Pressure-displacement Relationship Research Articles

Behavior of Steel Fiber Reinforced Concrete Panels under Surface Pressure

In this study, it is aimed to investigate the importance of the affecting parameters on the pressure–displacement relationship of steel fiber reinforced concrete panels. Among these parameters, panel thickness, panel dimensions, material type, and boundary conditions of the panels are the parameters that were examined. In this context, the effects of surface pressure on the steel fiber reinforced concrete panels were investigated. It was observed that as the thickness and the fiber ratio increased, the ultimate bearing capacity increased. It was determined that it may not be enough to support the panels only at the corner points, and intermediate supports are needed. As the support spacing decreased, the absorbed surface pressure increased. In addition, it was concluded that the increase in the amount of steel fiber in the concrete material increased the strength, deflection, and ductility values.

Base resistance of drilled shafts in soft rock using in situ load tests: A limit state approach

This paper presents a probabilistic limit state framework for the evaluation of the base resistance of drilled shafts in soft rock. In situ load tests and the Griffith fracture theory are used to evaluate the mode of failure for the rock mass under the drilled shaft base. The base resistance or the limit state in the context of this paper is defined by the contact pressure at which load induced vertical to subvertical cracks form and the contact pressure-displacement relationship passes into a steep and fairly straight tangent. The parameters affecting the base resistance are evaluated using an in situ load test database. A statistical approach using the maximum likelihood method is utilized for the development of the design model for the base resistance. Reliability analysis is used to calibrate the corresponding resistance factors. The in situ load tests and the Griffith fracture theory suggest that the soft rock mass underlying the drilled shaft base primarily fails by the formation of vertical to subvertical cracks. Field observations indicate that the displacements in the underlying rock mass are largely in the vertical direction and that the base displacements required to mobilize the proposed base resistance are generally less than 30 mm. Load test data show that the base resistance is chiefly related to the unconfined compressive strength of soft rock. The calculated resistance factors are found to slightly decrease with increase in the span length of the structure and increase with the increase in the foundation redundancy.

A continuum mechanics-based musculo-mechanical model for esophageal transport

In this work, we extend our previous esophageal transport model using an immersed boundary (IB) method with discrete fiber-based structural model, to one using a continuum mechanics-based model that is approximated based on finite elements (IB-FE). To deal with the leakage of flow when the Lagrangian mesh becomes coarser than the fluid mesh, we employ adaptive interaction quadrature points to deal with Lagrangian–Eulerian interaction equations based on a previous work (Griffith and Luo [1]). In particular, we introduce a new anisotropic adaptive interaction quadrature rule. The new rule permits us to vary the interaction quadrature points not only at each time-step and element but also at different orientations per element. This helps to avoid the leakage issue without sacrificing the computational efficiency and accuracy in dealing with the interaction equations. For the material model, we extend our previous fiber-based model to a continuum-based model. We present formulations for general fiber-reinforced material models in the IB-FE framework. The new material model can handle non-linear elasticity and fiber-matrix interactions, and thus permits us to consider more realistic material behavior of biological tissues. To validate our method, we first study a case in which a three-dimensional short tube is dilated. Results on the pressure-displacement relationship and the stress distribution matches very well with those obtained from the implicit FE method. We remark that in our IB-FE case, the three-dimensional tube undergoes a very large deformation and the Lagrangian mesh-size becomes about 6 times of Eulerian mesh-size in the circumferential orientation. To validate the performance of the method in handling fiber-matrix material models, we perform a second study on dilating a long fiber-reinforced tube. Errors are small when we compare numerical solutions with analytical solutions. The technique is then applied to the problem of esophageal transport. We use two fiber-reinforced models for the esophageal tissue: a bi-linear model and an exponential model. We present three cases on esophageal transport that differ in the material model and the muscle fiber architecture. The overall transport features are consistent with those observed from the previous model. We remark that the continuum-based model can handle more realistic and complicated material behavior. This is demonstrated in our third case where a spatially varying fiber architecture is included based on experimental study. We find that this unique muscle fiber architecture could generate a so-called pressure transition zone, which is a luminal pressure pattern that is of clinical interest. This suggests an important role of muscle fiber architecture in esophageal transport.

Progress Toward Optimizing Prosthetic Socket Fit and Suspension Using Elevated Vacuum to Promote Residual Limb Health.

Objective: Prosthetic sockets are custom made for each amputee, yet there are no quantitative tools to determine the appropriateness of socket fit. Ensuring a proper socket fit can have significant effects on the health of residual limb soft tissues and overall function and acceptance of the prosthetic limb. Previous work found that elevated vacuum pressure data can detect movement between the residual limb and the prosthetic socket; however, the correlation between the two was specific to each user. The overall objective of this work is to determine the relationship between elevated vacuum pressure deviations and prosthetic socket fit. Approach: A tension compression machine was used to apply repeated controlled forces onto a residual limb model with sockets of different internal volume. Results: The vacuum pressure-displacement relationship was dependent on socket fit. The vacuum pressure data were sensitive enough to detect differences of 1.5% global volume and can likely detect differences even smaller. Limb motion was reduced as surface area of contact between the limb model and socket was maximized. Innovation: The results suggest that elevated vacuum pressure data provide information to quantify socket fit. Conclusions: This study provides evidence that the use of elevated vacuum pressure data may provide a method for prosthetists to quantify and monitor socket fit. Future studies should investigate the relationship between socket fit, limb motion, and limb health to define optimal socket fit parameters.

The Evaluation of the Groundwater Influence on the Stress and Strain Behavior around a Tunnel by Analytical Methods

The presence of an aquifer in the soil causes a change in a relevant way of the stability conditions of a tunnel. The flow of water in the pores, in fact, modifies the stress and strain state of the soil and causes an increase in the thickness of the plastic zone. As a result the loads transmitted on the lining increase. In this study a calculation procedure by finite differences method, able to determine the stress and strain state of the soil in the presence of the water flow in the pores, is presented. More particularly, using the proposed procedure, it is possible to determine the convergence-confinement curve of the tunnel and the trend of the plastic radius varying the internal pressure. A calculation example is used to detect the great influence that the presence of the aquifer has on the stress and strain state of the soil and on the pressure-displacement relationship of the tunnel wall.

Interactive planar multi-blade flows with a global angle of attack

Planar flow past multiple successive blades and wakes is studied for locally non-symmetric blades aligned with a global angle of attack to the oncoming freestream. The typical blade lies relatively near the centreline of the oncoming wake from the preceding blade but is shifted due to the global attack angle. The central flow structure is of a periodic, pressure interactive boundary-layer over each blade and wake, embedded within a slowly growing Blasius-type flow. This is coupled through the inviscid outer flow via a pressure–displacement relationship. Differing amendments to this structure occur as the global angle of attack is increased in magnitude. The local and global non-symmetries require a leading-edge jump in pressure and velocities in the inner boundary-layer to ensure that the Kutta condition is satisfied at the trailing edge. The flow structure is described for a range of angles of attack, and numerical results are presented for the two cases of most interest where the innermost periodic layer is directly influenced by the global features. Studies are restricted to the condensed limit here. Separation is found to occur and can be caused by both local and global influences.

Mathematical Modeling of Vascular Stents

We present a mathematical model for a study of the mechanical properties of endovascular stents in their expanded state. The model is based on the theory of slender curved rods. Stent struts are modeled as linearly elastic curved rods that satisfy the kinematic and dynamic contact conditions at the “vertices” where the struts meet. This defines a stent as a mesh of curved rods. A weak formulation for the stent problem is defined and a finite element method for a numerical computation of its solution was developed. Numerical simulations showing the pressure-displacement (axial and radial) relationship for the entire stent are presented. From the numerical data and from the energy of the problem we deduced an “effective” pressure-displacement relationship of the law of Laplace-type for the mechanical behavior of stents, where the proportionality constant in the Laplace law was expressed explicitly in terms of the geometric and mechanic properties of a stent.

Study of a Flapper-Nozzle System for a Water Hydraulic Servovalve.

We discuss the characteristics of a flapper-nozzle system for water hydraulic servovalves. High-pressure water at the supply port is used for the first time as the working fluid for the hydrostatic bearings supporting the spool. Spool valve adhesion induced by poor lubrication with water is thus avoided. The fluid is then led to the ends of the spool and is used as the working fluid of the flapper-nozzle system. In this flapper-nozzle system the circumferential clearance of the spool becomes a laminar restriction that replaces the fixed orifice used in conventional servovalves. The linearity in the pressure-displacement relationship of the new flapper-nozzle system is better than that of conventional fixed orifice systems.

Study of a Flapper-Nozzle System for a Water Hydraulic Servovalve.

The paper discusses the characteristics of a flapper-nozzle system for water hydraulic servovalves. High pressure water at the supply port is first used as the working fluid for the hydrostatic bearings supporting the spool. Spool valve stiction induced by poor lubrication with water is thus avoided. The fluid is then led to the ends of the spool and is used as the working fllid of the flapper-nozzle system. In the new flapper-nozzle system the circumferential clearance of the spool becomes a laminar restriction that substitutes fixed orifice used in conventional servovalves. The linearity in the pressure-displacement relationship of the new flapper-nozzle system is better than that of conventional fixed orifice systems.

Prediction of load carrying capacity of deep snow by rammsonde hardness

The ability of a natural snowpack to support the weight of a vehicle is often difficult to predict. Misjudgement of the load-carrying capacity of a snowpack may result in hang-up failure (i.e. immobilization) or a degree of high sinkage producing low tractive efficiency. The load-carrying capacity of snow media may be predicted from measurements of vane and cone resistance in the various snow types. In a remote region where off-road vehicles normally travel, a portable, easy to operate, field device such as the Swiss Rammsonde is shown to provide a practical and alternative measure of snow strength. In addition, Rammsonde hardness may be correlated with vane and cone resistance parameters and provide input to a footing pressure-displacement relationship, thereby serving to indicate vehicle flotation or sinkage.

Vented Compression Molding

A new process for molding low density particulates, vented compression molding, is presented. Vented compression molding is a modification of standard compression molding that uses a perforated surface as the molding surface. The mold cavity is filled with an excess of material, which is forced through the openings in the surface of the mold as the mold closes. The resulting frictional forces, which can be determined approximately by a Mohr-Coulomb yield criterion, generate the pressure that compacts the material. Thus the pressure in the mold is governed by the geometry of the openings and the mechanical properties of the particulate, and not by the displacement or the volume of the mold. This uncoupling of the pressure-displacement relationship allows uniform material distribution and compaction without requiring large-scale flow of the particulates.

Pressure-radius relationships for elastic tubes and their application to arteries: Part 1-Theoretical relationships

The displacement relationships describing the deformation of an elastic vessel under excess internal pressure which are derived from different theories of elasticity are compared. The main result of the comparison is that theories which take account of the thickness of the wall of the vessel produce a significantly better representation than those theories which treat the wall as a membrane. The classical and statistical theories of thick-walled tubes result in complicated pressure-radius relationships. It is shown that there is little difference between the results of the more exact theories and those for a thin membrane corrected by means of a simple thickness factor. A review of the different theories is necessary to decide which pressure-displacement relationship to apply as an approximation for the elastic properties of arteries. An indication is given of the manner in which the relationship is used in numerical computations. In Part 2 the experimental determination of the pressure-radius relationship for a rubber tube is described. The results are in agreement with the conclusions of the comparison of theoretical treatments in Part 1.