Macroscopic Shrinkage Research Articles

Moisture-Related Shrinkage Behavior of Wood at Macroscale and Cellular Level.

Due to wood moisture sensitivity, shrinkage cracks tend to present wooden structures. These failures are caused by moisture-related shrinkage behavior. In order to avoid it, it is necessary to have a better understanding of shrinkage behavior. In this respect, studying the dimension changes in wood at different scales is of utmost significance for a better understanding of the shrinkage properties. Herein, the shrinkage behavior of Masson pines (Pinus massoniana) wood was investigated at macroscopic and cellular levels during moisture loss via digital image correlation using VIC-3D and digital microscopic systems, respectively. According to the full-field strain maps, shrinkage strain near the external face was higher than that at the internal face, which increased susceptibility to cracking at the external face of lumber. Additionally, the anisotropic shrinkage of wood was explored. The shrinkage ratio at the end of drying was about 5.5% in the tangential (T) direction and 3.5% in the radial (R) direction. However, at a cellular level, the shrinkage ratios in the T and R directions of earlywood tracheids were 7.13% and 2.46%, whereas the corresponding values for latewood tracheid were 9.27% and 5.52%, respectively. Furthermore, the maximum T/R shrinkage ratio at the macroscopic level (1.7) was found to be similar to the value of latewood tracheid (1.72). The earlywood showed high anisotropic, its T/R shrinkage ratio was 2.75. The macroscopic shrinkage was the result of the interaction of the tracheids of earlywood and latewood and was mainly dominated by latewood tracheids.

Multiscale numerical and experimental analysis of cooling-induced thermal shrinkage behaviors and residual stresses in 2.5D woven fiber/aluminum matrix composites

The cooling-induced thermal shrinkage behavior and residual stress in fabrication of 2.5D woven fiber reinforced Al composites were investigated by numerical and experimental approach. A microscale finite element (FE) model was established to determine the transversely isotropic thermal shrinkage of the Al-impregnated yarns. The validated properties were subsequently input into a mesoscale FE model for the composites, in which the temperature-dependent properties of the constituent materials were incorporated. Parallel experiments were carried out to verify the thermal shrinkage behaviors and the residual stresses that were predicted by the FE simulations. The residual stress distribution of the matrix pocket, warp and weft yarns were studied, and their contributions to the local damage of matrix pocket and interface were analyzed. Based on the verified model, the effect of fabric structure on the residual stresses and macroscopic shrinkage properties were parametrically evaluated. The results make a contribution to evaluating the cooling-induced residual stress, local damage, and shrinkage behavior of metal matrix composites reinforced with complex fabric.

Sulfur segregation and inclusion modification in steel using magnesium addition

In order to investigate the effect of magnesium treatment on the distribution and segregation of sulfides in carbon high-sulfur free-cutting steel in industrial tests, scanning electron microscope, energy dispersive spectrometer, electrolysis device, and other characterization methods are used to examine the sulfide morphology in the steel continuous casting billet. The sulfide type, spatial distribution and three-dimensional morphology of the slab in the casting slab are analyzed, and the law of sulfur segregation is calculated and summarized using the diffusion growth model. The results of the study showed that the area of cluster-like sulfides before and after magnesium modification decreased by 6.4%, the area of chain-like sulfides reduced by 6.6%, and the area of single-type sulfides increased by 12.7%. In the magnesium modified steel, a fine composite sulfide with MgO·Al2O3 as the core is formed, which provides a heterogeneous nucleation site for the later precipitated MnS, enhancing the shape and size of the sulfide. The sulfide segregation index was reduced from 1.30 to 1.04 before and after magnesium modification, and the sulfur concentration was 1.56 times the original precipitation when the middle position of the slab was entirely cemented. The macroscopic shrinkage cavity on the surface of the cast slab is minimized after magnesium treatment, which enhances sulfide dispersion and segregation dramatically.

Evolution of directionally freeze-cast Fe2O3 and Fe2O3+NiO green bodies during reduction and sintering to create lamellar Fe and Fe-20Ni foams

Directional freeze-casting (FC) of powder suspensions followed by freeze-drying and sintering is a versatile and scalable processing route for creating metallic foams with highly elongated pores. Because of the high propensity for oxidation of metal powders, the use of precursor oxide powders is studied here with an additional step of H2-reduction of oxides to metal before sintering. However, the large volume shrinkage due to oxide reduction causes foam deformations, making it difficult to optimize the FC parameters to obtain a particular foam structure. We use quasi in situ X-ray microtomography to analyze the three-dimensional structural evolution of directionally freeze-cast, lamellar Fe2O3 and Fe2O3+NiO green bodies as they are reduced by H2 at 725 °C to Fe and Fe-20Ni (at%), respectively, and sintered at 900 °C. These temperature and gas conditions result in sequential reduction and sintering steps that can be individually analyzed. Foam porosity, pore width, lamellae thickness, and macroscopic shrinkage are quantified by image analysis. Oxide green body structures match typical FC relationships: porosity increases with decreasing powder content in the FC suspension, and the lamellae spacing period, or FC wavelength, decreases with increasing freezing velocity. Upon H2-reduction, lamellae in Fe foams buckle due to mismatch stresses from spatially-inhomogeneous reduction rates, leading to anisotropic deformation. Buckling is absent in Fe-20Ni foams due to the faster reduction kinetics of Ni/NiO that lead to more spatially uniform reduction. Reduction is responsible for 73–86% of the total volumetric shrinkage, with sintering causing the remaining shrinkage, which is nearly isotropic for all foams. The observed relationships between FC parameters, green body and metal foam structure can help guide the design and optimization of metal foams for specific technological applications.

On factors defining the mechanical behavior of nanoporous gold

Nanoporous gold (NPG) made by dealloying takes the form of a network of nanoscale struts or “ligaments”. It is well established that the material’s mechanical behavior is strongly affected by its ligament size, L and by its solid volume fraction, φ. We explore the mechanical behavior of NPG, with an emphasis on establishing a consistent data set with comparable L but covering a significant range of initial φ. Specimens are prepared from Ag-Au master alloys with their Au atom fraction, xAu0 in the range 0.20–0.35. Since dealloying replaces Ag with voids, φ may be expected to agree with xAu0. Yet, spontaneous plastic deformation events during dealloying can result in macroscopic shrinkage, decoupling φ from xAu0. This raises the question, how do φ and xAu0 separately affect the mechanical behavior? We confirm two recent suggestions, namely i) a modified Roberts-Garboczi-type scaling law for Young’s modulus versus φ of the material in its as-prepared state and ii) the relevance of an apparent “load-bearing solid fraction” for Young’s modulus as well as strength. Yet, remarkably, we find that stiffness and strength of the as-prepared material show a much better correlation to xAu0 as compared to φ. This can be understood as a consequence of the microstructural changes induced by shrinkage. Studying the microstructure evolution during annealing, we also confirm the suggestion that coarsening entails an enhanced loss in stiffness for samples with lesser solid fraction. This finding confirms concerns about the notion of self-similar coarsening as a general behavior of dealloying-made network materials.

A Comparative Histological Study to the Effect of Adipose Derived Mesenchymal Stem Cells Versus Virgin Coconut Oil in Skin Wound Healing of Adult Male Albino Rat

Background: Skin wounds comprise a clinical load for many patients. Owing to their availability and ability for differentiation, adipose-derived stem cells (ADSCs) are considered a promising line in the tissue regenerative medicine. Virgin coconut oil (VCO) has been also reported to help in wound healing by decreasing time of complete re-epithelization. However, there was lack in literature about histological details.Aim: The study aimed to compare the effect of ADSCs versus natural VCO in wound healing. Material and methods: Thirty rats were used in three experimental groups, ten rats in each. All animals were exposed to excisional skin wound injury. Group I was used as control untreated group. Group II was injected intra-dermally with 1x106 ADSCs in four injection sites around the wound, while group III was treated with topical application of 0.5 gm VCO ointment. After 2 weeks, all rats were sacrificed. Macroscopic shrinkage of wounds was recorded and compared. Skin samples were harvested and processed for light microscopic examination. Morphometric measurements were done for both epidermal thickness & collagen fibers area percentage. Data was analyzed statistically.Results: Histological examination of group II revealed regenerated epidermis and dermal skin appendages. Masson s trichrome stained sections revealed thick collagen bundles running in different directions. In Group III, epidermis was thin with few developing dermal skin appendages. Masson s trichrome stained sections showed dense parallel bundles of collagen fibers.Conclusion: Virgin coconut oil enhanced skin wound healing. However, ADSCs proved to be more efficient in regaining mature skin structure.

Effects of conditions in hot-melt coating process on microphase-separated structures and macroscopic deformation in coated layers composed of di- and triblock copolymer blends

Effects of the coating rate, the cooling temperature and the discharge rate in the hot-melt coating process on the microphase-separated structure and the macroscopic deformation have been revealed using blend specimens of MA/MAM where MA and MAM are a poly(methylmethacrylate)-block-poly(n-butylacrylate) diblock copolymer and a poly(methylmethacrylate)-block-poly(n-butylacrylate)-block-poly(methylmethacrylate) triblock copolymer, respectively. It was found that the hot-melt coated specimen had the anisotropic distribution of the spheres where the d spacing of the nanostructure in the machine direction (MD) is longer than that in the transverse direction (TD) and had a lower ordering regularity of the spherical microdomains in the MD due to shear and elongational deformation. The change of the macroscopic size upon the release of the coated layer from the substrate also confirmed the elongation of the soft-segment (poly (n-butylacrylate)) chains in the MD during the hot-melt coating by exhibiting the macroscopic shrinkage in the MD upon the release. However, the extent of the microscopic elongation (d spacing) was lower than the macroscopic elongation in the MD. This implies that the soft-segment chains are relaxed due to pulling-out of the poly (methylmethacrylate) chains from the hard spherical microdomains. As for the effects of the coating rate, the extent of the chain stretching of the soft segment was increased with the coating rate when the discharge rate (the flux of materials provided onto the substrate through the die lip) was kept constant. However, no effects were confirmed when the discharge rate was so controlled to maintain the thickness of the as-coated layer constant. Thus, the effects of the coating rate and the discharge rate were compensated, and the effects on the chain stretching of the soft segment can be recognized simply in terms of the thickness of the as-coated layer. As for the effects of the cooling-roll temperature, it was found that the extent of the chain stretching of the soft segment was decreased with an increase in the cooling-roll temperature.

Intraperitoneal Administration of Paclitaxel Combined with S-1 Plus Oxaliplatin as Induction Therapy for Patients with Advanced Gastric Cancer with Peritoneal Metastases

BackgroundIntraperitoneal (IP) administration of paclitaxel (PTX) has a great pharmacokinetic advantage to control peritoneal lesions and can be combined with various systemic chemotherapies. In this study, we evaluate the efficacy and tolerability of a combination of IP-PTX and systemic S-1/oxaliplatin (SOX) for induction chemotherapy for patients with peritoneal metastases (PM) from gastric cancer (GC).Patients and MethodsPatients with GC who were diagnosed as macroscopic PM (P1) or positive peritoneal cytology (CY1) by staging laparoscopy between 2016 and 2019 were enrolled. PTX was IP administered at 40 mg/m2 on days 1 and 8. Oxaliplatin was IV administered at 100 mg/m2 on day 1, and S-1 was administered at 80 mg/m2/day for 14 consecutive days, repeated every 21 days. Survival time and toxicities were retrospectively explored.ResultsForty-four patients received SOX + IP-PTX with a median (range) of 16 (1–48) courses, although oxaliplatin was suspended due to the hematotoxicity or intolerable peripheral neuropathy in many patients. The 1-year overall survival (OS) rate was 79.5% (95% CI 64.4–88.8%) with median survival time of 25.8 months. Gastrectomy was performed in 20 (45%) patients who showed macroscopic shrinkage of PM with a 1-year OS rate of 100% (95% CI 69.5–100%). Grade 2 and 3 histological responses was achieved in four (20%) and one (5%) patients. Grade 3/4 toxicities included neutropenia (11%), leukopenia (39%), and anemia (14%). There were no treatment-related deaths.ConclusionsCombination chemotherapy using SOX + IP-PTX regimen is highly effective and recommended as induction chemotherapy for patients with PM from GC.

Assessing the reliability of dual-energy X-ray absorptiometry analyses in burned bones

ABSTRACT Although being a standard technique for bone mineral density (BMD) measurements and its study and application to defleshed bones started in the past decade, dual-energy X-ray absorptiometry (DXA) has not been applied to burned bones. However, DXA analyses on burned bones can foreseeably increase our knowledge regarding the changes that occur on bone microstructure. Femora, patellae and first metatarsals were selected from ten skeletons from the 21st century identified skeletal collection to access the impact of heat exposure on bone through DXA analyses. The potential of the crystallinity index (CI) as a proxy for DXA was also investigated. As expected, BMD augmented along with temperature increment, which can be explained by the recrystallization process leading to an increase in crystallinity and macroscopic shrinkage of bone. A similar behaviour was found for the CI. However, the latter does not seem to be a good proxy of DXA. Still, DXA shows good potential for the study of the inorganic part of bone when submitted to high temperatures and further studies with larger samples seems promising to add further data to this preliminary investigation.

Modelling macroscopic shrinkage of hardened cement paste considering C-S-H densification

Shrinkage of hardened cement paste is a direct result of its desorption isotherm. The relationship between the desorption isotherm and the relative humidity in a hydrating cement paste is mainly controlled by the pore size distribution (nanopores to micropores). There are several hydration models to describe the microstructure of cement paste, but the desorption isotherm and self-desiccation are not direct outputs from those models as they are usually given as constitutive inputs. In this study an attempt was made to fill this gap by predicting the sorption isotherm, the drying shrinkage and the self-desiccation of cement paste directly from the evolution of its microstructure. A simple hydration model was developed to predict the microstructure of Portland cement pastes, as well as the nanostructure of calcium silicate hydrate (C-S-H), considering its densification during cement hydration. Predictions from the model were compared with some recent experimental findings from studies in the literature where the influence of the water-to-cement ratio was evaluated. The main contribution of this work is the integration of nanoscale and microscale material models towards determining the macroscopic properties of cement paste.

Chemo-poro-elastoplastic modelling of an oilwell cement paste: Macroscopic shrinkage and stress-strain behaviour

Analysing the response of cement sheath in oil, gas or geothermal wells submitted to mechanical loadings needs an appropriate constitutive law for the cement paste in wells conditions. The knowledge of the actual initial state of stress is a key point which requires a simulation of cement paste behaviour from placement to hardened state. A chemo-poro-elastoplastic model for macroscopic shrinkage and stress-strain behaviour of cement paste at the early age is developed in this paper. A modified Cam-Clay type yield surface and an associate plastic flow rule are used. The hydration is considered as a hardening mechanism of the yield surface, which also evolves with the development of plastic strains. The model shows a good capacity in capturing the basic mechanisms of both macroscopic shrinkage and stress-strain behaviour of an oilwell class G cement paste hydrated under various conditions of temperature and pressure. A strong coupling is found between the macroscopic shrinkage and the stress-strain response.

Effects of ultrafine WC on the densification behavior and microstructural evolution of coarse-grained WC-5Co cemented carbides

The effect of ultrafine WC on the macroscopic shrinkage behavior and microstructural evolution of coarse-grained WC-Co cemented carbides during sintering was studied. WC-Co composite powders containing mixture of ultrafine (300 nm) and coarse (6.0 μm) WC powders were prepared using a novel sol-gel process. The results indicate that ultrafine WC addition enhanced shrinkage in the composite powder compacts during solid state sintering, while its influence on densification process in liquid-phase sintering can be ignored. The microstructural evolution confirmed that ultrafine WC addition promote the spreading of cobalt binder and the formation of WC-Co agglomerate in initial state of sintering. And, ultrafine WC addition resulted in a more uniform densification in the solid state sintering. Mechanisms of the enhanced shrinkage include the accelerated spreading of Co due to shortened diffusion distances and the increased surface diffusion velocity, and the activated sintering of WC skeleton due to grain boundary sliding.

Photodynamically Active Electrospun Fibers for Antibiotic-Free Infection Control.

Antimicrobial biomaterials are critical to aid in the regeneration of oral soft tissue and prevent or treat localized bacterial infections. With the rising trend in antibiotic resistance, there is a pressing clinical need for new antimicrobial chemistries and biomaterial design approaches enabling on-demand activation of antibiotic-free antimicrobial functionality following an infection that are environment-friendly, flexible and commercially viable. This study explores the feasibility of integrating a bioresorbable electrospun polymer scaffold with localized antimicrobial photodynamic therapy (aPDT) capability. To enable aPDT, we encapsulated a photosensitizer (PS) in polyester fibers in the PS inert state, so that the antibacterial function would be activated on-demand via a visible light source. Fibrous scaffolds were successfully electrospun from FDA-approved polyesters, either poly(ε-caprolactone (PCL) or poly[(rac-lactide)-co-glycolide] (PLGA), with encapsulated PS (either methylene blue (MB) or erythrosin B (ER)). These were prepared and characterized with regards to their loading efficiency (UV-vis spectroscopy), microarchitecture (SEM, porometry, and BET (Brunauer-Emmett-Teller) analysis), tensile properties, hydrolytic behavior (contact angle, dye release capability, degradability), and aPDT effect. The electrospun fibers achieved an ∼100 wt % loading efficiency of PS, which significantly increased their tensile modulus and reduced their average fiber diameter and pore size with respect to PS-free controls. In vitro, PS release varied between a burst release profile to limited release within 100 h, depending on the selected scaffold formulation, while PLGA scaffolds displayed significant macroscopic shrinkage and fiber merging, following incubation in phosphate buffered saline solution. Exposure of PS-encapsulated PCL fibers to visible light successfully led to at least a 1 log reduction in Escherichia coli viability after 60 min of light exposure, whereas PS-free electrospun controls did not inactive microbes. This study successfully demonstrates the significant potential of PS-encapsulated electrospun fibers as photodynamically active biomaterial for antibiotic-free infection control.

Numerical crack growth study on porosity afflicted cast steel specimens

This paper deals with the fatigue assessment of cast steel defects in terms of macroscopic shrinkage porosity. Within preliminary studies, a generalized Kitagawa diagram GKD was established by numerical analyses of V-notched specimens with varying opening angles. It was experimentally verified by the application of the notch stress intensity factor (NSIF) concept on fatigue tests under rotating bending and axial loading. This paper continuous the work by an application of the GKD to real cast steel pores. At first, casting simulations are performed to design representative cast specimen geometries. The study focusses on macroscopic shrinkage pores with different spatial shapes. At second, fatigue tests under axial loading are conducted. Subsequent fracture surface analysis by light optical and scanning electron microscopy provides fracture mechanical based geometry parameters. Finally, the results of the experiments related to the failure relevant defect sizes are assessed by the GKD. In order to define an equivalent defect size of the complexly shaped defects, numerical crack growth analyses are performed demonstrating crack coalescence path tendencies. Summing up, the application of the NSIF approach based on a GKD shows a sound accordance to the experimental results and thus provides an engineering-feasible fatigue assessment method of cast steel components with macroscopic imperfections.

Experimental investigation of the early-age mechanical behaviour of oil-well cement paste

The knowledge of the behaviour of oil-well cement paste from the early age to the hardened state is important in predicting the performances of the cement sheath in oil/gas wells, specially for prediction of the risk of micro-annulus creation between the cement sheath and the rock formation or the casing. Characterization of the early-age mechanical behaviour is of particular importance, because during the well construction, the cement sheath is submitted to various mechanical loadings when the cement paste is not completely hydrated, as for example during a casing test. In this paper, the early-age mechanical behaviour of a class G cement paste is studied experimentally. A specially designed experimental device is used to investigate the mechanical behaviour of cement paste from the first hour of hydration, under stress states close to in-situ conditions. The macroscopic shrinkage of the cement paste as well as its stress-strain response under oedometric loading are studied for various pressures during hydration, from 0.3 to 45 MPa, and for hydration temperatures from 7 to 30 °C. These relatively low temperatures are used to slow down the hydration rate. The experimental results show that the macroscopic shrinkage increases significantly with the pressure during hydration. When submitted to a mechanical loading cycles at a given age, the cement paste hydrated under lower pressures, corresponding to shallower depth, exhibits higher deformability, showing a higher risk of creation of a micro-annulus during the mechanical loadings, as for example during a casing test. The experimental results clearly show the influence of the loading history on the mechanical behaviour of the cement paste at a given age. The oedometric experiments are associated with UCA (Ultrasonic Cement Analyser) and isothermal calorimetry experiments for a deeper insight into the behaviour of early age cement paste.

Sintering mechanics of ceramics: a short review

Abstract The strength and reliability of ceramics is determined by the microstructure and small defects, such as voids and cracks, which are often formed during sintering. The continuum mechanics of sintering is a powerful method to analyze the internal stress developing during the constrained sintering and the formation of these defects. However, challenges remain in understanding microscopic physical mechanisms involved in sintering of powder compacts, the microstructure of which are heterogeneous and anisotropic, generally. Here, we report how the macroscopic sintering stress tensor and the viscosity tensor are determined by microscopic forces acting between particles. The reported theoretical approach will benefit the fundamental understanding of the underlying physics and provide insight on the relationship between the macroscopic shrinkage and the microscopic particle packing structures produced by powder processing.

In situ observation of plaster microstructure evolution during thermal loading

SUMMARYGypsum microstructural evolution at elevated temperatures has been characterized in situ by environmental scanning electron microscopy and high‐temperature X‐ray tomography. As temperature increases, the observed changes in gypsum crystal morphology are related to the consequences of water loss that leads to crystal reorganization in order to minimize the specific surface. The influence of environmental scanning electron microscopy experimental conditions on the mechanisms observed is also discussed. High‐temperature X‐ray tomography gives quantitative information on porosity evolution with thermal loading. The results obtained are successfully correlated with macroscopic shrinkage measurements performed during dilatometry tests. Copyright © 2016 John Wiley & Sons, Ltd.

Multiscale modeling of drying shrinkage and creep of concrete

Creep and shrinkage are complicated time-dependent processes taking place in cementitious materials. In typical concretes, the most significant part of shrinkage is represented by drying shrinkage. Experimental data indicate that the ultimate value of drying shrinkage measured on concrete and mortar specimens is a nonlinear function of the ambient relative humidity. The nonlinear behavior is partially caused by microcracking, and partially by creep of C-S-H gel. On the other hand, drying shrinkage of hardened cement paste, measured on very thin specimens at a gradually decreasing relative humidity, was found to be a linear function of relative humidity. The aim of this paper is to explore whether the nonlinearities observed for macroscopic shrinkage can be explained by finite element simulations at lower levels, starting from the description of the drying cement paste by a viscoelastic model based on the Microprestress-Solidification Theory (MPS) with tensile cracking and with a constant shrinkage ratio.

Mesoscale Modeling of Nonlinear Influence of Ambient Relative Humidity on Drying Shrinkage of Concrete

Creep and shrinkage are complicated time-dependent processes taking place in cementitious materials. In typical concretes, the most significant part of shrinkage is represented by drying shrinkage; it is caused by a decrease in relative humidity of pores which leads to an increase in capillary tension of pore water and in the solid surface tension at pore walls.Experimental data indicate that the ultimate value of drying shrinkage measured on concrete and mortar specimens is a nonlinear function of the ambient relative humidity. The nonlinear behavior is partially caused by microcracking, and partially by creep of the cement matrix. On the other hand, drying shrinkage of hardened cement paste, measured on very thin specimens at gradually decreasing relative humidity, is found to be a linear function of relative humidity.The aim of this paper is to assess the nature of the macroscopic shrinkage computed employing finite element simulations at the meso-scale level in which the drying cement paste is described by a viscoelastic model with tensile cracking and with a constant shrinkage coefficient.

粉体成形プロセスにおける微視的な粒子充填構造と焼結における巨視的な収縮との関連の3次元トモグラフィーによる解明

粉体成形プロセスにおける微視的な粒子充填構造と焼結における巨視的な収縮との関連の3次元トモグラフィーによる解明