In order to test 7-wire strand according to ASTM A370, A416, or ISO 156303, we decided to use an Industrial Series Model 600KPX. Since most wire strand applications require specimen lengths of 500 mm and greater, this frame was chosen primarily because of its convenient, large test space and long stroke actuator. This made it easy for the operator to install and remove specimens without a need for a ladder or pit mounting the machine.
We used a set of side-acting, hydraulic grips with wire strand inserts. The side-acting design helps eliminate problems associated with traditional wedge grips that include grip failures, time-consuming grip changes and inaccuracy of total elongation measurements. Clamping forces up to 900 kN (202,300 lbf) were available for positive gripping the wire strand specimen. The wire strand insert arrangement allows for quick changeovers between different specimen diameters. The semi-cylindrical inserts also helps reduce the chances for grip failures while effectively gripping all the wires in the stranded specimen.
In order to measure strain, we used an extra long, clip-on extensometer designed with a 24 inch (610mm) gauge length and 15 degree twist capability. The accurate strain measurements allowed the system to automatically perform required calculations, such as 1% yield strength and elongation at maximum load.
In addition, we relied on our Bluehill® Materials Testing Software to set up and run repeatable, accurate tests. The software auto-zeroes the strain measurement at the required preload values included in the test standards. Stress-Strain plots were clearly graphed and calculation results were indicated on the plots.