Anisotropic Shrinkage Research Articles

Interdependence of shrinkage behavior between wood macroscopic and cellular level during moisture content loss

Wood is widely considered to be a green and renewable building material. However, many of the challenges to using wood as an engineering material arise from the shrinkage and swelling behaviors during moisture content (MC) loss or gain. In this study, the shrinkage behavior of Queensland peppermint (Eucalyptus exserta F. V. Muell) wood was investigated at the macroscopic and cellular levels, and the interdependence between the two levels was explored. Results revealed that the tangential shrinkage of 2% and radial shrinkage of 1% was observed as MC decreased from about 60% to 32% in the macroscopic level. The most obvious anisotropic shrinkage was presented at the MC region of 32–22%, and the ratio of T/R was ranged from 1.6 to 1.75 below the fiber saturation point. At the cellular level, a considerable shrinkage was observed at MC of 42%. The cell wall was shrunk, but the lumen in radial (TR plane) was expanded with MC loss. The shrinkage of the total wood cell showed a linear relationship with MC. The shrinkage ratio of T/R was maintained around 1.5 below the fiber saturation point, indicating that the MC states have little effect on the anisotropic shrinkage. Besides, the shrinkage value at the macroscopic level was slightly smaller than the cellular level, but the anisotropic shrinkage showed an opposite trend.

Correlations of Geometry and Infill Degree of Extrusion Additively Manufactured 316L Stainless Steel Components

This study focuses on the effect of part geometry and infill degrees on effective mechanical properties of extrusion additively manufactured stainless steel 316L parts produced with BASF’s Ultrafuse 316LX filament. Knowledge about correlations between infill degrees, mechanical properties and dimensional deviations are essential to enhance the part performance and further establish efficient methods for the product development for lightweight metal engineering applications. To investigate the effective Young’s modulus, yield strength and bending stress, standard testing methods for tensile testing and bending testing were used. For evaluating the dimensional accuracy, the tensile and bending specimens were measured before and after sintering to analyze anisotropic shrinkage effects and dimensional deviations linked to the infill structure. The results showed that dimensions larger than 10 mm have minor geometrical deviations and that the effective Young’s modulus varied in the range of 176%. These findings provide a more profound understanding of the process and its capabilities and enhance the product development process for metal extrusion-based additive manufacturing.

3D printing of porcelain: finite element simulation of anisotropic sintering

Sintering is a key step that determines the mechanical performances and shape quality of 3D printed ceramics. In this domain, there is an increasing interest in complex thin structures and low fill density shapes. However, these complex structures may suffer from distortions by gravity forces developed on the light structure, friction with supports, shrinkage anisotropy, or thermal gradients. Finite element simulation of the sintering process is then of high importance for predicting the specimens distortions. This paper focuses on the identification of the model parameters in the special case of anisotropic sintering of porcelain with final stage swelling. This study points out the printed specimen high resistance to high temperature shear deformation due to the alignment of the printed rods. A mesoscale simulation has been carried out to explain this mechanism. The resulting model was tested for the sintering of a thin wall cup shape.

The influence of sintering procedure and porosity on the properties of 3D printed alumina ceramic cores

In order to obtain 3D printed alumina ceramic cores with isotropic shrinkage, a pore former was added into the photocurable slurry, and combined with an optimization of the sintering procedure. Micron scale pores were observed in the sintered ceramics when the pore former was present compared with the samples without pore former. The addition of the pore former significantly improved the pore interconnectivity and pore size of the 3D printed ceramics, due to the volatilization of the pore former. The resulting shrinkage of the ceramic parts in three directions was more uniform and smaller when they were fabricated using a slurry containing the pore former in comparison to those without pore former. The bulk density, shrinkage, and flexural strength of the ceramics increased with increasing the sintering temperature. Triple sintering significantly improved the flexural strength, and also lead to anisotropic shrinkage of the samples, due to the enhanced binding force between layers deriving from the increased number of sintering cycles. In addition, the triple sintering process enabled healing of the cracks developed during sintering, differently from a single sintering. The use of a pore former and the triple sintering procedure provides a new optimized strategy for the fabrication of 3D printed ceramic cores with suitable properties.

A radiographic method for the measurement of soil core volume in shrinkage analysis

Modeling of soil shrink-swell requires accurate measurement of volume changes in soil samples during drying-wetting cycles. Soil core samples are needed if anisotropy in shrinkage behavior has to be evaluated. The widely used caliper method allows soil core volume measurements but shows difficulties in providing accurate evaluation of horizontal deformation and risk of sample disturbance, particularly in wet conditions. Most recently proposed techniques (e.g.: laser, paraffin) either exhibit limitations in terms of complexity and equipment costs or are long and laborious. In this work an alternative method for accurately determining soil core volume, which is faster and relatively more simple and cheaper, is proposed. This method is based on simple 2D image analysis of two radiographs of the sample, whose results allow applying Pappus’ 2nd centroid theorem to calculate the volume of the soil core. A validation test performed by comparison with the caliper method has shown an error in accuracy lower than 1% for the proposed method versus 5% for the caliper method. The radiographic method has been more precise on a reference sample (standard deviations about 1.0% versus 1.4% of the average volume value) and also on four repacked cores of natural soils with different shrink-swell potentials (standard deviations ranged from 0.39% to 1.15% and from 0.34% to 3.00% of the volume for the radiography and caliper methods, respectively). Application of the method to the same soil samples during a drying process has highlighted its greater accuracy and suitability in assessing anisotropy of shrinkage at any soil water content.

Dimensional and geometrical precision of parts produced by binder jetting process as affected by the anisotropic shrinkage on sintering

Dimensional and geometrical precision of parts produced by binder jetting is a crucial issue to be considered aiming at promoting the transition to industrial production. The influence of both the printing and the sintering processes has to be evaluated, and the high shrinkage has to be considered. The task is further complicated by the anisotropy of dimensional change on sintering. The aim of this work is to investigate the dimensional and geometrical precision of cylindrical holes, as affected by the anisotropy of dimensional change on sintering after binder jetting. AISI 316 L powder was used to produce five different geometries, characterized by four holes with different orientation with respect to the printing direction. The geometrical features were measured both in the green and in the sintered state with a coordinate measuring machine, and the dimensional changes, as well as the geometrical variations, were calculated. According to the author’s previous experience, a theoretical model has been defined, which aims at predicting the geometry of the holes as derived by the anisotropic dimensional change on sintering. The expected dimensional change of hole diameters, the variation of cylindricity, and the variation of the axis inclination were calculated by the model and compared to those derived from measurement. Good agreement between predicted and measured results has been observed, providing that the influence of printing process parameters is considered.

Review of methods for predicting soil volume change induced by shrinkage

The shrinkage of soil induced by cyclic moisture variation from the post-compaction state needs to be addressed for understanding its long-term performance. The soil shrinkage curve is modeled to characterize the loss of moisture and the associated soil volume change from the initially saturated state to zero volume change phase. The volume change associated with gradual loss of moisture provides insight into the pore volume change, thus necessitating an accurate determination of soil volume. In this article, a detailed review of various measurement methods practiced to quantify the volume change of soil during the desiccation process in the laboratory is discussed. The procedure outlines, advantages, limitations, and the implication of results are discussed elaborately to understand their implications on shrinkage curve characterization. The absolute error of volume measurement by non-contact measurement method can be as low as 0.3% compared with direct measurement procedures. The study highlights the necessity to quantify the anisotropy in volumetric shrinkage and the advantage of using non-contact measurement methods. In particular, this review on the current state-of-the-art practices emphasizes digital image analysis as a cost-effective and reliable approach to quantify the shrinkage of fine grained soils, especially highly expansive clay.

3D printing of porcelain and finite element simulation of sintering affected by final stage pore gas pressure

Ceramic 3D printing involves various sintering phenomena such as shape distortions, crack formations, shrinkage anisotropy, and residual porosity that demands the development of a simulation tool. Moreover, liquid-phase sintering of materials such as porcelain exhibits an additional and challenging phenomenon at the end of the sintering process that reflects closed porosity growth and coalescence owing to the pressure created by the pore-trapped gases, which further implies swelling (or bloating) of the entire specimen accompanied by distortions. In this study, the swelling issue of 3D-printed porcelain samples was investigated through a sintering dilatometry parametric design to determine the optimal heating rate and holding temperature. A sintering modeling theory was employed to characterize the final stage pore gas pressure via an inverted sintering model formulation. Finally, a finite element sintering simulation was applied based on the analytical model data to predict the sintering shrinkage of a complex geometry.

Carbon phase adjustment by multi-configuration ligand in endohedral metallofullerene derivatives Gd@C82(morpholine)7 under high pressure

Abstract Metallofullerenes present an ideal research object for developing new carbon structures with improved properties under high pressure. In this study, high pressure investigation is realized on metallofullerene derivatives (Gd@C82(morpholine)7) by applying in situ synchrotron XRD, Raman, and IR spectroscopy, combined with high pressure density functional theory (DFT) calculations. The regulations of multi-configuration morpholine ligands avoid the direct collapse of the carbon cages commonly happened to fullerenes, making the fine structure transformation possible for the first time, including ligand configuration exchange, anisotropic shrinkage of cage, new constructed bonds, and even the encaged metal’s movement with increasing pressure. The charge-transfer principle as the beneath driving force of structural transition is found. These findings demonstrate that multi-configuration ligand maps an innovative strategy for phase transition control of metallofullerenes under high pressure, thus providing deep insight, step by step, into the phase transition mechanism of these hybrid molecular systems on molecular level.

Study of the Influence of Nanotechnogenic Raw Materials and Pyrophyllite on the Orientation of Clay Particles and the Water Permeability of Acid-Resistant Materials

The use of nanotechnogenic alumina-containing raw material and pyrophyllite in the compositions of ceramic bodies for the production of acid-resistant materials promotes reduction of the anisotropy of shrinkage during drying and firing and water permeability but in terms of water permeability the samples with nanotechnogenic aluminum-containing raw material have the best metrics. The introduction of pyrophyllite into the composition of ceramic bodies for the production of acid-resistant materials promotes formation of a significant accumulation of well-developed needle-shaped crystals of mullite in the samples and the introduction of nanotechnogenic raw material promotes the formation of filamentary crystals of mullite.

Construction of a three-dimensional S,N co-doped ZIF-67 derivative assisted by PEDOT nanowires and its application in rechargeable Zn–air batteries

PEDOT nanowires were obtained before pyrolysis to inhibit structural collapse and anisotropic shrinkage of the ZIF-67 in the pyrolysis process, and S,N co-doping is realized at the same time. The synthesized Co/C@NS NWs exhibit excellent performance towards ORR and OER.

Sintering shrinkage of cold compacted iron: effect of thermodynamic driving force, structural and geometrical activity

ABSTRACT The sintering shrinkage of tapped powders and prior cold compacted specimens of sponge and water atomised iron powders was investigated. The behaviour of the tapped powders is only determined by the driving force and that of the green compacts is strongly affected by modifications caused by cold compaction, which introduce a structural and a geometrical activity that enhance the kinetics of shrinkage. While the tapped powders display only an isothermal shrinkage, the green specimens display an additional large and anisotropic anisothermal shrinkage which is independent on the surface area of the powders. The effect of prior cold compaction tends to run out during the heating step of the sintering cycle.

4D Printing of Glass Fiber-Regulated Shape Shifting Structures with High Stiffness.

4D printing allows 3D printed structures to change their shapes overtime under external stimuli, finding a wide range of potential applications in actuators, soft robotics, active metamaterials, flexible electronics, and biomedical devices. However, most 4D printing uses soft polymers to accommodate large strain shape-changing capability at the price of low stiffness, which impedes their engineering applications. Here, we demonstrate an approach to design and manufacture self-morphing structures with large deformation and high modulus (∼4.8 GPa). The structures are printed by multimaterial direct ink writing (DIW) using composite inks that contain a high volume fraction of solvent, photocurable polymer resin, and short glass fibers as well as fumed silica. During printing, the glass fibers undergo shear-induced alignment through the nozzle, leading to highly anisotropic mechanical properties. The solvent is then evaporated, during which the aligned glass fibers enable anisotropic shrinkage in the parallel and perpendicular directions to the fiber alignment for shape shifting. A final postphotocuring step is applied to further increase the stiffness of the composite from ∼300 MPa to ∼4.8 GPa. A finite element analysis (FEA) model is developed to predict the influence of the solvent, fiber contents, and fiber orientation on the shape shifting. We demonstrate the anisotropic volume shrinkage of the structures can be used as active hinges to transform printed two-dimensional structures into complex three-dimensional structures with large shape-shifting and outstanding mechanical properties. This strategy for fabricating composite structures with programmable architectures and excellent mechanical properties shows potential applications in morphing lightweight structures with load-bearing capabilities.

Shrinkage vectors and volumetric shrinkage percentage of differently applied composites

Bulk-fill composites can be placed at a thickness of 4 mm due to their sufficient depth of cure. The aim of this study was to investigate the effects of bulk versus incremental application methods on the shrinkage vectors and the percentage of volumetric polymerization shrinkage of the composites. Twelve molars were divided into three groups (n = 4), and cylindrical cavities (diameter = 6 mm, depth = 4 mm) were prepared, etched and bonded with OptiBond FL (Kerr). Cavities were restored with a 4-mm bulk-fill composite of Tetric EvoCeram Bulk Fill (TBF, Ivoclar Vivadent) designated as “TBF-bulk”, with two 2-mm increments of a bulk-fill composite designated as “TBF-incremental”, and with two 2-mm increments of a hybrid composite Tetric EvoCeram (TEC, Ivoclar Vivadent) designated as “TEC-incremental”. Each material application was scanned twice in a micro-CT (uncured and cured states), and inherent air bubbles served as markers. Scans were subjected to image segmentation to calculate the shrinkage vectors and the percentage of volumetric polymerization shrinkage. Significantly greater mean values of the shrinkage vectors were observed in “TBF-bulk”, followed by “TBF-increment1”, with no difference between the remaining increments of the groups (ANOVA, Tamhane's T2, p < 0.001); the percentage of volumetric polymerization shrinkage did not differ among the groups (ANOVA, Tamhane's T2, p = 0.759). Bulk application resulted in greater shrinkage vectors than in the incremental applications, despite the volumetric evaluation displaying no difference regarding the application methods. The discrepancy between the evaluation methods can be explained by anisotropic shrinkage, which is displayed through the shrinkage vectors but cannot be quantified by the volumetric evaluation. Incremental application of resin composites remains the gold standard in class-I cavities.

An in situ Raman spectroscopic method for quantification of polyethylene glycol (PEG) in waterlogged archaeological wood

AbstractThe weakened microstructure of archaeological wood (AW) objects from waterlogged environments necessitates consolidation to avoid anisotropic shrinkage upon drying. Polymer impregnation through submergence or spraying treatments is commonly applied, and for larger and thicker objects, the impregnation period can stretch over decades. Thus, for efficient treatment, continuous monitoring of the impregnation status is required. Today, such monitoring is often destructive and expensive, requiring segments for extraction and chromatographic quantification. This study proposes an in situ Raman spectroscopic method for quantification of polyethylene glycol (PEG) in waterlogged AW. A calibration model was built on standards of PEG, cellulose powder, and milled wood lignin using orthogonal partial least squares (OPLS). The OPLS model had a strong linear relationship, and the PEG content in wood of varying degrees of degradation could be determined. However, the accuracy of the model was low with a root mean square error of prediction of 11 wt%. The low accuracy was traced to the heterogeneity in the calibration and validation set samples with regard to the small probing volume of the confocal instrumental setup.

Effect of silane grafted h-BN fillers on microstructure and mechanical properties of CVI-based C/C-BN composites

2.5D carbon fiber (Cf)-reinforced carbon and boron nitride dual matrix composites (C/C-BN) were prepared by a combined process of C/C silanization, hexagonal boron nitride (h-BN) slurry impregnation, and chemical vapor infiltration (CVI). The surface morphology of Cf after each step of modification, the fracture surface and microstructure of the C/C-BN composites were systematically characterized by scanning electron microscopy. Through the hydrolysis of silane, a polysiloxane network was successfully formed inside the porous C/C composites, which provided more attachment sites for the subsequent grafting of h-BN filler and the deposition of pyrocarbon (PyC). The microstructure and mechanical properties of the C/C-BN composites containing three different of h-BN fillers content were studied in comparison with pure C/C composites. The TEM characterization of the h-BN filler/PyC interface confirmed that the different crystal planes of the h-BN grains affect the structure of the PyC deposited thereon. The results show that the uniformly distributed h-BN filler reduces the size, thermal shrinkage anisotropy, and texture of the PyC deposited around it, resulting in the disappearance of the interlayer cracks in the matrix and the enhancement of the cohesion of the composite. The tight physical bond at the interface is due to the radial compressive stress caused by the thermal mismatch between the fiber, matrix, and h-BN fillers. Therefore, as the h-BN fillers content increases, the flexural strengths, compressive strength of the C/C-BN composites increase, which are both greater than that of C/C composite, and the compression properties gradually tended to be isotropic. However, when the h-BN content in the C/C composite is excessive (such as the volume content of 15 vol%), the densification efficiency of the subsequent CVI is reduced. As a result, the compactness of the transition interface and mixed matrix composed of h-BN and PyC decreased, which led to the decrease of mechanical properties of the composites.

Efficiency of radiofrequency-vacuum (RF/V) technology for mixed-species drying of wood disks with inherent defects

Freshly cut 30-mm-thick wood disks of Scots pine, Caucasian elm, narrow-leafed ash, wild cherry, black walnut, and European alder with various natural grade defects were dried together in a radiofrequency-vacuum (RF/V) dryer. A mild four-step drying schedule at the maximum temperature of 45 °C and power density in the range of 1-2 kWm−3 with an “on-off” control of RF radiation at the final step was used. The moisture content of the disks at the end of drying ranged from 10.6% to 13.4%. An almost uniform radial moisture gradient developed in the dried disks. The six wood species, however, exhibited variations in checking. The RF/V drying schedule used here was able to completely inhibit near-bark radial checking in all disks but pine and elm, whereas it failed to efficiently prevent V-cracking in pine and ash with a high mean tangential to radial shrinkage anisotropy (ST/SR). A strong positive correlation was also found between ST/SR and the proportion of V-cracked disks. The occurrence of ring failure within the reaction wood-containing disks of walnut, pine, and elm was almost completely prevented by the drying schedule, but a significant correlation was observed between the pith eccentricity and V-crack length in the compression wood-containing disks of pine. All other natural defects, i.e., scar in cherry, bark pocket, double or triple pithing in walnut and elm, sound knots in pine, and roundness deviation, exhibited no statistically significant effect (p > 0.05) on check formation.

Influence of debinding holding time on mechanical properties of 3D-printed alumina ceramic cores

Herein, alumina green bodies are fabricated by three dimensional (3D) printing technology, then, the influence of debinding holding time under vacuum and argon on mechanical properties is systematically investigated by comparing the changes in microstructure, bulk density, open porosity, grain connection situation and flexural strength of ceramics. The flexural strength of alumina ceramics acquired the maximum values of 26.4 ± 0.7 MPa and 25.1 ± 0.5 MPa after debinding under vacuum and argon for 120 min and 180 min, respectively. However, the alumina ceramics rendered the flexural strength of 19.4 ± 0.6 MPa and 9.5 ± 0.4 MPa under vacuum and argon without extended holding time, respectively. The relatively low mechanical properties can be mainly attributed to the weak interlayer binding force, which is caused by layer-by-layer forming mode during 3D printing process and anisotropic shrinkage during the sintering process. Moreover, the alumina ceramics exhibited moderate bulk density and open porosity of 2.4 g/cm3 and 42% after the sintering process, respectively, which are mainly influenced by the microstructural evolution of alumina ceramics during thermal treatment. Also, the diffusion of gases is achieved by curing of photosensitive resin and influenced by different holding times during debinding, affecting the mechanical properties of sintered ceramics. The mechanical properties of as-sintered ceramics are suitable for the utilization of ceramic cores in the manufacturing of hollow blades.

Manipulating the redistribution of single dopant via crystal-site engineering approach in Ba4Gd3(K1-xNax)3(PO4)6F2:Eu2+ phosphors for warm white light emitting diodes

Manipulating the redistribution of single dopant among multiple crystallographic sites can optimize and design luminescence materials for single-doped warm white phosphor with high color rendering. However, successful cases are barely reported, because the substitution of all sites and the warm white emitting of multiemission bands cannot be guaranteed. Herein, we synthesized a series of Ba4Gd3(K1-xNax)3(PO4)6F2:Eu2+ (0 ≤ x ≤ 1.0) solid solutions via crystal-site engineering approach to manipulate the redistribution of Eu2+ dopant for tunable photoluminescence property. Na+ ions preferentially substitution in the A and B columns along the c-axis direction gives rise to the anisotropic lattice shrinkage. The multiemission bands of Ba4Gd3(K1-xNax)3(PO4)6F2:Eu2+ phosphors almost cover the whole visible light range because Eu2+ dopant can occupy the M(1), Gd(2) and A(3) sites. The Na-substitution results in a redistribution of Eu2+ dopants among different cation sites, and induces a continuous increase of the relative emission intensities at longer wavelength with increasing Na+ doping content. Moreover, the unique optical feature enables the single-phased Ba4Gd3Na3(PO4)6F2:Eu2+ phosphor converted WLED to exhibit quite high color rendering index (Ra = 90.2) and moderate correlated color temperature (CCT = 4125 K). The manipulating the redistribution of single dopant via crystal-site engineering approach reported here can not only carve out a new avenue for warm WLEDs, but also be applied to develop novel potential phosphors for practical optical application.

Analysis of drying stresses in green-glued plywood of Bete (Mansonia Altissima) specie

The wood veneer dried artificially before gluing for the manufacture of plywood generally suffers several damages (cracks, deformations), decreasing the competitiveness of the process and limiting the use of nervous species of wood. The proposed solution is to glue them at the green state. However, during the drying process, superficial and internal cracks are observed. These cracks appear when stresses due to the anisotropic shrinkage of the plywood exceed the mechanical strength of the wood material. In the present study, the response of a 3-ply plywood of Bete (Mansonia altissima) glued at the green state is simulated in order to evaluate these stresses and deformations during drying using a finite element method program. The numerical results and associated experimental data make it possible to better analyze and understand the mechanical behavior of the plywood during drying in order to look for reliable plywood through new process.