62 M. Schaefer Fig. 2 Holding fixture used to restrain the specimens during annealing and subsequent quenching. There is an aluminum top cover (removed in the photo) to hold the specimens flat and reduce warping. (specifically, for printing the lengthwise specimens) the overall length of parts was reduced and thus the length of the narrow section of the specimen was also slightly reduced. The narrow test section of the specimens was 50 mm long (versus 57 mm according to the standard), 13 mm wide, by 3.2 mm thick [Figure 3]. Fig. 3 Nominal dimensions of test specimens are slightly modified from ASTM standard, with reduced length in the middle section. The was done to accommodate printing in the lengthwise orientation in the Prusa printer used. Method 1 & 3 – Print Orientation & Annealing Response Tensile testing was done on an Instron 6800-series machine with a model 2580 (50 kN) load cell. Specimens for testing print orientation and annealing response were run at crosshead speed of 0.5 mm/min., for a nominal strain rate of 0.01 mm/mm per minute (1% per minute). This rate is in accordance with the standard, which states “use the lowest speed that produces rupture in 0.5 to 5 minutes.” Strains in the experiment were not measured directly using an extensometer, rather they are derived (approximated) in the BlueHill software (Instron) based on crosshead displacement and specimen length in the reduced cross section area. This was done as a compromise which allowed quicker testing and more samples to be completed in limited lab time. All specimens were tested to rupture. Stress and derived strain were recorded as the representative results.
RkJQdWJsaXNoZXIy MTMzNzEzMQ==