15640 - Structural Diagnostics

Learning outcomes

Upon completion of the course, students acquire and know how to apply knowledge regarding the potential failure mechanisms of materials, stress measurement methodologies, non-destructive testing for component integrity, and the identification of failure modes through the examination of fracture surfaces. Students participate in laboratory experiments focusing on the application of the most common testing techniques: electrical resistance strain gauging, liquid penetrant testing, magnetic particle testing, ultrasonic testing, eddy current testing, and acoustic emission testing, and are capable of selecting the most appropriate method for specific cases.

Course contents

NON-DESTRUCTIVE TESTING (NDT): Main manufacturing defects in materials (from casting, heat treatments, and welding). Non-destructive testing techniques covered (also with the aid of photos and video projections):

• Direct observation via endoscope
• Liquid penetrant testing
• Magnetic particle testing and cable inspections (e.g., for cableway systems)
• Eddy current testing
• Ultrasonic testing

Practical applications, comparisons, and practical issues related to the application of non-destructive testing.
Laboratory exercises (or illustrations of laboratory results) on non-destructive testing are scheduled. Specialized seminars may also be held on this topic to illustrate the importance of this discipline in safety protection.

STRAIN GAUGE TESTING: General principles, characteristics of strain gauges (sensitivity, resistance, gauge factor, thermal output strain). Strain gauge rosettes for determining strains, stresses, and principal directions. Possible measurement circuits and review of the Wheatstone bridge theory. Practical applications of extensometry in various fields. Determination of residual stresses using strain gauge rosettes, specifically via the hole-drilling method. Causes of residual stress onset, experimental procedure, and theoretical formulation for data processing according to standards. Exercises and numerical examples.

LOW-CYCLE FATIGUE (strain-controlled): Application field and application examples, simulation of material behaviour in the elasto-plastic regime: Bauschinger effect, stress-strain hysteresis loop, cyclic softening, and cyclic hardening. Determination of the cyclic curve, Ramberg-Osgood model. Determination of the fatigue life curve and Coffin-Manson model. Mean stress effect (modified Morrow approach). Examples and numerical exercises.

In addition, practical applications of strain gauges, low-cycle fatigue, and non-destructive testing—including magnetic particle inspection of cables—will be presented, with references to various fields of mechanical and aeronautical engineering.

Readings/Bibliography

• Lecture notes provided by the Lecturer.
• Recommended textbook:
  A. Freddi, G. Olmi, L. Cristofolini, Experimental Stress Analysis for Materials and Structures. Stress Analysis Models for Developing Design Methodologies, Cham (ZG), Switzerland, Springer International Publishing, 2015.

Teaching methods

• Traditional lectures using a tablet. Projection of slides, photographs, and videos. Illustration of numerous practical applications.
• Specialized seminars delivered by experts from the Non-Destructive Testing sector, also in collaboration with companies.

Assessment methods

The exam consists of a written test (traditional paper-based): three theoretical and/or practical questions will be set on the topics covered during the course.
The total duration of the written exam is three hours.
Consulting textbooks or notes during the exam is strictly prohibited.

In compliance with the University Code of Ethics, students are reminded to maintain the utmost integrity. Any activity aimed at improperly altering the outcome of the tests (e.g., copying, plagiarism, accessing online learning resources, using unauthorised AI tools) is strictly forbidden. In particular, please note that the mere possession of unauthorised equipment or materials during the test will result in the immediate cancellation of the exam and a formal report to the relevant offices.
Behaviours that violate this prohibition may lead to disciplinary proceedings or referral to the competent authorities if criminally relevant; in the latter case, there is a risk that the students involved may face criminal prosecution.

Each question/exercise is assigned a maximum score of 11/30.
The exam is passed if an overall score (given by the sum of the partial scores) of at least 18/30 is achieved.
If the sum of the partial scores results in a grade strictly greater than 30, the final exam result will be "30 cum laude" (30 with honours).
In accordance with Art. 16, paragraph 5 of the Academic Regulations, the grade obtained in the written exam can be rejected only once. In this case, the result "RF" will be recorded in the Alma Esami online system.

Teaching tools

• A tablet will be used as a "virtual whiteboard" instead of a traditional blackboard. Copies of the slides written during lectures, properly revised and integrated where necessary, will be shared with students (via publication on virtuale.unibo.it) after the lectures (usually within 24 hours).
• Illustration of experimental results on: strain gauges, Non-Destructive Testing, and Low-Cycle Fatigue.
• Presentation of numerous practical applications in the mechanical and aeronautical fields (also with the aid of photographs and videos).

Office hours

See the website of Giorgio Olmi