Advancements in metals properties to improve performance characteristics have introduced materials to market that are stronger, tougher and many times more costly to produce. Tensile testing of these products can present a variety of gripping challenges. Use of a traditional grip arrangement consisting of a grip jaw or grip face will wear quickly and allow slippage. In addition, high production cost can mean limited material and shortened test samples. These are common challenges QC labs face and often lead to the need for machined, shoulder-end test specimens. Shoulder-end, or button-head test samples are outlined in ASTM E8, A370, A48, GOST 1497-1, as well as other general tensile test standards of metal products.

Challenge:

A high volume test lab performing tensile tests to ASTM E8/A370 using .505 inch shoulder-end specimens, is now required to also test .357, .252 and .161 inch shoulder-end specimens. Their test system configuration included the Model 300LX fitted with 300kN spherical alignment tension assembly and shoulder-end specimen holders, and a 2 inch gage length clip-on extensometer. They were experiencing difficulty with the existing holders and were concerned about the changeover time required for the holders and extensometers, as well as the expense that would be incurred to add the additional extensometers. Additionally, they were pursuing NADCAP accreditation and were concerned about the alignment of the load string.

Solution:

We recommended the newly improved Split Insert Tensile holders and (4) sets of interchangeable inserts to address the (4) separate specimen sizes. The new grips installed directly to the existing spherical tension alignment assembly, and improved per test time an average of 45 seconds due to the ease of use and interchangeability of the inserts. Instron Professional Services performed an alignment verification that was well within the specified limits as outlined in ASTM E1012 and NADCAP AC7101. The new specimen diameters and lengths also introduced the requirement for additional extensometers; Instron’s automated AutoX750 offered the ability to provide all of the gauge lengths in a single instrument.

Instron Split Insert Tensile Grips are the preferred solution for safe, high-volume production testing of shoulder-end or button-head machined specimens. Engineered with an operator focus, the split insert tensile grips are easy to install, offer quick change inserts for standard specimen sizes, and promote efficient testing of a wide range of metals and alloys.

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