Non-uniform Shrinkage Research Articles

Non-Uniform Drying Shrinkage in Robocasted Green Body Ceramic Products

The formation of defects, due to drying, in robocasted ceramic objects is an important issue arising from non-uniform shrinkage of the material during this step in the process. Common methods for shrinkage measurement are not well suited to the small size of robocasted cords or the complexity of robocasted objects. Innovative methods for shrinkage measurement were developed using non-destructive optical vision techniques with computer-controlled data acquisition, allowing measurement on millimetric cords and on specific zones of a product. The study of a single porcelain cord revealed an anisometric shrinkage related to the orientation of grains during extrusion. A differential shrinkage at the macroscopic scale was also measured on a robocasted object, indicating a moisture content gradient in the material. The methods presented in this paper are of particular relevance to real-time control of the drying process for robocasted objects.

The determination of the curing induced, nonlinear elastic field of an inclusion in photo-cured materials

A wide variety of photo-cured materials have recently been developed with the rapid advancement of three-dimensional (3D) printing technology. However, most of these materials are designed as soft functional materials, and their failure mechanisms have received little attention. This work studies the mesoscale residual stress defects of photo-cured materials that are generated due to non-uniform curing and volume shrinkage during the manufacturing process. The defects are simplified as uncured inclusions embedded within a fully cured, infinite matrix which are then additionally cured. A large deformation model, validated against finite element analysis, is established to determine the nonlinear elastic field induced by the curing of inclusions with different Poisson’s ratio and shape (i.e., sphere and prolate spheroid), and is shown to outperform the infinitesimal strain model. This large deformation model, which includes a phase evolution constitutive model to describe the inclusion’s behavior and a compressible neo-Hookean model to describe the matrix’s behavior, is derived based on the same elastic field distribution as that in the infinitesimal strain solution and an ellipsoid-ellipsoid transformation kinematics assumption. The final solution is expressed in a discrete formulation and is exact for the spherical inclusion and approximate for the prolate spheroid inclusion. The prediction results of the theoretical model are compared with the finite element analysis, and reasonable agreement is obtained. This study may lay a foundation for investigating the effects of mesoscale residual stress defects on the mechanical behavior of 3D printing materials.

Preparation and mechanical properties of Cf/SiC composites via pressure-assisted gel impregnation and PIP

Non-uniform shrinkage of SiC precursors will lead to cracking and thus weaken the mechanical properties of the Cf/SiC composites. This study used the pressure-assisted gel impregnation method to introduce SiC particles (SiCp) into the carbon fiber preform and combined the PIP technique to fabricate Cf/SiC composites. The mechanism of enhancing the mechanical properties of composites was studied. Results showed that SiCp effectively eliminated matrix cracking, and the PyC interface layer inhibited interfacial crack propagation. The combined effect of the two resulted in a significant improvement in the mechanical properties of the composites. Specifically, the maximum flexural strength of the Cf/SiC composites was 360.63±26.02 MPa, and the maximum fracture toughness was 8.57±1.82 MPa·m1/2.

Study on the fracture behavior in clayey geomaterials under moisture diffusion by phase field modeling

Clayey geomaterials are prone to cracking under changing moisture conditions, which substantially compromises their engineering properties. When moisture intrusion and boundary constraints act in tandem on geomaterials, the relevance of multi-physics field processes to complex cracking phenomena remains underexplored. To provide deeper insight into the effect of moisture transport on the cracking behavior of clayey geomaterials, a theoretical model for moisture-induced fracture is proposed. The model combines moisture diffusion, volume deformation dependent on moisture conditions, and phase field fracture, and is solved using the finite element method with a user-defined element subroutine. The developed subroutine is applied to simulate soil desiccation experiments and mudstone water absorption tests. The results reveal that moisture gradients induce non-uniform expansion or shrinkage within the clayey geomaterials. The neighboring geomaterial particles mutually constrain these deformations, resulting in an internal stress field that serves as the primary cause of cracking. Stability and sensitivity analyses validate the reliability of the numerical framework. The proposed model can effectively simulate crack initiation, extension, and convergence during humidification or desiccation processes in both two and three dimensions. This study charts a feasible path for numerical simulation and mechanical mechanism exploration of cracking behaviors in clayey geomaterials during water migration.

Multi-physical analysis of saturation-dependent creep behavior for RC beam under sustained load and wet-dry cycles

A multi-physical and multi-scale analytical method based on thermo-hydro-mechanical models is adopted to evaluate the long-term deflection of RC beams with cracking under sustained loads and cyclic wet-dry conditions. The major physical-mechanical coupling mechanisms considered in this study includes: 1) water transport and phase equilibrium in the microstructure of gel and capillary pores; 2) accelerated moisture transport affected by cracking in concrete; 3) saturation-dependent creep coefficient considering gel and capillary pores; 4) combination of creep deformation and non-uniform shrinkage. The numerical approach is firstly verified by experiments where the thermo-hydro-mechanical interactions are found to be well analyzed. Then, parametric cases of cyclic wet-dry conditions are investigated to achieve deeper and wider conclusions. It has been found that under the cyclic wet-dry ambient conditions, there is an extreme drying state for concrete members depending on the drying humidity and its period. For the long-term mid-span deflection of beams, generally it will grow faster if the drying humidity is lower, which owes to the saturation-dependent creep coefficient, which has been called as Pickett effect. Meanwhile, beam's bottom-side cracking caused by sustained loads may also accelerate the moisture transport, which leads to an uneven drying state between upper and lower part of beams and viaducts, and eventually causes up-warping of them. For some cases, this up-warping can be significant enough to alter the macroscale structural creep deformation. At last, the difference between wet-dry cycle and dry-wet one has also been discussed. It can be proved that for the long-term deformation under wet-dry cycles, the moisture state will greatly affect the time-dependency from many aspects, for which the thermo-hydro-mechanical numerical approach is beneficial and needed in practice.

Prediction of non-uniform shrinkage of steel-concrete composite slabs based on explainable ensemble machine learning model

The non-uniform shrinkage (NUS) of steel-concrete composite slabs has been proved to significantly affect the long-term performance of composite slabs. But the reliable analysis method has not yet been proposed due to the multi-factor coupling mechanism of material composition and boundary conditions. A database containing 782 samples was established in this paper, and the index set containing 5 feature parameters was selected by analyzing the physical mechanism of NUS of steel-concrete composite slabs. The predictive capabilities of 8 machine learning (ML) models with different working mechanisms were compared, and the reliability of ML models was verified by Taylor and box scatter from the perspective of global and single sample, respectively. Furthermore, sensitivity analysis was conducted using the SHapley Additive exPlanations (SHAP) method to evaluate the impact of each parameter on the NUS of steel-concrete composite slabs. Finally, a user-friendly graphical user interface (GUI) was developed to guide engineering design. The limitations and potential improvements of the ML models established in this paper were discussed. The results indicate that the variance inflation factor (VIF) method and correlation analysis can effectively mitigate the influence of data multicollinearity and variable collinearity, and the pearson coefficient and VIF value of the input variables are less than 0.35 and 5. Gradient boosting decision tree (GBDT) has the best prediction performance, with R2 of 0.933 and 0.927 on the training set and testing set, respectively. Relative distance (x) and age (t) are the key parameters affecting the NUS of steel-concrete composite slabs. The procedure and GUI developed in this paper can effectively guide the intelligent prediction of the composite slab NUS.

G.ridge: An R Package for Generalized Ridge Regression for Sparse and High-Dimensional Linear Models

Ridge regression is one of the most popular shrinkage estimation methods for linear models. Ridge regression effectively estimates regression coefficients in the presence of high-dimensional regressors. Recently, a generalized ridge estimator was suggested that involved generalizing the uniform shrinkage of ridge regression to non-uniform shrinkage; this was shown to perform well in sparse and high-dimensional linear models. In this paper, we introduce our newly developed R package “g.ridge” (first version published on 7 December 2023) that implements both the ridge estimator and generalized ridge estimator. The package is equipped with generalized cross-validation for the automatic estimation of shrinkage parameters. The package also includes a convenient tool for generating a design matrix. By simulations, we test the performance of the R package under sparse and high-dimensional settings with normal and skew-normal error distributions. From the simulation results, we conclude that the generalized ridge estimator is superior to the benchmark ridge estimator based on the R package “glmnet”. Hence the generalized ridge estimator may be the most recommended estimator for sparse and high-dimensional models. We demonstrate the package using intracerebral hemorrhage data.

Pick and place process for uniform shrinking of 3D printed micro- and nano-architected materials

Two-photon polymerization lithography is promising for producing three-dimensional structures with user-defined micro- and nanoscale features. Additionally, shrinkage by thermolysis can readily shorten the lattice constant of three-dimensional photonic crystals and enhance their resolution and mechanical properties; however, this technique suffers from non-uniform shrinkage owing to substrate pinning during heating. Here, we develop a simple method using poly(vinyl alcohol)-assisted uniform shrinking of three-dimensional printed structures. Microscopic three-dimensional printed objects are picked and placed onto a receiving substrate, followed by heating to induce shrinkage. We show the successful uniform heat-shrinking of three-dimensional prints with various shapes and sizes, without sacrificial support structures, and observe that the surface properties of the receiving substrate are important factors for uniform shrinking. Moreover, we print a three-dimensional mascot model that is then uniformly shrunk, producing vivid colors from colorless woodpile photonic crystals. The proposed method has significant potential for application in mechanics, optics, and photonics.

A review on long‐term behaviour of steel‐concrete composite structures

AbstractThe exceptional structural performance of steel‐concrete composite structures, which harness the advantages of both steel and concrete, has garnered considerable attention. Following a summary of the fundamental time‐dependent characteristics of concrete, this paper reviews the existing studies about the long‐term behaviour of various steel‐concrete composite components, including slabs, beams, columns and walls. For composite slabs, nonuniform shrinkage occurs along the thickness direction. The long‐term behaviour of composite beams is significantly affected by the degree of shear connection. While the creep and shrinkage effects of composite columns are substantially reduced in comparison to reinforced concrete columns, stress redistribution may cause yielding or buckling of the steel tube. However, there is currently limited research available on the long‐term behaviour of composite walls with profiled steel plates, and no studies have been conducted on composite walls made of double‐skinned flat steel faceplates infilled with concrete. This lack of knowledge may lead to design uncertainties for composite coupled wall‐frame structures. To bridge this gap, the authors are currently conducting a corresponding long‐term experimental program.

Long-term deformation and mechanical properties evolution of cement paste with ultra-low water-to-cement ratio driven by water migration

Degradation of cement-based materials with ultra-low water-to-cement ratio may occur under water and drying conditions. However, the mechanisms remain unclear. In this study, we compared the mechanical properties, deformation, and mass change of cement pastes with a water-to-cement ratio of 0.17, which had been cured in saturated calcium hydroxide solution, sealed, and drying conditions for one year. The results show that the compressive strength of the cement pastes enhances and afterwards degrades under the three curing conditions. In both self-desiccating and drying conditions, the non-uniform shrinkage induced by water consumption dominates the evolution of the mechanical properties. Hydration affected by water adsorption/desorption has a stronger influence on compressive strength development compared to the weakening effect induced by water adsorption/desorption itself. When there is enough additional space in cement paste, extra hydration products formed with the external water supply can repair defects and fill pores, increasing compressive strength. In contrast, in dense structures, further hydration can cause swelling, cracking, and reduction in compressive strength. This study also confirms the contribution of the swelling of the calcium-silicate-hydrates gel on the expansion of cement paste in saturated conditions.

Pengaruh Kultur Bakteri Pada Proses Biosementasi Tanah Laterit Terhadap Nilai CBR

Lateritic soils have a high rate of weathering and non-uniform shrinkage. So this land is not good for construction work. Biocementation is a method of soil improvement by using the ability of bacteria that have lived in the soil to do the MCIP (Microbial-induced Calcite Precipitation) process which is obtained from the bacterium Bacillus Subtilis. This biocementation stabilization can increase the strength of the soil by adding Bacillus Subtilis bacteria as an additive to stabilize the soil. The test was carried out to determine changes in the mechanical properties of CBR Laboratory soil, by mixing 3% bacteria into the soil to be stabilized. The results of testing the CBR value of the Soaked Laboratory with one day of culture increased 4.8-fold at the 28-day curing period and increasing the CBR value of the Soaked Laboratory of three-day culture increased up to 4.9 times the CBR value before stabilization, which was 19.5%. The results of the study with stabilization using bacteria variation of 3% one-day culture increased up to 95% and increased up to 96% in three-day culture. So that it can be used as a soil material for road foundations in class B.

Design Procedures for Predicting Long-Term Responses of Continuous Steel–Concrete Composite Slabs

Although the effect of nonuniform shrinkage on the time-dependent behavior of simply supported composite slabs has been extensively investigated, continuous composite slabs have not garnered enough attention. This paper aims to propose the routine design procedures for continuous composite slabs, including the hogging moment over the interior support and the mid-span deflection. Thus, the long-term test data on two-span continuous composite slabs provided by the authors and the related literature were collected to benchmark the current design methods in international specifications. The routine design procedures for calculating the long-term moment distribution and the mid-span deflection of two-span composite slabs were proposed considering the time-dependent range of hogging moment zones. Moreover, the effects of different shrinkage distributions and hogging moment ranges on the long-term performance of these slabs were further quantified. The results showed that the mid-span deflection and the hogging moment over the interior support increased significantly over time; both could not be accurately predicted using the typical design methods described in international specifications. The hogging moment declined by 28.0% when a uniform shrinkage profile was adopted for the design of composite slabs, and the mid-span deflection decreased by 15.0% when a constant range of the hogging moment zones was used. The design procedures proposed herein well described the long-term behavior of continuous composite slabs by accounting for the combined effects of the nonuniform shrinkage and time-dependent hogging moment range. The calculated hogging moment and mid-span deflection differed from the measured ones on average by 2.0% and 9.0%.

An Experimental Study of Cavitation Bubble Dynamics near a Complex Wall with a Continuous Triangular Arrangement

The mechanism of cavitation cleaning of complex surfaces has received more and more attention. In the present paper, with the help of a high-speed photography experimental system, the dynamic behavior of a cavitation bubble in symmetrical positions near a complex wall with a continuous triangular arrangement is investigated. In terms of the bubble size and the initial wall–bubble distance, the non-uniform shrinkage of the bubble collapse and the movement characteristics of the bubble centroid are revealed. The main conclusions are as follows: (1) The collapse dynamic behavior of the bubble near a complex wall with a continuous triangular arrangement can be divided into three typical cases. (2) According to a large number of experimental results under different parameters, the parameter ranges corresponding to the three cases and the critical values between different cases are given. (3) The larger the bubble size is, or the smaller the initial wall–bubble distance is, the more significant the effect of the complex wall is, and the greater the movement distance towards the complex wall during the collapse stage.

Long-term performance of steel-spontaneous combustion coal gangue aggregate concrete composite slabs considering the influence of non-uniform shrinkage

The long-term performance of steel-spontaneous combustion coal gangue aggregate concrete (S-SCGAC) composite slabs was investigated in this study. Shrinkage tests were performed on 20 groups of specimens to quantify the effects of the replacement ratio (rc) of spontaneous-combustion coal gangue aggregate (SCGA) and humidity boundary conditions on the shrinkage of SCGAC specimens. A non-uniform shrinkage model for S-SCGAC composite slabs was further proposed. A long-term performance design method of S-SCGAC composite slabs was put forward by using ABAQUS software to establish a finite element model of the long-term performance of composite slabs considering the influence of non-uniform shrinkage, and to quantify the influence of parameters on the long-term performance. The results showed that the shrinkage deformation of SCGAC specimens increased significantly with increasing rc, and humidity boundary conditions were found to have a significant effect on the shrinkage performance of SCGAC specimens. The exposed surface shrinkage of the concrete under single-sided humidity transfer conditions was 1.01–1.09 times that under double-sided humidity transfer conditions, and the sealed surface shrinkage of the concrete under single-sided humidity transfer conditions was only 5.4%–14.4% of that under double-sided humidity transfer conditions. The long-term deflection of S-SCGAC composite slabs proved to be significantly affected by rc. When rc increased from 0% to 100%, the long-term deflection of the composite slab increased on average by 67.2%. The long-term deflection calculation method considering the effect of non-uniform shrinkage was shown to yield promising prediction results.

Measurement of Restrained and Unrestrained Shrinkage of Reinforced Concrete Using Distributed Fibre Optic Sensors

Shrinkage is an important component of the behaviour of reinforced concrete (RC) structures, however, the number of variables that affect shrinkage make it a complex time-dependent phenomenon. Additionally, as new concrete materials with lower embodied carbon gain popularity, there is a need for an in-depth understanding into their shrinkage behaviour before they can be widely adopted by industry. Currently, the shrinkage behaviour of concrete is studied using discrete measurements on small-scale unrestrained prisms. Distributed fibre optic sensing (DFOS) potentially provides a method of measuring both restrained (with reinforcement) and unrestrained (without reinforcement) shrinkage in both small-scale specimens and structural elements. In the current study, methods of measuring distributed unrestrained shrinkage strains were developed and evaluated, and the restrained shrinkage strains in different types of structural members were studied. Unrestrained shrinkage strains were measured using fibres optic cables embedded in small concrete prisms, while restrained shrinkage strains were measured with fibres bonded to the longitudinal reinforcement. Unrestrained shrinkage strains were found to be highly variable (as large as 3800 microstrain range) depending on location, but further research needs to be undertaken to account for end effects, early-stage shrinkage, and bond between the fibre optic cable and the concrete. Restrained shrinkage strains from structural members revealed non-uniform shrinkage strain distributions along member length due to functional grading as well as high supplementary cementitious material concretes, suggesting that shrinkage models will need to account for this variability.

Reconfigurable network structure with tunable multiple deformation modes: Mechanical designs, theoretical predictions, and experimental demonstrations

Reconfigurable network structure with tunable multiple deformation modes exhibits promising applications in functional electromagnetic devices, frequency-reconfigurable antennas, flexible electronic devices, and robots with multiple motion modes due to its capability to realize multiple working characteristics in one device or system. In most previous studies on reconfigurable network structures with large deformation, researchers focus on tuning the deformation and mechanical properties for a specific deformation mode of the network structure. Therefore, designs for reconfigurable network structures to achieve multiple deformation modes and large deformation still remain a challenge. The inverse design of the reconfigurable network structure with desired mechanical responses under some specific external actuations is difficult due to the lack of theoretical models to describe the finite deformation of network structures actuated by external fields. This paper introduces a mechanical design strategy for the reconfigurable network structure to achieve a large deformation (over 45%) and multiple mechanical responses under the electrothermal actuation, including the uniform or non-uniform shrinkage and expansion, shearing, and bending deformation modes. Theoretical models for this reconfigurable network structure are developed to predict these unique mechanical responses and inversely design the reconfigurable network structure for the desired deformation modes in a facilitating method. The accuracy of the designed reconfigurable network structure is validated by the corresponding finite element analyses (FEAs) and experiments qualitatively and quantitatively. In accordance with these theoretical models, the deformed configuration and analytic solutions for some critical mechanical quantities, such as the electrothermally actuated effective strain for shrinkage, expansion and shearing deformation modes, and the bending angle for bending deformation modes, are obtained. The electrothermally actuated deformation of network structures can be tuned by the value of the normalized geometrical parameter d/t1 and the electrothermal actuation strategy. Furthermore, demonstrative experiments and FE simulations illustrate that multiple deformation modes can be achieved in the same network structure through the individual actuation strategy. This work provides guidelines from the aspects of theoretical predictions, FEAs, and experiments for future designs of the reconfigurable network structures to achieve desired mechanical responses.

Print-and-Grow within a Novel Support Material for 3D Bioprinting and Post-Printing Tissue Growth.

3D bioprinting holds great promise for tissue engineering, with extrusion bioprinting in suspended hydrogels becoming the leading bioprinting technique in recent years. In this method, living cells are incorporated within bioinks, extruded layer by layer into a granular support material followed by gelation of the bioink through diverse cross-linking mechanisms. This approach offers high fidelity and precise fabrication of complex structures mimicking living tissue properties. However, the transition of cell mass mixed with the bioink into functional native-like tissue requires post-printing cultivation in vitro. An often-overlooked drawback of 3D bioprinting is the nonuniform shrinkage and deformation of printed constructs during the post-printing tissue maturation period, leading to highly variable engineered constructs with unpredictable size and shape. This limitation poses a challenge for the technology to meet applicative requirements. A novel technology of "print-and-grow," involving 3D bioprinting and subsequent cultivation in κ-Carrageenan-based microgels (CarGrow) for days is presented. CarGrow enhances the long-term structural stability of the printed objects by providing mechanical support. Moreover, this technology provides a possibility for live imaging to monitor tissue maturation. The "print-and-grow" method demonstrates accurate bioprinting with high tissue viability and functionality while preserving the construct's shape and size.

Design formulae for Long-Term responses of continuous Steel-Recycled aggregate concrete composite slabs

The steel-recycled aggregate concrete (RAC) composite slab is a low-carbon structural member with higher constructional efficiency. However, no design method has been established for the serviceability limit state evaluation of such members accounting for long-term effects. The non-uniform shrinkage peculiar to composite slabs significantly deteriorates the long-term responses of slabs, which would be more significant when using RAC. Previous studies only focused on the long-term responses of simply-supported composite slabs using NAC. The investigated responses include member deflection and stress in steel decking. No research attention has been paid to the continuous composite slabs, in which non-uniform shrinkage further induces possible yielding of the negative reinforcement and the limit exceeding of concrete crack width in the negative moment zone. Furthermore, the recycled aggregate influence has not been accounted for in the long-term design of the composite RAC slabs. In this context, this study aims to establish simplified explicit design formulae for the long-term responses of continuous RAC composite slabs accounting for the non-uniform shrinkage effects and the recycled aggregate influence. The target long-term responses include deflection, steel decking stress, negative reinforcement stress, and the concrete crack width in the negative moment zone. The simplified explicit formulae were derived from cross-sectional analysis results with some variables reasonably simplified into constant values based on collected data from real applications. The validation results have shown that the proposed formulae are capable of predicting the long-term responses of continuous RAC composite slabs, with the prediction accuracy similar to the code formulae for reinforced concrete slabs.

Near‐net‐size preparation of porous mullite matrix ceramics with in situ formed 3D mullite whisker network

AbstractPorous mullite matrix ceramics have excellent thermal and mechanical properties suitable for applications such as in thermal insulation. However, their applications are limited by processing defects from nonuniform sintering shrinkage and the trade‐off between high porosity (preferred for low thermal conductivity) and high mechanical strength. Herein, we seek to minimize the sintering shrinkage by near‐net‐size preparation and improve the strength by in situ formed whisker network structure. Gelcasting forming technology and pressureless sintering were used to prepare porous mullite matrix ceramics using kyanite and α‐Al2O3 powders as the starting materials and using MoO3 to promote the growth of mullite whiskers. The results showed that the sintering shrinkage could be compensated by the volume expansion from solid‐state reaction during reaction sintering. The in situ formed three‐dimensional (3D) whisker network further reduced sintering shrinkage and effectively improved the strength of the ceramics. An ultralow sintering shrinkage of .78% was achieved. The near‐net‐shape porous mullite matrix ceramics strengthened by 3D whisker network had a high porosity of 63.9%, a high compressive strength of 83.8 MPa and a high flexural strength of 53.5 MPa.

Compounding effect between influences of fine and coarse recycled aggregates on non-uniform shrinkage behavior of steel-concrete composite slab section

The steel-recycled aggregate concrete (RAC) composite slab is a practical structural member for applying RAC with the fine recycled aggregate (FRA). Despite its advantages, the non-uniform shrinkage (NUS) of composite slabs makes its long-term behaviour the critical factor controlling its design. The use of recycled aggregates would further enlarge the influence of the NUS, while no study has focused on the influence of FRA. Therefore, this paper aims to investigate the influence of FRA on the RAC NUS with different coarse recycled aggregate (CRA) contents. Fifteen RAC slab specimens were fabricated to monitor the shrinkage strain development, considering the replacement ratios of CRA and FRA (rCRA and rFRA), slab thickness, and moisture-transferring boundary conditions. Experimental results showed that 1) the FRA significantly increased both the shrinkage strain value and its gradient through slab thickness, 2) the FRA and CRA had a significant compounding effect (i.e. the influence of FRA varied with rCRA) on the NUS of RAC, and the compounding effect varied with slab thickness. The test results were used to develop a model for the NUS of RAC made with both FRA and CRA. The predicted results well matched the test data from the literature and this study. Finally, a parametric analysis was conducted based on the proposed model.