The universal way

Materials World magazine
1 Mar 2018

This month, Dr Jennifer Unsworth, Patent Attorney at intellectual property law firm Withers and Roger, looks at an improved method for hardness testing.

Those familiar with materials testing will know that hardness is an indication of resistance to abrasion, scratching or cutting, rather than a physical property or characteristic. More specifically, it can be a measure of a material’s ability to resist plastic deformation. 

However, there is no fool-proof way to correlate hardness with other material properties, such as stiffness and strength. Furthermore, testing methods are only useful for a particular material system or hardness scale. This has led to the development of different tests, of which a popular subset are known as indentation-testing methods – the best-known of which are the Vickers, Rockwell, Brinnel and Knoop. 

Typically, a testing machine is set up to carry out one of these indentation methods and may include a range of weights and indenters in order to test a wide variety of materials. 

It is perhaps no surprise that some universal hardness-testing machines allow a variety of methods to be used. This can be difficult to achieve in a user-friendly and efficient manner however as it is necessary to vary the indenters, the applied load and the imaging apparatus. 

New and improved

However, the latest innovation in testing machines, developed by Michael Koehler of Indentec Hardness Testing Machines, seeks to address these challenges by providing a machine with bespoke capabilities. 

As described in the UK patent GB2525857, this apparatus features an indenter support (14) holding a combination of four indenters (12), coupled to a rotating optics-support turret (18), with four optical lenses. The turret rotates to select the appropriate indenter or optical lens. 

In a similar manner to many indentation-testing machines, the load applied to the sample is provided via a pivoted beam (26), which is made to rotate about a fulcrum by an applied force. However, in contrast to previous testing machines, this invention features an electric actuator, which applies a bespoke force to the sample via the beam, while the load is measured by a sensor. Therefore, not only can the load on the sample be controlled, the entire process can be tailored to a particular testing standard. As a result, the testing machine can be used with a range of methods.

Enhancing accuracy

In addition, the apparatus includes a number of features designed to improve accuracy. For example, the rotational coupling of the two supports means that when it is switched from an indenter to an optical lens, it remains in the same plane as the sample.

However, in some instances, this coupling could interfere with the test results. To solve this issue, the indenter and optics supports are coupled together by a drive pin (24), located in an elongated vertical slot and only engages with the indenter support when the turret is rotating, not when testing is taking place.

The turret also features a drive motor (22), which enables it to rotate automatically, and a location sensor to detect its angle of rotation. 

The optics and indenter supports also feature a spring-loaded locating pin (48) that slides into grooves in the supports and align with the sample when in use. However, when the turret needs to rotate, the pin is retracted.

In designing a testing machine that can be used universally, Indentec has relied on new and borrowed ideas. 

The result is a machine that is ready for the challenges posed by tomorrow’s materials. 

Read the full patent here: