Hydrostatic Loading Research Articles

On Stiffness, Strength, Anisotropy, and Buckling of 30 Strut‐Based Lattices with Cubic Crystal Structures

Architected cellular structures are increasingly receiving attention in numerous applications due to advances in additive manufacturing and their promising multi‐functional properties. Herein, 30 architected strut‐based lattices of cubic crystal symmetry are developed and their stiffness and strength are investigated computationally and experimentally. Finite element simulations are conducted to compute the effective stiffness, yield strength, and buckling strength under uniaxial, shear, and hydrostatic loadings. Also, elastic anisotropy is assessed and bifurcation analysis is performed to estimate the threshold relative density for each lattice. Selected lattices of various relative densities are 3D printed from a polymeric material using selective laser sintering (SLS). The numerical results show that the modes of deformation whether stretching‐dominated, bending‐dominated, or mixed differ for the various loading conditions. It is observed that by combining different lattice structures in a hybrid approach, a decrease in the anisotropic behavior is obtained, and an overall enhancement of the mechanical properties is achieved. The numerical results show rather good agreement with the experimental findings. The current study can be crucial for using the investigated lattices for enhancing the multi‐functional properties of structural systems.

Design and finite element analysis of gondola construction for multibeam echosounder (MBES) installation on RV Baruna Jaya III - BPPT

The revitalization of hydrographic equipment at the Research Vessel (RV) Baruna Jaya III has been carried out by the Technology Center for Marine Survey (BTSK) – BPPT to improve its service capabilities. A Multi-Beam Echosounder (MBES) for the deep-sea mapping up to 8000 meters depth has been chosen to replace the existing equipment which only has a mapping capability of 3000 meters depth. MBES requires a support construction mounted on the vessel hulls as its housing, considering the installation principle from both the shipowner and MBES maker. In this research, a gondola installation principle has been agreed to develop. The gondola construction has been designed in consideration of actual vessel conditions and several requirements by the MBES maker. The design construction is further analyzed using the finite element method (FEM) to ensure its strength and safety and meet Indonesian Classification Society (BKI) minimum requirements. The analysis conditions are divided into 3; hydrostatic load (A), sensors load (B), and the combination of hydrostatic and sensor load (C). The von Mises stress was obtained from finite element analysis for conditions A, B, and C, respectively, 164 MPa, 1.552 MPa, and 160.8 MPa. The analysis results in all loading conditions have met the minimum allowable stress required by Indonesia Classification Society rules, which is 180 MPa. In conclusion, the design of the gondola construction for MBES installation on RV Baruna Jaya III has good structural strength and safety, so it is feasible to use.

<i>In situ</i> X-ray diffraction measurement of shock melting in vanadium

The solid-liquid phase transition under shock wave loading in materials is called shock melting. Shock melting is important not only in fields like high pressure EOS or material dynamic response, but also in applications like device protection in modern industry and national defense construction. The obtaining of precise melting curve is more than understanding the high pressure melting behavior, and it can provide the reliable evidence for the theoretical model of melting mechanism. So the solid-liquid phase transition under extreme conditions is a research hotspot, and a lot of researches have been carried out. But, the enormous discrepancy between the melting curve of dynamic loading and hydrostatic loading in transition metals, especially, the vanadium has been unclear for decades. The difference in melting temperature under 200 GPa between dynamic loading and hydrostatic loadirng is as large as twice (about 4000 K). Recently, Errandonea and Zhang’s experiments present a new insight into this discrepancy, indicating that the new shock melting curve is consistent with the extrapolated melting curve contained by LH-DAC. But all the dynamic loading experimental data are measured by macroscopic quantities; they can determine the occurrence of the phase transition, but cannot provide the microscopic structure of the material under extreme conditions. So, as the technic of in situ X-ray diffraction has developed well in recent years, we use the high power laser driving technic combining with in situ X-ray diffraction measurement to explore the structure of vanadium near the melting line. We measure the micro structure of vanadium at up to 200 GPa in shock experiment for the first time. We find that the bcc phase transition is not observed at around 60 GPa, which is different from previous experiments in DAC or gas gun loading experiments, but consistent with Chen’s leaser driving experiment. The result confirms that when the impact pressure is 155 GPa, vanadium still remains solid BCC phase. It becomes liquid at about 190 GPa. In contract to Zhang’s results, the DXRD melting point is consistent with the new melting line. This work provides the evidence of the consistency of shock and hydrostatic melting curve, confirming the phase boundary of vanadium under 200 GPa. This work has important scientific significance in understanding the pressure melting behavior of transition metals. The method in this work can be applied to the research of melting properties of other materials.

Topology optimization of an oil tanker bulkhead subjected to hydrostatic loads

In the field of Naval Architecture, the conventional approach to design any vessel is to follow the classification societies’ rules to ensure adequate strength and structural integrity. Nowadays, owners’ demands and purposes of vessels are changing dramatically. To mitigate these demands, sometimes it is necessary to design new types of structures, but the classification society’s rules are not sufficient to prepare these advanced designs. Moreover, Naval Architects are always eager to minimize the lightweight of a vessel as this is directly related to cost and carrying capacity. Topology optimization has become a powerful tool for designing structures in an optimized way. The concept of topology optimization has been utilized by the automotive and aerospace industry for almost thirty years where problems associated with solutions meant to satisfy maximum stiffness and structural integrity with minimum weight which are of utmost importance. However, in the field of marine and offshore structures, the use of topology optimization is infrequent. As structural optimization aims to design structures under certain constraints to achieve better strength and lower cost, the introduction of this technique in ship structure can be lucrative. In this paper, a methodology to apply structural topology optimization in the field of ship design is presented. An Oil Tanker Bulkhead has been selected for this study. SIMULIA ABAQUS software is used in this regard. Topology optimization has been performed by minimizing the strain energy of the component as the objective function and a target stiffness and material volume of the structure as design constraints. Finally, the results demonstrate the general applicability of the methodology presented for obtaining the geometrical layout of the structure.

Nonlinear elasticity of prestressed single crystals at high pressure and various elastic moduli

A general nonlinear theory for the elasticity of pre-stressed single crystals is presented. Various types of elastic moduli are defined, their importance is determined, and relationships between them are presented. In particular, B moduli are present in the relationship between the Jaumann objective time derivative of the Cauchy stress and deformation rate and are broadly used in computational algorithms in various finite-element codes. Possible applications to simplified linear solutions for complex nonlinear elasticity problems are outlined and illustrated for a superdislocation. The effect of finite rotations is fully taken into account and analyzed. Different types of the bulk and shear moduli under different constraints are defined and connected to the effective properties of polycrystalline aggregates. Expressions for elastic energy and stress-strain relationships for small distortions with respect to a pre-stressed configuration are derived in detail. Under initial hydrostatic load, general consistency conditions for elastic moduli and compliances are derived that follow from the existence of the generalized tensorial equation of state under hydrostatic loading obtained from single crystal or polycrystal. It is shown that B moduli can be found from the expression for the Gibbs energy. However, higher-order elastic moduli defined from the Gibbs energy do not have any meaning since they do not directly participate in any known equations, like stress-strain relationships and wave propagation equation. The deviatoric projection of B can also be found from the expression for the elastic energy for isochoric small strain increments, and the missing components of B can be found from the consistency conditions. Numerous inconsistencies and errors in the known works are analyzed.

A bipotential-based macroscopic fatigue criterion of porous materials with a pressure-sensitive and non-associated plastic solid matrix and comparison with numerical simulation

The formulation of macroscopic strength criteria under cyclic loading of ductile porous media containing a pressure sensitive and non-associated plastic matrix is still a pending issue. In this paper, a new approach is developed by using the bipotential theory. In this framework, non Generalized Standard Materials (GSM) are transformed into a class of Implicit Standard Materials (ISM), allowing the recovery of the flow rule normality in a weak form of an implicit relation. The classical shakedown theorems are extended to the homogenization of ISM. The solution of a thick wall tube under uniform pressure is established with the assumption of vanishing plastic strain increment over a single stabilized cycle. A macroscopic fatigue criterion is further delivered for the first time for porous materials with a non-associated Drucker–Prager type solid matrix. It is now possible to separate the effects of frictional and dilatancy angles. It is found that the shakedown limit load under hydrostatic loading is only related to the friction angle, but not the dilatancy one. The safety domain defined by the established criterion under general cyclic loads is comparatively reduced with the decrease of dilatancy angle. The new criterion is fully assessed by comparing the theoretical predictions to FEM-based step-by-step simulations for different values of porosity and frictional and dilatancy angles. Finally, the new criterion can also be applied to associated solid matrix as a special case and it significantly improves the accuracy of predictions provided by previous works based on the Melan’s static theorem.

Hydrostatic pressure loads for a tank using “CID Distributed Loads” fields in a PATRAN FEM model

The purpose of this paper is to present a practical way to introduce distributed loads on the walls of a tank in order to perform a FEM analysis using PATRAN/NASTRAN programs. The problem is generated mainly by the fact that there are gravitational accelerations in the three directions of the moving airplane that produce a great number of combinations of inertial loads and consequently a great number of critical load cases. We compared the performed stress analysis with the loads obtained with this method in different cases for 𝑛𝑛=1. (Different forms of the fuel tanks and different placements of the tank inside the aircraft). The form and the density of the grid do not significantly affect the precision of the real inertia loads. Using the presented method one can reduce the volume of FEM files used in the analysis and can quite accurately reproduce the pressure loads on the fuel of a moving aircraft.

Principles of Stress-Strength Modelling of the Highly Thermally Loaded Materials-The Influence of an Effect of Strength Differential on the Material Effort.

This paper presents an improvement in the Huber–Mises–Hencky (HMH) material effort hypothesis proposed by Burzyński. Unlike the HMH hypothesis, it differentiates the plastic effort between compression and tensile load states, and links shear with tensile limit. Furthermore, it considers the fact that construction materials do not have infinite resistance in the pure tensile hydrostatic load state, which was proved by the static load experiment performed on St12T heat-resistant steel. The asymmetry between tensile and compressive loads is captured by the elastic region asymmetry coefficient , which was established by experiment for St12T steel in the temperature range between 20 °C and 800 °C.

Microstructural Deformation and Modulus Changes of Nuclear Graphite due to Hydrostatic Pressure Loading

For the first time, the influence of pore closure on elastic modulus in the UK's Magnox and Advanced Gas Cooled Reactors (AGRs) graphite was determined by subjecting the graphite samples to high hydrostatic pressure and dynamic loading. Two grades of nuclear graphite were tested; anisotropic Pile Grade A (PGA) which was used in the Magnox reactors, and semi-isotropic Gilsocarbon as used in the AGRs [1] . The volumetric strain was measured in two directions during compression and separately the velocity of sound through the samples was also determined as a function of confinement pressure. Under hydrostatic loading, the stiffness of PGA graphite was reduced after a few percent of volume strain before increasing again after about ∼20% volumetric strain. Gilsocarbon showed similar behaviour to PGA at lower volumetric strain (∼10 to 13%) however due to Gilsocarbon having a higher density and lower porosity compared to PGA, the response was generally stiffer than PGA. During unloading, significant hysteresis was observed in both graphite grades, with the sample volume almost fully recovering when the pressure was completely removed. Micromechanical models are used to explain the poro-elastic response of graphite during hydrostatic compaction, and to make comparisons and extend data on the influence of pore change due to oxidation on modulus.

Modeling and simulation of ductile damage in forged steel used to encapsulate high-level radioactive waste

Andra, the French national radioactive waste management agency, is in charge of studying the disposal of high-level and long-lived intermediate-level waste (HLW and ILW-LL) in a deep geological repository. According to the reference concept, it is planned to encapsulate high-level waste in non-alloy P285NH steel overpacks before inserting them into horizontal steel cased micro-tunnels. This work is a part of the study about the long-term behavior of a welded steel overpack subjected to external hydrostatic pressure and several localized loading paths. Indeed, the main objective of this work is to develop the most suitable model for non-alloy steel P285NH to be used in the prediction of the long-term overpack behavior. Dealing with a ductile steel, elastoplastic constitutive equations accounting for mixed nonlinear isotropic and kinematic hardening strongly coupled with ductile isotropic damage are adopted. They are formulated based on the classical thermodynamics of irreversible processes framework with state variables at the macroscopic scale, (Germain, 1973) (Lemaitre 1985, Saanouni 2012). In this paper, a new coupling formulation between the scalar isotropic ductile damage and the deviatoric and spherical part of the Cauchy stress and elastic strain tensors is proposed. In order to calibrate the developed model on P285NH steel, multiple tensile tests are performed using classical cylindrical specimens, notched specimens and double notched specimens. In the last part, some experimental fields are measured using digital image correlation. Application is made to a simplified overpack represented by thick walled cylinder subject to compressive loading path. A FEM (Finite Element method) crushing operation of an overpack’s cylindrical part has simulated and analysed.

Nonlocal damage modelling for finite element simulations of ductile steel sheets under multiaxial loading

AbstractThe finite element simulation of forming processes or vehicle crash scenarios involves multiaxial loading conditions in general. Thereby, damage and failure in ductile steel sheets is triggered by void growth under hydrostatic tensile loading or by void elongation within a narrow band under shear dominated loading. These different damage mechanisms are considered by a stress state dependent continuum damage model. The damage initiation and failure are represented by a critical and a failure strain. Both are HOSFORD‐COULOMB type functions of the stress triaxiality and the LODE parameter and, thus, incorporate the stress state dependence of the damage mechanisms. Due to the pathological mesh sensitivity for continuum damage models, an enhancement towards nonlocal damage evolution is carried out. Thereby, two options are investigated and compared: the integral nonlocal formulation and the gradient enhanced approach. Finally, the proposed nonlocal ductile damage model is verified for a wide range of stress states by test data of various tensile and shear specimens.

Analysis of Rectangular Reinforced Concrete Liquied Tanks by Using Yield Line Theory

In the analysis of rectangular reinforced liquid storage tanks, a method assuming linear-elastic behavior for material can be used, i.e., the strip method, the moment coefficient method, the finite element method, etc. In the analysis of these types of tanks, tank walls can be considered as slabs. In this study, tank walls were analyzed as slabs subjected to hydrostatic loading; in the analysis, the yield line theory is used because it is more suitable for the linear inelastic behavior of reinforced concrete slabs than the ones based on the linear elastic theory. An iterative algorithm based on yield line theory is presented for the design of isotropically reinforced recrangular concrete slabs supported along all four edges. A computer program is coded which predicts the location of yield lines for the slabs depending upon certain parameters. As a result of this prediction, the manual design of such slabs can be significantly simplified by the use of the coefficient obtained by using the program. It was shown that the analytical computation of the ultimate moment per unit length requires the solution of a highly nonlinear system of equations. This difficulty was overcome by utilizing an iterative technique within the computer program. It also gives the value of the ultimate moment per unit length of the yield line.

Dynamic implosion of submerged cylindrical shell under the combined hydrostatic and shock loading

Thin-walled cylindrical shells are commonly used in designing underwater structures. When subjected to the combination of hydrostatic pressure and underwater explosive loading, these cylindrical shells are prone to implosion failure. In this work the dynamic stability of submerged cylindrical shells subjected to underwater explosion was investigated through both numerical simulations and theoretical modeling. In particular, the effects of initial hydrostatic pressure and fluid–structure interaction on the dynamic stability of metallic cylindrical shells are revealed. The transient responses of cylindrical shells have been simulated using Abaqus/Explicit with the water domain discreted by acoustic elements. The simulation results show that the existence of initial hydrostatic pressure reduces the structure stiffness, and the structural response to the pressure wave loading primarily consists of initial axisymmetric vibrations and subsequent mode 2vibrations. There exists one critical threshold value for the initial hydrostatic pressure, below which these vibrations are stable and above which these vibration will trigger the implosion of the cylindrical shells. These threshold values are obtained via both numerical simulations and theoretical modeling. The analytic model considering the added mass effect of surrounding water and the effect of initial stress of the shell due to hydrostatic pressure shows good accuracy comparing with the numerical and experimental results. The dependence of the dynamic buckling strength of the metallic cylindrical shells on the material choice for either constant static buckling strength or constant weight is then discussed.

Analysis of steel-concrete-steel sandwich plate structure

The static behaviour of steel-concrete-steel sandwich plates is studied in this paper. Uniformly distributed and hydrostatic loads are applied on the plates. Two types of boundary conditions, clamped and simply supported on all edges, are considered. ANSYS Workbench 14.0, a finite element tool, is used for modelling and analysis of the sandwich plates. The sandwich plate results are compared with the results of isotropic steel plate. Maximum deflection and von Mises stress are computed on the sandwich plates. In actual condition, different steel connectors are used to make a bond between steel and concrete. But, due to the complexity in the analysis, the connectors are not modelled explicitly in the present study, and the bond between the two materials is established numerically. Considering the economy, the steel plate may be replaced with the steel-concrete-steel sandwich plate in many applications. Some of the applications of sandwich plate includes, building walls, offshore decks, tunnels, bridge decks, nuclear structure walls, etc. In the present study, the effectiveness of the plate having newer sandwich material, i.e., steel and composite, is checked based on the different loadings and boundary conditions. The results of the present study may be beneficial for the engineers/practitioners who deals in sandwich plates.

Low-frequency broadband absorption of semi-active composite anechoic coating with subwavelength piezoelectric arrays in hydrostatic environments

Considering the influence of hydrostatic pressure on geometric parameters of a lining, this paper first proposes a complete global four-terminal acoustic theoretical prediction method based on phenomenological theory for a semi-active composite coating with subwavelength piezoelectric arrays in deep-sea environment, aiming at exploring the energy dissipation mechanisms and broadening the low-frequency sound-absorbing bandwidth. The Neo-Hookean material model is incorporated into the phenomenological theory to analyze the finite deformation of rubber layers under hydrostatic load. Then, the global acoustic model is established by combining the effective medium method, shunt damping technique, and wave propagation theory in layered media. Moreover, the degraded validations are developed by FE simulation and hydroacoustic impedance tube experiment, and the influences of submergence depth and shunt circuit on the absorption characteristics are explored theoretically. It is expected to break the lower limit frequency of low-frequency sound-absorbing from 500 Hz to 200 Hz, and to expand the upper limit frequency thanks to the multi-modal resonant energy consumption mechanism of distributed circuits.

Boundary element method for the elastic contact problem with hydrostatic load at the contact interface

When a seal is applied to prevent leakage of a pressurized fluid it must be designed to sustain the hydrostatic load it is subjected to. One important aspect that the design must take into consideration is the possibility that the hydrostatic fluid load may deform the sealing surfaces to such an extent that leakage occurs. In this paper, we describe the development and implementation of a novel boundary element method (BEM) that can be used to study the effects of the pressurized fluid presents at the interface between the sealing surfaces. The proposed method utilizes a connected region labeling algorithm to identify the fluid-filled regions and it solves the coupled solid-solid and fluid-solid contact problem with an FFT-based boundary element method (DC-FFT). When benchmarked against a FEM implementation of the same problem, it is found that the results are in good agreement. In particular, it is shown that the proposed method can capture the deformation of the sealing surfaces, and how the fluid front advances when the hydrostatic pressure increases.

Occlusal Trauma and Bisphosphonate-Related Osteonecrosis of the Jaw in Mice.

Osteonecrosis of the jaw (ONJ) is a serious adverse event that is associated with antiresorptive agents, and it manifests as bone exposure in the maxillofacial region. Previous clinical reports suggest that mechanical trauma would trigger ONJ in a manner that is similar to tooth extractions. To the best of our knowledge, there have been few detailed pathophysiological investigations of the mechanisms by which occlusal/mechanical trauma influences ONJ. Here, we developed a novel mouse model that exhibits ONJ following experimental hyperocclusion and nitrogen-containing bisphosphonate (N-BP) treatment. This in vivo model exhibited ONJ in alveolar bone, particularly in the mandible. Moreover, the experimental hyperocclusion induced remarkable alveolar bone resorption in both mouse mandible and maxilla, whereas N-BP treatment completely prevented alveolar bone resorption. In this study, we also modeled trauma by exposing clumps of mesenchymal stem cells (MSCs)/extracellular matrix complex to hydrostatic pressure in combination with N-BP. Hydrostatic pressure loading induced lactate dehydrogenase (LDH) release by calcified cell clumps that were differentiated from MSCs; this LDH release was enhanced by N-BP priming. These in vivo and in vitro models may contribute further insights into the effect of excessive mechanical loading on ONJ onset in patients with occlusal trauma.

Microscale analysis demonstrating the significance of shear and porosity in hydrostatic compression of porous media

Experimental data for porous media exhibit nonlinear pressure-volumetric strain relations and a strong dependence on the Terzaghi pressure defined as confining pressure minus pore pressure . However, a clear explanation of why this pressure plays such a dominant role appears to be missing. Several authors have suggested that shear must be a significant factor in predicting change in porosity even for purely hydrostatic loading . Here this idea is explored in detail by analyzing a representative volume element consisting of a hollow sphere within a unit cube subjected only to hydrostatic compression. The results are presented independent of this particular geometry with the use of volume fractions . The analysis shows that the stress field within a relatively small region around a pore contains a measure of shear stress, called the Terzaghi shear, which is similar, but not equal, to the Terzaghi pressure. Shear strain in the hollow sphere does not affect the volumetric strain of the hollow sphere itself but is a major contribution to the volumetric strain of the pore, and hence to the bulk volumetric strain. The constitutive equation between Terzaghi shear and shear strain within a conditioned state is nonlinearly elastic, whereas transitioning from one conditioned state to another is governed by strain-hardening plasticity. The plastic strain that develops introduces a residual Terzaghi shear, which provides an explanation as to why the elastic response in a second conditioned state is different from that in the first. The formulation also explains the interesting phenomenon of shear-enhanced compaction under hydrostatic loading. Explicit expressions are given for the compressibilities relating increments of confining and pore pressures to increments of bulk and pore volumetric strains. Relations between the compressibilities are similar to classical equations with the exception that the new formulation extends beyond a single conditioned state.

Post-buckling path and free vibration of a symmetric laminated plate vertically coupled with fluid under in-plane load

In this paper, the effect of compressive in-plane load on the equilibrium paths and vibration characteristics of a vertical symmetric laminated plate coupled with fluid is studied theoretically both in the pre- and post-buckling state. The Third-order shear deformation theory and von Karman nonlinear strain displacement relationship are utilized to describe the nonlinear deformation of the plate consists of a number of fiber-reinforced layers. The Hamilton's principle is introduced to formulate the plate-fluid coupled governing equations. A two-step theoretical approach is developed. Firstly, based on the Cylindrical arc-length method, we solve the nonlinear static equations to trace the snap-back behavior and pass the limit points along the complex equilibrium paths obtaining the stable buckling deflection. Then the coupled vibration characteristics are calculated using the tangent stiffness at the stable positions. The present theoretical results are validated by the numerical results. The effects of added mass and hydrostatic load are compared and analyzed. It is noted that, in the post-buckling state, the number of limit points along the static unstable equilibrium path increases with the compressive in-plane load getting larger. The variation trends of the natural frequencies and modes under different in-plane loads in pre- and post-buckling state are investigated.

Determination of Stress and Deformation Zones of Historical Mus Murat Bridge

This study was carried out to determine the strength of long span stone bridges and stress areas of a historical bridge by using finite element method during earthquakes, floods, and vehicle traffic. The possible earthquake impact of the region and the behavior of the bridge under the effect of the 2011 Van earthquake were investigated. The stresses that will be caused by hydrostatic and vehicle loading applied to the bridge are dwelled on. This study aimed to shed light on future restoration work. As a result of the vehicle, hydrostatic load and dead load analysis, the biggest deformation occurred in the arch K9, which has the largest arch span. According to the results of the earthquake analysis, maximum deformation occurred in the K10 arch, which is one of the arches with the largest arch span of the bridge. In addition, inearthquakes affected in the X and Z direction, it was observed that the arches and piers in the middle of the bridge, that is, these relatively higher structural elements were subjected to more stress. It has been determined that the A11 pier of the bridge is the structural element exposed to the most pressure.