Damage, fatigue and creep

Course Description

1. Introduction

(1 session + I2B) Damage phenomena, microscopic causes – Mechanical tests (degradation of the elastic modulus) + tension & compression asymmetry, differences depending on materials (concrete, glasses, polymers, metals, composites).

2. Review

Continuum Mechanics, models.

3. Brittle Damage

• Isotropic damage: Concept of equivalent strain, isotropic damage variable, elastic energy release rate. Threshold surface in the principal strain space.
• Katchanov model: Calculation of damage D from the propagation of micro-cracks. Construction of loading surfaces (1D or 2D).
• Mazars model.
• Experimental identification.

4. Ductile Damage

• Damaged elasto-plasticity: (Lemaitre & Chaboche, Gurson).
• Experimental identification.

5. Numerical Issues and Non-local Models

6. Fatigue (3h lectures and 3h tutorials)

• Session 1: Definition of fatigue and the different fatigue regimes. Wöhler curves and fatigue design.
• Session 2: Physical mechanisms (initiation/propagation/fracture). Paris law and crack propagation design.

Numerical Labs:

• MSM: 1 lab on ductile damage (Gurson, Johnson Cook, etc./element deletion, stability, viscosity, etc.) & 1 lab on brittle damage (“concrete plasticity”).
• MS: Abaqus introduction & simple exercise on damage (introduction to the requirements for numerical labs in structural dynamics).

Prerequisites

Finite Elements 1 (concepts of weak formulation, stiffness matrix, assembly, …).

Objectives

At the end of this course, the student should be able to:

• Select an appropriate model for a given material and loading condition.
• Understand the constitutive equations of the model.
• Identify the material parameters.
• Analytically solve a simple problem.
• Select a numerical method for solving the problem.