20.8 : 应力集中

The equation for stress for a member under pure bending having a plane of symmetry and a uniform cross-section assumes that the stress is evenly distributed across the entire cross-sectional area.

However, in real-world applications, the cross-section of a member may vary, or it may have geometric irregularities, such as a flat bar with grooves.

In such cases, the maximum stress is expressed using the stress concentration factor. The stress concentration factor is the ratio of the maximum stress to the nominal stress.

The maximum stress is the highest stress present at the discontinuity, and the nominal stress is the stress calculated using the composite cross-section.

Consider a plate with a U-shaped notch under bending stress. For this scenario, the stress concentration factor increases as the geometry of the notch becomes more pronounced.

For a round bar with a circular hole subjected to pure bending, the stress concentration factor is calculated using the ratio of the diameter of the hole to the diameter of the round bar.