Issue 41

A. A. Ahmed et alii, Frattura ed Integrità Strutturale, 41 (2017) 252-259; DOI: 10.3221/IGF-ESIS.41.34 255 detail, the AM postulates that the effective stress has to be determined by averaging σ 1 over a semi-circular area centred at the notch tip and having radius equal to L [1]. In a similar way, the VM calculates σ eff by averaging the linear-elastic maximum principal stress over a hemisphere centred at the apex of the stress raiser being assessed and having radius equal to 1.54L [12]. In the present investigation, owing to its simplicity, the accuracy of the TCD in estimating static strength of notched additively manufacture PLA will be assessed by applying this theory solely in the form of the PM. The definitions for σ eff calculated according to Eqs (3) and (4) make it clear that inherent material strength σ 0 plays a role of primary importance when the TCD is used to assess static strength of notched components. As far as brittle materials are concerned, much experimental evidence suggests that these materials have inherent strength that is always very close to the ultimate tensile strength, σ UTS [1-3]. In contrast, when the final breakage is preceded by large scale plastic deformations, σ 0 is seen to be somewhat larger than σ UTS [1, 4, 6]. Further, σ 0 takes on a value that is higher than σ UTS also when the plain parent material fails by different mechanisms to those leading to the final breakage in the presence of stress raisers [1]. These considerations should make it evident that the only way to determine σ 0 accurately is by running bespoke experiments involving notches whose presence results in different stress distributions in the vicinity of the tested geometrical features [1-6]. Figure 3 : Experimental stress vs. strain curves generated by testing plain samples manufactured by adopting different values for manufacturing angle θ p . 0 5 10 15 20 25 30 35 40 45 50 0 0.05 0.1 0.15 0.2 Stress [MPa] Strain [mm/mm]  p =0  (a) 0 5 10 15 20 25 30 35 40 45 50 0 0.005 0.01 0.015 0.02 Stress [MPa] Strain [mm/mm]  p =30  (b) 0 5 10 15 20 25 30 35 40 45 50 0 0.005 0.01 0.015 0.02 Stress [MPa] Strain [mm/mm]  p =45  (c) 0 5 10 15 20 25 30 35 40 45 50 0 0.005 0.01 0.015 0.02 Stress [MPa] Strain [mm/mm]  p =60  (d) 0 5 10 15 20 25 30 35 40 45 50 0 0.05 0.1 0.15 0.2 Stress [MPa] Strain [mm/mm]  p =90  (e)