Sheet Metal Tensile Testing

Globally, there are increasing efforts to reduce the weight of automobiles, increasing fuel efficiency which aids in the reduction of emissions. Various grades of steel have been the predominant material used for manufacturing automobiles chassis' and body. A new generation of advanced high-strength steels (AHSS) are being developed and produced to maintain the automotive industry’s demand for steel. 

Despite this, automotive manufacturers are now also working with aluminum producers to increase the percentage of aluminum used in the production of automobiles. Aluminum offers low density, excellent formability, corrosion resistance, and high strength.

Determining r and n Values

tHE CHALLENGE

Sheet metal product development is currently driven by the demand for increased strength with minimal impact to formability. The automotive industry is the greatest driver for increasing strength, meaning thinner/lighter material can be used in the production of cars, reducing overall emissions. Plastic strain ratio (r-value) and the strain hardening exponent (n-value) are critical mechanical properties that define the formability of these products.

our Solution

During a tensile test, these formability properties can be determined automatically using Bluehill® Universal software. To determine n-value, axial strain needs to be measured after yield and determined at or between strain values. More traditional contacting extensometers are designed to be removed during the test and may be limited in total travel. Using the latest technology, such as the Advanced Video Extensometer (AVE 2) or the AutoXBiax, strain can be measured throughout the test while ensuring the highest accuracy of results. To determine r-value, the transverse strain must also be measured, traditionally done using an additional extensometer. With either of these devices (AVE 2 or AutoXBiax), axial and transverse strain can be measured at the same time.

Maintaining Specimen Strain Rate

tHE CHALLENGE

The mechanical properties of some metals will be affected by the speed of the test and are therefore ‘strain rate sensitive’. In more traditional stress rate control or crosshead separation rate control, the overall machine stiffness will affect the strain rate, which will cause differences in results. Strain rate control is becoming more and more common as it means results will be more comparable and tests can be faster.


our Solution

Using a 'stiff' load frame and gripping technology are vital to be able to achieve the tight tolerances of strain rate. Instron’s controller technology and Bluehill® Universal software with automatic tuning performs stable strain control and complies with ISO 6892-1, ASTM E8/E8M as well as GB/T 228.1.

Implementing Strain Control Will Mean:

  • More repeatable and comparable results - Test results reliable from machine to machine
  • Improved efficiency - Time per test minimized and setup time reduced
  • No need to tune with a specimen when using an Instron testing system
  • Future proofing your laboratory

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