Identification of defects in structures and its components is a crucial aspect in decision making about their repair and total replacement. Failure to detect the faults has various consequences, and sometimes may lead to a catastrophic failure. The conducted research work reported analytical and experimental investigations on the effects of a crack on the cantilever steel beam with circular cross section. The objective of this review is to quantify and to determine the extent of the damage magnitude and the location of the cantilever beams. In analytical study, finite element method (FEA) software was used in developing the model. The results showed that, by monitoring the change of the natural frequency it is a feasible and viable tool to indicate the damage occurrence and magnitude. Unlike for small crack depth, the natural frequencies are not a good damage detector. Mode shapes indicated good sensitivity to detect the damage magnitude for all crack parameters. Frequency Reduction Index (FRI) and Modal Assurance Criteria (MAC) were found to be in order a feasible tool to find the magnitude of the damage in beam structures. While, Coordinate Modal Assurance Criteria (COMAC) and Curvature Change Index (CCI) were used to predict the location of the crack tested beams and proved to be feasible.

Current study reported a facile method to investigate the effects of stacking sequence layers of hybrid composite materials on ballistic energy absorption by running the ballistic test at the high velocity ballistic impact conditions. The velocity and absorbed energy were accordingly calculated as well. The specimens were fabricated from Kevlar, carbon, and glass woven fabrics and resin and were experimentally investigated under impact conditions. All the specimens possessed equal mass, shape, and density; nevertheless, the layers were ordered in different stacking sequence. After running the ballistic test at the same conditions, the final velocities of the cylindrical AISI 4340 Steel pellet showed how much energy was absorbed by the samples. The energy absorption of each sample through the ballistic impact was calculated; accordingly, the proper ballistic impact resistance materials could be found by conducting the test. This paper can be further studied in order to characterise the material properties for the different layers.

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