Stiffness Reduction Research Articles

Multiparametric liver assessment in patients successfully treated for hepatitis C: a 4-year follow-up

Background Hepatitis C virus (HCV) is a major cause of chronic liver disease, in which liver stiffness increases. Liver stiffness measurements (LSM) are therefore essential in diagnosing liver diseases and predicting disease development. The study objective was to perform a comprehensive prospective assessment of the liver before, after and 4 years after treatment for HCV, including an assessment of the long-term outcome of fibrosis, steatosis and inflammation. Methods and findings Patients eligible for HCV treatment were included prospectively in 2018 (n = 47). Liver stiffness was measured using transient elastography and 2D shear-wave elastography (SWE). Blood tests, B-mode ultrasound (US) and SWE, were performed before, after (end of treatment [EOT]), 3 months after (EOT3) and 4 years after treatment (4Y). At the final visit, we added attenuation imaging and shear-wave dispersion slope (SWDS) measurements to assess steatosis and inflammation. Three months after treatment, the sustained virologic response rate was 93%. The median liver stiffness for baseline, EOT, EOT3 and 4Y was 8.1, 5.9, 5.6 and 6.3 kPa, respectively. There was a significant reduction in liver stiffness from baseline to EOT, and from EOT to EOT3. After 4 years, the mean attenuation coefficient (AC) was 0.58 dB/cm/MHz, and the mean SWDS value was 14.3 (m/s)/kHz. Conclusion The treatment for HCV was highly effective. Measurements of liver stiffness decreased significantly after treatment and remained low after 4 years. AC measurements indicated low levels of liver steatosis. Shear-wave dispersion values indicated inflammation of the liver, but the clinical implication is undetermined and should be explored in larger studies. Clinicaltrials.gov: NCT03434470 Abbreviations AC: attenuation coefficient; APRI: aspartate aminotransferase to platelet ratio index; ATI: attenuation imaging; cACLD: compensated advanced chronic liver disease; CAP: controlled attenuation parameter; FIB-4: Fibrosis-4 Index for liver fibrosis; HCC: hepatocellular carcinoma; LSM: liver stiffness measurement; NAFLD: non-alcoholic fatty liver disease; NASH: non-alcoholic steatohepatitis; SWDS: shear-wave dispersion slope; SWE: shear-wave elastography; US: ultrasound

Enhanced impact resistance of RC beams using various types of high-performance fiber-reinforced cementitious composites

This study investigates the impact resistance of reinforced concrete (RC) beams using various types of high-performance fiber-reinforced cementitious composites (HPFRCCs). A total of ten large-sized RC beams were fabricated and tested under static and impact loading conditions. Four different types of HPFRCCs with 2% by volume of steel, polyvinyl alcohol (PVA), and polyethylene (PE) fibers were considered. Ultra-high-performance fiber-reinforced concrete (UHPFRC) based on steel fibers demonstrated superior compressive and tensile strengths, while high-performance strain-hardening cementitious composite (HP-SHCC) based on PE fibers exhibited the highest strain and energy absorption capacities. The steel-bar reinforced (R-) UHPFRC and HP-SHCC beams showed superior flexural load capacity compared to reinforced normal strength concrete (R-NSC) beams. The highest ductility of 8.02 was found in the R-HP-SHCC beam, almost 5 times higher than that of the R-NSC beam. By drop hammer impact with a kinetic energy of 30 kJ, the R-UHPFRC beam completely failed due to its higher reaction load and lower structural ductility, while other RC beams made of NSC and HPFRCCs withstood the identical impact load. The R-HP-SHCC beam exhibited the best impact resistance, with a 29.1% lower maximum deflection compared to the R-NSC beam, and the largest residual load capacity after the impact damages. The R-HP-SHCC beam, despite being damaged, showed no reduction in flexural stiffness, yet it demonstrated an impressive 5.4% increase in load capacity compared to the undamaged beam.

On the Applications of a New Advanced PEPFG Mathematical Model for HTM Dynamic Behavior of SDF Sandwich Plates

Considering the crucial role of the flexoelectricity phenomena (the electrical polarization–strain gradient coupling) in the mechanical behavior of different structures on the micro/nanoscale, this paper is derives the motion equations of a size-dependent flexoelectric (SDF) sandwich plate to study its hygro-thermo-mechanical (HTM) dynamic behavior. The model is a three-layer microplate including a porous exponential and power–law functionally graded (PEPFG) mid-layer, and two flexoelectric face sheets. The whole structure is under hygrothermal loading and the Vlasov foundation serves as the stand for the structure. Then, Hamilton’s principle and modified couple stress theory (MCST) are implemented to derive the motion equations. The new PEPFG utilization besides evaluating the impact of the length scale parameter, hygrothermal loading, materials composition, porosity, foundation parameter, and boundary conditions on the normalized natural frequency (NNF) of such an SDF sandwich model is the novelty of this paper. It is revealed that the lateral ratio enhancement causes NNF and stiffness reduction in the model. Furthermore, among all considered boundary types, simply supported and clamped refer to the lowest and the highest NNFs, respectively. This paper serves as a good source to provide a better understanding of the dynamic response of high stiffness-to-weight ratio structures to different variable variations.

Buckling and vibro-acoustic behavior analysis of laminated immersed cylindrical shells with hydrostatic pressure based on Chebyshev-Fourier spectral approach

The buckling and vibroacoustic behaviour of laminated cylindrical shell structures is vital for the safety and operational efficiency of underwater vehicles. This paper introduces a Chebyshev-Fourier spectral approach for the comprehensive analysis of buckling and vibro-acoustic behaviour in water-immersed laminated cylindrical shells under external hydrostatic pressure. The approach combines Chebyshev polynomials and Fourier series to approximate the displacement of shell and acoustic pressure of the fluid-structure-interaction (FSI) surface in cylindrical coordinates. An approximate solution is used in the axial direction, while an analytical solution is used in the circumferential direction, allowing for the analysis of different circumferential wave numbers n. The influence of external fluid pressure is characterized through the Helmholtz boundary integral equation, while the effect of hydrostatic pressure is deduced using linear elastic theory. From a theoretical derivation standpoint, hydrostatic pressure leads to a reduction in equivalent stiffness, while the external fluid contributes to an increase in the effective mass matrix. Validated against established literature analysis, the study finds that hydrostatic pressure decreases the natural frequencies, though the impact is less significant for lower circumferential wave numbers. For these lower wave numbers, the overall radiated sound power remains largely independent of external hydrostatic pressure, regardless of being in air or water. However, at higher circumferential wave numbers, the effect is more pronounced. This study not only advances the theoretical framework for analysing submerged cylindrical shells but also provides crucial insights into designing more robust structures for underwater applications.

Understanding and phenomenological modeling of the pinching effect of the load–deflection curve of reinforced concrete beams subjected to bending

The reliable prediction of the seismic response of reinforced concrete (RC) structures hinges on accurate modeling of the cyclic behavior of their constituent elements. The load–deflection curve in RC beams exhibits a pinched hysteresis pattern corresponding to energy dissipations. This pinching effect, often observed under seismic loading conditions, reflects a reduction in stiffness and energy dissipation capacity at certain loading stages. Despite its significance, the detailed mechanisms underlying this phenomenon remain underexplored in existing literature. This paper aims to address this gap by presenting simplified models that directly represents the pinching effect at the crack scale. The model is grounded in a comprehensive analysis of shear stress interactions and crack closure dynamics, hypothesized as primary contributors to the pinching phenomenon. Our approach involves a meticulous examination of the hysteresis loops’ area and shape, facilitating the estimation of an equivalent viscous damping ratio to represent energy dissipation in seismic simulations, irrespective of changes in the structure’s damage or ductility levels. The paper unfolds in three key sections: The first section underscores the significance of a nuanced understanding of the pinching effect in seismic analysis. The second section presents an extensive literature review, consolidating crucial insights into the nature of the pinching phenomenon. The third section details the development and application of the proposed mesoscopic model, highlighting the impact of various geometrical and material parameters on the pinching effect.

JNK2-MMP-9 axis facilitates the progression of intracranial aneurysms

Intracranial aneurysm (IA) can cause subarachnoid hemorrhage or some other hemorrhagic stroke after rupture. Because of the poor outcome in spite of the intensive medical care after the onset of hemorrhage, the development of a novel therapeutic strategy like medical therapy to prevent the progression of the disease becomes a social need. As the reduction of arterial stiffness due to the degeneration of the extracellular matrix via Matrix Metalloproteinases (MMPs) becomes one of the central machineries leading to the progression of IAs through a series of studies, factors regulating the expression or the activity of MMPs could be a therapeutic target. In the present study, specimens from human IA lesions and the animal model of IAs were used to examine the expression of c-Jun N-terminal kinase (JNK) which might exacerbate expressions of MMPs in the lesions to weaken arterial walls resulting in the progression of the disease. In some human IA lesions examined, the expression of p-JNK, the activated form of JNK, could be detected mostly in the medial smooth muscle cells. In IA lesions induced in rats, the activation of JNK was induced during the progression of the disease and accompanied with the activation of downstream transcriptional factor c-Jun and importantly with the expression of MMP-2 or -9. The genetic deletion of Jnk2, not Jnk1, in mice significantly prevented the incidence of IAs with the suppression of the expression of MMP-2 or MMP-9. These results combined together have suggested the crucial role of JNK in the progression of IAs through regulating the expression of MMPs. The results from the present study provides the novel insights about the pathogenesis of IA progression and also about the therapeutic target.

Fully Bio-Based Blends of Poly (Pentamethylene Furanoate) and Poly (Hexamethylene Furanoate) for Sustainable and Flexible Packaging.

In the present study, bio-based polymeric blends have been prepared for applications in the field of sustainable food packaging, starting from two furan-based homopolymers, poly(hexamethylene 2,5-furanoate) (PHF) and poly(pentamethylene 2,5-furanoate) (PPeF). PHF and PPeF were synthesized by two-step melt polycondensation-a solvent-free synthetic strategy-and then binary physical mixtures, PHF/PPeF, with different weight compositions were prepared by dissolution in a common solvent. The blends were processed into compression-moulded films, and molecular, morphological, structural, thermal, and mechanical characterizations were subsequently carried out. Blending did not negatively affect the thermal stability of the parent homopolymers, and good compatibility between them was observed. This strategy also allowed for the modulation of the chain rigidity as well as of the crystallinity, simply by acting on the relative weight amount of the homopolymers. From a mechanical point of view, the presence of PPeF led to a reduction in stiffness and an increase in the elongation at break, obtaining materials with an elastomeric behaviour. Evaluation of the gas barrier properties confirmed that the good barrier properties of PHF were preserved by blending. Finally, lab-scale composting tests confirmed a greater weight loss of the mixtures with respect to the PHF homopolymer.

Health monitoring of bonded joints through electrical measurements

The aim of this research work is to explore the possibility of continuously monitoring the presence of damage in bonded joints through electrical measurements. Initially, an analytical model for estimating the crack length based on the electric resistance increase measured across the bond area is presented. The model is successfully validated through finite element analyses and experimental tests on single lap joints made of a conductive adhesive and aluminium or carbon/epoxy adherends. For the last case, the model is extended to account for damage scenarios where a residual conductivity is present across crack faces, due, for instance, to fibre bridging. Eventually, a procedure for predicting the crack length and the stiffness reduction in bonded joint based on electrical measurement is developed.

Deterioration of a compacted soil due to suction loss and desiccation cracking

This paper presents the results of laboratory testing of a clayey soil taken from a road subgrade in Tanzania. The results revealed a reduction in the soil water retention capacity, accompanied by shifts in the water retention curves with successive cycles. These changes affected the soil response to shear loading, resulting in decreased shear strength and stiffness with hydraulic cycles. While the soil experienced suction losses due to desiccation cracks and hysteresis effects, these suction variations alone could not account for the observed changes in shear strength, implying that the development of desiccation cracks contributed to reduced strength and stiffness. The results showed that the degradation effect of crack development on the shear strength and elastic modulus of the soil during hydraulic cycles could be justified using a macroscopic degree of saturation, i.e. the degree of saturation of large pores external to the aggregates, through a microstructural-based effective stress approach. This allowed the increase in the large pores resulting from crack development to be accounted for and hence the successive reductions in shear strength and stiffness with drying-wetting cycles. These deterioration effects need to be considered for design of geotechnical infrastructure to ensure stability, and resilience of infrastructure over time.

EFFECT OF TIME ELAPSED BETWEEN SUCCESSIVE CONCRETE POURINGS AND LOCATION OF THE COLD JOINTS ON THE FLEXURAL CAPACITY OF RC BEAMS

This research investigates the effect of the time interval between successive concrete pouring and the position of cold joints on properties and bending strength capacity in reinforced beams. Two horizontal cold joints were examined: another positioned in the zone of compressions (h=110 mm) and one situated in the beam's tension area ( h = 50mm). In both cold joint elevations, the time interval between two mert patches was varied as 1.5 hrs.,3 hr and 4 hrs. Furthermore, six nominally standardized RC beams were tested and analyzed with a reference beam devoid of cold joints. The obtained outcomes revealed the decrease of beams' ultimate flexural capacity with an increase in time elapsed between periods of pouring from 1.5 to 4.5 hours. The reduction in flexural strength was more evident when a cold joint went through the compression fibre of a beam. Additionally, the hardness and rigidity of the tested beams roughly inversely correlated with time intervals between consecutive pourings. More specifically, the percentage reduction in ultimate load, stiffness and toughness of cold joints for tension fibres at 1.5 hours was (4.36% ,9.7% and 9.3%) while that of compression fibre was (5.36%),(34.2%)and ( 34.5% ) % respectively when compared with control beam.

ASSESSMENT OF TRANSIENT VIBRATION EFFECTS OF A ROCKING STRUCTURE ON TWO-PARAMETER UPLIFTING FOUNDATION MODEL

This study is on assessment of transient vibration of a rocking structure on two-parameter uplifting foundation model. This foundation model, Filonenko-Borodich (F-B) considers effect of continuity and interactions of the structure with the surrounding foundation surface. The foundation model aids uplift because of its elastic and flexible nature. During ground movement, some forces are generated which cause foundation to vibrate, rock and sometimes uplift due to increasing upward forces and then leading to reduction in the spring stiffness and increase in soil flexibility. This sometimes causes upward trend in the structural response which might affect structural integrity and stability. The use of damping and its effects on the structure response considering uplift are evaluated for a structure on two-parameter foundation. Equations describing the motion were developed by summing forces acting on the structure and foundation, considering equilibrium of moments for the conditions of before uplift and during uplift of the system in accordance using Newton’s second law of motion, D’Alembert’s principles. The resulting equations were solved by applying them in Duhamel Integral form and Simpson’s method used for the numerical solution for the structure responses. The result showed an upward trend in the structural responses during uplifting hence uplift of building foundation is not always beneficial.

Combatting Antibiotic-Resistant Pathogens: Disrupting Pseudomonas Aeruginosa Biofilm Viscoelasticity Using Carbon Dot Nanoparticles

Bacterial infection is a global burden, killing one in every eight people worldwide, primarily due to antibiotic resistance. Pseudomonas aeruginosa is one of the top five bacteria responsible for around 7.7 million fatalities caused by bacterial infections. P. aeruginosa secretes biofilm, a biological substance with viscoelastic characteristics to avoid antimicrobial treatments particularly, in chronic and serious wound infections. In the bid to create topical treatments, we investigated the mechano-active potentials of cellulase-based carbon dots as a therapeutic agent against P. aeruginosa biofilm where we envisage the retaining of the cellulase hydrolytic activity in the cellulase-based carbon dots. Cellulase is a glycoside hydrolase that has already been shown to be effective in causing biofilm dispersal as well as reduction in biofilm stiffness and elasticity.The cellulase carbon dots were synthesized using the microwave while citric acid carbon dots (CA-CDs) were hydrothermally synthesized to serve as non-protein-based carbon dots and then characterized for surface properties, size, elemental compositions, and fluorescence profile. P. aeruginosa biofilms were grown in a microfluidic environment for 24 hours and then treated with these carbon dots at a range of concentrations. Using microrheology, it was seen that biofilms treated with cellulase-based carbon dots were more viscous and less stiff compared to those treated with citric acid-based carbon dots. This appears to be because the cellulase carbon dots impact PSL within the biofilm based on microrheology studies examining bacteria strains with specific EPS components removed. This is consistent with the impact of molecular cellulase on biofilms. In general, initial studies suggest that the cellulase-based carbon dots have the potential to act as an excellent multi-antibiofilm therapeutic in the future.

Shear Performance of Prefabricated Steel Ultra-High-Performance Concrete (UHPC) Composite Beams under Combined Tensile and Shear Loads: Single Embedded Nut Bolts vs. Studs

Ultra-high-performance concrete (UHPC) is widely used in precast concrete-steel composite beams because of its beneficial properties, including reduced structural weight, higher flexural rigidity, and reduced tensile crack formation. In comparison to conventional steel-concrete composite beams, steel-UHPC composite beams exhibit superior characteristics, including reduced structural deadweight, enhanced flexural stiffness, and the capacity to withstand tensile cracking. One successful attempt at meeting the current demands for expedited girder engineering is the development of steel-UHPC composite beams with full-depth precast slabs as key components affecting the overall structural performance using dismountable single embedded nut bolts (SENBs) and widely used studs as competitive alternatives. In contrast, shear connectors are exposed to a combined tensile and shear stress in service life rather than shear only. The corresponding scientific problem is the problem of combined effects under stress in practical applications, but there is currently no relevant research. The shear performance of SENBs in precast steel-UHPC composite beams under tension and shear loads remains unclear. For this purpose, ten push-out specimens and theoretical analyses were performed in this paper, considering the influence of the connector’s type and tensile-to-shear ratio. However, ten specimens were conducted to investigate the tensile-to-shear ratio, and the connector’s type on shear performance is limited. In the future, an increasing number of specimens and test parameters should be considered to investigate the shear performance of precast steel-UHPC composite beams. An increase in the tension-to-shear ratio resulted in a substantial reduction in the ultimate shear capacity, initial shear stiffness, and ductility of the studs. The increase in the tensile-shear ratio from 0 to 0.47 resulted in a 16.9% decline in the ultimate shear capacity, a 30.4% reduction in the initial shear stiffness, and a 21.7% decrease in the ductility of the Series I samples. However, an increase in the tensile-to-shear ratio of the Series II samples from 0 to 0.47 resulted in a 31.3% decline in ultimate shear strength, a 33.2% decline in initial shear stiffness, and a 41.9% decline in ductility. The SENBs demonstrated minimal deviations in ultimate shear capacity compared to their stud counterparts, despite exhibiting notable differences in shear stiffness, and ductility. A lower tensile-to-shear ratio was recommended in practical engineering, which might achieve a larger ultimate shear capacity, stiffness, and ductility. The design-oriented models with enhanced applicability were developed to predict the tension-shear relationship and the load-slip curve of SENBs in prefabricated steel-UHPC composite beams subjected to combined tensile and shear loads. For a tensile-shear relationship model, the point error range was 0 to 0.08, with an average error of 0.03. The square coefficient (R2) was 0.99 for a load-slip curve model. The study findings could offer a credible reference for the shear mechanism of such economical and environmentally friendly precast steel-UHPC composite beams in accelerated bridge construction.

Dapagliflozin Enhances Arterial and Venous Compliance During Exercise in Heart Failure With Preserved Ejection Fraction: Insights From the CAMEO-DAPA Trial.

Systemic arterial compliance and venous capacitance are typically impaired in patients with heart failure with preserved ejection fraction (HFpEF), contributing to hemodynamic congestion with stress. Sodium-glucose cotransporter-2 inhibitors reduce hemodynamic congestion and improve clinical outcomes in patients with HFpEF, but the mechanisms remain unclear. This study tested the hypothesis that Dapagliflozin would improve systemic arterial compliance and venous capacitance during exercise in patients with HFpEF. In this secondary analysis from the CAMEO-DAPA trial (Cardiac and Metabolic Effects of Dapagliflozin in Heart Failure With Preserved Ejection Fraction Trial), 37 patients with HFpEF (mean age 68 ± 9 years, women 65%) underwent invasive hemodynamic exercise testing with simultaneous echocardiography at baseline and following treatment for 24 weeks with Dapagliflozin or placebo. Radial artery pressure (BP) was measured continuously using a fluid-filled catheter with transformation to aortic pressure, central hemodynamics were measured using high-fidelity micromanometers, and stressed blood volume was estimated from hemodynamic indices fit to a comprehensive cardiovascular model. There was no statistically significant effect of Dapagliflozin on resting BP, but Dapagliflozin reduced systolic BP during peak exercise (estimated treatment difference [ETD], -18.8 mm Hg [95% CI, -33.9 to -3.7] P=0.016). Reduction in BP was related to improved exertional total arterial compliance (ETD, 0.06 mL/mm Hg/m2 [95% CI, 0.003-0.11] P=0.039) and aortic root characteristic impedance (ETD, -2.6 mm Hg/mL*sec [95% CI: -5.1 to -0.03] P=0.048), with no significant effect on systemic vascular resistance. Dapagliflozin reduced estimated stressed blood volume at rest and during peak exercise (ETD, -292 mm Hg [95% CI, -530 to -53] P=0.018), and improved venous capacitance evidenced by a decline in ratio of estimated stressed blood volume to total blood volume (ETD, -7.3% [95% CI, -13.3 to -1.3] P=0.020). Each of these effects of Dapagliflozin at peak exercise were also observed during matched 20W exercise intensity. Improvements in total arterial compliance and estimated stressed blood volume were correlated with decreases in body weight, and reduction in systolic BP with treatment was correlated with the change in estimated stressed blood volume during exercise (r=0.40, P=0.019). Decreases in BP were correlated with reduction in pulmonary capillary wedge pressure during exercise (r=0.56, P<0.001). In patients with HFpEF, treatment with Dapagliflozin improved systemic arterial compliance and venous capacitance during exercise, while reducing aortic characteristic impedance, suggesting a reduction in arterial wall stiffness. These vascular effects may partially explain the clinical benefits with sodium-glucose cotransporter-2 inhibitors in HFpEF. URL: https://www.clinicaltrials.gov; Unique identifier: NCT04730947.

Yoga as a complementary therapy for rheumatoid arthritis: a case-based review.

Rheumatoid arthritis (RA) presents patients with chronic pain and functional limitations due to its autoimmune nature. Despite symptomatic and pharmaceutical interventions, many patients experience inadequate relief, prompting exploration into non-pharmacological approaches such as yoga. This study aims to evaluate the effectiveness of yoga as an adjunctive therapy for RA by examining clinical data from patients experiencing chronic pain and limitations. This study analyzed several clinical cases at the Shymkent City Regional Clinical Hospital. Ten RA patients, irrespective of various demographic factors, were enrolled. Parameters including pain intensity, inflammation activity, systolic blood pressure, joint function, and morning stiffness were assessed to gauge the impact of yoga. The findings demonstrated notable positive changes following a three-month yoga program. These changes encompassed enhanced joint health, reduced pain severity, and decreased disease activity. Particularly noteworthy was the reduction in morning stiffness by an average of 31min, alongside a decrease in the average pain index from 80mm to 41.5mm. The mean RA activity level decreased from 5.8 to 4.7. Furthermore, mean systolic blood pressure decreased by 15.5 mmHg, and mean cholesterol levels decreased from 5.3 mmol/L to 4.8 mmol/L. These results underscore the potential significance of yoga as a supplementary intervention for RA. Yoga practice may enhance patients' quality of life and alleviate disease symptoms. Nevertheless, the study's limited sample size necessitates caution, and further research is warranted to validate these findings.

Acute effects of static stretching exercise-induced decrease in arterial stiffness on maximal aerobic capacity.

We recently have reported that individual day-to-day arterial stiffness variations are associated with maximal aerobic capacity. However, the evidence of this phenomenon was not provided sufficiently. The present study aimed to examine whether a decrease in arterial stiffness through static stretching exercise could enhance maximal aerobic capacity. Twelve healthy young men (age 22±2 years, mean and standard deviation) participated in this study and underwent two separate sessions in a randomized controlled crossover design: a single session of a whole-body static stretching exercise protocol that involved the trunk, upper limb, and lower limb (stretch condition), and sedentary control where they rested in the exercise room. Brachial-ankle pulse wave velocity (baPWV) was measured as an index of systemic arterial stiffness before, immediately after and at 30 min after both conditions. Maximal oxygen uptake (V̇O<inf>2</inf>max) was assessed using a graded power test on an electronically braked cycle ergometer after these measurements. As we expected, there was a significant decrease in the baPWV at 30 min after the stretch trial compared to baseline values (P=0.01). The baPWV in the stretch condition was lower than that of the control condition, while V̇O<inf>2</inf>max in the stretch condition was higher than that of the control condition (P=0.03). Based on these findings, it can be inferred that an acute reduction in arterial stiffness may contribute to change in maximal aerobic capacity.

Vibration-based methods for local damage identification of breathing cracks in truss-like structures

A vibration-based local damage identification method is proposed for truss-like structures with breathing cracks. Firstly, a bilinear model is established to represent the characteristics of breathing cracks, and the features of such cracks are detected through reciprocity and homogeneity tests on structural input-output signals. Since the crack is influenced by tensional and compressive forces on truss members, only one damage factor is required to quantify the stiffness reduction of each member. Subsequently, a dynamic equilibrium equation concerning the damage factor is constructed to identify the new load term. The integral equation method, which relies on the virtual work principle, is employed to obtain the displacement responses and loads under all tensile conditions. Finally, the mean value of cumulative damage coefficients for each truss member can be derived as their corresponding damage factor. Numerical examples involving a plane truss structure and a truss offshore platform are utilised to illustrate the effectiveness of this damage identification method. The results demonstrate exceptional precision and efficiency in accurately identifying various damages in truss structures under different excitations and signal-to-noise ratios. A actual space truss structure confirm that this damage identification method exhibits high-level precision in identifying single-member damages as well as multi-member damages with breathing cracks locally.

Experimental and theoretical analysis of mechanical properties of FRP laminated rubber bearing

Fiber reinforced polymer (FRP) laminated rubber bearing is a kind of high-performance isolator with simple structure, low cost, light weight and excellent mechanical properties. The mechanical properties of FRP laminated rubber bearings are investigated by experimental and theoretical methods. Based on the pseudo-static vertical compression test and compression-shear test experiment, the vertical and horizontal mechanical properties of the bearings under different vertical pressures are investigated. According to the deformation compatibility and boundary conditions of elastic composites, the modified calculation equations for the vertical and horizontal stiffness of FRP laminated rubber bearings are derived, and the theoretical analysis is verified by the results of laboratory tests. The influence law of characteristic parameters such as shape factor on the mechanical properties of bearings has been investigated. Tests and theoretical analysis show that the increase of vertical pressure causes a certain degree of increase in the vertical stiffness and a significant reduction in the horizontal stiffness of the bearing. By studying the effect of horizontal and vertical stiffness, the manuscript provides a useful reference for the design of FRP laminated rubber bearings.

Limb Position Influences Peripheral Arterial Stiffness Reduction with Reactive Hyperemia

The mechanism behind the acute reduction in peripheral arterial stiffness with reactive hyperemia is presumed to be flow-mediated; however, this has not been clearly demonstrated. We hypothesized that a larger reactive hyperemia magnitude would result in a greater reduction in peripheral arterial stiffness. Fourteen healthy young adults (5 females, 25 ± 5 yrs, mean ± SD) underwent reactive hyperemia with a rapid-release cuff on the upper arm inflated to 220 mmHg for 5 min: once with the arm positioned ~ 50ο above heart level and once with the arm positioned ~ 50ο below heart level. Brachial-radial pulse wave velocity (PWV) was measured with tonometers over brachial and radial arteries before cuff inflation and at 5, 15, and 30 min after release. Brachial blood flow was monitored with doppler ultrasound. At 5 min after reactive hyperemia, both the absolute (2.31 ± 1.22 vs 1.19 ± 1.19 m/sec, p = 0.007) and relative (24% vs 15%; p = 0.043) changes in brachial to radial PWV were greater with the arm below the heart compared to above the heart. The peak brachial blood flow was higher when the arm was below the heart compared to above the heart (477 ±\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\pm$$\\end{document} 145 vs 369 ±\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\pm$$\\end{document} 137 ml/min; p < 0.001). Reactive hyperemia acutely reduced peripheral arterial stiffness above and below heart level, with a greater decrease observed when the arm was positioned below the heart. These results demonstrate the contribution of conduit artery blood flow to the reduction of peripheral arterial stiffness after reactive hyperemia.

Cyclic behaviour of 3D-woven composites in tension: Experimental testing and macroscale modelling

Composites with 3D-textile reinforcement present several engineering advantages. However, their intricate yarn architecture also creates a material with a number of nonlinear behaviours and features, which need to be understood in order to enable their efficient use. To demonstrate the anisotropic development of such non-linear behaviours, and how they depend on loading mode, tensile samples of a 3D-woven layer-to-layer angle interlock carbon-fibre reinforced epoxy composite are tested experimentally (data shared publicly). More specifically, specimens are cut and tested at orientations of 0°, 15°, 30°, 45° and 90° relative to the direction of the warp yarns. The samples are tested cyclically by loading and unloading them at progressively higher displacement values. By monitoring the reduction in stiffness and the development of permanent strains it is possible to identify material parameter values used to calibrate an anisotropic macroscale elasto-plastic damage model. The model shows promising agreement with the experimental results.