Learning objectives
Knowledge and understanding
The advanced mechanical design requires knowledge and understanding of the problems of deformation and strength of materials that go beyond the notion of isotropic linear elasticity, static and fatigue strength simply based on knowledge of the elastic stress state, which is the traditional mechanical design approach. And this also because the CAE (Computer Aided Engineering) softwares incorporate, in an increasing number of cases, the structural finite element simulation also in the non-linear field, making it available at reasonable prices but also requiring material behavior skills over the traditional ones in order to exploit them correctly.
The student, therefore, at the end of the course will know the types of mechanical behavior and failure of materials and the related mathematical models for the design / verification of components and mechanical systems beyond the simple linear elastic behavior, i.e. based on the elastic stress state. He will also know the methods of experimental characterization and simulation of non-linear mechanical behavior by the finite element method.
Applying knowledge and understanding
The student will be able to identify the most appropriate mathematical model to approximate the stress-strain relationship of the material and the mechanical strength under service conditions. He can then resolve analytically and / or by finite element simulation problems of deformation and strength of mechanical components and systems beyond simple linear elastic evaluation.
Prerequisites
The knowledge of the finite element method is useful, though not mandatory.
Course unit content
The course is about the two fundamental aspects of the mechanical behavior of materials: i) the stress-strain behavior (mechanics of materials), ii) the failure mechanism and therefore the strength of the material (structural integrity). Each of these aspects will be illustrated from the phenomenological point of view (experimental) and the mathematical description (modeling).
As for the stress-strain relationship, the following behaviors will be presented:
- quasi-static elasto-plasticity
- cyclic elasto-plasticity
- anisotropic elasticity (composite materials)
- hyperelasticity (elastomeric materials)
- Creep (metallic materials) and viscoelasticity (polymeric materials)
Regarding failure mechanisms and strength, the following cases will be illustrated:
- mechanisms and failure criteria for composite materials
- fatigue strength by deformation approach
- brittle fracture; effect of plasticity in the case of ductile materials
- fatigue crack growth and fatigue life prediction
For each of the above topics lectures as well as classroom exercises will be given. In addition, simple applications of the finite element method with the software Abaqus (student edition) will be done in the lab.
Full programme
1. mechanical tests for the characterization of materials for structural use
2. elastoplasticity
3. true strains and strains
4. fatigue and basic mechanisms, approach to tensions
5. fatigue in the presence of random loads
6. cyclic plasticity, work hardening models
7. Low cycle fatigue, deformation approach
8. Linear elastic fracture mechanics and damage tolerant design
9. mechanics of elastic-plastic fracture (outline)
10. Fatigue defect propagation, closure effect
11. creep behavior of materials
12. elasticity under large deformations, Strain Energy Function
13. ductile fracture, damage modeling
14. CFRP composite materials, lamination theory, damage modeling
Bibliography
N.E. DOWLING: "Mechanical behaviour of materials", 4th Ed., Prentice-
Hall, 2012.
Teacher notes concerning the composite materials topic.
Teaching methods
Lectures and exercises. Lectures are given with the support of PowerPoint slides. The exercises consist in solving by hand examples on the topics covered in class. Laboratory application of the finite element method to problems of mechanical behavior of materials using Abaqus (student edition)
Assessment methods and criteria
The exam consists of a written test and the oral presentation and discussion of problems of mechanical behavior assigned at the beginning of the course, solved by finite element simulation with Abaqus software (student edition). The written exam is composed of three questions, consisting in open-ended questions or exercises on the topics of the course. The maximum score is 30/30. The oral discussion of the problems assigned at the beginning of the course allows an increase in the score of the written part up to three points, according to the methodological appropriateness, originality, content, and clarity of exposition.
Other information
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2030 agenda goals for sustainable development
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