Constant Pressure Loading Research Articles

How bulk nanobubbles respond to elevated external pressures

Bulk nanobubbles, nanoscopic gaseous domains in aqueous solutions, exhibit surprising long-term stability and unique properties under varying environmental conditions. This study investigates the effects of external pressure on nanobubble stability and behavior through three experimental setups: pressurization at room temperature, pressurization at elevated temperatures, and constant pressure loading. Our findings reveal that increasing external pressure reduces nanobubble concentration and reshapes the bubble size distribution. Larger nanobubbles either disappeared or transformed into microbubbles, while smaller ones expanded, significantly narrowing the size distribution. These changes were found to be irreversible. Additionally, nanobubble stability is influenced by both the magnitude and duration of the applied pressure. Elevated temperatures further narrowed the size distribution at atmospheric pressure, and subsequent pressurization caused these nanobubbles to shrink, showing different response characteristics compared to room temperature. This research highlights the complex interplay between pressure, temperature, and nanobubble stability, offering valuable insight for practical applications in fields such as drug delivery, water treatment, and nanomaterial synthesis.

Smoothed point interpolation methods for phase-field modelling of pressurised fracture

The problem of hydraulic fracturing is of great relevance to various areas and is characterised by the occurrence of complex crack patterns with bifurcations and branches. For this reason, an interesting approach is the modelling of hydraulic fracture using a phase-field model. In addition to the discretisation using the Finite Element Method (FEM), some works have already explored the discretisation of the phase-field model with meshfree methods, including the Smoothed Point Interpolation Methods (SPIM) family. Seeking to take advantage of the good convergence results of SPIM for phase-field modelling of brittle fractures, this paper proposes the use of SPIM for phase-field modelling of pressurised fractures. In order to limit the computational cost, a prescribed SPIM-FEM coupling is employed, with the purpose of concentrating the meshless discretisation only in the regions of expected crack propagation. The model is characterised by a constant internal pressure load along the fracture that is applied indirectly from the formulation of the phase-field model. A series of numerical simulations is presented. The aim is to evaluate the proposed model, verify the results and point out characteristics of the phase-field model with internal pressure.

Experiment and analysis of physical, mechanical, and viscoelastic properties of the roots and stalks of green leafy vegetables.

Green leafy vegetables are an essential component of Chinese leafy vegetables. Due to their crisp stems and tender leaves, orderly harvester generally causes significant mechanical clamping damage. The physical and mechanical properties of green leafy vegetables are one of the important basis to design the orderly harvester. At the same time, they provide important parameters for the simulation and optimization of harvester. So, this paper measured the physical characteristic parameters of roots and stems of green leafy vegetables. Then, based on the TMS-Pro texture analyzer, the elasticity modulus of the roots and stems of green leafy vegetables were measured. The static friction coefficient, dynamic friction coefficient, and restitution coefficient of green leafy vegetables root-root, stem-stem, root-steel, and stem-steel were measured separately using a combination method of inclined plane and high-speed photography. Uniaxial compression creep experiments were carried out on whole and single leaf of green leafy vegetables using the TA.XT plus C universal testing machine. The constitutive equation of the four-element Burgers model was used to fit the deformation curve of the sample with time during the constant-pressure loading stage. The fitting determination coefficients R2 were all higher than 0.996, which verified the reasonable validity of the selected model. The above experimental results provide a parameter basis and theoretical support for the design and discrete element simulation optimization of orderly harvester critical components of green leafy vegetables.

P35: Characterization and Comparison of Thermoplastic Material Performance Using Pressure-Volume Relationships

Purpose: Characterizing mechanical performance of finished materials can be challenging due to geometric constraints and the effects of downstream processing on raw material behavior. The following describes a more sensitive test method to accurately characterize the performance of a thin polymeric sheet material. Methods: Two different polymers, Thermoplastic Polyurethane, TPU, and Thermoplastic Elastomer, TPE, were selected for characterization. Each was molded and assembled into a manifold. Both polymers were under a constant pressure load over time, as a control and measurement technique. Fluid was injected incrementally into the assembly and the resulting injectate volume was measured by mass difference up to a limit volume to understand material behavior post processing. Results: The plotted pressure-volume relationships were distinct between TPU and TPE at two time intervals, as shown in Figure 1. A reduced pressure response to the same volume at test repetition demonstrated that both materials showed permanent set over time. Volume offset between sample runs illustrated reduced mechanical performance over time due to material creep. Conclusion: The pressure-volume testing method successfully characterized performance of the materials over time to discriminate the material set properties between two thin polymeric sheet material, which could not be detected for a finished component using traditional tensile test methods. This repeated method can be used during material selection in various applications for materials with a manufactured finished component, especially for the medical device industry where polymers are carefully chosen and designed for a specific function.

Buckling of viscoelastic spherical shells

Viscoelastic spherical shells exhibit a wide range of time/rate-dependent buckling behaviors when subjected to pressure. For certain loadings, buckling can even occur after a significant time delay, termed creep buckling. To gain a thorough understanding of the nonlinear time-dependent buckling behavior of viscoelastic spherical shells, this work develops an analytical model employing the small-strain, moderate-rotation shell theory combined with a linearly viscoelastic material law. Numerical results are presented for axisymmetric spherical shells with geometric imperfections for two types of loading: a prescribed rate of volume change and a prescribed pressure that remains constant after it is applied. The first type reveals the rate-dependent behavior of viscoelastic buckling while the constant pressure loading is used to quantify creep buckling phenomena. The results show that viscoelasticity and loading rates play important roles in the load-carrying behavior of these shells, and the results for the constant pressure loading reveal an unexpected and important connection between the short-time elastic buckling limit and the long-time creep buckling limit. An imperfection sensitivity map is constructed for the constant pressure loading showing three regimes with qualitatively different behaviors: near-instantaneous buckling, creep buckling and no buckling.

Design of Test Equipment for Hydrostatic Transducers and Hydraulic Fluids

The article refers to the proposed test equipment used to monitor the service life of hydrostatic transducers and fluids under constant or dynamic operating pressure loading. The proposed laboratory test equipment enables simultaneous testing of hydrostatic transducers and energy carriers in two hydraulic circuits and is designed to measure the flow characteristics and technical life of hydrostatic transducers with different energy carriers. The benefit of the proposed device is the possibility of simultaneous testing of the transducers as well as the performance of verification measurements of individual circuits, which was preceded by the development of a theoretical design. This includes the calculations necessary to determine the power of the drive, the cooling power as well as the definition of other parameters and elements of the hydraulic system. The design of the device was based on technical characteristics, load characteristics obtained by own measurements, and characteristics of individual hydraulic and electrohydraulic elements. On the basis of the prepared laboratory test equipment, it is possible to significantly shorten the time of operational tests and perform repeated tests under the same operational load with different types of energy carriers. The hydraulic circuit (primary or secondary) can be loaded through a proportional electrohydraulic pressure valve, which is able to simulate the load with the operational pressure curve obtained by measurement, as well as the cyclic stress, the frequency, amplitude, and rate of increase of which can be defined according to the selected methodology. A verification measurement of the flow characteristics of the used transducers was also carried out, which confirmed the correct function and design of the test laboratory equipment. The achieved results can be used in mechanical engineering for the accelerated life test of hydrostatic transducers, which are often used in mobile energy devices working in environmentally sensitive areas. The proposed laboratory test equipment will be used for testing ecological energy carriers, increasing the efficiency of energy conversion in agricultural facilities using biomass.

Shakedown limit of elbow pipe under coupled cyclic thermal-mechanical loading based on the LMM

In this paper, the linear matching method (LMM) is used to study the shakedown limit of elbow pipes under coupled cyclic mechanical-thermal load. Firstly, the thermal stress analyses of elbow pipes under constant internal pressure and cyclic temperature load are investigated. Further, the shakedown limits of the elbow pipes are calculated using the LMM. For the verification purposes, step-by-step inelastic analyses are performed, showing different structure responses under different loading conditions. All the obtained results indicate that the LMM is able to simulate large range of coupled cyclic mechanical-thermal loading conditions with high computational efficiency, and provide shakedown limit with high accuracy. In addition, the effects of bend angles, mean radius to wall thickness ratio (r/t) and five load conditions on the shakedown behavior are also presented.

Shakedown and ratcheting analysis of Printed Circuit Heat Exchangers under multiple cyclic mechanical and thermal loads

Printed Circuit Heat Exchangers (PCHEs) is a kind of compact plate heat exchanger with a lot of fine channels in a solid block, called PCHE core. It can withstand high temperature and high pressure. And beyond that, it has many advantages, such as high heat exchange efficiency, low pressure drop, high compactness, good corrosion resistance, long service life and many other advantages. However, PCHEs will endure complex mechanical and thermal loads in service. Meanwhile, shakedown and ratcheting assessment, especially how to determine shakedown and ratcheting boundary for PCHEs in an efficient and accurate way, is still an intractable problem so far. This article makes deep research and analysis to shakedown and ratcheting boundary for PCHEs subjected to complex cyclic load combinations as well as the effect of channel shape and size effects based on the linear matching method (LMM). The influences of load parameters, e.g. temperature difference and pressure difference between hot and cold channels, and geometric parameters, e.g. channel radii, channel shapes, arrangement of channels, and transition radius of the local corner of the semicircular channel, were all discussed in detail. Based on these different types of influence parameters, two-dimensional shakedown and ratcheting boundaries for different kinds of PCHEs models under complex mechanical-thermal load combinations are presented in this paper. It is demonstrated that pressure differences between the hot and cold channel have significant effect, but different channel radii are not so significant. Core size and channel shape are observed to influence the shakedown and ratcheting responses significantly, however, the corner radius shows more significant effect on the shakedown boundary than the ratcheting limit boundary. The PCHE core arrangement, i.e. total number and position, is also found to influence the shakedown and ratcheting responses significantly, especially for the constant pressure loading case. Based on a series of LMM analysis results, it can be concluded that accumulative incremental plastic strain will occur at the region between the cold and the hot channel when the combination of mechanical and thermal loads exceeds the ratcheting limit, which should be under strict control. The results from current parametric studies can be an effective reference for design and optimization of the diffusion bonded PCHE channels in high temperature nuclear applications.

Mechanical properties and acoustic emission data analyses of crumb rubber concrete under biaxial compression stress states

Crumb rubber concrete (CRC) is increasingly becoming one of the environmental protection ways to solve the problem of waste rubber tires. This paper mainly analyzes the mechanical properties and acoustic emission (AE) parameters under biaxial compression stress states of CRC with different rubber contents (0%, 5% and 10%). Two biaxial loading modes, constant lateral pressure loading mode (LPM) and proportional loading mode (PM), were used to determine the failure modes, strength characteristics and peak strain of the concrete under different stress ratio conditions. The experiment results show that the compressive strength and peak strain of CRC are improved under biaxial stress like plain concrete (PC), but due to the weak bond between rubber and cement-based materials, the strength growth rate of CRC is not as much as PC. Therefore, the modified Kupfer failure criterions are proposed to describe its strength growth laws. Meanwhile, under the uniaxial loading mode and LPM, the initiation and growth of concrete cracks were monitored based on AE technology. The analysis used various AE statistical parameters, including the AE ringing counts, cumulative energy, amplitude distribution, b-value and RA-AF value analyses. Based on the above AE parameters can be related to the mechanical characteristics of the concrete, and the similarities and differences between CRC and PC are analyzed in the whole failure stage. The results show that CRC has better integrity in main collapse stage with mainly microcracks, which means the plastic failure characteristics. This paper provides experimental and theoretical foundations for the strength analyses and failure characteristics of CRC structures under complex stress states.

Study of the Fracture Behavior under the Effect of Cross-ply and Angle-ply Arrangement of FRP Composite Laminate Subjected to Central Circular Cut-out with Mechanical and Thermal Loading Conditions

In advance composite material the propagation of crack is a regular failure problem in various engineering applications especially in aircrafts body. The aircraft body components are subjected to various thermal and mechanical loading conditions. It is very difficult, time-consuming and costly process of testing the aircrafts components failure due to various thermal and mechanical conditions. Strain energy release rate (SERR) is the significant parameter for the composite materials and quality of composite materials depends in SERR values.The present investigation is based on ANSYS analysis for finding the strain energy release rate (SERR) value using Virtual Crack Closure Technique (VCCT) to understand the fracture behavior of the composite lamina. The circular crack present in the middle of the composite plate and subjected to Pressure and temperature loading for different angle (cross-ply& and angle-ply) composite structure laminas. The angle-ply shows less SERR in mode I & II while cross-ply shows less SERR in mode III under the constant Pressure loading conditions. Mode II shows the maximum SERR in cross-ply compared to mode I and III for temperatures 30ºC,80ºC, 130 ºC & 180ºC. SERR for mixed-mode was found by considering the total mode of fracture and validation based on published literature for SERR due to the Thermal load of mode I (GI) for different fiber layup configurations of the circular cut-out.

Analysis of fuselage skin reinforcements with beam element models in flexible aircraft panels for ditching simulations

This paper is dedicated to the use of beam element models for skin structural reinforcements in guided ditching simulations with a flexible aircraft panel. This approach was analysed by means of finite element simulations of the structure subjected to a constant pressure load and guided ditching loading conditions. To verify this approach, finite element models of different discretization types and different mesh sizes were considered in the computations. Moreover, guided ditching simulations were enhanced by comparisons with the coupled Finite Element-Smoothed Particle Hydrodynamics and the Arbitrary Lagrangian Eulerian methods.

Simulation and Experimental Study on Load-bearing Deformation Characteristics of 11R22.5 Vehicle Retreaded Tire

The finite element bearing deformation simulation was implemented on 11.00R22.5 retreaded tires by ANSYS software in the paper in order to further clarify the bearing deformation characteristics of retreaded tires and improve the performance of retreaded tires effectively. The characteristic laws of bearing radial deformation and bearing lateral deformation of retreaded tire and new tires of the same model under different working conditions were obtained through load deformation tests. The radial deformation calculation results, simulation results and measured results of retreaded tires were comparatively analyzed. The calculation formula of bearing radial deformation of retreaded tires was proposed based on the linear regression principle. The difference of bearing deformation characteristics and ground area characteristics of retreaded tires and new tires were comparatively analyzed. The results showed that the radial and lateral deformation of retreaded tires and new tires is increased with the increase of radial load when the tire pressure was constant, and the increase trend is approximately linear. The radial stiffness of retreaded tires is similar to that of new tires under certain tire pressure and low load. The radial stiffness of retreaded tires is larger than that of new tires, and the stiffness difference is increased with the increasing of load under constant tire pressure and high load. Rubber aging phenomenon in retreaded tire carcass have an impact on the bearing deformation characteristics of retreaded tires, thereby producing great impact on the remaining service life of retreaded tires.

Influence of microcirculation load on FFR in coronary artery stenosis model

BackgroundThe coronary artery hemodynamics are impacted by both the macrocirculation and microcirculation. Whether microcirculation load impact the functional assessment of a coronary artery stenosis is unknown. The purpose of this study is to investigate the effect of porous media of the microcirculation on fractional flow reserve (FFR) in stenotic coronary artery model.MethodsA three dimensional computational simulation of blood flow in coronary artery symmetric stenotic model was constructed. The computational fluid dynamics (CFD) model was developed with Fluent 16.0. Blood was modeled as a shear thinning, non-Newtonian fluid with the Carreau model. A seepage outlet boundary condition and transient inlet conditions were imposed on the model. Coronary physiologica diagnostic parameter such as pressure, velocity and fractional flow reserve (FFR) were investigated in the model and compared with the microcirculation load (ML) and constant pressure load (PL) condition.ResultsThe present study showed the different hemodynamics in the ML and PL condition. The pre-stenotic pressure is almost the same in the two model. However the pressure in the post-stenotic artery domain is much lower in the PL model. The fluctuation range of the pressures is much higher in ML model than those in PL model. The velocity flow was more steady and lower in the ML model. For the PL model with 75% artery stenosis the FFR was 0.776, while for the ML model with the same stenosis, the FFR was 0.813.ConclusionsThis study provides evidence that FFR increased in the presentation of ML condition. There is a strong hemodynamic effect of microcirculation on coronary artery stenosis.

Linkage-based device for creep testing of coal rock.

The creep properties of coal rock have been extensively investigated under conventional uniaxial stress conditions, whereas few studies have considered its characteristics or the process of seepage under triaxial stress. This study proposes and verifies a linkage-based creep test device for coal rock to study its creep characteristics under triaxial stress. The deformation, pressure, and signals of acoustic emission under triaxial stress were measured by using a specially designed data measurement system. The experimental device uses the connecting rod loading mechanism for continuous constant pressure loading. Through theoretical calculations and finite element analysis, the authors show that the strength and stiffness of the device satisfy the requirements of a maximum load of 300 kN. A creep test was carried out to verify the operation of the proposed device and analyze the creep characteristics of sandstone under different confining pressures. The results show that the device can analyze the catastrophic characteristics of sandstone, and this proves its validity and reliability in terms of monitoring the continuous pressure or constant pressure of sandstone during creeping. The device provides a new method to study the creep properties of coal rock under different stresses and seepage conditions.

A Flexible and Highly Sensitive Inductive Pressure Sensor Array Based on Ferrite Films.

There is a rapid growing demand for highly sensitive, easy adaptive and low-cost pressure sensing solutions in the fields of health monitoring, wearable electronics and home care. Here, we report a novel flexible inductive pressure sensor array with ultrahigh sensitivity and a simple construction, for large-area contact pressure measurements. In general, the device consists of three layers: a planar spiral inductor layer and ferrite film units attached on a polyethylene terephthalate (PET) membrane, which are separated by an array of elastic pillars. Importantly, by introducing the ferrite film with an excellent magnetic permeability, the effective permeability around the inductor is greatly influenced by the separation distance between the inductor and the ferrite film. As a result, the value of the inductance changes largely as the separation distance varies as an external load applies. Our device has achieved an ultrahigh sensitivity of 1.60 kPa−1 with a resolution of 13.61 Pa in the pressure range of 0–0.18 kPa, which is comparable to the current state-of-the-art flexible pressure sensors. More remarkably, our device shows an outstanding stability when exposed to environmental interferences, e.g., electrical noises from skin surfaces (within 0.08% variations) and a constant pressure load for more than 32 h (within 0.3% variations). In addition, the device exhibits a fast response time of 111 ms and a good repeatability under cyclic pressures varying from 38.45 to 177.82 Pa. To demonstrate its practical usage, we have successfully developed a 4 × 4 inductive pressure sensor array into a wearable keyboard for a smart electronic calendar application.

Ratcheting boundary of pressurized pipe under reversed bending

Ratcheting boundary is firstly determined by experiment, elastic-plastic finite element analysis combined with C-TDF and linear matching method, which is compared with ASME/KTA and RCC-MR. Moreover, based on elastic modulus adjustment procedure, a novel method is proposed to predict the ratcheting boundary for a pressurized pipe subjected to constant internal pressure and cyclic bending loading. Comparison of ratcheting boundary of elbow pipe determined by the proposed method, elastic-plastic finite element analysis combined with C-TDF and linear matching method, which indicates that the predicted results of the proposed method are in well agreement with those of linear matching method.

The importance of spectrum loading in 2% milled MoS2 powder greases using four ball wear test

PurposeLoading condition and minimizing friction and wear using molybdenum disulfide grease in aircraft engine bearings are the focus of this research. The relationship between the milled and unmilled MoS2 (molybdenum disulfide) greases to its tribological properties, such as coefficient of friction, wear and chemical-mechanical properties of tribofilms, is examined for constant extreme pressure loading and spectrum or actual loading.Design/methodology/approachIn this study, the design of experiments (DOE) approach was used to analyze the different loadings and speeds at a specific duration of 36,000 revolutions to examine the lithium base grease wear behavior with milled and unmilled MoS2 powder. Load is treated as variable that simulates actual conditions under 1,200 and 600 rpm rotational speeds using the four-ball test with chromium steel ball bearing aircraft grade E52100.FindingsThe results indicated that ball-milled MoS2 grease tests showed reduction in wear and friction under all conditions, especially spectrum or actual loading. Unmilled MoS2 powder exhibited worse wear outcomes than the milled one. The SEM and AES analyses indicated that a tribofilm is formed on the wear surface of the milled powder grease, especially at variable loading and initially at lower loads in the ramp-up tests that significantly enhanced the contact characteristics and prevented abrasion at higher loads.Originality/valueThis research indicated that the wear resistance in actual loading might be due to frictional heating generated during the ramping-up conditions where it provided a protective film that enhanced the steady-state friction for the duration of the test. Several researchers used ASTM standards to work on constant loading conditions. This is the first time that reduced milled MoS2 powder showed significant improvement in grease performance.

Pressure-time loading profile for tube superplastic free bulging

An analytical model to determine the pressure-time loading profile for tube superplastic free bulging was presented in this work. The analytically determined loading profile was in good accordance with that determined by FEM codes, which proved the analytical model effective and correct. The pressure-time loading curve starts at a peak pressure, and then declines with time. Initial tube radius r0 and strain rate significantly affect the loading curves. Peak pressure at 880 °C is from 7.7 MPa for r0 = 5 mm to 2.2 MPa for r0 = 25 mm and from 5.8 MPa to 1.6 MPa at 920 °C. The tube bulging experiment showed that tube superplastic forming under the optimized pressure-time loading profile got more uniform thickness distribution than that under the constant pressure loading curve, and thinning was improved from 77 to 64.7% at 920 °C.

Evaluation of horizontal stiffness of fibre‐reinforced elastomeric isolators

SummaryUnbonded fibre‐reinforced elastomeric isolator (U‐FREI) is relatively new seismic base isolator in which fibre layers are used as reinforcement to replace steel shims as are normally used in conventional isolators. Further, the top and bottom end steel connector plates of conventional isolators are also removed. In general, the horizontal response of U‐FREI is nonlinear because of reduction in contact area due to rollover deformation and reduction in shear modulus of isolator under large deformation. Thus, evaluation of horizontal stiffness of U‐FREI is a challenging problem. Most previous studies were focused on the investigation of horizontal response of scaled models of U‐FREIs with low shape factors. A few analytical approaches were suggested for predicting the horizontal response of U‐FREI; but their results were not in good agreement with experimental observations. In the present study, the horizontal responses of prototype U‐FREIs are evaluated under a constant vertical pressure and cyclic loading using both experiments and finite element analysis. Prototype U‐FREIs with different shear moduli and with different shape factors are considered. Finite element simulations of corresponding bonded FREIs are also performed under the same loadings as in U‐FREIs. A rational analytical approach including the influence of rollover deformation and simultaneous reduction in shear modulus is proposed as a basic analytical tool for predicting the horizontal stiffness of FREIs (both bonded and unbonded). It is in reasonably good agreement with the results obtained from experiments and numerical analysis. Copyright © 2017 John Wiley & Sons, Ltd.

Laminate circular cylindrical shell

The paper deals with a numerical approach of optimal design modelling of laminate circular cylindrical shell. For thin-walled shells the classical shell theory is capable of accurately predicting the shell behaviour. In the frame of numerical optimization of circular cylindrical shell there is made the minimization of weight subject to displacement constraint. Thickness of layers is taken as design variable. In the example there is found the thickness of the shell laminate roof under constant pressure loading using Modified Feasible Direction method.