Contact Interface Pressure Research Articles

Modeling method and dynamic analysis of blade with double friction damping structure considering time-varying pressure distribution

A modeling and analytical method considering contact interface pressure characteristics is presented in this paper. Firstly, a high-fidelity model of a blade with a double friction damping structure is established by solid element, and a three-dimensional friction contact element is used to describe the nonlinear friction interface between the blade contact interfaces. Then, the static pressure distribution characteristics of the contact interface of the blade are obtained through the experimental device of the blade with double friction damping structure, and the accuracy of the pressure characteristics is verified. Based on the static pressure distribution, the time-varying dynamic pressure formula of blade contact interface is derived. The influence of the pressure distribution on the contact characteristics of the contact interface is analyzed and applied to the dynamic calculation of the rotating blade. The influence of different parameters on the blade dynamics is obtained. And the optimum mass ratio of the under-platform damper is obtained by simulating the operation condition of the aero engine blade acceleration process.

Factors Affecting Contact Pressure Distribution on Bolted Joint Interface

To investigate factors affecting contact interface pressure distribution in bolted joint, a parametric model was established by ANSYS APDL language in this paper. The contact pressure distribution on bolted joint interface was obtained through interpolating and revising contact interface forces. It is observed that the position of peak interface pressure is between the edge of bolt hole and the edge of bolt head. The contact pressure linearly changes with the bolt load while the distribution trend and radius remain unchanged. When the total thickness of clamped members is fixed, the contact pressure distribution varies from concentrated to uniform with the increasing member thickness ratio, and the maximum contact radius is reached while the member thickness is equal. When one clamped member thickness is fixed, increasing the other’s thickness can also reduce the contact pressure concentration, but the effect gradually weakens. Increasing bolt diameter can slightly increase the absolute contact radius but decrease the normalized contact radius. The inclusion of a washer under the nut can slightly promote interface clamping.

Force Sensing Resistor and Evaluation of Technology for Wearable Body Pressure Sensing

Wearable technologies are gaining momentum and widespread diffusion. Thanks to devices such as activity trackers, in form of bracelets, watches, or anklets, the end-users are becoming more and more aware of their daily activity routine, posture, and training and can modify their motor-behavior. Activity trackers are prevalently based on inertial sensors such as accelerometers and gyroscopes. Loads we bear with us and the interface pressure they put on our body also affect posture. A contact interface pressure sensing wearable would be beneficial to complement inertial activity trackers. What is precluding force sensing resistors (FSR) to be the next best seller wearable? In this paper, we provide elements to answer this question. We build an FSR based on resistive material (Velostat) and printed conductive ink electrodes on polyethylene terephthalate (PET) substrate; we test its response to pressure in the range 0–2.7 kPa. We present a state-of-the-art review, filtered by the need to identify technologies adequate for wearables. We conclude that the repeatability is the major issue yet unsolved.

Footprint Contact Area and Interface Pressure Comparison Between the Knotless and Knot-Tying Transosseous-Equivalent Technique for Rotator Cuff Repair

To quantify and compare the footprint contact area and interface pressure on the greater tuberosity between knotless and knot-tying transosseous-equivalent (TOE) repair using pressure-sensitive film. We used 11 pairs of fresh-frozen cadaveric shoulders (22 specimens), in which rotator cuff tears were created before repair. Each pair was randomized to either conventional medial knot-tying TOE repair (group A) or medial knotless TOE repair using the modified Mason-Allen technique (group B). Pressure-sensitive film was used to quantify the pressurized contact area and interface pressure between the greater tuberosity and supraspinatus tendon. The mean pressurized contact area was 33.2 ± 2.5 mm(2) for group A and 28.4 ± 2.4 mm(2) for group B. There was a significant difference between groups (P=.005). Although the overall contact configuration of both groups was similar and showed an M shape, group A showed a greater pressurized configuration around the medial row. The mean interface pressure was 0.20 ± 0.02 MPafor group A and 0.17 ± 0.02 MPa for group B. There was a significant difference between groups (P=.001). Contrary to our hypothesis, in this time-zero study, medial knotless TOE repair using a modified Mason-Allen suture produced a significantly inferior footprint contact area and interface pressure compared with conventional medial knot-tying TOE repair. Even though we found a statistically significant difference between the 2 repair methods, it is still unknown if this statistical difference seen in our study has any clinical and radiologic significance.

Effect of Contact Interface Nonlinear Coefficient on Ultrasonic Transducer

The model of ultrasonic propagation through contact interface, which is an important factor in the ultrasonic transducer used in wire bond, was established by Hertz contact theory. From the Hertz contact theory, it is found that higher order harmonic wave and waveform distortion occur when the ultrasonic wave propagate through a contact interface between two isotropic solids pressed together. Based on the model, the effect of the contact interface between horn and capillary in wire bond transducer are tested by Laser Doppler vibrometer. The experiment results show that when contact interface pressure is in the range of 6 kPa to 10 kPa, higher harmonic wave and nonlinear coefficient is minimum. When contact interface pressure is more than 10 kPa, the nonlinear coefficient increases and bonding strength decreases as increasing of the interface pressure.

Prevention of pressure ulcer: interaction of body characteristics and different mattresses

We analysed the effect of different body features on contact area, interface pressure and pressure distribution of three different mattresses. Thirty-eight volunteers (age ranged from 17 to 73 years, 23 females) were asked to lie on three different mattresses in a random order: I, standard hospital foam mattresses; II, higher specification foam mattresses (Viscorelax Sure® ); III, constant low pressure devices (CareMedx® , AirSystems). Measurements were performed in supine position and in a 90° left- and right-sided position, respectively, using a full-body mat (pressure mapping device Xsensor X2-Modell). Outcome variables were contact area (CA) in cm(2) , mean interface pressure (IP) in mmHg and pressure distribution (PD) estimated as rate of low pressures between 5 and 33 mmHg on each mattress in percent. Mean CA was lowest in the standard hospital foam mattresses and increased in the higher specification foam mattresses and was highest in the constant low pressure device (supine position: 491 ± 86 cm(2) , 615 ± 95 cm(2) , 685 ± 116 cm(2) ). Mean IP was highest in the standard hospital foam mattresses and lower but similar in the higher specification foam mattresses and the constant low pressure devices (supine position: 22·3 ± 1·5 mmHg, 17·6 ± 1·7 mmHg, 17·6 ± 2·2 mmHg). Models were estimated for CA, IP and PD including the independent variables height, weight and waist-to-hip-ratio (WHR). They show that body morphology seems to play a minor role for CA, IP and PD, but very thin and tall patients and very small and obese people might benefit from different mattresses. Our data show that CA increases with increasing specification of mattresses. Higher specification foam mattresses and constant low pressure devices show similar IP, but constant low pressure devices show a wider pressure distribution. Body morphology should be considered to optimise prevention for single patients.

Effect of Contact Interface Pressure on Higher-Order Harmonic Wave and Bond Strength

The model of ultrasonic propagation at a solid-solid contact interface was established. Higher-order harmonic wave generation and waveform distortion take place when the ultrasonic wave propagation at the solid-solid contact interface. Aluminum wire bond experiments were performed on a laboratory test bench. The relation of bond strength, nonlinear coefficient and contact interface pressure was studied. The experiment results show that when contact interface pressure is less than 6 kPa, higher-order harmonic wave component and the nonlinear coefficient decrease and bond strength increases with contact interface pressure increasing, when contact interface pressure is in range of 6 kPa to 10 kPa, higher harmonic wave and the nonlinear coefficient is the least and bond strength is the highest, however, when contact interface pressure is more than 10 kPa, the nonlinear coefficient increases and bond strength decreases with pressure increasing. The nonlinear coefficient of ultrasonic is a method of forecast bond strength.

Higher Order Harmonic Wave and its Effect on Thermosonic Bond System

Thermosonic bond is widely used in package of semiconductor chip due to its advantages, such as simple process, high efficiency, and no pollution. Ultrasonic play important role inspired interconnection interface atomic energy and soften metallic materials in thermosonic bond. The vibration of bond tool is nonlinear and bond strength is unstable with contact interface condition changing due to discontinuity characteristic parameters of contact interfaces. In order to improve bond strength of chip, model of ultrasonic propagation across a rough contact interface was established. Aluminium wire bond was performed on a thermosonic bond test platform. The harmonic waves of bond tool and the bond strength were measured. The experiment results show that the best bond strength and the less higher order harmonic is achieve when the contact interface pressure is in moderate range.

Alternating pressure air mattresses as prevention for pressure ulcers: A literature review

Objectives The purpose of this paper is to examine and synthesise the literature on alternating pressure air mattresses (APAMs) as a preventive measure for pressure ulcers. Design Literature review. Data sources PubMed, Cinahl, Central, Embase, and Medline databases were searched to identify original and relevant articles. Additional publications were retrieved from the references cited in the publications identified during the electronic database search. Results Thirty-five studies were included. Effectiveness and comfort of APAMs were the main focuses of the studies evaluating APAMs. Pressure ulcer incidence, contact interface pressure, and blood perfusion were the most frequently used outcome measures to evaluate the effectiveness of APAMs. Fifteen randomised controlled trials (RCTs) analysed the pressure ulcer incidence. One RCT compared a standard hospital mattress with an APAM and found that the APAM was a more effective preventive measure. RCTs comparing APAMs with constant-low-air mattresses resulted in conflicting evidence. There was also no clear evidence as to which type of APAM performed better. All RCTs had methodological flaws. The use of contact interface pressure and blood perfusion measurements to evaluate the effectiveness of APAMs is questionable. Comfort of APAMs was the primary outcome measure in only four studies. Different methods for assessment were used and different types of APAMs were evaluated. Better measures for comfort are needed. A few studies discussed technical problems associated with APAMs. Educating nurses in the correct use of APAMs is advisable. Conclusion Taking into account the methodological issues, we can conclude that APAMs are likely to be more effective than standard hospital mattresses. Contact interface pressure and blood perfusion give only a hypothetical conclusion about APAMs’ effectiveness. Additional large, high-quality RCTs are needed. No conclusions can be drawn regarding the comfort of APAMs. A number of technical problems associated with APAMs are related to nurses’ improper use of the devices.

Compare maximum and minimum pressures

EDITOR,—R K Vohra and C N McCollum's use of measurements of contact (interface) pressure to express the effectiveness of pressure redistributing devices in preventing pressure sores have repeated common misconceptions of the use of such data.1 The authors comment that the use of alternating air mattresses should be …

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).

Boundary element method application to bolted joints analysis

The extent of contact region and interface pressure distribution are important parameters for the stress analysis of bolted joints. This note shows how they were computed by the boundary element method in the case of two linear elastic axisymmetric plates of the same thickness. The bolt load distribution was assumed to be constant; three thickness values and two configurations of the bolt load were examined. A comparison was made between BEM results obtained by the authors and FEM results available in literature.