Measurement Of Contact Pressure Research Articles

Load Distribution Effect of Sheet Plates and Its Estimation Technique.

In this paper, the load distribution effect of sheet plate that is put on the fundamental parts subjected to a load is analyzed by using the finite-element method. In the analyses, the thickness and material property of the sheet plate and the composition of fundamental parts are changed. Moreover, the sheet plates composed of several materials are analyzed. The load influence factor R between the sheet plate and the fundamental part is defined and the values for several models are calculated. By using the factor R, the theoretical technique estimating the load distribution effect is proposed. The technique is applied to the practical system measuring contact pressure distribution and the load distribution effect is discussed.

A method for measuring contact pressure instantaneously in articular joint

A method for measuring contact pressure instantaneously in articular joint

Measurement of contact pressure distributions between soles and floor surface using a photoelastic technique and its clinical significance. (Mechanical analysis of standing posture in children with down syndrome).

A photoelastic method was used for a new device to measure contact pressure distribution between soles and the floor surface. The size of a first fringe was linearly correlated with weight loaded upon the point. Its error ranges were within 3%. When 17 individuals with Down syndrome (ages 1-15 years) and 27 controls (ages 1-50 years) were analysed by this method, it was revealed that, in the former, the number of points with a first fringe was increased and, in the latter, an average loading weight for each point with a first fringe was increased. From the patterns of contact pressure distribution of soles, the center of gravity for each sole and that of a whole body were determined. In the Down syndrome group, the position was shifted forward at 50% the length of the sole from the ankle; meanwhile, it was only 35% in the control.

A method for measuring contact pressure instantaneously in articular joint

A method whereby instrumented pipes are inserted part of the way into articular cartilage from the underlying subchondral bone has been developed for measuring instantaneous contact pressures acting within articular joints. Contact pressures developed between two specimens cut from fresh cadaveric knee joints were measured with this technique and then subsequently with pressure-sensitive paper. Average contact pressures (load/contact area) were also calculated. Comparisons of the three sets of data show that contact pressures measured with the pressure pipe system are linearly related (p less than 0.001) to both the contact pressures measured with the pressure-sensitive paper and the calculated average contact pressures.

Contact pressures from an instrumented hip endoprosthesis.

A pressure-measuring Moore-type endoprosthesis was implanted in a seventy-three-year-old patient who had sustained a displaced fracture of the femoral neck. The measurement and telemetry of contact pressures in the hip began in the operating room, and data were acquired periodically for more than thirty-six months. Unexpectedly high localized contact pressures between the acetabular cartilage and the prosthesis were recorded. Early in the period of recovery, activities such as using a bedpan or performing isometric exercise produced pressures that were close to those recorded during normal walking. The highest pressure, eighteen megapascals, was recorded one year postoperatively, while the patient was rising from a chair. High pressures occurred in the superior and posterior aspects of the acetabulum.

Comparison of contact pressures measured at the sacrum of young and elderly subjects

Contact (interface) pressure measurements were made between the sacrum of groups of young and elderly subjects lying upon two special mattresses used to prevent pressure sores. One mattress was an alternating air pressure mattress, the other a foam mattress. Contact pressures were measured using a hydraulic sensor taped directly to the skin over the sacrum. All mean pressures and ‘pressure impulses’ (total applied pressure per standard time period) appeared higher when measured among the elderly subjects. Compared with the pressures measured from young subjects, the maximum contact pressures were significantly higher (p < 0.05) on both mattresses, with the pressure impulse higher while lying upon the foam mattress (p < 0.05).

Contact pressures in the patellofemoral joint during impact loading on the human flexed knee.

Currently, a bone fracture criterion is used by the automotive industry to assess the potential for a lower extremity injury from impact directed on the flexed knee. However, recent studies with animal models indicate irreversible damage to articular cartilage due to overpressures generated within the patellofemoral (P-F) joint without bone fracture, and suggest this injury may lead to a progressive, degenerative disease of the joint. The purpose of this investigation was to measure contact pressure in the human P-F joint during impact loading on the isolated, flexed knee. Loads were delivered on the patella with a free-flight inertial mass that had a rigid or foam padded interface. The experiments were conducted by serially increasing the impactor velocity in repeated tests until bone fracture was observed. The distribution of maximum pressures generated within the joint was recorded with a pressure-sensitive film. Fracture of the patella or the femur occurred at impact loads of approximately 8.5 kN. The average P-F pressure was approximately 25 MPa for 8 kN of impact load on the 90 degrees flexed joint. The P-F contact area varied with the level of contact load and degree of joint flexion. The distribution of P-F pressures was nonuniform. At approximately 70% of the fracture load for the 90 degrees flexed knee, nearly 35% of the contact area was exposed to pressures greater than 25 MPa. In an earlier study by others using subchondral bone-cartilage preparations, this level of pressure resulted in fissures and lacerations of the cartilage.

Experimental verification of facet load transmission by direct measurement of facet lamina contact pressure

This paper presents results of a new measuring technique by means of which facet tip contact pressure data were obtained. The aim of the paper is to demonstrate by direct measurement the existence of a load transmission mechanism through the facet joint. Six lumbar spine motion segments were used in 21 tests. Simulated extensor muscle action was provided to overcome moments due to eccentric loads which represented body weight and an external hand-held load acting 340 mm anterior to the center of the disc. Facet pressure was measured in all cases when muscle load was applied to counteract body weight. This pressure increased when more muscle force was applied to balance the externally applied flexion moment. When the anterior load was released suddenly, there was a large increase in facet pressure with a concomitant decrease in disc pressure.

Evaluation of the effect of flatness on the contact pressure distribution between jointed plates by means of ultrasonic techniques.

A contact pressure distribution in jointed plates has been investigated by using an ultrasonic technique, especially by varying the flatness of joint surfaces. At first, the relations between contact pressure and sound pressure of reflected waves by using a normal probe and angle probes are obtained by compressing calibration blocks under various surface roughnesses. Next, when two rectangular plates and two disks with a circular hole are compressed under various convex flatnesses of the joint surfaces, the sound pressure of reflected waves is measured by the normal probe or the angle probes. From these relations, the contact pressure distribution in these jointed plates is quantitatively assesed. The experimental results are presented graphically and compared with an analytical one. It is clarified that the contact pressure distribution is influenced significantly by the very small flatness deviation, thus the proposed ultrasonic method is practically useful for the measurement of contact pressure.

Development of sensing system of piezoelectric ceramics measuring contact pressure distributions. On techniques to increase measuring points and speed.

Improvement techniques of the sensing system proposed in the previous paper are described. By the sensing system, optional contact pressure distributions are measured automatically. In the system, piezoelectric ceramics are used and a special electric circuit is designed to measure electric charge in the material. In the electric circuit, the FET with the integral and peak hold circuits is used to increase the measuring points and speed. A sensing system of 20×10 measuring points and a 2-second measuring time is designed. By using this system, the contact pressure distributions for several problems are measured. The obtained total force and the pressure distributions are compared with the corresponding acting forces and the theoretical values.

Development of sensing system of piezoelectric ceramics measuring contact pressure distributions.

In this paper, an automatic sensing system measuring contact pressure distributions is proposed. The sensing material is made of piezoelectric ceramics. To measure electric charge in the material produced by contact pressures, a special electric circuit is designed by using a peak hold circuit. A micro computer (NEC PC-9801) and a multiplexer controller are used to automatically measure the contact pressure distributions. By using the ceramic sensor for 5×5 measuring points, the pressure distributions for several contact problems are measured. The obtained total forces and the pressure distributions are compared with the corresponding acting forces and the theoretical values, From the results, it is recognized that the proposed sensing system is excellent in reliability and durability.

Direct measurement of dynamic contact pressure on the tibial plateau of the knee

Although the management of meniscal injuries by open or closed surgical procedures is very common, the role of the menisci in normal knee function is still unclear. Fairbank (6) suggested that the menisci play an important part in the transmission of inter-articular loads. In explaining their function, he accounted for the high incidence of degenerative changes following meniscectomy have been made by others (2,8,9,19).

Dynamics of a rotating cylinder-friction block contact pair

The rotating cylinder-friction block contact pair is a model of wearing joints such as drum brakes, contact seals and journal sliding bearings. In this paper the results of a theoretical and experimental study of a rotating cylinder-friction block, which is considered to be a contact pair with distributed parameters, are discussed. Differential equations which describe the dynamics of sliding, friction and wear are derived and numerical solutions are given. The friction block is assumed to be a rigid or an elastic body. Formulae for calculating the wear, friction torque and contact pressure distribution under constant load are proposed. The test apparatus and the results of the model experiments are presented. A pneumatic multichannel device for the measurement of contact pressure and its distribution in wearing joints is described. This device can be used in dry and boundary friction conditions under varying loads and velocities. The theoretical relationships are in good agreement with the experimental results.

Contact Pressure Measurements by Means of Ultrasonic Waves : On a Method of Quantitative Measurement

A quantitative measurement of contact pressure by means of ultrasonic waves has been proposed to measure the contact pressure distribution between two elastic beams. At first, in a new proposed calibration method, the relation between mean contact pressure and sound pressure of reflected waves is obtained by using calibration blocks made of the same material and height as the beams. After such preparation, both sides of the laminated beams are compressed under locally uniform pressure, and the sound pressure of reflected waves is measured. From these relations, the contact pressure in beams is directly obtained. It is clarified that the experimental results agree approximately with the theoretical ones and the proposed ultrasonic method is practically useful.

Contact pressure measurement by means of ultrasonic waves using angle probes.

A quantitative measurement of contact pressure by means of ultrasonic waves using angle probes has been proposed to measure contact pressure distributions between two elastic beams. At first, in a proposed calibration method, the relation between mean contact pressure and sound pressure of reflected waves is obtained for various surface roughnesses by using calibration blocks made of the same material as the beams. Both sides of the laminated beams are compressed under locally uniform pressure, and the sound pressure of reflected waves is measured. The experimental results agree fairly well with the theoretical ones and the experimental ones obtained by a normal probe. It is clarified that the proposed ultrasonic method is practically useful.

Contact Pressure Measurement by Means of Ultrasonic Waves : On a Bolted Joint with a Solid-metal Flat Gasket

A quantitative measurement of contact pressure by means of ultrasonic waves using a normal probe has been proposed to measure the contact pressure on a bolted joint with a solid-metal flat gasket. At first, in a proposed calibration method, the relation between mean contact pressure and sound pressure of reflected waves is obtained using the calibration blocks with various surface roughnesses and heights made of the same material as the bolted joint. Both sides of the laminated finite hollow cylinders are compressed under a locally uniform pressure, and the sound pressure of reflected waves is measured. From these relations, the contact pressure is obtained. The experimental results agree approximately with the theoretical ones. It is demonstrated that the gasket has an effect of preventing the leakage and the proposed ultrasonic method is practically useful.

Contact Pressure Measurement by Means of Ultrasonic Waves Using Angle Probes

A quantitative measurement of contact pressure by means of ultrasonic waves using angle proves has been proposed to measure contact pressure distributions between two elastic beams. At first, in a proposed calibration method, the relation between mean contact pressure and sound pressure of reflected waves is obtained using calibration blocks with various surface roughnesses made of the same material as beams. Both sides of laminated beams are compressed under a locally uniform pressure, and the sound pressure of reflected waves is measured. The experimental results agree fairly well with the theoretical ones and the experimental ones obtained by a normal probe. It is confirmed that the proposed ultrasonic method is practically useful.

Ferroelectric polymer tactile sensors for prostheses

Abstract The use of ferroelectric polymers such as polyvinylidene fluoride (PVF2) for tactile sensors for prostheses has been investigated. A few sensory capabilities peculiar to human skin, such as the ability to measure contact pressure, to evaluate hardness of different materials, to ‘‘feel'’ roughness and the surface textures of different objects and to discriminate materials on the basis of their thermal conductivity, have been identified as potentially reproducible by PVF2 sensors. Different PVF2 transducers have been designed and constructed to study the possibility of mimicking each sensory capability. Details of sensors construction are given, results of testing are discussed and some problems are identified. Based on experimental results we conclude that the development of a sensorized skin-like transducer for prostheses based on the use of ferroelectric polymers is feasible.

Measurement of Contact Pressure in Metal Forming by Pressure Sensitive Film

A simple method is presented for measuring the distribution of tool contact pressure in metal forming by using a pressure sensitive film which detects the contact pressure from the change in color density. In the method, a sufficiently hard sheet metal compared to the workpiece is inserted between the workpiece and the pressure sensitive film in order to eliminate the influence of frictional shear stress at the tool-workpiece interface on the measured result. Since the maximum pressure which can be determined by the film is 150MPa, lead is used as a workpiece material. Distributions of tool contact pressure are measured in upsetting of cylindrical billets, in free forging of plates of various shapes, and also in backward extrusion of a can. The measured distributions agree well with those computed by the rigid-plastic finite element method.

Contact Pressure Measurement by Means of Ultrasonic Waves : On a Bolted Joint with a Solid-Metal Flat Gasket)

Contact Pressure Measurement by Means of Ultrasonic Waves : On a Bolted Joint with a Solid-Metal Flat Gasket)