Numerical and experimental study of composite bulkhead partition strength with in-situ x-ray monitoring

The current work presents a qualitative and quantitative assessment of microdamage occurring in the structure as a result of different loading tests by the example of the "U"-shaped bulkhead segment made of carbon fiber reinforced plastic (CFRP) using microfocus X-radiography. The resin transfer molding (RTM) technology was used to manufacture this structure. X-ray images with the fixed tensile force were made during the sample tests. These images were analyzed in order to reveal a delamination as the basic damage type occurring in the tested part. The areas of interlayer cracks localization and their estimated sizes were identified at the various load levels. It was noted that the cracks were completely closed after unloading; and it was difficult to identify them by any non-destructive testing methods. The three-dimensional computer model was created to carry out the stress-strain analysis of the sample. A detailed ply-by-ply analysis allowed us to estimate the interlaminar normal and shear stresses which determine the structural failure. The numerical simulation of this problem was carried out using the finite element method (FEM) with ANSYS Workbench software. Due to a high dimensionality of the FE model, the high-performance computing complex was used. The numerical simulations results with regard to the mechanical tests of the bulkhead segment were compared with the X-ray radiography results, and a good qualitative correlation was found. Thus, it was shown that the areas of maximal interlaminar stresses are localized in the part’s bending areas. The difference between the experimental and numerical values of the bearing strength was about 23% but it could be corrected after testing a series of similar samples and refining the material interlaminar gap strength.