Testing

Answer to question one

(a)    Ductility is the ability of the material to deform easily under tensile stress without fracturing. Or it is the ability of the material to be drawn into a wire. Considering the tensile test plot, material 2 is more ductile than material 1 because it underwent large deformation under tensile force before it could fracture (Davis 45).

(b)   Strength of a material is defined as the resistance exhibited by a material against irreversible deformation. From the graph, Material 2 is stronger than material 1 because it reached elastic (upper) limit later than material 1(Davis 45).

Answer to question two

Elastic deflection occurs when the shape of the material changes upon tensile stress but the material regains its original shape when the strain is removed.  On the other hand, plastic deflection occurs when the shape of material under tensile stress changes permanently even after the strain is removed (Davis 45).

Answer to question three

(a)  Stress= force / area

2.5 cm= 1inch

Force= 25000ibs

Area= 0.025 ×0.025

 =0.000625m².

Therefore, stress =25000÷0.000625

 =40,000,000Nm²

Or it can be

F/A =25000/5²

  =1000psI²

(b) The local stress will be higher than (a) at the bottom edge of the column.

(c) The local stress will be lower than (a) at the centre of the column.

Answer to question four

Material B will more likely fail at a lower stress than A. the notch introduced the point of weakness. The stress lines will be concentrated around the not weakening the region around the notch which will finally lead to fracture.

Stress will first reach the highest value at the tip of the notch. Or the area around the notch and failure starts at the point f weakness (notch).

Answer to question five

As per the definition of stress (i.e., F/A) mathematically is most like: b. pressure.

 Answer to question six

The definition of Young’s Modulous,”E” is most similar to:  c. the “spring constant”, k

 Answer to question seven

You can easily distinguish a brittle material from a ductile material by looking at their stress-strain plots because, a brittle material fractures at lower strains while ductile materials withstand large strains before rupturing.  Additionally, the yielding region of the ductile material takes up the majority of the stress-strain curve while for the brittle material the yielding region is almost non-existent. Ductile materials have less Young’s Modulus than brittle materials (ratio of stress against strain) (McAlister102).

Answer to question eighth

An “ideal” stress-strain plot, as produced from an imaginary tensile test for some material with appropriate Label of regions including the elastic region, plastic region, yield and failure points (McAlister102).