A. Pirondi

Fatigue crack growth in bonded DCB specimens

Fatigue crack growth tests were conducted on double cantilever beam bonded specimens with the aim to characterize an adhesive for structural applications. The tests were conducted in lab air at two different load ratios, R=Pmin/Pmax, and at two different loading frequencies, f. Crack propagation was monitored using the unloading compliance method. The da/dN vs. ΔG experimental showed the typical sigmoidal shape of bulk materials. Crack closure considerations were successfully used to explain the R-ratio effect. The role of loading frequency was also addressed.

Characterisation of ductile mixed-mode fracture with the crack-tip displacement vector

Abstract Mixed-mode I/II fracture experiments were performed on a ferritic steel. The crack growth mechanism was studied and the fracture toughness was measured in terms of crack-tip displacement vector δ v and J -integral. A change in the fracture mechanism at high mode II loading accompanied a marked decrease of the J -measured fracture toughness while the δ v -measure was little affected. The stress/strain field in the vicinity of crack tip at the onset of growth was then evaluated via finite element analysis (FEA). A highly strained, narrow band spreading from the crack-tip developed close to mode II in the experimental crack propagation direction. The total energy dissipated prior to crack growth associated with this kind of deformation was lower than in mode I and, therefore, the associated J -integral fracture toughness J c was lower than the mode I fracture toughness J Ic . The decrease of J c with increasing mode II components was finally rationalised in a relationship between δ v and J . Under the condition of a mixed-mode independent δ v – measured fracture toughness, the decrease if J c for increasing mode II of the present experiments and of literature studies was predicted.

Suitability of mixed-mode I/II assessment methods for implementation into the SINTAP procedure

Several engineering methods are available for the assessment of structures containing defects. They belong essentially to two categories: FAD methods and CDF methods. The recent SINTAP procedure unifies both FAD and CDF routes for the assessment of mode I loaded defects. In this paper, fracture assessment methods containing guidelines for mixed-mode I/II loading conditions are examined and compared with the aim to discuss their suitability for implementation into the SINTAP procedure.