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Cell–cell adhesions are often subjected to mechanical strains of different rates and magnitudes in normal tissue function. However, the rate-dependent mechanical behavior of individual cell–cell adhesions has not been fully characterized due to the lack of proper experimental techniques and therefore remains elusive. This is particularly true under large strain conditions, which may potentially lead to cell–cell adhesion dissociation and ultimately tissue fracture. In this study, we designed and fabricated a single-cell adhesion micro tensile tester (SCAμTT) using two-photon polymerization and performed displacement-controlled tensile tests of individual pairs of adherent epithelial cells with a mature cell–cell adhesion. Straining the cytoskeleton–cell adhesion complex system reveals a passive shear-thinning viscoelastic behavior and a rate-dependent active stress-relaxation mechanism mediated by cytoskeleton growth. Under low strain rates, stress relaxation mediated by the cytoskeleton can effectively relax junctional stress buildup and prevent adhesion bond rupture. Cadherin bond dissociation also exhibits rate-dependent strengthening, in which increased strain rate results in elevated stress levels at which cadherin bonds fail. This bond dissociation becomes a synchronized catastrophic event that leads to junction fracture at high strain rates. Even at high strain rates, a single cell–cell junction displays a remarkable tensile strength to sustain a strain as much as 200% before complete junction rupture. Collectively, the platform and the biophysical understandings in this study are expected to build a foundation for the mechanistic investigation of the adaptive viscoelasticity of the cell–cell junction.

In this study, phosphogypsum-based composite cementitious materials (PGCMs) were prepared by adding fixed proportions of additives to calcined phosphogypsum (PG). Samples with dimensions of 40 × 40 × 80 mm and 150 × 150 × 300 mm were used to study the effect of the PG calcination time on the PGCM compressive strength, stress–strain relationship, and failure mode and its mechanism. The test results indicated that the PGCM compressive strength gradually increased as the calcination time increased. When the PG calcination time was 180 min, the compressive strengths of the smaller and larger samples increased by 3 and 3.6 times, respectively, compared with the strengths at a calcination time of 20 min. The main reason for the strength increase was the formation of ettringite and hydrated calcium sulfate dihydrate in the PGCM gel system. Additionally, the PGCM compressive strength was significantly related to the sample size, and its reduction coefficient was between 0.60 and 0.69 at different PG calcination times. As the PG calcination time increased, the peak stress of the PGCM stress–strain curve and the corresponding axial strain increased gradually; moreover, brittle failure became more evident.

Freeze-thaw damage gradients lead to non-uniform degradation of concrete mechanical properties at different depths. A study was conducted on the stress-strain relationship of stressed concrete with focus on the freeze-thaw damage gradient. The effects of relative freeze-thaw depths, number of freeze-thaw cycles (FTCs) and stress ratios on the stress-strain curves of concrete were analyzed. The test results demonstrated that freeze-thaw damage was more severe in the surface layers of concrete than in the deeper layers. The relative peak stress and strain of concrete degraded bilinearly with increasing depth. The stress-strain relationship of stressed concrete under FTC was established, and it was found to agree with the experimental results.

The recycled powder (RP) from construction wastes can be used to partially replace cement in the preparation of reactive powder concrete. In this paper, reactive powder concrete mixtures with RP partially replacing cement, and natural sand instead of quartz, are developed. Standard curing is used, instead of steam curing that is normally requested by standard for reactive powder concrete. The influences of RP replacement ratio (0, 10%, 20%, 30%), silica fume proportion (10%, 15%, 20%), and steel fiber proportion (0, 1%, 2%) are investigated. The effects of RP, silica fume, and steel fiber proportion on compressive strength, elastic modulus, and relative absorption energy are analyzed, and theoretical models for compressive strength, elastic modulus, and relative absorption energy are established. A constitutive model for the uniaxial compressive stress-strain relationship of reactive powder concrete with RP is developed. With the increase of RP replacement ratio from 0% to 30%, the compressive strength decreases by 42% and elastic modulus decreases by 24%.

Compacted graphite iron (CGI) is considered to be an ideal diesel engine material with excellent physical and mechanical properties, which meet the requirements of energy conservation and emission reduction. However, knowledge of the microstructure evolution of CGI and its impact on flow stress remains limited. In this study, a new modeling approach for the stress–strain relationship is proposed by considering the strain hardening effect and stored energy caused by the microstructure evolution of CGI. The effects of strain, strain rate, and deformation temperature on the microstructure of CGI during compression deformation are examined, including the evolution of graphite morphology and the microstructure of the pearlite matrix. The roundness and fractal dimension of graphite particles under different deformation conditions are measured. Combined with finite element simulation models, the influence of graphite particles on the flow stress of CGI is determined. The distributions of grain boundary and geometrically necessary dislocations (GNDs) density in the pearlite matrix of CGI under different strains, strain rates, and deformation temperatures are analyzed by electron backscatter diffraction technology, and the stored energy under each deformation condition is calculated. Results show that the proportion and amount of low-angle grain boundaries and the average GNDs density increase with the increase of strain and strain rate and decreased first and then increased with an increase in deformation temperature. The increase in strain and strain rate and the decrease in deformation temperature contribute to the accumulation of stored energy, which show similar variation trends to those of GNDs density. The parameters in the stress–strain relationship model are solved according to the stored energy under different deformation conditions. The consistency between the predicted results from the proposed stress–strain relationship and the experimental results shows that the evolution of stored energy can accurately predict the stress–strain relationship of CGI.

Self-compacting concrete (SCC) is special high-performance concrete type with a high flowability that can fill formwork without any mechanical vibration. SCC is being used in high-rise buildings and industrial structures which may be subjected to high temperatures during operation or in case of accidental fire. The proper understanding of the effects of elevated temperatures on the properties of SCC is essential. In this study, constitutive relationships are developed for normal and high-strength self-compacting concrete (NSCC and HSCC) subjected to fire to provide efficient modeling and specify the fire-performance criteria for concrete structures. They are developed for unconfined NSCC and HSCC specimens that include compressive and tensile strengths, elastic modulus, strain at peak stress as well as compressive stress–strain relationships at elevated temperatures. The proposed relationships at elevated temperature are compared with experimental results. These results are used to establish more accurate and general compressive stress–strain relationships. Further experimental results for tension and the other main parameters at elevated temperature are needed in order to establish well-founded models and to improve the proposed constitutive relationships, which are general, rational, and fit well with the experimental results.

This paper presents a new constitutive model that simulates the mechanical behavior of methane hydrate‐bearing soil based on the concept of critical state soil mechanics, referred to as the “Methane Hydrate Critical State (MHCS) model”. Methane hydrate‐bearing soil is, under certain geological conditions, known to exhibit greater stiffness, strength and dilatancy, which are often observed in dense soils and also in bonded soils such as cemented soil and unsaturated soil. Those soils tend to show greater resistance to compressive deformation but the tendency disappears when the soil is excessively compressed or the bonds are destroyed due to shearing. The proposed model represents these features by introducing five extra model parameters to the conventional critical state model. It is found that, for an accurate prediction of ground settlement, volumetric yielding plays an important role when hydrate soil undergoes a significant change in effective stresses and hydrate saturation, which are expected during depressurization for methane gas recovery. Key Points A new constitutive model for hydrate‐bearing soil was presented The model incorporates volumetric yielding and degradation of hyrate effects The model also considers stress relaxation due to hydrate dissociation

To date, many models of fiber reinforced polymer (FRP)-confined concrete have been developed to predict the axial stress-strain relationship of concrete circular column (or concrete cylinder) with strain-hardening-curve. This paper focuses on the prediction level of the selected designed-oriented models of FRP-confined concrete circular columns, especially for the prediction of ultimate condition of confined cylinder (i.e., compressive strength f’ cc and ultimate strain ε cc ) and the slope of the second portion, E 2 , of stress-strain curve as well as the transitional point. The comparison between the collected models and the experimental data shows that some models can effectively capture properties of axial stress-strain relationships of concrete cylinders wrapped with conventional type FRP composites.

A combined support scheme was proposed to address the issue of large deformation in the deep soft rock roadway at the Tangkou coal mine in Shanxi Province, China. This support scheme includes high constant resistance, elongation, and prestressed negative Poisson's ratio (NPR) bolts as the core element, along with metal mesh, shotcrete, cable, and bottom angle grouting bolt. A numerical simulation test using Flac3D was conducted to verify the feasibility of the NPR bolt-anchored soft rock roadway. In addition, a constitutive model for a rock mass supported by NPR bolts was established. The model is based on a parallel model of a generalised Kelvin body and elastic–viscous sliding body, which was used to reveal the mechanical behaviour of an NPR bolt-anchored rock mass. The results showed that the stress–strain relationship of the NPR bolt-anchored rock mass was obtained as a piecewise function consisting of the initial, slipping, and sticking stages. The stress and strain of the NPR bolt-anchored rock mass exhibit distinct patterns under different stress conditions. Specifically, when the stress remains constant, the strain of the NPR bolt-anchored rock mass increases continuously while the stress decreases in a step-like manner. On the other hand, when the stress increases linearly with time, the strain of the anchored rock mass increases linearly, while the stress of the anchorage rock mass increases slowly in a sawtooth pattern. Furthermore, a field support test fully confirmed the effective control of the NPR bolt support on the large deformations of soft rock roadways. These findings can guide further theoretical research, engineering design, and field applications of NPR bolt-anchored rock masses.HighlightsA new combined support scheme is proposed using the NPR bolt as the core.The mechanical behaviour of an NPR bolt-anchored rock mass is revealed.Both numerical simulations and field tests demonstrated that the combined support scheme effectively controls the large deformations of soft rock roadways.

Grade 14.9 superhigh-strength bolts (SHTBs) are a type of high-strength steel bolt with a nominal tensile strength of 1400 MPa, which is significantly higher than the commonly used Grade 10.9 high-strength bolt (HSB), which has a nominal tensile strength of 1000 MPa. The use of an SHTB can reduce the number of bolts required in connections or joints, leading to material savings and improved construction efficiency. However, like HSB, the mechanical properties of an SHTB can be significantly degraded at high temperatures, though the extent of this reduction may differ. In this study, the authors designed and conducted experiments on SHTBs under elevated temperatures including both vibration and tensile coupon tests. Based on the test data, the stress–strain curves and key mechanical properties such as the Young’s modulus, yield stress, ultimate stress, ultimate strain, percentage elongation, cross-sectional area reduction, and failure strain were obtained and analyzed for various high-temperature conditions. Furthermore, a new three-stage model was proposed to describe the stress–strain relationship of SHTBs under fire conditions. Additionally, empirical formulae were developed to predict the mechanical properties of SHTBs under elevated temperatures, providing valuable insights for engineering applications and fire safety design.