Issue 41

A. A. Ahmed et alii, Frattura ed Integrità Strutturale, 41 (2017) 252-259; DOI: 10.3221/IGF-ESIS.41.34 258  according to Figs. 4b and 4c, the static strength and the fracture toughness of the additively manufactured material being tested were assumed to be independent from manufacturing angle θ p ;  as per PMMA [17], the inherent strength, σ 0 , of the additively manufactured material under investigation was taken invariably equal to 2·σ UTS – i.e., σ 0 =2·σ UTS =2·42.5 MPa=85 MPa;  the linear-elastic stress fields in the vicinity of the stress concentrators being tested were estimated by simply using the analytical solutions devised by Glinka and Newport [18]. Fig. 5 shows the linear-elastic stress fields determined in the incipient failure condition, where the centre of the adopted system of coordinates was taken coincident with the notch tip (Fig. 1a). It is worth observing here also that, for any considered notched geometry, the corresponding stress field was calculated by setting the nominal net stress equal to the average failure stress determined from the nine tests run by using the specimens manufactured with angle θ p equal to 0º, 30º, and 45º (Fig. 2). As shown in Fig. 5, the critical distance value was estimated according to the PM via the point at which the linear-elastic stress-distance curve due to the sharp notch and the horizontal straight line modelling the plain material inherent strength intersected each other [1]. According to Fig. 5, this simple procedure returned a value for L of 0.934 mm. Fig. 5 makes it evident also that by setting L/2=0.467 mm and σ 0 =85 MPa, the PM was seen to be very accurate also in estimating the average static strength of the specimens containing both the intermediate and the blunt notches. In order to show the overall accuracy of the PM in performing the static assessment of notched additively manufactured PLA, the chart of Fig. 6 summarises the error associated with the individual experimental results, with the error being calculated as:         0 0 % 100 eff Error (6) According to the error diagram reported in Fig. 6, it is possible to conclude by observing that the TCD applied in the form of the PM was seen to be capable of accurately estimating the static strength of notched additively manufactured PLA, with its usage returning predictions falling within an error interval of ±20%. Figure 6 : Overall accuracy of the TCD applied in the form of the PM in estimating static strength of additively manufactured PLA. C ONCLUSIONS ccording to the analyses summarised in the present paper, the following conclusions can be drawn:  the TCD is successful in predicting static failures in notched additively manufactured PLA;  the estimates obtained by applying the TCD in the form of the PM were seen to fall within an error interval of ±20%; -100 -80 -60 -40 -20 0 20 40 60 80 100 0 5 10 15 20 25 30 35 40 45 Error [%] Deposition Angle, θ p [  ] Point Method (PM) Kt=4.76 Kt=3.51 Kt=2.22 Error= +20% Error= -20% A