Hydrostatic Pressure Loading Research Articles

軟骨細胞-アガロース複合体の力学的特性に対する培養条件の影響(第2報)(G02-2 細胞,G02 バイオエンジニアリング部門)

In this study, the influence of hydrostatic pressure loading on mechanical properties of chondrocytes-agarose specimens was investigated. After 1 day, 8 days and 22 days in unstrained culture, the specimens were exposed to hydrostatic pressure (1MPa, 1Hz, 6h/day) for 7 days. Then, tangent and equilibrium moduli of the specimens were obtained by unconfined compression test. The results showed that the hydrostatic pressure loading at the early stage of culture improved tangent moduli of specimens, but if the extracellular matrix was formed around the cells in advance, the effect of hydrostatic pressure loading did not appear.

905 静水圧応力負荷による培養神経細胞損傷評価(GS-2 バイオエンジニアリング(1))

905 静水圧応力負荷による培養神経細胞損傷評価(GS-2 バイオエンジニアリング(1))

Lifetime prediction for ABS pipes subjected to combined pressure and deflection loading

AbstractAs part of an investigation into the performance of acrylonitrile‐butadiene‐styrene (ABS) systems for water transportation, this paper presents a method for predicting the service lifetimes of buried pipes under in‐service loading conditions. A linear fracture mechanics approach was used to analyze brittle failure initiating from adventitious flaws located at the bore surface of pipe. Failure criteria were determined using the time‐dependent, quasistatic, plane strain fracture toughness of the ABS material, combined with empirical parameters that describe slow, steady crack growth. The expected operating conditions of a buried pipe were then separated into static loading contributions from internal pressure, diametrical deflection and residual stress. Idealized stress intensity factors associated with mode‐I crack opening under each of these components were determined using a finite element analysis and superposed to describe the general case in service. The computed nett stress intensity factor was then combined with the previously determined fracture toughness and slow crack growth data in an algorithm to simulate incremental radial crack growth from the pipe bore. Predicted failure times compared well with an experimental model of expected operating conditions, which combined hydrostatic pressure and parallel‐plate deflection loading of an internally notched pipe. The prediction method was also used to identify the factors that control the lifetime of a pipe in service. The influence of material visco‐elasticity was investigated by simulating variations in fracture toughness and slow crack growth resistance. It was proposed that, in practice, these variations are governed by opposing changes in visco‐elasticity. The effect of changing diametrical deflection and residual stress distribution were also simulated, allowing recommendations on pipe manufacture and installation conditions to be made.

Phase sensitivity of conventional single-mode and holey optical fibers: a comparison study

A comparison of phase sensitivity is conducted for two different types of optical fiber designs with the same outer diameter. The optical fibers are subjected to a hydrostatic pressure load. The finite element model validates well with the analytical solutions. The holey fiber selected for this study showed a 130% phase sensitivity gain over a conventional single-mode optical fiber due to its hollow structure, enabling the external pressure load to strain the core beyond that observed in solid optical fibers. The holey fiber's outer coating also enhances the phase sensitivity, with improved performance over conventional single-mode optical fibers with the same coating.

Instability and ductile failure of thin cylindrical tubes under internal pressure impact

The finite strain behaviour of a thin cylindrical specimen under hydrostatic pressure loading is studied numerically considering plane-strain deformations in the cross-sectional plane. The numerical results in the finite-strain range are generated by a finite element program developed for the problem analyzed. The strain-rate effects are taken into account by an elastic–viscoplastic material model. Only thin shells are considered in accordance with the membrane theory formulation employed. Dynamic instability with respect to time as well as deformation instability as strain localization are investigated. New results regarding the experimentally observed multiple neck formation phenomenon are presented. The onset of the instability as a weak discontinuity is discussed from the examination of the computed responses.

Assessment of Cumulative Lifetime Seaway Loads for Ships

ABSTRACTThis paper presents a reliability‐based design methodology for primary seaway loadings on surface ships. The goal for such a design methodology is to have one consistent method for developing extreme primary hull girder loads for reliability‐based strength design criteria as well as lifetime exceedance loads for reliability‐based fatigue strength design criteria. The primary hull girder loads, i.e., vertical bending, lateral bending, and torsion, include contributions from both the low frequency (wave‐induced) and the high frequency (slam‐induced) domains for vertical and lateral bending. The contributions of secondary loads, such as hydrostatic and dynamic pressure loads, are important but are beyond the scope of this paper. A method is presented for calculating lifetime seaway loads as functions of ship and seaway parameters. The method is embodied in a PC based computer program called SPECTRA.

2232 軟骨細胞の静水圧負荷に対する細胞内シグナル応答

2232 軟骨細胞の静水圧負荷に対する細胞内シグナル応答

Parametric stress distribution in shell-of-revolution sludge digesters of parabolic ogival form

Egg-shaped sludge digesters have become popular in relatively recent times owing to their superior functional performance and lower maintenance costs in comparison with conventional cylindrical digesters. These innovative structures are usually constructed as thin shells of revolution in concrete, designed to withstand principally the hydrostatic pressure loading from the contained liquid. As regards the precise shape of the egg shell, a number of mathematical shell surfaces may be envisaged, and the stress distribution will very much depend on the chosen form. In this paper, it is desired to explore the possible adoption of the parabolic ogival shell as a sludge digester. The stress distribution in such a shell is expressed in terms of a single governing parameter ξ, greatly facilitating the investigation. For various values of ξ covering the most practical range for egg-shaped digester shells, recommendations are made regarding the positioning of supports. Taking into account maximisation of tank capacity, minimisation of peak stress resultants in the shell, and ease of prestressing, the best range of ξ for parabolic ogival digester shells is identified. The overall conclusion is that from a structural and functional point of view, the parabolic ogival profile is suitable for adoption in the design of egg-shaped concrete sludge-digester shells.

Primary chondrocytes resist hydrostatic pressure-induced stress while primary synovial cells and fibroblasts show modified Hsp70 response

Objective During joint loading, chondrocytes in the articular cartilage are subjected to gradients of high compressive hydrostatic pressure (HP). In response to diverse chemical or physical stresses, heat shock genes are induced to express heat shock proteins (Hsps). This study sought to examine the role of Hsps in baroresistance in primary bovine chondrocytes and synovial cells, as well as in primary human fibroblasts.Methods Northern blotting was used to analyze the steady-state levels of hsp70 mRNA in the primary cells exposed to HP or heat stress. Hsp70 protein accumulation was analyzed by Western blotting, and the DNA-binding activity was examined by gel mobility shift assay.Results Primary bovine chondrocytes which have been adapted to live under pressurized conditions showed negligible Hsp70 response upon HP loading, whereas primary bovine synovial cells and human fibroblasts accumulated hsp70 mRNA and protein when subjected to HP. The response was initiated without activation of the heat shock transcription factor 1. Interestingly, pre-conditioning of the barosensitive fibroblasts with HP or heat shock reduced the Hsp70 response, indicating induction of baroresistance.Conclusion This study suggests that Hsp70 can play an important role in the early stages of adaptation of cells to HP. Thus, the Hsp70 gene expression upon HP loading may serve as one indicator of the chondrocytic phenotype of the cells. This can be of use in the treatment of cartilage lesions.

Nonclassical Stability Problems: Instability of Slender Tubes under Pressure

Several nonclassical stability problems dealing with simple cantilever columns of practical engineering importance are comprehensively presented. The salient feature of these rather peculiar problems is that column instability with a tubular cross section filled with a liquid or subjected to gas pressure may occur while its cross section remains axially unstressed. Interesting subcases are also discussed where the static stability criterion of existence of two adjacent equilibria fails to predict the actual critical load. This leads to the erroneous conclusion that the undeformed configuration is the only equilibrium position, being stable irrespective of the level of external loading. Hence, the dynamic stability criterion which is of general validity must be employed for establishing the critical load. It has also been clarified that the hydrostatic pressure load, although nonconstant-directional, cannot be identified as nonconservative.

132 軟骨細胞の静水圧負荷に対する応答 : シグナル伝達タンパク (ERK) の活性化

132 軟骨細胞の静水圧負荷に対する応答 : シグナル伝達タンパク (ERK) の活性化

Yielding Behaviour in Axial Compression of Cylindrical Metal Powder Assembles Under High Pressure.

We present the method of constructing a pressure sensitive yield function which accounts for the porosity, incorporating the data from the compression of cylindrical metal powder assembles. The load paths consist of fluid hydrostatic pressure loading up to a set value, followed by the addition of an increasing mechanical axial load. The yield function (yield curve) for less than fully dense states is represented in the relation of deviatoric stress q to hydrostatic stress p. In powder metal assembles the curve which gives the relation between p and q at constant density has been frequently used as yield curve. However, it does not seem to have been examined experimentally whether the constant density curves are consistent with the yield curve. For the prediction of yield function two quantities are required, for example, axial stress and volumetric strain developing with an increasing axial strain. Here, the data obtained by Jin and Cristescu and by Gurson and McCabe are used. Our results indicate that several current models proposed for powder metal deformation do not represent actual constitutive behaviour under the assumption that associated flow rule is valid and yield curve expands in a similar shape with compressive deformation.

Hydrostatic pressure and thermal loading induced optical effects in double-coated optical fibers

The stresses, microbending losses, and refractive index changes induced simultaneously by hydrostatic pressure and thermal loading in double-coated optical fibers are analyzed. The lateral pressure and normal stresses in the optical fiber, primary coating, and secondary coating are derived. Also presented are the microbending losses and refractive-index changes in the glass fiber. The normal stresses are affected by the hydrostatic pressure, temperature drop, material properties of the primary and secondary coatings, and their thickness. To minimize the microbending losses, the polymeric coatings should be suitably selected, and it is found that the thickness, Young’s modulus, and Poisson’s ratio of the secondary coating should be increased, but the Young’s modulus and Poisson’s ratio of the primary coating should be decreased. Similarly, in order to reduce the changes of refractive index in the glass fiber, the thickness, Young’s modulus, and Poisson’s ratio of the secondary coating should be increased, and on the contrary the Young’s modulus and Poisson’s ratio of the primary coating should be decreased.

The influence of aging and aortic stiffness on permanent dilation and breaking stress of the thoracic descending aorta.

To assess the influence of aging and aortic stiffness on the extent of irreversible deformation and breaking stress of the human thoracic aorta. From 14 human heart valve donors without aortic disease (mean age 35 years, range 8-59 years), 14 intact segments of the thoracic descending aorta were studied within 48 h after cardiac arrest. In an experimental setup, the segments were submitted to increasing hydrostatic pressure loads, both statically and dynamically, while radius and wall thickness were monitored echocardiographically. Pressure-radius curves were constructed. Radius and wall thickness were determined at a pressure of 100 mmHg. Radius at elastin resting length and collagen recruitment pressure (Pcol, mmHg) were derived from the pressure-radius relationship and stress-strain curves were constructed to yield Young's moduli of elastin and collagen. Distensibility (D, mmHg-1) was determined while loading the segment with a sinusoidal pressure wave of 120/50 mmHg at both 0.5 and 1 Hz. Subsequently increasing static pressure loads of 400, 800, 1200 and 1600 mmHg were applied. After each pressure load, the increase in aortic radius at a pressure of 100 mmHg (Rinc) was determined. The experiment continued until rupture occurred and breaking stress (sigma break, N m-2) was calculated, donor age and aortic stiffness were correlated with Rinc and sigma break of the aortic segments. Mean breaking stress of the 14 segments was 2.7 x 10(6) N m-2. Breaking stress was negatively correlated with age (r2 = 0.66) and positively with D (r2 = 0.44) and with Pcol (r2 = 0.18). Seven segments survived a pressure load of 800 mmHg, in these vessels, the extent of irreversible dilation was positively correlated with age (r2 = 0.42) and negatively with D (r2 = 0.40) and Pcol (r2 = 0.40). Permanent deformation and rupture of the human thoracic aorta following pressure overload are influenced by age, distensibility and collagen recruitment pressure.

Evaluation of the pressure transfer system in the intracranial cavity by coherency.

Coherency provides a method to evaluate model linearity. The characteristics of pressure wave transmission in the intracranial cavity were studied by coherency in 16 cats with hydrostatic pressure loading to assess the linearity of the system, which is an assumption for use of the transfer function. Linearity was observed in only the fundamental waves of the respiration-induced component and the cardiac-induced component of intracranial pressure oscillation, and in the second harmonic wave of the latter. Linearity at the other frequencies was close to zero. The pressure transfer system in the intracranial cavity was basically a non-linear system. As intracranial pressure rose, the increase in the pressure transfer efficiency was largest in the low-frequency domain and smallest in the high-frequency domain, indicating that the cerebral blood vessels are characterized by inferior transmission of high frequency due to increased intracranial pressure. In addition, the correlation between the coherencies of the cardiac-induced fundamental wave component and intracranial pressure, and between those of the cardiac-induced second harmonic wave component and intracranial pressure, showed that the slope of the straight line was greater between 45 and 70 mmHg than between 10 and 45 mmHg. This suggests that there is a break point, located between 45 and 70 mmHg, where the increase in the coherency values is accelerated, caused by an increase in the intracranial elastance, as well as an increase in the cerebrovascular compliance due to the reduced vascular transmural pressure.

Buckling stresses of composite tubes under biaxial compressive loads

An analytical model describing the instability of specially orthotropic composite tubes with geometric imperfections subject to biaxial compressive loads and under clamped-clamped boundary conditions is developed. Furthermore, the range of validity of the present solution is clarified, and comparisons are made to some studies on isotropic cylindrical shells. Six E-glass woven fabric-epoxy composite tubes with the same internal radius and different thicknesses and longitudinal lengths were fabricated and subjected to various combinations of external hydrostatic pressure and axial compressive load simultaneously. The normalized buckling stresses were found to agree in general with the theoretical predictions at various biaxial loadings. The buckling envelopes in normalization form provide useful design data on the strength of specially orthotropic composite tubes under a realistic range of biaxial loading conditions.

Study of the nonlinear responses of a submersible pressure hull

A submarine pressure hull normally experiences hydrostatic pressure at different operating depths and, during wartime, it bears shock loading produced by underwater explosions. In this study we examine the transient dynamic responses of a typical submarine hull subjected to hydrostatic pressure and shock loading, in which geometrically large deformation effects involving elastoplastic material behavior are considered. The finite element procedure based on Hibbitt and Karlsson's methodology is used to analyze the nonlinear response of the entire pressure hull. From the numerical results of a nonlinear static analysis under operating depth hydrostatic pressure, we attempt to provide the maximum operating depth at which the behavior varies from elastic to plastic. In transient dynamic analysis under shock environment, this study not only presents the elastoplastic response of the structure but also the critical region of the model. Finally, the implications of these results for future submarine design and maintenance are discussed.

The forms of the shell with zero bending stresses subjected to hydrostatic pressure and other loads

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Experimental modal analysis comparison of the vibration damping properties of composite cylinders measured in-air and underwater

Self-noise is problematic in many underwater applications, since it interferes with the performance of onboard sensors. To reduce self-noise, experiments investigated using composite materials for cylinders subjected to hydrostatic pressure loading. This paper presents the test procedure and results of modal analysis testing conducted in-air and underwater on some composite cylinders. The in-air tests used impact force excitation, whereas the underwater tests used sound excitation. The results include resonant frequencies, damping factors, and mode shapes at resonance. In order to ensure a valid comparison, the natural frequencies and damping factors are compared on a mode-by-mode basis. Despite the increased complexity of the underwater experiments, it is shown that the in-air and underwater levels of damping observed at relatively low frequencies are comparable. Further, an appropriate choice of composite materials can increase damping by at least an order of magnitude over conventional metals. The damping can additionally be increased by using a double-hollow core or triple-shell configuration, with reinforced polyurethane ribs. The paper discusses this new reinforced polyurethane as a structural component of the cylinder, and proposes various mechanisms of damping that this material form provides.

Molecular dynamics simulations of densification processes in nanocrystalline materials

Molecular dynamics computer simulations were employed to investigate the dynamic processes of diffusion, grain growth, sintering, and consolidation in nanocrystalline copper (n-Cu). At room temperature, fully dense n-Cu was found to be stable. At 1100 K, a large fraction of atoms in the n-Cu became amorphous which provides a new mechanism of grain growth and recrystallization. Atomic mobility in dense n-Cu decreased with time as the grain boundaries relaxed. The initial configurations of the grains were shown to have a strong influence on pressureless sintering. Both hydrostatic pressure and uniaxial stress loading accelerated the process of densification on porous n-Cu. The latter, however, was found more efficient due to grain boundary sliding.