Rupture Strain Research Articles

Probabilistic calibration of strength and strain enhancement models for FRP-confined concrete in circular section

Lateral confinement with fiber-reinforced polymer (FRP) jackets can effectively improve the axial compressive behavior of concrete but with considerable variability in outcomes. Therefore, that there is a need for calibrations of deterministic models for strength enhancement (SEE) and strain enhancement (SAE) based on proposed probabilistic prediction models and comprehensive available databases. The probabilistic models that incorporate the essential factors identified from the previous study were updated based on the Bayesian theory, and Markov Chain Monte Carlo (MCMC). Moreover, nine representative deterministic SEE models and six SAE models were evaluated by credible interval (CI) and confidence level (CL) under different conditions of the axial strain of unconfined concrete in the literature, the hoop rupture strain, the peak axial compressive stress of unconfined concrete, and the lateral confinement stiffness. Analysis of different FRP types was also conducted individually for more critical results. The proposed probabilistic models are capable of predicting the characteristics of ultimate axial stress and corresponding strain and providing an efficient approach to calibrate the confidence level and computational accuracy of deterministic models in literatures.

Axial impact behavior of Large-Rupture-Strain (LRS) fiber reinforced polymer (FRP)-confined concrete cylinders

This paper presents an experimental study on the impact performance of concrete columns confined with large-rupture-strain (LRS, tensile rupture strain ≥ 5%) fiber reinforced polymer (FRP) jackets. A total of 32 concrete specimens were prepared and tested using large-capacity drop-weight equipment. The test variables included four impact heights (2, 3, 4 and 5 m), three types of FRP, i.e., aramid FRP (AFRP), polyethylene naphthalate (PEN) FRP and polyethylene terephthalate (PET) FRP and two layers of FRP jackets (1 and 2). The time histories of impact force and FRP rupture strain as well as failure modes were obtained from the test. Compared to the AFRP-confined concrete specimen with similar jacket stiffness, the core concrete of the LRS FRP-confined specimen was less damaged due to the large-rupture-strain characteristic. The impact force increased and the impact duration decreased with increasing impact height. The impact duration of concrete specimens confined with LRS FRP was longer than that of the AFRP-confined concrete column. Results showed that the impact-resistance behaviours of LRS FRP-confined concrete column outperformed its companion column confined with AFRP. Besides, increasing the thickness of FRP jacket can enhance the impact resistance capacity. These findings may facilitate the impact resistance strengthening/retrofitting of RC structures with the application of LRS FRP composites.

Nanocomposite hydrogels enhanced by cellulose nanocrystal-stabilized Pickering emulsions with self-healing performance in subzero environment

Nowadays, hydrogels as flexible materials have attracted considerable attention in frontier fields such as wearable electronic devices, soft actuators and robotics. However, water-based hydrogels inevitably freeze at subzero temperatures and suffer damage from contact with objects, which greatly reduce their service life and practical value. Herein, nanocomposite hydrogels with self-healing performance at subzero temperatures were proposed by introducing binary water-glycerol continuous phase and dual self-healing interactions. The binary solvents were emphasized in preventing the formation of ice crystals, enhancing flexible and self-healing abilities of hydrogels in subzero environment. Linseed oil as healing agent was effectively loaded in Pickering droplets by cellulose nanocrystals. Owing to non-covalent bonding and external healing agent, the obtained hydrogels showed improved mechanical properties and self-healing abilities. Particularly, after incorporating Pickering droplets, the rupture stress of nanocomposite hydrogels was 0.24 MPa, the rupture strain was 1900% and the healing efficiency could be up to 80.1% for 12 h at − 20 °C. Therefore, the obtained hydrogels with frost resistance, stretchability and self-healing properties should have broader potential applications, especially in subzero environment.

Comparison of monotonic axial compressive behavior of rectangular concrete confined by FRP with different rupture strains

Axial compressive behavior of rectangular concrete might differ greatly when it is confined by fiber reinforced polymer (FRP) with different rupture strains. To address this issue, this study experimentally investigated and compared the monotonic axial compressive behavior of rectangular concrete confined by FRP with three rupture strains. Axial compression experiments of 28 rectangular concrete stub columns confined by FRP were carried out. The FRP utilized in this study included conventional FRP with small rupture strain, i.e., carbon FRP (CFRP) and glass FRP (GFRP), and large rupture strain FRP (LRS-FRP), i.e., polyethylene terephthalate (PET) FRP. The key test parameters were the rupture strain of FRP, the FRP thickness, and the cross-sectional aspect ratio. Failure modes, stress vs. strain behavior, axial stress and strain relationship, hoop rupture strain, the effect of FRP confinement stiffness ratio, and the effect of cross-sectional aspect ratio were analyzed, respectively. Results of this research showed that the rupture strain of FRP exhibited significant influence on the failure mode and the axial deformation of rectangular concrete confined by FRP. FRP strain reduction factors were decreased with the increasing rupture strains of FRP. This is because the rectangular concrete confined by FRP with larger rupture strains dilated more non-uniformly than its counterpart using smaller rupture strain FRP. In addition, based on the transition point and the ultimate condition, the axial stress vs. strain curves of rectangular concrete confined by FRP could be categorized into three types, including sufficient, moderate, and insufficient FRP confinement, respectively.

Hot corrosion-creep interaction in IN718 under simulated marine environment: Introducing strain-associated-time (SAT) plots for comprehensive understanding

Creep-rupture behaviour of IN718 with deposit of 87.5 wt.%Na2SO4+5 wt.%NaCl+7.5 wt.%NaVO3 (3SM) in the stress range of 550–850 MPa at 650 °C is investigated. 3SM shortens the creep-rupture time by ≈70–90 %. Comprehensive microstructural analysis suggests that oxygen-induced-dynamic- embrittlement, sulphidation followed by oxidation, and vanadic-hot corrosion operate during creep. Creep-hot corrosion interaction influence on rupture strain is explained by introducing strain-associated-time (SAT) and Δtε plots, for the first time. These plots accompanied by detailed microstructural examination demonstrate that deleterious influence of 3SM increases with decreasing stress. Further, SAT plots and EPMA analysis confirm that oxygen-induced-dynamic-embrittlement commences from ∼9% strain under 3SM at 550 MPa.

Axial Compressive Strength Models of Eccentrically-Loaded Rectangular Reinforced Concrete Columns Confined with FRP.

The majority of experimental and analytical studies on fiber-reinforced polymer (FRP) confined concrete has largely concentrated on plain (unreinforced) small-scale concrete columns, on which the efficiency of strengthening is much higher compared with large-scale columns. Although reinforced concrete (RC) columns subjected to combined axial compression and flexural loads (i.e., eccentric compression) are the most common structural elements used in practice, research on eccentrically-loaded FRP-confined rectangular RC columns has been much more limited. More specifically, the limited research has generally been concerned with small-scale RC columns, and hence, the proposed eccentric-loading stress-strain models were mainly based on the existing concentric-loading models of FRP-confined concrete columns of small scale. In the light of such demand to date, this paper is aimed at developing a mathematical model to better predict the strength of FRP-confined rectangular RC columns. The strain distribution of FRP around the circumference of the rectangular sections was investigated to propose equations for the actual rupture strain of FRP wrapped in the horizontal and vertical directions. The model was accomplished using 230 results of 155 tested specimens compiled from 19 studies available in the technical literature. The test database covers an unconfined concrete strength ranging between 9.9 and 73.1 MPa, and section’s dimension ranging from 100–300 mm and 125–435 mm for the short and long sides, respectively. Other test parameters, such as aspect ratio, corner radius, internal hoop steel reinforcement, FRP wrapping layout, and number of FRP wraps were all considered in the model. The performance of the model shows a very good correlation with the test results.

Elucidating Axonal Injuries Through Molecular Modelling of Myelin Sheaths and Nodes of Ranvier.

Around half of the traumatic brain injuries are thought to be axonal damage. Disruption of the cellular membranes, or alternatively cytoskeletal damage has been suggested as possible injury trigger. Here, we have used molecular models to have a better insight on the structural and mechanical properties of axon sub-cellular components. We modelled myelin sheath and node of Ranvier as lipid bilayers at a coarse grained level. We built ex-novo a model for the myelin. Lipid composition and lipid saturation were based on the available experimental data. The model contains 17 different types of lipids, distributed asymmetrically between two leaflets. Molecular dynamics simulations were performed to characterize the myelin and node-of-Ranvier bilayers at equilibrium and under deformation and compared to previous axolemma simulations. We found that the myelin bilayer has a slightly higher area compressibility modulus and higher rupture strain than node of Ranvier. Compared to the axolemma in unmyelinated axon, mechanoporation occurs at 50% higher strain in the myelin and at 23% lower strain in the node of Ranvier in myelinated axon. Combining the results with finite element simulations of the axon, we hypothesizes that myelin does not rupture at the thresholds proposed in the literature for axonal injury while rupture may occur at the node of Ranvier. The findings contribute to increases our knowledge of axonal sub-cellular components and help to understand better the mechanism behind axonal brain injury.

An Innovative Tubular Standing Support Incorporating PVC and FRP Composites: Laboratory Tests

The importance of developing innovative support structure for underground mines has drawn much attention with the depletion of shallow resources. This paper presents a hybrid tubular standing support consisting of an exterior container made of the polyvinyl chloride (PVC) and fibre-reinforced polymer (FRP) while the infill is the coal rejects based backfill material. The FRP jacket featured with the high strength-to-weight ratio is attached on the exterior surface of the PVC tube with the large rupture strain to provide confinement to infilled backfill material. A series of laboratory tests were conducted on this FRP-PVC tubular standing support (FPTSS) with different FRP thickness. Meanwhile, the FRP tubular standing support and the PVC tubular standing support with the sole confining material were also prepared and tested. Tests results showed that the FPTSS specimen exhibited the typical strain hardening behaviour attributed to the effective confinement provided by the combined container. It is also indicated that the enhancement of either the compressive strength or the axial deformation ability is closely related to FRP thickness. The other comparative advantage of FPTSS obtained from this research is its ductile post-peak behaviour after the rupture of the exterior FRP jacket, indicating the importance of using PVC tube in FPTSS. Except for its superior compressive behaviour, the cost effectiveness and ease of construction of FPTSS are also attractive from the design aspect.

Rate-dependent compressive behavior of concrete confined with Large-Rupture-Strain (LRS) FRP

The polyethylene naphthalene (PEN) and polyethylene terephthalate (PET) fibers have a tensile rupture strain of over 5%, and hence they are referred to as large-rupture-strain (LRS) fiber reinforced polymer (FRP) materials. Their large rupture strain characteristics may contribute to significant improvement of the impact resistance of reinforced concrete (RC) structures. This study investigates the strain rate effect on LRS FRP-confined concrete through Split Hopkinson Pressure Bar (SHPB) test. Results revealed that LRS FRP-confined concrete specimens exhibited superior impact resistance behaviors compared to the counterpart confined with CFRP composites when subjected to a single impact. The critical strain, compressive strength and toughness of the LRS FRP-confined concrete specimen increased with increasing strain rate. Due to the large rupture strain characteristics, the LRS FRP-confined concrete specimen virtually had no visible damage after a single impact. To study the damage evolution mechanism of concrete, the specimens were impacted for multiple times with the same energy until the failure of the specimen. Due to progressive concrete damage, the dynamic compressive strength and toughness experienced a decrease during multiple impacts. These findings might promote the application of LRS FRP materials in the field of impact resistance design of RC structures as a promising external jacketing material.

Compressive behavior and modelling of engineered cementitious composite (ECC) confined with LRS FRP and conventional FRP

A combination of core engineered cementitious composite (ECC) and external fiber-reinforced polymer (FRP) composites can solve the problems of insufficient ductility and durability of normal concrete (NC) in adverse environments and improve bearing capacity. However, existing studies on the performance of ECC strengthened by FRP are very limited—particularly the research on large rupture strain (LRS) FRP-confined ECC. In this study, an experimental investigation of LRS FRP and conventional glass FRP-confined ECC cylinders with different confinement levels under axial compression is presented. It is found that the application of external FRP jackets leads to a significant improvement in the compressive strength and deformation of the core ECC. LRS FRP-confined ECC exhibits a higher ultimate deformation than conventional FRP-confined ECC. The dilation behavior, axial stress–strain behavior, and energy dissipation capacity between FRP-confined ECC and FRP-confined NC under the same confinement level are compared, and the former exhibits a significantly larger ductility and energy dissipation capacity than the latter. The results also indicate that most existing models are unable to accurately predict the compressive behavior of FRP-confined ECC. To address this, a dilation model and an axial stress–strain model of FRP-confined NC are modified to extend their application to FRP-confined ECC.

Flexural strengthening of steel beams using pultruded CFRP composite sheets with anchorage mechanisms

Experimental and numerical study on the flexural strengthening of rolled steel beams using intermediate modulus pultruded Carbon Fibre Reinforced Polymer (CFRP) composite sheets is presented in this paper. De-bonding is the commonly observed failure mode in external strengthening of steel structural elements using CFRP composite sheets. One control and seven strengthened steel beams bonded with CFRP composite sheets along with different anchorage systems such as mechanical fasteners and intermittent carbon fibre fabric composite wraps were tested up to failure. The influence of anchorage systems on load/deflection behaviour, load-carrying capacity, toughness, stiffness, failure strain, failure mode, and deflection ductility of strengthened beams were found from the test data. Finite element (FE) models of the specimens generated using FEA software ABAQUS were analysed and compared with experimental data. The test results show that steel beams with external bonding along with intermittent U-wraps have better performance in terms of load-carrying capacity, toughness, and deflection ductility. The increase in load carrying capacity was up to 19% and the maximum strain in CFRP sheet reached up to 69% of its rupture strain. Parametric studies were also conducted for strengthening steel girders to find the effect of dimensions and orientation of CFRP composites used in the strengthening schemes.

Tensile stress strain model of polyvinyl chloride/calcium carbonate (PVC/CaCO3) nanocomposite plank

This paper presents the tensile stress strain model of a recyclable polyvinyl chloride/calcium carbonate (PVC/CaCO3) thermo-formable, fire/water proof resistant, and durable composite mineral plank. The paper presents experimentally obtained material stress-strain properties in direct tension as a function of its parameters including thickness, surface texture and grain alignment. With an increase in thickness from 1 mm (0.039 in.) to 12 mm (0.47 in.) for rough surface texture and parallel grain alignment, tensile and rupture strengths decreased from 27.4 MPa (4.11 ksi) to 14 MPa (2.1 ksi) and from 14 MPa (2.1 ksi) to 6 MPa (0.9 ksi) respectively. Strains at rupture increased from 0.01 to 0.02 while the modulus of elasticity decreased from 23078 MPa (3462 ksi) to 2139 MPa (320.85 ksi). Smoothness of surface texture increased the ultimate and rupture stresses by 16% while rupture strains increased by 45% leading to a more ductile material. Grain orientation perpendicular to the load direction resulted in an 18% reduction in ultimate strength. The paper proposes models for predicting the stress strain relationship including modulus of elasticity, toughness, stress and strain in the proportional, ultimate and rupture states in terms of the material parameters. The developed models are essential for establishing code requirements and design criteria for structural members retrofitted with this type of composite.

Crashworthiness design for multi-cell circumferentially corrugated thin-walled tubes with sub-sections under multiple loading conditions

Multi-cell, multi-corner and adding edge-junctions structures are widely used approaches to enhance the crash characteristic of the thin-walled structures. In this study, the crashworthiness of twenty-one structures combining these three structures is examined under axial and oblique loading angles. The finite element models under axial loading are validated by experimental data from the literature and theoretical approach. In the theoretical approach, removing the corner elements in the inner structure from the theoretical calculation in multi-cell tubes has increased the accuracy. With the validations performed in axial loadings, it is predicted that the finite element model will be accurate also in oblique loadings. On the other hand, rupture strain has not been used in finite element models, which may cause some errors. Crashworthiness performance has improved as the cell number increases under all loading conditions except the C2 tube under 20-degree oblique loading. Also, the sub-sections added to the inner wall corners of the tubes significantly increase the energy absorption capacity. The complex proportion assessment (COPRAS) method and the technique for order of preference by similarity to ideal solution (TOPSIS) are utilized to get the tube with the best crashworthiness performance. The entropy method is used for weighting to avoid human intervention. The best tube varies depending on the weighting and selection method. Finally, the radial basis function (RBF) approximation approach and four multiobjective optimization methods are used to obtain optimum sizes of the C4O tube. The results of the optimizations show that the optimum structure does not differ depending on the optimization method, and the results are very close to each other.

Experimental Study on the Confinement of Concrete Cylinders with Large Rupture-Strain FRP Composites

Large rupture strain (LRS) fiber-reinforced polymer (FRP) composites, typically formed from polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) fibers, generally exhibit ultimate rupture strains >5%. Such fibers are particularly suited to the confinement of concrete columns on account of their LRS and sufficient elastic modulus. There are currently a limited number of studies on LRS FRP-confined concrete, particularly with high- and ultrahigh-strength concrete, so their behavior across a range of variables is still unknown. To improve this understanding, this paper systematically investigates the influence of fiber type, fiber thickness, and concrete strength on the behavior of FRP-confined concrete. To achieve this objective, the current investigation presents the results of 66 circular FRP-confined cylinders that are loaded concentrically. Three main parameters are investigated, namely, fiber type (i.e., PEN, PET, carbon, glass, and aramid), concrete strength (i.e., normal, high, and ultrahigh strength), and fiber thickness. The results show that regardless of fiber type, the stress–strain response is bilinear when the concrete is sufficiently confined. However, when there is insufficient confinement provided to the concrete core, the stress–strain response becomes trilinear. This trilinear response is more pronounced for LRS FRP-confined specimens because the confinement stiffness of the LRS FRP jacket is lower than that of a traditional FRP-confined specimen with an equivalent confinement ratio. Increasing the confining hoop stiffness (i.e., increasing FRP layers) reduces the magnitude of strength reduction after initial concrete cracking. It is also evident that as the unconfined concrete strength increases, the minimum confinement stiffness ratio necessary to prevent strength reduction after initial concrete cracking increases.

Compressive deformation behavior of ultrafine-grained Mg-3Zn-1.2Ca-0.6Zr alloy at room temperature

In this study, ultrafine-grained (UFG) Mg-3Zn-1.2Ca-0.6Zr alloy is prepared by a novel extrusion-shear (ES) process. The microstructure, twinning and dislocation evolution of UFG Mg-3Zn-1.2Ca-0.6Zr alloy under compressive deformation at room temperature are studied by electron back-scattering diffraction and transmission electron microscopy techniques. According to the results, the compressive deformation follows a sequence of the three stages in which the work hardening rate first decreases, then increases, and finally decreases, inducing the tensile {101̅2} twinning in UFG alloy. With the coordinated deformation of twinning and dislocation slip, the compressive yield strength and rupture strain of UFG alloy reach 206 MPa and 20.9%, respectively. With the increase of strain rate, the interaction between the twin and the dislocation slip promotes deformation, resulting in a continuous increase in the twin boundary fraction and dislocation density. Furthermore, the {0001} basal texture intensity first increases and then decreases, and basal poles appear separated. When the twin nucleation is saturated, the twins make almost no contribution to grain refinement and plastic deformation, and the dislocation mechanism is dominant in the later stage. As the dislocation density gradually increases, the formation of dislocation cells reduces the work hardening rate.

Seismic Performance of LRS-FRP–Concrete–Steel Tubular Double Coupling Beam

To improve the ductility and seismic performance of a double coupling beam, the authors applied a polyethylene terephthalate (PET) sheet and steel tube to form fiber-reinforced polymer (FRP)–concrete–steel double-skin tubular (DST) composite coupling beams. A low-cyclic reversed experimental program was carried out which factored in the member form, steel tube diameter, and construction methods. The results indicate that the ductility and energy dissipation performance of double coupling beams—whether wrapped with a PET-FRP sheet or surrounded by an FRP–concrete–steel DST composite system—is a substantial improvement over the traditional reinforced-concrete double coupling beam (RC-DCB). The ductility coefficient and accumulated energy dissipation of the DST-DCB members improved above 170% and 2300%, respectively. These percentages compare to the RC-DCB and are based on the rupture of a PET-FRP sheet. The results are similar to those of the large rupture strain double coupling beam (LRS-DCB). Meanwhile, the external wrapped PET-FRP sheet does not affect the initial stiffness and peak strength of the RC-DCB. Relatively, the inner steel tube will improve the initial stiffness, yielding strength, and peak strength. DST-DCB members still have considerable deformability after 85% of peak strength since the external PET-FRP sheet provided an effective constraint effect on the core concrete and the inner steel tube could bear excellent shear deformation.

Behavior and modeling of double-skin tubular columns filled by ultra-lightweight cement composites (ULCCs)

Double skin tubular columns (DSTCs) filled by ultra-lightweight cement composites (ULCCs), as primary load-bearing elements, are a practical and reasonable structural asset in lightweight civil infrastructure. This DSTC-ULCC system combines the advantages of three materials, 1) outer fiber-reinforced polymer (FRP) 1–3 ply jackets, 2) filled ULCCs, and 3) inner steel tubes to achieve lightweight, high strength and superior ductility. This article presents an experimental study on the mechanical behavior of DSTCs with FRP and ULCCs under axial compressive loading. The experiment designed a total of 26 DSTCs that were all filled with ULCCs. The key parameters were the number of FRP layers and the inner steel tube properties, (i.e., thickness and diameter of the steel tube). The test results indicate that the properties of the inner steel tube not only influences the effective FRP rupture strain ratio but also the ultimate axial strain of confined ULCCs. This calls attention to the inward buckling behavior for larger void ratios; moreover, thinner steel tubes result in more axial deformation of ULCC-filled DSTCs. In addition, ULCCs showed a much lower elastic modulus compared with normal concrete, which helped cause the change of transition stress of ULCCs in DSTCs, and FRP confinement can effectively increase the elastic length of the stress–strain curves for ULCCs. The experimental results are subsequently compared with predictions from an FRP-confined ULCC model, which led to a new ultimate strain model proposed herein for ULCC-filled DSTCs. The comparison demonstrates that the model can provide reasonably accurate predictions of the stress–strain curves of ULCCs in hollow DSTCs.

Umbilical Cord Pericytes Provide a Viable Alternative to Mesenchymal Stem Cells for Neonatal Vascular Engineering.

Reconstructive surgery of congenital heart disease (CHD) remains inadequate due to the inability of prosthetic grafts to match the somatic growth of pediatric patients. Functionalization of grafts with mesenchymal stem cells (MSCs) may provide a solution. However, MSCs represent a heterogeneous population characterized by wide diversity across different tissue sources. Here we investigated the suitability of umbilical cord pericytes (UCPs) in neonatal vascular engineering. Explant outgrowth followed by immunomagnetic sorting was used to isolate neural/glial antigen 2 (NG2)+/CD31− UCPs. Expanded NG2 UCPs showed consistent antigenic phenotype, including expression of mesenchymal and stemness markers, and high proliferation rate. They could be induced to a vascular smooth muscle cell-like phenotype after exposure to differentiation medium, as evidenced by the expression of transgelin and smooth muscle myosin heavy chain. Analysis of cell monolayers and conditioned medium revealed production of extracellular matrix proteins and the secretion of major angiocrine factors, which conferred UCPs with ability to promote endothelial cell migration and tube formation. Decellularized swine-derived grafts were functionalized using UCPs and cultured under static and dynamic flow conditions. UCPs were observed to integrate into the outer layer of the graft and modify the extracellular environment, resulting in improved elasticity and rupture strain in comparison with acellular grafts. These findings demonstrate that a homogeneous pericyte-like population can be efficiently isolated and expanded from human cords and integrated in acellular grafts currently used for repair of CHD. Functional assays suggest that NG2 UCPs may represent a viable option for neonatal tissue engineering applications.

Influence of boiling, steaming, and sous-vide on oral processing parameters of celeriac (Apium graveolens var. rapaceum)

Influence of three cooking methods (boiling, steaming, and sous-vide) and three cooking times (15, 30, and 45 min) was studied concerning oral processing of celeriac. Jointly, color difference, mechanical properties, and dynamic perception of selected sensory attributes were observed. In parallel, a triangle test was used to inspect the existence of perceptible differences between the cooking method/time combinations (treatments).Two-way ANOVA showed the existence of the main effects’ interactions for the number of chews (p = 0.024) and consumption time (p < 0.001). Very significant effects of the cooking method were found for the cycle duration (p < 0.005) and chewing rate (p < 0.001), while the other oral processing parameters were not influenced by the effects of the factors nor with their interaction. In the case of mechanical properties, a very significant interaction of the two factors was revealed for the toughness (p < 0.001), and a significant interaction for the shear force (p < 0.05). A very significant interaction (p < 0.001) was also found for weight loss. Oppositely, the interactions were not significant for the rupture stress and strain and deformability modulus, but the main effects of the cooking method and cooking time were significant. Sous-vide treated products needed twice more chews and time for consumption and had the highest sample compression and shearing forces compared to the boiled and steamed samples while boiling and steaming produced similar products concerning the oral processing and mechanical properties. Sous-vide celeriac also maintained the dominance of perceived firmness regardless of the cooking time. Otherwise, the firmness of boiled and steamed celeriac decreased as cooking prolonged. The same trend of decreasing the dominance rate with longer cooking time is observable for the other sensory attributes. The number of chews, consumption time, and eating rate were strongly correlated to mechanical properties and weight loss. Triangle test revealed the existence of differences for all combinations of treatments within the cooking method, except between celeriac boiled for 30 and 45 min and sous-vide for 15 and 30 min.

Plastic temperature-dependent constitutive modeling of pure aluminum diaphragms at large strains by using bulge test

A plastic temperature-dependent constitutive model is developed for 0.05 mm thickness pure aluminum diaphragms at large strains by using bulge test method. Rupture strain of the material is recorded below two percent according to tensile tests. In order to achieve the material behavior at larger strains, an own bulge test apparatus is used to extract equi-biaxial stress–strain curves at different temperatures, i.e. from room to 150 °C. Effective stress–strain behavior is then computed via a transformation scheme using the plastic work definition as well as the room temperature uniaxial stress–strain curve. It is illustrated that the Johnson–Cook constitutive model is not able to capture this stress–strain behavior. Thus, a modified Johnson–Cook model is developed in which the strain hardening is assumed to be temperature-dependent accompanying by a novel thermal softening relation. Using the Least-square method as well as the Ant colony optimization algorithm, the material parameters of the both models are calculated. It is depicted that the new model follows the material behavior more precisely than the Johnson–Cook model. The new model is then numerically implemented into finite element software via a user subroutine. In order to compare the accuracy of both models in capturing the hot bi-axial deformation of pure aluminum, an experiment is performed and numerically simulated.