Mikrorisse

Mikrorisse, or microcracks, are tiny cracks or fissures that form in solid materials. They typically measure from nanometers to micrometers in length and can be found in metals, ceramics, polymers, concrete, and rocks. Microcracking often occurs as part of a material’s deformation history or in response to external stimuli, and they may remain dormant or grow into larger fractures under appropriate conditions.

Causes and formation mechanisms include the accumulation of elastic and plastic stresses that exceed local strength, thermal cycling that creates differential expansion, phase transformations, chemical attack such as corrosion or hydration reactions, and environmental effects like freeze-thaw cycles. Microcracks may originate at grain boundaries, interfaces, inclusions, or defects and can nucleate from stress concentrations around these features.

Impact on material properties can be significant despite their small size. Microcracks can reduce stiffness and strength, increase permeability, and serve as initiation sites for macrocracks under loading. In fatigue, microcracks can propagate slowly, following subcritical crack growth laws, and alter the durability and lifetime of components. In geoscience, microcracking affects porosity, permeability, and seismic properties of rocks.

Detection and characterization rely on several techniques. Optical and scanning electron microscopy allow direct observation on prepared samples. X-ray computed tomography provides 3D imaging of crack networks. Nondestructive methods such as ultrasonic testing, dye penetrant inspection, infrared thermography, and acoustic emission monitoring help assess crack presence and growth, especially in service.

Mitigation strategies focus on improving material microstructure and processing, reducing residual stresses, protecting against environmental attack, and controlling temperature and moisture exposure to limit microcrack initiation and growth.