Creep-recovery Data Research Articles

Interpretable machine‐learning models for predicting creep recovery of concrete

AbstractCreep recovery of concrete is essential for accurately assessing the performance of concrete structures over service time. Existing creep recovery models exhibit low accuracy, and the influencing factors of creep recovery remain inadequately elucidated. In this paper, interpretable machine learning (ML) techniques were employed to develop a prediction model for concrete creep recovery. Several ML techniques were selected including random forest (RF), support vector regression (SVR), extreme gradient boosting (XGBoost) and light gradient boosting machine (LGBM). In order to maximize the sample size of the dataset, 109 sets of creep recovery data were collected from existing literatures for model training. Feature selection is utilized to determine the input parameters for ML models, and 12 input variables were selected. The model is fine‐tuned using Bayesian optimization techniques. To ensure the reliability of ML models, 10‐fold cross‐validation and random data splitting were implemented. The results indicate that the ML models exhibited higher accuracy compared to the existing creep recovery model. Among these ML models, LGBM demonstrated superior accuracy, efficiency and stability (with R2 = 0.993, 0.978, and 0.973 for the training, testing, and validation sets, respectively). Shapley additive explanations (SHAP) were employed to interpret the significance of each input parameter on ML model prediction. Duration after unloading, stress magnitude, and ambient relative humidity were the main feature variables influencing concrete creep recovery. Upon comparing the influencing factors, it was discerned that there exists a distinct difference between creep and creep recovery of concrete.

Tunable architectures of electrospun cellulose acetate phthalate applied as thickeners in green semisolid lubricants

Lubricants play a pivotal role in reducing wastage-to-energy caused by friction and increasing efficiency and durability by decreasing production and manufacturing costs. In this work, an efficient and innovative methodology founded on the electrospinning technique aiming to develop eco-friendly cellulose acetate phthalate (CAph) dispersions in castor oil with potential application in lubrication was proposed. With this in mind, the electrospinnability of CAph solutions and the ability of the different micro- and nano-architectures generated to thicken castor oil were studied. Particles, beaded-fibers and defect-free fibers were successfully produced by using CAph solutions with concentration between 10 and 30 wt%. The formation of bead-free nanofibers was favored at concentration above 20 wt%, achieving relaxation times of at least 13 ms, and non-Newtonian character in shear tests. All the electrospun CAph micro- or nano-structures leaded to physically stable oleo-dispersions, even at low concentrations (3 wt%), providing a wide variety of rheological and tribological as the dispersions undergone structural transitions due to changes in the thickener morphologies and/or concentrations, as shown by SAOS and creep-recovery data, oil holding capacity, and tackiness, wear and friction performance in metal–metal contact. Some of the oleo-dispersions formulated with defect-free CAph nanofibers exhibited similar rheological response and better tribological properties than traditional lithium lubricating greases which are the current benchmark.

Thermo-viscoelastic multiscale homogenization of additively manufactured short fiber reinforced polymers from direct microstructure characterization

Short fiber reinforced polymers (SFRPs) processed by Fused Filament Fabrication (FFF) show great promise for applications requiring high weight-specific mechanical properties, such as aerospace. However, the unique morphology created by the printing process and the relationship between processing parameters and part behavior is not sufficiently well understood, making structural analysis a largely empirical task. The limited ability to predict the effective viscoelastic properties and their thermal dependence is a problem from a mechanical design standpoint and is an obstacle to the widespread adoption of SFRPs made by FFF. In this work, those properties are evaluated using high-resolution imaging of physical samples, enabling the accurate prediction of time-dependent stress–strain relations across different temperatures. Multiscale homogenization is performed considering individual components (fibers, pores, matrix) at the microscale, and the regular pattern created by the printing process at the mesoscale. The efficiency of the Fast Fourier Transform (FFT) based homogenization procedure is leveraged to allow for large Representative Volume Element (RVE) sizes, which are required due to the complexity of real microstructures. The predicted thermo-viscoelastic behavior is validated against creep-recovery data of specimens printed from 30 wt% short carbon fiber reinforced poly-ether-ether ketone (PEEK), and the experimental data can be predicted within 3% mean relative error for axial loading, both at 21°and 120 °C. Imaging data and pre-processed RVEs as well as original source code are made publicly available.

A novel epoxy-terminated polyethylene modified asphalt with low-viscosity and high storage stability

The storage stability of polyethylene (PE) modified asphalt is a major constraint to its wide application. In addition, PE raises the mixing and compaction temperature of asphalt, causing environmental pollution. The effective synthesis of stable and environmentally friendly PE modifiers is an important and challenging topic. We propose a strategy to reduce the molecular weight of PE while adding functionalized end group to PE. The obtained low molecular weight epoxy-terminated-polyethylene (EPE) for modified asphalt is storage stable, reduces mixing and compaction temperatures of asphalt, and reduces environmental pollution. The difference between the top and bottom softening points of asphalt containing 3 wt% and 5 wt% EPE was 1.25 °C and 0.7 °C, which exceeded most previously reported PE-modified asphalt. In addition, EPE, due to its low molecular weight, reduces the high temperature viscosity of asphalt, achieving lower mixing and compaction temperatures. Besides, dynamic shear rheometer (DSR) and multiple stress creep recovery (MSCR) data showed that the rheological properties of EPE modified asphalt were also significantly improved. This work will provide further guidance for the application of PE in asphalt.

Viscoelastic behavior of glass fiber reinforced rubber-modified epoxy

Abstract Epoxies as a thermoset polymer have got a great attention in different applications. To elaborate their employing and surmount their brittleness, many polymers were blended with them. The results confirm that the good mechanical properties are obtained when 6wt% of Polysulfide Rubber (PSR) is blended with epoxy and reinforced with fiber glass. The effect of rubber and glass fiber on the viscoelastic properties of epoxy were investigated using creep-recovery data under different stress levels (5, 10, 15 and 20 MPa) and temperatures (30, 50, 70 and 90°C). Polysulfide addition caused larger creep and creep recovery. In addition, the creep resistance of glass fiber reinforced blend was significantly enhanced.

Study on the viscoelastic behaviour of the modified asphalt containing multi-walled carbon nanotubes (MWCNTs) and crumb rubber (CR)

Asphalt binder plays an important role on the performance of asphalt mixture, especially for the high-temperature performance. The purpose of this research is to investigate the viscoelastic behaviours of the modified asphalt containing multi-walled carbon nanotubes and crumb rubber. By adding multi-walled carbon nanotubes and crumb rubber to the base asphalt, the multi-walled carbon nanotubes modified asphalt, crumb rubber modified asphalt and multi-walled carbon nanotubes and crumb rubber composite-modified asphalt were prepared. The high-temperature viscosity and rheological property indices were obtained through the viscosity test and small amplitude oscillatory measurement. Besides, multiple stress creep recovery test and stress relaxation test were utilized to explore creep recovery behaviours and stress relaxation characteristics of the asphalt samples. Based on the time-temperature superposition principle, the master curves of complex shear modulus and phase angle were generated. Han curves of the asphalt samples were established based on superposition principle of Blotzmann. Furthermore, the Burgers model was used to model the creep-recovery data. The relaxation functions of Maxwell model and Burgers model were applied to fit stress relaxation curves of the asphalt samples. Results indicate that, the addition of multi-walled carbon nanotubes and crumb rubber caused an increase in high-temperature viscosity, and reduce the temperature susceptibility of base binder. In addition, the permanent deformation resistance, creep-recovery behaviours and stress relaxation characteristics of asphalt were enhanced remarkably by the two modifiers modification. Lastly, the composite-modified asphalt exhibited better viscoelastic behaviours than asphalt modified with either crumb rubber or multi-walled carbon nanotubes alone.

A nonlinear viscoelastic–viscoplastic constitutive model for adhesives under creep

In this study, we consider the nonlinear viscoelastic–viscoplastic behavior of adhesive films in scarf joints. We develop a three-dimensional nonlinear model, which combines a nonlinear viscoelastic model with a viscoplastic model using the von Mises yield criterion and nonlinear kinematic hardening. We implement an iterative scheme for the viscoplastic solution and a numerical algorithm with stress correction for the combined viscoelastic–viscoplastic model into finite element analysis. The viscoelastic component of the model is calibrated using creep-recovery data from adhesive films in scarf joints. The viscoplastic parameters are calibrated from the residual strains of recovered creep tests with varying load durations. A two-dimensional form of the model shows good agreement with the three-dimensional model for the scarf joint considered in this work and is compared with experiment. The numerical results show favorable agreement with the experimental creep and recovery responses of two epoxy adhesive systems. We also discuss the contribution of nonlinear viscoelasticity and viscoplasticity to the stress/strain distribution along the adhesive center lines. Viscoplasticity tends to lower the stress concentration.

A new approach to estimates the adhesion durability of an epoxy coating through wet and dry cycles using creep-recovery modeling

Estimation of adhesion durability of an epoxy coating through wet and dry cycles has been investigated. For this purpose, we endeavor to find a correlation between adhesion durability and viscoelastic parameters of coatings. An epoxy resin was cured with four types of hardeners (polyamine, polyamidoamine, polyether polyamine, and cycloaliphatic polyamine-based hardener) and a mixture of two hardeners (polyether polyamine and cycloaliphatic polyamine) in four different mixing ratios (20:80, 50:50, 70:30, 90:10) to achieve various viscoelastic properties. The storage modulus, viscoelastic creep-recovery, electrochemical parameters, and glass transition temperature were determined. Adhesion loss and recovery of adhesion were measured under wet and dry conditions during the time. It was found that creep recovery data correlated exactly with the recovery of adhesion. Creep recovery data were modeled and for the first time, two rheological parameters (viscous ratio and elastic ratio) were defined to predict adhesion durability. Pearson correlation coefficient was used as a statistical measure of the strength of a linear relationship between the paired data. It was found that adhesion durability and recovery of adhesion after wet and dry cycles have a strong linear relationship with viscous and elastic ratios. A coating with a higher viscous behavior in creep recovery tests acts more weakly in the recovery of adhesion. It may be referred to as irreversible strain in a coating that may not be recovered after the elimination of stress.

Determination of creep compliance of asphalt mixtures at intermediate and high temperature using creep-recovery test

The linear viscoelastic (LVE) characterisation of asphalt mixtures in time domain is generally performed at temperature lower than 30°C to prevent the effect of permanent deformation. Although LVE properties in frequency and time domain can be mathematically interconverted, the determination of relaxation modulus and creep compliance through experiment is also necessary. This paper presents a method for determining the creep compliance of asphalt mixtures at intermediate and high temperature, at which permanent deformation takes place. Since the recovery of creep-recovery test is a pure LVE process, it was used to back-calculate the creep compliances (CCs) at various investigating temperatures. The results show that the CCs back-calculated from creep-recovery data achieve a good level of accuracy and repeatability. In addition, the obtained master curves of CCs agree well with those interconverted from dynamic modulus test data and the same shift factors are applicable for both creep compliance and dynamic modulus, phase angle.

Rheological studies of SBS/EVA blends modified with bio-based cashew nut shell liquid

Research on bio-plasticizers is a topic of strategic interest in polymer blends. A bio-plasticizer, cashew nut shell liquid (CNSL), was studied in blends of ethylene-vinyl acetate copolymer (EVA) and styrene-butadiene-styrene copolymer (SBS). In the literature does not report the addition of plasticizers to SBS/EVA blend. Statistical analyses showed that there was a significant difference in mechanical properties (tension at break, hardness and elongation at break) vs. the unplasticized blend. The minimum CNSL concentration required for a statistical difference was 10 phr. The Carreau-Yasuda rheological model was used to obtain rheological parameters in these blends. The plasticizing influence of CNSL was confirmed by rheology. The effects of CNSL on creep and recovery were evaluated for the SBS/EBA blends. Burger´s model explained well SBS/EVA creep compliance. Moreover, its parameters (Newtonian dashpots and Hookean springs) were evaluated as a function of the CNSL concentrations. The bio-plasticizer concentration influenced significant correlations among the rheological creep-recovery tests, thus enabling a considerable increase in the elastic phase. Experimental creep-recovery data and curve fit were in good agreement.

Mixed starch/chitosan hydrogels: elastic properties as modelled through simulated annealing algorithm and their ability to strongly reduce yellow sunset (INS 110) release

Biopolymers mixtures appear as a strategy to improve sensorial/technological characteristics of gel-like products. Thus, self-sustaining starch (S100/C0) hydrogels were prepared with a partial replacement of the gelling agent by 5.0 % (S95/C5), 7.5 % (S92.5/C7.5), or 10.0 % chitosan (S90/C10), and containing yellow sunset (INS 110). Major visual changes or significant differences on L*a*b* parameters were not observed for starch/chitosan hydrogels. Creep-recovery data was modeled using the simulated annealing algorithm, and relative recovery results showed an increase for S95/C5 (82.6 %), when compared to S100/C0 (72.9 %). After 312 h, chitosan strongly reduced the INS 110 release from hydrogels to an ethanolic solution (3.1∙10−4 and 4.1∙10-3 g/100 mL for S95/C5 and S100/C0, respectively) or to a sucrose solution (1.1∙10-3 and 6.5∙10-3 g/100 mL for S95/C5 and S100/C0, respectively). Such results highlighted that chitosan not only presented a techno-functionality on starch hydrogels by improving their elasticity but also by hindering the release of yellow sunset.

A nonlinear viscoelastic\u2013viscoplastic model for adhesives

We consider the nonlinear viscoelastic–viscoplastic behavior of adhesives. We develop a one-dimensional nonlinear model by combining Schapery’s nonlinear single integral model and Perzyna’s viscoplastic model. The viscoplastic strain was solved iteratively using the von Mises yield criterion and nonlinear kinematic hardening. The combined viscoelastic–viscoplastic model was solved using Newton’s iteration and implemented into a finite element model. The model was calibrated using creep-recovery data from bulk adhesives and verified from the cyclic behavior of the bulk adhesives. The finite element model results agreed with experimental creep and cyclic responses, including recoverable and permanent strain after load removal. Although the contribution of the viscoplastic strain was small, both viscoplastic and viscoelastic components of strain response were required to describe the adhesive creep and cyclic response.

The effects of acetylated distarch phosphate from tapioca starch on rheological properties and microstructure of acid-induced casein gel

This study aimed to investigate the effects of acetylated distarch phosphate (ADSP) from tapioca starch on the rheological properties and microstructure of acid-induced casein gel using dynamic rheological tests, creep recovery, confocal laser scanning microscopy (CLSM), and scanning electron microscopy (SEM). The rheological results showed that the casein and casein/ADSP gels displayed shear-thinning behavior. The apparent viscosity and viscoelasticity (G′ and G″) of casein/ADSP gels increased with ADSP content, except for 2.0% ADSP. The power law model indicated that ADSP increased the structural strength of the casein/ADSP gels. The creep recovery data were fitted using Burger's model, which showed that the highest instantaneous elasticity and stiffness was observed when the ADSP concentration was 1.5%. The fractal dimension obtained from CLSM indicated that the disorder of the casein network decreased with ADSP concentration. SEM micrographs suggested that the porosity of casein/ADSP gels was decreased by ADSP and that a higher concentration of ADSP (2.0%) broke the continuity of the network structure. The results of this study could potentially facilitate the improvement of the stability of yogurt and provide valuable information for the manufacturers.

Effect of the viscoelastic properties of modified starch as a wall material on the surface morphology of microcapsules.

Since microcapsule technology has a good protective effect on unstable bioactive substances, many studies have focused on exploring the best technical conditions for forming microcapsules. Modified starch is a microcapsule wall material with good emulsifying and film-forming properties. The objective of this work was to study the creep-recovery behavior of modified starch pastes for various creep time, shear stress and temperature. Furthermore, the effect of creep-recovery behavior on the morphology of microcapsules made of the modified starch was investigated. The maximum creep compliance (Jmax ), instantaneous compliance (J0 ) and retardation compliance (J1 ) of modified starch increased proportionally with increasing creep time and shear stress but decreased with increasing temperature. The Newtonian viscosity (η0 ) increased with increasing creep time and temperature but decreased with increasing shear stress. The recovery rate of the modified starch pastes varied from 0.92 to 33.68% in the creep-recovery test conditions. Creep-recovery data could be well explained by a four-parameter Burgers model (R2 > 0.918). Modified starch pastes exhibited time-, stress- and temperature-dependent creep-recovery behavior. The Jmax values of modified starch pastes were low(<0.20 Pa-1 ) and the η0 values high (>3.5×103 Pa s) for all test conditions. The results revealed the modified starch pastes had a good rigid network structure to resist deformation but recovery was difficult once deformation occurred. Microcapsules produced using the modified starch exhibited a small deformation with regular spheres and some dents, consistent with the results of creep-recovery tests. © 2019 Society of Chemical Industry.

Preparation and Characteristics of Ethylene Bis(Stearamide)-Based Graphene-Modified Asphalt.

In this study, graphene-modified asphalt (GMA) was prepared from SK-70# matrix asphalt and ethylene bis(stearamide) (EBS). Based on the uniform design method, a model was created using Data Processing System (DPS) software and First Optimization (1stOpt) software using the graphene mixing amount, EBS mixing amount, shear rate, shear time, and shear temperature as factors and using the asphalt penetration, softening point, force ductility, SHRP-PG test, and multistress creep recovery data as indices. Calculations and analysis showed that the optimal composition and preparation parameters of GMA are as follows: the graphene proportion is 20‰, the EBS proportion is 1%, the shear rate is 6000 r.p.m., the shear time is 180 min, and the shear temperature is 140 °C. The prepared GMA had a significantly improved softening point, low-temperature fracture energy, antirutting factor, and creep recovery rate, indicating that adding graphene can improve the high- and low-temperature performance of asphalt. The prepared GMA was characterized by X-ray diffraction (XRD). The dispersibility of graphene in asphalt was evaluated by fluorescence microscopy and Image-Pro Plus imaging software. The results show that graphene can exist in asphalt in a stable form, which increases the loose-layered structure of stacked asphalt or gum. The intense adsorption effect of graphene strengthens the ordered structure of asphalt. However, due to its dispersibility characteristics, some graphene exists in asphalt in clustered form. When the graphene-to-dispersant ratio approaches the optimal value, the dispersant changes the form of graphene in asphalt from irregular clusters to regular clusters and from large, distinct clusters to small, indistinct clusters. When dispersant cannot uniformly disperse graphene in asphalt, graphene clusters primarily form medium-sized grains.

Rheological Characterization of Hydrogels from Alginate-Based Nanodispersion.

The interest toward alginate and nanoemulsion-based hydrogels is driven by the wide potential of application. These systems have been noticed in several areas, ranging from pharmaceutical, medical, coating, and food industries. In this investigation, hydrogels prepared through in situ calcium ion release, starting from lemongrass essential oil nanodispersions stabilized in alginate aqueous suspensions in the presence of the nonionic surfactant Tween 80, were evaluated. The hydrogels prepared at different concentrations of oil, alginate, and calcium were characterized through rheological tests. Flow curves demonstrate that the hydrogels share shear thinning behavior. Oscillatory tests showed that the strength of the hydrogel network increases with the crosslinker increase, and decreases at low polymer concentrations. The hydrogels were thixotropic materials with a slow time of structural restoration after breakage. Finally, by analyzing the creep recovery data, the hydrogel responses were all fitted to the Burger model. Overall, it was demonstrated that the presence of essential oil in the proposed hydrogels does not affect the mechanical characteristics of the materials, which are mainly influenced by the concentration of polymer and calcium as a crosslinker.

Rheological Analysis of Wheat Flour Dough as Influenced by Grape Peels of Different Particle Sizes and Addition Levels

The present study was undertaken to assess the effects generated by grape peels flour (GPF), as a source of dietary fibers, on the white wheat flour (WF) dough rheological behavior. Dynamic and empirical rheological measurements were carried out in order to study the viscoelasticity of GPF-enriched wheat flour-based dough matrices and to identify the main actions of GPF particle size (large, medium, and small) at replacement levels from 0% up to 9%. The water competition of GPF is explained by different water binding and gelling capacities, synergistic and/or antagonistic effects of GPF compounds on the major rheological properties. Power low and Burgers models were successfully fitted with the dynamic oscillatory and creep-recovery data being suitable to interpret viscoelastic behavior of dough. Composite flour dough with smaller particle size presented higher G′ and G″ values at addition level above 5% GPF, exhibiting higher viscous component with concomitantly higher peak viscosity. Creep-recovery tests for samples with small particle size at 5% addition level showed that the elasticity and the recoverable proportion was higher compared to the rest of GPF formulations and control sample. Significant correlations (p < 0.05) were found between several parameters determined by both dynamic and empirical rheological measurements which have essential roles in monitoring GPF-enriched wheat flour dough in a wide set of different kinds of samples. This information could be helpful to optimize the particle size and addition level of GPF that could be useful to produce GPF-enriched designed bread.

Influence of Low Acyl and High Acyl Gellan Gums on Pasting and Rheological Properties of Rice Starch Gel

The pasting, viscoelastic, morphological and retrogradation properties of rice starch as affected by low acyl (LA) and high acyl (HA) gellan gums were studied. The additions of both LA and HA gums increased the peak and trough viscosities, while decreased the final and setback viscosities of rice starch paste. The starch-HA mixed pastes exhibited superior viscoelastic properties to the starch-LA pastes as evidenced by their higher storage modulus and lower loss tangent values. The starch-HA system exhibited higher resistance to the stress and more pronounced recovery rate in in-shear structural recovery test. The creep recovery data were well fitted by a 4-element Burger’s model. The shrinkage measurements showed that the addition of both hydrocolloids, especially the HA gellan gum retarded the retrogradation of rice starch gel during cold storage. It was concluded that the addition of LA and HA gellan gums modified the rheology and textural properties of rice starch gel in different ways and interacted under different mechanisms based on their molecular structures.

Creep-recovery of normal strength and high strength concrete

The creep-recovery behavior of both normal and high strength concrete (HSC) under various load conditions has not been studied thoroughly. Although the use of HSC is long-established, rational creep-recovery prediction of HSC is still unavailable since current study just regards recovery deformation as a secondary result of creep experiments. In this paper, a new prediction model for creep-recovery of normal strength concrete (NSC) with considering the influence of stress level and load history was proposed at first. Then, a model for HSC creep-recovery was established according to creep-recovery data of NSC and HSC in literatures and the influence of compressive strength of concrete. To validate the HSC model, an experimental study of the creep behavior of C80 concrete was conducted. Creep and residual strain after unloading of specimens at various compression stress levels (30% and 50% of the compression strength) were compared with the HSC creep-recovery model. Although the HSC model tends to underestimate the first 7days’ creep-recovery value, the results show high overall prediction accuracy. Moreover, parametric analysis results indicate that the recoverable creep of HSC reduces significantly than that of NSC. The effect becomes stronger with the increase of loading age and weaker with a prolongation of load duration.

The Effect of Hybrid Carrageenan on the Thermo-rheological Properties of Gluten-Free Flour Doughs Using a Modified Kneading Protocol

Thermo-rheological behaviour of chestnut flour doughs supplemented with kappa/iota-hybrid carrageenan (HC) (up to 2.0%, flour basis (f.b.)) and sodium chloride (1.8%, f.b.) was determined at both target (C1) and final (C5) mixing peaks. For this purpose, small amplitude oscillatory shear (0.01 to 100 Hz), creep–recovery (loading of 50 Pa for 60 s, 30 °C), temperature sweeps (from 30 up to 180 °C) and heating/cooling cycles (between 30 and 60 °C) were conducted on a controlled stress rheometer. Previously, the thermal-mixing behaviour at proposed mixing temperature (50 °C) was conducted on Mixolab® apparatus. Results showed that the dough stability (from 2.2 to 5.8 min) in mixing stage and starch heat resistance to dough processing were significantly improved at proposed mixing temperature, even in the absence of HC. No statistical differences in rheological properties were observed for doughs evaluated in C1; however, those analysed in C5 were significantly modified in the presence of HC, mainly in terms of viscous behaviour (from 52.1 × 106 to 39.1 × 106 Pa s). Creep–recovery data sets, successfully fitted using Burgers model, revealed that the elasticity (J r/J max from 73.3 to 87.6%) of doughs analysed in C5 improved with HC addition. Thermal tests showed that the starch transitions were significantly promoted and stabilized with HC addition.