Hairline crack
Hairline cracks are very fine cracks in the surfaces of solids. Hairline cracks in technology are particularly important when testing the materials of workpieces. In medicine, the hairline crack is the easiest form of bone fracture .
Emergence
Hairline cracks are classic material defects , some of which arise during the original molding. They often arise as stress cracks during forming and processing . But they also arise as material fatigue or as environmental stress cracking .
Hairline cracks in materials technology
Hairline cracks are of particular importance in the processing industry, especially in foundry technology, in steel construction, in welding technology in body construction , aircraft construction and mechanical engineering.
Hairline cracks are a potentially growing ( crack growth ) static material weakness in highly stressed assemblies and parts (e.g. wing of a passenger aircraft ). Hairline cracks are particularly dangerous because they can only be detected with special technical tests , but as a sudden chain reaction under normal loads, they can unexpectedly lead to complete material breaks, which in turn lead to serious and fatal accidents. In addition, hairline cracks promote crevice and pitting corrosion .
Hairline crack test
In materials testing, the test for hairline cracks is a standard test due to its high safety-related importance, in which special test methods such as magnetic particle testing and eddy current testing are used. A frequently used alternative, especially for larger test parts, is an intensive visual inspection using special, thin, fluorescent paints that collect in the cracks due to the capillary effect and make the hairline cracks very recognizable under special lighting.
Hairline cracks in construction technology
In components made of concrete, in plastered surfaces and in paint, cracks are considered hairline cracks, provided they are no wider than 0.2 mm. They occur as network cracks with network widths of 1 to 10 cm and are referred to as shrinkage cracks if their cause can be traced back to the rapid drying out of the previously damp building material.
In the event of the impact of impulse-like water pressure forces ( e.g. pressure hammer , pressure surge ) on water-filled imperfections, local blasts can occur in the event of shock wave-like propagation in / on building surfaces.
In structures that are exposed to hydrostatic or hydrodynamic loads, liquid-generated compressive stresses in hairline cracks can lead to their enlargement and ultimately to structural failure.
Web links
- Classification, assessment and repair of cracked plasters and similar Facades (accessed June 26, 2020)
- Repair cracks (accessed June 26, 2020)
- Crack ruler (accessed June 26, 2020)
- Detection of cracks and determination of the crack depth with inductive thermography (accessed on June 26, 2020)
- Structural cracks (accessed on June 26, 2020)
Individual evidence
- ↑ Archive link ( Memento of the original from December 14, 2007 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
