The Characteristics of Elastically Contacting Ideal Rough Surfaces

1996 ◽  
Vol 118 (1) ◽  
pp. 90-97 ◽  
Author(s):  
Leng Yongsheng ◽  
Yang Guiping ◽  
Huang Yan ◽  
Zheng Linqing

The analysis of the elastic contact of ideal rough surfaces is presented in this paper. The rough asperities are assumed to be spherical with the same vertical height and spatial distance. The mutual influence of asperities is considered. Numerical results show that for the same load, the contact area is less than the Hertzian prediction, while the pressure distribution is still of a Hertzian type, but is increased to some extent. We find that the asperity interaction is associated with a parameter, called the “loading level,” which combines the surface texture, mechanical properties, and the nominal mean pressure. Of significant importance is the discovery of the variation of the reference plane position with the contact load. In the classical theory of rough contact (Greenwood and Williamson, 1966), the reference plane was in fact assumed to be in the mean line position. We prove that the location of the reference plane is determined by the number of contacting asperities and the loading level, thus making the analysis of the contact of rough surfaces somewhat complex.

2000 ◽  
Vol 123 (4) ◽  
pp. 857-864 ◽  
Author(s):  
Yongwu Zhao ◽  
L. Chang

This paper presents a micro-contact model incorporating asperity interactions in elastic-plastic contact of rough surfaces. The effect of the asperity interactions on the local deformation behavior of a given micro-contact is first modeled based on the Saint-Venant’s Principle and Love’s Formula. The local contact interference is related in closed form to the local contact load, the global mean pressure and material parameters. This micro-contact model equation is then integrated into the elastic-plastic contact model developed in Zhao et al. (2000) to allow the asperity interactions and plastic deformation to be considered simultaneously. The effects of the asperity interactions on the mean surface separation, the real area of contact and the redistribution of the contact load among contacting asperities of different heights are studied. The results show that the asperity interactions can significantly affect the mean surface separation and micro-contact load redistribution. The results also reveal that the effect of asperity interactions can be largely cancelled out by the effect of asperity plastic deformation.


2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
K Piayda ◽  
A Wimmer ◽  
H Sievert ◽  
K Hellhammer ◽  
S Afzal ◽  
...  

Abstract Background In the era of transcatheter aortic valve replacement (TAVR), there is renewed interest in percutaneous balloon aortic valvuloplasty (BAV), which may qualify as the primary treatment option of choice in special clinical situations. Success of BAV is commonly defined as a significant mean pressure gradient reduction after the procedure. Purpose To evaluate the correlation of the mean pressure gradient reduction and increase in the aortic valve area (AVA) in different flow and gradient patterns of severe aortic stenosis (AS). Methods Consecutive patients from 01/2010 to 03/2018 undergoing BAV were divided into normal-flow high-gradient (NFHG), low-flow low-gradient (LFLG) and paradoxical low-flow low-gradient (pLFLG) AS. Baseline characteristics, hemodynamic and clinical information were collected and compared. Additionally, the clinical pathway of patients (BAV as a stand-alone procedure or BAV as a bridge to aortic valve replacement) was followed-up. Results One-hundred-fifty-six patients were grouped into NFHG (n=68, 43.5%), LFLG (n=68, 43.5%) and pLFLG (n=20, 12.8%) AS. Underlying reasons for BAV and not TAVR/SAVR as the primary treatment option are displayed in Figure 1. Spearman correlation revealed that the mean pressure gradient reduction had a moderate correlation with the increase in the AVA in patients with NFHG AS (r: 0.529, p<0.001) but showed no association in patients with LFLG (r: 0.145, p=0.239) and pLFLG (r: 0.030, p=0.889) AS. Underlying reasons for patients to undergo BAV and not TAVR/SAVR varied between groups, however cardiogenic shock or refractory heart failure (overall 46.8%) were the most common ones. After the procedure, independent of the hemodynamic AS entity, patients showed a functional improvement, represented by substantially lower NYHA class levels (p<0.001), lower NT-pro BNP levels (p=0.003) and a numerical but non-significant improvement in other echocardiographic parameters like the left ventricular ejection fraction (p=0.163) and tricuspid annular plane systolic excursion (TAPSE, p=0.066). An unplanned cardiac re-admission due to heart failure was necessary in 23.7% patients. Less than half of the patients (44.2%) received BAV as a bridge to TAVR/SAVR (median time to bridge 64 days). Survival was significantly increased in patients having BAV as a staged procedure (log-rank p<0.001). Conclusion In daily clinical practice, the mean pressure gradient reduction might be an adequate surrogate of BAV success in patients with NFHG AS but is not suitable for patients with other hemodynamic entities of AS. In those patients, TTE should be directly performed in the catheter laboratory to correctly assess the increase of the AVA. BAV as a staged procedure in selected clinical scenarios increases survival and is a considerable option in all flow states of severe AS. (NCT04053192) Figure 1 Funding Acknowledgement Type of funding source: None


Author(s):  
S. Elhanafi ◽  
K. Farhang

This paper considers leakage in mechanical seals under hydrostatic operating condition. A contact model based on the Greenwood and Williamson contact of rough surfaces is developed for treating problems involving mechanical seals in which both the micron scale roughness of the seal face and its macro scale profile are used to obtain either a closed-form equation or a nonlinear equation relating mean plane separation to the mass flow rate. The equations involve the micron scale geometry of the rough surfaces and physical parameter of the seal and carriage. Under hydrostatic condition, it is shown that there is an approximate closed-form solution in which mass flow rate in terms of the mean plane separation, or alternatively, the mean plane separation in terms of the leakage mass flow rate is found. Equations pertaining to leakage in nominally flat seal macro profile is considered and closed form equation relating to leakage flow rate to pressure difference is obtained that contain macro and micron geometries of the seal.


1999 ◽  
Vol 42 (3) ◽  
pp. 443-452 ◽  
Author(s):  
Yuan-Zhong Hu ◽  
Gary C. Barber ◽  
Dong Zhu

2017 ◽  
Vol 2017 ◽  
pp. 1-6 ◽  
Author(s):  
Antonio Scarano

Background. One of the most problematic regions for endosseous implants is the posterior maxilla, not only having poor bone density, but also lacking adequate vertical height as a result of sinus pneumatization. The purpose of the present study was a radiologic, histological, and histomorphometrical evaluation, in humans, of specimens retrieved from sinuses augmented with decellularized bovine compact particles, after a healing period of 6 months. Methods. Four patients, with atrophic resorbed maxillas, underwent a sinus lift augmentation with decellularized bovine compact bone from bovine femur. The size of the particles used was 0.25–1 mm. A total of four grafts and 5 biopsies were retrieved and processed to obtain thin ground sections with the Precise 1 Automated System. Results. The mean volume after graft elevation calculated for each of the 4 patients was 2106 mm3 in the immediate postoperative period (5–7 days), ranging from 1408.8 to 2946.4 mm3. In the late postoperative period (6 months) it was 2053 mm3, ranging from 1339.9 to 2808.9 mm3. Histomorphometry showed that newly formed bone was 36±1.6% and marrow spaces were 34±1.6%, while the residual graft material was 35±1.4%. Conclusion. In conclusion, based on the outcome of the present study, Re-Bone® can be used with success in sinus augmentation procedures and 6 months are considered an adequate time for maturation before implant placement.


Micromachines ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 368
Author(s):  
Shengguang Zhu ◽  
Liyong Ni

A novel static friction model for the unlubricated contact of random rough surfaces at micro/nano scale is presented. This model is based on the energy dissipation mechanism that states that changes in the potential of the surfaces in contact lead to friction. Furthermore, it employs the statistical theory of two nominally flat rough surfaces in contact, which assumes that the contact between the equivalent rough peaks and the rigid flat plane satisfies the condition of interfacial friction. Additionally, it proposes a statistical coefficient of positional correlation that represents the contact situation between the equivalent rough surface and the rigid plane. Finally, this model is compared with the static friction model established by Kogut and Etsion (KE model). The results of the proposed model agree well with those of the KE model in the fully elastic contact zone. For the calculation of dry static friction of rough surfaces in contact, previous models have mainly been based on classical contact mechanics; however, this model introduces the potential barrier theory and statistics to address this and provides a new way to calculate unlubricated friction for rough surfaces in contact.


1993 ◽  
Vol 75 (1) ◽  
pp. 148-154 ◽  
Author(s):  
S. Isono ◽  
D. L. Morrison ◽  
S. H. Launois ◽  
T. R. Feroah ◽  
W. A. Whitelaw ◽  
...  

The static mechanics of the hypotonic pharynx were endoscopically evaluated in nine sleeping patients with obstructive sleep apnea, having a primary narrowing only at the velopharynx. The velopharynx closed completely at a mean pressure of 0.18 +/- 1.21 cmH2O, and the mean half-dilation pressure was 1.93 cmH2O above closing pressure. The dependence of area on pressure was distinctly curvilinear, being steep near closing pressure and asymptotically approaching maximum area (mean = 1.32 cm2). The data for each patient were satisfactorily fitted by an exponential function (mean R2 = 0.98), and a single exponential relationship usefully represented the dependence of relative area on pressure above closing pressure for the population (R2 = 0.85). During the test inspiration, flow limitation was consistently observed when mask pressure exceeded closing pressure by 0.5–3.0 cmH2O. In summary, the static mechanics of the hypotonic velopharynx of patients with obstructive sleep apnea can be described by an exponential pressure-area relationship, with a closing pressure near atmospheric pressure and a high compliance in the range of airway pressure 0–3 cmH2O above closing pressure.


1977 ◽  
Vol 99 (3) ◽  
pp. 503-509 ◽  
Author(s):  
B. E. Lee ◽  
B. F. Soliman

A study has been made of the influence of grouping parameters on the mean pressure distributions experienced by three dimensional bluff bodies immersed in a turbulent boundary layer. The range of variable parameters has included group density, group pattern and incident flow type and direction for a simple cuboid element form. The three flow regimes associated with increasing group density are reflected in both the mean drag forces acting on the body and their associated pressure distributions. A comparison of both pressure distributions and velocity profile parameters with established work on two dimensional bodies shows close agreement in identifying these flow regime changes. It is considered that the application of these results may enhance our understanding of some common flow phenomena, including turbulent flow over rough surfaces, building ventilation studies and environmental wind around buildings.


2005 ◽  
Vol 26 (6) ◽  
pp. 442-448 ◽  
Author(s):  
Craig I. Title ◽  
Hung-Geun Jung ◽  
Brent G. Parks ◽  
Lew C. Schon

Background: The goal of this study was to identify pressure changes throughout the peroneal groove after a groove deepening procedure. We hypothesized that pressures would decrease. Methods: Twelve fresh-frozen foot and ankle specimens were used. A thin pressure strip containing four sensor pads was secured within the peroneal groove with pads 1 through 4 positioned at the calcaneofibular ligament (CFL) and at the distal, middle, and proximal groove, respectively. The midstance phase of gait was simulated with loads applied to the plantar foot and posterior tibial tendon and to the peroneus longus and brevis tendons. Pressures were recorded with the ankle in neutral, plantarflexion, dorsiflexion, inversion, and eversion. Groove deepening was done by osteotomizing the posterior fibular wall. Pressure readings were then recorded. Average pressures for each of the four sensor pads after the procedure were compared to those obtained before the procedure. Results: The mean pressure overlying the CFL increased at all five ankle positions; however, these changes were not significant. Significant decreases in pressure were noted within the distal and middle groove at all ankle positions after the peroneal groove deepening procedure. Pressure within the proximal groove increased at all but one position, with a significant difference noted in neutral and plantarflexion. Conclusion: Pressures within the middle and distal peroneal groove significantly decreased after a groove deepening procedure. Combining this technique with peroneal tendon debridement may be advantageous for treatment of partial peroneal tendon tears or recalcitrant peroneal tendinitis.


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