Tension Test of a Bar

In the tension test of a bar, the fractured surface can provide valuable information about the material properties. One particular feature that can be observed on the fractured surface is the shape of the fracture, which can help determine the type of material.

Truncated Cone Fracture

When the fractured surface of a bar exhibits a truncated cone shape, it suggests that the material is medium steel. This type of fracture is characteristic of ductile materials like medium steel, which have the ability to undergo significant plastic deformation before failure.

Explanation

When a material is subjected to tension, it experiences elongation along the axis of the applied force. In ductile materials, such as medium steel, the deformation is not localized and occurs uniformly throughout the specimen. This ductile behavior allows the material to absorb energy and exhibit noticeable plastic deformation before failure.

During the tension test, as the applied load increases, the material undergoes elastic deformation until it reaches the yield point. Beyond the yield point, the material enters the plastic deformation stage, where it continues to deform without a significant increase in stress. This plastic deformation is reversible, meaning the specimen can return to its original shape once the load is removed.

However, as the applied load further increases, the material eventually reaches its ultimate tensile strength (UTS), which is the maximum stress it can withstand. At this point, the material starts to neck down, and the localized deformation becomes more pronounced. Eventually, the necked region becomes unstable, leading to rapid fracture.

The fracture surface of a ductile material like medium steel is typically characterized by a cup-and-cone shape. The cup represents the region where the material necked down, while the cone corresponds to the area where the material underwent plastic deformation before fracture. The cone shape is truncated because the fracture occurred before the entire cone could form.

Conclusion

Based on the fractured surface showing a truncated cone shape, it can be concluded that the material is medium steel. This is because medium steel exhibits ductile behavior, allowing it to undergo significant plastic deformation before failure.