Pressure-displacement Curves Research Articles

Study on single particle compression crushing characteristics of iron ore with five different particle sizes

The mechanical properties of particulate materials are among the main factors affecting the grinding and crushing of ball mills. To quantitatively describe the relationship between the breakage characteristics and the stress intensity of irregular particulate materials, this study takes iron ore particles as the research object. It selects five particle size grades of iron ore particles (−4.75 + 3.35, −6.7 + 4.75, −9.5 + 6.7, −13 + 9.5, and −16 + 13 mm) for single particle strength tests. The results showed that the iron ore particles were irregular with certain slenderness and flatness characteristics. The larger the particle size, the lower the sphericity, and the greater the degree of irregularity. As the size of the iron ore particles increased, the number of peak points on the pressure–displacement curve of the particles increased significantly, and the crushing load increased. The single-particle strength of the iron ore particles followed a Weibull distribution, and the Weibull modulus parameter ranged between 2.03 and 2.49.

Exploring Mechanical Properties Using the Hydraulic Bulge Test and Uniaxial Tensile Test with Micro-Samples for Metals

The hydraulic bulge test with micro-samples is expected to be useful in the damage assessment of long-service-period metals to understand the degeneration of their mechanical properties. Since the hydraulic bulge test has a different stress state from the classical uniaxial tensile test, we need to understand their correlation and differences. In this study, the hydraulic bulge test and the uniaxial tensile test are employed to analyze the mechanical properties of three typical metals used in pressure vessels: 316L, 16MnDR, and Q345R. By utilizing Kruglov’s vertex thickness and Panknin’s curvature radius equivalent, the pressure–displacement curves from the hydraulic bulge test are converted into biaxial stress–strain curves. Based on the equivalent plastic energy model, the biaxial stress–strain curves are converted into uniaxial stress–strain curves with an error less than 10% in the strain hardening stage, achieving the unified characterization of mechanical properties under different stress states. Moreover, the hydraulic bulge test provides a more extensive strain hardening stage, and the fracture strains are 9–16.5% larger than those of uniaxial tensile test. This paper provides a reference for using the hydraulic bulge test with micro-samples in studying the mechanical properties and presents the advantages of this novel test method.

Experimental investigation on the dynamic response of vent plate under methane-air mixtures explosion load

The dynamic response study of explosion venting components is of great significance for the assessment of explosion disasters and the determination of damage. Based on the self-developed rectangular explosion venting device, a series of experimental investigations on the dynamic response and failure mode of calcium silicate vent plates under the methane explosion loads induced by a detonator were conducted. The results show that the vent plate mainly exhibits brittleness and presents a plastic hinge failure mode under the blasting loads. When the gas concentration is closer to the stoichiometric concentration, P2 (the peak overpressure generated by the vent plate rupture) and its pressure rise rate dP2/dt are higher. Conversely, when the methane concentration is closer to the upper or lower limits of the explosion, the explosion load tends to be static, the yield line of the vent plate is shorter, and there are fewer fragments generated by the failure of the plate. The pressure-displacement curve and the correlation diagram of failure modes proposed provide a reference for predicting the failure mode of light and fragile explosion venting components.

Mechanical Characteristics Analysis of Composite Rubber Elements in Elastic Cam of Large Coal Cake Tamper

The phenomenon of coal cake collapse is often caused by the unstable operation of the elastic cam in a large coal cake tamper. Aiming at this problem, the mechanical characteristics of the composite rubber elements during cam rotation are studied. A rubber piecewise-function constitutive model is established based on phenomenological theory, and different rubber constitutive model coefficients are obtained according to rubber test data. A contact simulation model between the elastic cam and the tamping hammer friction plate is established to obtain the stress–strain law of the composite rubber elements and the pressure-displacement curve of the elastic cam. The stiffness test platform of the elastic cam is designed, and the differences in results between the test and the simulation are discussed. The results show that the stress–strain curve of rubber has a nonlinear increasing trend and the error between the proposed piecewise function and the test value is less than 2%. As the cam displacement increases from 1 mm to 10 mm, the cam pressure increases from 7715 N to 40,000 N. The simulation results of the rubber stress–strain relationship using the piecewise-function constitutive model are closer to the test data than the simulation results using the elastic modulus as a constant, and the error is less than 6.18%.

Mechanical study of the application of compression screw nails in the cross-inverted triangular pattern for internal fixation of femoral neck fractures

ObjectiveTo design a cross-inverted triangular pattern to insert compression screw nails for the treatment of femoral neck fractures and to compare the biomechanics of inserting compression screw nails in cross-inverted triangular patterns and inverted triangular patterns.MethodsThe reasonableness of the model is first analyzed using finite elements. A total of 6 adult human specimens were selected, of which 3 males and 3 females were divided into the A1, B1, and C1 groups and the A2, B2, and C2 groups by the random number table method. The A1 and A2 groups were made into subhead femoral neck fracture models, the B1 and B2 groups were made into trans-neck femoral neck fracture models, and the C1 and C2 groups were made into basal femoral neck fracture models. The right femur of each group had a compression screw nail inserted in the crossed-inverted triangular pattern, and the left femur of each group had a compression screw nail inserted in the inverted triangular pattern. The static compression test was performed by an electronic universal testing machine. The maximum load of the femoral neck and the load of 3.00 mm axial displacement of the femoral head were read according to the pressure-displacement curve drawn in the experiment.ResultsThe finite element analysis showed that the cross-inverted triangular hollow threaded nail has better conductivity and more stable fixation than the inverted triangular hollow threaded nail. The maximum load of the femoral neck and the load of 3.00 mm axial displacement of the femoral head of the left femur were greater than those of the right femur in the A1, A2, B1, B2 and C2 groups, while the maximum load of the femoral neck and the load of 3.00 mm axial displacement of the femoral head of the left femur were smaller than those of the right femur in the C1 group. There was no statistically significant difference in the maximum load of the femoral neck or the load of 3.00 mm axial displacement of the femoral head between the A1 and A2 groups, the B1 and B2 groups, or the C1 and C2 groups (P > 0.05). After the K-S test, the maximum load of the femoral neck and the load of 3.00 mm axial displacement of the femoral head were normally distributed (P = 0.20), and the LSD-t test was conducted for the two load data; the difference was not statistically significant (P = 0.235).ConclusionThe effect of compression screw nails in the cross-inverted triangular pattern was the same in males and females, and stability was better in the fixation of subhead and trans-neck femoral neck fractures. However, its stability in fixation of basal femoral neck fracture is worse than that of the inverted triangular pattern. The cross-inverted triangular hollow threaded nail has better conductivity and more stable fixation than the inverted triangular hollow threaded nail.

Strain localization of Mohr-Coulomb soils with non-associated plasticity based on micropolar continuum theory

To address the problems of strain localization, the exact Mohr-Coulomb (MC) model is used based on second-order cone programming (mpcFEM-SOCP) in the framework of micropolar continuum finite element method. Using the uniaxial compression test, we focused on the earth pressure problem of rigid wall segment involving non-associated plasticity. The numerical results reveal that when mpcFEM-SOCP is applied, the problems of mesh dependency can be effectively addressed. For geotechnical strain localization analysis involving non-associated MC plasticity, mpcFEM-SOCP in conjunction with the pseudo-time discrete scheme can improve the numerical stability and avoid the unreasonable softening issue in the pressure-displacement curves, which may be encountered in the conventional FEM. It also shows that the pressure-displacement responses calculated by mpcFEM-SOCP with the pseudo-time discrete scheme are higher than those calculated by mpcFEM-SOCP with the Davis scheme. The inclination angle of shear band predicted by mpcFEM-SOCP with the pseudo-time discrete scheme agrees well with the theoretical solution of non-associated MC plasticity.

Kinematic and quasi-static analysis model of a novel variable stiffness pneumatic artificial muscle

A novel variable stiffness axial expansion pneumatic artificial muscle based on hexagonal origami is proposed. Based on the presented assumptions, a kinematic analysis model of the pneumatic artificial muscles is presented, and the changes in crease angles, air cavity volume and geometric configurations of the pneumatic artificial muscles during the actuation process are obtained. The equivalent elastic modulus of the hyperelastic material is obtained by fitting the stress-strain curve. The stress state of the crease is simplified as the pure bending model of a straight beam, and the rotational stiffness of the crease is formulated. Based on the energy method, a quasi-static characteristic analysis model of the pneumatic artificial muscles is developed. The pressure-displacement curve under the unloading state and the output force-displacement curve under the loading state are calculated. The variable stiffness characteristics of the pneumatic artificial muscles are evaluated. Compared with the experimental and numerical simulation results, the analysis models are verified. The work will provide analysis models for the mechanical design and force-displacement control of this type of pneumatic artificial muscles.

Undrained Spherical Cavity Expansion in Unsaturated Soils: Semianalytical Solution Coupling Hydraulic and Mechanical Behaviors

A coupled hydromechanical solution to undrained spherical cavity expansion problem in unsaturated soil is proposed with an elastoplastic model for unsaturated soil. The mechanical response and hydraulic behavior of soil during expansion are coupled together through a soil–water characteristic curve (SWCC) that evolves with the void ratio. A system of four first-order differential governing equations is derived based on the equilibrium equation, large stain theory and coupled hydromechanical constitutive relationship of soil. The present solution can reduce to unified hardening parameter model based solution under saturated condition, which validates the proposed solution. The effects of overconsolidation ratio and initial suction on expansion responses are explored based on extensive parametric studies. Special attention is paid to investigate the distributions of the principal stresses, suction, and saturated degree of soil around the expanded cavity; the stress trajectory of a representative element at the cavity surface; and cavity pressure–displacement curves. The proposed analytical solution can serve as a theoretical framework for modelling of some fundamental geotechnical problems in unsaturated soils using critical state soil models.

Three-dimensional finite element analysis of laterally loaded bridge caisson foundations in gravelly soil

In this paper, we propose a three-dimensional finite element model that can simulate the caisson foundation behavior in gravelly soil. The soil model adopts a combination of the porous elastic model and the modified Drucker–Prager/Cap model for simulating the gravelly soil. For avoiding problems in laboratory testing on gravel specimens, a practical approach is proposed to determine and calibrate the parameters of the soil model using results of field geotechnical tests, such as a shear wave velocity profile, strength parameters of direct shear tests, and pressure–displacement curves of vertical and horizontal plate loading tests. The proposed finite element model was applied to simulate in situ lateral load tests on bridge caisson foundations in gravelly soil. Using the calibrated soil model, responses of caisson displacement, caisson head rotation, and soil displacement analyzed were observed to be in agreement with the measured responses. Caisson and surrounding soil responses were also investigated in detail.

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.

Analytical and Numerical Analyses of Tunnel Excavation Problem Using an Extended Drucker–Prager Model

This paper presents a semi-analytical solution as well as finite element numerical simulations for the tunnel excavation problem, based on an extended Drucker–Prager model and under the drained condition. The adopted plasticity model is capable of accounting for the strain-hardening behavior of soils/rocks through both the internal friction angle and the cohesion. The analytical formulations show that this problem can be reduced to solving a system of ordinary differential equations, with the radial, tangential and vertical stresses, as well as the specific volume being the basic unknowns. Parametric studies are conducted to illustrate mainly the tunnel support pressure–displacement curve and the distributions of stress components, and, in particular, the critical support pressure required to stabilize the tunnel on the basis of three different collapse criteria. With regards to the numerical aspect, an integration algorithm has been developed by employing the return mapping scheme for the extended Drucker–Prager model and subsequently implemented into ABAQUS through the user subroutine UMAT. The agreement between the ABAQUS numerical results and the analytical solution predictions is overall excellent, which demonstrates the accuracy and reliability of the proposed integration scheme.

Structural Forces in Mixtures of Ionic Liquids with Organic Solvents.

Using molecular dynamics simulations, we study the impact of electrode charging and addition of solvent (acetonitrile, ACN) on structural forces of the BMIM PF6 ionic liquid (IL) confined by surfaces at nanometer separations. We establish relationships between the structural forces and the microscopic structure of the confined liquid. Depending on the structural arrangements of cations and anions across the nanofilm, the load-induced squeeze-out of liquid layers occurs via one-layer or bilayer steps. The cations confined between charged plates orient with their aliphatic chain perpendicular to the surface planes and link two adjacent IL layers. These structures facilitate the squeeze-out of single layers. For both pure IL and IL-ACN mixtures, we observe a strong dependence of nanofilm structure on the surface charge density, which affects the simulated pressure-displacement curves. Addition of solvent to the IL modifies the layering in the confined film. At high electrode charges and high dilution of IL (below 10% molar fraction), the layered structure of the nanofilm is less well defined. We predict a change in the squeeze-out mechanism under pressure, from a discontinuous squeeze-out (for high IL concentrations) to an almost continuous one (for low IL concentrations). Importantly, our simulations show that charged electrodes are coated with ions even at low IL concentrations. These ion-rich layers adjacent to the charged plate surfaces are not squeezed out even under very high normal pressures of ∼5 GPa. Hence, we demonstrate the high performance of IL-solvent mixtures to protect surfaces from wear and to provide lubrication at high loads.

Continuum damage modeling and progressive failure analysis of a Type III composite vessel by considering the effect of autofrettage

This paper aims to study the damage mechanisms and mechanical responses of a Type III composite vessel by considering the effect of autofrettage. Firstly, damage models using Hashin failure criteria and 3D strain-based damage evolution laws for composite layers are implemented by implicit finite element codes using ABAQUS-UMAT (user material subroutine module). Secondly, the appropriate autofrettage pressure is determined by finite element analysis (FEA), in which the fiber stress ratio and the generated residual stress in the aluminium liner are investigated according to the related regulations. Finally, the effects of the autofrettage process on the internal pressure-displacement curves and damage evolution behaviors for matrix and fiber are discussed. For a composite vessel after autofrettage, the stresses in the composite layers and aluminium liner are also explored. Results show that the progressive damage evolution behaviors of the composite vessel with autofrettage and without autofrettage are basically consistent except there is some difference during the unloading process and the repressurization process in respect of matrix damage.

Design, Use, and Interpretation of an Instrumented Flat Dilatometer Test

Abstract The flat dilatometer test (DMT) has been increasingly used as a routine geotechnical site characterization tool in numerous parts of the world for over 30 years. In the meantime, with the rapidly growing metal 3D printing technique, engineers now can design robust, durable devices that are impossible to make by traditional means. This paper presents the development of an instrumented dilatometer (idilatometer) that has continuous measurements of a piston expansion up to 2.35 mm and pore pressure at the piston center with the assistance of a metal 3D printing technique. A field-testing program consisting of an instrumented flat dilatometer test (iDMT), a DMT, and a cone penetration test (CPT) positioned 1 m apart from each other was carried out in a site in Belgium composed of soil that ranged from silty sands to sandy silts. Interpretation techniques are provided to evaluate the test results, such as the conceptual contact pressure pc based on the full pressure-displacement curve in the iDMT as an alternative for p0 in the DMT. The pressure required for a 0.56-mm piston expansion is found to be equivalent to that of a 1.1-mm central membrane displacement, based on a finite element method (FEM) simulation approach with the assumption of linear elastic soils and a modified displacement boundary. A comparison made between test results from the iDMT, the DMT, and the CPT shows reasonable trends and suggests the use of the iDMT in future soil investigation.

Mechanical Characterization of APA Microcapsules by Parallel-Plate Compression

We produced microcapsules of alginate-poly(L)lysine-alginate (APA)with diameters on the order of 10 µm. To characterize their mechanical properties, we conducted an experiment on the parallel-plate compression of a microcapsule and modeled its deformation. In the modeling task, the microcapsule was assumed to be a spherical liquid-filled elastic membrane with negligible bending stiffness and permeability. The membrane thickness was estimated by applying Reissner's linear elastic theory to the experimental force-displacement relationship during loading in the small displacement region. The initial stretch of the membrane was taken into account; it was mainly caused by the osmotic pressure difference across the membrane. The initial stretch of the microcapsule was determined by fitting the calculated and experimental force-displacement relationships during loading at small to medium displacements. At large displacements, the calculated force was smaller than the experimentally measured force because of fluid permeation across the APA membrane. The calculated and experimentally imaged shapes of the deformed microcapsule were compared. The effects of varying the membrane thickness on the force-displacement and transmural pressure-displacement curves were shown, and the limitations of applying the present deformation model were examined.

Experimental and numerical simulation studies of the squeezing dynamics of the UBVT system with a hole-plug device

In this paper, a method is proposed to secure an autonomous underwater blasting vibration test (UBVT) system with plugs to deep-water rock, and its specific configuration concept and plugging principle are illustrated. Using the principle of statics, a mathematical model is established for the squeezing force in the process of pressing the hole-plug device (HPD) into holes in rocks. The tension-compression test is conducted on the plugs in round granite holes to obtain the axial pressure-displacement curves of the pressing process with the HPD spring parameter K, friction coefficient μ between the HPD and the rock-wall, and the dynamic contact friction attributes between the metallic HPD and the rock-wall of hole in granite. The axial pressure with such parameters as K, μ, and the squeezing velocity v, among others, and the four steps of the pressing process are numerically simulated. The relations of the characteristic squeezing force with K, μ, and v, as well as the mechanisms of these parameters that influence HPD usage and the sensitivity coefficient, are revealed. The findings of the present study provide references for setting the HPD configuration parameters and for formulating plug-specific construction methods.

Developing a new methodology to characterize in vivo the passive mechanical behavior of abdominal wall on an animal model

The most common surgical repair of abdominal wall hernia goes through implanting a mesh that substitutes the abdominal muscle/fascia while it is healing. To reduce the risk of relapse or possible complications, this mesh needs to mimic the mechanical behavior of the muscle/fascia, which nowadays is not fully determined. The aim of this work is to develop a methodology to characterize in vivo the passive mechanical behavior of the abdominal wall. For that, New Zealand rabbits were subjected to pneumoperitoneum tests, taking the inner pressure from 0mmHg to 12mmHg, values similar to those used in human laparoscopies. Animals treated were divided into two groups: healthy and herniated animals with a surgical mesh (polypropylene SurgiproTM Covidien) previously implanted. All experiments were recorded by a stereo rig composed of two synchronized cameras. During the postprocessing of the images, several points over the abdominal surface were tracked and their coordinates extracted for different levels of internal pressure. Starting from that, a three dimensional model of the abdominal wall was reconstructed. Pressure–displacement curves, radii of curvature and strain fields were also analysed. During the experiments, animals tissue mostly deformed during the first levels of pressure, showing the noticeable hyperelastic passive behavior of abdominal muscles. Comparison between healthy and herniated specimen displayed a strong stiffening for herniated animals in the zone where the high density mesh was situated. Cameras were able to discern this change, so this method can be used to measure the possible effect of other meshes.

Hot Extrusion of A356 Aluminum Metal Matrix Composite with Carbon Nanotube/Al2O3 Hybrid Reinforcement

Over the years, the attention of material scientists and engineers has shifted from conventional composite materials to nanocomposite materials for the development of light weight and high-performance devices. Since the discovery of carbon nanotubes (CNTs), many researchers have tried to fabricate metal matrix composites (MMCs) with CNT reinforcements. However, CNTs exhibit low dispersibility in metal melts owing to their poor wettability and large surface-to-volume ratio. The use of an array of short fibers or hybrid reinforcements in a preform could overcome this problem and enhance the dispersion of CNTs in the matrix. In this study, multi-walled CNT/Al2O3 preform-based aluminum hybrid composites were fabricated using the infiltration method. Then, the composites were extruded to evaluate changes in its mechanical properties. In addition, the dispersion of reinforcements was investigated using a hardness test. The required extrusion pressure of hybrid MMCs increased as the Al2O3/CNT fraction increased. The deformation resistance of hybrid material was over two times that of the original A356 aluminum alloy material due to strengthening by the Al2O3/CNTs reinforcements. In addition, an unusual trend was detected; primary transition was induced by the hybrid reinforcements, as can be observed in the pressure–displacement curve. Increasing temperature of the material can help increase formability. In particular, temperatures under 623 K (350 °C) and over-incorporating reinforcements (Al2O3 20 pct, CNTs 3 pct) are not recommended owing to a significant increase in the brittleness of the hybrid material.

Test Method for Compression Resilience Evaluation of Textiles

A test method was proposed and a measurement system was developed to characterize the compression resilience properties of textiles based on the mechanical device, microelectronics, sensors and control system. Derived from the typical pressure-displacement curve and test data, four indices were defined to characterize the compression performance of textiles. The test principle and the evaluation method for compression resilience of textiles were introduced. Twelve types of textile fabrics with different structural features and made from different textile materials were tested. The one-way ANOVA analysis was carried out to identify the significance of the differences of the evaluation indices among the fabrics. The results show that each index is significantly different among different fabrics. The denim has the maximum compressional resilience and the polar fleece has the minimum compressional resilience. DOI: http://dx.doi.org/10.11591/telkomnika.v11i2.1992

Measurement System for Characterizing Compression Properties of Textile Materials

A new measurement system was developed to characterize the physical compression properties of textile materials based on the mechanical device, microelectronics, sensors and control system. Derived from the typical pressure-displacement curve and test data, three indices were defined to characterize the compression performance of textile materials. The measurement principle and the evaluation method for compression properties of textile materials were introduced. Twelve types of fabrics with different structural features and made from different textile materials were tested. The one-way ANOVA analysis was carried out to identify the significance of the differences of the evaluation indices among the fabrics. The results show that each index is significantly different (P<0.05) among different fabrics.