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Reasons for crack closure and possibilities for detection and sizing by NDE

: Deuster, G.

International journal of pressure vessels and piping 35 (1988), S.173-188
ISSN: 0308-0161
International Seminar on Non-Destructive Examiniation in Relation to Structural Integrity <5, 1987, Davos>
Fraunhofer IZFP ()
acoustic emission; crack analysis; crack closure; crack detection; phased array; rayleigh-wave; residual stress; SAFT; SH-wave

It is known that in surface near regions the cumulative effect of - residual stresses (weld, cladding) and the - interacting operation conditions, can lead to crack closure effects which render more difficult the detection, the reconstruction and the evaluation of defects. As disturbing crack closure effects one can distinguish between - plasticity induced crack closure after for instance cyclic fatigue loading or hydrotest - deposit induced crack closure caused for instance by corrosion products, coupling medium, sometimes by dye penetrant liquids - roughness induced crack closure by bridge forming for instance after high cycle or low cycle fatigue loading. (Fig.1) In addition there are undersizing dangers for branched single defects (stress crack corrosion) and for dominant cracks in crack fields originating from thermal shock and corrsion loading.