Surface Roughness, Texture, and Tribology Full Course

Surface texture consists of a spectrum of spatial wavelengths (spatial frequencies, in some applications). Filtering is the process in which you select the range of spatial wavelengths to analyze. This is one of the central topics in surface texture/ surface roughness measurement. This lecture discusses the various "cutoffs" that define the wavelength range of interest. We look at their affect on surface measurement result and how they are specified.

Almost all surface texture measurement and analysis involves software to calculate parameters and display results. This example serves as an introduction to surface texture analysis software and also provides a practical example of the application of filtering.

The standards that define surface texture parameters make it clear that the cutoff wavelengths must be specified along with parameter values in order for the data to be meaningful. Yet, some drawings do not include the appropriate cutoffs. This section explains the process for determining the most appropriate cutoffs when none have been specified.

In this lecture we look at the symbology that is used to create surface finish/surface roughness specifications per the ASME 14.36-1996 standard.

In this lecture we look how surface finish/surface roughness is specified per the ISO 1302-2002 standard, and how it differs from the ASME 14.36 standard described in the previous lecture.

This lecture introduces the concepts module introduces common and advanced surface texture parameters, starting with We discuss the various international standards that define parameters. And, we reiterate the concept and importance of "filtering" data by wavelength/frequency in order t o generate meaningful parameter values.

We discuss the origins of surface texture parameters, beginning with 2-dimensional parameters that measure heights along profiles. "Amplitude parameters" include the common surface roughness parameters Average Roughness (Ra) and RMS Roughness (Rq). We also discuss the various interpretations of the Rz parameter, which can lead to confusion and errors.

Spatial surface texture parameters deal with lateral spacings in a profile rather than heights. These parameters are important in such functions as sealing, appearance and adhesion.

The "Hybrid" group of surface texture parameters combine, and are affected by, both amplitude and spacing.

Functional parameters try to predict how well a surface will perform a particular function, rather than just describing its mathematical shapes. We introduce a range of parameters based on the bearing ratio (material ratio) curve among others.

So far in this course we described 2-dimensional parameters. We now introduce parameters that were designed specifically to support 3D surface texture datasets. Many of the 2D parameters have counterparts in 3D, but there are also a variety of parameters that can only be calculated in 3D.

The basics of how to interpret and write surface texture / surface roughness specifications

In this section we cover Power Spectral Density, BRDF, surface area calculation, volume analysis, and fractal/multi-scale analysis.

In this module you will learn about the mechanisms of wear, methods for wear measurement, surface texture parameters that relate to wear, and applications of wear analysis for improving component performance.

Wear is not just a single mechanism—in fact, it's not always a removal of material. We discuss a range of wear mechanisms that gradually alter a surface, including abrasive wear, corrosive wear, adhesive wear, fatigue and many others.

We talk about the range of techniques that are used to measure wear, focusing on 2D and 3D surface profilometry. We also discuss methods for accelerating wear in order to quantify processes that often take months or years to significantly alter a surface.

Building on the previous modules in this course we look at the many different surface texture parameters that can be used to measure wear and track it over time.

Wear is closely related to the properties of the materials themselves. We discuss elastic and plastic deformation, stress and strain, surface energy, and other physical properties as they relate to wear.

In this module we discuss the basic mechanisms and physics of dry friction, the methods we use to measure it, and the relationships between surface texture (surface roughness) and dry friction.

Friction has been studied from antiquity. We look at how our understanding of friction has changed and grown from ancient Egypt through Leonardo Da Vinci and on to modern day.

This lecture reviews strength of materials concepts including, stress, strain, spring constant, Modulus of Elasticity, etc.

The real area of contact is the actual amount of material tat is in contact between to adjacent surfaces. We look at various approaches to estimate this value, which is central to the study of friction.

In this lecture we show how the degree of friction depends upon whether deformation at the surface texture level is plastic or elastic. We also tie these concepts in with the concepts of strength of materials and real area of contact, from earlier lectures.

This lecture begins to look at the complex relationship between surface texture and friction.

The plowing mechanism requires its own calculations to determine the amount of friction caused during the operation.

We now go into great depth about the relationships between surface texture affects dry, sliding friction, how spatial wavelengths affect the real area of contact, and the surface texture parameters that come into play when we are examining sliding friction.

This module covers the mechanics of lubricated systems. The first lecture explains the nature of lubricated systems, and the important distinction between "friction force" and "friction coefficient."

The understanding of lubricants and lubricated systems has changed and grown for centuries. This lecture traces developments in lubrication from antiquity through recent years.

How does surface texture affect friction in a lubricated system? It's a complex question, and the answer depends on film thickness, load, temperature, and many other factors which we discuss here.

In the Elastohydrodynamic (EHD) regime two surfaces come together under high contact stresses, and the viscosity increases dramatically. We look at the dynamics of lubricated systems operating in the EHD regime.

This lecture includes a video from Vern Wedeven (used with permission) that does a great job of illustrating the mechanics of lubrication in action.

In this module we discuss the basic mechanisms and physics of rolling friction, the methods we use to measure it, and the relationships between surface texture (surface roughness) and rolling friction. We show why rolling friction is so much higher than sliding friction, and we discuss how lubrication reduces rolling friction.

Following this module we encourage you to watch the modules on Lubricated Friction and Rolling Friction for a more complete view.

We start with the basic case of frictionless rolling to understand the mechanics at play.

How do we get an object to roll? This lecture describes the important difference between rolling friction and tractive rolling.

How do we stop a car? Does that have something to do with rolling friction? Again, not quite. We look at the dynamics of the tractive force, which is distinct and different from the rolling frictional force.

Now we get to the dynamics of the friction that develops once a surface is already rolling. A better name may be "rolling resistance," and we talk about why.

Why is rolling friction so much lower than sliding friction? We look at the difference between the force that it takes to peel two surfaces versus the force required to shear them.

Surface texture and lubricants play a role in reducing rolling friction. This lecture covers how and why texture makes a difference, both in dry rolling (where, generally, smoother is better) and lubricated rolling (where they answers are more complex).

What causes a fluid to wet a surface or to bead into a drop that rolls off? In this first lecture we introduce and define the  terms "surface energy," "surface wetting," and "surface tension," and we begin to look at the role that surface texture plays in the process.

As a drop grows or deflates its angle of contact changes with local surface roughness. This lecture introduces hysteresis and the hysteresis angle and what it means for surface wetting.

This lecture looks at why a surface may be hydrophilic (interacts with water) vs hydrophobic (repels water). Much of it depends on surface texture. We discuss why this is and why it matters for applications such as cell phone screens and semiconductors.

This lecture discusses the surface texture parameters that help quantify surface wettability.

In this section we show how surface energy and wetting affect applications such as industrial lubrication, painting, biomedical devices and printing.

This lecture introduces several types of seals and how we quantify sealing in static applications.

Waviness can often have a greater impact on seal performance than roughness. We look at why this is the case and how waviness can be controlled.

We show how a morphological filter in software can act as a "virtual gasket" to predict how well a material will conform to, and seal with, a mating surface.

This lecture covers various types of static seals, showing how surface texture affects their performance.

We begin looking at "dynamic" seals, starting with O-rings, which perform a number of functions, particularly in rotary machinery.

In this lecture we cover rotary lip seals and how macro-and micro- "lead" in the surface texture impacts their ability to seal. A time lapse video from Matthias Baumann provides insight into the dynamics of these interfaces.

We look at the complex sealing system that enables pistons in an engine to retain compression and lubrication for hundreds of thousands of miles. We re-visit the Bearing Ratio (Material Ratio) curve and show how it is used in this application.

This lecture surveys a variety of dealing materials and discusses the common applications for each.

This lecture began with a challenging problem: why would the front doors of a car being painted appear differently from the rear doors being painted at the same time?  The answer is in the surface texture...but there's even more to it than that.

In this lecture we look at how the various spatial wavelengths of a paint surface texture scatter light differently and affect the appearance.

This lecture discusses how surface texture parameters, applied to particular spatial wavelength bands, can differentiate "good" from "bad" paint appearance. We look at how the texture of both the substrate and paint film surfaces impact the final finish quality.

Several different technologies have been developed now to measure the critical spatial wavelength bands in order to quantify paint appearance quality.

We look at an example of software that has been developed for measuring the critical spatial wavelengths of painted surfaces and substrates.