Issue 50

N. Chatzidai et alii, Frattura ed Integrità Strutturale, 50 (2019) 407-413; DOI: 10.3221/IGF-ESIS.50.34 411 (a) (b) Figure 3 : Temperature profiles as recorded by thermocouples together with the temperature peak values as calculated by FEA for embedding locations: (a) 1 st layer and (b) 21 st layer. is followed by a rapid decrease in the temperature. The temperature profile shows a declining pattern with time. However, it is obvious that the temperature profile is fluctuating, with gradually lower maxima even when the fabrication of the speci- men is well above the 1 st layer. At the end of the printing process the temperature at the first layer exhibits a value of 93°C (due to the heat generated by the heated platform) which is very close to the glass transition temperature (T g ). For ABS the T g is 94°C. This shows the importance of heat transfer through conduction within the structure. In Fig.3b the temperature profiles as a function of building time in the case of specimen 2 are presented. The thermocouple was integrated in 21 st layer, so the reordered data refers to only half the specimen (21 layers). It is seen that the tempera- ture profile is similar to the one presented in Fig.3a, while the effect of the printing nozzle is more intense at the layers de- posited at the end of the printing process. In Fig.4 the temperature data of specimen 3 are shown. In this case two thermocouples were integrated in the same speci- men, one at 1 st layer and the other at the 21 st layer. The exhibited recording presents a similarity to the previously presented experimental data. The sudden temperature drop recorded by the thermocouple integrated in the first layer shows the time that the building process was paused temporarily for the integration of the 2 nd thermocouple. In Figs.5(a,b) the temperature profiles for specimens 4 and 5 of Table 1 are shown. These specimens were built with higher printing speed (65 sec/layer), compared to the previous ones. The recorded temperature profile is similar to the correspond- ing ones of the previous specimens, but the temperature values remain higher and well above T g . This suggests that the adjacent rasters have more time to bond. The higher speed of the printing nozzle contributes to the maintenance of the higher temperatures inside the specimen. Additionally, the printing speed together with the shorter toolpath of the printing nozzle (specimen 5, Fig.5b), allow for a more uniform temperature profile inside the specimen. The irregularities observed for the temperature profile at the first four layers of the 3D printed rectangular specimen are likely to be due to possible levitation of the embedded thermocouple. As far as the simulated temperature profiles are concerned, they are in good agreement with the experimental ones, especially for specimens 4 and 5. Increasing the speed of the printing nozzle, and even more in the case of shorter build path (specimen Figure 4 : Temperature profiles as recorded by the two thermocouples integrated in1 st and 21 st layer.