Impact Testing
Impact Testing
Sheffield Hallam University Department of Engineering and Maths Faculty of Arts, Computing, Engineering and Science
For the attention of:
Liang Bo
Report author:
Avinash Gorania
Report author ID:
23042594
Module name & code: Mechanical Engineering Course name:
Automotive Engineering
Date:
11-03-2014
Introduction: A method for determining behaviour of material subjected to shock loading in bending, tension, or torsion. The quantity usually measured is the energy absorbed in breaking the specimen in a single blow, as in the Charpy Impact Test, Izod Impact Test, and Tension Impact Test. Impact tests also are performed by subjecting specimens to multiple blows of increasing intensity, as in the drop ball impact test, and repeated blow impact test. Impact resilience and scleroscope hardness are determined in non-destructive impact tests. Impact resistance is one of the most important properties for a part designer to consider, and without question, the most difficult to quantify. The impact resistance of a part is, in many applications, a critical measure of service life. More importantly these days, it involves the perplexing problem of product safety and liability. The aim of this experiment is to analyze fracture of materials (using the Hounsfield Balanced impact test machines) and the dependency on the temperature. In this experiment we use four different types of materials for analysis. The materials used are Steel, Brass, zinc and Nylon 66. Each material is tested by maintaining their temperatures at -78, 0, room temperature (23), 50 and 100 degree centigrade. We use ovens, ice, dry CO2, flasks to accomplish this. Each specimen piece is notched to guide the fracture in desired path. Each material sample used is of the same size and shape and loads used are also alike. Background: The fracture of a solid almost always occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displacement develops in this case perpendicular to the surface of displacement, it is called a normal tensile crack or simply a crack; if a displacement develops tangentially to the surface of displacement, it is called a shear crack, slip band, or dislocation Fracture strength, also known as breaking strength, is the stress at which a specimen fails via fracture. This is usually determined for a given specimen by a
tensile test, which charts the stress-strain curve. The final recorded point is the fracture strength. Ductile materials have fracture strength lower than the ultimate tensile strength (UTS), whereas in brittle materials the fracture strength is equivalent to the UTS. If a ductile material reaches its ultimate tensile strength in a load-controlled situation, it will continue to deform, with no additional load application, until it ruptures. However, if the loading is displacement-controlled, the deformation of the material may relieve the load, preventing rupture.
Procedure: Materials are prepared according to dimensions and a notch of 2mm with 45 degree angle is made to guide the fracture when impacted with load. Four materials are taken namely Steel, Brass, zinc and Nylon 66. From each material five specimen are taken. Each specimen of each material is maintained at different temperatures. Specimens maintained at -780C are cooled using solid CO2. Specimens maintained at 00C are cooled using normal ice and specimens maintained at 50 0C and 1000C are heated using oven. The cooled specimens are cooled in thermally insulated flasks and heated specimens are kept in oven. Before the experiment starts all safety measures are to be taken. As the experiment involves use of heavy loads and there is a change of material shutter, safety goggles are mandatory. As the materials involved are of different temperatures, safety gloves or tongues are to be used.
Now each material is taken and kept in the apparatus. The impact equipment is started and the load is impacted on the specimen to fracture. The experiment is repeated for the temperatures of -780, 00, room temperature, 500 and 1000 for each
material. For each impact, the digital impact reading shown on the digital display is noted. The residual material after impact is removed using tongues. Once the experiment is completed for all temperatures of one material, the platform is cleared and the experiment is repeated for all the materials. The Samples collected after impact is tested under a microscope and analysis is made for each material. The similarities and differences are drawn and the nuclear structure is studied.
Results:
Material
Testing Temperature -78oc
0oc
+50oc
Room
+100oc
Temperature (22oc) Mild Steel
27.92 J
48.29 J
49.89 J
49.88 J
49.13 J
Brass
19.07 J
34.38 J
17.98 J
16.68 J
16.06 J
Zinc
0.44 J
0.89 J
1.57 J
2.34 J
28.31 J
Nylon 66
0.17 J
0.53 J
0.47 J
1.88 J
5.35 J
The experiment is carried out for mild steel, brass, zinc and nylon 66 and it is repeated at different temperatures. The corresponding readings are noted as shown in the above table. The samples after being tested are shown in the figure below. Based on the material property, the samples reacted for the impact load. For example, Nylon and zinc are clearly broken into two pieces where as mild steel had a partial fracture as its toughness is high.
Discussion of Results: The below graph shows the relationship between impact energy and temperature for each of mild steel, brass and zinc. Now, if we consider mild steel, the impact energy at -780C is very less and is increasing till 00C. Then, the impact energy of mild steel almost became constant. The same for zinc is completely different. By looking at the graph, we can say that the impact energy of zinc at lower temperature is very less. As the temperature rises from 500C impact energy starts rising steeply. For brass, from the graph, we can clearly say that impact energy is almost independent of temperature as the variation in energy is very less across different ranges of temperature.
Impact energy vs Testing temperature 60
Impact energy
50 40 Mild Steel
30
Brass 20
Zinc
10
Nylon 66
0 -78
0
22
50
100
Testing Temperature
For Nylon 66 the impact energy required is across all the temperature ranges. You can see from the graph that there is not much variation in the Impact Energy across the temperature. A Comparison of the structure of the zinc and mild steel is studied under microscope. When relating the two micro structural features of zinc and mild steel, there are some resemblances and variances that can be seen. The zinc at -78oC, the edges are built up in layers and have a smooth appearance where as In mild steel at -78oC, it appears that the material is not divided but is cut off in to pieces by the impact. It has a likeness to a rocky surface. On the other hand, when carefully observing zinc at
100oC, it looks comparable to the look of mild steel at -78oC, in terms of how the fracture initiated by the cut forms shapes. Mild steel at 100oC appears to have numerous small shapes that are of all sizes. It shows that mild steel is more brittle on -78oC because the size of the crystals have become bigger, resulting in it being easier to break. At 100 oC on the other hand, is much smaller meaning it is more difficult to break as it is more malleable. This is why the value for impact energy absorbed is much higher at the higher temperature. The pores on the zinc are the same on the mild steel. If the zinc has large crystals under the microscope then it is easier to break whereas if the crystals are smaller, than it is harder to break as it is less brittle. Another discussion can be made as to what would have happened if un-notched and unbiased specimens are used instead on notched specimens. There would have been a lot of variation in results if un notched specimens are used. Notch directs the fracture and would make material break at lower impact energies. If we were to discuss the Impact energies of the materials rather than their behaviour at various temperatures then use of un-notched specimens would have been more appropriate.
Conclusion: From the experiment we can conclude that the impact energy at which the material fractures depends on the temperature of the material. The results are consistent and have repeatability. The Nilon 66 has lowest impact energy as compared with remaining materials under consideration as nilon is a non metal and brittle in nature we can support the results.
Also The steel has highest impact energy required for
material to fail, as steel is ductile and is a touch metal the results can thus be explained. The ductility and brittleness of the material is also studied and can be concluded that both will vary depending on the temperature of the material. According to results we can say that at the low temperatures the materials are becoming more ductile and as the temperature increase the ductility of the material increases. Thus we can say that metals are well suited for high temperature uses and if any metal is used to be used for low temperature uses like ship or space shuttle construction much focus is to be kept on selection of material and exclusive study is to be done on the nature and behaviour of the material before using it.
References: 1. Cherepanov, G.P., Mechanics of Brittle Fracture 2. Jump up to: a b Degarmo, E. Paul; Black, J T.; Kohser, Ronald A. (2003), 3. Materials and Processes in Manufacturing (9th ed.), Wiley, p. 32, ISBN 0-47165653-4. 4. Jump up C. H. Chen, H. P. Zhang, J. Niemczura, K. Ravi-Chandar and M. Marder (November 2011).
Sheffield Hallam University Department of Engineering and Maths Faculty of Arts, Computing, Engineering and Science
For the attention of:
Liang Bo
Report author:
Avinash Gorania
Report author ID:
23042594
Module name & code: Mechanical Engineering Course name:
Automotive Engineering
Date:
11-03-2014
Introduction: A method for determining behaviour of material subjected to shock loading in bending, tension, or torsion. The quantity usually measured is the energy absorbed in breaking the specimen in a single blow, as in the Charpy Impact Test, Izod Impact Test, and Tension Impact Test. Impact tests also are performed by subjecting specimens to multiple blows of increasing intensity, as in the drop ball impact test, and repeated blow impact test. Impact resilience and scleroscope hardness are determined in non-destructive impact tests. Impact resistance is one of the most important properties for a part designer to consider, and without question, the most difficult to quantify. The impact resistance of a part is, in many applications, a critical measure of service life. More importantly these days, it involves the perplexing problem of product safety and liability. The aim of this experiment is to analyze fracture of materials (using the Hounsfield Balanced impact test machines) and the dependency on the temperature. In this experiment we use four different types of materials for analysis. The materials used are Steel, Brass, zinc and Nylon 66. Each material is tested by maintaining their temperatures at -78, 0, room temperature (23), 50 and 100 degree centigrade. We use ovens, ice, dry CO2, flasks to accomplish this. Each specimen piece is notched to guide the fracture in desired path. Each material sample used is of the same size and shape and loads used are also alike. Background: The fracture of a solid almost always occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displacement develops in this case perpendicular to the surface of displacement, it is called a normal tensile crack or simply a crack; if a displacement develops tangentially to the surface of displacement, it is called a shear crack, slip band, or dislocation Fracture strength, also known as breaking strength, is the stress at which a specimen fails via fracture. This is usually determined for a given specimen by a
tensile test, which charts the stress-strain curve. The final recorded point is the fracture strength. Ductile materials have fracture strength lower than the ultimate tensile strength (UTS), whereas in brittle materials the fracture strength is equivalent to the UTS. If a ductile material reaches its ultimate tensile strength in a load-controlled situation, it will continue to deform, with no additional load application, until it ruptures. However, if the loading is displacement-controlled, the deformation of the material may relieve the load, preventing rupture.
Procedure: Materials are prepared according to dimensions and a notch of 2mm with 45 degree angle is made to guide the fracture when impacted with load. Four materials are taken namely Steel, Brass, zinc and Nylon 66. From each material five specimen are taken. Each specimen of each material is maintained at different temperatures. Specimens maintained at -780C are cooled using solid CO2. Specimens maintained at 00C are cooled using normal ice and specimens maintained at 50 0C and 1000C are heated using oven. The cooled specimens are cooled in thermally insulated flasks and heated specimens are kept in oven. Before the experiment starts all safety measures are to be taken. As the experiment involves use of heavy loads and there is a change of material shutter, safety goggles are mandatory. As the materials involved are of different temperatures, safety gloves or tongues are to be used.
Now each material is taken and kept in the apparatus. The impact equipment is started and the load is impacted on the specimen to fracture. The experiment is repeated for the temperatures of -780, 00, room temperature, 500 and 1000 for each
material. For each impact, the digital impact reading shown on the digital display is noted. The residual material after impact is removed using tongues. Once the experiment is completed for all temperatures of one material, the platform is cleared and the experiment is repeated for all the materials. The Samples collected after impact is tested under a microscope and analysis is made for each material. The similarities and differences are drawn and the nuclear structure is studied.
Results:
Material
Testing Temperature -78oc
0oc
+50oc
Room
+100oc
Temperature (22oc) Mild Steel
27.92 J
48.29 J
49.89 J
49.88 J
49.13 J
Brass
19.07 J
34.38 J
17.98 J
16.68 J
16.06 J
Zinc
0.44 J
0.89 J
1.57 J
2.34 J
28.31 J
Nylon 66
0.17 J
0.53 J
0.47 J
1.88 J
5.35 J
The experiment is carried out for mild steel, brass, zinc and nylon 66 and it is repeated at different temperatures. The corresponding readings are noted as shown in the above table. The samples after being tested are shown in the figure below. Based on the material property, the samples reacted for the impact load. For example, Nylon and zinc are clearly broken into two pieces where as mild steel had a partial fracture as its toughness is high.
Discussion of Results: The below graph shows the relationship between impact energy and temperature for each of mild steel, brass and zinc. Now, if we consider mild steel, the impact energy at -780C is very less and is increasing till 00C. Then, the impact energy of mild steel almost became constant. The same for zinc is completely different. By looking at the graph, we can say that the impact energy of zinc at lower temperature is very less. As the temperature rises from 500C impact energy starts rising steeply. For brass, from the graph, we can clearly say that impact energy is almost independent of temperature as the variation in energy is very less across different ranges of temperature.
Impact energy vs Testing temperature 60
Impact energy
50 40 Mild Steel
30
Brass 20
Zinc
10
Nylon 66
0 -78
0
22
50
100
Testing Temperature
For Nylon 66 the impact energy required is across all the temperature ranges. You can see from the graph that there is not much variation in the Impact Energy across the temperature. A Comparison of the structure of the zinc and mild steel is studied under microscope. When relating the two micro structural features of zinc and mild steel, there are some resemblances and variances that can be seen. The zinc at -78oC, the edges are built up in layers and have a smooth appearance where as In mild steel at -78oC, it appears that the material is not divided but is cut off in to pieces by the impact. It has a likeness to a rocky surface. On the other hand, when carefully observing zinc at
100oC, it looks comparable to the look of mild steel at -78oC, in terms of how the fracture initiated by the cut forms shapes. Mild steel at 100oC appears to have numerous small shapes that are of all sizes. It shows that mild steel is more brittle on -78oC because the size of the crystals have become bigger, resulting in it being easier to break. At 100 oC on the other hand, is much smaller meaning it is more difficult to break as it is more malleable. This is why the value for impact energy absorbed is much higher at the higher temperature. The pores on the zinc are the same on the mild steel. If the zinc has large crystals under the microscope then it is easier to break whereas if the crystals are smaller, than it is harder to break as it is less brittle. Another discussion can be made as to what would have happened if un-notched and unbiased specimens are used instead on notched specimens. There would have been a lot of variation in results if un notched specimens are used. Notch directs the fracture and would make material break at lower impact energies. If we were to discuss the Impact energies of the materials rather than their behaviour at various temperatures then use of un-notched specimens would have been more appropriate.
Conclusion: From the experiment we can conclude that the impact energy at which the material fractures depends on the temperature of the material. The results are consistent and have repeatability. The Nilon 66 has lowest impact energy as compared with remaining materials under consideration as nilon is a non metal and brittle in nature we can support the results.
Also The steel has highest impact energy required for
material to fail, as steel is ductile and is a touch metal the results can thus be explained. The ductility and brittleness of the material is also studied and can be concluded that both will vary depending on the temperature of the material. According to results we can say that at the low temperatures the materials are becoming more ductile and as the temperature increase the ductility of the material increases. Thus we can say that metals are well suited for high temperature uses and if any metal is used to be used for low temperature uses like ship or space shuttle construction much focus is to be kept on selection of material and exclusive study is to be done on the nature and behaviour of the material before using it.
References: 1. Cherepanov, G.P., Mechanics of Brittle Fracture 2. Jump up to: a b Degarmo, E. Paul; Black, J T.; Kohser, Ronald A. (2003), 3. Materials and Processes in Manufacturing (9th ed.), Wiley, p. 32, ISBN 0-47165653-4. 4. Jump up C. H. Chen, H. P. Zhang, J. Niemczura, K. Ravi-Chandar and M. Marder (November 2011).
