Unfortunately, Si-based materials suffer from poor cycling performance and dimensional instability induced by the large volume changes during cycling. To resolve such problems, nanostructured silicon-based materials with delicately controlled microstructure and interfaces have been intensively investigated. Nevertheless, they still face problems related to their high synthetic cost and their limited electrochemical properties and thermal stability. To overcome these drawbacks, we demonstrate the strategic design and synthesis of a gyroid three-dimensional network in a Si@SiOx/C nanoarchitecture (3D-Si@SiOx/C) with synergetic interaction between the computational prediction and the synthetic optimization. This 3D-Si@SiOx/C exhibits not only excellent electrochemical performance due to its structural stability and superior ion/electron transport but also enhanced thermal stability due to the presence of carbon, which was formed by a cost-effective one-pot synthetic route. We believe that our rationally designed 3D-Si@SiOx/C will lead to the development of anode materials for the next-generation lithium ion batteries.

Multi-Scale Evaluation of the Effect of Phenol Formaldehyde Resin Impregnation on the Dimensional Stability and Mechanical Properties of Pinus Massoniana Lamb.

The local chemistry and mechanics of the control and phenol formaldehyde (PF) resin modified wood cell walls were analyzed to illustrate the modification mechanism of wood. Masson pine (Pinus massoniana Lamb.) is most widely distributed in the subtropical regions of China. However, the dimensional instability and low strength of the wood limits its use. Thus, the wood was modified by PF resin at concentrations of 15%, 20%, 25%, and 30%, respectively. The density, surface morphology, chemical structure, cell wall mechanics, shrinking and swelling properties, and macro-mechanical properties of Masson pine wood were analyzed to evaluate the modification effectiveness. The morphology and Raman spectra changes indicated that PF resin not only filled in the cell lumens, but also penetrated into cell walls and interacted with cell wall polymers. The filling and diffusing of resin in wood resulted in improved dimensional stability, such as lower swelling and shrinking coefficients, an increase in the elastic modulus (Er) and hardness (H) of wood cell walls, the hardness of the transverse section and compressive strength of the wood. Both the dimensional stability and mechanical properties improved as the PF concentration increased to 20%; that is, a PF concentration of 20% may be preferred to modify Masson pine wood.

2D Nanosheets and Their Composite Membranes for Water, Gas, and Ion Separation

AbstractTwo‐dimensional nanosheets have shown great potential for separation applications because of their exceptional molecular transport properties. Nanosheet materials such as graphene oxides, metal–organic frameworks, and covalent organic frameworks display unique, precise, and fast molecular transport through nanopores and/or nanochannels. However, the dimensional instability of nanosheets in harsh environments diminishes the membrane performance and hinders their long‐term operation in various applications such as gas separation, water desalination, and ion separation. Recent progress in nanosheet membranes has included modification by crosslinking and functionalization that has improved the stability of the membranes, their separation functionality, and the scalability of membrane formation while the membranes’ excellent molecular transport properties are retained. These improvements have enhanced the potential of nanosheet membranes in practical applications such as separation processes.

2D Nanosheets and Their Composite Membranes for Water, Gas, and Ion Separation.

Two‐dimensional nanosheets have shown great potential for separation applications because of their exceptional molecular transport properties. Nanosheet materials such as graphene oxides, metal–organic frameworks, and covalent organic frameworks display unique, precise, and fast molecular transport through nanopores and/or nanochannels. However, the dimensional instability of nanosheets in harsh environments diminishes the membrane performance and hinders their long‐term operation in various applications such as gas separation, water desalination, and ion separation. Recent progress in nanosheet membranes has included modification by crosslinking and functionalization that has improved the stability of the membranes, their separation functionality, and the scalability of membrane formation while the membranes’ excellent molecular transport properties are retained. These improvements have enhanced the potential of nanosheet membranes in practical applications such as separation processes.

Hygroscopicity and dimensional stability of Populus euramericana Cv. modified by furfurylation combined with low hemicellulose pretreatment

Hygroscopicity and dimensional instability usually impair the service of wood products. To upgrade the property, fast-growing poplar wood (Populus euramericana Cv.) was treated with furfuryl alcohol at a concentration of 25% combined with low hemicellulose pretreatment. Equilibrium moisture content and dimensional changes were measured within the range of 0–96% relative humidity (RH) at 25 °C. New voids caused by hemicellulose loss suggested by the scanning electron microscope contributed to higher weight percent gain of furfural resin with more obvious bulking of cell walls. The size distribution of mesopores increased after low hemicellulose pretreatment but decreased much more after furfurylation from the analysis of nitrogen adsorption. After hemicellulose loss, moisture sorption was weakened indicated from the decrease in moisture content (MC) and hydrated MC as well as dissolved MC due to the decrement of accessible hydroxyl groups calculated by Hailwood–Horrobin theory. Furthermore, dimensional stability was improved. Furfurylation led to further reduction in moisture sorption and enhancement of dimensional stability, since water paths were blocked and less hydroxyl groups were accessible. The bulking also limited the swelling of cell walls. After the combined modification, over 45% reduction in moisture content and dimensional changes of wood at 60% RH can be achieved. Such upgraded fast-growing wood could be utilized more widely with a longer service life as a potential replacement for traditional high-quality solid wood and helpful with building a more efficient and environmentally friendly material industry.

Monolithic 3D printing of embeddable and highly stretchable strain sensors using conductive ionogels

Medical training simulations that utilize 3D-printed, patient-specific tissue models improve practitioner and patient understanding of individualized procedures and capacitate pre-operative, patient-specific rehearsals. The impact of these novel constructs in medical training and pre-procedure rehearsals has been limited, however, by the lack of effectively embedded sensors that detect the location, direction, and amplitude of strains applied by the practitioner on the simulated structures. The monolithic fabrication of strain sensors embedded into lifelike tissue models with customizable orientation and placement could address this limitation. The demonstration of 3D printing of an ionogel as a stretchable, piezoresistive strain sensor embedded in an elastomer is presented as a proof-of-concept of this integrated fabrication for the first time. The significant hysteresis and drift inherent to solid-phase piezoresistive composites and the dimensional instability of low-hysteresis piezoresistive liquids inspired the adoption of a 3D-printable piezoresistive ionogel composed of reduced graphene oxide and an ionic liquid. The shear-thinning rheology of the ionogel obviates the need to fabricate additional structures that define or contain the geometry of the sensing channel. Sensors are printed on and subsequently encapsulated in polydimethylsiloxane (PDMS), a thermoset elastomer commonly used for analog tissue models, to demonstrate seamless fabrication. Strain sensors demonstrate geometry- and strain-dependent gauge factors of 0.54–2.41, a high dynamic strain range of 350% that surpasses the failure strain of most dermal and viscus tissue, low hysteresis (<3.5% degree of hysteresis up to 300% strain) and baseline drift, a single-value response, and excellent fatigue stability (5000 stretching cycles). In addition, we fabricate sensors with stencil-printed silver/PDMS electrodes in place of wires to highlight the potential of seamless integration with printed electrodes. The compositional tunability of ionic liquid/graphene-based composites and the shear-thinning rheology of this class of conductive gels endows an expansive combination of customized sensor geometry and performance that can be tailored to patient-specific, high-fidelity, monolithically fabricated tissue models.

Thermal effects compensation and associated uncertainty for large magnet assembly precision alignment

Big science and ambitious industrial projects continually push technical requirements forward beyond the grasp of conventional engineering techniques. An example of these are the extremely tight micrometric assembly and alignment tolerances required in the field of celestial telescopes, particle accelerators, and the aerospace industry. Achieving such extreme requirements for large assemblies is limited, largely by the capability of the metrology used, namely, its uncertainty in relation to the alignment tolerance required. The current work described here was done as part of Maria Curie European research project held at CERN, Geneva. This related to future accelerators requiring the spatial alignment of several thousand, metre-plus large assemblies to a common datum within a targeted combined standard uncertainty (uctg(y)) of 12 μm. The current work has found several gaps in knowledge limiting such a capability. Among these was the lack of uncertainty statements for the thermal error compensation applied to correct for the assembly's dimensional instability, post metrology and during assembly and alignment. A novel methodology was developed by which a mixture of probabilistic modelling and high precision traceable reference measurements were used to quantify the uncertainty of the various thermal expansion models used namely: Empirical, Finite Element Method (FEM) models and FEM metamodels. Results have shown that the suggested methodology can accurately predict the uncertainty of the thermal deformation predictions made and thus compensations. The analysis of the results further showed how using this method a ‘digital twin’ of the engineering structure can be calibrated with known uncertainty of the thermal deformation behaviour predictions in the micrometric range. Namely, the Empirical, FEM and FEM metamodels combined standard uncertainties ( uc(y) ) of prediction were validated to be of maximum: 8.7 μm, 11.28 μm and 12.24 μm for the studied magnet assemblies.

Shrinkage behaviour of semi-crystalline polymers in laser sintering: PEKK and PA12

Shrinkage is extensively mentioned in the literature as one of the main causes for dimensional instability or poor performance in Laser Sintering (LS). This study proposes and examines a methodology to describe shrinkage in cooling from a material perspective. Thermal behaviour and crystallisation effects were measured to determine the influence of powder structure and density on the overall LS shrinkage. PEKK and PA12 powders were used to assess such behaviour. The shrinkage parameter associated with powder bulk properties has the greatest impact in PEKK, contributing to 57% of the total shrinkage observed in cooling for this material as supported by the low values of bulk density, irregular morphology and internal porosity observed for these particles. For PA12, crystallisation is responsible for 60% of the overall shrinkage observed. In LS, PEKK shows an overall shrinkage approximately 30% lower than PA12, which makes it a promising material for maintaining final part dimensions.

Nanosilica Coatings to Improve the Tensile Bond Strength of Cementitious Grouts

The use of prefabricated bridge elements (PBEs) is becoming more common as bridge owners strive to construct robust bridges with minimal impacts on the traveling public. Concrete PBEs offer advantages with regards to quality and construction safety; however, to perform adequately, the installed structural system must include strong, durable connections between the components. Typically, field-cast cementitious grouts are used to connect the PBE. This type of material has at times shown serviceability problems associated to dimensional instability, primarily in the form of shrinkage cracking. A direct consequence is the potential bond degradation between the grout connections and the concrete PBE. This study investigated the use of colloidal nanosilica suspensions as a surface preparation technique to increase the bond strength between the precast components and the field-cast grout. Experimental results, including pull-off bond data and a careful microstructural analysis, strongly suggest that nanosilica coatings interact at the concrete–grout interface to increase the bond strength. A simple initial cost analysis is also discussed.

Mechanical behaviour of acetylated rubber wood subjected to artificial weathering

Abstract Rubber wood utilization in Nigeria has become a viable alternative because of over-exploitation of more durable species. The use of rubber wood in its native form has some disadvantages including dimensional instability, low durability and susceptibility to weathering in outdoor uses. However, it may be improved through chemical modification such as acetylation. In this study, we revealed the effectiveness of acetylation on the protection of rubber wood against weathering in terms of weight loss (WL), colour change, lignin degradation, and mechanical properties. Acetylation was carried out using two different reaction times to achieve weight percent gains (WPG) of around 7% and 10%. Understanding of the effect of acetylation and subsequent weathering on mechanical properties was enabled by analysing wood chemistry with Fourier transform infrared (FTIR) analysis and Raman spectroscopy. The mechanical tests of weathered unmodified and acetylated rubber wood revealed a decrease of tensile stiffness of the unmodified samples as a function of weathering time, while stiffness was retained for the acetylated samples. Weathered unmodified samples showed a bi-phasic stress-strain pattern with a high strain at breakage indicating a slippage of fibres under stress due to degradation of the middle lamella. This was hardly visible for acetylated samples. Thus, acetylation was shown to be effective for protecting rubber wood used in outdoor conditions.

Attapulgite-reinforced polyimide hybrid aerogels with high dimensional stability and excellent thermal insulation property

Strong low-density polymer aerogels have received intensive attention as thermal or sound insulator, filtration media and sensors, etc. However, dimensional instability has been regarded as one of issues that limits the wide application of polymer aerogels in a harsh temperature. In present work, polyimide aerogels were reinforced with attapulgite (AT) nanorods, one of natural fibrillar minerals, through the strong hydrogen-bonding interaction. In hybrid aerogels, AT nanorods act as the rigid skeleton that supporting the framework of aerogels. The resultant hybrid aerogels exhibit improved mechanical properties. At the 80% strain, the compressive stresses for the aerogels containing 10 wt% AT are 100% as high as those of the pure polyimide aerogels. Interestingly, modulus of hybrid aerogels increases as the density decreases. For example, the compression Young's and specific modulus increase by 100% and 105% for the hybrid ODA-based aerogel compared to the pristine sample, meanwhile, the density decreases by 10%. Furthermore, the AT nanorods show strong supporting effects in maintaining the structural integrity of aerogels, which produce a significant effect on reducing the shrinkage of hybrid aerogels at high temperatures and retaining their excellent thermal insulation performance. The detailed investigation reveals that the AT is an effective and low-cost additive for preparing high performance polymer nanocomposites aerogels with improved mechanical property and thermal dimensional stability.

How does delignification influence the furfurylation of wood?

To investigate the influence of delignification on wood furfurylation, poplar wood (Populus euramericana Cv.) was partly delignified prior to the impregnation of furfuryl alcohol (FA) at concentration of 25%. The observation by using scanning electron microscope (SEM) and confocal laser scanning microscopy (CLSM) showed that many intercellular spaces appeared in middle lamella and cell corners in the wood with 8.86% lignin loss (LL), after further furfurylation, these spaces were filled with polymerized furfural resin, which contributed to the more uniform distribution of modifier and larger bulking of cell wall in furfurylated wood with low lignin (LF) than furfurylated control (CF). The size distribution of mesopores increased after delignification but decreased after furfurylation, and the specific surface area was reduced over 20% for LF with about 50% total pore volume decrease compared with the control from the analysis of nitrogen adsorption. Lignin loss and chemical polymerization of furfural resin were confirmed but without chemical reaction between FA and cell wall components by both results of Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). Delignification resulted in increased equilibrium moisture content (EMC) and dimensional instability, after further furfurylation, the EMC and dimensional changes of LF decreased and were lower than those of control by 16.3% on average, suggesting the availability of furfurylation in reducing moisture sorption and improving dimensional stability of low lignin content wood. The number of accessible hydroxyl groups in wood calculated by using Hailwood-Horrobin theory exhibited in the following order: LL > control > LF > CF. The results can potentially help with understanding the action of delignification in wood furfurylation, as well as providing information on the possibility of make sustainable use of wood products with degraded lignin by furfurylation.

HYDROTHERMAL TREATMENT OF EUCALYPTUS GRANDIS WOOD

Among the technological alternatives to improve the quality and use of eucalyptus wood is heat treatment, as the wood has some features that may limit its use, such as dimensional instability, high anisotropy, and heterogeneous coloring. This study is aimed at evaluating the effect of time of hydrothermal treatment on physical, chemical, and mechanical properties of solid wood of Eucalyptus grandis . We used three trees of E. grandis , selecting only the heartwood, and prepared test specimens with dimensions of 30cmx8cmx3cm (length, width, and thickness). The hydrothermal treatment was performed in a Parr reactor using three reaction times (5, 15, and 25min) at 140°C. Partial removal of extractives occurred, especially in the outer layer of wood. There was an increase of up to 58% of its permeability because of the partial clearing of the vessel elements. There was no degradation of the main constituents of the wood, so loss of mechanical strength was observed. The hydrothermal treatment promoted the partial removal of the hydroxyl groups and/or a structural rearrangement of the hemicelluloses and cellulose, causing a reduction of the hygroscopicity of E. grandis .