Stress concentration
Stress concentrations may also occur from accidental damage such as nicks and scratches.
[2] For ductile materials, large loads can cause localised plastic deformation or yielding that will typically occur first at a stress concentration allowing a redistribution of stress and enabling the component to continue to carry load.
However, repeated low level loading may cause a fatigue crack to initiate and slowly grow at a stress concentration leading to the failure of even ductile materials.
Geometric discontinuities cause an object to experience a localised increase in stress.
Examples of shapes that cause stress concentrations are sharp internal corners, holes, and sudden changes in the cross-sectional area of the object as well as unintentional damage such as nicks, scratches and cracks.
Inclusions on the surface of a component may be broken from machining during manufacture leading to microcracks that grow in service from cyclic loading.
of the gross cross-section and defined as[3] Note that the dimensionless stress concentration factor is a function of the geometry shape and independent of its size.
The maximum stress felt near a hole or notch occurs in the area of lowest radius of curvature.
In practice, however, material inconsistencies such as internal cracks, blowholes, cavities in welds, air holes in metal parts, and non-metallic or foreign inclusions can occur.
Contact Stress: Mechanical components are frequently subjected to forces that are concentrated at specific points or small areas.
This localized application of force can result in disproportionately high pressures at these points, causing stress concentration.
Geometric Discontinuities: Features such as steps on a shaft, shoulders, and other abrupt changes in the cross-sectional area of components are often necessary for mounting elements like gears and bearings or for assembly considerations.
While these features are essential for the functionality of the device, they introduce sharp transitions in geometry that become hotspots for stress concentration.
Additionally, design elements like oil holes, grooves, keyways, splines, and screw threads also introduce discontinuities that further exacerbate stress concentration.
These imperfections, although often small, can significantly impact the durability and performance of mechanical components by initiating stress concentration.
During the design phase, there are multiple approaches to estimating stress concentration factors.
The drilled hole, with its relatively large size, serves to increase the effective crack tip radius and thus reduce the stress concentration.
[16] Another example is in a threaded component, where the force flow line is bent as it passes from shank portion to threaded portion; as a result, stress concentration takes place.
The optimal mitigation technique depends on the specific geometry, loading scenario, and manufacturing constraints.
