- Stress in the Thin Cylinder Subjected to Internal Pressure
- Discussion on Lab Results
I would like to start with the proverb “Err is Human”. All the scientific experiments conducted in the research lab are always subjected to the errors. Most of the errors are due to the human mistakes while taking the reading, and it was called as the parallax errors. This report may contain the certain types of errors. Now, we can analysis about Table 1 and Table 2.
The table 1 speaks about pressure (N/MM 2) and gauge (ε). If a pressure increases the strain also increases. This is a quite physical phenomenon that if a pressure on the material increases, then the material has to deform from its original shape. The deformation is called strain. Deformation depends on the type of material. The table 2 speaks about the practical stress to the theoretical stress. There is a difference between the practical value and theoretical value due to the errors. The errors can be calculated by the following method.
Following the above equation the results for longitudinal stress are shown belowPercentage error for σL=10.97-11.6611.66 ×100% = 5.91%
The experiment results for circumferential stress σLshows very small amount of errors. The reading and experiment we done are most accurate.
Percentage error for σL=22.34-23.3323.33 ×100% =4.24%
The experimental results for circumferential stress σL show that the reading and experiment done by us are accurate because the error values are low. The correct measurement of reading always gives the correct result. The increase in internal pressure increases the strain value. Both longitudinal and circumferential errors are considerably small. The accurate reading on pressure and gauge 1 and gauge 5 provides a good practical value. This gives a good overall result.
- Computer Generated Graph of Pressure Vs Strain
- Comparison/discussion of Slope 1 and 2, obtained from the manual and computer-generated graphs
- Impact Test
- Explain the need of impact testing of engineering materials, and explain the physical meaning of energy absorption.
The impact testing is used to find out the objects ability to resist the high rate of loading. The impact testing is used to determine the energy absorbed in fracturing of an engineering materials at high velocity. The impact testing is one of the important properties that the engineers should consider. The impact testing is a way to measure the service life of the engineering material. Impact testing is used to select the material for aparticular life span. The impact testing is used to find out whether the material is a brittle or ductile. There are two types of impact testing notched bar impact testing and charpy testing. The notched bar impact testing is used to determine the tendency of the material behaves in the brittle manner. The charpy testing is to measure the total energy absorbed in fracturing of the material. Absorption is the process of a substance to attract and hold the particle of another substance. The absorption involves the internal penetration of the substance. The energy absorption is used to absorb the various forms of energy, which is utilized in some way. The absorbed energy is converted into the physical strength. Energy absorption is done in contact with kinetic, electrical, radiation and heat energy.
b. Calculating the energy absorbed for each material used
The energy absorption phenomenon is calculated using the below equation.
Eabsorbed=12mprojectileVBegin2- VEnd2Equation 2
The above equation will calculate the amount of kinetic energy absorbed. This equation will calculate the energy absorbed in the steel.
Eabsorbed=12×23.111.992--0.192
Eabsorbed=45.3418 JThe material tested was mild steel with the dimension of 60*60mm, 1mm thick. Mild steel has a good impact strength because of increasing in yield strength with the rate of a screen. Increase in work hardening at high strain rates. The steel has good standard force.
Testing of Aluminum gives the following result.
Eabsorbed=12×23.111.992--0.072Eabsorbed=45.70 J
The aluminum has absorbed quite good amount of energy because the energy absorption increases in relation to the axial displacement. Aluminum has low standard force as compare to that of steel.
Now, the plastic materials have been tested with the dimension of 60*60mm and 2mm thick.
Eabsorbed=12×23.111.982-1.922Eabsorbed=2.27 J The energy absorbed by the plastic is very low compared to that of mild steel and aluminum because it is very easy to break the plastic materials with a low impact force. The plastic is the weak material compare to steel and aluminum. The standard force value of plastic is very low; it is nearly 500, but the standard force value of the plastic is high compare to that of the other materials; the value is more than 13. The steel has the highest standard force compare to that of aluminum. The standard force of the steel is more than 1000. The aluminum has absorbed the good amount of energy, but not completely. The test result shows the weak energy absorbing nature of the plastic because plastic needs low impact energy to break the structure.
