Introduction: In tensile testing, we can apply load to a metallic specimen, until it breaks. By doing we can determine the tensile strength of materials. When we apply load to specimen, the length of specimen will increase up to a point called yield point. After that point specimen will break. This characteristic of material is called plastic deformation. This quality of these materials is useful for constructions.
Tenso meter:
Tenso meter is used to measure the tensile properties of materials. Applying load and the elongation are displayed on the display.
Universal elongation gage:
Universal elongation gage is used to set initial elongation as zero and measure the elongation of specimen.
Reduction area gage:
Reduction area gage is used to set initial area reduction as zero and measure the area reduction after the experiment.
We can draw this diagram by taking strain as the dependent variable and stress as the independent variable. We can calculate young’s modulus by getting the slope of elastic deformation area. Ultimate tensile strength can be determined as the highest point of the stress –strain diagram.
Procedure:
• Gage length of metallic specimen was measured by Vernier Caliper.
• Diameter of the metallic specimen was measured by Vernier Caliper in three different places.
• Average diameter was taken by using those three diameters.
• Initial cross sectional area was calculated.
• By using universal elongation gage, elongation was set as zero.
• By using area reduction gage, area reduction was set as zero.
• Metallic specimen was fixed in to tenso meter.
• After that, mode of the tenso meter was changed.
• Load was applied to specimen by rotating the axis of tenso meter until it breaks.
• Load and elongation was displayed on the display.
• Load and the elongation were captured by a camera.
• After it broke, two pieces of specimen were taken out.
• Elongation was measured again by using universal elongation gage.
• Area reduction was measured again by using area reduction gage.
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Discussion:
Tensile testing is doing for measure the strength of metals under tensile forces. In this practical we apply tensile forces to metallic specimen by using tenso meter. Because of the force some features like gage length and cross sectional area are changed in specimen. When force is increased, specimen is expand. Because of that gage length will be increased and cross sectional area will be reduced.
Gage length will increase to a maximum point and after that point specimen will be broken.
Stress-Strain curves:
At elastic deformation area stress and strain are proportional to each other.
? = E? ? = stress
? = strain
This is Hooke’s law. E is young’s modulus.
Stress- If force change the material, material is under stress
Strain- change of dimensions respect with original shape
Plasticity- The ability materials have that stay without fracture, after force is removed
Elasticity- The ability that materials have, become to original point after force is removed
Stress-Strain graph of steel
Steel is a ductile material. The stress-strain diagram of steel has elastic strain and plastic strain. So steel has many stages before fracture.
• Yield point
• Ultimate tensile strength point
• Fracture point
Aluminum is a ductile material. Aluminum can be formed in to thin plates, wires and sheets by giving force. In elastic deformation zone aluminum has a straight line. Aluminum can absorb large amount of force. So it takes more time than metal to break. So its plastic strain period is larger than metals.
If we give force to rubber it will stretched and after we remove the force it will return to its natural length. Elastic strain is large and rubber hasn’t plastic strain.
Rubber has plastic deformation
Importance of tensile testing:
By doing this experiment we ca get a knowledge about strength of materials and how much force that materials can bear. So we can use suitable materials for our work by looking at their strength. We can quickly detect problems in the materials by doing this experiment. Tensile testing is very important to engineers. When they designed buildings, bridges or other constructions tensile testing is help them to construct safe and durable constructions. And also material manufactures should know about this tensile testing. If they know about the strength of materials they can make materials in best quality. Tensile testing helps to improve materials.
Errors happened during the experiment
We did experiment three times. First two times experiment was not done in a correct way. At the first time we forgot to set the, initial elongation as zero and initial area reduction as zero. That was our mistake. Because of that calculations might get wrong. So we did experiment again. In the second time specimen was broken at wrong place. This happened because specimen was not a good quality one. We did experiment for third time.
Conclusion:
We got to know about tensile strength of materials through this experiment. And we got an idea about how to measure tensile strength and different stages that materials pass before them break. It helps us to know about characteristics of materials.
