Issue 30

G. Zucca et alii, Frattura ed Integrità Strutturale, 30 (2014) 409-416; DOI: 10.3221/IGF-ESIS.30.49 414 Figure 14 : Transition between two halves of the actuator case. Hardness Test Hardness test (Tab. 3) was performed on the actuator internal and external surface in accordance to HRB. Moreover, MHV method was used across the thickness in order to evaluate the shot peening effect. Location Hardness Mean Std. Dev. Internal Surface (HRB) 86.3 0.9 External Surface (HRB) 82 1.6 On the section (from outside to inside) (MHV) 175.7 3.5 Table 3 : Hardness results. The results confirm a T73 heat treatment [5] [6], while the values taken across the thickness highlight an increase in hardness where the shot peening should have been applied, confirming the correct procedure was applied during production. Finite Element Analysis A FEA model was performed in order to evaluate the effect of forced coupling between the actuator case and the cap. The Geometric 3D model of DBA was reproduced by the design drawings Fig. 15. 4768 hexahedrons [7] elements were applied to provide the mesh for mathematical model Fig. 15 . Being impossible to reproduce exactly the geometry of the interference, it was assumed as a conservative hypothesis the perfect fit between the two parts: no gap and no interference. The hydraulic system oil works oil within a range of 60°C - 90°C, while the pressurized cabin compartment where the DBA is placed is at about 20° C. This implies a thermal variation of ΔT= 40 – 70 ° C that becomes a thermal load to the structure due to the different thermal expansion coefficient of the case assy and the cap. Indeed, the cap is made of copper alloy AMS 4631, while the case assy is AA7049. Therefore an average ΔT= 55° C was applied. Pressure and inertial loads were not simulated because no findings during the failure analysis suggested they could have been abnormal.