Surface Roughening and Contact Behavior in Forming of Aluminum Sheet

1999 ◽  
Vol 121 (2) ◽  
pp. 224-233 ◽  
Author(s):  
Sy-Wei Lo ◽  
Tzu-Chern Horng
Keyword(s):  
Plastic Deformation ◽  
Contact Area ◽  
Low Frequency ◽  
Area Ratio ◽  
Aluminum Sheet ◽  
Contact Behavior ◽  
Asperity Angle ◽  
Frequency Components ◽  
Asperity Flattening ◽  
Contact Area Ratio

The evolution of the surface topography and tool-workpiece contact behavior of an aluminum sheet during plastic deformation has been investigated by a series of indentation tests for various loads, strain rates, and bulk strains. A simple formulation for estimating the roughness of the indented surface and a model of asperity flattening have been proposed. Dynamic balance between the flattening and roughening processes, such as changes of asperity angle and spacing, is considered. Theoretical predictions of the variation of real area of contact with strain show good agreement with experiments. It is found that the very different frictional behavior of aluminum compared with steel sheets is due to the serious change of roughness, including asperity angle and spacing. When the angle is small, the increases in asperity angle and spacing have strong effect on increasing the contact area ratio. However, when the asperity angle is large, increased asperity angle has a significant contribution to the resistance to flattening. The asperity flattening velocity and the increasing rate of contact area ratio arise with the prestrain; however, they are not affected by the strain rate significantly. From FFT analysis, low frequency components (below 10 cycle/mm) due to the rotation of single grains or grain groups are observed on free surface during plastic straining. While in the contact area, in all cases, the low frequency components generated by plastic deformation are compressed.

scholarly journals Critical shoe contact area ratio for sliding on a tennis hard court

2017 ◽  
Vol 232 (2) ◽  
pp. 112-121 ◽  
Author(s):  
John Eric Goff ◽  
Luke Boswell ◽  
Daniel Ura ◽  
Mark Kozy ◽  
Matt J Carré
Keyword(s):  
Friction Coefficient ◽  
Contact Area ◽  
Sliding Friction ◽  
Static Friction ◽  
Area Ratio ◽  
Critical Ratio ◽  
Static Friction Coefficient ◽  
The Creation ◽  
Contact Area Ratio

Dimples have been used in the design of some modern tennis shoe outsoles to enhance sliding ability on hard courts. Experiments were performed with bespoke rubber samples possessing various numbers of holes, which served to simulate dimples in tennis shoe treads. The aim of the research was to assess the effect of contact area on sliding friction. As the ratio of holes to solid rubber increased, a critical ratio was reached whereby the static friction coefficient decreased by more than 11% for tread-to-court pressures comparable to real tennis play. Although this study analyzed bespoke rubber samples and not actual tennis shoe treads, shoe manufacturers should be interested in the existence of a critical dimple ratio that could aid them in the creation of tennis shoes suited for sliding on hard courts.

Partial Film Lubrication Characteristics of Inlet Zone in Cold Strip Rolling

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Kuo Fu ◽  
Yong Zang ◽  
Zhiying Gao
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Contact Area ◽  
Friction Stress ◽  
Area Ratio ◽  
Work Zone ◽  
Zone Length ◽  
Inlet Zone ◽  
Pressure Stress ◽  
Contact Area Ratio

According to the average flow Reynolds equation and rolling theory, a partial film lubrication model of inlet zone has been developed. The model mainly simulates and reflects the influence of surface topography on the inlet film thickness and inlet zone length. Based on the surface topography analysis, a method to judge the friction condition was proposed. All the calculation was conducted by a numerical method. The result shows that the transverse stripe increases the inlet film thickness and the inlet zone length, while the longitudinal stripe decreases them. The surface roughness will enhance this effect. The surface roughness and the stripe direction also have a significant influence on the contact area ratio and the distribution of stress and film thickness in work zone. Transverse stripe increases the lubricant film thickness and separates the roll and the sheet with a larger distance in work zone. It also decreases the contact area ratio, the pressure stress and friction stress of the work zone. Whereas longitudinal stripe decreases the film thickness and increases the contact area ratio, pressure stress and friction stress. The surface roughness increases the contact area ratio, pressure stress and friction stress.

FEM Analysis of Hydrostatic Pressure Generated Within Lubricant Entrapped Into Pocket on Workpiece Surface in Upsetting Process

1999 ◽  
Vol 122 (4) ◽  
pp. 822-827 ◽  
Author(s):  
Akira Azushima
Keyword(s):  
Hydrostatic Pressure ◽  
Contact Area ◽  
Plastic Material ◽  
Quantitative Relationship ◽  
Normal Pressure ◽  
Area Ratio ◽  
Real Contact Area ◽  
Bulk Deformation ◽  
Rigid Plastic ◽  
Contact Area Ratio

In order to investigate into the quantitative relationship between the hydrostatic pressure generated within the surface pocket of the workpiece and the normal pressure acting on the real contact area at the interface of metal forming such as drawing, rolling, forging and so on, the hydrostatic pressure is calculated accompanied with reduction in height in upsetting of cylinders having a central conical impression or a central conical dent filled with lubricant on the top surface, using the rigid-plastic finite element method. The formulated is based on the plasticity theory. The material is assumed to be rigid perfectly plastic material. It is assumed that the hydrostatic pressure is generated accompanied with a volume change in the surface pocket for compressible lubricants. The results obtained from the calculation are as follows: (1) The hydrostatic pressure generated within the lubricant in a central conical impression in cylindrical upsetting approaches the yield stress at a reduction in height of about 4 percent; (2) The hydrostatic pressure generated within the lubricant in a central conical dent in cylindrical upsetting having an annular asperity increases linearly and abruptly with increasing height reduction when the contact area ratio is small and the bulk deformation is elastic, and it increases gradually and the maximum value approaches the normal pressure acting on the contact area when the contact area ratio becomes large and the bulk deformation is plastic. [S0742-4787(00)00503-8]

scholarly journals Dynamic contact area ratio in shoulder instability: an innovative diagnostic technique measuring interplay of bony lesions

2019 ◽  
Vol 28 (7) ◽  
pp. 2361-2366
Author(s):  
Hanneke Weel ◽  
Peter R. Krekel ◽  
Nienke Willigenburg ◽  
W. Jaap Willems ◽  
Pietro Randelli ◽  
...  
Keyword(s):  
Contact Area ◽  
Shoulder Instability ◽  
Diagnostic Technique ◽  
Dynamic Contact ◽  
Area Ratio ◽  
Ct Scans ◽  
Anterior Shoulder Instability ◽  
Control Group ◽  
Level Of Evidence ◽  
Contact Area Ratio

Abstract Purpose The hypothesis of this study is that Dynamic Contact Area Ratio of the humerus and glenoid, measured with CT scans, is significantly reduced in patients with anterior shoulder instability compared to the Dynamic Contact Area Ratio in a control group of people without shoulder instability. Methods Preoperative CT scans of patients who underwent surgery for anterior shoulder instability were collected. Additionally, the radiologic database was searched for control subjects. Using a validated software tool (Articulis) the CT scans were converted into 3-dimensional models and the amount the joint contact surface during simulated motion was calculated. Results CT scans of 18 patients and 21 controls were available. The mean Dynamic Contact Area Ratio of patients was 25.2 ± 6.7 compared to 30.1 ± 5.1 in healthy subjects (p = 0.014). Conclusion Dynamic Contact Area Ratio was significantly lower in patients with anterior shoulder instability compared to controls, confirming the hypothesis of the study. The findings of this study indicate that calculating the Dynamic Contact Area Ratio based on CT scan images may help surgeons in diagnosing anterior shoulder instability. Level of evidence III.

Tribological Applications Considering Roughness Effects on Grain Flow

2011 ◽  
Vol 328-330 ◽  
pp. 837-842
Author(s):  
Hung Jung Tsai ◽  
Jeng Haur Horng ◽  
Hung Cheng Tsai ◽  
Pay Yau Huang
Keyword(s):  
Contact Area ◽  
Chemical Mechanical Polishing ◽  
Flow Theory ◽  
Area Ratio ◽  
Mechanical Polishing ◽  
Roughness Effects ◽  
Slider Bearings ◽  
Grain Flow ◽  
Contact Area Ratio ◽  
Cmp Model

The grain flow lubrication, based on Haff's grain flow theory and the Patir/Cheng flow factors method, is applied in the simulations of rough slider bearings and chemical mechanical polishing. In this paper, the results of flow factor, the performance of rough slider bearings and the mechanism of the CMP process for grain flow are briefly demonstrated. An improved CMP model, considering the partial hydrodynamic grain flow lubrication and elastic-plastic microcontact theory, is also proposed. The contact area ratio and the elastoplastic contact area ratio are presented to improve the understanding of CMP mechanisms.

Three-Body Microcontact Model of Rough Surfaces and Its Application on Polishing of Wafer

2006 ◽  
Vol 505-507 ◽  
pp. 445-450 ◽  
Author(s):  
Jeng Haur Horng ◽  
Jian Shing Lee ◽  
D.C. Du
Keyword(s):  
Lower Bound ◽  
Contact Area ◽  
Rough Surfaces ◽  
Area Ratio ◽  
Body Contact ◽  
Contact Situation ◽  
Three Body ◽  
Straight Lines ◽  
Contact Area Ratio ◽  
Ratio Versus

In this study, a three-body microcontact model for rough surfaces is proposed in order to understand the effects of particles between surfaces on contact characteristics and its application on polishing of wafer. Both transitional surface-to-surface and particle-to-surface two-body microcontact simulations can be obtained according to the simplification of this model. In the three-body contact situation, the curves of contact area ratio versus dimensionless load are located in the range between two straight lines. The surface-to-surface two-body contact situation is the upper bound and the particle-to-surface two-body contact situation is the lower bound. As the value of D/σ increases, the contact situation will approach the pure particle-to- surface 2-body contact situation. The model also is used to study the wear mechanisms of the silicon wafer.

A Raman study of aqueous DMF and DMA solutions at low temperatures

2004 ◽  
Vol 82 (10) ◽  
pp. 1468-1473 ◽  
Author(s):  
K Tomikawa ◽  
H Kanno ◽  
H Kimoto
Keyword(s):  
Aqueous Solution ◽  
High Frequency ◽  
Low Temperatures ◽  
Low Frequency ◽  
Frequency Component ◽  
Solute Concentration ◽  
Area Ratio ◽  
High Frequency Component ◽  
Frequency Components ◽  
Raman Study

Hydrogen bonding in aqueous N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) solutions was studied by Raman spectroscopy of the OH-stretching spectra of water as functions of solute concentration and temperature (from –50 to 50 °C). The Raman spectra were decomposed successfully into two components (the low- and high-frequency components). The peak area ratio of the low-frequency component to the high-frequency component increases exponentially with decreasing temperature. The frequency of the low-frequency component decreases linearly with lowering temperature down to –50 °C at all solute concentrations (solute mol fraction from 0.3 to 0.7). It is shown that the hydrogen bonds in the clathrate structures around DMA molecules are stronger than those around DMF molecules.Key words: Raman spectrum, DMF, DMA, aqueous solution, low temperature.

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