Quasi-static Pressure Research Articles

The analysis of the equivalent bare charge of aluminum cased charge exploding in confined space

The blast loadings from a cased charge, which include a cluster of fragments and shock waves, would cause severe damage to the structures, especially in the scenario of a confined space. In this paper, experiments of the dynamic response of steel plates subjected to the confined blast loading from a cased charge were performed, in which two set warhead models of aluminum cased TNT charge were employed. By using the explicit dynamic code AUTODYN and the Smoothed Particle Hydrodynamic (SPH) method, the rapture process of the aluminum shell was reproduced and the equivalent bare charge was determined by analyzing the results from numerical simulations. In addition, the dynamic response of steel plates subjected to confined blast loadings from cased charges were calculated numerically. Then, the method for calculating the equivalent bare charge that related to the deflection of blast loaded plates was proposed. In addition, this method was further used to determine the approximate mass of TNT charge that contributing to the blast loading of shock wave and subsequent quasi-static pressure in the confined space, in which the energy released by the burning of the detonation products and aluminum shell were taken into account. The present paper presented a reliable method to analyze the response of steel plates under confined blast loadings from a cased charge, which would be useful in the design of the protective structures.

Effects of concentration and initial turbulence on the vented explosion characteristics of methane-air mixtures

The testing of vented explosion of methane-air mixtures was conducted in a custom-designed 4.5-m3 steel chamber. Methane concentrations in the mixed gas varied between 7 and 13 vol% and the static hysteresis time was set as 0, 1, and 5 min to characterize strong, medium and weak turbulence levels. The effects of concentration and initial turbulence on pressure characteristics and flame development were investigated. It is found that the quasi-static pressure in the chamber during vented explosion can be divided into three stages: pressure release, Helmholtz oscillation, and acoustic oscillation. The Helmholtz oscillation at a frequency of about 20–40 Hz is produced after the peak pressure P1 caused by the pressure release at all concentrations; however, the acoustic oscillation at a frequency of about 300 Hz only occurs after Helmholtz oscillation when the concentration is near the optimum. In the early stage of internal flame development, the cellular structure is generated due to hydrodynamic instability and diffusive-thermal instability, and the flame front is distorted owing to the instability caused by venting. Initial turbulence distorts the flame front, significantly increases the peak pressure, and stimulates the generation of acoustic oscillation at the upper and lower limits of concentration. Under the influence of initial high turbulence, the internal flame propagation distance has a power function relationship with time, and the turbulence acceleration factor and distance also show a power function relationship.

Eardrum displacement and strain in the Tokay gecko (Gekko gecko) under quasi-static pressure loads

The eardrum is the primary component of the middle ear and has been extensively investigated in humans. Measuring the displacement and deformation of the eardrum under different quasi-static loading conditions gives insight in its mechanical behavior and is fundamental in determining the material properties of the eardrum. Currently, little is known about the behavior and material properties of eardrums in non-mammals. To explore the mechanical properties of the eardrum in non-mammalian ears, we investigated the quasi-static response of the eardrum of a common lizard: the Tokay gecko (Gekko gecko). The middle ear cavity was pressurized using repetitive linear pressure cycles ranging from −1.5 to 1.5 kPa with pressure change rates of 0.05, 0.1 and 0.2 kPa/s. The resulting shape, displacement and in-plane strain of the eardrum surface were measured using 3D digital image correlation. When middle-ear pressure is negative, the medial displacement of the eardrum is much larger than the displacement observed in mammals; when middle-ear pressure is positive, the lateral displacement is much larger than in mammals, which is not observed in bird single-ossicle ears. Peak-to-peak displacements are about 2.8 mm, which is larger than in any other species measured up to date. The peak-to-peak displacements are at least five times larger than observed in mammals. The pressure-displacement curves show hysteresis, and the energy loss within one pressure cycle increases with increasing pressure rate, contrary to what is observed in rabbit eardrums. The energy lost during a pressure cycle is not constant over the eardrum. Most energy is lost at the region where the eardrum connects to the hearing ossicle. Around this eardrum-ossicle region, a 5% increase in energy loss was observed when pressure change rate was increased from 0.05 kPa/s to 0.2 kPa/s. Other parts of the eardrum showed little increase in the energy loss. The orientation of the in-plane strain on the eardrum was mainly circumferential with strain amplitudes of about +1.5%. The periphery of the measured eardrum surface showed compression instead of stretching and had a different strain orientation. The TM of Gekko gecko shows the highest displacements of all species measured up till now. Our data show the first shape, displacement and deformation measurements on the surface of the eardrum of the gecko and indicate that there could exist a different hysteresis behavior in different species.

A prediction model for debris scattering in vented gas deflagration

As one of the main modes of damage caused by gas explosions in industrial production, the debris generated by the explosion threatens the safety of surrounding personnel and buildings. By means of experimental research and theoretical modelling, the debris generated by the vented component was experimentally studied, and a predictive model of the scattering range of explosion-induced debris was proposed. Through experiments using a self-designed explosion test apparatus, it is found that the gas explosion exerts a quasi-static pressure, and the vented plate is cracked by the plastic hinge under deflagration load. According to the force and the motion equation of the debris, the predictive model of the debris trajectory was proposed by differentiating the scattering process. The distribution of random variables in the model was determined by experimental data, and the scattering range of explosive debris was obtained using the Monte Carlo method. By comparing the calculated results with experimental data gathered under three typical conditions, the model values were seen to agree with the experimental values, and this model can predict the scattering range of debris. The proposed prediction model for debris scattering can provide a reference for the design of works used to protect against debris damage and subsequent domino effect.

Effects of different loading forces and storage periods on the percentage of bruising and its relation with the qualitative properties of pear fruit.

Nowadays, due to the necessity of increasing quality awareness in the food sector and its health, the non-destructive computed tomography (CT) method, which is one of the most widely used methods because of the ability to detect internal bruise in a non-destructive way, attracted so much attention. By using the non-destructive CT method a total of 81 healthy pears was selected and then subjected to quasi-static and dynamical loading. The experiment was performed on wide edge quasi-static pressure of 70, 100, 130 N and thin edge of 15, 20, 25 N and dynamic load of 300, 350, 400 g and storage period for 5, 10 and 15 days, to investigate the different effects of loading forces and storage periods on the percentage of the bruise and its relation with the qualitative properties such as phenol, antioxidant and vitamin C contents and firmness. The results of the experiments showed that the highest and lowest percentages of the bruise were related to a load of 400 N of 15 days and a 15 N 5-day thin line with values of 47.36 and 0.007, respectively. The highest and lowest physiological values were 15 N load of the 5-day thin edge and the 400 N of 15-day impact. Finally, the highest antioxidant content was 51.5% for 300 g dynamic loading force and 5- day storage, 28.86 mg/100g phenol for loading force of 70 N wide edge and 5 day storage and 7.4 mg/100ml vitamin C for loading force of 70 N wide edge and 5 day storage. Finally, according to the obtained results, there was an inverse relationship between the amount of bruising and chemical properties of pear.

Electrothermal Explosion of a titanium-soot Mixture under Quasistatic Compression. III. The Effect of Quasistatic Compression Pressure

The results of diagnostics of thermal conditions of an electric thermal explosion (ETE) of a mixture of titanium and soot powders under quasistatic compression are presented. The effect of quasistatic compression pressure on the thermal and electrical parameters of an ETE is studied. It is shown that nonuniform heating occurs at low pressure, while uniform heating occurs at high pressure. A criterion is proposed for determining the thermal regime of the ETE of a heterogeneous mixture, based on the ratio of the exothermic interaction times and the electric current variation during a thermal explosion. It is established that the dependence of the electric current variation rate on time has one peak when the sample is heated nonuniformly and two peaks when it is heated uniformly. An abnormally low effective flash point of the heterogeneous titanium-soot mixture is explained.

Theory of composite cylindrical shells under quasistatic vibrations, based on an asymptotic analysis of the general viscoelasticity theory equations

A theory of thin multilayer anisotropic viscoelastic cylindrical shells with allowance for quasistatic oscillations, based on the application of asymptotic analysis of small geometric parameters to the general three-dimensional equations of the viscoelasticity theory for curvilinear coordinates, is proposed. Recurrent sequences of local problems of the viscoelasticity theory for shells under the quasistatic pressure oscillations are formulated and analytical solutions are obtained. It is shown that with this approach it is possible to obtain expressions for all 6 components of the stress tensor over the thickness of the shell. An example of the calculation of a cylindrical viscoelastic shell with axisymmetric bending with allowance for quasistatic oscillations is considered. The graphs of the dependences of the components of the stress tensor on the local coordinate are given for different angles of layers in the material. An algorithm is proposed for obtaining explicit analytical equations for calculating the distribution of the total stress tensor components over a cylindrical shell under the action of quasistatic oscillations.

A Modified Johnson–Cook Constitutive Model for the Compressive Flow Behaviors of the SnSbCu Alloy at High Strain Rates

The SnSbCu alloy is widely used as the material for the main bearing in low-speed marine engines, and an accurate constitutive model is the foundation for studying the frictional behaviors of bearings. In this work, the compressive flow behaviors of the SnSbCu alloy were considered under the different strain rates (1000-5000 s−1) and temperatures (20-110 °C) by quasi-static and split-Hopkinson pressure bar dynamic compression tests. First, the original Johnson–Cook model was used to describe the constitutive relation of the SnSbCu alloy at high strain rates, and the results predicted by the original model showed relatively large errors compared with the experimental results since the coupled effect of temperature and strain rate was omitted. Then, a modified Johnson–Cook constitutive model was developed to describe the compressive flow behaviors of the SnSbCu alloy, and the results predicted by this modified model agreed well with the experimental data. Moreover, a finite element analysis was also conducted to verify the accuracy of the modified Johnson–Cook model.

A Non-linear Viscoelastic Model of the Incudostapedial Joint.

The ossicular joints of the middle ear can significantly affect middle-ear function, particularly under conditions such as high-intensity sound pressures or high quasi-static pressures. Experimental investigations of the mechanical behaviour of the human incudostapedial joint have shown strong non-linearity and asymmetry in tension and compression tests, but some previous finite-element models of the joint have had difficulty replicating such behaviour. In this paper, we present a finite-element model of the joint that can match the asymmetry and non-linearity well without using different model structures or parameters in tension and compression. The model includes some of the detailed structures of the joint seen in histological sections. The material properties are found from the literature when available, but some parameters are calculated by fitting the model to experimental data from tension, compression and relaxation tests. The model can predict the hysteresis loops of loading and unloading curves. A sensitivity analysis for various parameters shows that the geometrical parameters have substantial effects on the joint mechanical behaviour. While the joint capsule affects the tension curve more, the cartilage layers affect the compression curve more.

Study on theoretical calculation of quasi-static pressure for explosion in confined space

Objectives The process of explosion in confined space involves not only the propagation and reflection of shock waves, but also complex afterburning effect. The afterburning effect not only enhances the shock wave intensity, but also has a great influence on the final quasi-static pressure. In order to give a prediction of the quasi-static overpressure for explosion inside confined space, Methods a theoretical model for calculation of the peak valve of the quasi-static overpressure for confined explosions considering afterburning effects was proposed based on the analysis of chemical reactions and the law of conservation of energy. The results calculated by the model were then analyzed and compared with the literatures' as well as the empirical formulas' to verify the reliability and correctness of the proposed model. Results The results show that, the peak value of the quasi-static overpressure calculated by theoretical model is in good agreement with the results of the experimental measurement and from the empirical formulas in the literature; the Anderson's empirical formula is inapplicable to the confined explosion condition in case of a small mass volume ratio of less than 0.5 kg/m3, and the formula given in the reference [ 8 ] may not be extrapolated to the confined explosion conditions with a large ratio of greater than 8.87 kg/m3. Conclusions The study in this paper can provide a better understanding of the physical mechanism of the contribution of afterburning effect to quasi-static pressure, and provide some reference and guidance for the design of explosion-resistant structures and damage assessment.

Tests and Numerical Studies on Strain-Rate Effect on Compressive Strength of Recycled Aggregate Concrete

AbstractIn this study, the compressive strength of recycled aggregate concrete (RAC) was investigated by conducting quasi-static and split Hopkinson pressure bar (SHPB) tests. Three types of RAC sp...

Study on the constitutive model of porous titanium alloy

Porous titanium (Ti) alloys usually need high-speed precision machining before they are put into practical applications. Therefore, it is necessary to study the materials’ mechanical properties under conditions of larger strain rate and higher temperature in order to understand the processing mechanism and determine the appropriate processing parameters. In this study, the mechanical properties of porous titanium alloys of two porosities were first investigated by quasi-static compression tests and split Hopkinson pressure bar tests under different conditions. Then, the constitutive models of the flow stress were fitted. From the results of quasi-static compression tests, it was found that the static mechanical properties of porous titanium alloys decreased rapidly with increase in porosity. From the result of the split Hopkinson pressure bar tests, the strain rate sensitivity and temperature sensitivity of porous titanium alloys were determined. The mechanical properties of porous titanium alloys increased with strain rate increase in the range 1000–3000 s−1. The alloys exhibited a temperature-softening effect at 100°C, while they had a temperature-hardening effect at 300°C. The constitutive model could describe the strain-hardening rate of the material appropriately, but the accuracy of the simulated results needed to be improved compared with experimental values.

An experimental study on the mitigation effects of fine water mist on confined-blast loading and dynamic response of steel plates

The blast loading from an explosion of a condensed explosive in a confined space is quite different from that in an open environment. Due to the confinement effect, a confined-blast load usually causes more severe damage. The detonation products from a fuel-rich explosive, such as Trinitrotoluene (TNT), can react with the surrounding air under specific conditions and release additional energy, resulting in a significant increase of reflected shockwaves and quasi-static pressure in a confined space. Mitigation of the confined-blast loading is an effective way to protect structures from destruction. In this paper, a detailed experimental investigation of the influence of water mist on both the mitigation of blast load and dynamic response of the structure is presented. Six cases of experimental tests, with different charge masses of 80, 120 and 160 g of TNT explosive, with and without the presence of water mist, are performed in a confined chamber, with the shock pressure and deflection-time history curves of blast-loaded steel plates being recorded, as well as quasi-static pressure and temperature of the contained gas. By analysing the experimental data, it is found that the water mist decreases the reflected blast wave and quasi-static pressure by restraining the combustion effect and subsequent energy release of detonation products. As a consequence, both the first peak deflection and the residual deformation of the blast-loaded steel plates decrease greatly. Furthermore, based on a non-dimensional analysis of the experimental results for plates with different thickness subjected to different loading conditions, a new empirical relationship between non-dimensional deflection of the plate and a non-dimensional load parameter (for fully confined blast loading) was obtained. By employing this new empirical relation, the mitigation effect of fine water mist on confined blast load was determined quantitatively. The use of water mist is a very good alternative to mitigate the damage of structures subjected to a confined-blast load in the design of anti-blast structures.

The structural evaluation of a large floating dock in head design waves by strength criteria

This study is developed for the strength analysis of a large floating dock, with length over all of 209.2 m, obtained from a conversion of an off-shore barge. The docking operations are evaluated by global and local strength criteria. The first operation scenario includes an entire translation process of a ship from the quay to the floating dock railway system, in a river shipyard location, including the main intermediate steps. A second set of operation scenarios include several trial docking cases, at full capacity, considering also the initial state without docking ship that is specific for transit condition between ports. The structural numerical analysis is developed on a very large 3D-FEM model, one sided, full extended over the length, involving an own iterative algorithm for the dock and head design wave equilibrium parameters computation and user functions for the quasi-static head wave pressure application on the external dock shell. The large floating dock has operations in sheltered and unsheltered environments and can be relocated on river and costal waterways, under specific wave’s conditions, according to the shipbuilding classification societies design rules. The numerical results are making possible to evaluate the several operations of the large floating dock by strength criteria.

A continuum damage mechanics framework for modeling the effect of crystalline anisotropy on rolling contact fatigue

Abstract Rolling contact fatigue (RCF) is the primary mode of fatigue failure in well-lubricated rolling element bearings. Typical fatigue failures in bearings are characterized by microcrack formation (initiation phase), which then coalesce to a large crack that grows to the surface (propagation phase). Hence, RCF is a micromechanical phenomenon driven by microstructural inhomogeneity. This paper presents a coupled damage mechanics - cohesive element method (DM-CEM) to model crack initiation and propagation in polycrystalline material aggregates subject to RCF loading. The material microstructural topology is represented using Voronoi tessellations. The grain boundaries are modeled using cohesive elements. Each grain is composed of cubic anisotropic material and is randomly oriented in material space. A quasi-static Hertzian pressure profile is passed over the surface to simulate a bearing race under dynamic loading. Damage is initiated at the grain boundaries by degradation of the cohesive elements and the rate of damage/degradation is used to characterize the fatigue life evolution. The resulting final spall patterns and fatigue life scatter corroborate well with existing results from open literature. The model was extended and used to demonstrate the feasibility of the Fatemi - Socie criterion as a possible approach for estimating RCF life.

Effect of particle gradation of aluminum on the explosion field pressure and temperature of RDX-based explosives in vacuum and air atmosphere

Abstract To optimize the energy output and improve the energy utilization efficiency of an aluminized explosive, an explosion device was developed and used to investigate the detonation pressure and temperature of R1 (Al6) aluminum powder and the aluminum powder particle gradation of R2 (Al6+Al13), R3 (Al6+Al24) and R4 (Al6+Al flake) in a confined space. By using gas chromatography, quantitative analysis and calculations were carried out to analyze the gaseous detonation products. Finally, the reaction ratios of the aluminum powder and the explosion reaction equations were calculated. The results show that in a confined space, the quasi-static pressures and equilibrium temperature of the aluminum powder in air are higher than in vacuum. In vacuum, the quasi-static pressures and equilibrium temperatures of the samples in descending order are R1>R3>R4>R2 and R3>R4>R1>R2, respectively. In air, the quasi-static pressures and equilibrium temperatures of the samples in descending order are R1>R2>R4>R3 and R1>R4>R2>R3, respectively. R4 (Al6+Al flake) and R3 (Al6+Al24) have relatively higher temperatures after detonation, which shows that the particle gradation method can enhance the reaction energy output of aluminum during the initial reaction stage of the explosion and increase the reaction ratio by 10.6% and 8.0%, respectively. In air, the reaction ratio of Al6 aluminum powder can reach as high as 78.16%, and the reaction ratio is slightly reduced after particle gradation. Finally, the reaction equations of the explosives in vacuum and in air were calculated by quantitative analysis of the explosion products, which provides a powerful basis for the study of RDX-based explosive reactions.

Synchrotron-based visualization and segmentation of elastic lamellae in the mouse carotid artery during quasi-static pressure inflation.

In computational aortic biomechanics, aortic and arterial tissue are typically modelled as a homogeneous layer, making abstraction not only of the layered structure of intima, media and adventitia but also of the microstructure that exists within these layers. Here, we present a novel method to visualize the microstructure of the tunica media along the entire circumference of the vessel. To that end, we developed a pressure-inflation device that is compatible with synchrotron-based phase-contrast imaging. Using freshly excised left common carotid arteries from n = 12 mice, we visualized how the lamellae and interlamellar layers inflate as the luminal pressure is increased from 0 to 120 mm Hg in quasi-static steps. A graph-based segmentation algorithm subsequently allowed us to automatically segment each of the three lamellae, resulting in a three-dimensional geometry that represents lamellae, interlamellar layers and adventitia at nine different pressure levels. Our results demonstrate that the three elastic lamellae unfold and stretch simultaneously as luminal pressure is increased. In the long term, we believe that the results presented in this work can be a first step towards a better understanding of the mechanics of the arterial microstructure.

Interplay between random and correlated fracture processes induced by shock-waves in compressed granites

In contrast to damage accumulation in rocks subjected to constant or growing load wherein local failures increase with time, the strongest fracture events at the shock forcing occur at the very beginning of the loading. An inverse trend in the stress variation could be expected to affect some parameters of the rock behavior specific for a quasi-static pressure exposure. In this study, shock waves in uniaxially compressed granites were generated by an electric discharge, and the nucleation of microcracks was detected by the acoustic emission (AE) method. The experiment represented some conditions, under which deep underground rocks response on the impact forcing (explosions, shocks, etc.). The compression varied from zero to a pre-damage level. Fine-grained Sesam Black granite (grain size ∼1 mm) and coarse-grained Rapakivi granite (5–7 mm) were tested. The energy release distributions in all AE time series followed a Gutenberg-Richter type relation (power law) in both compressed and free samples with a departure from the log-linear dependences for the most intensive AE peaks. At the same time in a compressed fine-grained sample, a high-energy reminder of the power law distribution followed a well-defined exponential (Poisson-like) function; in coarse-grained granite, the higher-energy part of the energy distribution could not be described with any explicit expression. The specificities in the mechanical behavior of the tested fine- and coarse-grained granites were considered from the viewpoint of the hierarchical structure of rocks.

Ballistic limit predictions for perforation of aluminium armour plates by rigid nose-pointed projectiles

We start with a derivation of a new formula for the spherical cavitation yield stress of aluminium targets with Ludwik power-hardening response. As part of this analysis we have suggested simple and accurate formulae for spherical and Mises plane-strain cylindrical cavitation pressures. These algebraic relations simplify the well-known integral expressions for quasi-static cavitation pressures in a material exhibiting Ludwik work hardening. A comprehensive comparison with experimental data has clearly demonstrated that the ratio between ballistic limits of targets with thicknesses kh and h, against the same threat, is higher than the commonly accepted value of k. A new integral formulation of the specific cavitation energy, which directly depends on target material stress-strain curve, reveals the coupling between hole slenderness ratio and hardening characteristics of the target. This formulation is shown to be more accurate than currently existing models for perforation resistance, and has led to an efficient and accurate ballistic limit formula. While a general integral formulation is valid for arbitrary stress-strain relations, further simplifications are given for linear, power and Voce hardening laws in terms of classical functions from mathematical physics. Extensive comparison with about 200 available experimental results for perforation of different aluminium alloys by several armour-piercing bullets and nose-pointed projectiles is provided in support of main findings. The aluminium alloys response is mostly modelled by Ludwik stress-strain curve and also by the Voce hardening model, and the vast majority of ballistic limit predictions represent deviations of up to ± 5% from experimental data. A few comparisons are made for Weldox steel alloys to demonstrate the accuracy of the specific formula for linear hardening response of material target.

Study on mechanical properties and constitutive model of 5052 aluminium alloy

The stress–strain relationship of 5052 aluminium alloy was investigated via quasi-static tensile tests and split Hopkinson pressure bar tests. The specimens were exposed to various temperatures (25–500°C) and strain rates (10−4–0.7 × 104 s−1). At strain rates ranging from 0.001 to 3000 s−1, the material underwent significant work hardening. When the strain rate exceeded 5000 s−1, the work hardening effect decreased and the flow stress was relatively constant. The Johnson–Cook constitutive model was modified to describe the deformation behaviour of the material subjected to high temperatures and strain rates. The accuracy of the modified model was verified through ballistic impact testing.