In the design of a military helicopter, with the aim to operate at low altitude into enemy territory, the damage of critical components, caused by ballistic impact, plays a primary role in assessing the survival of the entire machine. In this work an experimental study is proposed, concerning the capability of a helicopter to carry out a mission of return to the base at reduced power, in the presence of a tail rotor shaft damaged by ballistic impact of 7.62 NATO projectile. In the first part of this study, some specimen representatives of the tail rotor shaft are subjected to experimental ballistic impact tests. Subsequently, static and dynamic torsional tests have been performed on the damaged components in order to asses the residual strength under the loads encountered during the mission.

Non-destructive testings (NDT) based on ultrasonic methods are extensively used for their effectiveness and reliability in detecting defects. The generation of ultrasonic waves and propagation in non-regular geometries are difficult to analyze, especially if the source used is a laser. Numerical techniques to simulate the phenomenon found in literature have proved to be limited in their applicability by the frequencies in the MHz range and very short wavelengths. In this paper we present a numerical method to accurately and efficiently solve problems of laser-generated ultrasounds, with frequencies in the MHz range, and propagation in relatively large bodies. Detection is simulated with the propagation of ultrasounds in air, to optimize the complete configuration for non-contact ultrasonic NDT. Different configurations of inspections have been first simulated using numerical analysis and then reproduced experimentally to compare the results.

High speed MODE I crack growth in elastic-plastic materials, involving large scale plasticity and dynamic effects connected to rapid propagation, is faced through a cohesive model to compute force nodal release. As it is well known, the search of a maximum stress in the crack tip is not worthwhile in the elastic case, only field factors may be used instead. In the elastic-plastic case, hardening and softening due to geometric reasons or due to local damaging have a deep influence on the exponential behaviour of the measured stress field. However, it is possible to introduce a reference value (finite), which is the stress at the beginning of the softening zone. This entity is taken as a scale factor for cohesive force evaluation that is necessary for the accounting of the dissipated energy. In the present work a procedure to compute this reference value by stress-strain field is presented, for a variety of T-stress conditions.