Fatigue Crack Growth
Fatigue crack growth is the enlargement of a crack through repeated loads. With each opening and closing of the crack tip, the crack grows stepwise.
Physico-chemical mechanism of action
Under cyclic loading, the stress in the material structure alternates between tensile and compressive stress. This causes the crack tip to open and close frequently, leading to microscopic damage in the material and enlarging the crack.
Metallurgical relevance & risks in welding
Fatigue cracks can occur in weld areas, especially under high stress fields and many loading cycles. They lead to crack propagation and can cause material fracture. A common example is fatigue failure of components in machinery.
Workshop practice & action instructions
To avoid fatigue crack growth, during welding:
• High stress field distribution in the material should be minimized.
• The number of load cycles should be reduced by making the material stronger or optimizing the load.
• Under high loads, an additional weld inspection should be performed.