13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- to establish material characteristics. Basically this should be a matter of course. But it is time and money consuming and studying the literature often reveals an opposite practice. Usually, conventional techniques as machine load cells and clip-on transducers cannot be applied to measure the true mechanical response of the specimen due to the short duration of dynamic fracture mechanics tests (microseconds up to milliseconds), inertial effects and resulting signal oscillations. The information which is given on that by relevant test standards [1,2] is shortly summarized in Table 1. Table 1 is limited to single edge bend specimens (SE(B)) since this type of specimen is primarily tested under dynamic loading at BAM. Table 1. Standard information on force and displacement measurement in dynamic fracture mechanics tests on SE(B) specimens with thickness/width-ratios 1 ≤ B/W ≤ 4 Information on BS 7448-3 [1] ASTM E 1820 [2] Main body Annex A Annex A13 Annex A14 Annex A17 loading rate 3 < K& < 3000 MPa√m/s K& > 3000 MPa√m/s K& > 2,75 MPa√m/s, not for impact or quasi- -impact testing (free-falling or swinging masses), minimum loading time 1 ms K& > 2,75 MPa√m/s, minimum test time to be calculated to avoid presence of a significant kinetic energy component in the specimen relative to the internal energy and to assure applicability of static J-integral equations no restriction on impact velocity provided the time to fracture is greater than the calculated minimum test time force measurement machine load cell resistance strain gages attached to both sides of the specimen, wired as two quarter bridges, positions: W/2 from ligament and at W/2 in width machine load cell as used for static plane strain fracture toughness test generally suitable, but response characteristic to be checked to avoid inertial effects on-specimen force measurement recommended (remote load cells allowed if requirements are met), full bridge of 4 strain gages on the specimen midplane at the specimen span quarter points (on upper and lower specimen side) strain gage instrumented striker displacement measurement direct load line displacement via horizontal comparator bar approximation by test machine ram displacement the same transducers as used for static plane strain fracture toughness test generally suitable, but response characteristic to be checked to avoid inertial effects fibre-optic transducers calculation from force/time record, no measurement COD measurement clip gage - cantilever beam displacement gages like in static fracture toughness testing down to loading times of 1 ms -
RkJQdWJsaXNoZXIy MjM0NDE=