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The applicability of the classical fracture criteria for the evaluation of the ultimate state and of the fatigue life-time of thin-walled tubular specimens under combined loading by axial tension-compression with torsion and bending with torsion is considered. The criterion of maximum normal stresses, the criterion of maximum shear stresses and the distortion energy density criterion are chosen as fracture criteria. The problems of the ultimate amplitudes of normal and shear stresses calculation and the problems of fatigue life-time calculation have been solved and experimentally approved, Рассматривается применимость классических критериев разрушения для оценки предельного состояния и усталостной долговечности тонкостенных трубчатых элементов при комбинированном нагружении осевым растяжением-сжатием и кручением, изгибом и кручением. В качестве критериев разрушения выбраны критерий максимальных нормальных напряжений, критерий максимальных касательных напряжений и критерий удельной энергии формоизменения. Решены и апробированы экспериментально задачи расчета амплитуд предельных нормальных и касательных напряжений и задачи расчета усталостной долговечности, Розглядається застосування класичних критеріїв руйнування задля оцінки граничного стану та довговічності внаслідок втоми тонкостінних трубчатих зразків за умов комбінованого навантаження осьовим розтягом-стиском та скрученням, згином та скрученням. У якості критеріїв руйнування обрано критерій максимальних нормальних напружень, критерій максимальних дотичних напружень, та критерій питомої енергії зміни форми. Розв’язано та апробовано експериментально задачі розрахунку амплітуд граничних нормальних та дотичних напружень та задачі розрахунку довговічності внаслідок втоми

Objective- To compare the biomechanical properties of 3.5 locking compression plate (LCP) fixation to 3.5 limited contact dynamic compression plate (LC-DCP) fixation in a canine cadaveric, distal humeral metaphyseal gap model in static axial compression and cyclic axial compression and torsion. Study Design- Biomechanical in vitro study. Sample Population- 30 paired humeri from adult, medium to large breed dogs. Methods- Testing was performed monotonically to failure in axial compression on ten pairs of humeri, cyclically in axial compression for 10,000 cycles on ten pairs and cyclically in torsion for 500 cycles on the last ten pairs. Results- Humeral constructs stabilized with LCPs were significantly stiffer than those plated with LC-DCPs when loaded in axial compression (P=0.0004). When cyclically loaded in axial compression over 10,000 cycles, the LC-DCP constructs were significantly stiffer than those constructs stabilized with LCPs (P=0.0029). Constructs plated with LC-DCPs were significantly more resistant to torsion over 500 cycles than those plated with LCPs (P<0.0001), though no difference was detected during the first 280 cycles. Conclusions- The increased stiffness of LCP constructs in monotonic loading compared to constructs stabilized with non-locking plates may be attributed to the stability afforded by the plate-screw interface of locking plates. The LCP constructs demonstrated less stiffness in dynamic testing in this model, likely due to plate-bone offset secondary to non-anatomic contouring and occasional incomplete seating of the locking screws when using the torque-limiting screw driver. Clinical Relevance- LCPs yield less stiff fixation under dynamic loading than conventional LC-DCPs when applied to severely comminuted, metaphyseal fractures. Improving anatomical contouring of the plate and insuring complete screw insertion into the locking plate hole may improve stiffness when using LCPs in comminuted fractures.