Aerospace Tribology is the science and technology that is related to surfaces interacting in relative motion, and it includes the study of friction, lubrication and wear. Being able to evaluate surfaces that touch each other are of vital importance to a failure investigation. For example, the unwanted fretting and wear of hinges, tracks, bearings, and gearboxes in airframes and engines is a constant problem in aircraft, because it induces failures and jamming. DVI’s Aviation Tribology Experts understand how to evaluate the failures caused by the different types of wear and friction that can be imparted on an aircraft component. Some of the more common types of wear include the following:
Abrasive wear is due to hard particles or hard protuberances that are forced against and move along a solid surface. Abrasive wear is commonly classified according to the type of contact and the contact environment. The type of contact determines the mode of abrasive wear. The two modes of abrasive wear are known as two-body and three-body abrasive wear. Two-body wear occurs when the grits or hard particles remove material from the opposite surface. The common analogy is that of material being removed or displaced by a cutting or plowing operation. Three-body wear occurs when the particles are not constrained, and are free to roll and slide down a surface. The contact environment determines whether the wear is classified as open or closed. An open contact environment occurs when the surfaces are sufficiently displaced to be independent of one another.
Adhesive wear can be found between surfaces during frictional contact and generally refers to unwanted displacement and attachment of wear debris and material compounds from one surface to another. Generally, adhesive wear occurs when two bodies slide over or are pressed into each other, which promote material transfer. This can be described as plastic deformation of very small fragments within the surface layers. The asperities or microscopic high points or surface roughness found on each surface, define the severity on how fragments of oxides are pulled off and adds to the other surface, partly due to strong adhesive forces between atoms but also due to accumulation of energy in the plastic zone between the asperities during relative motion. There are several major types of adhesive wear. Sliding wear: any solid sliding on any other solid; Galling: severe form of adhesive wear; Scoring/scuffing wear: grooves and scratches in the sliding direction; Oxidative wear: mild wear in hard/hard unlubricated ferrous systems. In addition, there are four types of relative sliding motions to consider: unidirectional continuous, reciprocating, complex (slide, roll, etc.), and intermittent.
Erosive wear is caused by the impact of particles of solid or liquid against the surface of an object. The impacting particles gradually remove material from the surface through repeated deformations and cutting actions. The rate of erosive wear is dependent upon a number of factors. The material characteristics of the particles, such as their shape, hardness, impact velocity and impingement angle are primary factors along with the properties of the surface being eroded.
To assist in the evaluation of wear and friction, DVI’s Tribology Experts will often times utilize the ASTM bench scale tests listed below. Our Tribology Experts have the experience to know how to properly choose the appropriate sub-scale bench test that will correlate correctly to the real world applications. Our Tribology Experts also have access to some of the most comprehensive Tribology test labs in the country, including highly specialized government facilities.
ASTM Wear Tests:
D2266 Test Method for Wear Preventive Characteristics of Lubricating Grease (Four-Ball Method)
D2670 Test Method for Measuring Wear Properties of Fluid Lubricants (Falex Pin and Vee Block Method)
D2714 Test Method for Calibration and Operation of the Falex Block-on-Ring Friction and Wear Testing Machine
D3702 Test Method for Wear Rate and Coefficient of Friction of Materials in Self-Lubricated Rubbing Contact Using a Thrust Washer Testing Machine
D3704 Test Method for Wear Preventive Properties of Lubricating Greases Using the (Falex) Block on Ring Test Machine in Oscillating Motion
D4170 Test Method for Fretting Wear Protection by Lubricating Greases
D4172 Test Method for Wear Preventive Characteristics of Lubricating Fluid (Four-Ball Method)
G32 Test Method for Cavitation Erosion Using Vibratory Apparatus
G40 Terminology Relating to Wear and Erosion
G56 Test Method for Abrasiveness of Ink-Impregnated Fabric Printer Ribbons and Other Web Materials
G65 Test Method for Measuring Abrasion Using the Dry Sand/Rubber Wheel Apparatus
G73 Test Method for Liquid Impingement Erosion Using Rotating Apparatus
G75 Test Method for Determination of Slurry Abrasivity (Miller Number) and Slurry Abrasion Response of Materials (SAR Number)
G76 Test Method for Conducting Erosion Tests by Solid Particle Impingement Using Gas Jets
G77 Test Method for Ranking Resistance of Materials to Sliding Wear Using Block-on-Ring Wear Test
G81 Test Method for Jaw Crusher Gouging Abrasion Test
G83 Test Method for Wear Testing with a Crossed-Cylinder Apparatus
G98 Test Method for Galling Resistance of Materials
G99 Test Method for Wear Testing with a Pin-on-Disk Apparatus
G105 Test Method for Conducting Wet Sand/Rubber Wheel Abrasion Tests
G117 Guide for Calculating and Reporting Measures of Precision Using Data from Interlaboratory Wear or Erosion Tests
G118 Guide for Recommended Format of Wear Test Data Suitable for Databases
G119 Guide for Determining Synergism Between Wear and Corrosion
G132 Test Method for Pin Abrasion Testing
G133 Test Method for Linearly Reciprocating Ball-on-Flat Sliding Wear
G134 Test Method for Erosion of Solid Materials by Cavitating Liquid Jet
G137 Test Method for Ranking Resistance of Plastic Materials to Sliding Wear Using a Block-On-Ring Configuration
G163 Guide for Digital Data Acquisition in Wear and Friction Measurements
G171 Test Method for Scratch Hardness of Materials Using a Diamond Stylus
G174 Test Method for Measuring Abrasion Resistance of Materials by Abrasive Loop Contact
G176 Test Method for Ranking Resistance of Plastics to Sliding Wear Using Block-on-Ring Wear Test--Cumulative Wear Method
G181 Test Method for Conducting Friction Tests of Piston Ring and Cylinder Liner Materials Under Lubricated Conditions
