The Importance of Metals Testing and Testing Standards

Interview conducted by G.P. ThomasMay 14 2013

David Fry, Metals Market Manager for Instron, talks to AZoM about the need for metals testing and the equipment required for this.

What are the main industries that require the kind of metals testing that Instron provides?

Metals testing solutions, which Instron provides, encompass a variety of industries, including nearly every aspect of tensile or fatigue testing within metal production, mainly R&D and quality control. These materials are then used by a wide range of industries such as automotive, aerospace, consumer goods, construction, power generation, and transportation.

Could you please briefly explain the principles of strain-control and how this is an important consideration in metals testing?

Strain control is a control technique where the increase of strain, measured typically by an extensometer, is maintained at a near constant rate during a tensile test. The wider introduction of strain control is intended to reduce uncertainty in strain rate sensitive results, such as offset yield, and reduce variability between testing systems.

Could you please outline the European testing standard ISO 6892-1, when it was introduced and what this replaced?

ISO 6892 had been in place for many years, EN 10002-1 had also been commonly used for ambient metals testing. ISO 6892-1 was introduced in 2009 superseding both ISO 6892:1998 and EN 10002-1:2001. ISO 6892-1:2009 specifies the method for tensile testing metallic materials and defines the mechanical properties that can be determined during a room temperature test.

What will a typical testing system include in order to comply with this standard?

The typical metals testing system for ISO 6892-1 includes a tensile testing machine coupled with grips of appropriate capacity, a high-accuracy extensometer with appropriate travel alongside a suitable controller, and a software package.

To be able to fully comply with the latest section of the standard, referred to as Method A or strain rate control, a suitable system comprising of high stiffness load frame, controller, grips, and extensometer need to be used in combination. The challenging part of this test is to maintain the set strain rate on the specimen through calculation points, such as proof stress, to a tolerance of ±20%. Utilising Instron’s Automatic Control algorithm the requirement to tune the system manually is eliminated, making this test simple to perform.

Instron has recently released the AutoX Extensometer – how does this machine meet the current needs of the metals testing sector?

The AutoX 750 is the latest product in our line of automatic extensometers. It couples an incredibly robust design with outstanding ±1µm accuracy. When used in conjunction with our controllers, the AutoX is capable of performing closed loop strain control to ISO 6892-1 Method A and is robust enough to stay attached through specimen failures.

What mechanical properties can the AutoX measure and to what accuracy?

The AutoX 750 is designed to measure material properties that require either small or large displacements with a single device, while maintaining exceptionally high accuracy. In the context of ISO 6892-1 this includes the determination of proof strength, upper/lower yield strength and a range of elongation or extension calculations at maximum force or fracture.

What further benefits does the AutoX provide that makes it unique in its field?

With the AutoX’s combination of 750 mm travel and very high accuracy of ±1µm, infinitely adjustable automatic gauge lengths, automatic opening and closing arms and robust design capable of measuring strain through fracture make this device unique in the marketplace. These not only make this device suitable for metals testing but also testing plastics, composites, elastomers, and a wide range of other materials.

Another recent release is the DuraSync grip – how has this been manufactured to benefit the individual user in terms of ease-of-use and safety?

Our DuraSync grips incorporate features that help improve efficiency, throughput, durability, and safety. The patent-pending mechanism used to synchronise the closing of the two pistons has been designed for resilience to bent or curved specimens. The hydraulic oil is intensified locally at each grip removing the need for high-pressure flexible hoses. All moving parts are enclosed to prevent the ingress of debris that is often present in metals tensile testing applications.

How does the self-centring mechanical synchronizer mark a leap forward in metals testing?

Metals tensile specimens being tested are often bent or curved due to various upstream processes. The sealed DuraSync mechanism isolates the mechanical synchronisation elements from uneven load while gripping, protecting them from damage. This removes the need to flatten specimens prior to testing while also being a more robust long lasting solution.

Looking to the future, how do you see the metals market changing over the next decade?

With an ever increasing focus on energy efficiency and improved performance the steel industry will likely evolve into a more sustainable industry. Materials being produced will also likely be of a higher quality and exhibit improved performance characteristics specifically designed for the application in which they are destined to be used.

About David Fry

David Fry is currently the Metals Market Manager for Instron, having worked with the company for eight years. He holds a degree in Mechanical Engineering from the Cardiff University.