Evolution of the Electrical Displacement and Energy Dissipation of Lead Zirconate-Titanate Ceramics under Cyclical Load

In this paper, the electromechanical behavior of lead zirconate-titanate ceramics (P51) has been characterized and modeled. The variation of the energy dissipation and peak electrical displacement of the P51 ceramic has been investigated in details. The total strain of P51 under cyclical loading consists of elastic deformation (εije), immediate ferroelectric domain switching deformation (εijd), and time-dependent deformation (εijc). Thus, an expression for the energy dissipation of P51 can be theoretically derived. In addition, a practical method for calculating the dissipated energy has been proposed by integrating the curve of a hysteresis loop. The experimental results show that the peak electrical displacement and dissipated energy both decrease monotonously with the increase of the number of cycles. Furthermore, ferroelectric 90° domain switching was observed by X-ray diffraction (XRD) and the percentage of domain switching has been calculated by the variation of the peak intensity ratio of (002) to (200) at about 45 degrees. Then, grain debonding, crack, and crush were found around voids inside the specimen by using scanning electron microscope (SEM). It is indicated that switching of more capable-switch domains stimulates larger dissipated energy and a bigger peak electrical displacement at the initial cyclic loading. Finally, an exponential functional model has been proposed to simulate the peak evolution of electrical displacement based on the energy dissipation of P51 ceramics under cyclical load.

Анализ усталостного разрушения рельсовой стали

In present paper attempt was made to find a relationship between the mechanical properties of the material in microvolumes and the properties of the material under load. A fractograph-ic analysis of the surface of the fatigued scrap rail with the inner transverse crack is given. The relationship between the fractographic features and the structure of the material is dis-cussed. A sample with an internal transverse crack in the head of the rail was removed from service after an intense cyclical load in the railway switch. For metallographic research, the sample was subjected to three-point bending. On the surface of the destruction of the rail re-vealed three areas, differing in the degree of brittleness of the material.

The Effects of Foot Position and Load on Tibial Nerve Tension

Patients with tarsal tunnel syndrome of unknown etiology do poorly after surgical decompression. Although surgical decompression addresses the soft tissue constraints, it ignores the role of osseous support. Some authors have suggested that a pes planus deformity (i.e., valgus hindfoot and abducted forefoot) is an unrecognized cause of tarsal tunnel syndrome due to increased tibial nerve tension. An in vitro study was performed on nine cadaveric feet to determine the effects of foot position and load on tibial nerve tension. Tensile forces placed through the tibial nerve were measured when the foot was placed in dorsiflexion, eversion, combined dorsiflexion-eversion, and then under cyclical load and increasing internal rotation at 5° increments from 0° to 20°. The nerve tension was reassessed after the creation of a pes planus deformity under the previous conditions. Tibial nerve tension in the stable and unstable foot was significantly increased by eversion, dorsiflexion, and combined dorsiflexion-eversion. Tibial nerve tension was significantly greater in an unstable foot when compared with a stable foot during eversion, dorsiflexion, and combined dorsiflexion-eversion. In the stable foot, tibial nerve tension was significantly increased during axial loading with increasing internal rotation when compared with 0° rotation. The increased tibial nerve tension in the stable foot was significant with increasing internal rotation when 0° was compared with 10°, 15°, and 20°. In the unstable foot, the tibial nerve tension was significantly increased with increasing internal rotation compared with the nerve tension at 0° of rotation. The increased tibial nerve tension in the unstable foot was significant with increasing internal rotation when 0° was compared with 5°, 10°, 15°, and 20°. When stability of the foot and internal rotation were compared independently, each factor increased tibial nerve tension. However, these factors acting together did not significantly compound the increase in nerve tension. This study demonstrates that tibial nerve tension is increased in an unstable foot compared with a stable foot during eversion, dorsiflexion, combined dorsiflexion-eversion, and cyclical load with increasing internal rotation.