Throughcracks

Throughcracks are cracks that extend completely through the thickness of a material or component, creating an opening that connects opposite faces. They are a major concern in structural integrity, particularly for plates, shells, welds, and pressure-containing vessels. By contrast, surface cracks do not penetrate through the full thickness, and subsurface cracks remain contained within the interior.

Causes and formation

Throughcracks typically originate from defects, stress concentrators, or weak interfaces. They can initiate at surface flaws and propagate inward, or begin at internal flaws and advance toward the exterior. Fatigue, corrosion or stress corrosion cracking, thermal gradients, and high tensile stresses drive through-thickness propagation. The crack path may be predominantly mode I opening, though mixed-mode loading is common in real structures, especially near welds and geometric discontinuities.

Detection and inspection

Detecting throughcracks requires nondestructive evaluation methods capable of penetrating or revealing the full thickness. Ultrasonic testing (including phased-array and C-scan imaging), radiography, and eddy current testing are commonly used for metals. Dye penetrant or magnetic particle inspection can identify surface-accessible propagation paths, while infrared thermography and acoustic emission monitoring may aid in locating active crack growth. Regular inspection intervals and load path analysis help manage through-crack risk in critical components.

Prevention and mitigation

Design strategies include maintaining adequate thickness, using tougher materials, and controlling residual stresses. Surface treatment such as shot peening, proper heat treatment, and protective coatings reduce crack initiation and slow growth. In service, implementing crack arresters, regular inspections, and corrective maintenance are essential to prevent catastrophic failure.

See also: fracture mechanics, fatigue, nondestructive testing.