Stress-strain Dependence Research Articles

High-temperature plastic deformation of langle 110rangle-oriented BaTiO3 single crystals

BaTiO3 single crystals were deformed in compression along the langle 110rangle crystal axis to study the plastic deformability and dislocation structures at high temperatures under different loading conditions. The yield strength is determined from stress–strain curves under strain rate control, load control, strain rate cycling tests, and under step-wise loading conditions to elucidate the impact of measurement approach in yield strength behavior. A comparison between the chosen methods based on stress-dependent strain rate plots indicates that load control measurements are a suitable alternative to the commonly used strain rate-control experiments in metals. This allows avoiding overloading and providing an estimate of the overall achievable strain rates in a ceramic. Activation energies and activation volumes in the temperature range of 1100–1170 °C indicate a similar mechanical deformation behavior to SrTiO3.Graphical abstract

EXPERIMENTAL AND NUMERICAL RESEARCH OF JOINTED ROCK MASS ANISOTROPY IN A THREE-DIMENSIONAL STRESS FIELD

Joints often have a significant influence on material characteristics. The discontinuities’ coalescence mechanism and complex jointed rock mass structure as a composite need to be further explored. In this study, compression and shear tests were carried out on a jointed rock mass. The purpose of the jointed rock mass behaviour study was to determine the deformation-strength dependencies and to determine the parameters for a quantitative assessment of the joints’ influence on mechanical characteristics. The results show that compression strength depends on the materials’ structure, and there is a detailed description of the joints’ orientation influence on stress-strain dependencies during compression experiments. The numerical method used in this study could be used for the modelling of composite materials and their properties.

Effect of Strain Rate on Mechanical Behavior and Microstructure Evolution of Ti-Based T110 Alloy

Recently developed thermally hardenable medium-level alloyed titanium alloy T110 was studied from the viewpoint of microstructure influence on the mechanical behavior under quasi-static and high-strain rate deformation. The globular microstructures of two types differing in aspect ratio of α-globules were formed under thermomechanical processing conditions with different reductions (εtotal = 2, and 3) and final annealing at 850 °C, 3 h. The thermally hardened state was formed by conventional solid-solution treatment at a temperature of two-phase α+β field (880 °C, 45 min), water quenching, and final aging (550 °C, 5 h). Stress–strain dependencies were estimated on tension with strain rates varied from 8·10−4 to 4·10−2 s−1, as well as compression with a strain rate of 10−3 s−1 (quasi-static) and under high-strain rates varied from 870 s−1 to 3520 s−1; the deformation with high-strain rates has been achieved using split Hopkinson pressure bar (SHPB) technique. The tested material was also assessed using strain energy (SE) parameter. A parallel study of the microstructure and crystallographic texture formed during testing allowed to propose a reliable deformation and fracture mechanisms, depending on the stress state (tension, compression) and strain rate. A special role of the initial microstructure is noted, which determines the plasticity of the tested alloy, the sites of pore nucleation, features of crack growth, as well as the localization of deformation, which is determined by the mode and rate of loading. It is established and explained why the best balance of strength and ductility, and thus, the highest SE values in the all tests carried out were ensured by the alloy in the state with a more uniform microstructure of globular morphology (after the rolling with reduction εtotal =3), which, in turn, provided general superiority over the widely used Ti-6Al-4V alloy.

Регулирование деформационных свойств бумаги путем варьирования степени ее анизотропии

Mechanical properties are crucial in assessing the paper quality. Deformation and strength properties of paper are determined by the strength and stiffness of the interfiber and intermolecular hydrogen bonds. The contribution ratio of interfiber and intermolecular hydrogen bonds to the strength of paper can be changed by adjusting the degree of its anisotropy. The article presents the results on a study of the deformation properties of laboratory anisotropic paper samples from kraft bleached softwood pulp with a beating degree of 30 °SR. The samples had basic weight of 90 g/m2 and the degree of stiffness anisotropy TSIMD/CD of 1.75–4.08. They were made by using Techpap SAS automatic dynamic handsheet former (Grenoble, France), with varying forming parameters – diameter of the nozzle, motion speed of the forming wire, and injecting speed of pulp. Deformation properties were determined by tensile test and processing of the stress-strain dependence (σ−ε). The outcomes have shown that, an increase of the fiber orientation degree in paper structure by changing the forming parameters caused a change in the nature of the paper deformation under tension. Increasing the fiber orientation degree in the structure of paper made it possible to increase the strength by 55 %, tensile stiffness by 63 % in the machine direction, while reducing the extensibility by 10 %. In the cross direction, it was possible to decrease tensile stiffness by 33 %, strength by 55 %, and increase the extensibility by 5 %. Anisotropy of tensile strength was 1.73–6.00. The greatest effect was obtained for the elasticity modulus in the pre-failure zone E2 (2.8–38.6). It means that, fiber orientation had a key importance when large deformations in the samples took place. The established quantitative regularities allowed optimizing the values of the deformation and strength properties of paper, and their ratio in the machine direction and cross direction due to the variation of the forming parameters. For citation: Rech D., Potasheva A.N., Kazakov Ya.V. Regulating the Deformation Properties of Paper by Varying the Degree of Its Anisotropy. Lesnoy Zhurnal [Russian Forestry Journal], 2021, no. 5, pp. 174–184. DOI: 10.37482/0536-1036-2021-5-174-184

Numerical and experimental study of premolars strength properties with pin zirconium inserts at different load angles

To study the physical and mechanical properties of zirconium dioxide post stump structures made by computer modeling and milling (CAD/CAM), the stress-strain state and their strength characteristics, numerical and experimental studies were carried out. The test specimens were a system consisting of previously extracted premolar teeth with an absent anatomical crown, a prepared root canal and a post stump inlay fixed in it, an artificial zirconium dioxide crown fixed on the pin insert, and a part of the root. The prepared teeth for the placement of the posts were scanned in the dental laboratory, after which the pin insert of zirconium dioxide were milled. Investigated 2 groups of samples: specimens of the first group were processed in a sandblasting unit; the specimens of the second were not subjected to any mechanical and temperature treatment. To test the compressive strength of the specimens, we used an Instron 5982 universal floor electromechanical testing machine in static mode under conditions of a single increasing load. The specimens were tested with vertical load and at an angle of 15° with and without sandblasting with aluminum oxide powder. The value of the force for each variant was obtained, at which the samples were destroyed. Also, a numerical study was carried out by the finite element method on the developed mathematical model of the stress-strain state dependence of the sample on the applied functional load acting vertically on the occlusal surface of the tooth and at an angle of 15°. The problem was considered in an axisymmetric setting. The computer model included a premolar tooth with a crown, a root and a pin insert, taking into account the mechanical properties of the materials of each of these elements. With an increase in the angle of the load acting on the crown from 0° to 15°, the destruction of the sample occurs at its lower values, by about 10–12 %; the maximum values of stresses were determined in the upper part of the crown and the neck of the tooth (connection of the crown to the root) – in the experiments, destruction occurred precisely in these places. Comparison of the experimental averaged values of the loads at which the destruction of the samples occurs with the numerical values showed their good agreement.

Strength and deformability of fibrin clots: Biomechanics, thermodynamics, and mechanisms of rupture

Fibrin is the major determinant of the mechanical stability and integrity of blood clots and thrombi. To explore the rupture of blood clots, emulating thrombus breakage, we stretched fibrin gels with single-edge cracks of varying size. Ultrastructural alterations of the fibrin network correlated with three regimes of stress vs. strain profiles: the weakly non-linear regime due to alignment of fibrin fibers; linear regime owing to further alignment and stretching of fibers; and the rupture regime for large deformations reaching the critical strain and stress, at which irreversible breakage of fibers ahead of the crack tip occurs. To interpret the stress-strain curves, we developed a new Fluctuating Spring model, which maps the fibrin alignment at the characteristic strain, network stretching with the Young modulus, and simultaneous cooperative rupture of coupled fibrin fibers into a theoretical framework to obtain the closed-form expressions for the strain-dependent stress profiles. Cracks render network rupture stochastic, and the free energy change for fiber deformation and rupture decreases with the crack length, making network rupture more spontaneous. By contrast, mechanical cooperativity due to the presence of inter-fiber contacts strengthens fibrin networks. The results obtained provide a fundamental understanding of blood clot breakage that underlies thrombotic embolization. Statement of significanceFibrin, a naturally occurring biomaterial, is the major determinant of mechanical stability and integrity of blood clots and obstructive thrombi. We tested mechanically fibrin gels with single-edge cracks and followed ultrastructural alterations of the fibrin network. Rupture of fibrin gel involves initial alignment and elastic stretching of fibers followed by their eventual rupture for deformations reaching the critical level. To interpret the stress-strain curves, we developed Fluctuating Spring model, which showed that cracks render rupture of fibrin networks more spontaneous; yet, coupled fibrin fibers reinforce cracked fibrin networks. The results obtained provide fundamental understanding of blood clot breakage that underlies thrombotic embolization. Fluctuating Spring model can be applied to other protein networks with cracks and to interpret the stress-strain profiles.

Temperature Dependent Stress–Strain Behavior and Martensite Stabilization in Magnetic Shape Memory Ni51.1Fe16.4Ga26.3Co6.2 Single Crystal

The superelastic properties and stress-induced martensite (SIM) stabilization have been studied in a shape memory Ni51.1Fe16.4Ga26.3Co6.2 single crystal. The single crystal, characterized by a thermally induced forward martensitic transformation temperature around 56 °C in the initial state, has been submitted to compression mechanical testing at different temperatures well above, near and below the martensitic transformation (MT). After each mechanical test, the characteristic MT temperatures and the transformation enthalpy have been monitored by means of differential scanning calorimetry. At temperatures below MT, the stress–strain (σ–ε) curves show a large strain, around 6.0%, resulting from the detwinning process in the martensitic microstructure, which remains accumulated after unloading in the detwinned state of the sample as a typical behavior of the shape memory alloys (SMAs). After just two “σ–ε + heating” cycles the accumulation of strain was not observed any more indicating the formation of a two-way shape memory effect which consists in a spontaneous recovery of the aforementioned detwinned state of the sample during its cooling across the forward MT. Whereas the thermally induced shape recovery in conventional SMAs occurs at the fixed value of the reverse MT temperature, the heating DSC curves of the mechanically deformed martensite in the present work show a burst-like calorimetric peak at the reverse MT arising at temperatures essentially higher than the thermally activated one. This behavior is the result of the SIM stabilization effect. After a short thermal aging in the stress-free state, this effect almost disappears, showing a slight impact on the MT characteristic temperatures and the enthalpy. At temperatures higher than the transformation one, the SIM is not stabilized, as the mechanically induced martensite fully retransforms into austenite after the unloading. From the σ–ε curves, the critical stress, σc, as well as the values of Young’s moduli of martensite and austenite are determined showing linear dependences on the temperature with a slope of 3.6 MPa/°C.

Increased MMP-9 levels with strain-dependent stress resilience and tunnel handling in mice

Increased perineuronal net (PNN) deposition has been observed in association with corticosteroid administration and stress in rodent models of depression. PNNs are a specialized form of extracellular matrix (ECM) that may enhance GABA-mediated inhibitory neurotransmission to potentially restrict the excitation and plasticity of pyramidal glutamatergic neurons. In contrast, antidepressant administration increases levels of the PNN-degrading enzyme matrix metalloproteinase-9 (MMP-9), which enhances glutamatergic plasticity and neurotransmission. In the present study, we compare pro-MMP-9 levels and measures of stress in females from two mouse strains, C57BL/6 J and BALB/cJ, in the presence or absence of tail grasping versus tunnel-associated cage transfers. Prior work suggests that C57BL/6 J mice show relatively enhanced neuroplasticity and stress resilience, while BALB/c mice demonstrate enhanced susceptibility to adverse effects of stress. Herein we observe that as compared to the C57BL/6 J strain, BALB/c mice demonstrate a higher level of baseline anxiety as determined by elevated plus maze (EPM) testing. Moreover, as determined by open field testing, anxiety is differentially reduced in BALB/c mice by a choice-driven tunnel-entry cage transfer technique. Additionally, as compared to tail-handled C57BL/6 J mice, tail-handled BALB/c mice have reduced brain levels of pro-MMP-9 and increased levels of its endogenous inhibitor, tissue inhibitor of metalloproteinase-1 (TIMP-1); however, tunnel-associated cage transfer increases pro-MMP-9 levels in BALB/c mice. BALB/c mice also show increases in Western blot immunoreactive bands for brevican, a constituent of PNNs. Together, these data support the possibility that MMP-9, an effector of PNN remodeling, contributes to the phenotype of strain and handling-associated differences in behavior.

A rate-dependent cohesive zone model with the effects of interfacial viscoelasticity and progressive damage

A generalized rate-dependent cohesive zone model for describing the interfacial viscoelasticity and progressive damage of mode I fracture is presented. The proposed model has efficiently extended the traditional bi-linear cohesive traction-separation law to remove the assumptions that some of the rate-dependent parameters such as elastic stiffness, initial separation and strength, critical separation are constant at different loading speeds. Furthermore, the rate-dependency of the damage evolution, which is observed in experiments but largely neglected in the previous models, is established to describe the rate-dependent fracture process linked with the generalized traction-separation law, and an equivalent generalized Maxwell model (GMM), based on the Kohlrausch-William-Watts function with significant fewer material parameters required as input, is proposed to describe the time and history dependent stress–strain relationship of the viscoelastic interface material. The proposed model is validated by the simulations of the DCB tests with both the SBR/NR rubber interface and Polyurethane interface.

Superelastic behavior of single crystalline Ni48Fe20Co5Ga27 micro-pillars near austenite–martensite critical point

Micro-pillars oriented in austenite along [100], [110], and [111] crystallographic directions were fabricated on the corresponding edges of a single crystalline plate of the Ni48Fe20Co5Ga27 magnetic shape memory alloy exhibiting martensitic transformation (MT) at 150 K. Superelastic behavior of pillars, due to micro-compression-induced MT, was investigated at different temperatures from 298 K to 373 K. At room temperature, Young’s moduli of the [100], [110], and [111] pillars in austenite are equal to 5.3 GPa, 7.9 GPa, and 9.9 GPa, respectively, resulting in the linear dependences of the elastic strain reaching up to the record-breaking value of 10%. On increasing temperature, the stress–strain dependencies exhibit changes that are interpreted in terms of the critical behavior on approaching to the end points on the martensite–austenite stress–temperature phase diagrams.

The development of the method for identifying the hardening curves of materials based on the results of torsion tests of notched specimens

The article is devoted to studying the rheological properties of metals and alloys in a cold state. The method is proposed to identify the hardening curve of a material based on torsion tests of round specimens with a notch. Determining the hardening curve is based on measuring the coordinates of points on the surface of the specimen after testing and determining the corresponding value of the torque. Based on these values the coefficients in an equation for the stress-strain dependence can be determined by minimizing the derived functional. The paper proposes the algorithm for the numerical implementation of the new identification method. The results of the computer simulation confirmed its effectiveness.

Nonlinearity of the stress-strain dependence of quasi-isotropic CFRP laminate under re-static loading

As part of the task of studying the degradation of material properties under re-static loading of a quasi-isotropic CFRP laminate the nonlinearity of the stress-strain dependence in the areas of active deformation is proved. The optimal curve approximating the experimental data from the point of view of the problem is chosen. The change in the derivatives of this curve can be use σ to assess the degradation of the material properties during re-loading.

Stabilisation effect of strain hysteresis loop for steel 45

The adaptability of steel 45 to low-cycle deformation from 100 to 1000 cycles at different constant strain amplitudes, characterised by the effect of plastic-strain stabilisation, is considered. In this study, the proposed structural–temporal model of cyclic deformation simultaneously predicted the stress-strain dependence and the effect of plastic-strain stabilisation based on hysteresis width. Experiments show that range of cycles for stable plastic deformation decreases with an increase in the strain amplitude and strain rate. The proposed model takes into account deformation history experimental data of low-cycle deformation of steel 45 and the presence of an established stabilisation effect.

Selective laser melting of iron: Multiscale characterization of mechanical properties

The complex study of the mechanical properties of pure iron produced by selective laser melting (SLM) revealed enhanced values of the yield stress and ultimate tensile strength as compared to the material produced in a classic way. These values result from high dislocation density, presence of interstitial carbon and small precipitates. In-situ tensile experiments revealed that the basic mechanism of plastic deformation in this material, the structure of which was described in detail previously [Mater. Charact. 154 (2019) 222], is the emission of dislocations from dislocation walls in the material. From the yield drop at the stress-strain dependence, the effective binding energy of carbon to dislocations is estimated. SLM iron also exhibits anisotropy of nanohardness showing maxima for orientations in the middle of the orientation triangle but also at {100} and {110} corners. This anisotropy suggests that the deformation is affected by the splitting of ½⟨111⟩ dislocations on {110} planes into partials on {112} planes.

Temperature relaxation model of plasticity for metals under dynamic loading

Temperature-time effects on metals based on the relaxation model of plasticity have been evaluated. The plastic deformation of 7xxx and 2xxx aluminium alloys and EUROFER97 steel in a strain rate range from 0.001 to 4200 s−1 and a temperature range from −100 to 700 °C was analysed to determine the structural and temporal characteristics of the material, independent of loading history. Expressions of the static yield stress and the characteristic time as a function of temperature are formulated based on the “temperature multiplier” of the Johnson-Cook model (Johnson and Cook, 1985), which is obtained for the case of static loading and zero plastic strain. It is shown that the expanded relaxation model of plasticity is effectively capable to predict material responses of metals in wide ranges of strain rates and temperatures with a constant characteristic relaxation time. Based on theoretical stress-strain dependence, calculated by the relaxation model of plasticity, estimations of the ductile-brittle transition temperature of 2519A aluminium alloy at strain rates of the order 103 s−1 are given.

Experimental investigation of temperature and loading rate effects on the initial shear stiffness of polymeric interlayers

There are many examples of glass load bearing structures used in a contemporary architecture, such as panes, balustrades, and even stairs. For safety reasons, these structural elements are made of laminated glass which is a composition of glass plies bonded with polymeric interlayer. The distribution of stress in a perpendicularly loaded laminated glass panel depends on the shear stiffness of the used interlayer. There are various interlayers for laminated glass applications available on the market with wide variety of shear stiffness. To correctly evaluate the shear coupling provided by the interlayer, great research efforts have been made followed by appropriate national Standards and Codes for laminated glass in bending in recent years. Polymeric interlayers are viscoelastic materials and their stiffness is time and temperature dependent, which makes the reliable design of laminated glass panel in bending rather complicated. This paper is focused on experimental investigation of six polymeric interlayers (Trosifol® BG R20; Trosifol® Extra Strong; Evalam® 80/120; Evasafe®; SentryGlas® 5000; Krystalflex® PE399) loaded in displacement-controlled shear test in various temperatures and loading rates. The experiments showed nonlinear stress–strain dependence and confirmed the viscoelastic behaviour of presented interlayers. In addition, the values of their initial shear stiffness are listed and failure modes of testing specimens are presented. Results obtained in this study can be used for the estimation of the rate of glass plies interaction in short-term loaded laminated glass structures. All experiments were performed in Klokner Institute CTU.

Dynamic necking of a near α titanium alloy at high strain rates: Experiments and modelling

The tensile behaviour of near α Ti3Al2.5 V alloy, conceived for applications in aerospace and automotive engineering, is characterized from quasi-static to high strain rates. The material is found to present noticeable strain rate sensitivity. The dynamic true strain rate in the necking cross-section reaches values up to ten times higher than the nominal strain rate. It is also observed that beyond necking the dynamic true stress-strain curves present limited rate dependence. The experimental results at different strain rates are used to determine a suitable constitutive model for finite element simulations of the dynamic tensile tests. The model predicts the experimentally macroscopic force-time response, true stress-strain response and effective strain rate evolution with good agreement.

Dynamic Necking of a Near α Titanium alloy at High Strain Rates: Experiments and Modelling

The tensile behaviour of near α Ti3Al2.5V alloy, conceived for applications in aerospace and automotive engineering, is characterized from quasi-static to high strain rates. The material presents noticeable strain rate sensitivity. The dynamic true strain rate in the necking cross-section reaches values up to one order of magnitude higher than the nominal strain rate. It is also observed that beyond necking the true stress-strain curves present limited rate dependence in the dynamic loading regime. The experimental results at various strain rates and temperatures are used to determine the material parameters of a suitable constitutive model for finite element simulations of the dynamic tensile tests. The model predicts the experimentally macroscopic force-time response, true stress-strain response and effective strain rate evolution with good agreement.

A novel model to predict the stiffness and strength of unidirectional glass/epoxy composites at different strain rates

In the present research, a novel rate-dependent micromechanical model was presented to predict the stiffness and strength of unidirectional glass/epoxy composites. To predict the strain-rate dependent stress–strain behavior of glass fibers, using the Maxwell model with the aid of semi-empirical relations, a new viscoelastic constitutive model was proposed. Moreover, to predict the strain-rate dependent ultimate strength of brittle glass fibers, the elasto-plastic strain-rate dependent Cowper-Symonds material model was simplified by deleting the plastic terms. The strain-rate dependent mechanical properties of the polymer were also investigated by using the modified Goldberg model. Then, by modifying the Mori-Tanaka micromechanical model, a rate dependent micromechanical model was developed to predict the effective elastic properties (stiffness and strength) of unidirectional fibrous composites at arbitrary strain rates. The present model was called the strain-rate dependent Mori-Tanaka micromechanical model. As inputs, the present model just needs the viscoelastic and viscoplastic properties of fibers and polymer. Therefore, the present model reduces the necessary experimental data to predict the rate-dependent mechanical properties of unidirectional composites. For verification of the present model, the results were compared with experimental data and very good consistency in predicting the rate-dependent behavior of unidirectional composites was observed.

Analytical description of stress-strain dependence for segmented polyurethane ureas swollen in physically aggressive media

The article is devoted to the problem of analytical description of the strain behavior of elastomers under various conditions. It summarizes experimental data on the stress versus strain dependences of polyurethane urea elastomers swollen in two plasticizers. These data can be adequately described using the approach taking into account relaxation properties of elastomers and non-relaxation ones. All factors affecting the strain behavior of investigated elastomers are considered.