This work investigated the effect of a composite of tetragonal zirconia with alumina-reinforced Ceria (ATZ) previously synthesized, on the properties of alumina-based ceramics (Al2O3). Monolithic alumina powder and Al2O3 powder mixtures containing 5, 10, 15 and 20 wt.% of Ce-TZP/Al2O3 were processed by high energy milling, compacted and then sintered at 1600 °C - 2 h. Sintered pure alumina and composites were characterized by relative density, scanning electron microscopy, X-ray diffraction and surface roughness. Then, the elastic modulus, the Vickers hardness, the fracture toughness and the 4-point flexural strength were evaluated. The results indicated an increase in relative density as a function of the addition of ATZ, with values between 94.3 ± 0.8% and 98.9 ± 0.7%. The observed microstructure after sintering showed tetragonal ZrO2 grains with average sizes of 0.6 μm well dispersed in the Al2O3 matrix, which presents average grain sizes of around 1.5 μm. The crystalline phases identified in the composites were ZrO2-tetragonal and Al2O3 hexagonal. The addition of the composite (ATZ) in the alumina matrix generates a gradual reduction in the elastic modulus (398 ± 15 GPa ~366 ± 34 GPa) and in the hardness (20.5 ± 1 GPa ~17.3 ± 0.7 GPa) of the sintered ceramics. On the other hand, the addition of this same composite (ATZ) in the alumina matrix considerably increases the materials fracture toughness, reaching values of approximately 6.7 ± 0.9 MPa.m1/2. The same trend was observed in the flexural strength results which ranged from 258 MPa (5wt.% Ce-TZP/Al2O3) to 316 MPa (20wt.% Ce,Y-TZP/Al2O3). The Ce-TZP reinforcement acts as a toughening agent of the Al2O3 matrix due to the coupled mechanisms of toughening by zirconia phase transformation, residual stresses due to the difference in thermal expansion of the crystalline phases and differences in microstructural morphologies.

This work investigated the effect of adding ceria-stabilized tetragonal zirconia (Ce-TZP) on the fatigue behavior of alumina-based ceramic composites. Alumina powder (control group) and mixtures containing 5 wt.% (group A) and 20 wt.% (group B) of a commercial m-ZrO2/Al2O3/CeO2 powder mixture were milled/homogenized, compacted, sintered at 1600°C-2h, and submitted to hydrothermal degradation. The samples were characterized by relative density, microstructure, crystalline phases, and static mechanical properties. The cyclic fatigue strength was determined using the modified staircase method in 4-point bending tests. The results indicate that adding the m-ZrO2/Al2O3/CeO2 powder mixture to the Al2O3-matrix increases the tetragonal-ZrO2 grains (Ce-TZP) content, presenting 2.9 wt.% of Ce-TZP and 11.9 wt.% of Ce-TZP for group A and group B, respectively. Furthermore, the addition of Ce-TZP improves densification (98.5% → 99.1%) with a slight reduction in hardness and modulus of elasticity and a significant KIC increase of the composite (KIC = 6.7 MPa.m1/2, group B) when compared to monolithic alumina (KIC=2.4 MPa.m1/2). The fatigue strength limit of the control group was around 100 MPa, while the composites (groups A and B) presented the values of 279 MPa and 239 MPa, respectively. The results indicated that the incorporation of Ce-TZP significantly improves the fracture toughness of alumina-based ceramics. On the other hand, regarding the fatigue behavior, there was an increase in fatigue resistance in group A, resulting from the benefits of the t→m Ce-TZP grains transformation, which occurs during cyclic loading, producing a zone shielding that involves the tip of the crack, slowing its growth. The increase in the amount of Ce-TZP (group B) leads to an increase in the internal residual stresses between the phases due to anisotropy and difference in the thermal expansion coefficients, which accelerates the phase transformation and formation of microcracks at grain boundaries, reducing the fatigue strength of composites of group B.

RESUMO Com a necessidade de aperfeiçoamento do processo de transmissão e distribuição de energia elétrica, as indústrias e concessionárias desse setor estão em busca de componentes mais otimizados para suas linhas de transmissão. Em consequência, há a necessidade de aprimorar a formação do cabo condutor, que é o elemento mais oneroso das linhas elétricas. Nestas circunstâncias, condutores formados apenas por fios de alumínio aparentam ser mais vantajosos em relação aos cabos com alma de aço, obtendo melhores índices de ampacidade/peso, diminuindo assim, o custo de transmissão. Neste cenário, o objetivo deste artigo, foi verificar a influência do fenômeno de fadiga por fretting sob condições controladas, nos fios de liga de alumínio AA 6201 T81 e AA 1120 H19, que formam os condutores CAL 900 MCM e CAL 823 MCM, respectivamente. Para alcançar tal fim, criou-se um programa experimental capaz de adquirir os dados sobre a resistência à fadiga dos cabos condutores e dos fios de forma separada, a fim de analisar a influência do fretting sob o parâmetro de carga normal de contato de 750 N. Ao examinar os resultados, o condutor CAL 900 MCM obteve a menor resistência à fadiga, apesar de ser constituído por uma liga com melhores propriedades mecânicas. O mesmo resultado foi obtido nos ensaios de fadiga por fretting nos fios, deste modo, pôde-se inferir que a liga AA 6201 T81, embora possua melhor resistência à fadiga, ela é mais suscetível a falha na presença de fretting quando comparada a liga AA 1120 H19.

ABSTRACT The electric transmission and distribution industries and utilities are looking for the most optimized components for their transmission lines. Thus, there is a need to improve the formation of the overhead conductor, which is the costliest element of electric transmission lines. Under these circumstances, conductors formed solely of aluminum wires appear to be more advantageous over aluminum conductor steel reinforced, obtaining better ampacity/weight ratios, thus lowering the transmission cost. The objective of this article was to verify the influence of the fretting fatigue phenomenon under controlled conditions, on the AA 6201 T81 and AA 1120 H19 aluminum alloy wires, which form the overhead conductors CAL 900 MCM and CAL 823 MCM, respectively. To achieve these goals, an experimental program was created capable of acquiring the data on the fatigue life of the overhead conductors and the wires separately, in order to verify the influence of fretting under a 750 N normal contact load parameter. In the results, the CAL 900 MCM achieved the lowest fatigue life, despite it made of an alloy with better mechanical properties. The same result was obtained in the fretting fatigue tests on wires, so it can be inferred that the AA 6201 T81 alloy, although it has better fatigue resistance, is more susceptible to failure in the presence of fretting when compared to AA 1120 H19 alloy.

ABSTRACT This study aimed to use a simulated vehicle to asses quantitatively the head and neck injuries of the occupants, in a frontal car crash, when the driver has only one hand on the steering wheel, such as while using a cell phone when driving. First, we conducted a survey of NHTSA reports on real laboratory tests of frontal collisions involving sedans. The effects of these collisions on the neck of a Hybrid III 50th percentile male crash test dummy were measured in terms of average head acceleration and force along the X, Z, and Y-axes. These acceleration, force and torque values obtained from the NHTSA database were used to validate the simulated model. The results obtained were compared with case E, the standard dummy position used in frontal collision tests. The results obtained in the simulation of the four cases of driving with only one hand demonstrate a probability of more than 67% that the driver will sustain AIS+2 injuries during a frontal crash. In all the cases, the skull fracture percentage was the most representative, occurring between 89 and 94% of cases where the driver had only one hand on the steering wheel.