Answer any two of the following: (i) Distinguish between microscopic and macroscopic examination of metals; (ii) With reference to metals, explain the term creep - Leaving Cert Engineering - Question 2 - 2008

Creep is defined as the slow, permanent deformation of a metal when subjected to a constant load over time. This phenomenon is particularly significant at high temperatures where materials are more prone to deformation.

The two factors influencing creep include:

1. Time: The longer the material is under stress, the more it is likely to deform.
2. Temperature: Higher operating temperatures can accelerate the creep process as atomic movement becomes easier.

In the Brinell hardness test, the indenter is a hardened steel or tungsten ball, typically 10 mm in diameter, which is pressed into the material under a specific load. This method measures the diameter of the indentation left on the surface.

Conversely, the Vickers hardness test uses a diamond indenter shaped like a pyramid with an angle of 136 degrees. The load applied causes a diamond-shaped impression, and the size of this impression is used to determine hardness.

To plot the stress-strain graph, take the given values from the table and mark them on graph paper, ensuring that the x-axis represents strain (in thousands) and the y-axis represents stress (in N/mm²). Connect the points to form the curve, indicating the elastic limit and regions of plastic deformation.

From the plotted stress-strain graph, the 0.1% proof stress can be determined at the point where the graph deviates from linearity, typically calculated as approximately 325 N/mm².

Young's Modulus (E) can be calculated using the formula:

$E = \frac{Stress}{Strain}$

Using the values at 125 N/mm² stress and 1.4% strain:

$E = \frac{125 \text{ N/mm²}}{1.4} = 90 \text{ kN/mm²}$

A – Penetrant or magnetic particle tests can be employed to identify surface flaws at point A.

B – X-ray testing is suitable for detecting internal faults at point B.

The X-ray testing method involves passing radiation through the metallic component. Should a defect exist, it alters the intensity of the rays detected, yielding a radiographic negative. A diagram could illustrate the setup of the X-ray equipment and the component being tested, marking areas of potential defects based on intensity variations.