Diagnostics of the presence of a fatigue crack in the compressor blade using the spectrum of vibration amplitudes at the superharmonic resonance

In this study, the solution of the forced vibration response of a structural element with a fatigue crack was carried out using the finite element method to determine the influence of its presence on the flexural forced vibration behaviour of the compressor blade airfoil at the superharmonic resonance of the order 1/2. The blade airfoil with a low twisted angle was used as an object of investigation to perform the computational analysis. Its vibrations in the plane of minimum stiffness were excited by the kinematic displacement of root edge elements. The fatigue crack was modelled as a mathematical cut. Two locations of the crack were investigated – on the leading edge and convex side of the blade airfoil. The nonlinearity due to the intermittent contact of the crack surfaces, which is caused by the opening and closing of the crack during each vibration cycle, was taken into account by solving the contact problem. To quantify this kind of nonlinear dynamic behaviour, the vibration diagnostic parameter was defined as the displacement amplitude ratio of the dominant harmonics at the superharmonic resonance of the order 1/2. Based on the results of the calculations it has been found that regardless of the crack location, the ratio nature is the same for all vibration axes. However, with vibrations in the plane of minimum stiffness, the crack on the convex side of the airfoil has an opening mode propagation, which makes it possible to fix its location due to a sharp change in the ratio of the amplitudes of the dominant harmonics along the corresponding axis.

Study on bending and tensile properties of a T-shaped hook-connected structure made of two-and-a-half-dimensional woven composites and laminated composites

In this paper, a kind of T-shaped hook-connected structure, which consists of a T-shaped plate made of two-and-a-half-dimensional woven composites and a groove structure made of T300/BMP316 laminated composites, was designed as the simulator specimen of the connection structure between the vane and the case in an aero-engine. As the bending strength and tensile strength are important mechanical properties, bending tests and tensile tests, respectively, of the T-shaped hook-connected structure were conducted to study the mechanical properties and failure modes under bending and tensile loads on web. Experimental results showed that the initial damages both occur at the root-edge, and then the damages extend to the root-middle during the bending test or extend perpendicular to the root-edge to the margin of the flange during the tensile test. Then, a strength prediction method based on the progressive damage theory was developed to simulate the mechanical properties and damage processes of the T-shaped hook-connected structure under bending and tensile loads, respectively. Compared with experimental results, the maximum error is less than 10%, and the damage modes are similar.

Structural Analysis of Light Aircraft Wing Components

This paper aims to demonstrate the structure analysis of strut-braced wing of a typical manufactured Light-Aircraft by using FEM software (MSC PATRAN/NASTRAN) and determine the safety margin in all of its components, which are useful to determine the structure strength requirements. The geometrical model of the wing was created in CATIA and then exported to PATRAN, which is the modeler to build the finite element model. PATRAN model geometry was modified and prepared to create the mesh. The structural components have various functions and shapes, thus different element mesh was created. After creating the finite element model for all parts, the elements and material properties were assigned and the model was fixed at the spar root edge and strut-braced end, and loaded by distributing the inertia load and aerodynamic load, calculated using (CFD), acting on the rib edge. Then the model was submitted to NASTRAN for linear static analysis. The obtained Stress Results and Safety Margins of each part were calculated and found to be acceptable.

On the Average Number of Trees in Certain Maps

For a formal definition of “map” the reader is referred to (7, §2). The maps in this paper are rooted by specifying an orientation for one of the edges. This also specifies a root vertex, the negative end of the root, and a root face, the face on the left of the root edge. Counting is, as usual, defined on isomorphism classes.Regular maps of even valence have been enumerated in a recent paper by Tutte. In this paper we determine the average number of trees in such maps, and include similar results for regular tri valent maps, that is, maps with three edges incident on every vertex. In the development for the latter, a formula for the number of trivalent maps with 2t vertices is produced.