This work tackles crack propagation mechanisms of styrene butadiene and natural rubbers, both subject to cyclic loading under a positive load ratio. The experimental evidence is based on pure shear loading of notched specimens supported by SEM analysis of fracture surfaces. Relationship between crack growth rate and tearing energy is revisited. The experimental results show that the fatigue behaviour of studied vulcanisates can be clearly separated in the power-law regime. Furthermore, the reported results from the literature extend this statement to any load condition. Fracture surface observations reveal also differences in energy dissipation mechanisms inferred to structural mutations in the case of natural rubber. Alternation of rough and smooth fracture surfaces associated with change in crack growth rate is more likely to occur for styrene butadiene rubber. All observations suggest that crack branching is a secondary ranked dissipation mechanism for the studied materials compared to crack deviation.
Modelling of a crack propagating through a finite element mesh under mixed mode conditions is of prime importance in fracture mechanics. In this paper, three different crack growth criteria and the respective crack paths prediction in the cement mantle of the reconstructed acetabulum are compared. The maximum tangential stress (MTS) criterion, the minimum strain energy density (MSED) criterion and the new general fracture criterion based on the energy release rate G(θ) are investigated using advanced finite element technique. The displacement extrapolation technique (DET) is used, to obtain the SIFs at crack tip. Several examples are presented to show the robustness of the numerical techniques. The effect of the inclusions and cavities on the crack propagation in cement orthopedic are highlighted.
In this paper, the finite element method is used to analyse the crack behaviour in the orthopedic cement of the total hip replacement by computing the stress intensity factors (SIFs) arround the crack tip. In this work, three cases are studied: crack emanating from a cavity, interaction effect of the crack emanating from a cavity with another cavity and the interaction effect of two cracks emanatingfrom two cavities. The stress intensity factors under mixed mode problems at the crack tip are computed for three zones of prosthesis: proximal, median and distal. The obtained results show that the crack initiated from a micro-cavity in the distal zone of cement can be propagated at the same time by opening and shearing of its lips. It is contrary to that initiated in the proximal zone which cannot be propagated. The mechanical behaviour of cracks in the medial zone depends of the crack initiation position.
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