Sustained Tensile Stress Research Articles

Mount for spectroscopic analysis of samples under sustained tensile stress.

Spectroscopic methods offer valuable insights into the molecular and structural changes induced by stress, but existing techniques are often unable to perform real-time measurements during deformation. A novel solid open mount design is presented that enables spectroscopic investigations of materials under sustained tensile stress while maintaining crucial alignment of the optical system. The mount design allows for sample movement in response to applied strain while maintaining the position of the sample plane, ensuring consistent and reliable spectroscopic measurements. The effectiveness of the mount design is demonstrated with vibrational sum-frequency generation measurements of an elastomer, cured hydroxyl-terminated polybutadiene, and a plastic, high-density polyethylene, taken before, during, and after tensile deformation. The application of this mount to other spectroscopic techniques is discussed. The ability to collect spectroscopic data during a stress event would provide valuable insights into the behavior of stressed materials.

Strengthen oriented poly (L-lactic acid) monofilaments via mechanical training

Polymer materials have found extensive applications in the clinical and medical domains due to their exceptional biocompatibility and biodegradability. Compared to metallic counterparts, polymers, particularly Poly (L-lactic acid) (PLLA), are more suitable for fabricating biodegradable stents. As a viscoelastic material, PLLA monofilaments exhibit a creep phenomenon under sustained tensile stress. This study explores the use of creep to enhance the mechanical attributes of PLLA monofilaments. By subjecting the highly oriented monofilaments to controlled, constant force stretching, we achieved notable improvements in their mechanical characteristics. The results, as confirmed by tensile testing and dynamic mechanical analysis, revealed a remarkable 67 % increase in total elongation and over a 20 % rise in storage modulus post-mechanical training. Further microscopic analyses, including Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM), revealed enhanced spacing and cavity formation. These mechanical advancements are attributed to the unraveling and a more orderly arrangement of molecular chains in the amorphous regions. This investigation offers a promising approach for augmenting the mechanical properties of PLLA monofilaments, potentially benefiting their application in biomedical engineering.

Healing capacity of Ultra High Performance Concrete under sustained through crack tensile stresses and aggressive environments

This study investigates the self-healing capabilities of Ultra-High Performance Concrete (UHPC) under the combined influence of mechanical and environmental factors. Specifically, it delves into the long-term self-healing process in pre-cracked UHPC samples that endure continuous sustained tensile stresses across the cracks and are exposed to aggressive environmental conditions for one year. The results reveal that UHPC with narrow cracks exhibits a higher degree of self-healing, especially when exposed to tap water, where its self-healing capacity is most pronounced and improves with extended exposure. Furthermore, these self-healing mechanisms contribute to the restoration of mechanical properties and prevent chloride ion penetration by sealing the cracks. While a reduced level of self-healing is observed in saltwater and geothermal water exposure, prolonged exposure mitigates the inhibitory effect of aggressive ions on self-healing. SEM and EDS results provide evidence that samples subjected to extended exposure to salt and geothermal water exhibit a substantial presence of self-healing product-CaCO3. This study not only emphasizes that pre-cracked UHPC, when exposed to both mechanical stresses and aggressive environments, can maintain excellent durability and mechanical strength due to its self-healing effect but also lays the foundation for evaluating the self-healing potential of cement-based materials under conditions representative of real-world structural scenarios. This is essential for advancing the integration of self-healing advantages into design concepts and performance-based verification approaches.

Linear and nonlinear tensile creep of steam-cured UHPC

In bridges, UHPC can bear significant sustained tensile stress without cracking under service loading. Its significant impact on the long-term behavior of large-span bridges due to tensile creep characteristics becomes evident. In this paper, both linear and nonlinear tensile creep behavior of steam-cured UHPC was experimentally investigated by using dog-bone-shaped specimens under sustained direct tension for a duration of 360 days. The tensile creep test was conducted under varied tensile stress levels ranging from 0.3ft to 0.9ft. Tensile creep coefficients were calculated by using the experimental results. Nonlinear tensile creep occurs in the steam-cured UHPC when the sustained tensile stress is larger than 0.3ft. The threshold of nonlinear tensile creep is lower than that of normal-strength concrete under compression. When the sustained tensile stress is larger than 0.8ft, tensile creep failure occurs a short time after loading. The nonlinear creep impact under tension is less pronounced than that under compression due to the distinct function of steel fibers within UHPC when subjected to compression and tension force. The findings in the scanning electron microscopy (SEM) test reveal that the mechanism driving the nonlinear tensile creep of UHPC is the damage growth at the fibers-matrix interface under the high sustained tensile stress. A design-oriented model for the creep coefficient of UHPC is developed, which incorporates both linear and nonlinear creep effects. The model’s credibility is verified using the experimental results.

Experimental and modelling investigation on chloride transport and flexural behaviour of RC beams subjected to simultaneous deteriorating factors of carbonation, FT cycles and multi-type sustained stress

Reinforced concrete (RC) structures are often exposed to coinstantaneous deterioration effects such as carbonation, chloride corrosion, freeze–thaw cycles and external loads which causing deterioration of concrete and reinforcement. This paper discussed the effects of carbonation, freeze–thaw cycles and sustained loads on chloride ion transport and proposed a chloride ion transport model taking porosity as the main coupling variate. The attenuation law of the corroded beams under coupling corrosion factors was studied. Through chloride immersion tests, it was found that applying freezing and thawing cycles and sustained tensile stress can enhance chloride transport capacity by coarsening the pores; Carbonation and low compressive stress can repress the chloride ion transport by densifying concrete, but the compressive stress beyond about 0.7 times the compressive strength and tensile stress would enhance the penetrating capacity due to the damage of the internal microstructure of concrete. Then, a comprehensive and unified theoretical model of chloride ion transport considering the coupling of carbonation, freeze–thaw cycle, sustained loading and other factors was proposed and verified by taking porosity as the main coupling variable quantity. This model could essentially explain the effects of various factors on chloride ion transport and has good consistency with the test results. Finally, the flexural bearing capacity of the corroded beams was tested, and the failure characteristics, crack characteristics, ultimate bearing capacity, load–displacement relationship and strain distribution of the corroded beams under different corrosion conditions were researched. The results show that the flexural capacity of the corroded beams suffered the coupling effects of multiple corrosion factors degrades, and the bearing capacity decreases with the increase of the corrosion degree of carbonation-freezing thawing cycles; The continuous tensile stress applied to the test beams in the corrosion process intensifying the degradation of bending bearing capacity and ductility, the continuous compressive stress increases the flexural capacity and improves the ductility slightly, but excessive compressive stress significantly degrades the flexural capacity; When chloride ions are used as the third kind of corrosive substance for coupling corrosion, the tensioned or without-load corroded beams have obvious degradation in bending bearing capacity, while the corrosion beams bearing continuous compressive stress have no obvious degradation in bending bearing capacity.

3D Prestress Bioprinting of Directed Tissues.

Many mammalian tissues adopt a specific cellular arrangement under stress stimulus that enables their unique function. However, conventional 3D encapsulation often fails to recapitulate the complexities of these arrangements, thus motivating the need for advanced cellular arrangement approaches. Here, an original 3D prestress bioprinting approach of directed tissues under the synergistic effect of static sustained tensile stress and molecular chain orientation, with an aid of slow crosslinking in bioink, is developed. The semi-crosslinking state of the designed bioink exhibits excellent elasticity for applying stress on the cells during the sewing-like process. After bioprinting, the bioink gradually forms complete crosslinking and keeps the applied stress force to induce cell-orientated growth. More importantly, multiple cell types can be arranged directionally by this approach, while the internal stress of the hydrogel filament is also adjustable. In addition, compared with conventional bioprinted skin, the 3D prestress bioprinted skin results in a better wound healing effect due to promoting the angiogenesis of granulation tissue. This study provides a prospective strategy to engineer skeletal muscles, as well as tendons, ligaments, vascular networks, or combinations thereof in the future.

Mass transport properties of recycled aggregate concrete under coupling the action of chloride salt attack and uniaxial tensile loading

Water and chloride permeability are two important parameters for the evaluation of recycled aggregate concrete (RAC) durability. In service, the tensile loading plays an extremely important role in the generation and propagation of microcracks inside the RAC. Thus, aiming at understanding the mass transport properties of RAC under the coupled action of chloride salt attack and uniaxial sustained tensile loading, an improved experimental set-up was self-designed. And then a series of tests involving the effects of different uniaxial sustained tensile stress levels (10%, 30% and 50% of ultimate tensile stress, namely λt = 0.1, 0.3 and 0.5) and different replacement ratios of recycled coarse aggregate (RCA) (0, 30%, 50% and 100% mass replacement of normal coarse aggregate, namely R0, R30, R50 and R100) on the transport properties of RAC were conducted, and their coupling effects were further analyzed. Generally, the results indicate that both the sorptivity and chloride diffusion coefficient of RAC increase with the increase of RCA replacement ratio and tensile stress level. The synergistic effect of RCAs and tensile stress significantly accelerates the process of water and chloride invasion into concrete. The initial sorptivity of R100 specimens at λt = 0.5 was about 4.44 times that of R0 specimens without loading. Moreover, the chloride diffusion coefficient exhibits a linear relationship with the RCA content, while it has a quadratic relationship with the tensile stress level.

Computational Model of Mechano-Electrochemical Effect of Aluminum Alloys Corrosion

Abstract Stress corrosion is a critical issue that leads to high costs in lost equipment and maintenance, affecting the operation and safety of aircraft platforms. Most aerospace structural components use the aluminum alloys 7xxx series, which contain Al, Cu, Zn, and Mg, due to the combined advantage of its high-strength and lightweight. However, such alloys, specifically AA7075-T4 and AA7075-T651, are susceptible to stress corrosion cracking when exposed to both mechanical stresses and corrosive environments. Stress corrosion cracking gives rise to a major technological challenge affecting aerospace systems as it leads to the degradation of mechanical properties. In addition, such corrosion presents an important yet complex modeling challenge due to the synergistic action of sustained tensile stresses and an aggressive environment. In light of this, we develop a finite element multiphysics model to investigate the interplay of mechanical loading and electrochemistry on the stress corrosion of aluminum alloys. The model includes a multiphysics coupling technique through which the kinetics of corrosion can be predicted in the presence of elastic and plastic deformation modes. The presented model provides useful information toward the kinetics of corrosion via tracking localized corrosion and stress distribution. Although the model is general, it has been made considering the characteristics of AA7xxx series, more specifically, taking AA7075.

Investigation of tensile creep for Ultra-High-Performance Fiber Reinforced Concrete (UHPFRC) for the long-term

The research presented in this paper is associated with the time-dependent tensile behavior of UHPFRC, especially on tensile creep for the long-term. This study outlines the experimental program for the implication of the newly developed testing rig, installation and preparation of test specimens, and studies of the research findings. The time-dependent tensile behavior was evaluated in terms of tensile creep under different sustained tensile loads. The sustained tensile loads were harnessed following the different percentages (50% and 75%) of cracking loads. The cracking loads were determined from the instantaneous tensile tests of unreinforced UHPFRC prism specimens at 28-day. A newly designed test rig was introduced to perform the tensile creep test for the long-term, and the test rig was designed in a way to overcome limitations found throughout the critical literature review. This study demonstrates that the tensile creep of UHPFRC is significantly influenced by the shrinkage strain. The experimental results demonstrate that under higher sustained tensile stress directs to a higher tensile creep rate for the first 13 days. Afterward, the total tensile creep strain was dominated by the shrinkage strain.

Effects of Different Parameters on Initiation and Propagation of Stress Corrosion Cracks in Pipeline Steels: A Review

The demand for pipeline steels has increased in the last several decades since they were able to provide an immune and economical way to carry oil and natural gas over long distances. There are two important damage modes in pipeline steels including stress corrosion cracking (SCC) and hydrogen induced cracking (HIC). The SCC cracks are those cracks which are induced due to the combined effects of a corrosive environment and sustained tensile stress. The present review article is an attempt to highlight important factors affecting the SCC in pipeline steels. Based on a literature survey, it is concluded that many factors, such as microstructure of steel, residual stresses, chemical composition of steel, applied load, alternating current (AC) current and texture, and grain boundary character affect the SCC crack initiation and propagation in pipeline steels. It is also found that crystallographic texture plays a key role in crack propagation. Grain boundaries associated with {111}∥rolling plane, {110}∥rolling plane, coincidence site lattice boundaries and low angle grain boundaries are recognized as crack resistant paths while grains with high angle grain boundaries provide easy path for the SCC intergranular crack propagation. Finally, the SCC resistance in pipeline steels is improved by modifying the microstructure of steel or controlling the texture and grain boundary character.

Assessment of creep-fatigue behavior, deformation mechanisms, and microstructural evolution of alloy 709 under accelerated conditions

Alloy 709 is a leading candidate structural material for sodium-cooled fast spectrum reactors (FSR), where creep-fatigue is a potential failure mode. Low cycle fatigue (LCF) and creep-fatigue tests with 30 min tensile hold times have been conducted to failure at 550 and 650 °C, corresponding to potential service and accelerated test temperatures, respectively. Creep-fatigue life is reduced relative to LCF at both temperatures, though significantly more at 550 °C compared to 650 °C. Differences in slip behavior, dynamic recovery, precipitate evolution, and strain-aging effects result in less stress relaxation and sustained high tensile stresses in creep-fatigue at 550 °C; thus, there is more intergranular damage compared to 650 °C.

Flexural Properties and Fracture Behavior of Nanoporous Alumina film by Three-Point Bending Test.

This study investigated the influence of porosity on the flexural property of a nanoporous alumina film. When the porosity of the alumina film increased, both bending strength and modulus declined. The results from the bending test revealed that the setting of the film during the bending test had significant influence on the flexural property. Fracture only occurred when the porous side of the alumina film suffered tensile stress. The ability to resist fracture in the barrier layer was higher than in the porous side; the magnitude of the bending strength was amplified when the barrier layer sustained tensile stress. When the porous layer suffered a tensile stress, the bending strength decreased from 182.4 MPa to 47.7 Mpa as the porosity increased from 22.7% to 51.7%; meanwhile, the modulus reduced from 82.7 GPa to 17.9 GPa. In this study, the most important finding from fractographic analysis suggested that there were a localized plastic deformations and layered ruptures at the porous side of the alumina film when a load was applied. The fracture behavior of the nanoporous alumina film observed in the present work was notably different from general ceramic materials and might be related to its asymmetric nanostructure.

Tensile creep and early-age concrete cracking due to restrained shrinkage

Concrete structures are prone to cracking due to restraint provided to early age autogenous and drying shrinkage. In addition, the risk of early-age thermal cracking is increased by increasing the degree of restraint to early-age thermal contraction. At this early-age, tensile creep plays a key role in relaxing shrinkage induced tensile stresses and delaying the time to cracking. However, limited data are available concerning tensile creep of concrete and the magnitude and rate of development of the early-age shrinkage of concrete. As a consequence, restraint to shrinkage is often poorly modelled in structural design. In order to accurately quantify the early-age shrinkage and tensile creep of concrete, a comprehensive experimental program is being conducted at the UNSW Centre for Infrastructure Engineering and Safety. Tensile creep is measured on dog-bone shaped specimens subjected to constant sustained tensile stress, while shrinkage is measured on identical unloaded specimens. Restrained ring tests were also performed to validate the tensile creep coefficients calculated from dog-bone specimens. A simple analytical procedure to accurately predict the degree of restraint and the tensile stresses in concrete induced by shrinkage is described for the restrained ring specimens.

On the ultimate tensile strength of tantalum

Strain rate, temperature, and microstructure play a significant role in the mechanical response of materials. Using non-equilibrium molecular dynamics simulations, we characterize the ductile tensile failure of a model body-centered cubic metal, tantalum, over six orders of magnitude in strain rate. Molecular dynamics calculations combined with reported experimental measurements show power-law kinetic relationships that vary as a function of dominant defect mechanism and grain size. The maximum sustained tensile stress, or spall strength, increases with increasing strain rate, before ultimately saturating at ultra-high strain rates, i.e. those approaching or exceeding the Debye frequency. The upper limit of tensile strength can be well estimated by the cohesive energy, or the energy required to separate atoms from one another. At strain rates below the Debye frequency, the spall strength of nanocrystalline Ta is less than single crystalline tantalum. This occurs in part due to the decreased flow stress of the grain boundaries; stress concentrations at grain boundaries that arise due to compatibility requirements; and the growing fraction of grain-boundary atoms as grain size is decreased into the nanocrystalline regime. In the present cases, voids nucleate at defect structures present in the microstructure. The exact makeup and distribution of defects is controlled by the initial microstructure and the plastic deformation during both compression and expansion, where grain boundaries and grain orientation play critical roles.

Intergranular Oxidation Effects During Dwell-Time Fatigue of High-Strength Superalloys

The present paper summarizes experimental work to identify the mechanisms of dwell-time cracking during service operation of polycrystalline nickel-base superalloys, such as Alloy 718 and AD730. By means of crack growth monitoring during various kinds of cyclic loading in vacuum and in air using the potential drop technique, it was shown that the combination of sustained tensile stress, load reversal, and oxidizing atmosphere leads to an increase in the crack propagation rate by orders of magnitude, as compared to cyclic reference tests without dwell time and/or under vacuum conditions. By careful metallographic and theoretical analysis, the embrittling effect was attributed to stress-induced oxygen diffusion ahead of the intergranular crack tip followed by decohesion in a nanometer scale and had been termed “dynamic embrittlement.” More recently, atom probe tomography of the near-crack tip region revealed that the damage zone consists of Cr-rich transition oxides rather than elemental oxygen. This is in qualitative agreement with TGA measurements on Alloy 718 specimens without mechanical loading, which shows that crack propagation velocities of 50 µm/s do not allow massive Cr2O3 or NiO scale formation. By means of a quantitative analysis of the fracture surface, it became evident that grain-boundary attack depends on the grain-boundary character. This observation was supported by four-point bending experiments on grain-boundary-engineered samples with a high fraction of coincident site lattice boundaries and bicrystalline samples with well-defined grain-boundary misorientation relationships with respect to the loading axis. Taking the experimental results into account, semiquantitative modeling concepts have been developed to correlate crack propagation rates with the oxygen grain-boundary diffusivity, the local microstructure, and the mechanical stress states. These concepts are discussed in terms to adapt grain size and precipitate microstructure of polycrystalline superalloys.

Combined Effects of Sustained Loads and Wet-Dry Cycles on Durability of Glass Fiber Reinforced Polymer Composites

This paper deals with durability of glass fiber reinforced polymer (GFRP) composites under the combined effects of sustained tensile loads and wet-dry (WD) cycles. Two different solutions (distilled water and saltwater) were used to imitate the freshwater and marine environments, respectively. Tensile properties of the unconditioned and conditioned specimens were measured to study the durability of GFRP composites under these 2 effects. The response indicated that both tensile strength and elastic modulus increased initially upon WD cycles, which was attributed to both the postcuring of resin and the sustained tensile stress allowing for fastec cure. Further exposure to WD cycles in distilled water or saltwater led to a steady decrease in tensile strength and modulus. WD cycles of saltwater and distilled water have similar effects on the degradation of the tensile properties for unstressed specimens. However, the elastic modulus and elongation at rupture of stressed specimens under WD cycles of saltwater decreased more than those specimens under WD cycles of distilled water. Moreover, increase of sustained loads led to a decrease in tensile strength. Based on Arrhenius method, a prediction model which accounted for the effects of postcure processes was developed. The predicted results of tensile strength and elastic modulus agree well with those obtained from the experiments.

Stabilization of electrical sensing properties of carbon fiber sensors using pre-tensioning approach

Owing to fabrication defects in carbon fiber (CF) tows, the unevenness of fiber roves, such as local bends, misalignments, and skewness, results in irregular distribution of the electrical resistance in the transverse direction along the gauge length of a sensor, which affects its performance. In this study, a pre-tension approach was developed according to the creep mechanism of composites to straighten the CFs. In addition, the resin relaxation was controlled by tensioning the fibers during and after hardening of the epoxy resin using a double-tension method to enhance the electrical sensing properties of long gauge carbon fiber line (CFL) strain sensors. Different levels of sustained tensile stresses were studied to obtain the optimal tensile stress level both during and after hardening to be applied in the double-tension method. The results of static and dynamic tests showed that the double-tension technique could significantly straighten the fibers, and stabilize the transverse connections of CFL sensors in the case of tensioning the fibers during and after hardening under a sustained stress of 60% of the ultimate tensile stress of the CFs. The proposed double-tension method was utilized to improve the response of the CFL sensors with short gauge lengths.

ISRM Suggested Methods for Determining the Creep Characteristics of Rock

It is important to note that creep is only one aspect of the time-dependent behavior of rocks. In Fig. 1, three cases are illustrated with respect to the complete stress–strain curve: creep, i.e., increasing strain when the stress is held constant; stress relaxation, i.e., decreasing stress when the strain is held constant; and a combination of both, when the rock unloads along a chosen unloading path. This ISRM suggested method deals only with the case of creep, which is particularly relevant for cases where the applied load or stress is kept constant. Creep tests have also been carried out on soft rocks such as tuff, shale, lignite, and sandstone, medium-hard rocks such as marble, limestone, and rock salt, and hard rocks such as granite and andesite (i.e., Akagi 1976; Akai et al. 1979, 1984; Ito and Akagi 2001; Berest et al. 2005; Doktan 1983; Passaris 1979; Serata et al. 1968; Wawersik 1983; Okubo et al. 1991, 1993; Masuda et al. 1987, 1988; Ishizuka et al. 1993; Lockner and Byerlee 1977; Boukharov et al. 1995; Fabre and Pellet 2006; Aydan et al. 1995; Chan 1997; Cristescu and Hunsche 1998; Hunsche 1992; Hunsche and Hampel 1999; Ito et al. 1999; Mottahed and Szeki 1982; Perzyna 1966; Slizowski and Lankof 2003; Yang et al. 1999). These experiments were mostly carried out under compressive loading conditions. There are few studies on rocks using creep tests under a tensile loading regime (Ito and Sasajima 1980, 1987; Ito et al. 2008; Aydan et al. 2011). In particular, shallow underground openings may be subjected to a sustained tensile stress regime, which requires the creep behavior of rocks under such conditions. Please send any written comments on this ISRM suggested method to Prof. Resat Ulusay, President of the ISRM Commission on Testing Methods, Hacettepe University, Department of Geological Engineering, 06800 Beytepe, Ankara, Turkey.

Co-regulation of LPS and tensile strain downregulating osteogenicity via c-fos expression

AimsOrthodontic forces are known to aggravate inflammation-induced destruction of the periodontium, but the underlying mechanism has not been elucidated. The present study investigates how inflammation and forces co-regulate periodontium damage. Main methodsCultures of MC3T3-E1 osteoblasts were pre-treated with conditioned medium from RAW264.7 macrophages exposed to 100ng/ml Porphyromonas gingivalis (Pg)-LPS. Conditioned medium was analyzed by ELISA for interleukin-1 beta (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α). Osteoblasts were then subjected to tensile strain (0.5Hz; 1000μ or 3000μ) for 0min, 5min, 15min, 30min, 1h, 3h, and 6h. The cultures were analyzed for mRNA and protein levels of c-fos. Cells were also analyzed for alkaline phosphatase (ALP) activity. Key findings(Pg)-LPS stimulated the secretion of all three cytokines from RAW264.7 cells in a dose- and time-dependent manner. Medium from (Pg)-LPS stimulated cells induced a 10-fold increase in c-fos expression, which decreased to a 4-fold plateau after 3h. In contrast, ALP activity of control osteoblasts decreased during the first 60min, then recovered over the next 4h. Pretreatment with conditioned medium generated the same initial decrease during tensile strain but prevented the recovery. SignificanceOur study showed, for the first time, that the inhibitory effect of inflammation and tensile strain on osteogenicity is associated with the upregulation in c-fos expression. In addition, inflammation may reduce the ability of osteoblasts to restore their osteogenic capacity during sustained tensile stress and contribute to periodontium damage.

Behaviour of Stress Corrosion Cracking of Austenitic Stainless Steels in Sodium Chloride Solutions

Click Stress Corrosion Cracking (SCC) is an environmentally well-known as a failure caused by exposure to a corroding while under a sustained tensile stress. SCC is most often rapid, unpredictable. Failure can occur in a short time as a few hours or take years and decades to happen. Most alloys are liable to SCC in one or more environments requiring careful consideration of alloy type in component design. In aqueous chloride environments austenitic stainless steels and many nickel based alloys are common to perform poorly. Stress corrosion cracking (SCC) of austenitic stainless steels of types 316 was investigated as a function of applied stress at room temperature in sodium chloride solutions using a constant load method. The experiment uses a spring loaded fixture type and is based on ASTM G49 for experiment method, and E292 for geometry of notched specimen. The stress dependence of fracture appearance and parameters of time to cracking, and cracking growth. The results are explained in terms of comparison between the two concentrations of sodium chloride solutions.