ISO 12108:2018 pdf free

ISO 12108:2018 pdf free.Metallic materials一Fatigue testing一Fatigue crack growth method
In terms of testing machine alignment, asymmetry of the crack front is an indication of misalignment. For tension-compression testing, the length of the force train should be as short and stiff as practical. Non-rotating joints should be used to minimize off-axis motion. It is important that adequate attention be given to alignment of the testing machine and during machining and installation of the grips in the testing machine. Regarding the relevance of alignment, a distinction shall be made between:
一 Crack growth tests with rigid gripping and rigid load train which can also undergo compressive forces and stresses (e.g. corner crack test pieces): a sufficient alignment of the load train can be important for these test pieces to obtain correct and reproducible crack growth data, and
一Crack growth tests only with tensile load and fixed with bolts and using cardanic joints (e.g. CT-specimens): due to the use of cardanic or similar joints in the load train alignment checks are not necessary.
If an alignment check is appropriate (e.g. when using a rigid load train and grips) and required (e.g. by the purchaser), it should be conducted according to ISO 23788 and using an alignment class 5 according to ISO 23788. If alignment check is conducted, the results shall be reported.
Accuracy of the force measuring system shall be verified periodically in the testing machine.The calibration for the force transducer shall be traceable to a national organization of metrology. The force measuring system shall be designed for tension and compression fatigue testing and possess great axial and lateral rigidity. The indicated force, as recorded as the output from the computer in an automated system or from the final output recording device in a non-computer system, shall be within the permissible variation from the actual force. The force transducer’s capacity shall be sufficient to cover the range of force measured during a test. Errors greater than 1 % of the difference between minimum and maximum measured test force are not acceptable.
The force measuring system shall be temperature compensated, not have zero drift greater than 0,002 % of full scale, nor have a sensitivity variation greater than 0,002 % of full scale over a 1 °C change. During elevated and cryogenic temperature testing, suitable thermal shielding/compensation shall be provided to the force measuring system so it is maintained within its compensation range.ISO 12108 pdf free.