This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Residual Stress”.
1. Residual stresses are also known as locked-in stresses.
a) True
b) False
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Explanation: Residual stresses or locked-in stresses are defined as the stresses existing within a body in the absence of external loading or thermal gradients. In other words, residual stresses in a material or component are those stresses which exist in the body without the application of any other external loads or forces.
2. Manufacturing process is the only consideration which can cause residual stresses in the casting.
a) True
b) False
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Explanation: Manufacturing process is not only the single consideration which can cause stress. Residual stresses may be present in any mechanical component because of many causes. Residual stresses can be due to the technological process used to make the parts of casting, but manufacturing processes are the most common causes of residual stress.
3. Localized yielding of material can also be the reason for the generation of residual stresses in the casting.
a) True
b) False
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Explanation: Localized yielding of material can induce residual stresses in the casting, because of a sharp notch or from various surface treatments like shot peening or surface hardening. To relieve residual stresses from the casting. Usually, heat treatment of the casting is done which also enhances mechanical properties in the casting product.
4. Residual stresses can cause any defects in the casting except distortion of the casting component.
a) True
b) False
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Explanation: Residual stresses can be sufficient to cause any defects in the casting. It can split the metal part into two or more pieces abruptly without any application of external load or force. Residual stresses can also result in distortion of the casting component, which cannot regain its original shape easily.
5. Residual stresses can also be calculated the same way as the stresses due to the external loads is calculated.
a) True
b) False
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Explanation: Residual stresses have the same role in a component’s strength as common mechanical stresses. However, the stresses due to external loads can be calculated with accuracy, but residual stresses are difficult to calculate. Therefore, it is very necessary to have a reliable method able to measure them with minimum damage to the surface of the casting.
6. The presence of residual stresses in a component can prevent failure of the casting component.
a) True
b) False
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Explanation: Residual stresses may play an important role in explaining or preventing failure of a component at times. For example, shot peening of component to induce surface compressive stresses, in which residual stresses prevent failure and also improves the fatigue life of the component. But the internal or residual stresses should be kept balanced in the casting component.
7. By using resin bonded sand in the making of mould, the stresses produced in the casting can be reduced.
a) True
b) False
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Explanation: By using resin bonded sand in the making of mould, the deformability of the mould and core is always improved which helps in reducing the internal stresses in the casting produced. The stresses are also reduced by increasing the holding time of casting in the mould, so as to reduce the difference in temperature distribution.
8. Natural aging treatment is a fast and accurate method for reducing residual stresses in the casting compared to the heat treatment.
a) True
b) False
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Explanation: In natural aging treatment, generally the casting component is stored for several years to make the residual stress released slowly. This method takes long time and it is only suitable for the production of small-batch and larger casting components. And heat treatment does not take much of time depending on the type of heat treatment.
9. Machinability of the casting product can be improved by reducing the residual stresses in the casting.
a) True
b) False
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Explanation: Reducing the casting of residual stresses can improve the machinability of the casting and increases tool life also. On the other hand, the castings machined after reducing the residual stresses have good dimensional stability, persistent precision and good reliability of the casting products.
10. Cold cracking failure of the casting product can be avoided by shot peening method which induces internal stresses in the casting.
a) True
b) False
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Explanation: Cold cracking is basically caused by residual stresses exceeding the limitation of the casting’s strength. It normally appears at the tensile sites of the castings, especially at the sites of stress concentration. Shot peening method, instead of avoiding this defect, it increases the chances of cold cracking by inducing more stresses into the casting product.
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