Crack Closure
Crack face rubbing is the premature closure of crack faces due to plastic deformation or oxide layers. This reduces the stress intensity and enlarges the crack opening.
Physical-Chemical Mechanism of Action
Crack surface friction occurs when cracks close too early during the unloading phase. This can be caused by plastic deformation or oxide layers. Oxide layers mechanically close the cracks, and plastic deformation can directly press the crack faces together.
Metallurgical Relevance & Risks in Welding
Crack surface friction increases the stress at the crack faces, which can lead to larger crack openings. This can alter the microstructure and impair the mechanical properties of the material. In the workshop, this can lead to undesirable weld defects such as hot cracking or distortion.
Workshop Practice & Instructions
To avoid crack surface friction, it is important to perform careful stress relief and cleaning of the weld. This can be achieved by using deoxidizing agents and controlled cooling. A correct cooling time (t8/5) is crucial to stabilize the microstructure and prevent crack surface friction.