Task 9. Match the terms (1-6) with their definitions (a-f).
Task 12. Write two paragraphs, one about the advantages and the other about the disadvantages of such mechanical elements as rivets and belts in engineering. Describe their functions and applications. Write your report using 120-150 words.
Task 13. Solve the crossword.
UNIT 10. MECHANICAL FAILURE MODES
Task 1. What do you know about the history of industrialization? Name the most prominent scientists in the field of mechanical engineering and describe their inventions.
Task 2. Watch the video file and answer the following questions:
1) Give the title to the video.
2) Where can this device be applied?
3) What are advantages and disadvantages of such an invention?
4) How can a modern engineer improve this gadget?
Task 3. Read the text.
Mechanical Failure Modes
Forces imposed on systems can cause failures in many different ways. Engineers have to take system and environmental forces into account when designing a system or a component, whether the system is a microchip or a skyscraper.
Components can fail in a variety of different ways based on geometry, load direction, environmental conditions, or other variables. By understanding how something could fail, engineers can design the component to minimize the probability of failure. Designers generally use a factor of safety when designing critical parts. A factor of safety is a multiplier added to design criteria to ensure that not only does the part perform properly under normal loadings, but also performs properly under occasional overloading.
The ten primary modes for failure of mechanical components include:
1. Buckling – Buckling is the failure of a long, slender column that has been subjected to a compressive, axial load. As the load is applied, the center of the column span bulges outward, and then either cracks or yields, depending on the material properties of the specific component.
2. Corrosion – Corrosion is the chemical alteration (generally, but not always, oxidation), of a material due to environmental exposure to corrosive elements. For example, iron or steel that is exposed to air can undergo oxidation, forming iron oxide, commonly known as rust. This reddish-brown material has virtually no structural strength, and can reduce the effective material cross section, and therefore strength of a structure.
3. Creep – Creep is the slow deformation of a solid material over time due to applied loads and often increased temperatures. Creep can result in changes in material properties and part geometries that can cause failures.
4. Fatigue – Fatigueis a reduction in the ultimate strength of a material due to cyclic loading of a part. Micro-deformations can occur in loads that are larger than the normal working load. Even elastic deformations can result in material changes that can reduce the ultimate strength over a large number of cycles.
5. Fracture – Fracture begins as a localized microcrack in a part that slowly grows over time, or grows rapidly when exposed to a large overload. Failure occurs when the crack growth becomes critical and the part breaks. Crack growth often begins in areas of high stress concentration, such as corners.
6. Impact – Impact failure, just as it sounds, is the failure of a part due to impact with or by another object. A baseball shattering a window is an impact failure.
7. Rupture – Rupture generally occurs in pressure vessels or other containers when the pressure within the vessel exceeds the strength of a vessel, either globally or locally. Overpressure can cause rupture, as well as localized reduction in wall thickness due to corrosion or wear.
8. Thermal Shock – Thermal shock is the result of a component moving quickly from one temperature extreme to another. For example, brittle materials such as cast iron experience thermal shock if a hot part is suddenly cooled. The part can then crack or shatter because the material does not have the ductility to withstand the sudden thermal contraction of the material.
9. Wear – Wear is the gradual removal of material by two parts rubbing against each other, or environmental contact with a part, such as water or sand. As material is removed, the effective cross section of a load bearing part is reduced, increasing the stress on the part even though the applied load is constant.
10. Yielding – Yielding is the stress failure of a part due to overloading. As a load is applied to the component, the stress in the part increases. Based on the stress-strain curve for that particular material, the yield point is essentially the peak load that the part can hold before the material stretches apart.
While every operating environment contains different variables, engineers need to understand the different modes of failure so that they can design their parts with a factor of safety large enough to minimize the probability of failure during normal working operations and during potential overloading conditions.
Task 4. Answer the following questions and put 5 different type questions to the text:
1. What is a mechanical failure?
2. Components can fail in a variety of different ways based on geometry and load, can`t they?
3. What are ten primary modes for failure of mechanical components?
4. Give the definition to each of the ten modes.
5. What should engineers do to design parts?
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