Mechanical Behavior of Materials: Case Study Assignment and Fracture Toughness Analysis

Lecture sessions and seminars

Lecture sessions and seminars

The “Case Study” assignment will be supported by weekly lectures, and seminars, as well as lab sessions whenever required, to work on various parts of the assignment. Students can also seek advice on various aspects of their work, e.g. comments on proposed methods/approaches; advice on sources of information; etc.  

Scope

Designing machines, vehicles and structures that are safe, reliable and economical requires both efficient use materials and assurance that structural failure will not occur. Therefore, this module is appropriate for postgraduate students to study the mechanical behavior of materials, specifically for topics such as fracture toughness, fatigue, creep and corrosion. Structural Integrity: Design against Failure module covers topics such as types of materials and their properties and types of failure in materials. Also focuses on stress-based fatigue analysis, relatively new methods of fracture mechanics, creep and corrosion resistance.

Part 1 – Case Studies

For the following three case studies, you are required to:

• Justify the precautions about the failed pieces before starting investigations
• Discuss the given microstructure and/or fractography of the failed pieces.  
• Diagnose the failure, core issues and discuss the causes
• Explore feasible solutions based on theories and research

Case Study One

Austenitic stainless steel plate was used as heat exchanger tubes to produce a steam generator in a milk processing plant. The heat exchanger tubes located in the central part were exposed to high heat input during welding of the tubes with the tube wall. The service conditions of the heat exchanger were dry saturated steam (9 bar, 180^oC) for heating softened water, around 36^oC, 25 ppm Cl^-. After few months of the operation, numerous cracks on the heat exchanger tubes near welded joints to tube wall were started.

25%

Case Study Two

A martensitic microstructure of low alloy steel, AISI/SAE 4330V was used as an oil and gas well tubular drilling tool. The tool operated with severe torque variation, creating multiple cracks at the external diameter, and led to the fracture. The drilling tool was already close to the end of its life.

25%

Case Study Three

Two dissimilar metallic alloys, a plate of mild steel with a larger piece of austenitic stainless steel, were lap joint TIG-welded using 308 AISI filler metal, serviced in an offshore environment for one year.

                                                                                                                                          25%

Maximum 500 Words for each case study                                                                             

Part 2

Fracture Toughness

Crack length versus cycle data is given in the table below from a test on a center-cracked plate of 7075-T6 aluminum. The specimen dimensions: h = 445, b = 152.4, and t = 2.29 mm. The force was cycled between 10 kN and a maximum value of 48 kN.

image

• Obtain the da/dN and DK values.
• Illustrate the K_thand K_iC values on a sketched diagram.
• Discuss the methods to increase the life of the component.

Indicate to all the graphs, charts and diagrams that will be used to solve this question.

Guidelines for writing in general: 5Cs – Clear, Concise, Complete, technically Correct, Critical analysis.

All references must be appropriately indicated within the text and will be listed at the end of the coursework.