The mechanical characteristics of salt rock are investigated using uniaxial compression tests and creep tests in a salt diapir located in the south of Iran. To investigate how the microstructure ...evolution of salt rock due to creep test affects the stress-strain behavior, the crept samples were again tested at a constant displacement rate. The test results showed that the axial peak stress, axial peak strain, and modulus of elasticity gradually increase with increasing strain rate. The stress-strain curves were typical for a ductile material characterized by moderate strain hardening. The creep strain and creep rate increased with increasing axial stress. The Burgers viscoelastic creep model agreed quite well with the experimental creep data. The microstructure observations indicated that grain-boundary cracking and grain boundary sliding were the dominant deformation mechanisms. Under the uniaxial compression test, the crept samples showed a slightly higher modulus of elasticity compared to the intact salt samples. Finally, it seems that free dislocations increased during the creep test led to strain hardening of salt samples through the uniaxial compression test.
The strain glassy phase is produced by doping a small percentage of impurity in a martensitic alloy. Its ground state is conceived to consist of martensitic nanodomains spatially separated from each ...other by a defect phase. The present study, by probing the local structure around the Ni and Ti in martensitic and strain glassy compositions of Ni50+x Ti50−x, identifies the defect phase that is responsible for inhibiting the long range ordering of the elastic strain vector leading to the formation of the strain glassy phase.
Chronic lower airway infection with
is a major contributor to morbidity and mortality in individuals suffering from the genetic disease cystic fibrosis (CF). Whereas it was long presumed that each ...patient independently acquired unique strains of
present in their living environment, multiple studies have since demonstrated that shared strains of
exist among individuals with CF. Many of these shared strains, often referred to as clonal or epidemic strains, can be transmitted from one CF individual to another, potentially reaching epidemic status. Numerous epidemic
strains have been described from different parts of the world and are often associated with an antibiotic-resistant phenotype. Importantly, infection with these strains often portends a worse prognosis than for infection with nonclonal strains, including an increased pulmonary exacerbation rate, exaggerated lung function decline, and progression to end-stage lung disease. This review describes the global epidemiology of clonal
strains in CF and summarizes the current literature regarding the underlying biology and clinical impact of globally important CF clones. Mechanisms associated with patient-to-patient transmission are discussed, and best-evidence practices to prevent infections are highlighted. Preventing new infections with epidemic
strains is of paramount importance in mitigating CF disease progression.
There is a wide variety of stainless steel alloys, but all are characterized by a rounded stress–strain response with no sharply defined yield point. This behaviour can be represented analytically by ...different material models, the most popular of which are based on the Ramberg–Osgood formulations or extensions thereof. The degree of roundedness, the level of strain hardening, the strain at ultimate stress and the ductility at fracture of the material all vary between grades, and need to be suitably captured for an accurate representation of the material to be achieved. The aim of the present study is to provide values and predictive expressions for the key parameters in existing stainless steel material models based on the analysis of a comprehensive experimental database. The database comprises experimental stress–strain curves collected from the literature, supplemented by some tensile tests on austenitic, ferritic and duplex stainless steel coupons conducted herein. It covers a range of stainless steel alloys, annealed and cold-worked material, and data from the rolling and transverse directions. In total, more than 600 measured stress–strain curves have been collected from 15 international research groups. Each curve from the database has been analysed in order to obtain the key material parameters through a curve fitting process based on least squares adjustment techniques. These parameter values have been compared to those calculated from existing predictive models, the accuracy of which could therefore be evaluated. Revised expressions providing more accurate parameter predictions have been proposed where necessary. Finally, a second set of results, containing material parameters reported directly by others, with information of more than 400 specimens, has also been collected from the literature. Although these experimental results were not accessible as measured raw data, they enabled further confirmation of the suitability of the proposed equations.
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•Tensile tests on austenitic, ferritic and duplex stainless steel coupons are presented.•A database of over 600 stainless steel stress–strain curves has been collected.•Key material parameters for different stainless steel families have been obtained.•Existing equations for the determination of material parameters have been assessed.•Revised expressions providing more accurate material parameter predictions have been proposed and verified.
Four groups (1 × 10
–5
/s, 1 × 10
–4
/s, 1 × 10
–3
/s and 1 × 10
–2
/s) of triaxial compression tests at a confining pressure of 30 MPa are carried out to clarify the strain rate effect and damage ...evolution of siltstone. The elastic modulus, peak stress, strain energy evolution and failure modes of siltstone at different strain rates are analyzed, followed by an interpretation based on statistical damage theory. In the range of the quasi-static strain rate, as the strain rate increases, the elastic modulus, peak stress, total strain energy density and elastic strain energy density at the peak stress of siltstone increase, and the failure mode of the siltstone gradually change from single-plane shear failure to extensile failure. The plastic shear strain is adopted as the random variable of the Weibull distribution to formulate a new statistical damage model, which can better reproduce the post-peak characteristics of the stress–strain curve and interpret the damage evolution process of siltstone; this also reveals that the nonlinear evolution of random variables with axial strain should be considered to capture the post-peak stress–strain curve. The damage variable evolution curves are similar to the dissipated strain energy density curves, which are ‘L-shaped’. Finally, a simplified method for determining the influence of strain rate on damage at peak stress
D
cr
is proposed and discussed.
Highlights
In the range of the quasi-static strain rate, four groups of triaxial compression tests are carried out to reveal the strain rate effect of siltstone.
Incorporating the plastic shear strain, a statistical damage model is proposed to better interpret the mechanical behaviour of siltstone.
Based on the damage theory, a simplified method for determining the influence of strain rate on damage at peak stress Dcr is proposed.
This study presents an investigation on dynamic tensile properties of high-performance fiber reinforced cementitious composites (HPFRCC). Direct tensile tests were performed on dumbbell plate ...specimens with the strain rate ranging from 1.98 × 10−5 s−1 to 90.01 s−1. The strain rate effect on the initial cracking strength and strain, tensile strength and strain, elastic modulus and energy absorption capacity of the HPFRCC was analyzed. The results indicated that with an increase in the strain rate, both the initial cracking and tensile strength increased, whereas the tensile strain capacity decreased, especially at rates over 1 s−1. Furthermore, several functions were employed to fit the relationship between the dynamic increment factors (DIF) and strain rate. A dynamic direct tensile model with a significant strain-hardening section was suggested to describe the stress-strain relationship. Finally, through the two-dimensional digital image correlation technology (2D-DIC) and scanning electron microscopy imaging (SEM), it was demonstrated that both HPFRCC specimens and polyvinyl alcohol (PVA) fibers showed rate-dependent failure patterns.
•Static and dynamic direct tensile tests of UHTCC was conducted.•The maximum actual tensile strain rate nearly reached 100 s−1.•The mechanical parameters of UHTCC perform significant rate-sensitivity.•Strain-hardening phenomenon and energy absorption capacity were analyzed.•A dynamic direct tensile model and some microscopic scanning were investigated.
SARS-CoV-2 virus is the cause of COVID-19 pandemic and belongs to RNA viruses, showing great tendency to mutate. Several dozens of mutations have been observed on the SARS-CoV-2 virus, during the ...last two years. Some of the mutated strains show a greater infectivity and are capable of suppressing the earlier strains, through interference. In this work, kinetic and thermodynamic properties were calculated for strains characterized by various numbers and locations of mutations. It was shown that mutations lead to changes in chemical composition, thermodynamic properties and infectivity. Through competition, the phenomenon of interference of various SARS-CoV-2 strains was explained, which results in suppression of the wild type by mutant strains. Standard Gibbs energy of binding and binding constant for the Omicron (B.1.1.529) strain were found to be ΔBG⁰ = −45.96 kJ/mol and KB = 1.13 ∙ 10+8 M−1, respectively.
•Nonequilibrium thermodynamics was used to analyze SARS-CoV-2 binding rate.•Analyzed strains include wild type, Alpha, Beta, Gamma, Delta and Omicron.•Standard enthalpy, entropy, Gibbs energy of binding, and KB were calculated.•Mechanistic model of virus strain competition was presented.•The influence of phenomenological coefficients on binding rate was highlighted.
Three different types of strain-hardening, cement-based composites (SHCC) as well as their constitutive cementitious matrices were investigated under uniaxial quasi-static and impact tensile loading. ...The normal-strength matrix was combined with polyvinyl-alcohol (PVA) fiber in one composite and with high-density polyethylene (HDPE) fiber in another. The third composite material consisted of high-strength matrix and HDPE fiber. A modified Hopkinson bar was used to assess the impact resistance of SHCC in terms of stress-strain relationships at displacement rates of 6m/s. The experiments were performed on specimens of two different lengths, for which, the strain rates were approximately 100s−1 and 200s−1, respectively.
SHCC made of normal-strength matrix and PVA, the composite with considerable ductility under quasi-static loading, performed substantially worse at high strain rates than SHCC made with HDPE fiber. This could be traced back to the peculiar alteration of the fiber-matrix interaction depending on the type of fiber and corresponding bond properties (chemical bond in case of PVA fiber versus frictional bond in case of HDPE fiber). Furthermore, it was demonstrated that the effect of the increasing strain rates on the tensile performance of SHCC made with HDPE fibers can be controlled by adjusting the matrix composition, this being facilitated by the consistent and predictable strain rate sensitivity of the interfacial interaction between the HDPE fibers and the surrounding cement-based matrix.
•A unified design-oriented model was established for LRS FRP-confined square and circular concrete columns.•The model has simple expressions and avoids the discontinuity of predictions for columns ...with different cross-sections.•A threshold confinement level that determines the hardening or softening compressive behavior was established.•The effective rupture strain of FRP and the equivalent diameter were reviewed and examined.•Seven existing theoretical confinement models were evaluated.
Large rupture strain (LRS) fiber-reinforced polymer (FRP) composites with an ultimate elongation of greater than 5% offer superior deformation and energy dissipation abilities over traditional carbon or glass FRP when used them in lateral confinement of concrete under the same confinement level. However, a flexible model for predicting the stress-strain relationship of concrete columns confined with LRS FRP is not yet perfectly developed, especially for noncircular columns experiencing nonuniform confining stress. Accordingly, an extensive database of LRS FRP-confined square and circular concrete columns with corner radius ratios varying from 0 to 1 was employed to establish a unified stress-strain model. This model not only includes the determinations of key points, but also attempts to define the threshold confinement level to distinguish the post-peak strain-hardening and strain-softening behaviors. The mathematical expression of the model is simple; it also avoids discontinuities in the prediction of different cross-sections. The proposed model is verified to be accurate in predicting the complete stress-strain curves of LRS FRP-confined square and circular concrete columns with hardening and softening behaviors. In addition, it outperforms the existing theoretical models in predicting the ultimate strength and the ultimate axial strain.
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