TORSION TEST.docx

TORSION TEST OF MILD STEEL AND CAST IRONName: Tian Yunfan Student ID: 09332005Sun Yat-sen University 09 Civil EngineeringDATE: 2010.11.201) INTRODUCTIONThis Lab investigates the different properties of mild steel and cast iron when they are in torsion. More specifically, we will analyze the stresses and strains in members of circular cross section subjected to twisting couples, or torques. The torsion strength is the capacity of a material to withstand twisting couples.And for the torsion test, which is a fundamental material science test, defined as a standard test piece is gripped at either end by suitable apparatus in a testing machine which slowly exerts torques so that the test piece is rotated until it breaks. The test provides information on yield torsion strength, breaking torsion strength, and shear modulus of the material. Construction members in engineering not only bear tension, compression and shearing stress but also bear torsion, like transmission shaft. In order to design the members better, we should understand the mechanical properties of materials under torsion. So the torsion test plays an important role in engineering material test.2) OBJECTIVES1. Measure the shear modulus of mild steel G.2. Measure the yield torsion strength s and breaking torsion strength b.3. Measure the breaking torsion strength b of cast iron.4. Compare the torsion-angle curves of mild steel and cast iron and find the differences. 5. Observe the characteristics of the region of fracture.3) EQUIPMENT1. The torsion testing machine ND-500C.2. Vernier caliper.3. Troptumeter.4) Specimen The shape and dimensions are as shown in Figure 3.1 according to the Chinese standard 金属室温扭转试验方法GB10128-88. Recommend d0=10mm, l0=50 or 100mm, then lc=70 or 120mm. If d0 is not 10mm ,then lc=l0+2d0。 Measure the diameters respectively in two perpendicular directions at the two ends and in the center of the specimen, and then calculate arithmetic mean. We will apply the arithmetic mean in the three places to calculate the polar moment of inertia Ip. But apply the minimum average diameter in the three places to calculate section modulus W。4) PRINCIPLE AND METHODS1. Torsion Test for Mild SteelMild steel is a typical ductile material. The typical T- diagram of mild steel is shown below.In the elastic stage, the angle of twist under torque T is: =TLGIIn the loading process, the computer can draw the T- curve automatically. In the elastic stage, grows linear to T, so as shear strain and shear stress, see Fig. (a). As T increase, the shear stress at the edge of plane reach the yield torsion strength s, and the T- curve begin to turn down. The plastic region begins to expand to the origin gradually, but the center area is still elastic, see Fig. (b). Then the torque T increase, when the entire plane become plastic, see Fig. (c), the T- curve become smooth, the corresponding torque is Ts. After the yield point, as the angle of twist increases, the torque T increases slowly. Continue to load until the maximum torque Tb, the corresponding breaking torsion stress is b.2. Torsion Test for Cast IronCast iron is a typical brittle material, it will repute under small deformation. The typical T- diagram of cast iron is shown above. Because of the linearity of curve, we can calculate b by: b=TcJBecause the cast iron is brittle material, it doesnt have a yield process and the proportional line is not obvious. 3. Measure the shear modulus G. We can measure G by using graphic method. According to the T- curve, read the corresponding increment of torque and angle, and calculate G by: G= T L IWhere L is the length of troptumeter.5) PROCEDURES1. Torsion Test for Mild Steel1. Measure the size of mild steel.2. Adjust the position of grip. Grip the specimen at either end by suitable apparatus. 3. Set the computer, select the torque, angle of twist, and set zero to T and . Before the yield point, the loading speed is 6/min, after the yield point the load speed is 360/min.4. Clump the specimen.5. Start the machine; record the T- curve.6. The mild steel is broken, stop the machine, and print the result.2. Torsion Test for Cast Iron1. Measure the size of cast iron2. Adjust the position of grip. Grip the specimen at either end by suitable apparatus. 3. Set the computer, select the torque, angle of twist, and set zero to T and . the loading speed is 6/min.4. Clump the specimen.5. Start the machine; record the T- curve.6. The cast iron is broken, stop the machine, and print the result.6) DATE AND RESULT1. Torsion Test for Mild SteelTable 1: Size of Mild SteelMaterialTop(cm)Middle(cm)Bottom(cm)121212Mild Steel0.9981.0000.9820.9860.9940.992average0.9990.9840.993Average diameter d0 = (0.999+0.984+0.993) / 3 = 0.992cm.Table 2: Shear ModulusTorque (Nm)Angle of twist ()Shear Modulus(GPa)15.00291.04334686.6608715.163211.05697586.4574915.309141.06608286.5438915.466081.07518886.6906115.62151.08881786.4657415.773851.09792486.584815.929271.10703186.7186116.078251.1206686.4651516.232141.12976686.5891516.384491.13887386.7029416.535011.15250286.4647316.685831.16160886.569416.837881.17523886.3451216.996661.18434486.4892117.152071.19799486.2855617.310851.207186.4273817.470861.21620786.573117.626581.22983686.3767917.783521.23894386.5052817.940461.24804986.6319618.092821.26167886.4239218.249761.27530886.2418918.408541.28441486.3754918.557531.29352186.46153We select the 25 torque values between 15 and 20 Nm, because it is the linear stage. And we calculate Modulus by formula:G= T L JWhere J= 12 (d0/2)4 = 9.5070676*10-10 m4Mean value of shear modulus = 86.5021 GPa.Table 3: The T- curve of Mild SteelTable 4: Performance IndexesYield Torque Ts (Nm)39.50Moment of Inertia J (m4)9.5070676*10-10 m4Yield Torsion Stress s (MPa)206.78Breaking Torque Pb (Nm)99.71Breaking Torsion Stress b (MPa)520.20Shear modulus G (GPa) 86.50212. Torsion Test for Cast IronTable 1: Size of Cast IronMaterialTop(cm)Middle(cm)Bottom(cm)121212Cast Iron1.0061.0041.0101.0041.0061.008average1.0051.0071.007Average diameter d0 = (1.005+1.007+1.007) / 3 = 1.006cmJ=12 （d0/2）4=1.006*10-9 m4Table 2: The T- curve of Cast IronTable 3: Performance IndexesBreaking Torque Pb (Nm)58.46Moment of Inertia J (m4)1.006*10-9Breaking Torsion Stress b (MPa)292.37). DISCUSSION AND CONCLUSION1. Torsion Test 1. From the lab, we can know the yield torsion stress s, breaking torsion stress b, and the average shear modulus G of mild steel.2. We also know the breaking torsion stress b of cast iron.3. T- curves of different materials vary widely. It is possible to distinguish some common characteristics among the P- curves and divide materials into two board categories on the basis of these characteristics, namely, the ductile materials and the brittle materials.4. Mild steel is a typical type of ductile materials, which has 2 particular stages and behaves typically in each part; cast iron is a typical type of brittle materials, which has no yielding at all. In fact cast iron fails directly at a very small angle of twist without any additional phenomenon visible.5. And for the fracture region, mild steel breaks along a plane perpendicular to its longitudinal axis. On the other hand, cast iron is weaker in tension than in shear. Thus, when subjected to torsion, cast iron tends to break along surface which f