Downloaded from https://www.everyspec.com MIL-sTD-1312B ‘.40. 12 Alignment cell. An elastic device, normally cylindrical in cross section, with strain gages affixed to the outer surface so as to provide indications of axial strain at 90 degree intervals around the circumference. Comparison of strain readings at a constant load provides a measure of bending induced by the loading system. 50. FATIGUE TEST MACHINES 50.1 Load measuring eystem. The dynamic load measuring system shall be accurate within t 2 percent of the indicated maximum load and amplitude, for loads-greater than 10 percent of the maximum capacity of the dynamometer. 50.2 Loading maintaining system.
The load maintaining system shall be capable of maintaining the required load within t 2 percent. Machines operating without load maintainers shall be monitored at intervals by the operator. The intervals shall be determined according co the expected cycle life and equipment capability. 50.3 Static alignment. Static alignment of each fatigue test machine shall be verified at any time necessary to ensure meeting the alignment requirements of this appendix. Align- ment check may be accomplished by mechanical or strain gaged alignment cell systems.
The method employed (see Section 7) shall be capable of proving that the stress caused by misalign- ment (eccentric loading) shall not exceed 6 percent of the average stress. 0 50.4 Dynamic load verification. The load accuracy of each mschine shall be verified after each 1000 hours of oDeratine time or every 6 months, whichever occurs first, and after any machine modification which could affect the load accuracy. The verification procedure shall be in accordance with Section 8. 60. EQUIPMENT AND CALIBRATION OF ALIGNMENT AND DYNAMIC LOAD VERIFICATION * EQUIPMENT 60.1 General. A dynamometer of any suitable configuration and material may be used.
The dynamometer should normally have dimensions such that a strain in tbe range from 0.0012 to 1 0.0015 in./in. is obtained at the maximum load of the dynamometer range. The dynamometer shall have a length of uniform cross section for attachment of the’transducer (see Figure 1). il . The verification procedure consists of the following principal steps: