ISO 7257:2016 specifies a flexure test procedure to determine and classify the fatigue strengths of reconnectable or permanent hydraulic tube joints.

The procedure is intended for conducting flexure tests of fittings and joints with high-strength hydraulic tubes of various alloys such as corrosion resistant steel, Nimonic[1], titanium and aluminium alloy hydraulic tube for use on commercial and military aircraft.

A mean stress is applied by holding system pressure in the specimens and then flexing in a rotary bending test machine.

[1] Nimonic is the trademark of a product supplied by Special Metals Corporation. This information is given for the convenience of users of this document and does not constitute an endorsement by ISO of the product named. Equivalent products can be used if they can be shown to lead to the same results.