Freeze-thaw Cycles Research Articles

Investigating Mechanical Characteristics of Rocks Under Freeze–Thaw Cycles Using Grain-Based Model

AbstractBased on the discrete element method (DEM), a water-contained grain-based model (GBM) is developed in this study to evaluate the effects of freeze–thaw cycles (FTCs) on the mechanical characteristics of the rock. A set of freeze–thaw and uniaxial compression tests is carried out to explore the impact of micro damage caused by FTCs on the mechanical prosperities of rock samples. By monitoring the development and distribution of micro-cracks during freeze–thaw test and uniaxial compression test, the damage mechanism of FTCs is revealed from a microscopic perspective, which shows that FTCs deteriorate the strength and brittleness parameters as exponential functions. The parametric analysis is carried out to explore the influence of porosity and mineral components on the mechanical behaviors of rock against freeze–thaw and uniaxial loadings. Based on the parametric analysis results, it is found that UCS, Young’s modulus, and total strain energy at peak stress decrease with the increase of porosity and clay content, which emphasizes the contributions of porosity and mineral components on the mechanical properties of rock samples. It is proved that the water-contained grain-based model developed in this study can capture the damage caused by FTCs on the mechanical performance of rock from a microscopic perspective, which provides novel perspectives on the phenomenon of rock degradation in response to fluctuations in temperature.

Study on the weakening of mechanical properties and damage constitutive model of pre-cracked cyan sandstone after freeze–thaw cycles

Study on the weakening of mechanical properties and damage constitutive model of pre-cracked cyan sandstone after freeze–thaw cycles

Assessing the flexural fatigue life of engineered cementitious composites exposed to freeze-thaw cycles

In cold regions, the infrastructure, particularly roads, bridges, and airport runways, faces prolonged exposure to the coupled effects of freeze-thaw (FT) cycles and fatigue loads. This makes the damage mechanism more complex, seriously affecting the durability of these structures. To investigate the influence of FT damage on flexural fatigue life, this study equated FT damage to the effect of increased stress levels and conducted FT cycles test, nuclear magnetic resonance test, and flexural fatigue test on engineered cementitious composites (ECC). The test results showed that the critical FT cycles number, predicted by using mass loss rate, relative dynamic elastic modulus, and porosity as characteristic parameters, was 507 cycles. The error in representing FT cycles using pore structure characteristic parameters was within 2.0 %. When the stress level S = 0.8, the flexural fatigue life gradually decreased from 22217 cycles to 724 cycles as the number of FT cycles increased. The Weibull distribution was used to obtain flexural fatigue life at different probabilities. Anderson-Darling test verified that the Weibull distribution is a reliable model for predicting material life. By equating FT damage to the effect of increased stress levels, the flexural fatigue equation based on different FT cycles number was established. The study found that the maximum error between the flexural fatigue equation and the Weibull-distributed flexural fatigue life was 18.76 %. Through the application of entropy weight method and grey relational analysis, it was found that the entropy weight grey incidence, euclidean grey correlation, fuzzy affiliation, and fuzzy grey correlation of stress level were 0.799, 0.888, 0.588, and 0.753, respectively. These values indicate that the influence of stress level on flexural fatigue life is greater than that of FT cycle numbers. This research aims to provide new insights for accurately calculating the flexural fatigue life of ECC in cold regions and improving the durability of structures.

Fish oil-based bigels with outstanding sensory and antioxidant properties: Application in low-fat mayonnaise

Low-fat mayonnaise has gained widespread popularity as a condiment, driven in part by the global rise in obesity rates, which is partially linked to excessive fat consumption. In this study, the bigel systems were designed by preparing fish oil oleogels and gelatin hydrogels to produce low-fat mayonnaise. As the oleogel content increased in bigels, a phase inversion shifted from oil-in-water (O/W) systems to water-in-oil (W/O) systems. Rheology and mechanical property analysis revealed that the hardness and gel strength of bigels improved as the oleogel content increased. The freeze-thaw stability of bigels was impacted by the ratio of oil and water phases, with O/W systems enduring one additional freeze-thaw cycle compared to W/O systems. The bigel containing 40% oleogel (BG 40) and lemon essential oil significantly enhanced antioxidant properties, as measured by the levels of primary and secondary oxidation products. The antioxidative capacity of the gel, as indicated by the reduced development of primary and secondary oxidation products, was 301.4% and 196.7% greater, respectively, compared to that of the pure oleogel. Based on magnetic resonance imaging and sensory rating analysis, sample BG 40 demonstrated the most homogeneous structure and the best sensory properties. The sample BG 40, used as the fat substitute in preparing low-fat mayonnaise, reduced total oil content compared to full-fat mayonnaise. Our findings contributed to the development of low-fat mayonnaise using fish oil-based bigels, which exhibit exceptional sensory and antioxidant properties.

Frost Resistance and Microscopic Properties of Recycled Coarse Aggregate Concrete Containing Chemical Admixtures.

In order to increase the suitability of coarse recycled concrete aggregates and improve the frost resistance of recycled coarse aggregate concrete, this study aims to investigate the effects of an antifreeze-type water-reducing admixture, air-entraining admixture, and antifreeze admixture on the frost resistance of recycled coarse aggregate concrete. The effectiveness of these admixtures is gauged by the mass loss rate and the relative dynamic modulus of elasticity (RDM). Mercury-impressed porosimetry (MIP), super depth of field microscopy, and scanning electron microscopy (SEM) were employed to characterize the hydration products, microstructure, and pore structure of recycled coarse aggregate concrete, with a view to establishing a connection between the microstructural characteristics and the macro properties and analyzing the micro-mechanism of the improvement effect of frost resistance. The test results demonstrate that the admixtures have a significant impact on the frost resistance of recycled coarse aggregate concrete. In particular, the recycled coarse aggregate concrete with an antifreeze admixture (dosage of 1%) and a water-cement ratio of 0.41 exhibited a mass loss of only 1.23% after 200 freezing and thawing cycles, a relative dynamic modulus of elasticity of up to 93.97%; however, the control group had reached the stopping condition at 150 freeze-thaw cycles with more than 10% mass loss. The recycled coarse aggregate concrete with added antifreeze admixture had a tight connection between the aggregate and the paste and a more pronounced improvement in the pore structure, indicating excellent resistance to frost damage.

Mechanical properties investigation on recycled rubber desert sand concrete

The mechanical properties of recycled rubber desert sand concrete were studied to determine the effect of the replacement rate of recycled rubber and desert sand. The replacement rates of recycled rubber aggregates were set to 0 %, 5 %, 10 %, and 15 %, respectively, and for dessert sand aggregates were set to 0 %, 10 %, 20 %, and 30 %, respectively, during concrete preparation. The concrete's compressive, tensile, and freeze-thaw mechanical properties were tested at each replacement rate. The experimental results show that when the replacement rate of desert sand increases from 0 % to 30 %, the replacement rate of recycled rubber is 15 %, and the splitting tensile strength of concrete shows a pattern of first increasing and then decreasing. When the replacement rate for desert sand is 30 %, the replacement rate for recycled rubber rises from 0 % to 15 %, and the splitting tensile strength shows a pattern of first decreasing. With replacement rates of 10 percent for recycled rubber aggregate and 20 percent for desert sand aggregate, the damage to the concrete from external forces is relatively ideal. The compressive strength values are the highest, and the split tensile strength is the best, demonstrating good compressive and tensile strength. The results of CO2 emission analysis show that as the amount of recycled rubber increases, the CO2 emissions per unit volume of concrete also increase. The interface of the micro-optical structure in the concrete is straightforward, the pores are few, and it exhibits good mechanical properties. The concrete undergoes freeze-thaw cycles with relatively stable changes in compressive strength and split tensile strength, demonstrating a solid freeze-thaw resistive mechanical property.

Effects of freeze-thaw cycles on fatigue performance of asphalt mixture and a fatigue-freeze-thaw damage evolution model

To study the effect of freeze-thaw (FT) cycles on the fatigue performance of composite crumb rubber modified asphalt mixtures (CCRMA), a semicircular bending fatigue test based on the digital image correlation technique (DIC) was used to measure the fatigue life (Nf) of CCRMA and SBS modified asphalt mixtures (SBSMA) and the horizontal strain (Exx) of the DIC deformation field under repeated loading. The variation laws of Nf, Exx and the damage factor (D) defined based on Exx were analyzed under FT cycle conditions. In addition, considering the important influence of FT cycles on the Nf and damage evolution characteristics of asphalt mixtures, based on the classical Chaboche damage evolution model, the influence of FT cycle was considered, a fatigue-freeze-thaw damage evolution model that reflects the effects of FT cycling variables and stress levels on asphalt mixtures was constructed. The results indicate that the Exx peak of asphalt mixture shifts forward with increasing FT cycle number. After 20 FT cycles, the Nf of CCRMA decreased by 73.4 %, 62.1 %, and 75.1 %, while that of SBSMA decreased by 76.5 %, 58.6 %, and 74.6 % at stress ratios of 0.2, 0.3, and 0.4, respectively. The fatigue-freeze-thaw damage evolution model predictions were in agreement with experimental results, with the goodness of fit (R2) of all Nf prediction models being greater than 0.9. With the exception of a few outliers, the relative error between the measured and predicted Nf for the two asphalt mixtures was within 15 %. This indicates that the model can effectively predict the Nf and damage evolution laws of asphalt mixtures at different stress levels after an arbitrary number of FT cycles. The related research results provide a theoretical basis for predicting the Nf of new roads in cold regions under FT cycles.

Insights into the shallow landslide mechanism of expansive soil slope induced by freeze-thaw cycles and snowmelt infiltration

For rigorous understanding the shallow landslide mechanisms and deformation characteristics of expansive soil slopes, a comprehensive in-situ monitoring platform is established. Triaxial creep tests and microstructure analysis with scanning electron microscopy (SEM) are also conducted on expansive soil samples obtained from Binxi station. Field monitoring data indicates that freeze-thaw (F-T) cycle and snowmelt infiltration significantly increase the creep deformation of expansive soil slope during spring melting period. Due to the influence of F-T cycle and snowmelt infiltration, more soil grains are involved in the shear deformation contributing to a large, localized shearing. Additionally, the microstructural analysis shows that F-T cycle influence the relationship between expansive soil grains that gradually change from face-face contact to point-face contact or edge-edge contact form. The shallow landslide mechanisms of expansive soil slope are revealed from creep deformation and microstructure characteristics of soils after the F-T cycle and snowmelt infiltration, which can be summarized into two stages, namely, the snowfall accumulation state and snow melt-shallow infiltration stage. These results can serve as a good reference for the prevention of expansive soil slopes in seasonally frozen regions.

Study on the freeze-thaw damage degree and its influence on the shear strength parameters of sandstones

The variations of shear strength parameters against the freeze-thaw cycles are not well understood in the previous study. This research mainly investigated the influence of freeze-thaw treatment on the shear strength parameters and their relationship with the freeze-thaw damage variable for sandstones. The fraction dimensions of sandstone surfaces and basic friction angles display an increasing trend under freeze-thaw cycles. It implies that the sandstone surface becomes rougher due to the freeze-thaw loss of cementation minerals and thus induces the increase in the basic friction angle. Another interesting finding is that although the cohesion of sandstone reduces, the internal friction angle also increases with increasing freeze-thaw cycles. Thus, the reduction in the shear strength under freeze-thaw actions should be attributed to the loss of cohesion. Moreover, the change of shear strength parameters is also related with the freeze-thaw damage degree. As the number of freeze-thaw cycles increases, the increase in porosity and reduction in P-wave velocity are much larger for the YY and YR sandstones with higher porosities, thus, they suffer much more serious freeze-thaw damage, and they have a much larger variation in shear strength parameters. The novel finding is that the growth in basic friction angle is positively correlated with the increase of freeze-thaw damage, and the internal friction angle exponentially increases with the increase of freeze-thaw damage. This study provides a much better understanding of the change of the shear strength parameters under freeze-thaw cycles.

Model test of in-situ remediation for heavy metal-contaminated clayey soil by artificial freezing and shaft washing

The low permeability of clayey soil and the pressure of liquid extraction and injection tend to form preferential flow paths in the soil, diminishing the remediation efficiency of shaft washing. Therefore, a new in-situ repair method combining artificial freezing and shaft washing is proposed. Using Pb and Cd contaminated clayey soil as the research object, in-situ model tests of different eluent types, concentrations, and suction modes were conducted to investigate the removal rate of heavy metals and the distribution of temperature and water field. The results demonstrated that the artificial freezing method can effectively induce the water (eluent) migration from the unfrozen zone to the freezing front. Besides, it effectively resolved the issue of poor washing efficiency caused by preferential flow between the extraction and injection wells during the extraction process. After five freeze-thaw cycles, the removal rate of Pb and Cd reached 46.16 % and 59.04 %, respectively. The combination of artificial freezing and plastic drainage plate technology merges artificial freezing and shaft washing methods to achieve the remediation of heavy metal-contaminated soil, providing a reference for the in-situ remediation of heavy metal-contaminated clayey soil.

Microwave self-healing characteristics of the internal voids in steel slag asphalt mixture subjected to salt-freeze-thaw cycles

Microwave heating technology can be used to repair freeze-thaw (F-T) cycle damage and cracks caused by the use of snow melting salts and de-icers in winter. This study utilized three different gradations of asphalt mixtures: AC-13, SMA-13, and OGFC-13, and enhanced their microwave absorption performance with steel slag (SS). The heating uniformity was evaluated through surface and internal temperature tests. Additionally, the mechanisms of damage and healing of the asphalt mixtures under salt freeze-thaw (S-F-T) damage conditions were explored using S-F-T cycles test and X-ray computed tomography scans (CT). The results showed that OGFC-13 exhibits a significantly higher rate of temperature increase compared to the other two types due to its stronger wave absorption capacity. The thermal hysteresis caused by steel slag leads to uneven spatial temperature distribution. The study recommends an optimal microwave heating time of 40 s for SS asphalt mixtures, which has minimal impact on the mixture structure, by defining an evaluation method for the uniformity index and local overheat ratio. After undergoing S-F-T cycles, the porosity of all three asphalt mixtures increased, particularly at the top and bottom of the specimens. Among them, OGFC-13 exhibited the poorest durability under S-F-T conditions, with the S-F-T cycles having a significant impact on medium-sized voids (0.15–0.6 mm). After microwave heating, AC-13 and SMA-13 showed good repair effects, with porosity levels returning to their initial states. For large voids (>2.36 mm) in OGFC, microwave heating may not effectively reduce the number of voids. Additionally, the healing rate of mixture specimens at certain mid-height ranges is higher due to elevated surface temperatures in these areas, making it especially effective in repairing F-T damage. This study shows that microwave heating of SS asphalt mixtures can improve the durability of pavement in cold regions. However, implementation challenges include the need for specialized equipment and potential uneven heating. Future research should explore optimizing microwave heating techniques to minimize local overheating and investigate the long-term performance of microwave-repaired asphalt pavements under various environmental conditions.

Effects of biochar and compost on the abundant and rare microbial communities assembly and multifunctionality in pesticide-contaminated soil under freeze‒thaw cycles

Biochar and compost are effective ways to improve soil quality and reduce pesticide pollution. However, the effects of them on the abundant and rare microbial communities in freeze‒thaw soil need to be further clarified. Therefore, this study took biochar, compost, and their combination as examples to explore their effects on the abundant and rare microbial communities and multifunctionality in glyphosate, imidacloprid and pyraclostrobin contaminated soil under freeze‒thaw cycles. We found that freeze‒thaw cycles enhanced the functional groups and surface aromaticity of biochar and compost, thereby improving the adsorption capacity. Biochar and compost reduced the concentration and half-life of three pesticides and enhanced the degradation function of rare taxa in soil. Biochar and compost improved the structure composition and co-occurrence relationship of abundant and rare taxa. Meanwhile, the assembly processes of abundant and rare sub-communities were mainly driven by stochastic processes and the Combined treatment promoted the transition from dispersal limitation to homogenizing dispersal and homogeneous selection. Moreover, the Combined treatment significantly improved the multifunctionality before and after freezing and thawing by increasing the diversity of rare taxa and assembly processes. The results provide new insights for farmland soil remediation in seasonal frozen areas, especially the soil functional cycle of abundant and rare microorganisms.

Experimental Study on the Frost Resistance of Basalt Fiber Reinforced Concrete.

In this paper, the effect of basalt fiber (BF) on the frost resistance of concrete under different curing conditions was investigated, and its frost resistance mechanism was analyzed. Three different curing conditions (normal curing, short-term curing, and seawater curing) were adopted, and concrete with different BF volume contents was designed. Freeze-thaw (FT) tests were carried out using the rapid freezing method to test the frost resistance of basalt fiber reinforced concrete (BFRC). Additionally, the mass loss rate (MLR), relative dynamic modulus of elasticity (RDME) change, and compressive strength reduction of specimens during the freeze-thaw cycles (FTCs) were evaluated. The results show that when the BF content is 0.15%, under normal curing, short-term curing, and seawater curing conditions, the residual compressive strength of BFRC after FTCs was increased by 5.4%, 28.1%, and 30.9%, respectively, compared to plain concrete. By incorporating BF into concrete, the development of microcracks can be effectively retarded, and damage generation during FTCs can be reduced. In addition, the microscopic morphological characteristics and pore structure characteristics of concrete further elucidate the frost resistance mechanism of BFRC from a microscopic perspective.

Study on Freeze–Thaw Resistance of Cement Concrete with Manufactured Sand Based on BP Neural Network

In this study, experiments were conducted on the freeze–thaw performance of manufactured sand cement concrete with different sand ratios and fly ash contents. The research found that during 200 freeze–thaw cycles, as the fly ash content increased, the concrete exhibited a higher mass loss rate and a decline in the relative dynamic modulus of elasticity. This was due to the lower activity of SiO2 and Al2O3 in the fly ash, which reduced the hydration products. Incorporating an optimal amount of manufactured sand can increase the density of concrete, thereby improving its resistance to freeze–thaw cycles. However, when the content of manufactured sand was high, its large surface area could interfere with the hydration process and reduce strength, thereby diminishing the freeze–thaw resistance of the concrete. Given that studying the freeze–thaw resistance of manufactured sand concrete is time-consuming and influenced by many factors, a prediction model based on a BP (back propagation) neural network was developed to estimate the mass loss rate and the relative dynamic modulus of elasticity following freeze–thaw cycles. After validation, the model was found to be highly reliable and could serve as a foundation for mix design decisions and freeze–thaw performance prediction of manufactured sand cement concrete.

Rapid and sensitive liquid chromatographic–tandem mass spectrometric methods for the quantitation of dolutegravir in human plasma and breast milk

BackgroundDolutegravir (DTG) is part of a first-line antiretroviral therapy (ART) for HIV management in drug-naïve individuals and is recommended for the treatment of HIV during pregnancy. Robust analytical tools to quantify DTG are necessary to support clinical trials that characterize its multi-compartment drug distribution. MethodsPotassium EDTA (K2EDTA) plasma or whole breast milk was spiked with DTG and an isotopically labeled internal standard. Samples were prepared via protein precipitation prior to LC–MS/MS analysis. The assays were validated in accordance with regulatory recommendations. ResultsAnalytical measuring ranges for DTG quantitation in plasma and breast milk were 100–10,000 ng/mL and 0.500 to 1000 ng/mL, respectively. Inter-assay precision and accuracy were 2.73 % to 3.41 % and −10.6 % to −5.37 % for plasma, and 4.24 % to 12.4 % and −5.63 % to 7.49 % for breast milk, respectively. DTG was stable for three freeze–thaw cycles and for at least 72 h at room temperature in matrix (plasma or breast milk). Additionally, whole blood was stable for 24 h at room temperature and 2 h under conditions of extended heat and humidity. Matrix effects for DTG in plasma and breast milk ranged from 101 % to 108 % and 78.2 % to 99.3 %, respectively. Quantitation in remnant plasma samples yielded measurable concentrations within the primary linearity of the assay. ConclusionsMethods to quantify DTG in human plasma and breast milk have been developed and validated. These assays were designed to satisfy all criteria for implementation in clinical and clinical trial settings.

Advances in Highly Ductile Concrete Research.

In recent years, high-ductility concrete (HDC) has gradually become popular in the construction industry because of its excellent ductility and crack resistance. Concrete itself is a kind of building material with poor tensile properties, and it is necessary to add a large number of steel bars to improve its tensile properties, which increases the construction cost of buildings. However, most of the research studies on high-ductility concrete are scattered. In this paper, the basic mechanical properties of high-ductility concrete and the effects of dry and wet cycles, freeze-thaw cycles, and salt erosion on the durability of high-ductility concrete are obtained by comprehensive analysis. The results show that the tensile properties of HDC can be significantly improved by adding appropriate fiber. When the volume fraction of steel fiber is 2.0%, the splitting tensile strength of concrete is increased by 98.3%. The crack width threshold of concrete chloride erosion is 55-80 μm, and when the crack width threshold is exceeded, the diffusion of CL-1 will be accelerated, and the HDC can control the crack within the threshold, thereby improving the durability of the concrete. Finally, the current research status of high-ductility concrete is analyzed, and the future development of high-ductility concrete is proposed.

Comprehensive Analysis of Cetuximab Critical Quality Attributes: Impact of Handling on Antigen-Antibody Binding.

Cetuximab, formulated in Erbitux® (5 mg/mL), is a therapeutic monoclonal antibody (mAb) widely used in several cancer treatments. Currently, there is insufficient knowledge about the behavior of cetuximab with regard to the risk associated with its routine handling or unintentional mishandling in hospitals. Forced degradation studies can simulate these conditions and provide insights into the biophysical and biochemical properties of mAbs. In this study, we conducted a deep physicochemical and functional characterization of the critical quality attributes of cetuximab in control samples and under controlled degraded conditions, including freeze-thaw cycles, heat, agitation, and light exposure. To achieve this purpose, we used a set of proper analytical techniques, including CD, IT-FS, DLS, SE/UHPLC-UV, UHPLC-MS/MS, and ELISA, to check functionality based on antigen-antibody binding. The results revealed that light exposure was the stress stimuli with the greatest impact on the drug product, leading to the formation of non-natural oligomers, fragmentation, and oxidation of methionine residues. Additionally, cetuximab (Erbitux®, 5 mg/mL) showed a tendency to aggregate when submitted to 60 °C for 1 h. In terms of functionality, cetuximab (Erbitux®, 5 mg/mL) samples were found to be affected when subjected to freeze-thaw cycles, 60 °C (1 h), and when exposed to light (daylight with room temperature excursion and accelerated light exposure). Thus, we suggest that Erbitux® (5 mg/mL) should be shielded from these environmental conditions, as they compromise both the safety and efficacy of the drug product.

Co-Culture of Gut Bacteria and Metabolite Extraction Using Fast Vacuum Filtration and Centrifugation.

This protocol describes a robust method for the extraction of intra and extracellular metabolites of gut bacterial mono and co-cultures. In recent years, the co-culture techniques employed in the field of microbiology have demonstrated significant importance in regard to understanding cell-cell interactions, cross-feeding, and the metabolic interactions between different bacteria, fungi, and microbial consortia which enable the mimicking of complex co-habitant conditions. This protocol highlights a robust reproducible physiologically relevant culture and extraction protocol for the co-culture of gut bacterium. The novel extraction steps are conducted without using quenching and cell disruption through bead-cell methods, freeze-thaw cycles, and sonication, which tend to affect the physical and biochemical properties of intracellular metabolites and secretome. The extraction procedure of inoculated bacterial co-cultures and monocultures use fast vacuum filtration and centrifugation. The extraction methodology is fast, effective, and robust, requiring 4 h to complete.

Mechanical properties and acoustic emission characteristics of basalt fiber reinforced cemented silty sand subjected to freeze–thaw cycles

Freeze–thaw (F–T) cycling poses a significant challenge in seasonally frozen zones, notably affecting the mechanical properties of soil, which is a critical consideration in subgrade engineering. Consequently, a series of unconfined compressive strength tests were conducted to evaluate the influence of various factors, including fiber content, fiber length, curing time, and F–T cycles on the unconfined compression strength (UCS) of fiber-reinforced cemented silty sand. In parallel, acoustic emission (AE) testing was conducted to assess the AE characteristic parameters (e.g., cumulative ring count, cumulative energy, energy, amplitude, RA, and AF) of the same material under F–T cycles, elucidating the progression of F–T-induced damage. The findings indicated that UCS initially increased and then declined as fiber content increased, with the optimal fiber content identified at 0.2%. UCS increased with prolonged curing time, while increases in fiber length and F–T cycles led to a reduction in UCS, which then stabilized after 6 to 10 cycles. Stable F–T cycles resulted in a strength loss of approximately 30% in fiber-reinforced cemented silty sand. Furthermore, AE characteristic parameters strongly correlated with the stages of damage. F–T damage was segmented into three stages using cumulative ring count and cumulative energy. An increase in cumulative ring count to 0.02 × 104 times and cumulative energy to 0.03 × 104 mv·μs marked the emergence of critical failure points. A sudden shift in AE amplitude indicated a transition in the damage stage, with an amplitude of 67 dB after 6 F–T cycles serving as an early warning of impending failure.

Detection of natural pulse waves (PWs) in 3D using high frame rate imaging for anisotropy characterization

IntroductionNumerous studies have shown that natural mechanical waves have the potential to assess the elastic properties of the myocardium. When the Aortic and Mitral valves close, a shear wave is produced, which provides insights into tissue stiffness. In addition, the Atrial Kick (AK) generates a wave similar to Pulse Waves (PWs) in arteries, providing another way to assess tissue stiffness. However, tissue anisotropy can also impact PW propagation, which is currently underexplored. This study aims to address this gap by investigating the impact of anisotropy on PW propagation in a phantom.MethodsTube phantoms were created using Polyvinyl Alcohol (PVA). Anisotropy was induced between two sets of two freeze-thaw cycles by stretching and twisting the material. The study first tests and validates the procedure of making helical anisotropic vessel phantoms using the shear wave imaging technique (by estimating the shear wave speed at different probe angles). Using plane wave ultrasound tomography synchronized with a peristaltic pump, 3D high frame rate imaging is performed and used to detect the 3D propagation pattern of PW for each manufactured vessel phantom. Finally, the study attempts to extract the anisotropic coefficient of the vessel using pulse wave propagation angle.ResultsThe Shear wave imaging results obtained for the isotropic vessel show very similar values for each probe angle. On the contrary, the results obtained for the axial anisotropy vessel show a region with a higher shear wave speed at about 0°, corresponding to the long axis of the vessel. Finally, the results obtained for the helical anisotropy depicted increasing shear wave velocity value from −20° to 20°. For the axial phantom, the wavefront of the pulse wave is perpendicular to the long axis of the vessel, while oriented for the helical anisotropic vessels phantom. The pulse wave propagation angle increased with the number of twists made during the vessel manufacturing.DiscussionThe results show that anisotropy can be induced in PVA vessel phantoms by stretching and twisting the material in freeze-thaw cycles. The findings also suggest that vessel anisotropy affects pulse wave propagation angles. Estimating the pulse wave propagation angle may be interesting in characterizing tissue anisotropy in organs where such waves are naturally present.