Torsion Test on Mild Steel and Cast Iron - Lab Report

对

1. 碳钢样品
2. Cast iron specimen

Purpose:

1. To study the shear stress ~ shear strain behavior of the material.
   
2. To study the failure pattern of these materials in torsion.
   
3. To determine the mechanical properties, e.g, Modulus of elasticity, Modulus of rigisity, Shear strength, shear strain and ductility in torsion.

仪器：

1. 10 Ton Buskton Universal Testing Machine
2. Vernier caliper
3. Steel Rule

Procedure of the Test:

1. 注意尺寸并绘制样品的形状。
   （注意有效长度，总长度，直径表等）
   
2. Fix specimen into 10 Ton Buckton UTM.
   
3. Use twist control method (other one is torsional strain control method)
   
4. To apply the twist to the sample, rotate the handle counter clock wise for required degree of twist. Machine’s one complete cycle will give 4° of twist.
   
5. Balance arm of the machine will get disturbed again. Try to balance it with the help of concerned handle and note down the value of balancing load.
   
6. 重复相同的步骤，并增加扭曲价值，直到成员失败为止。
   Lever arm = 50.8mm
   扭矩=杠杆臂x负载16T
   
   
7. Examine the failure pattern of the specimen and draw sketch after failure.(same for cast iron )

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Observations and Calculations:

Related Theory:

1. Torque:

Twisting effect of couple or force is called as torque. It is denoted by double head arrow.

2. Torsion:

Torque applied in a plane perpendicular to the longitudinal axis of a member is called as
扭转。

3. Difference between Torque and Moment:

4. Twisting Moment:

It is the summation of torque either left or right of the section.

5. Bending Theory:

6. Torsion Theory:

Assumptions:

1. Material is homogenous.
   
2. Circular section remains circular and do not warp.
   
3. 一架飞机的部分a material perpendicular to its longitudinal axis remain plane and do not warp after the torque is applied.
   
4. Shaft is loaded by a couple or torque in a plane perpendicular to the longitudinal axis of the plane.
   
5. 剪切应力与剪切应变成正比，这意味着钩的定律适用。
   
6. In circular shafts subjected to torque shearing strain varies linearly.

Where,

t, Shearing stress in MPa
r，轴的半径为mm。
T，扭曲的时刻。
J，极性惯性。
G, Modulus of rigidity.
θ扭曲角度。
L，标本 /轴的长度

7. Polar moment of inertia:

The geometric rigidity of the X-sec is termed as polar moment of inertia. It is the resistance against twisting, summation of 2 moment of area about x-axis.

Circular Section:

For Hollow Shaft:

Torsional Rigidity / Modulus of Rigidity / Modulus of Elasticity in Shear:

"When material is subjected to pure twist loading, the slope of shear stress verses shear strain curve is termed as modulus of rigidity ( modulus of elasticity in shear, torsional rigidity)

9.毒药比率：

当材料承受轴向载荷并且始终小于1时，侧应变与纵向应变的比率。

10. Relation between yield strength in tension to torsion for mild steel:

The relationship between yield stress in simple tension and that in pure shear can be found from VON MISES for a yield criteria.

11. Torsional Strength:

• 它是承受扭转载荷的材料的最终强度。
  
• 材料在破裂前持续的最大扭转应力。
  
• 它类似于拉伸强度。

12. Torsional Deformation:

Angular displacement of specimen caused by specified torque in torsion test. It is equal to angle of twist in radians divided by gauge length or effective length.

13. Torsional Strain, y:

Strain corresponding to specified torque in torsion test. It is equal to torsional deformation multiplied by the radius of the shaft. It's units are radians.

14. Torsional Stress, T:

在旋转轴扭转试验中经受特定扭矩的材料中产生的剪切应力。可以使用表达式计算。

15. Expected failure for Mild Steel and Cast Iron Specimens and reasoning:

Fracture in torsion for ductile materials generally occur in the plane of maximum shear stress perpendicular to the axis of bar where as for the brittle material failure occurs along 45° hilux to the axis of bar due to tensile stress across that plane.