Mario Rosario Chiarelli

A computation of the three-dimensional J-integral for elastic materials with a view to applications in fracture mechanics

Abstract After a definition of the J-integral which includes three-dimensional effects, concentrated loads inside the integration path and thermal gradients, a numerical method is proposed for the computation of the J-integral on the basis of the results of a finite element analysis using 20-node isoparametric elements. The method allows the assessment of the values of the J-integral along any given crack front with a direct computation in the isoparametric space. Examples of computation are given concerning a bidimensional stiffened panel as well as three-dimensional problems such as a penny-shaped crack, elliptical embedded and surface cracks, and a thick specimen under a thermal gradient.

Computation of crack extension energy rate for elastic-plastic hardening materials under variable loading

Abstract The Crack Extension Energy Rate (CEER) for an elastic-plastic hardening material is assessed starting from the flow theory of plasticity. Knowledge of the work done by internal forces as a function of the elastic-plastic state variables, permits numerical evaluation of the CEER under general loading conditions. First results show that if monotonic loading conditions are considered, the Rice J-integral completely describes the fracture behaviour of a ductile material; on the other hand, when dealing with variable loading conditions, the energy available to extend the crack strongly depends on loading history and hardening rules.

The lifting system with minimum induced drag

The lifting system with minimum induced drag is a closed wing with a box shaped front view and was named Best Wing System by Prandtl; on the horizontal wings, the circulation results from the superposition of an elliptical and a constant distributions and, on the the side walls, it is butterfly shaped. Very recently, the Prandtl results (obtained by an approximate procedure) were confirmed by a closed form solution, briefly described in the paper. The concept of minimum induced drag can give rise to a family of aircraft, ranging from very small to very large (larger than the A3XX) aircraft and still compatible with the actual airport areas. These aircraft are named as PrandtlPlane, in honor of Prandtl. An example of a 600 seat category aircraft is presented.

COMPUTATION OF THE CRACK EXTENSION ENERGY RATE IN ELASTO-PLASTIC FRACTURE MECHANICS AND APPLICATIONS IN ENGINEERING

A central cracked elasto-plastic plate undergoing three blocks of alternate loads is examined. Use is made of a numerical procedure for the computation of the crack extension energy rate, appropriately defined, by finite element method.