Axial Shrinkage Research Articles

Solution Doping of PMMA-Based Step-Index Polymer Optical Fibers by Rhodamine B Near Glass Transition Temperature of PMMA

Solution doping is a facile approach to fabricating photoactive polymer optical fibers (POFs). However, previous studies reveal that only the cladding of step-index POFs can be doped by the solution doping method in methanol or aqueous solutions, whereas the fiber core is hardly doped. To dope the fiber core as well as the cladding, this study attempts to dope PMMA-based step-index POFs by raising the doping temperatures to near the Tg of PMMA. The results show that a considerable amount of rhodamine B (RhB) is doped in the fiber core, though the amount is still much less than that in the cladding. The highest content in the fiber core is 0.479 mg/g, which is achieved by doping the POFs in water at 110 °C for 8 h. At the same condition, the RhB content of the cladding is 11.5 mg/g. It is found that the high-temperature doping process leads to dramatic axial shrinkage and radial expansion of the POFs, due to the relaxation of the fiber core. The wrinkled cladding after doping suggests that the macromolecule orientation of the core is much higher than that of the cladding, and high orientation should be the main reason why the core is much more difficult to dope than the cladding. Additionally, the doping process at 90 °C in water does not increase the fiber loss regardless of the tremendous POF structure change. In short, the core of PMMA-based step-index POFs can be doped at a temperature near the Tg of the PMMA, making the solution doping technique more practicable for POF doping.

Spatio-temporal autogenous shrinkage and cracking behavior of core concrete in full-scale CFST: Insights from the world's largest span arch bridge

A full-scale concrete-filled steel tube (CFST) examination was performed on the Tian'e Longtan Bridge, featuring a 600-meter span and 0.9-meter steel tube diameter, to assess internal autogenous shrinkage distribution. This study employed vibrating wire strain gauges and distributed optical fibers to measure the shrinkage and detect cracking in the core concrete. Analysis of the test results led to the formulation of models that describe the axial and radial shrinkage behavior over time and space. Increased optical fiber strain highlighted regions undergoing local plastic softening and cracking. This research facilitates the early prediction and precise identification of potential cracking areas in the core concrete through optical fiber monitoring.

Investigating the effect of axial fan shrinkage obtained by centrifugal casting technology on aerodynamic characteristics

Centrifugal casting technology was developed for the application of manufacturing axial fans. In the literature, these fans were usually manufactured by injection molding, mechanical processing or heat pressing. The main characteristic of this molding technology allows the creation of thick and hollow blades. This characteristic of the blades gives useful advantages of the fan that cannot be achieved by conventional methods. The centrifugal casting technology has been applied to fabricate axial fans in recent research. However, the issue of quality control and especially the shrinkage of the resulting fan compared to the molding has not yet been considered. Therefore, more in-depth studies and approaches are required. In this study, 3D scanning method is used to evaluate the shrinkage of the blades. The used 3D scanner is the Comet L3D 5M type based on structured light (blue LED) with a 5-megapixel sensor. This device achieves high accuracy and reliability (resolution 18 μm). The theoretical basis for determining fan shrinkage compared to CAD molds is based on the following main parameters: Chord line L (mm), relative thickness Emax (%), and stagger angle ( (degrees). In addition, the aerodynamic characteristics of the proposed fan are compared to those of a fan made of aluminum (blades are identical, but different in fabricating technology). Characteristics of this aluminum rigid-fan are assumed as reference. The results showed that the difference was not large between the blades. Besides, the results of aerodynamic testing on the test bench of the two fans are almost similar. This indicates the good adaptability of the axial fan received by the centrifugal casting technology.

Densification of visco-elastic powders during free and pressure-assisted sintering

This study presents an advanced computational model designed for the analysis of the densification process in visco-elastic powders during sintering. The model incorporates thermo-mechanical aspects into the discrete element method (DEM), and a thermo-rheological model to describe the rate of sintering when visco-elastic particles are in contact at variable temperatures. First, a novel contact model is developed and calibrated using experimental data obtained from dilatometric experiments on PA12 pellets. The calibration process involves measuring the linear (axial) shrinkage of the powder compact pellets with dilatometers and employs Bayesian filtering to identify the model parameters. The calibrated model accurately characterizes the linear shrinkage observed in the PA12 pellets. Subsequently, the study delves into the influence of various process parameters on the evolution of bulk density, commonly referred to as relative density. These investigations provide valuable insights into the impacts of maximum process temperature, holding time process duration, and external pressure, for which our model is capable of providing qualitative descriptions. The findings support the notion that longer process durations and the application of higher external pressure are the main drivers of densification, aligning with expectations in metallurgy techniques. This work offers a predictive DEM tool for computing the densification of pellets made of visco-elastic powders.

Study on process, microstructure and mechanical properties of 6061/AZ31 dissimilar metal joining with direct contact reaction brazing

In this study, 6061-Al and AZ31-Mg were successfully joined using the contact reaction brazing process without an interlayer under a pressure of 2 MPa and a vacuum of 1 Pa. The study examined the microstructure and mechanical properties of 6061/AZ31 joints, as well as the impact of process parameters including heating mode, cooling rate, heating temperature, and holding time on the joints. The results show that the 6061/AZ31 brazing seam can be divided into two zones: the liquid-phase solidification zone and the diffusion reaction zone. The liquid-phase solidification zone consists of the (α-Mg + Al12Mg17) eutectic organization and precipitation phases distributed therein. The diffusion reaction zone mainly consists of the Al3Mg2 layer in the brazing seam close to the 6061. Fractures in joints mainly occur in the diffusion reaction zone, where the hard and brittle Al3Mg2 layer is located and extends into the liquid-phase solidification zone. Brazing joint quality was better with a cooling rate of 5 °C/s and heating without pre-weld and post-weld holding processes. The highest joint shear strength of 37 MPa was achieved at 445 °C with a holding time of 5 s. The joint exhibited no obvious defects, and the axial shrinkage of the specimen was 0.414 mm, with minimal deformation.

Finite element modeling in heat and mass transfer of potato slice dehydration, nonisotropic shrinkage kinetics using arbitrary Lagrangian–Eulerian algorithm and artificial neural network

AbstractThe present study optimized the drying temperature (50–80°C) for potato slices based on color, texture, and visual observations. At an optimized temperature (60°C), a 2D axisymmetric finite element method (FEM) was developed in COMSOL Multiphysics to predict the heat and mass transfer (HMT) in a disk‐shaped potato slice. The nonisotropic shrinkage was predicted for the potato slice by the arbitrary Lagrangian–Eulerian approach. The experimental dehydration results revealed that axial shrinkage (27.44%) was 2.5 times higher than radial shrinkage (67.39%). The simulated outcomes based on FEM revealed the realistic visualization of spatial heat transfer, moisture migration, and nonisotropic slice deformation. The predicted moisture content, surface temperature, and shrinkage properties were in good agreement with the experimental results. The shrinkage behavior was further validated using artificial neural network (ANN) to simulate the slice shrinkage. Results showed that both the COMSOL and ANN approaches can precisely predict the shrinkage‐dependent HMT model. The ANN model outperformed the COMSOL determined by mean absolute error, mean square error (MSE), root MSE, and Chi‐square (χ2) values. The successful application of the presented approach for determining dehydration characteristics may have potential for quality assessment and management of different fruits and vegetables.Practical applicationsThis journal article explores the practical industrial applications of combining finite element method (FEM)‐based heat and mass transfer model and artificial neural networks (ANNs) to improve the efficiency and quality of food drying processes. FEM is employed to simulate and predict the realistic visualization of heat and mass transfer phenomena along with non‐isotropic shrinkage, while ANN serves as a data‐driven modeling tool for process control and prediction. The integration of these two technologies offers significant advantages in the food industry, including quantification of precise temperature and moisture content, as well as to monitor the drying process of various food products, reduced energy consumption, and time.

Effect of particle size distribution on the cryogenic mechanical properties of triple‐base propellants

AbstractFillers play a decisive role in the mechanical properties of polymer composites. In this paper, different particle sizes of nitroguanidine were obtained to regulate the internal filler structure of triple‐base propellants (TBP) to improve their mechanical response in different environments. A series of morphological and structural characterizations on nitroguanidine (NQ) particles were conducted using techniques. The results indicated that the obtained NQ particles maintained a high level of crystalline quality while preserving their molecular integrity. The mechanical properties of TBP were systematically evaluated under various loading conditions, including cryogenic tensile, compressive, and impact loads, as well as dynamic thermomechanical effects. Additionally, three‐point bending simulations were employed to elucidate the mechanical responses and damage mechanisms. Under axial tensile and compressive loads, reducing the particle size of NQ significantly enhanced the tensile and compressive strength. The maximum tensile strength and compressive strength can reach 344.62 MPa and 104.79 MPa. Moreover, the compressive failure mode transitioned from cracking to axial shrinkage. Conversely, when subjected to radial bending loads, TBP exhibited contrasting behavior, including a decrease in the glass transition temperature from 84.73°C to 76.93°C and a non‐monotonic trend in impact strength (initially increasing from 4.96 to 8.85 kJ/m2 and then decreasing to 2.27 kJ/m2). This study provides valuable insights into the mechanical performance of TBP, supporting the development of high‐energy, high‐strength TBP formulations.Highlights SEM analysis confirms the pronounced orientation effect of rod‐like NQ. The orientation and particle size of NQ decide TBP's radial impact resistance. Submicron NQ enhances the compression resistance property of TBP. Submicron NQ brings about a shift in the microscopic damage morphology of TBP.

Densification change due to effect of liquid phase sintering on 90 W–7Ni–3Fe alloy at different pressing loads

The current investigation explores how compaction under different loads affects the sintering performance of the 90 W-7Ni-3Fe alloy. Four different loads were used to compact Tungsten, Nickel, and Iron powder to make a cylindrical green pellet of 90 W-7Ni-3Fe alloy, namely 150 MPa, 250 MPa, 350 MPa, and 450 MPa. After compaction, the green pellets were sintered in liquid phase at a temperature of 1500 °C in a conventional furnace under a hydrogen gas environment to investigate their effect on densification and dimensional shrinkage of the sintered compact. It was found that the sintered density increased as the compaction load increased, resulting in enhanced densification. Due to the use of hydrogen gas in liquid state sintering, high densification was achieved by the compacts since it rapidly reduced the oxides and the porosity of the pellet. Compact pressed under a 450 MPa load and sintered attained 98.44 % density, which is nearly equal to the industrially prepared 90 W-7Ni-3Fe compact. The radial shrinkage of cylindrical compacts has been observed to be greater in relation to the axial shrinkage. As the compaction load increases, the shrinkage of the sintered pellet decreases.

Multiphysics Simulation and Experimental Investigation of the Densification of Metals by Spark Plasma Sintering

Multivariant experimental investigations and multiphysics microstructural modeling of the spark plasma sintering process of metallic powders have been performed up to a relative density of approximately 80%. In comparison, the effect of sintering temperature, pressure, and particle size on the interparticle contact area growth and axial shrinkage of cylindrical specimens of copper and nickel particles is measured in laboratory scaled tests. Herein, for the first time all relevant for sintering phenomena are considered simultaneously: the fully coupled thermo‐electro‐mechanical modeling of the spark plasma sintering processes, additionally taking into account for lattice, grain boundary, surface diffusion, electromigration, and thermomigration, has been carried out. The computational analysis of various physical phenomena allows to identify dominant and insignificant mechanisms. The two‐level numerical simulation includes the modeling of the sintering setup at the macroscopic level and the neck formation process in particle chain systems at the microscopic level. The results of the numerical simulations show a very good agreement with the experimental data. Therefore, the impact of electrical and mechanical loads as well as of particle size on microscopic distribution of temperature, inelastic strain, and on densification has been studied by the finite element simulations.

Failure Analysis of Casing in Shale Oil Wells under Multistage Fracturing Conditions

During the multistage fracturing in shale oil and gas wells with tieback and liner, one of the major challenges is the wellbore temperature variation due to the high-rate fracturing. In such a case, the axial shrinkage trend of the casing string could be caused due to the sudden drop in temperature, but the actual axial length of the casing string would not change due to the cement constraints. Therefore, this could lead to cementation damage between the casing and cement due to excessive load from the casing string. A wellbore seal that is out of control often leads to irreversible consequences, even well abandonment. In order to study the mechanism of casing deformation in shale oil and gas wells with tieback and liner quantitatively, in this paper, take LS1 well (a typical shale oil and gas well with tieback and liner, and casing deformation is caused) for example, the transient changes of temperature and pressure in the whole wellbore during multistage fracturing are studied. Moreover, the cementing strength test of the interface between casing and cement is also tested. Then, the testing results are carried out and extended to model the finite element (FE) model with the whole vertical section casing string with tieback and liner. The model is used to simulate the internal force changes under fracturing conditions with different stages of fracturing. Meanwhile, the casing deformation mechanism in LS1 well is analyzed and studied in detail. Our simulation results indicated the failure process and mechanism of cementation between casing and cement in shale oil and gas wells with tieback and liner. Our work can provide a detailed theoretical reference and a basis for field application.

Development of Clay-Composite Plasters Integrating Industrial Waste.

This research investigates the feasibility of developing clay composites using natural materials and incorporating waste by-products suitable for plastering diverse support structures. The study identified a versatile composition suitable for a wide range of support materials and explored the potential of revaluing industrial waste and by-products by reintegrating them into the Circular Economy. The experimental investigation outlines the process of evaluating the influence of different raw materials on the performance of the clay composite. The findings confirm that using limestone sludge and fly ash as additives to clay contributes to reducing axial shrinkage and increasing mechanical strengths, respectively. The optimal percentage of additives for the clay used are identified and provided. Using hydraulic lime as a partial substitute for clay reduces the apparent density of dried clay composites, axial shrinkage, and fissures formation while improving adhesion to the substrate. Introducing dextrin into this mix increases the apparent density of the hardened plaster while keeping axial shrinkage below the maximum threshold indicated by the literature. Mechanical strengths improved, and better compatibility in terms of adhesion to the support was achieved, with composition S3 presenting the best results and a smooth, fissure-free plastered surface after drying.

Towards low-temperature shrinkable synthetic fibers for internally self-prestressing concrete

Matrix cracking caused by temperature stress during the hydration heating/cooling phase of cement is one of the main causes of cracking of bulk concrete. In this study, low-cost, low-temperature shrinkable (LTS) fibers were developed, which can be stimulated to shrink by cement hydration heat in bulk concrete. The contraction stress of LTS fibers then transfers to the cement matrix through interfacial bonding, therefore, a uniform, three-dimensional self-prestressing executes on the bulk concrete matrix, to improve its cracking resistance. The modified polyester (MPET) with a low melting point was used to prepare LTS fibers with an activating temperature of about 60 °C, and their shrinkage behaviour can be activated in the temperature range caused by hydration heat in bulk concrete. The results confirmed that prestressing the cement matrix by activating LTS fibers’ axial shrinkage is an efficient approach for improving the mechanical properties of the cement matrix. This kind of fibers have demonstrated great potential in self-prestressing bulk concrete to improve its cracking resistance in engineering structures.

Effect of biochar and attapulgite amendment on saline soil hydraulic parameters and shrinkage

AbstractSaline soil reduces soil productivity and exacerbates food security problem. Therefore, it is increasingly necessary to find sustainable farming practices for soil and water conservation. In this regard, conditioning the soil with biochar (BC) or attapulgite (ATP) has been proved as a feasible method of improving water conservation and soil hydraulic characteristics. However, the interactive effect of BC and ATP on saline soil is still unclear. The objective of this study was to investigate the effect of BC and/or ATP on water retention, pore size distribution, hydraulic characteristic parameter, and shrinkage strain of saline soil through laboratory trials. For this purpose, BC and/or ATP were added to the loam soil at three levels of 0%, 2%, and 4% by weight, and saturated in the sodium chloride solution with a concentration of 5 g L−1. Results showed that the Van Genuchten model accurately fitted the obtained soil water characteristic curve (R2 > 0.99). BC and/or ATP amendments increased saline soil water retention capacity compared to the unamended soil. Soil water retention capacity increased as the ATP application rate increased. The saturated water content, field water holding capacity, soil microporosity, and soil retention effect of 2%BC combined with 4%ATP were higher than other treatments. BC facilitated the reduction of soil shrinkage, and ATP increased soil shrinkage. Axial shrinkage strain was negatively correlated with the application rate of BC, and positively correlated with ATP. 4%BC combined with 2%ATP had the least shrinkage strain. The present results could serve as a theoretical foundation for soil amendments to improve soil quality.

Wood quality of residual branches of Hymenaea courbaril L. from logging in the Amazon rainforest

Abstract Branches remain in the forest environment as logging activity residue. Considering the large size of many Amazonian trees, their branches have considerable dimensions and can contribute to a sustainable wood alternative for various applications. Due to the formation of reaction wood in the branches, relevant macro and ultrastructural changes can occur in its characteristics in relation to the trunk wood. However, the woods of the branches are not technologically well known. Therefore, this work aimed to evaluate the wood quality of branches of Hymenaea courbaril L., comparing it with wood of trunks. The extractives and lignin contents, basic density, shrinkage, fiber biometry, microfibril angle and mechanical resistance to compression parallel to the fibers were analyzed. The branch wood had smaller fiber dimensions and a higher microfibril angle than the trunk wood. The basic density was similar between these materials. The linear and volumetric shrinkages were smaller in the branch wood than in the trunk, while the axial shrinkage was higher in the branch. The parallel compressive strength was also lower in the branch wood than in the trunk. The branch wood has properties suitable for products with higher added value such as furniture, decorative objects, floors and utensils in general.

Study on Welding Deformation and Optimization of Fixture Scheme for Thin-Walled Flame Cylinder.

In this paper, the best fixture scheme for the TIG welding torch of nickel-base solid solution superalloy GH3536 in the welding process is explored. First of all, to meet the extremely high-dimensional accuracy requirements of the flame cylinder, a multifield coupling analysis model based on the flame cylinder is established on SYSWELD software. By studying the stress and deformation of welded parts under different line constraint positions and applied pressure, the trend of welding deformation is obtained, and the relevant mathematical model is established based on this. Finally, the particle swarm optimization (PSO) algorithm is used to calculate the best fixture scheme to make the welding stress and deformation better. The simulation results show that the welding deformation is negatively related to the line constraint distance and positively related to the applied pressure. According to the optimized clamping scheme of PS0, through simulation calculation, the average axial deformation is reduced by 82.5%, the maximum radial shrinkage deformation is reduced by 60.6%, and the maximum residual stress is reduced by 60.3%. Finally, it is verified by the flame barrel experiment that it meets the acceptance requirements and successfully solves the problem of serious axial shrinkage during the TIG welding of the outer ring of the flame barrel.

Parameter Optimization of PET Plastic Preform Bottles in Injection Molding Process Using Grey-Based Taguchi Method

The paper investigated the optimization design of plastic injection molding process parameters for preformed bottle production using the grey-Taguchi method to minimize shrinkage defects. Diametrical (radial) and length (axial) shrinkage were taken as the responses for one-liter PET plastic preform bottle to perform optimization by controlling four injection molding process parameters. The obtained optimum parameter combination was 260°C melting temperature, 70°C molding temperature, 120 MPa holding pressure, and 15 s cooling time. Melting temperature was the most significant factor according to the ANOVA in PET plastic preform of bottle production. The experimental validation test was also performed using the optimal level settings, five samples of preforms were taken, and the result showed that the shrinkage of the preform was reduced by 22.55%. The average grey relational grade, 0.853, of the confirmation results was found between the confidence intervals of 0.581 and 1.125 for the 95% confidence level. Therefore, the confirmation test showed a good agreement between the predicted and experimental values.

Cure-induced stress build-up in adhesives: model building and parameter studies

ABSTRACT Prediction of stresses in adhesively bonded joints requires high effort in determination of relevant material properties, which change during cure. In addition, the computational effort using complex viscoelastic finite element (FE) models impends efficient prediction of stress build-up. Rotational and oscillatory rheometry can help to reduce the experimental effort by measuring of modulus of elasticity (MoE) and axial shrinkage along curing. In this publication, shrinkage, development of MoE and Poisson’s ratio of a curing adhesive were numerically modelled between two parallel rheometer plates in order to calculate cure-induced stresses using finite element analysis (FEA). To identify effects of different material properties on stress distribution, a parameter study was carried out and the reciprocal influence of the varied parameters was investigated. Consequently, resulting stresses within the adhesive layer and occurring deformations were investigated with respect to curing time as well as their location. The results showed that final shrinkage and MoE need to be considered not only in final values but also in terms of course of shrinkage and reaction. Stress build-up led to deformation of the rheometer plates, which has to be considered when using rheometry for determination of cure shrinkage.

Detailed modeling of hydrogen release and particle shrinkage during pyrolysis of inhomogeneous wood

Hydrogen release during pyrolysis of woody biomass is studied considering anisotropicity and inhomogeneity of wood structure. A new anisotropic shrinkage model is proposed based on the decomposition of main wood constituents, i.e., cellulose, hemicellulose, and lignin. The new shrinkage model can predict the temporal evolution of the wood structure, and the differences between axial and radial shrinkage during pyrolysis. The model agrees very well with several experimental data from the literature. Based on particle temperature during conversion, the pyrolysis is partitioned into four stages, and the hydrogen release and H2 formation from each stage are investigated. Stage (IV) of pyrolysis, from 1000 to 1273 K, is found to be efficient for H2 production owing to the production of considerable mass of H2 with a minimal amount of tar species. Furthermore, the char quality is found to be different at the end of stages (II), (III), and (IV), where around 67.7, 80.5, and 93.4% wt. of solid residue is made of carbon, respectively. The model is also used to explain how the heating rate affects the temperature distribution inside the particle and how it shifts the peak of hydrogen release. Finally, the pyrolysis of two inhomogeneous wood samples — a beech twig with bark and a beech dowel with growth rings — are investigated. The bark can affect the pyrolysis rate, products, and flow pattern inside the particle. The growth rings do not have a considerable effect on the pyrolysis rate and products, but they have a significant impact on the flow pattern. This has an important implication for char conversion studies where the internal surface area and porosity field distribution have a significant effect on the gasification and oxidation rates.

Mechanical Behavior and Optimization of Tubing String with Expansion Joint during Fracturing in HTUHP Wells

During the formation testing in high-temperature (HT) and ultra-high-pressure (UHP) wells, one of the major challenges is packer failure in the downhole caused by high-rate fracturing. In such a case, the axial shrinkage trend of the tubing string could be caused by the sudden drop in temperature, but the actual axial length of the tubing string would not change because of the constraints at wellhead and packer. Therefore, this could lead to the upward pull-out of the packer that is due to excessive load from the tubing string. This out-of-control downhole pressure often leads to irreversible consequences, even well abandonment. An expansion joint, as a movable splicer, has the characteristic of mitigating packer load, which can theoretically enhance packer safety. To study the protective effect of an expansion joint on the packer quantitatively, the microscopic characteristics and macroscopic properties of the tubing material (13Cr110) are obtained through experimental tests. Moreover, the mechanical properties of the material at different temperatures are also tested. Then, the testing results are extended to modeling the finite element model (FEM) of the whole section of tubing string with the expansion joint—casing and simulating its internal force changes under fracturing conditions with different injection rates. Our simulation results indicated that an expansion joint can significantly change the distribution of the internal forces in the tubing string, and this change can effectively reduce the load on the packer. Eventually, a tubing string buckling identification plate that considers the injection rate and expansion joint–packer length is obtained to optimize the placement of an expansion joint in the tubing string. Our work can provide a detailed theoretical reference and basis for an expansion joint in field application.

Prediction of mechanical characteristics of friction welded dissimilar EN 10028P 355 GH steel and AISI 430 steel joint by fuzzy logic analysis

A solid state friction welding is one of the metal fastening processes is to produce defect free joints when compared to fusion welding techniques. The material EN 10028P 355 GH Steel and AISI 430 Steel find extensive applications in heat exchanger tubes, pressure vessels, and pump shafts. In the present study, the artificial intelligence tool fuzzy logic analysis was utilized for earlier prediction of mechanical characteristics like tensile strength, impact toughness and axial shrinkage of friction welded dissimilar joint. The necessary parameters considered in this process are rotational speed, forging pressure, friction pressure, friction time, and forging time. The L27 based experimental plan is used to execute the experiment. The Mamdani model and triangular membership function methods are adopted in the fuzzy logic analysis. The developed 3D surface model helps to analyze the variation of the parameter to attain the desired properties. The forecasted values from the fuzzy model are compared with experimental values and found that the fuzzy model is good as it yields a minimum percentage of error.