Wear & Friction Resources

WHAT IS WEAR

Introduction

Wear is the gradual removal or damage of the surface of an object. It is distinguished from other modes of failure (fracture, fatigue and corrosion) by the relatively slow failure rate that occurs on surfaces due to mechanical contact.

Tribology is the science and art of wear. The root word “Tribos” is Greek and refers to rubbing surfaces and friction. The word “Tribology" was first used by the Jost Commission in England in the 1960s. This commission and several studies since have estimated the cost of wear to be between 5% and 10% of a country’s GDP. In the U.S. this conservatively estimates the cost of wear to be approximately $9,900,000 per year.


Wear Mechanisms

There are still differences of opinion on how to describe particular wear mechanisms, however most discussions include abrasion, adhesion (galling) and erosion.

Abrasion

Silica sand abrasion after a G-65 Dry Sand Rubber Wheel test

Silica sand abrasion after a G-65 Dry Rubber Wheel test

Abrasive Sear on a material with hard includsions - this is an example of "pedastalling", where base material is removed around harder inclusions.

Abrasion consists of some type of particle or abrasive being pressed into a surface and then moved along the surface. The abrasive removes (or damages without removing) material from the part of interest (Figures 1-3).

Two-body abrasion refers to situations where two materials (the component of interest and an abrasive) interact. An example would be aggregate sliding in a chute or trough.

Three-body abrasion adds a third component that captures the abrasive between itself and the other surface. The loads that force the abrasive into the surfaces are applied by the two components.

Adhesion

One pair of metallic surfaces (a and b) after undgoing a galling test (ASTM 98 - Standard Test for Galling Resistance of Materials)Adhesion, also referred to as galling, is the joining of two high spots or asperities on the surfaces of two surfaces in contact. When relative motion occurs, the joint (sometimes described as a cold weld) breaks and causes damage on one or both components (Figure 4). Often in this type of situation, a particle breaks free and forms an independent abrasive particle.

Watch this page for more detailed discussions of specific wear mechanisms, case studies and details on other tribological topics.