ISO 16842-2021 pdf free download – Metallic materials — Sheet and strip — Biaxial tensile testing method using a cruciform test piece.
6 Testing method
6.1 Testing machine The specifications required for the biaxial tensile testing machine (hereinafter referred to as testing machine) are as follows (for examples of typical testing machines, see Annex C):
a) It shall have sufficient functions and durability to hold four grips of a cruciform test piece (hereinafter referred to as test piece) in one single plane with a tolerance of ±0,1 mm during testing.
b) Two opposing grips shall move along a single straight line (hereinafter referred to as x-axis and y-axis), and the x- and y-axes shall intersect at an angle of 90° ± 0,1° (The plane that contains the x- and y-axes is referred to as the reference plane, while the intersection of x- and y-axes is referred to as the centre of testing machine).
c) It shall have a function for adjusting the two opposing grips to the position at an equal distance from the centre of the testing machine with a tolerance of ±0,1 mm before the installation of a test piece to the grips.
d) It shall have a function for enabling the installation of a test piece to the grips while aligning the centre of the test piece to the centre of the testing machine.
e) It shall have a function for enabling equal displacement of two opposing grips or the maintenance of the centre of the test piece always on the centre of the testing machine with a tolerance of ±0,1 mm during biaxial tensile test (for example, the testing machines shown in Figures C.1 and C.2 use a link mechanism to ensure equivalent displacement of two opposing grips).
f) It shall have a capability of servo-controlled biaxial tensile testing to perform a test with a constant nominal stress ratio (constant force ratio) and/or a test with a constant true stress ratio, and/or a test with a constant strain-rate ratio, according to the purpose of the test (see C.2). For a link type biaxial tensile testing machine, it shall ensure equal displacement of two opposing grips (see C.3).
g) Modern control electronics allow independent and combined control of each actuator. This is called modal control (see C.4).
h) It shall have a function for measuring and storing the values of the tensile forces (two channels, one for each of the two axes, x and y) and strain components (two channels, one for each of the two axes, x and y) during biaxial tensile test with the specified accuracy and time interval agreed by the parties concerned.
6.2 Measurement method of force and strain
6.2.1 General This subclause specifies the method for measuring the tensile forces (F x , F y ) and nominal strain components (e x , e y ) applied to the x and y directions of a cruciform test piece.
6.2.2 Measurement method of force For measurement of F x and F y , load cells shall be used in the x and y directions. The force-measuring system of the testing machine shall be calibrated in accordance with ISO 7500-1, class 1, or better.
6.2.3 Measurement method of strain For measurement of e x and e y , strain gauges or other methods (e.g. an optical measurement system) shall be used. Measure e x and e y to the nearest 0,000 1 or better.
6.2.4 Strain measurement positions Figure 2 shows the position(s) of a strain gauge (or strain gauges) for measuring e x and e y . e x and e y shall be measured at a position, with a distance of (0,35 ± 0,05)B from the centre of test piece, on the centreline parallel to the maximum tensile force. The strain measurement position can also be determined according to the agreement between parties involved in transaction.
NOTE According to the finite element analyses of the cruciform test piece as recommended in Clause 5 and the strain measurement position as specified in Figure 2, the stress calculation error is estimated to be less than 2,0 % [2][3] .ISO 16842 pdf download.