Low-Energy Effective Action in Non-Perturbative Electrodynamics in Curved Spacetime

We study the heat kernel for the Laplace type partial differential operator acting on smooth sections of a complex spin-tensor bundle over a generic $n$-dimensional Riemannian manifold. Assuming that the curvature of the U(1) connection (that we call the electromagnetic field) is constant we compute the first two coefficients of the non-perturbative asymptotic expansion of the heat kernel which are of zero and the first order in Riemannian curvature and of arbitrary order in the electromagnetic field. We apply these results to the study of the effective action in non-perturbative electrodynamics in four dimensions and derive a generalization of the Schwinger's result for the creation of scalar and spinor particles in electromagnetic field induced by the gravitational field. We discover a new infrared divergence in the imaginary part of the effective action due to the gravitational corrections, which seems to be a new physical effect.Comment: LaTeX, 42 page

BEM Simulation and Experimental Test of a FML Full Scale Aeronautic Panel Undergoing Biaxial Static Load

This paper concerns the numerical and experimental characterization ofthe static and fatigue strength of a flat stiffened panel, designed as a fiber metal laminates (FML) and made of Aluminum alloy and Fiber Glass FRP. The panel is full scale and was tested under both static and fatigue biaxial loads, applied by means of an in house designed and built multi-axial fatigue machine. The static test is simulated by the Boundary Element Method (BEM) in a two-dimensional approach (only allowance for membrane stresses). The strain gauge outcomes are compared with corresponding numerical results, getting a satisfactory correlation. After the static test, an initial notch is created in the panel and the aforementioned biaxial fatigue load is applied, causing a crack initiation and propagation; the related experimental initiation times and crack growth rates are provided

FEM simulation of a crack propagation in a round bar under combined tension and torsion fatigue loading

An edge crack propagation in a steel bar of circular cross-section undergoing multiaxial fatigue loads is simulated by Finite Element Method (FEM). The variation of crack growth behaviour is studied under axial and combined in phase axial+torsional fatigue loading. Results show that the cyclic Mode III loading superimposed on the cyclic Mode I leads to a fatigue life reduction. Numerical calculations are performed using the FEM software ZENCRACK to determine the crack path and fatigue life. The FEM numerical predictions have been compared against corresponding experimental and numerical data, available from literature, getting satisfactory consistencyN/