PSI - Issue 5

F. Romano et al. / Procedia Structural Integrity 5 (2017) 721–728 Author name / Structural Integrity Procedia 00 (2017) 000 – 000

725 5

Fig. 2. Design of the reference panels.

2.2. Weight sensitivity analysis by SHM

As illustrated in Fig. 3 (a), the detection by SHM of a BVID smaller than that one identified by visual inspection (0.8/1 mm), implies the adoption of a higher material allowable (  , i.e. strain, cu, i.e. compressive ultimate) for the design of the composite structure with a consequent potential reduction in weight.

Fig. 3. (a) Higher compressive strain allowable by SHM; (b) Increment of the design value.

Different sensitivity limits of the SHM system to detect the BVID have been taken into account, by assuming different values of the BVID knock-down factor and consequently increasing the compressive design value. Lower design weight of the stiffened panels is related to a specific capability to identify damages by using SHM systems, with respect to the visual inspection. The evaluation performed in this chapter supposes that different sensitivity levels of the SHM systems are linked to different amounts of damage that have as consequence different residual strength levels. Therefore, the analyses have been performed using different values of the compressive strain allowable as if we were in presence of different SHM capabilities. The numerical analyses developed in this part of the work have supplied, for each reference panel and for each test case, new panel configurations; they are different in terms of layups, thicknesses, stringer spacing, and therefore weight, with respect to the reference ones. K BVID has been incremented, for the selected prepreg material, from the classical design value (K BVID = 0.70) up to the ideal case of NO K BVID (i.e. K BVID = 1) by increasing the compressive failure strain. Fig. 3 (b) illustrates the levels of the compressive failure strain that have been applied for the redesign of the panels.