To determine tensile strength of a metal.
AIM: -To determine tensile strength of a metal.
OBJECTIVE: โTo conduct a tensile test on a mild steel specimen andย determine the following:
(i) Limit of proportionality
(ii) Elastic limit
(iii) Yield strength
(iv) Ultimate strength
(v) Youngโs modulus of elasticity
(vi) Percentage elongation
(vii) Percentage reduction in area.
APPARATUS:-
(i) Universal Testing Machine (UTM)
(ii) Mild steel specimens
(iii) Graph paper
(iv) Scale
(v) Vernier Caliper
THEORY:-
The tensile test is most applied one, of all mechanical tests. In thisย test ends of test piece are fixed into grips connected to a straining device and to aย load measuring device. If the applied load is small enough, the deformation ofย any solid body is entirely elastic. An elastically deformed solid will return to itsย original form as soon as load is removed. However, if the load is too large, theย material can be deformed permanently. The initial part of the tension curve whichย is recoverable immediately after unloading is termed. As elastic and the rest ofย the curve which represents the manner in which solid undergoes plasticย deformation is termed plastic. The stress below which the deformationsย essentially entirely elastic is known as the yield strength of material. In someย material the plastic deformation is denoted by a sudden drop in load indicatingย both an upper and a lower yield point. However, some materials do not exhibitย a sharp yield point. During plastic deformation, at larger extensions strainย hardening cannot compensate for the decrease in section and thus the load passesย through a maximum and then begins to decrease. This stage the โultimateย strengthโโ which is defined as the ratio of the load on the specimen to original cross-sectional area, reaches a maximum value. Further loading will eventuallyย cause โneckโ formation and rupture.
ย Schematic universalย testingย machine |
PROCEDURE:-
1. Measure the original length and diameter of the specimen. The lengthย may either be length of gauge section which is marked on the specimenย with a preset punch or the total length of the specimen.
2. Insert the specimen into grips of the test machine and attach strain โmeasuring device to it.
3. Begin the load application and record load versus elongation data.
4. Take readings more frequently as yield point is approached.
5. Measure elongation values with the help of dividers and a ruler.
6. Continue the test till Fracture occurs.
7. By joining the two broken halves of the specimen together, measure theย final length and diameter of specimen.
OBESERVATION:-ย
A) Material:
i) Original dimensions
Length = โโโโ
Diameter = โโโ
Area = โโ
ii) Final Dimensions:
Length = โโโโ
Diameter = โโโ
Area = โโ-
OBESERVATION TABLE:-
To plot the stress โ strain curve determine the following
stress โ strain curve |
RESULT:-
i) Average Breaking Stress =
ii) Ultimate Stress =
iii) Average % Elongation =
PRECAUTIONS:-
1. If the strain measuring device is an extensometer, it should be removed
before necking begins.
2. Measure deflection on scale accurately & carefully