Stress Concentration Factor in Welded Joints

Stress concentration factor (Kt) is defined as the ratio of maximum stress to the nominal stress. In welded joints, Kt is used to evaluate the effect of the weld geometry on the stress distribution and the fatigue life of the joint.

Factors affecting the Kt value in welded joints are:

1. Weld Geometry
2. Material properties
3. Loading conditions

Among these factors, weld geometry has a significant effect on the Kt value.

Effect of Weld Geometry on Kt Value

Weld geometry refers to the shape and size of the weld. The weld geometry affects the stress distribution in the joint and hence the Kt value.

The following are the weld geometries that affect the Kt value:

1. Reinforced butt welds
2. Toe of transverse fillet welds
3. End of parallel fillet welds
4. T-butt joint with sharp corner

Among these, the end of parallel fillet welds and T-butt joint with sharp corner have the highest Kt value.

Explanation of the Correct Answer

Option C is the correct answer, which states that the stress concentration factor is highest at the end of parallel fillet welds. The following are the reasons why the Kt value is highest at the end of parallel fillet welds:

1. Stress concentration at the end of the weld: At the end of the parallel fillet weld, the stress concentration is high due to the sudden change in geometry. The stress concentration causes a high Kt value.

2. High bending stress: The end of the parallel fillet weld is subjected to high bending stress due to the applied load. The bending stress causes a high Kt value.

3. Fatigue crack initiation: The high Kt value at the end of the parallel fillet weld promotes the initiation of fatigue cracks. The cracks propagate due to cyclic loading, leading to failure of the joint.

Conclusion

The stress concentration factor (Kt) is used to evaluate the effect of weld geometry on the stress distribution in the joint. Among the weld geometries, the end of parallel fillet welds has the highest Kt value due to stress concentration, high bending stress, and fatigue crack initiation. Therefore, it is necessary to consider the weld geometry while designing the joint to ensure a longer fatigue life.