Ferroelasticity was observed in 18-mol% ceria-stabilized zirconia using polarized confocal Raman spectroscopy. Samples were either indented using a diamond Vickers indenter or loaded uniaxially in a diamond anvil cell to induce the ferroelastic behavior. The presence and formation of the ferroelastic domains were observed by monitoring the relative intensities of the B 1g and A 1g Raman modes for the tetragonal phase. Domain switching was found to be present on the surfaces in the damaged materials both inside and around cracks. Loading of the ceramic materials revealed hysteresis in the relative intensities of the Raman peaks as a function of loading and unloading.

The development of thermal stresses in solid oxide fuel cells (SOFCs), and thus their structural stability and reliability, depends directly on the thermal expansion and elastic moduli of the constituent materials. Therefore, it is important to study these properties of SOFC materials. In this study, the thermal expansion and elastic properties of common electrolyte materials, namely yttria stabilized zirconia (YSZ), scandia and ceria stabilized zirconia (SCSZ) and gadolinia doped ceria (GDC), are reported. High temperature X-ray diffraction (HT-XRD) was used to show that the cubic structure of YSZ and GDC samples is stable throughout the temperature range of 30-800 C. However, SCSZ undergoes partial cubic to rhombohedral phase transition at around 300 C but transferred completely back to cubic phase at around 500 C upon heating. The coefficient of thermal expansion (CTE) of electrolyte materials was measured using

The strength of brittle ceramic materials is typically tested using simple uniaxial compression or by three-or four-point bending techniques. While these methods provide reliable results, they do not depict a realistic characterisation of the load-bearing capacity of structural materials, and a method that involves the application of multiaxial stress is required, such as the ring-on-ring biaxial flexural strength test. In this paper, an in-house ring-on-ring fixture was developed and validated by comparing the experimental and simulated biaxial strength tests of a model ZrB 2 -30wt-%SiB 6 ceramic composite. A description of the simulated finite element analysis is provided, and the stress field acting on the sample with maximum principal stress located at the surface under tension at the centre of the ceramic disk is shown.

No abstract

No abstract

Future space exploration will likely include teams of autonomous robots that can perform various tasks in order to minimize human risk and maximize mission efficiency. One particular task may include the autonomous construction of a lunar or Martian habitat to prepare for long-duration human habitation on an extraterrestrial surface. This paper describes the development of an autonomous team of two robots that cooperatively transports a long construction object. Three major aspects of the project are discussed: the measurement of robot states, the design of cooperative control laws that govern the motion of the two-robot team, and the design of the central-PC infrastructure.

Stabilized zirconias with high ionic conductivity are currently essential electrolyte materials for solid oxide fuel cells (SOFCs). Study of mechanical properties of oxide ceramics is significant to reliability and durability of SOFCs which work under harsh environment including high temperature, mechanical stress, electric fields, etc. In this paper, we report on the temperature dependent elastic properties of two stabilized zirconias, namely Yttria Stabilized Zirconia (YSZ) and Scandia-Ceria Stabilized Zirconia (SCZ). The elastic properties were studied using Resonant Ultrasound Spectroscopy (RUS), Dynamic Mechanical Analysis (DMA) and Cyclic Compression Testing. It was found that elastic moduli change with temperature in non-linear manner with large peaks in the mechanical loss coefficients (or mechanical damping) at different temperatures. A strong mechanical damping or attenuation is related to the stress induced anelastic relaxation due to hopping of the oxygen vacancies in dopant-vacancy defect complexes. Effects of applied stress, stress frequency, electric field and temperature on the changes of elastic moduli are discussed in more details in this paper.