Fixturing Effects in the Thermal Modeling of Laser Cladding

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
M. F. Gouge ◽  
P. Michaleris ◽  
T. A. Palmer
Keyword(s):  
Surface Roughness ◽  
Laser Cladding ◽  
Contact Area ◽  
Contact Region ◽  
Thermal Modeling ◽  
Model Error ◽  
Effective Contact ◽  
Contact Conductivity

Fixturing of components during laser cladding can incur significant conductive thermal losses. However, due to the surface roughness at contact, interfacial conduction is impeded. The effective contact conductivity, known as gap conductance, is much lower than the contacting material conductivities. This work investigates modeling conduction losses to fixturing bodies during laser cladding. Two laser cladding experiments are performed using contrasting fixturing schemes: one cantilevered substrate with a minimal substrate-fixture contact area and one with a substrate bolted to a work bench, with a significant substrate-fixture contact area. Using calibrated gap conductance values, error for the cantilevered fixture model decreases from 20.5% to 6.49% in the contact region, while the bench fixtured model error decreases from a range of 60–102% to 11–45%. The improvement in accuracy shows the necessity of accounting for conduction losses in the thermal modeling of laser cladding, particularly for fixturing setups with large areas of contact.

Rough Air-Soft Elastohydrodynamic Lubrication

2013 ◽  
Vol 420 ◽  
pp. 30-35
Author(s):  
Khanittha Wongseedakaew ◽  
Jesda Panichakorn
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Modulus Of Elasticity ◽  
Contact Region ◽  
Elastohydrodynamic Lubrication ◽  
Multilevel Methods ◽  
Inlet Temperature ◽  
Film Pressure ◽  
Air Inlet ◽  
Air Film

This paper presents the effects of rough surface air-soft elastohydrodynamic lubrication (EHL) of rollers for soft material under the effect of air molecular slip. The time independent modified Reynolds equation and elasticity equation were solved numerically using finite different method, Newton-Raphson method and multigrid multilevel methods were used to obtain the film pressure profiles and film thickness in the contact region. The effects of amplitude of surface roughness, modulus of elasticity and air inlet temperature are examined. The simulation results showed surface roughness has effect on film thickness but it little effect to air film pressure. When the amplitude of surface roughness and modulus of elasticity increased, the air film thickness decreased but air film pressure increased. However, the air inlet temperature increased when the air film thickness increased.

A simplified formulation of adhesion problems with elastic plates

2009 ◽  
Vol 465 (2107) ◽  
pp. 2217-2230 ◽  
Author(s):  
Carmel Majidi ◽  
George G. Adams
Keyword(s):  
Potential Energy ◽  
Contact Area ◽  
Contact Region ◽  
Bending Moment ◽  
Total Potential Energy ◽  
Work Of Adhesion ◽  
Contact Radius ◽  
Algebraic Complexity ◽  
Elastic Plates ◽  
Total Potential

The solution of adhesion problems with elastic plates generally involves solving a boundary-value problem with an assumed contact area. The contact region is then found by minimizing the total potential energy with respect to the contact area (i.e. the contact radius for the axisymmetric case). Such a procedure can be extremely long and tedious. Here, we show that the inclusion of adhesion is equivalent to specifying a discontinuous internal bending moment at the contact region boundary. The magnitude of this moment discontinuity is related to the work of adhesion and flexural rigidity of the plate. Such a formulation can greatly reduce the algebraic complexity of solving these problems. It is noted that the related plate contact problems without adhesion can also be solved by minimizing the total potential energy. However, it has long been recognized that it is mathematically more efficient to find the contact area by specifying a continuous internal bending moment at the boundary of the contact region. Thus, our moment discontinuity method can be considered to be a generalization of that procedure which is applicable for problems with adhesion.

Capillary Forces Described by Effective Contact Angle Distributions via Simulations of the Centrifuge Technique

MRS Advances ◽  
2016 ◽  
Vol 1 (31) ◽  
pp. 2237-2245
Author(s):  
Myles Thomas ◽  
Elizabeth Krenek ◽  
Stephen Beaudoin
Keyword(s):  
Surface Roughness ◽  
Contact Angle ◽  
Smooth Surface ◽  
Adhesion Force ◽  
Capillary Forces ◽  
Angle Distribution ◽  
Particle Adhesion ◽  
Multiple Factors ◽  
Effective Contact ◽  
Condensed Moisture

ABSTRACTUnderstanding particle adhesion is vital to any industry where particulate systems are involved. There are multiple factors that affect the strength of the adhesion force, including the physical properties of the interacting materials and the system conditions. Surface roughness on the particles and the surfaces to which they adhere, including roughness at the nanoscale, is critically important to the adhesion force. The focus of this work is on the capillary force that dominates the adhesion whenever condensed moisture is present. Theoretical capillary forces were calculated for smooth particles adhered to smooth and rough surfaces. Simulations of the classical centrifuge technique used to describe particle adhesion to surfaces were performed based on these forces. A model was developed to describe the adhesion of the particles to the rough surface in terms of the adhesion to a smooth surface and an ‘effective’ contact angle distribution.

scholarly journals Study of Wire Deformation Characterization and Size Effects during the Micro-Flat-Rolling Process

Metals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 405 ◽  
Author(s):  
Haibo Xie ◽  
Ken-ichi Manabe ◽  
Zhengyi Jiang
Keyword(s):  
Surface Roughness ◽  
Contact Area ◽  
Rolling Process ◽  
Lateral Spread ◽  
Curvature Radius ◽  
Element Simulation ◽  
Flat Rolling ◽  
Set Up ◽  
Rolling Deformation

A comprehensive research on the flat rolling deformation characterization of microwire has been conducted systematically through finite element simulation and testified by the results from the experimental analysis. The obtained results are compared in terms of lateral spread, geometrical characteristic, contact area width and surface roughness considering the effects of pass reduction and initial wire diameter. The size effect has been identified and surface layer modeling has been set up based on surface grain share and grain size distribution. The numerical method combined with varied flow stress has been verified by experimental value with a maximum difference of 3.7% for the 1.5 mm wire. With the increase of the height reduction, the curvature radius is decreased while the lateral spread and contact area width are increased. Surface roughness evolution in the range of 0.52–0.85 µm for the rolled wire has also been investigated.

Study on Factors which Make CBN Insert can Turn S45C Steel Have Surface Roughness Less than Ra 0.4

2019 ◽  
Vol 805 ◽  
pp. 3-7
Author(s):  
Manus Sriswat ◽  
Kittipong Kimapong ◽  
Atthakorn Chanchana
Keyword(s):  
Surface Roughness ◽  
Contact Area ◽  
Cubic Boron Nitride ◽  
Cutting Speed ◽  
Medium Carbon Steel ◽  
Depth Of Cut ◽  
Grinding Process ◽  
Standard Type ◽  
Good Surface ◽  
Cylindrical Parts

Grinding process is necessary final process of making cylindrical parts with less than Ra 0.4 surface roughness. Generally we cannot obtain good surface quality without grinding process. As the experience of the authors, using CBN (Cubic Boron Nitride) insert to turning cylindrical parts could be obtained Ra 0.438 surface roughness. The surface roughness result is similar to ground parts. This result becomes the main focus of the study. Authors study to find out factors affecting CBN performance in turning with CBN to obtain less than Ra 0.4 surface roughness. According to the study, it was found that tool contact area allied to surface roughness. The experiment is turning S45C medium carbon steel under the following condition: Cutting speed is 300 m./min, Feed is 0.05 mm./rev and depth of cut is 0.1 mm. Experiment under the same condition in different contact area. Modify contact area of CBN insert to be 5,10,15,20 and 25 mm. and testing in order. CBN insert standard type contact area is 0 mm. Compare test results of modified CBN inserts with standard type result. The results of experiments were as follows: 1) Turning steel with CBN contact area 10 mm. was obtained Ra 0.456 surface roughness, 2) Turning steel with CBN contact area 15 mm. was obtained Ra 0.293 surface roughness, Thus less than Ra 0.4 surface roughness.

Elastic-Plastic Microcontact Analysis of a Sphere and a Flat Plate

2007 ◽  
Vol 23 (4) ◽  
pp. 341-352 ◽  
Author(s):  
J. L. Liou ◽  
J. F. Lin
Keyword(s):  
Surface Roughness ◽  
Flat Plate ◽  
Contact Pressure ◽  
Contact Area ◽  
Normal Load ◽  
Contact Load ◽  
Asperity Contact ◽  
Elastic Plastic ◽  
Deformation Regime ◽  
Maximum Contact

ABSTRACTThe elastic-plastic microcontact model of a sphere in contact with a flat plate is developed in the present study to investigate the effect of surface roughness on the total contact area and contact load. From the study done by the finite element method, the dimensionless asperity contact area, average contact pressure, and contact load in the elastoplastic regime are assumed to be a power form as a function of dimensionless interference (δ/δec). The coefficients and exponents of the power form expressions can be determined by the boundary conditions set at the two ends of the elastoplastic deformation regime. The contact pressures evaluated by the present model are compared with those predicted by the Hertz theory, without considering the surface roughness and the reported model, including the roughness effect, but only manipulating in the elastic regime. The area of non-zero contact pressure is enlarged if the surface roughness is considered in the microcontact behavior. The maximum contact pressure is lowered by the presence of surface roughness if the contact load is fixed. Under a normal load, both the contact pressure and the contact area are elevated by raising the plasticity index for the surface of the same surface roughness.

A Study of the Effect of m and n Coefficients of the Hertzian Contact Theory on Railroad Vehicle Dynamics

2007 ◽  
Author(s):  
J. P. Pascal ◽  
Khaled E. Zaazaa
Keyword(s):  
Contact Area ◽  
Contact Region ◽  
Local Deformation ◽  
Hertzian Contact ◽  
Vehicle Dynamic ◽  
Railroad Vehicle Dynamics ◽  
Original Table ◽  
Data Points ◽  
Railroad Vehicle ◽  
Contact Ellipse

For the wheel/rail contact problem, the Hertz theory for two elastic bodies in contact is commonly used to determine the shape and dimensions of the contact area and the local deformation of the wheel and rail surfaces at the contact region. The shape of the contact area is assumed to be elliptical. The ratio of the contact ellipse semi-axes is equal to the ratio of two non-dimensional contact area coefficients, known as m and n coefficients. Hertz presented a table of these two coefficients, determined as a function of an angular parameter, θ. Most railroad vehicle dynamic codes use this table with online interpolation to determine the contact ellipse semi-axes. Recently, it was found that this original table may be too coarse, and that more data points are needed within the table for solving the wheel/rail contact accurately. This paper discusses the effect of the accuracy of the m and n coefficients in solving for wheel/rail contact, and demonstrates this effect with two numerical examples that show the resulting differences in the dynamic behavior of railroad vehicles dependent on this accuracy. A new table with more data points is presented that is recommended for use in railroad vehicle dynamic codes that employ the Hertzian contact for solving the wheel/rail contact interaction. This modified table was originally derived by Jean-Pierre Pascal as a part of collaborative research between the Federal Railroad Administration (FRA) and the French Ministry of Transportation.

Effects of External Hard Particles on Brake Friction Characteristics During Hard Braking

2012 ◽  
Vol 58 (2) ◽  
Author(s):  
M. K. Abdul Hamid ◽  
G. W. Stachowiak
Keyword(s):  
Standard Deviation ◽  
Friction Coefficient ◽  
Contact Area ◽  
Oscillation Amplitude ◽  
Stopping Time ◽  
Hard Particle ◽  
Friction Coefficients ◽  
Hard Particles ◽  
Effective Contact ◽  
Friction Oscillation

The effects of external hard particles on the friction coefficients and its oscillation amplitudes during hard braking were investigated. Silica sands of the size between 180 to 355 μm were used during the experiments. The results were compared to the results obtained without the grit particles present in order to determine the change in friction coefficient and the fluctuation of frictional oscillation amplitude. Different sliding speeds were applied and external hard particle of different size is found to significantly affect the friction coefficient and standard deviation of friction oscillation amplitude values. The friction coefficients increase with hard particle due to the rapid changes of the effective contact area and the abrasion mode. Some embedded particles operating in two body abrasion mode help to increase the disc surface roughness and influence the stopping time of the disc. The standard deviation values of friction oscillation amplitude however were stable due to more wear debris produced and get compacted to form friction films assisting friction and they tend to reduce at medium speeds because many contact plateaus and effective contact area started to stabilize.

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