Improvements in Means for Testing the Durability of Material which is Exposed to Repeatedly Applied Stresses.

摘要

29,998. Kapp, G. Dec. 24. Testing physical qualities of materials.-Intermittent or reciprocating tensional, torsional, shearing, or bending stresses are applied to testpieces by means of an apparatus comprising one or more electro-magnets, the coils of which are energized by an alternating current of variable frequency; the induced magnetic forces cause an intermittent stress in one or more directions to be applied to an armature, to which one portion of the test-piece is attached. In the form shown in Fig. 1, the coils c of the laminated electro-magnet a, b are energized by an alternating current which causes the armature h to be attracted twice in each period. One end of the test-piece g is attached to a cross-bar d carried by the frame e of the magnet, and the other end is fixed to the armature f, h which is arranged so that a very small air-gap is always left between the poles band the armature. Intermittent bending stresses are applied to a test-bar i, Fig. 3, by means of a knife-edge n attached to the armature f, h. If the magnet and armature be duplicated, the armatures being fixed together and the magnets being energized by currents having a phase difference of 90 degrees, reciprocating stresses can be applied to the specimen. Intermittent stresses in directions at right - angles to one another can be applied by an apparatus constructed in a similar manner. If the waveform, frequency, and electromotive force of the current utilized to excite the electro-magnets are not identical in value with those of the current employed in the calibration of the apparatus, a two-phase alternator is employed, the applied stresses being regulated by varying the excitation of the alternator. In all cases, the stress is measured by a voltmeter.