Tribometer
Encyclopedia
A tribometer is an instrument that measures tribological quantities, such as coefficient of friction, friction force, and wear volume, between two surfaces in contact. It was invented by the 18th century Dutch
scientist Musschenbroek
A tribotester is the general name given to a machine or device used to perform tests and simulation
s of wear
, friction and lubrication
which are the subject of the study of tribology
. Often tribotesters are extremely specific in their function and are fabricated by manufacturers who desire to test and analyze the long-term performance of their products. An example is that of orthopedic implant
manufactures who have spent considerable sums of money to develop tribotesters that accurately reproduce the motions and forces that occur in human hip joints so that they can perform accelerated wear tests of their products.
A simple tribometer is described by a hanging mass and a mass resting on a horizontal surface, connected to each other via a string and pulley. The coefficient of friction, µ, when the system is stationary, is determined by increasing the hanging mass until the moment that the resting mass begins to slide. Then using the general equation for friction force:
Where N, the normal force, is equal to the weight (mass x gravity) of the sitting mass (mT) and F, the loading force, is equal to the weight (mass x gravity) of the hanging mass (mH).
To determine the kinetic coefficient of friction the hanging mass is increased or decreased until the mass system moves at a constant speed.
In both cases, the coefficient of friction is simplified to the ratio of the two masses:
In most test applications using tribometers, wear is measured by comparing the mass or surfaces of test specimens before and after testing. Equipment and methods used to examine the worn surfaces include optical microscope
s, scanning electron microscope
s, optical interferometry
and mechanical roughness testers.
Bouncing ball tribometers have been used to determine the shear characteristics of lubricants under high pressures such as is found in ball bearings or gears.
The pin on disc test has proved useful in providing a simple wear and friction test for low friction coatings such as diamond-like carbon
coatings on valve train components in internal combustion engine
s.
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
scientist Musschenbroek
Pieter van Musschenbroek
Pieter van Musschenbroek was a Dutch scientist. He was a professor in Duisburg, Utrecht, and Leiden, where he held positions in mathematics, philosophy, medicine, and astrology. He is credited with the invention of the first capacitor in 1746: the Leyden jar. He performed pioneering work on the...
A tribotester is the general name given to a machine or device used to perform tests and simulation
Simulation
Simulation is the imitation of some real thing available, state of affairs, or process. The act of simulating something generally entails representing certain key characteristics or behaviours of a selected physical or abstract system....
s of wear
Wear
In materials science, wear is erosion or sideways displacement of material from its "derivative" and original position on a solid surface performed by the action of another surface....
, friction and lubrication
Lubrication
Lubrication is the process, or technique employed to reduce wear of one or both surfaces in close proximity, and moving relative to each another, by interposing a substance called lubricant between the surfaces to carry or to help carry the load between the opposing surfaces. The interposed...
which are the subject of the study of tribology
Tribology
Tribology is the science and engineering of interacting surfaces in relative motion. It includes the study and application of the principles of friction, lubrication and wear...
. Often tribotesters are extremely specific in their function and are fabricated by manufacturers who desire to test and analyze the long-term performance of their products. An example is that of orthopedic implant
Implant (medicine)
An implant is a medical device manufactured to replace a missing biological structure, support a damaged biological structure, or enhance an existing biological structure. Medical implants are man-made devices, in contrast to a transplant, which is a transplanted biomedical tissue...
manufactures who have spent considerable sums of money to develop tribotesters that accurately reproduce the motions and forces that occur in human hip joints so that they can perform accelerated wear tests of their products.
Theory
A simple tribometer is described by a hanging mass and a mass resting on a horizontal surface, connected to each other via a string and pulley. The coefficient of friction, µ, when the system is stationary, is determined by increasing the hanging mass until the moment that the resting mass begins to slide. Then using the general equation for friction force:
Where N, the normal force, is equal to the weight (mass x gravity) of the sitting mass (mT) and F, the loading force, is equal to the weight (mass x gravity) of the hanging mass (mH).
To determine the kinetic coefficient of friction the hanging mass is increased or decreased until the mass system moves at a constant speed.
In both cases, the coefficient of friction is simplified to the ratio of the two masses:
In most test applications using tribometers, wear is measured by comparing the mass or surfaces of test specimens before and after testing. Equipment and methods used to examine the worn surfaces include optical microscope
Optical microscope
The optical microscope, often referred to as the "light microscope", is a type of microscope which uses visible light and a system of lenses to magnify images of small samples. Optical microscopes are the oldest design of microscope and were possibly designed in their present compound form in the...
s, scanning electron microscope
Scanning electron microscope
A scanning electron microscope is a type of electron microscope that images a sample by scanning it with a high-energy beam of electrons in a raster scan pattern...
s, optical interferometry
Optical interferometry
Optical interferometry combines two or more light waves in an opticalinstrument in such a way that interference occurs between them.Early interferometers used white light sources and also monochromatic light from atomic sources...
and mechanical roughness testers.
Types
Tribometers are often referred to by the specific contact arrangement they simulate or by the original equipment developer. Several arrangements are:- Four ball
- Pin on disc
- Block on ring
- Bouncing ball
- Schwingungs-, Reibungs- und Verschleisstest (SRV) test machine
- Twin disc
Bouncing ball
A bouncing ball tribometer consists of a ball which is impacted at an angle against a surface. During a typical test, a ball is slid on an angle along a track until it impacts a surface and then bounces off of the surface. The friction produced in the contact between the ball and the surface results in a horizontal force on the surface and a rotational force on the ball. Frictional force is determined by finding the rotational speed of the ball using high speed photography or by measuring the force on the horizontal surface. Pressure in the contact is very high due to the large instantaneous force caused by the impact with the ball.Bouncing ball tribometers have been used to determine the shear characteristics of lubricants under high pressures such as is found in ball bearings or gears.
Pin on disc
A pin on disc tribometer consists of a stationary "pin" under an applied load in contact with a rotating disc. The pin can have any shape to simulate a specific contact, but spherical tips are often used to simplify the contact geometry. Coefficient of friction is determined by the ratio of the frictional force to the loading force on the pin.The pin on disc test has proved useful in providing a simple wear and friction test for low friction coatings such as diamond-like carbon
Diamond-like carbon
Diamond-like carbon exists in seven different forms of amorphous carbon materials that display some of the typical properties of diamond. They are usually applied as coatings to other materials that could benefit from some of those properties. All seven contain significant amounts of sp3...
coatings on valve train components in internal combustion engine
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
s.