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Near crack tip strain fields in a stationary and a growing fatigue crack have been studied in situ using the Digital Image Correlation (DIC) technique in a compact tension specimen of stainless steel 316 L under tensiontension cyclic loading. The evolution of near-tip strains normal to the crack plane was monitored at selected locations ahead of the crack tip in consecutive cycles during fatigue crack growth experiments. A stationary crack was examined first to provide a baseline reference whilst the evolution of the strain field ahead of a growing crack was monitored in situ at peak loads during fatigue cycling. The results show that strain accumulation with loading cycle occurred at all tracked locations in both cases, and it is particularly evident close to the crack tip. Moreover, a higher strain accumulation rate was found near the growing crack tip than that near the stationary crack tip. The results on near-tip strain evolution were collected for the first time in situ during the fatigue crack growth experiments, which may hopefully inform a physical-based modelling strategy of fatigue crack growth.

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The full‐field of a fatigue crack, ahead and behind the crack tip, has been examined in this work using Digital Image Correlation. We measured, in situ, the surface crack opening displacements at selected locations behind the crack tip and the evolution of the near‐tip displacements and strains ahead of the crack tip, during loading and unloading in a model material of a standard compact tension specimen. In addition, the stress intensity factor for the compact tension specimen was also estimated from the Williams' series expansion by using the displacements obtained from Digital Image Correlation as a function of applied load. The results present a complete picture of the crack tip field at the selected load levels, where events both ahead and behind of the crack tip were studied for the first time in crack driving and attenuation effects. We hope that the results provide some fundamental insights into the full‐field behaviour of a crack tip under cyclic loading conditions and shed light on the phenomenon of crack closure and its relevance to fatigue crack driving force ΔK under small‐scale yielding conditions.

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The long-term stability of cemented total hip replacements critically depends on the lasting integrity of the bond between bone and bone cement. Conventionally, the bonding strength of bone–cement is obtained by mechanical tests that tend to produce a large variability between specimens and test methods. In this work, interfacial fracture toughness of synthetic bone–cement interface has been studied using sandwiched Brazilian disk specimens. Experiments were carried out using polyurethane foams as substrates and a common bone cement as an interlayer. Selected loading angles from 0° to 25° were used to achieve full loading conditions from mode I to mode II. Finite element analyses were carried out to obtain the solutions for strain energy release rates at given phase angles associated with the experimental models. The effects of crack length on the measured interfacial fracture toughness were examined. Microscopic studies were also carried out to obtain the morphology of the fractured interfaces at selected loading angles.The implication of the results on the assessment of fixation in acetabular replacements is discussed in the light of preliminary work on bovine cancellous bone–cement interface.

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