Issue 42

M. Peron et alii, Frattura ed Integrità Strutturale, 42 (2017) 214-222; DOI: 10.3221/IGF-ESIS.42.23 216 plates with different diameters were tested only for the highest density (708 kg/m 3 ), geometries and maximum load presented in Tab. 2. Tests were performed at room temperature, on a Zwick/Roell Z005 testing machine with 5 kN maximum load, using a loading rate of 2 mm/min. Four tests were performed for each notch geometry. The specimens’ dimensions and the average maximum load are listed in Tab. 2. The obtained load-displacement curves show a linear behavior without plasticity, the failure occurs suddenly and the behavior is brittle. Table 2 : Geometrical parameters and average maximum load of notched components. Table 3 : The average maximum load from testing of specimens with hole on tensile. Bending of asymmetric semi-circular bend (ASCB) ASCB specimens with vertical crack were considered, Fig. 1.d. The crack tip was introduced using a razor blade. Different types of applied mixed mode are easily obtained only by changing one of the supports position ( S 2 ) and keeping constant the other support ( S 1 ). The load is applied on the symmetry axis of the specimen using three point bending grips. Stress intensity factors (SIFs) solution for ASCB specimen [31]: 1 2 ( / , / , / ) , 2 max i i P K aY a R S R S R i I II Rt    (1) were obtained by finite element analysis (Lazzarin and Filippi, [32] and are plotted for a crack length a = 20 mm, specimen radius R = 40 mm, distance to fixed support S 1 = 30 mm, thickness t = 10 mm, resulting a/R = 0.5, S 1 /R = 0.75. It could be observed that changing the distance S 2 from 30 mm to 3 mm, the loading conditions change from pure mode I to dominant mode II conditions. Moreover, using a polynomial interpolation the exact position of left support, leading to pure mode II loading condition, was determined at distance S 2 = 2.66 mm. The recorded load–displacement curves were linear (no significant non-linearity identified) and the fracture occurred suddenly, indicating that the specimens failed in a brittle manner, Fig. 1.e. Tab. 4 presents the average fracture load values F max obtained at each loading configuration for the four considered materials. For all the tested specimens the thickness was equal to 10 mm. The mixed mode ratio was quantified using the mode mixity through the dimensionless parameter M e , proposed by Ayatollahi and Torabi [33]. M e (S 2 [mm]) Density [Kg/m 3 ] 1(30) 0.83 (12) 0.651 (8) 0.472 (6) 0.206 (4) 0.004 (2.66) 100 43.8 88.5 91.47 102.55 97.3 92.4 145 67.8 133.5 152.5 158 151.25 148.67 300 190 397.5 535.5 645 601.75 712.3 708 704.3 1340 1680 1910 2133 2130 Average Fracture Load Value [N] Table 4 : Average fracture loads values for ASCB specimens. Notch Shapes Geometrical parameters [mm] PUR Density [kg/m 3 ] 100 145 300 708 l W b D R Average Maximum load F max [N] V 100 25 15 - 0.25 146.39 185.92 353.74 1811.43 U 100 25 15 - 2 189.45 262.4 397.71 2109.96 100 30 14 - 4.25 236.5 329 443.6 2173.4 O 100 25 - 10 - 187.89 267.31 521.5 1960.31 Notch shape: O Length l = 100 mm Width W = 25 mm Hole diameter [mm] 10 8 7 6 5 3.5 Average maximum load [N] 1960.31 2197.27 2290.76 2491.03 2544.66 2944.64