Purpose The pedicle screw is a surgical device that has become widely used in spinal fixation and stabilization. Postsurgical complications such as screw loosening due to fatigue loading and screw breakage still need investigations. Clinical parameters such as the screw insertion type and depth, the bone density, and the patient degree of mobility greatly affect the mechanisms of the implant's failure/success. Methods The current finite element study focused on the prediction of the pedicle screw pullout strength under various conditions such as insertion type, insertion depth, bone quality, and loading mode. Results As depicted in this study, the preservation of the pedicle cortex as in the N1 insertion technique greatly enhances the pullout resistance. In addition, the higher the screw-anchoring depth, permitting to gear a maximum number of threads, the better the protection against premature breakouts of pedicle screws. Conclusions In agreement with experimental data, the type of insertion in which the first screw thread is placed immediately after the preserved pedicle cortex showed the best pullout resistance for both normal and osteoporotic bone.

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A software has been developed to conduct constant amplitude fatigue crack growth tests on the lines of a standard test method proposed by the American Society for Testing and Materials (ASTM E 647). In this paper, after a brief description of this software, the results of calibration tests conducted using compact tension specimens of the high-strength aluminum alloy 2024-T351 are presented and discussed. The crack length was monitored by the compliance technique and the d-c potential drop technique for automated tests and by optical means for manual verification. Analysis of the results shows that both crack-following techniques are suitable for automated crack growth monitoring. The maximum absolute error for the compliance technique is on the order of 2.5% and on the order of 1.3% for the potential drop technique. Calibration functions relating the crack length to normalized compliance for measurements under the loading axis and to the potential drop have been determined for the studied specimen geometry. Finally, the experimental results relating the crack growth rate to the amplitude of the stress intensity factor by the different techniques used are compared.

Some mechanical components cease to function satisfactorily, failing either under excessive elastic deformation or extensive plastic yielding. In the case of constrained plastification, the researcher is faced with some difficulties in evaluating plastic and elastic-plastic strain behavior near the crack tip. In the present study local strains are measured by microstrain gages, mounted near the crack tip on CT specimens made from the high strength aluminum alloy 2024-T351 under cyclic loading at constant ΔK. The behavior and the evolution of the elastic-plastic zone are studied as a function of the stress ratio R, the thickness of the specimen and the level of ΔK. The experimental results are compared with those given by numerical and theoretical analyses based on the concepts of linear elastic fracture mechanics (LEFM).