Effect of Thermal Cycling and Thermal Aging on the Mechanical Properties of, and Residual Stresses in, Ni-YSZ/YSZ Bi-Layers

Radović, Miladin; Trejo, Rosa M; Cofer, Cameron G.; Watkins, Thomas R.; More, Karren L.

doi:10.1002/9780470291337.ch37

Cited by 5 publications

(9 citation statements)

References 3 publications

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“…References [23,44] report an affected characteristic strength and/or Weibull modulus, while Ref. [45] does not observe any significant variation.…”

Section: Degradation During Combined Ageing and Thermal Cyclesmentioning

confidence: 97%

“…Besides the anode/electrolyte bilayer geometries corresponding to XRD measurements available in literature [18][19][20][21]23], this study focuses on the most common layer configurations used in intermediate-temperature, anode-supported SOFCs. These are depicted in Figure 3, together with the range of allowed variations of the thickness of the layers and considered positions of the delaminations.…”

Section: Investigated Casesmentioning

confidence: 99%

“…Different zero-stress temperatures lead to very strong variations in the computed stress in the electrolyte. Lara-Curzio et al [23] followed the evolution of stresses in the electrolyte during ageing and thermal cycling. As expected, the magnitude of the compressive stress in the electrolyte first decreased at the beginning of both ageing and cycling, but then unexpectedly increased again.…”

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confidence: 99%

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Sensitivity of Stresses and Failure Mechanisms in SOFCs to the Mechanical Properties and Geometry of the Constitutive Layers

2011

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A model based on the Euler–Bernoulli theory is used to assess the sensitivity of residual stresses in solid oxide fuel cells to the mechanical properties and geometry of the constituents. It considers different cell configurations, characterised by the presence or not of a compensating layer, and a cathode based on either lanthanum strontium manganite (LSM) or lanthanum strontium cobaltite ferrite (LSCF). The implementation of creep in the model provides insights into the parameters that affect the zero‐stress temperature and behaviour during ageing. The amount of irreversible deformation generated in the cell layers after the sintering step depends on the mechanical properties of the layers, type of cell and to some extent, cooling rate. X‐ray diffraction measurements from literature are used to verify the prediction. Depending on the mechanical properties, the stress state in the LSM cathode changes from tensile to compressive with respect to temperature. During combined ageing and thermal cycling, tensile stress might arise in the compatibility layer of LSCF‐based cells, due to the relief of the initial compressive stress at operating temperature. The Weibull analysis provides the assessment of mechanical failure. A simplified approach is used for buckling‐driven delamination, but the propagation of cracks is predicted for unlikely large pre‐existing defects.

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“…References [23,44] report an affected characteristic strength and/or Weibull modulus, while Ref. [45] does not observe any significant variation.…”

Section: Degradation During Combined Ageing and Thermal Cyclesmentioning

confidence: 97%

Section: Investigated Casesmentioning

confidence: 99%

mentioning

confidence: 99%

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Sensitivity of Stresses and Failure Mechanisms in SOFCs to the Mechanical Properties and Geometry of the Constitutive Layers

2011

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“…The shear and bulk moduli of NiO were determined from these values of Young's modulus and assuming a value of 0.42 for Poisson's ratio. 25,26 The coefficient of thermal expansion of the porous NiO-YSZ substrate was calculated using the following relationship 27 :…”

Section: Temperature Dependence Of the Properties Of Nio And Yszmentioning

confidence: 99%

On the nonlinear temperature dependence of residual stresses in solid oxide fuel cells

et al. 2020

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The residual stresses in a dense yttria-stabilized zirconia (YSZ) layer bonded to a porous NiO-YSZ substrate were measured by X-ray diffraction in air between 25°C and 900°C. It was found that the residual stresses on the outer surface of the YSZ layer were compressive, that their magnitude increased with decreasing temperature, and that the temperature dependence was nonlinear particularly at temperatures below 600°C. An elastic model that incorporates micromechanics and laminate theory was formulated to successfully predicts the nonlinearity of the temperature dependence of the residual stresses by accounting for the effect of the order-disorder transition experienced by YSZ around 600°C and the magnetic transition of NiO at the Néel temperature around 265°C, on the properties of these materials. The implications of the results for the reliability of solid oxide fuel cells are discussed.

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“…The central component, the membrane electrode assembly (MEA), is a multilayer device that mechanically and chemically interacts with the other components of a single repeating unit (SRU). During operation, the physico-chemical alterations that arise from the hightemperature and aggressive environment [6e12] affect the mechanical durability [13,14]. Mechanical failures can occur as well during the last manufacturing steps of the stack.…”

Section: Introductionmentioning

confidence: 99%

Mechanical reliability and durability of SOFC stacks. Part I : Modelling of the effect of operating conditions and design alternatives on the reliability

Nakajo

Mueller

Brouwer

et al. 2012

International Journal of Hydrogen Energy

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Creep Contact analysis a b s t r a c tElectrochemical and mechanical aspects in solid oxide fuel cell stack must be understood to meet the reliability targets for market implementation. This study presents a stack modelling framework that combines thermo-electrochemical models, including degradation and a contact finite-element thermo-mechanical model. It considers rate-independent plasticity and creep of the component materials and proposes periodic boundary conditions to model the stacking of repeating units. This Part I focuses on the effects of the operating conditions and design alternatives.In the present conditions, the stresses in both the anode and the cathode contribute to the probability of failure (P f ), which can be lowered by adjusting the operating conditions.The requirements for mechanical reliability are here opposite to those that alleviate electrochemical degradation. Gas-diffusion layers (GDL) and interconnect design alternatives and stacking have a lower impact on the P f , but affect the contact pressure on the GDLs, which can cause electrical contacting challenges.Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. IntroductionSufficient mechanical reliability is a major hurdle to overcome for the commercial viability of solid oxide fuel cell (SOFC) devices [1]. Despite the evidence of this shortcoming, structural issues in SOFC stacks are practically solved by progressive design adjustments while efforts to understand the underlying processes have been limited. The need for a more solid, comprehensive and versatile background is now acknowledged, as the SOFC technology approaches market introduction. Strong coupling between the phenomena characterises the SOFC field. Stack and system design and operation must be integrated with structural and lifetime analysis to meet performance, reliability, durability, versatility and availability requirements, in the view of the lowest price of electricity delivered to the end-user. Numerous trade-offs govern the development of a functional SOFC system. They act at all scales and affect to similar extents the choice of an electrode microstructure and material, and that of a system layout. In a simplified view, the risks of structural failure scale with power density and number of thermal cycles. Effective mitigation requires the precise knowledge of the mechanisms. Available online at www.sciencedirect.com journal h om epa ge: www.elsev ier.com/locate/he i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 9 2 4 9 e9 2 6 8

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Effect of Thermal Cycling and Thermal Aging on the Mechanical Properties of, and Residual Stresses in, Ni-YSZ/YSZ Bi-Layers

Cited by 5 publications

References 3 publications

Sensitivity of Stresses and Failure Mechanisms in SOFCs to the Mechanical Properties and Geometry of the Constitutive Layers

Sensitivity of Stresses and Failure Mechanisms in SOFCs to the Mechanical Properties and Geometry of the Constitutive Layers

On the nonlinear temperature dependence of residual stresses in solid oxide fuel cells

Mechanical reliability and durability of SOFC stacks. Part I : Modelling of the effect of operating conditions and design alternatives on the reliability

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