Internal Pressure Changes Research Articles

Mechanical effects of circular liquid inclusions inside soft matrix: role of internal pressure change and surface tension

The mechanical effects of dilute liquid inclusions on the solid-liquid composite are explored, based on an analytical circular inclusion model incorporating the internal pressure change of the liquid and the surface tension of the interface. Several simple explicit dependences of the stress field and effective stiffness on the bulk modulus and the size of the liquid, the surface tension, and Poisson’s ratio of the matrix are derived. The results show that the stresses in the matrix are reduced, and the stiffness of the solid-liquid composite is enhanced with the consideration of either the surface tension or the internal pressure change. Particularly, the effective Young’s modulus predicted by the present model for either soft or stiff matrices agrees well with the known experimental data. In addition, according to the theoretical results, it is possible to stiffen a soft solid by pressured gas with the presence of the surface tension of the solid-gas interface.

Effects of Left Ventricular Hypertrophy and Myocardial Stiffness on Myocardial Strain Under Preserved Ejection Fraction.

Despite numerous experimental observations regarding heart failure with preserved ejection fraction (HFpEF), which is characterized mainly by left ventricular hypertrophy and a left ventricular ejection fraction over 50%, myocardial dynamics under HFpEF have not yet been fully clarified, particularly regarding the relationship between myocardial strain distribution and myocardial work. To address this issue, we numerically investigated radial distribution of myocardial strain during a cardiac cycle with fixed internal volume at the end of the systolic and diastolic phases under different mechanical conditions, such as those involving myocardial thickness and elasticity of myocardial fibers. The myocardium was a modeled as a visco-hyperelastic continuous material. This model was taken into account that active contractile stress along the myocardial fiber direction depends on membrane potential change. Our numerical results showed that both radial and circumferential strains decreased as wall thickness increased, which reflected cardiac hypertrophy, but that myocardial work became larger than that observed with thin ventricular walls. Further, the change in left ventricular diastolic internal pressure caused circumferential strain, while fiber stiffness contributed to radial strain. Since peak circumferential strain was well estimated by the maximum difference between total internal and myocardial volumes, measuring the epicardial contraction rate should be helpful in understanding patients with HFpEF.

Blunt injury of liver: mechanical response of porcine liver in experimental impact test

Objective. The liver is frequently injured in blunt abdominal trauma caused by road traffic accidents. The testing of safety performance of vehicles, e.g. belt usage, head support, seat shape, or air bag shape, material, pressure and reaction, could lead to reduction of the injury seriousness. Current trends in safety testing include development of accurate computational human body models (HBMs) based on the anatomical, morphological, and mechanical behavior of tissues under high strain. Approach. The aim of this study was to describe the internal pressure changes within porcine liver, the severity of liver injury and the relation between the porcine liver microstructure and rupture propagation in an experimental impact test. Porcine liver specimens (n = 24) were uniformly compressed using a drop tower technique and four impact heights (200, 300, 400 and 500 mm; corresponding velocities: 1.72, 2.17, 2.54 and 2.88 m s−1). The changes in intravascular pressure were measured via catheters placed in portal vein and caudate vena cava. The induced injuries were analyzed on the macroscopic level according to AAST grade and AIS severity. Rupture propagation with respect to liver microstructure was analyzed using stereological methods. Main results. Macroscopic ruptures affected mostly the interface between connective tissue surrounding big vessels and liver parenchyma. Histological analysis revealed that the ruptures avoided reticular fibers and interlobular septa made of connective tissue on the microscopic level. Significance. The present findings can be used for evaluation of HBMs of liver behavior in impact situations.

Mechanism of Increasing the Permeability of Water-Bearing Coal Rock by Microwave Steam Explosion

Microwave heating of water-bearing coal can promote pore water evaporation. The pores are broken under the action of steam pressure, increasing the permeability of the coal. This study is aimed at investigating the mechanism of permeability improvement of water-bearing coal rock by microwave steam explosion. First, a microwave oven was used to irradiate and heat five groups of coal rock with different water contents; the NMR test was then conducted on the heated sample. Second, the internal vapor pressure and temperature changes during the heating process were obtained through the T-connector for samples with different water contents. Finally, a numerical experiment was used to explore the deformation characteristics of pores under three filling conditions. The experimental results showed that the total porosity increased significantly when the water content of coal increased from 0% to 8%, while the permeability increased by nearly 4.78 times. The extreme value of gas pressure inside the sample showed an increasing trend. The gas pressure and temperature were in line with the equation of state for an ideal gas during the rising phase. Numerical experiments showed that the pore boundary shrunk inward under vacuum conditions, and compressive stress appeared at the tip. The saturated humid air and liquid water conditions expanded the pore boundaries outward and caused tensile stress at the tip, with the latter being nearly 2.3 times larger than the former, making it more conducive to the development of pores. The findings of this study can be used as a reference value for the expansion of coalbed methane extraction technology.

Performance analysis of embedded tri-screw pump based on computational fluid dynamics

To meet the stringent size and noise requirements for hydraulic pumps used in submarines, an embedded tri-screw pump is proposed. The pump is embedded in the core of the servo motor to form a new servo motor pump. This paper first presents the embedded triscrew pump, as well as the cross-section profile design and parameter equations of the driving and driven screws. Velocity and pressure field distributions as well as changes in internal pressure and shear stress inside the embedded tri-screw pump with different radial and interlobe clearances were investigated using computational fluid dynamics. Furthermore, screw deformation under multi-field coupling was analyzed. In contrast to torque or fluid pressure acting alone, under the fluid-solid coupling effect, screw deformation and stresses are inversely proportional to the rotational speed of the pump and directly proportional to the power and output pressure. The simulation and experimental results were consistent for various outlet pressures and rotational speeds. Radial clearance of the screw has a more significant influence on leakage than inter-lobe clearance and therefore, more impact on the volumetric efficiency of the pump.

Consistent modelling of material weight loss and gas release due to pyrolysis and conducting benchmark tests of the model-A case for glovebox panel materials such as polymethyl methacrylate.

It is necessary to consider how a glove box's confinement function will be lost when evaluating the amount of radioactive material leaking from a nuclear facility during a fire. In this study, we build a model that consistently explains the weight loss of glove box materials because of heat input from a flame and accompanying generation of the pyrolysis gas. The weight loss suggests thinning of the glove box housing, and the generation of pyrolysis gas suggests the possibility of fire spreading. The target was polymethyl methacrylate (PMMA), used as the glove box panel. Thermal gravimetric tests on PMMA determined the parameters to be substituted in the Arrhenius equation for predicting the weight loss in pyrolysis. The pyrolysis process of PMMA was divided into 3 stages with activation energies of 62 kJ/mol, 250 kJ/mol, and 265 kJ/mol. Furthermore, quantifying the gas composition revealed that the composition of the pyrolysis gas released from PMMA can be approximated as 100% methyl methacrylate. This result suggests that the released amount of methyl methacrylate can be estimated by the Arrhenius equation. To investigate the validity of such estimation, a sealed vessel test was performed. In this test, we observed increase of the number of gas molecules during the pyrolysis as internal pressure change of the vessel. The number of gas molecules was similar to that estimated from the Arrhenius equation, and indicated the validity of our method. Moreover, we also performed the same tests on bisphenol-A-polycarbonate (PC) for comparison. In case of PC, the number of gas molecules obtained in the vessel test was higher than the estimated value.

Mechanics of adhesives under annular confinement: internal pressure, force, and interfacial area.

Closed annular adhesive interfaces are commonly found in nature as well as in many existing and developing technologies. Such contacts provide enhanced control of interfacial history by prescribing whether interfacial separation occurs at the outer or inner edge, and whether internal pressure affects the required force for separation. To facilitate the development of technologies involving annular contacts, we have experimentally measured the relationship between applied displacement, resulting force and internal pressure, and annular interface dimensions for the contact between a rigid annular probe and an adhesive layer with finite thickness. Experiments were validated by finite element analysis models, which were used to develop semi-empirical analytical relationships for the changes in contact compliance as a function of material properties and geometric constraints. Additionally, the change in internal pressure was modeled as a function of annular contact dimensions and adhesive layer material properties. This model predicts the critical volume where internal pressure changes alters critical force for separating an annular contact interface. The results discussed here provide a foundation for new experimental protocols for characterizing soft materials, including pressure-sensitive adhesives, as well as guidelines for designing annular interfacial materials with controlled separation histories.

Integrated Reference Electrodes in Anion-Exchange-Membrane Electrolyzers: Impact of Stainless-Steel Gas-Diffusion Layers and Internal Mechanical Pressure

Alkaline-membrane electrolyzers operating in pure water might provide scalable low-cost H2 production but currently lag in performance and durability compared to commercial technologies. Typically, membrane–electrode assemblies (MEAs) are optimized in electrolyzers by changing one parameter at a time and assessing the resulting system performance via two-electrode polarization and impedance measurements. These approaches are limited in their ability to assign performance changes and durability to specific electrodes or processes. We integrate a reference electrode with the MEA to separate anode and cathode responses in both polarization and impedance measurements. We illustrate the power of the approach by showing how the fiber diameter of stainless-steel gas-diffusion layers (GDLs) affects performance solely at the anode, while changing the thickness of the cathode GDL simultaneously affects the performance of the anode and cathode due to changes in internal pressure from mechanical compression. This finding was obscured in conventional two-electrode measurements. The work thus guides both high-performance alkaline-membrane water-electrolyzer development and illustrates a useful strategy to study structure–activity relationships in the MEA.

Study on the effect of interface failure between casing and cement sheath on casing stress under non-uniform in-situ stress

The interface failure (micro-annulus and de-bonding) at the first interface between cement sheath and formation, or at the second interface between cement sheath and casing can be easily caused by alternating change of internal pressure and temperature in the casing during large-scale multistage hydraulic fracturing in shale-gas well. It is likely to have a great impact on casing stress and pose a potential threat to casing failure, especially the casing under non-uniform in-situ stress (NUS). Hence, based on the generation mechanism of micro-annulus in the first and second interface, the mechanical model coupling the casing and cement sheath as well as formation under non-uniform in-situ stress is presented with due consideration of the effect of interface failure status on casing stress. In the model, the failure interface with micro-annulus is considered by adopting boundary conditions of smooth contact, and the interface without micro-annulus is considered by adopting boundary conditions of ideal complete contact. The stress and displacement equations are derived by the semi analytical method, and the linear algebra equations and analytical solution of the equations are obtained based on the different contact status. The associated calculating program to calculate stress distribution of casing and cement sheath is developed and programmed. The effects of physical parameter and geometrical parameters of formation, cement sheath and casing, contact status of cement sheath boundary and non-uniformity of in-situ stress on casing stress have been systematically investigated.

高用量アンチトロンビン投与が血小板機能と凝固機能に及ぼす影響(The influence of a high dose antithrombin on the platelet function and blood coagulability)

要旨【目的】KyberSept trialのサブグループ解析では，アンチトロンビン高用量投与群はプラセボ群に比べて有意に死亡率が低かった。しかし，高用量アンチトロンビン投与による，凝固系への影響に関しては詳しく知られていない。今回アンチトロンビン高濃度検体の凝固特性について調査を行った。【対象】健常者10人より血液検体を採取し，アンチトロンビン製剤を添加することでアンチトロンビン濃度が異なる検体を作成した。凝固特性の調査には生体内での反応に近づけるため，全血を利用するT–TAS®およびROTEM®を使用した。【結果】血小板機能を反映するPL測定では，血栓閉塞開始時間はアンチトロンビン濃度に依存し有意差をもって延長した。AR測定でも同様に，血栓閉塞開始時間はアンチトロンビン濃度に依存し延長した。また血栓閉塞時間もアンチトロンビン濃度に依存し延長した。健常検体内では十分量存在し飽和状態と考えられていたアンチトロンビンであるが，高用量投与された場合には抗凝固作用が増強することが証明された。さらに，T–TAS®を用いたPL測定を行うことで，血小板血栓形成能にも抑制効果が認められることが証明された。【結語】アンチトロンビンは濃度依存性に抗凝固作用を発揮する。また血小板粘着能に対しても影響を及ぼしており，濃度依存性に血小板血栓形成能を抑制する。

Estimation of the resource of pipes of the main circulation pipeline of a NPP by the criterion of crack resistance with account of operational degradation of properties

The results of an experimental determination of the characteristics of cyclic crack growth resistance of specimens made of stainless steel 08Kh18N12T are given. Compact samples 20 mm thick cut from Du 550–30 pipes of the primary circuit of the main circulation pipeline (MCР) were studied under eccentric tension in the initial state and after 100 thousand hours of operation in the conditions of the Novo-Voronezh NPP. Using a new engineering approach based on measuring the specimen tightening and constructing a cyclic elastoplastic fracture diagram for a specimen with a crack in the coordinates “tightening – the stress intensity factor, calculated taking into account the plasticity correction”, a calculated life estimation is given for the pipe of Du 550–30 MCР NPP, made of 08Kh18N12T steel, according to the criterion of cyclic crack growth resistance, taking into account operational degradation of properties caused by the running time of 100 thousand hours. The life (survivability), expressed in a number of cycles of change in internal pressure, for a pipe with the most dangerous defects (surface semi-elliptical crack and combined defect “pitting + crack”) is determined. An analysis of the influence of the level of initial damage and the type of hazardous defect on the survivability of the pipes is made. The results can be used to analyze damage and predict the life of pipes made of ductile metals and alloys, in cooling systems of reactors, as well as main pipelines of hydrocarbon transport.

A new insight into impact of thermal cycling on the un-notched and circular hole polymeric composite rings via naval ordnance laboratory-ring test

In this paper, different mechanical responses of polymer matrix composite rings under thermal cycling are analyzed. The polymer matrix composite rings are classified to un-notched and open-hole specimens and tested based on the naval ordnance laboratory-ring tensile test method. Internal pressure, fracture and surface degradation changes as a function of the hole diameter and number of cycles are investigated. Experimental results suggest that specimens with larger hole radius have more mechanical property variations during thermal cycling. Also, it is revealed that the mechanical properties of laminates degrade as a function of the number of cycles and the hole diameter. The results also demonstrate that long splitting fiber breakage is the main mode for the failure of un-notched specimens, whereas fiber breakage and fiber matrix debonding are the two main modes for the failure of open-hole specimens. Finally, a multiple regression model is proposed to predict the tensile response of un-notched and open-hole polymer matrix composite rings subjected to thermal cycling condition.

Stress concentration analysis of butt welds with variable wall thickness of spanning pipelines caused by additional loads

In the field of oil and natural gas gathering and transportation, the pipeline is likely to be span under the geological load. With the influence of gravity, internal pressure and other additional loads the stress concentration at the variable wall thickness weld on the spanning pipeline would further threaten the safe operation of pipelines. In this paper, finite element method is used to establish the numerical model of variable wall thickness butt weld of free spanning pipelines. The SCF(Stress Concentration Factor) is used to reflect the stress concentration degree of the weld with variable wall thickness under the affect of additional stress, and the stress distribution of variable wall thickness welds is studied. The influence of spanning pipe length, welding positions, internal pressure, thickness ratios and conical surface lengths on the SCF of the spanning pipe are obtained. The results illustrate that under the action of additional stress the existence of variable wall thickness weld has a great influence on the welding root at the bottom of the pipeline, which is not conducive to the stress of the spanning pipeline. The change of pipe spanning length has great influence on the SCF at the weld root at the bottom of the pipe. As the length of the spanning increases, the SCF growth rate at the root of the weld is greater. The position of variable wall thickness weld has a certain impact on the SCF of spanning pipeline. As the variable wall thickness weld is close to the mid-span position of pipeline, the stress concentration part of the weld gradually transfers from the top of the pipe to the bottom of the pipe. The change of pipeline internal pressure has little influence on SCF. The wall thickness ratio and the conical surface length have a great influence on the pipeline, which is the main influencing factor of the stress concentration of the spanning pipeline. Reducing the wall thickness ratio or increasing the conical surface length can effectively reduce the stress concentration of the variable wall thickness weld.

Anisotropic continuum damage analysis of thin-walled pressure vessels under cyclic thermo-mechanical loading

The present study intends to analyze damage in thin-walled steel cylinders undergoing constant internal pressure and thermal cycles through use of anisotropic continuum damage mechanics (CDM) model coupled with nonlinear kinematic hardening rule of Chaboche. Materials damage in each direction was defined based on plastic strain and its direction. Stress and strain distribution over wall-thickness was described based on the CDM model and the return mapping algorithm was employed based on the consistency condition. Plastic zone expansion across the wall thickness of cylinders was noticeably affected with change in internal pressure and temperature gradients. Expansion of plastic zone over wall-thickness at inner and outer surfaces and their boundaries demarking elastic and plastic regions was attributed to the magnitude of damage induced over thermo-mechanical cycles on the thin-walled samples tested at various pressure stresses.

Osmotic squat actuation in stiffness adjustable bacterial cellulose composite hydrogels.

Mechanically adaptive hydrogels can change their mechanical characteristics in response to external stimuli and have potential applications in biomechanical fields. To eliminate the undesired swelling/shrinkage in the responding process, poly(acrylic acid) (PAA) was grafted to acryloyl chloride (AC)-modified bacterial cellulose (BC) by free-radical polymerization. The obtained BC-g-PAA composite hydrogels showed adjustable stiffness in compression, remained soft at pH lower than 6 (compression strain over 49% at a stress of 0.1 MPa), and stiffened when pH reached 7 (compression strain lower than 27% at a stress of 0.1 MPa), while the volume change ratio was consistently lower than 15%. Based on this, the hydrogels showed interesting squat actuation to lift a weight. The BC composite hydrogels exhibited dual pH-responsiveness after grafting PAA with poly[2-(dimethylamino)ethyl methacrylate], confirming the general availability of this strategy in fabricating volumetrically stable and mechanically adaptive hydrogels. The surrounding solution-independent softening of BC-g-PAA hydrogels was observed in 8 min under UV irradiation via a photo-triggered pH jump reaction. By virtue of the selective UV irradiation, spatiotemporally controllable softening with actuation in BC-g-PAA hydrogels was realized. The developed pH-responsive mechanically adaptive BC composite hydrogels with high dimensional stability and UV-activated spatiotemporal squat actuating capability are expected to provide more options in developing novel bioimplants and smart structures.

Analytical Model for Air Flow into Cracked Concrete Structures for Super-Speed Tube Transport Systems

The super-speed tube transport (SSTT) system, which enables high-speed transportation in a partially vacuumed tube by minimizing the air resistance, is drawing attention as a next-generation transportation system. To evaluate the applicability of concrete as a material for the system, the effect of cracks on the airtightness of the system needs to be considered. This study aims to establish an analytical relationship between the cracks induced on a concrete tube structure and the system airtightness. An analytical model for the leakage rate through the concrete cracks is first applied to establish a differential equation, which can help determine the air flow rate into the concrete tube structure through the cracks. A mathematical formula for predicting the internal pressure changes over time in the concrete tube structure is then derived. The effect of crack development on the system airtightness is assessed through parametric analysis and a crack index for describing the extent of crack development is proposed by investigating the correlation with the system airtightness. Finally, assuming that the cracks due to external loadings are closely related to the displacement, the correlation between displacements and the airtightness of concrete tube structures is demonstrated through a set of experimental tests. As a result, the necessity of crack analysis for evaluation of the airtightness performance is emphasized.

Improvement of the toolset for diagnosing underground pipelines of oil and gas enterprises considering changes in internal working pressure

Improvement of the toolset for diagnosing underground pipelines of oil and gas enterprises considering changes in internal working pressure

Effects of Ambient Temperature Change on the Internal Pressure Change of Multi-Layered Subsea Pipeline

Effects of Ambient Temperature Change on the Internal Pressure Change of Multi-Layered Subsea Pipeline

Deformation of a cell monolayer due to osmotic treatment: a case study of onion scale epidermis

We performed a combination of experiments and mechanical simulations to assess the importance of cell geometry and wall structure in tissue and cell mechanics. Osmotic treatments combined with live imaging were used to quantify deformations at the tissue, cellular, and subcellular levels. We used the adaxial epidermis of onion scale as a model system. We found that the osmotically induced surface strain in onion is small because outer periclinal walls are thick and stiff, requiring bending stiffness to be considered in our mechanical models. As expected, the mechanical behaviors of the tissue and its component cells are related. Upon changes in internal pressure, cells embedded in the tissue undergo deformation that is different from isolated cells, while the tissue undergoes a somewhat counterintuitive deformation, e.g., shrinking upon pressurization, that depends on cell geometry. At the subcellular level, the amount of deformation and its anisotropy vary within the walls of individual cells, and are affected by the cell shape and vicinity of three-way wall junctions. When the turgor pressure is lost, the protoplast-facing wall surface wrinkles due to buckling, with the pattern of wrinkles depending on the strain anisotropy and the local wall geometry.

Computational Fluid Dynamics–Population Balance Modeling of Gas–Liquid Two-Phase Flow in Bubble Column Reactors With an Improved Breakup Kernel Accounting for Bubble Shape Variations

Traditionally, bubble shapes have been assumed to be spherical in breakup models such as the one developed by Luo and Svendsen in 1996. This particular breakup model has been widely accepted and implemented into computational fluid dynamics (CFD) modeling of gas–liquid two-phase flows. However, simulation results from this model usually provide unreliable predictions about the breakage of very small bubbles. The incorporation of bubble shape variation into breakup models has rarely been documented in literature but the bubble shape plays an important role in the interactions with the surrounding eddies, especially when the effects of bubble deformation, distortion, and bubble internal pressure change are considered during the events of eddy-bubble collision. Thus, the assumption of spherical bubbles seems to be no longer appropriate in reflecting this phenomenon. This study proposes and implements a modified bubble breakup model, which accounts for the variation of bubble shapes when solving the population balance equations for CFD simulation of gas–liquid two-phase flows in bubble columns. The key parameters predicted by the modified breakup model have been compared with the ones predicted by the original model. The simulation results of interfacial area and mass transfer coefficient for larger bubbles have been greatly enhanced by the modified breakup model.