Lab Report on the Tensile, Torsion and Bend testing of Mild Steel
Nomenclature:
Symbol Description Units
A Area m2
E Tensile modulus n/a
G Shear modulus n/a
J Polar 2nd moment of area n/a
L Gauge length mm
M Bending moment Nm
R Radius mm
T Torque Nm b Breadth mm d Depth of beam mm h height mm r Secondary radius mm θ Angle of twist radians π pi n/a
ϒ Shear strain mm Shear stress N/m2 Poissons ratio n/a
Ɛ Strain mm σ Stress N/m2 σy Yield stress N/m2
Ixx 2nd Moment of area n/a
Ɛz Longitudinal strain mm
Ɛy Lateral strain mm y Yield strength in shear N/m Objectives
(ii)
To investigate the relationship between Torque (T), and angle of twist θ of a circular cross
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The load on the beam was then unloaded to zero in increments of 10 kg and all 6 strain gauges were then again recorded at each increment.
Results:
(i)
The graph produced a straight line when the specimen was loaded up to 6 kN. The specimen was then unloaded to 0 kN again. This produced a straight line returning to the same place, the origin. The specimen was then loaded up to 11 kN and unloaded again. As the specimen was being loaded to 11 kN it followed the same straight line to 6 kN but as it went beyond this point it started to become non-linear. When it reached 11 kN it was unloaded back to 0 kN. This unloading produced a straight line which was parallel with the original loading of the specimen. When the specimen was being reloaded to its fracture point it followed this new line up to 11 kN and after that it started to level out until it reached it maximum point then started to decrease until the specimen fractured.
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This shows that for this particular specimen between these loads that stress and strain are proportional to each other. The slope of this straight line is known as the young’s modulus. This means that as long as the specimen is not loaded above 6 kN, when it is unloaded it will return to its original state. After this point the graph starts to level out. The specimen is no longer in its elastic stage and has exceeded its yield point. There will be permanent deformation and strains when the specimen is unloaded. This can be seen as the specimen is loaded from 0 kN to 11 kN and unloaded back to 0 kN again. As the graph is being unloaded,