Theory
To conduct direct tensile test
on the given steel specimen according to I.S. 1608 – 1972 draw the stress
strain diagram and determine its mechanical properties.
Apparatus
1. Universal
testing machine
2. Vernier
calipers
3. Extensometer
scale
4. Punch
and steel specimen
General
Top steel is almost replacing
mild steel in reinforced cement concrete construction because of its increased
tensile strength with nominal increase in cost moreover the band strength of
mild steel bars moreover the increase in strength is a compared by increase in
ductility.
Diagram
Universal Testing Machine
Procedure
The test procedure is almost
similar to that on mild steel bar. However the bar is not machined. The
dimensions of the specimen are measured accurately. The dimensions of the
specimen are measured accurately. The initial length is carefully marked by
punch mark.
The specimen is placed between
grips and the load is applied gradually. The extensometer readings are taken at
regular intervals unlike in the case of mild steel no. definite yield point is
observed for plain steel specimens. However when the strain is about 0.5% the
extensometer is removed and further extensions are measured with vernier
calipers. The work load and bearing load are noted. After the specimen breaks the
final gauge length is plotted upto failure. All the required mechanical
properties are calculated.
Observation
1. Length
of the bar is É» = 59.5 cm
2. Diameter
of the bar is D = 1.0029 cm
3. Weight
of the bar is w = 369 gm
4. Area of
the bar A = 3.14
/ 4 x
d2
= 3.14 / 4 x
(1.0029)2
= 0.789 cm2
5. Stress
δ = P/A = 680 / 0.789 = 861.85 N/mm2
Conclusion
As per I.S. 432 part I, the
minimum recommended values for yield stress for I.S. grade I
The ultimate tensile stress =
52.75 kg/mm2
Percent minimum elongation =
3.19 x 100 =
As per I.S. 1786 – 1966, the
minimum recommended values are 0.2 % proof stress is 47 kg/mm2.
Ultimate stress 48.5 kg/mm2
Percent of elongation = 3.19 %
The values obtained more than
recommended values.
Result
The obtained values are more
than specified values.
