Assignment: Materials Failure Analysis
Background -
Despite our understating of the behaviour of materials, failures frequently occur. The source of these failure include improper design, materials selection, and materials processing as well as abuse.
Failure analysis and prevention are important functions to all of the engineering disciplines. The materials engineer often plays a lead role in the analysis of failures, whether a component or product fails in service or if failure occurs in manufacturing or during production processing. In any case, one must determine the cause of failure to prevent future occurrence, and/or to improve the performance of the device, component or structure.
Materials failure analysis is a technique whereby facts are gathered through the process of investigations and testing, and analysed to determine the root cause of a product failure. The product can be anything, from a sheared bolt on a construction site, to a turbine blade in an aircraft engine, with tests being scaled up or down as the job demands.
Question 1 - Investigation of an automobile accident revealed that an axle for a rear wheel was broken, Expert witnesses disagree on whether the axle failed by fatigue, thereby causing the accident, or whether the axle failed in impact as a consequence of the accident. Discuss the features on the axle and the fracture surface would you look for to analyse in an attempt settle this dispute?
Question 2 - A wire rope made up of many strands of small diameter wire passes over a pulley before being used to lift heavy loads. After several months of use, the wire rope fails while lifting a load. Expert witnesses disagree on whether the strands in the rope failed due to fatigue (when a rope passes over a pulley whose diameter is too small, the stresses are unusually high) or because the load being lifted exceeded the limit or the rope. Discuss the features of the rope would you look for to analyse in order to determine the cause of failure.
Question 3 - Two thick steel plates are joined by an arc welding process as part of an assembly for a missile-carrying transport vehicle, After the vehicle is placed in service, the assembly fails. Inspection of the failure indicates that the crack propagated through the heat affected area of the weld, right next the actual fusion zone. Suggest possible causes of the failure, intruding the role of the welding process and the microstructure that the welding process may have produced in the heat affected one. What recommendation might you have to avoid such failures in the future?
Assignment: Materials and Manufacturing Process Selection for Repeatable Vehicle
Background
The fundamental idea of manufacturing or production is to create something that has a useful form. This form is most likely predetermined and calculated, with a certain physical geometry. Usually this geometry has certain tolerances that it must meet in order to be considered acceptable. A tolerance outlines the geometric accuracy that must be achieved in the manufacturing process. The "tightness'' of the tolerances, or in other words the allowed variance between the manufactured product and the ideal product, is a function of the particular application of the product.
When different manufacturing processes and methods are considered, "it is fundamental to develop an understanding of the relationship between the process used and the properties of the finished product," For this it is important to know what conditions a particular process will subject a material to and how different manufacturing materials respond to different conditions such as stress and heat.
All manufactured products are made from some sort of material. Similar to the geometric tolerance, the properties of the material of the final manufactured product are of utmost importance. Due to the availability of a wide variety of materials, the manufacturer must consider the properties of these materials with respect to the desired properties of the manufactured goods. Simultaneously, one must also consider manufacturing process. Although the properties of a material may be great, it may not be able to effectively, or economically, be processed into a useful form. Also, since the microscopic structure of materials is often changed through different manufacturing processes-dependent upon the process-variations in manufacturing technique may yield different results in the end product. Therefore, a constant feedback must exist between manufacturing process and materials optimization.
Task -
1. Select a minimum of two components of the Repeatable Vehicle', (Mechanical Engineering Design Challenge Project) which you are currently working in EG4160.
2. Identify and appraise the most relevant material and manufacturing processes you intend to use to produce these components.
3. Discuss the product design considerations and guidelines of each individual processes.
Suggested References -
1. Asby, M.F. (2012) Engineering materials: An introduction to properties, applications and design, 4th edition, Oxford : Butterworth-Heinemann.
2. Kalpakjian, S.S and Kok, C.W (2009) Manufacturing Engineering and Technology, 6th edition, Pearson