What is ISO 7257:2016- Rotary flexure test Hydraulic tubing joints and fittings about?
ISO 7257 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, titanium, and aluminium alloy hydraulic tubes 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. ISO 7257 establishes a flexure test procedure to determine and classify the fatigue strengths of reconnectable or permanent hydraulic tube joints. 
Who is ISO 7257:2016- Rotary flexure test Hydraulic tubing joints and fittings for?
ISO 7257 on hydraulic tubing joints and fittings is useful for:
- Aircraft manufacturers
- Strength and fatigue testers
- Safety regulatory bodies
- Quality assessment engineers
- Aeronautical engineers
Why should you use ISO 7257:2016- Rotary flexure test Hydraulic tubing joints and fittings?
ISO 7257 describes a flexure fatigue test procedure that allows the evaluation of various tube fitting designs or material combinations. This evaluation is performed by fatigue testing the tube joints over a spectrum of bending stresses and then plotting the cycles to failure. Other test methods may be used if they develop the same data as the rotary flexure test.
ISO 7257 provides requirements for rotary flexure test including the specifications for the flexure test device, flexure test specimen, and preparation of flexure test.
According to ISO 7257, to measure the flexure stress, the headstock should be initially adjusted to produce a strain gauge reading about 5% below the required bending stress value. The machine needs to be briefly turned on up to stationary rpm and the dynamic reading (i.e., the maximum absolute value of the two strain gauges reading at full test revolutions per minute) is recorded.
What’s changed since the last update?
ISO 7257:2016 supersedes BS M 55:1984 which is withdrawn.
ISO 7257:2016 cancels and replaces the first edition (ISO 7257:1983), which has been technically revised to add imperial unit equivalents, three DN sizes, and additional clarifications.
