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An algorithm for hiding patient's data from JPEG ultrasound images, applied directly on DCT (Discrete Cosine Transform) coefficients is presented. The algorithm can detect textual information using the amount of energy, computed using only AC coefficients, without converting medical images/video back to the spatial (uncompressed) domain. In order to offer a high quality care for patients, textual information containing the patient data is hidden or eliminated. Further, the processed medical images can be accessed and analyzed, for a second-opinion, by physicians, or in medical research, keeping the patients privacy provided of the ultrasound medical images. The algorithm has been implemented and verified with good performances.

Fracture failure of engineering structures is caused by cracks that extend beyond a safe size. For modeling the stable fatigue crack propagation it is necessary to determine the angle of crack initiation, i. e. the angle under the crack growth takes place. There are several criteria that try to model this aspect, such as: Sih, MTS, M, T, Ip. The S-criterion (Sih) was used to simulate the fatigue growth of an internal crack situated in the substrate of a certain spur gear, taking into account the rolling contact fatigue. S-criterion states that the direction of crack initiation coincides with the direction of minimum strain energy density along a constant radius around the crack tip. Since the stress intensity factor Ki is negligible (because of the compression stresses in the substrate of the gear tooth), calculations were made for these conditions and it was obtained a constant and unique angle of crack initiation angle 9 ∼ 80°, that is in concordance with the experimental observations. This study serves to determine the fatigue crack initiation angle in a compression stresses field, as well as its use in modeling the propagation of the fatigue cracks.

The most outstanding parameter that governs the fatigue crack growth under tensile stresses field is the stress intensity factor, mode I, KI. This is a sufficient parameter to describe the whole stress field at the crack tip. An accurate stress intensity factor KI evolution was worked out taking into account the position of the crack centre depth, and also, the residual stresses that act on the surface of the tooth, tensions that are linearly decreasing with the depth in the contact zone. On the other hand, the parameter that governs the crack fatigue growth in the case of compression stresses field is the stress intensity factor mode II, KII. This paper also presents the KII variation along pitch line with respect to the Hertzian contact stresses, the residual stresses and the crack centre depth of an initial crack in the sub-surface of the pinion tooth, having different inclination angle α. As result of this study, some particular factors favorable to the propagation of the fatigue cracks towards the surface of the gear tooth were identified. The availability of a master curve for a particular material relating fatigue crack growth rate and range of stress intensity factor enables a designer to predict growth rates for any cracked body, and it is not limited to situations similar to those pertaining to the cracked stressed specimen used to generate the original data.

The values of the stress intensity factor (SIF) KI are almost always negative in the substrate of the gear teeth, due to the compressive stresses field. The more negative values are higher, respectively, the positive values are lower, the crack faces are more compressed, so the probability of crack propagation after the mode I is lower. Thus, the analysis of the factors leading to the minimum KI values may reveal the conditions that favor the fatigue crack propagation by opening mode. Instead, SIF KII is determinant in the growth rate of the fatigue crack by mode II, in terms of compressive stresses field. Thus, the more KII is higher, the propagation speed is higher, so an analysis of the factors that lead to its maximum value is very useful. The equivalent stress intensity factor Keq corresponds to a mixed-mode of loading and take into account the simultaneous influence of both stress intensity factors KI and KII. The variation of this factor can be used as a parameter of the modified Paris law, in order to study the propagation of the fatigue cracks in the case of mixed-mode loading of contact area between teeth flanks. SIFs variations were analyzed according to the state of stresses, position on the pitch line between the gear teeth flanks, position and angle of an initial crack in the gear tooth substrate, residual tensions etc.