A thermal creep model for nominally flat surface contact: Jeffrey's linear viscoelastic model
2011, International Journal of Mechanical Sciences
A slightly improved version of the GW model presented in  still treats the rough surface asperities as spherical shells, but there the curvature of the spheres is not constant and instead depends on the height of the asperity . Other studies [7,8] have shown that the statistical parameters are ambiguous and depend on the length of the sample examined and the resolution of the measuring device. Due to this fact, using these parameters represents an oversimplification of real surfaces containing different roughness scales.
This thesis deals with the contact mechanics of thermoviscoelastic materials. In particular, the creep behavior of a nominally flat rough surface in contact with a rigid half-space is studied. The rough surface is modeled using fractal geometry. A synthesized profile, a Cantor structure, is used to model the surface. Such a profile has two scale parameters and different heights for each generation of bumps. The influence of temperature is accounted for by the concept of activation energy using the Arrhenius equation.
The aim of this model is to study the normal onset of creep of the surface (stamp) as a function of the applied creep load, time and temperature. The stamp material is assumed to behave according to the Jeffreys model. Such a model is an arrangement of springs and dampers in parallel and/or in series.
The creep approach of linear viscoelastic materials is investigated using an elastic-viscoelastic correspondence analysis. An asymptotic power law is obtained relating the global force and temperature acting on the stamp to its approximation. This model is only valid if the approach between the punch and the half-gap is in the range of the roughness size. The proposed model allows an analytical solution in case the deformation is linear thermoviscoelastic. The obtained model shows a good agreement in comparison with the experimental results from the literature.
Evaluation of technical surfaces using a combined method of fractal modeling and wavelet analysis
2001, International Journal of Machine Tools and Manufacturing.
A new approach based on the combination of wavelet and fractal theories is proposed. The purpose is to provide a mechanism to more accurately and completely evaluate the properties of engineered surfaces. Wavelet transformation models and fractal representations of technical surfaces are presented and the combination of wavelet models and fractal representations is examined. With the proposed approach, experimental samples of the workpiece surface obtained by grinding are examined. The results show that the proposed approach is correct and complete.(Video) GTC2018_Session2-Anderson
Surface Roughness Modeling for Piston Ring Lubrication: Solving the Problems
1996, Tribology Series
Friction models for piston rings and other machine elements often include the Greenwood and Tripp contact model and the Patir and Cheng average flow model for the mixed lubrication mode. However, problems arise from the non-Gaussian roughness height distributions of cylinder liners and from the unsteadiness of the surface roughness parameters used in these models. This article shows how to solve these problems. From this it is concluded that the upper part of the coating roughness height profile has a Gaussian distribution and this is used to determine the appropriate roughness height for use in the friction model. The non-stationarity is solved using the plasticity criterion proposed by T R Thomas. This idea has not received much attention in the literature and experimental support is still lacking. In this work, an experimental validation is provided and it is concluded that both the use of the proposed solution for the non-Gaussian liner roughness and the application of the Thomas plasticity criterion allow an accurate prediction of the piston ring friction.
Fractal characterization and simulation of rough surfaces
1990, wear and tear
Roughness measurements on various machined steel surfaces and a structured thin-film magnetic disk have shown that their topographies are multiscale and random. The power spectrum of each of these surfaces follows a power law within the considered length scales. This spectral behavior implies that as the surface is repeatedly magnified, statistically similar images of the surface continue to appear. In this paper, the fractal dimension is identified as an intrinsic property of such a multiscale structure and the Weierstrass-Mandelbrot (W-M) fractal function is used to introduce a new and simple method for roughness characterization.
The power spectra of the stainless steel surface profiles coincide at high frequencies and correspond to a fractal dimension of 1.5. It is hypothesized that this coincidence occurs on small length scales, since the surface remains rough on such scales. Surface processing such as grinding or lapping reduces power at lower frequencies up to a certain corner frequency, above which all surfaces behave like raw surfaces.
The W-M function is also used for deterministic simulation of rough Brownian and non-Brownian surfaces that show statistical similarity to real surfaces.
1990, Tribology series(Video) Straumann SLActive®
2017, Electrical Contacts: Fundamentals, Applications and Technology
A mathematical model for simulating and manufacturing ball end mills
Computer Aided Design, Band 50, 2014, S. 16-26
The performance of ball end mills in cutting operations is affected by the configuration of the rake and flank faces on the spherical component. From the mathematical design of a cutting edge curve, the rake face can be defined by the rake angle and rake width at each cross-section along the cutting edge. We propose the basic conditions that should govern the coupling between the grinding wheel and the release surface in order to avoid interference during the processing of a ball mill. As a result, a new mathematical model for determining the position of the wheel and a software program for simulating the generation of the contact surface of a ball mill are proposed. In addition, methods for grinding the flank in both concave and planar forms are presented. The groove area created by a disc during the grinding process is determined using a tangent condition. The results of the experiment and the simulation are compared to validate the proposed model.
Determination of friction in metal cutting with tool wear and flank effects
Wear, Vol. 317, Numbers 1–2, 2014, pp. 8-16(Video) Straumann SLActive Surface
This article examines the friction of bevel cutting in bevel Si turning.3norte4Ceramic tools with a large negative rake angle. The flank friction in particular is included in the tribological equilibrium. The values of the force components recorded during the tool wear tests at different cutting speeds served as input data. The usual force components were transformed into the coordinate system of the tool used in order to be able to calculate the normal and frictional forces acting on the rake and flank surfaces and finally the corresponding friction coefficients. It was found that both friction coefficients change significantly with progressive tool wear and deviate from those determined for the orthogonal friction model. The new friction pattern was tested for machining ductile iron (SCI) with coated nitride ceramic inserts and further validated by tribo testing using cylinder-on-disk methods.
Modeling and analysis of a novel approach to machining and structuring flat surfaces through the milling process
International Magazine of Machine Tools and Manufacturing, Band 105, 2016, S. 32-44
In this article, a new and innovative method for regular structuring and special modeling of the workpiece surface using face milling is presented. The patterns were created on the surface by specific positioning of the workpiece and tool, milling passes in different directions, and the specific angular position of the spindle on a typical vertical milling machine. First, the model for the geometry of the cutting tool was developed and then a new simulation model for the surface pattern was created through the face milling process. Mathematical models are presented to describe the geometry and position of the cutting tool (including orientation and position) in space. Calculation and simulation programs (MATLAB and CAD programming software) are developed to verify this method. This study provides a basic understanding of the pattern milling process. Based on this, the influence of various milling process parameters on the pattern geometry (including the lead-in angle and radius) is analyzed. The simulation results could be used to optimize the traditional milling and pattern milling processes, as well as to improve the surface quality of the workpiece or to predict the surface pattern based on given face milling parameters.
Optimization of process parameters during temperature rise during CNC milling of Al 7068 using hybrid techniques
Materials Today: Proceedings, Band 5, Nummer 2, Teil 2, 2018, S. 7037-7046
Temperature measurement and estimation of heat distribution in metal cutting is important as it controls the contribution to tool deflection, tool life, cutting force and vibration, and the quality of the machined part. In this paper, a statistical model was developed to estimate the temperature rise using design parameters such as helix angle, radial inclination angle of the cutting tool, and machining parameters such as cutting speed, cutting speed, etc., feed and axial depth of cut in dry conditions. Reaction surface methodology and experimental design were used to conduct the experiments. The workpiece material was 7068 Al aluminum and the tool was a high speed steel end mill with a different tool geometry. The temperature rise was evaluated with a pyrometer. The second-order mathematical model related to machining parameters was developed to estimate temperature rise. The competence of the model was calculated using ANOVA. The direct and interacting effect of the process parameter on the temperature rise was analysed, which helped to select the process parameter to keep the temperature rise to a minimum, indicating the immobility of the final milling process. The prediction models in this study are believed to produce temperature rise values that are close to the experimentally recorded readings with a 95% confidence interval. A Matlab genetic algorithm solver was used to perform the optimization.(Video) LiDAR Surface Models in ArcGIS Pro
Strategy to optimize energy consumption in D2 steel ball micro milling by TLBO together with 3D FEM simulation
Measure, Band 132, 2019, S. 68-78
The current challenge in the manufacturing industry is to improve the efficiency of production activities while reducing wasteful energy consumption. Previous research has focused on optimizing multiple responses of process parameters to improve process performance. The present study proposed an optimization-based strategy to reduce energy consumption in end milling with D2 steel microspheres. Since power consumption is directly proportional to cutting forces, process parameters such as cutting speed, feed rate and depth of cut were optimized to reduce cutting forces using the Gauge-Based Optimization Technique (TLBO) along with 3D Finite Element Method (FEM) simulation. During the optimization, limit values of 60 µm (ISO 10816) and 2 µm (ISO 1302) were assumed for the vibration amplitude of the milling cutter and the surface roughness. The three best combinations of cutting speed, feed and depth of cut for minimum cutting force were determined. Among other things, the combination of a cutting speed of 15 m/min, a feed of 112.5 µm/tooth and a cutting depth of 85.25 µm has a low power consumption of 67 W with a tool vibration of 36.5 µm. However, the remaining two combinations were also considered to be the next best optimal cutting conditions. For the three best solutions, a numerical simulation was carried out and the cutting forces and the amplitude of the vibration of the milling cutter were predicted. There was good agreement between the simulation results and the experimental results, confirming the acceptability of the simulation. It was also found that the three best candidate solutions had the same cutting speed of 15 m/min (minimum cutting speed). Therefore, it was found that the induced stresses in the workpiece have low values around 350 MPa.
Modeling of chip geometry in spherical milling of superalloys using the Deformed Chip Deformation (SDC) approach
International Magazine of Machine Tools and Manufacturing, Bände 130–131, 2018, S. 49-64
Since it is known that chip geometry helps to predict machining forces, energy and thus the quality of the machined surface, several models have been developed in the past to predict deformed and undeformed chip geometries in spherical milling. It can be observed that most models use the volume constancy (VC) between the undeformed and deformed chip geometry to evaluate the deformed chip thickness. This work presents a new approach to assess deformed chip geometry, which includes considering deformations in deformed chips (SDC). In the strains developed using the deformed chip (SDC) approach, bending, compression/shear, and thermal strains were modeled using a simplified shape of a conical overhang of the undeformed chip. When developing the model, the interactions between the cutting edge and machining on horizontal work surfaces and those inclined at different angles were taken into account. As the slope of the workpiece increases from 0° (horizontal) to 60°°, deformed chip thickness increases by 63% due to greater effective feed per tooth. However, it was found that the instantaneous shear angle is constant at 50°°along the cut for a typical parametric machining combination. A comparison of the SDC and VC approaches shows that the magnitudes of deformed chip thickness, rake angle and resulting cutting forces obtained from SDC models are the closest (within 90%) in agreement with experimental data. It is expected that such models, when integrated with shear force models, would help predict shear forces more accurately.
Copyright © 1982 Published by Elsevier B.V.
In heat transfer and thermodynamics, a thermodynamic system is said to be in thermal contact with another system if it can exchange energy through the process of heat. Perfect thermal isolation is an idealization as real systems are always in thermal contact with their environment to some extent.What is the definition of the following terms thermal conductivity? ›
Thermal conductivity can be defined as the rate at which heat is transferred by conduction through a unit cross-section area of a material, when a temperature gradient exits perpendicular to the area.What is the thermal contact resistance between surfaces? ›
Thermal Resistance (R-Value)
Thermal resistance is the temperature difference, at steady state, between two defined surfaces of a material or construction that induces a unit heat flow rate through a unit area, K⋅m2/W.
A heating plate is heated up through a heat flux. Parts on top of this plate can exchange heat via contacts. This is shown in this example.What does it mean for two objects to be in thermal contact? ›
Thermal Contact. Two objects are in thermal contact if energy can be exchanged between them. Thermal Equilibrium. Two objects are in thermal equilibrium if they are in thermal contact and there is no net exchange of energy.When two objects are in thermal contact and are at different temperatures? ›
If two objects at different temperatures are brought in contact with each other, energy is transferred from the hotter object (that is, the object with the greater temperature) to the colder (lower temperature) object, until both objects are at the same temperature.What is thermal conductivity through a material? ›
Thermal conductivity is the property of a material to conduct heat. Heat transfer occurs at a lower rate across materials of low thermal conductivity than across materials of high thermal conductivity. This property is temperature dependent and its reciprocal is thermal resistivity.What is the simple definition of thermal conductivity in physics? ›
Thermal conductivity refers to the ability of a given material to conduct/transfer heat. It is generally denoted by the symbol 'k' but can also be denoted by 'λ' and 'κ'.What is thermal conductivity for dummies? ›
Thermal Conductivity: A measure of the ability of a material to transfer heat. Given two surfaces on either side of a material with a temperature difference between them, the thermal conductivity is the heat energy transferred per unit time and per unit surface area, divided by the temperature difference .What are thermal properties of surfaces? ›
Thermal surface properties can be assigned to surfaces of thermal conductive materials. A thermal surface property definition describes the radiation and convection losses from a surface. Declare the name for the thermal surface. Each surface must have a unique name.
Imperfect contact of solid surfaces due to roughness and presence of surface layers, having properties different from the bulk materials, is the main reason for thermal contact resistance that appears between solids transferring heat across the junction.What affects thermal contact resistance? ›
Some additional factors which may affect the contact resistance are the direction of the heat flux, surface scratches or cracks, nonuniform loading which causes uneven contact pressure, relative motion or slipping between the surfaces, and the presence of oxides or contaminants on the contacting surfaces.What are three examples of thermal conduction? ›
Three examples of heat conduction would be the following: (1) burning your feet on hot sand; (2) the heat from a stovetop transferring to a pot filled with water; and (3) burning a marshmallow in a campfire by accidentally touching the marshmallow to the flame.What are three common examples of a thermal conductor? ›
Metals like copper and aluminium have the highest thermal conductivity while steel and bronze have the lowest. As copper is an excellent conductor of heat, it is good for heat exchangers also. Example: Gold, Silver, Iron, etc are some examples of good heat conductors and electrical conductors.How is thermal contact resistance measured? ›
The measurement of thermal contact resistance can be realised by two different methods. The direct and steady-state method as depicted in Fig. 1 measures the linear temperature profile in two bodies and gains the gradients and thus the heat flux following Fourier's law.How does thermal energy move between objects that are in contact? ›
Conduction happens when materials or objects are in direct contact with each other. The molecules in the warmer object vibrate faster than the ones in the cooler object. The faster vibrating molecules collide with the slower molecules. This makes the cooler molecules vibrate more quickly, and the object gets warmer.How does thermal energy move between objects? ›
Thermal energy transfers occur in three ways: through conduction, convection, and radiation. When thermal energy is transferred between neighboring molecules that are in contact with one another, this is called conduction.What is the transfer of thermal energy from objects in contact? ›
Conduction is the transfer of heat energy from one substance to another or within a substance.What happens when thermal energy is removed from a substance? ›
Substances can change between the states of matter by adding or removing heat, also known as the transfer of thermal energy. Adding thermal energy causes a substance's particles to move faster and farther apart; removing thermal energy causes a substance's particles to move slower and closer together.What happens to the transfer of thermal energy when two objects reach the same temperature? ›
The heat transfer continues until the two objects have reached thermal equilibrium and are at the same temperature. Heat can move from one point to another in three basic ways: by conduction, by radiation, or by convection.
Radiation is the transfer of heat energy through space by electromagnetic radiation.Is a high or low thermal conductivity better? ›
In SI units, thermal conductivity is expressed in watts per meter kelvin whereas in imperial units it can be expressed in BTU per hour per foot Fahrenheit . Materials with a higher thermal conductivity are good conductors of thermal energy.Which material has highest thermal conductivity? ›
Diamond (2000 – 2200 W/m•K) is the most thermally conductive substance, with conductivity levels 5 times those of copper, the most commonly produced metal in the US. Diamond atoms have a simple carbon backbone, which makes them an optimal molecular structure for heat transmission.Is a higher or lower thermal conductivity better? ›
As a rule of thumb, the lower the thermal conductivity the better, because the material conducts less heat energy. Thermal conductivity is a property of the material and does not take into account thickness.What are the different types of thermal conductivity? ›
When discussing thermal conductivity trends, materials can be divided into three categories; gases, non metallic solids, and metallic solids. The differing abilities of these three categories in terms of heat transfer can be attributed to the differences in their structures and molecular movements.What are the factors that affect thermal conductivity? ›
Temperature, moisture content, and density are the most important factors. Other factors include thickness, air velocity, pressing, and aging time. The relationship between main factors with thermal conductivity is presented. Uncertainty about thermal conductivity of insulation materials commonly used.How do you determine thermal conductivity? ›
It is most often used in physics and is useful in determining how a material conducts electricity. To measure thermal conductivity, use the equation Q / t = kAT / d, plug in your area, time, and thermal constant, and complete your equation using the order of operations.What is a real life example of thermal conductivity? ›
Thermal conductivity is actually about the conduction of heat or transfer of heat. 2) Pouring of hot tea in a cup will make the cup of the also warm because of the heat transfer from tea to the cup. 3)Transfer of heat from iron to shirt while pressing is also a good example.What is the difference between thermal and heat conductivity? ›
By definition, electrical conductivity is a measure of how well electrical current (charge in motion) can pass through a material under the influence of an applied voltage/electric field. Thermal conductivity measures how well heat (thermal energy in motion) can pass through a material under a temperature differential.What instrument is used to measure thermal conductivity? ›
The heat flow meter (HFM) is a special instrument for quality control in factories. It needs bigger sample sizes but can measure the thermal conductivity with highest accuracy, using an exact controlled temperature gradient.
The major components of thermal properties are: Heat capacity. Thermal Expansion. Thermal conductivity.What are the 3 thermal properties of materials? ›
- Heat capacity. Heat capacity is a property that indicates the ability of a material to absorb heat and change its temperature, thus measuring the external energy required to increase a unit of temperature (typically 1°C or 1°C). ...
- Thermal conductivity. ...
- Thermal expansion. ...
- Fusibility. ...
Diamond is the leading thermally conductive material and has conductivity values measured 5x's higher than copper, the most manufactured metal in the United States.How do you reduce thermal contact resistance? ›
Introducing a thin layer of oil or grease between the surfaces [2,16-19] is the most popular to reduce the thermal contact resistance. The optimum thickness of the interstitial material depends on the thermal conductivity of the grease, which can be further improved by adding metallic particles to the silicone greases.What is good thermal contact? ›
Perfect thermal contact of the surface of a solid with the environment (convective heat transfer) or another solid occurs when the temperatures of the mating surfaces are equal.What is the formula for thermal contact? ›
Using the electrical-thermal analogy, you can write Q = DT/Rt, where Rt is the thermal contact resistance and is given by Rt = 1/(A hc). The interfacial conductance, hc, depends on the following factors: The surface finish of the contacting faces.What are three factors affect thermal conductivity? ›
- Material. The kind of material being used in thermal conductivity can affect the rate of energy flowing between the two regions. ...
- Length. The length of the material the energy must flow through can affect the rate at which it flows. ...
- Termperature Difference. ...
- Cross-Section Types.
Electrons flowing through a conductor are impeded by atoms and molecules. The more these atoms and molecules bounce around, the harder it is for the electrons to get by. Thus, resistance generally increases with temperature.What decreases thermal shock resistance? ›
Thermal shock can be prevented by reducing the thermal gradient through changing the temperature more slowly, or by improving the robustness of a material against thermal shock through increasing a 'thermal shock parameter'.What is thermal in simple words? ›
Thermal means caused by or related to heat or temperature. The word thermal is used in science to describe a specific kind of energy: thermal energy. Thermal energy is produced by heating up molecules and atoms until they move fast enough to collide into each other.
Boiling water on a stove is an example of thermal energy. Thermal energy is produced when the atoms and molecules in a substance vibrate faster due to a rise in temperature.Does thermal mean hot or cold? ›
The Greek word therme, meaning “heat,” is the origin of the adjective thermal. Something that is thermal is hot, retains heat, or has a warming effect. If your sweatshirt has a thermal lining, its texture might remind you of a waffle-that's what traps your body heat.What are the factors that affect thermal contact resistance? ›
Some additional factors which may affect the contact resistance are the direction of the heat flux, surface scratches or cracks, nonuniform loading which causes uneven contact pressure, relative motion or slipping between the surfaces, and the presence of oxides or contaminants on the contacting surfaces.What causes thermal contact resistance? ›
Imperfect contact of solid surfaces due to roughness and presence of surface layers, having properties different from the bulk materials, is the main reason for thermal contact resistance that appears between solids transferring heat across the junction.What does thermal contact resistance depend on? ›
The contact resistance depends on the surface roughness greatly, and the pressure holding the two surfaces together also influences the contact resistance. Thermal contact resistance decreases with decreasing surface roughness and increasing interface pressure.What is the difference between thermal and temperature? ›
Temperature measures the average kinetic energy of the particles in a substance. Thermal energy measures the total kinetic energy of the particles in a substance. The greater the motion of particles, the higher a substance's temperature and thermal energy.What is the difference between thermal and heat? ›
Heat Energy is the flow of thermal energy between two objects of different temperature whereas the thermal energy tells about how much is the transfer of energy due to temperature difference between two bodies.Is thermal and heat the same thing? ›
Thermal energy refers to the energy contained within a system that is responsible for its temperature. Heat is the flow of thermal energy. A whole branch of physics, thermodynamics, deals with how heat is transferred between different systems and how work is done in the process (see the 1ˢᵗ law of thermodynamics).What are the 3 types of thermal energy? ›
There are three types of thermal energy transfer: conduction, radiation, and convection. Convection is a cyclical process that only occurs in fluids.What are the different types of thermal? ›
- Convection and.
Types of Thermal Energy
The thermal energy of the matter is increased by three methods, namely, conduction, convection and radiation.
Thermals form when warm air is beside cooler air. Warm air rises (red) above cool air (blue). Where air at two different temperatures meets, the faster-jumping warm air, being less dense than the slower-jumping cool air, floats above.How do you know if something is thermal? ›
Scratching with your fingernail is the easiest way to determine whether a paper is thermal paper. Since the thermal paper has a chemical coating on the surface, it generates heat when you scratch the paper. As a result of the heat, the paper will produce black marks.What is another name for thermal energy? ›
Thus, heat energy is also called as thermal energy.