EXPERIMENTAL AND NUMERICAL ADVANCED DESIGN

This course aims at enabling the students to perform the advanced mechanical design and the integrty assessment of structures and components, according to the most modern procedures.

Extensive training about finite elements modeling (FEM) will be carried out, for enabling the students to predict the structural response within the frameworks of elastoplasticity, dynamics, structural integrity and damage tolerance.

In order to achieve such objective, notions of material mechanics and experimental characterization will be delivered with a pragmatical approach, respectively addressing the latest models of material behavior (static/dynamic plasticity, material damage/failure), and the most recent laboratory procedures for calibrating such models.

The students will assist to laboratory experiments for static and dynamic testing (motor driven and hydraulic testing machines, Hopkinson bar equipment, data acquisition and image analysis); they will then use the experimental data for calibrating selected material models which, then, will be implemented either in the FEM analyses by way of user subroutines or in the postprocessing phase of FEM results by way of simple spreadsheet calculations.

A 3-C.F.U. section of the course will be also oriented at thermal methods for fatigue asessment; this will train the students at acquiring infrared imagery data and at processing data from thermal acquisitions, aimed at determining the fatigue response of components/structures subjected to cyclical loads.

Lessons and classroom / laboratory exercitations.

Contents of the course (C = classes, L = lab., E = exercitation).

1) Elastoplastic response of materials (45 h, prof. G. Mirone)

• C1) Introduction to plasticity - Normality rule and consistency condition – hardening – associate plasticity and yield surface – von Mises plasticity –Path dependence of plastic straining – Pressure and Lode dependent yield surfaces – Experimental determination of the hardening curve – Necking – Experimental characterization – Engineering, True and Flow curves – MLR and MVB methods for round and rectangular section specimens - Practical notions for Finite Elements (FEM) modeling;
• L1) Laboratory experiments for characterization and flow curve validation: (tensile tests of round/flat smooth/notched specimens);
• E1) - Finite elements implementation of tensile tests and comparison of results with experimental data for FEM validation;

2) Damage mechanics and ductile failure (25 h, prof. G. Mirone)

• C2) Triaxiality factor and Lode angle – Rice-Tracey introductory model - Phenomenological damage models (Bao-Wierzbicki, Xue-Wierzbicki etc.) –Problems of mesh dependence for failure propagation in finite elements;
• E2) Finite elements design of simple components / special specimens inculding damage models via postprocessing and/or via user subroutines;
• L2) Lab. Testing of components designed in E2), verificarion of the design predictive accuracy;

3) Dynamics and High Strain Rate effects (20 h, prof. G. Mirone)

• C3) Strain rate effect and models of dynamic hardening – Plastic work dissipation and self heating in dynamics – Experimental procedures for high strain rate testing – Elastic waves propagation in rods – Split Hopkinson Tensile Bar equipment (SHTB);
• L3) Lab. Experiments with Split Hopkinson Tensile Bar (SHTB) - evaluation of dynamic stress-strain curves – calibration of simple models for dynamic hardening;
• E3) Finite Elements implementation of dynamic SHTB tests;

4) Thermal methods for fatigue asessment (30 h, prof. G. Fargione)

• C4) Review of advanced fatigue concepts – random loading and multiaxial fatigue – staircase method - infrared (IR) detection of heat – Training on Thermocamera Flir model…. commands and software – Procedure for determination of the fatigue limits by thermocamera – Laboratory activity tests.
• L4) thermocamera acquisition from static/fatigue tests;
• E4) Postprocessing of experimental IR data;

[1] Lecture notes provided online