Experiment No. 4
Name: Stress concentration.
Aim: To study the effect of notch and welding
joint through comparing the tensile and fracture strength of these processed
pieces with non deformed standard tensile specimen of same dimensions.
Introduction: In order
to understand the effect of machining process on the pieces like making a notch
or scratch occurred during a process, or welding two pieces together it is
required to make a tensile test for these pieces to compare the mechanical
properties under different conditions. From this comparison a clear idea was
taken for the effect of any process on the original mechanical properties.
Theory:
σ
max = Kt * σnom , σnom = F / Area
Notched
Rectangular bar in Tension
Procedure & Calculations:
1-
Fix the first sample [non deformed sample] in the tensile test
machine and record the value of the yield, ultimate & fracture load.
2-
Measure the new dimensions of tested sample after fracture [Gauge
length & width].
3-
Calculate the yield, ultimate & fracture strength and the percentage
of elongation & area reduction of the first sample after fracture.
4-
Repeat the steps 1, 2 &
3 for sample 2 (with notch) & sample 3 (with welding).
5-
Compute the percentage of strengths change, elongation change
between the three samples.
The samples
test that to be used in the experiment [as per the standard] are:
Discussions:
1-
What is the importance of getting the stress concentration factor
on design process? What the factors that
should be taken in consideration in the elements design?
2-
Compare the results of sample 2 & 3 with sample 1 independently
by getting the percentage stresses increasing or reduction? Also repeat the calculation for the
percentage area & elongation increasing or reduction?
3-
Is the fracture of the notched sample occurred at the notched area?
How can you reduce the effect of the notches on stress concentrating?
4-
Is the failure occurred in
the welding area or away? What indications you got from both cases? How can you
improve the welding?
