Engineering Studies
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Suggested answers
Activity 1
Visit the website given above to identify the differences between quantitative and qualitative tests then complete the statements below.
A quantitative test is one that provides data that will be used for design purposes - the tensile test.
A qualitative test is one where the results will be used for making comparisons - Brinell hardness or Charpy inpact tests, or for example as a 'go/no go test' such as the bend test.
Activity 2
Visit this URL:
http://www.instron.com.au/wa/applications/test_types/tension/default.aspx 
Identify the name of this relationship and explain it using the spaces below to insert your answers.
RELATIONSHIP NAME: Hooke's Law
RELATIONSHIP TYPE: For most tensile testing of materials, it will be observed that in the initial portion of the test, the relationship between the applied force, or load, and the elongation the specimen exhibits is linear. In this linear region, the line obeys the relationship defined as "Hooke's Law" where the ratio of stress to strain is a constant,
The constant E is the slope of the line in this region where stress (σ) is proportional to strain (ε) and is called the "Modulus of Elasticity" or "Young's Modulus".
Activity 3
Visit the website:
http://www.twi.co.uk/j32k/protected/band_3/jk69.html
Locate the image of the stress-strain curve and identify its parts. Insert the names of areas and critical points on the incomplete diagram given below.
Activity 4
What can be learned from a tensile test?
Visit the URL
http://www.twi.co.uk/j32k/protected/band_3/jk69.html
Identify and explain the data, which can be obtained from the results of a tensile test. Complete the omitted sections of the table.
| Aspect of the Tensile Test | Explanation | Calculation Formula |
|---|---|---|
| Tensile strength | Also known as the ultimate tensile strength, the load at failure divided by the original cross sectional area | Where
the ultimate tensile strength (U.T.S.),  max = P max /A 0 ,
where P max = maximum
load, A 0 = original
cross sectional area. |
| Yield point (YP), | the stress at which deformation changes from elastic to plastic behaviour. ie: below the yield point unloading the specimen means that it returns to its original length, above the yield point permanent plastic deformation has occurred. | YP
or y
= P yp /A 0 where P yp = load at the yield point. |
| Percentage elongation, El% | By reassembling the broken specimen a measure of how much the test piece had stretched at failure can be determined. | Where El% = (L f - L 0 /L o) x100 where Lf = gauge length at fracture and L0 = original gauge length. |
| Percentage reduction of area | How much the specimen has necked or reduced in diameter at the point of failure | Where R of A% =(A 0 - A f /A 0) x 100 where A f = cross sectional area at site of the fracture. |
| Young's Modulus of Elasticity | The
slope of the elastic portion of the curve, essentially a straight line,
will give, a measure of how much a structure will elastically deform
when loaded. A low modulus means that a structure will be flexible, a high modulus a structure that will be stiff and inflexible. |
The ratio of stress to strain is a constant,
or  . E is the slope of the line in this region where stress (σ) is proportional to strain (ε) |
End of unit.
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