A method of diagnosis of a health of an electrical, mechanical or electro-mechanical apparatus based on radiation emitted by the apparatus where the method includes establishing a baseline profile for the apparatus and establishing a checkup profile for the apparatus and comparing the checkup profile to the baseline profile to determine a difference indicative of the health of the apparatus.

In a first aspect, the instant invention relates to process for virtually predicting the durability performance of a structure enabling the optimization of the durability performance. This process comprises several steps. In a first step, the structure is modeled by a series of calculation points. Then, for each point, the stresses and strains (4) brought by load cycles (2) and defining hysteresis branches are determined (3). Then, an accumulated damage due to the load cycles is predicted (5) (6) and stored (8). For the prediction, first, using a hysteresis operator (5), a change in the stress (7) along a portion of a hysteresis branch is calculated as a function of a change in the load in time, and, second, using the change in the stress (7) and the stored accumulated damage, a change in the damage is calculated (6). Hence, also a change in the properties (14), including the stiffness, of the structure is calculated. Then, a further change in the stresses and strains (16) is calculated (15) on the basis of the change in these properties (14) to determine a new adapted hysteresis branch. Then, a further change in the stress (7) along a further portion of the adapted hysteresis branch is calculated (5) as a function of a further change in the load in time. At the end of the process, the structure is manufactured accordingly. In a second and third aspect the invention also relates to a system and software program product.

The present invention relates to a method for determining modal parameters of a system under test. The method comprises the steps of

- taking a first set of values of output signals obtained under a first loading condition of the system and a second set of values of the output signals obtained under a second loading condition of the system,

- determining for each loading condition a parametric matrix model for the system, said parametric matrix model representing a space orthogonal to the space spanned by the output signals,

- determining for each loading condition parameters of the parametric matrix model,

- expressing a polynomial eigenvalue problem derived by combining the parametric matrix models and the corresponding parameters for each loading condition

- obtaining the modal parameters by solving the polynomial eigenvalue problem.

A method and apparatus for determining stiffness of a plate-like structure including a monolithic or composite laminate plate entails disposing a device for generating an acoustical pulse against a surface of the plate and disposing a detecting device against the same surface spaced a known distance from the pulse-generating device, and using the pulse-generating device to emit a pulse so as to create an extensional wave in the plate. The detecting device is used to determine a time of flight of the wave over the known distance, and the wave velocity is calculated. A Young's modulus of the plate is determined by a processor based on the wave velocity. Methods and apparatus for evaluating both isotropic plates and anisotropic laminates are disclosed.

According to one non-limiting embodiment, a method includes accessing flight regime rates of occurrence distributions associated with one or more flight regimes for a fleet of aircraft. Using the accessed flight regime distributions, a factor for at least one of the flight regimes is determined that provides a predetermined amount of reliability for a component on each aircraft on the fleet of aircraft known to be affected through at least fatigue damage by the at least one flight regime.