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This paper herein studies subcritical crack growth ( SCG) behavior of a perovskite-structured Ba0.5Sr0.5Co0.8Fe0.2O3−δ ( BSCF) as an oxygen transport membrane material. The SCG behavior of BSCF is evaluated by a constant load method and constant stress rate method at room temperature ( RT) and 800°C in air, respectively. The low crack velocity measurements are carried out by ring-on-ring bending tests while the high crack velocity measurements by compact tension tests. The stress rates vary approximately from 0.1012 to 101.2 MPa/min. The fracture stress increases with increasing stress rate at 800°C. The SCG parameter, n, of BSCF is determined to be 24.32 and 13.83 at RT and 800°C in air, respectively. This indicates that BSCF is more susceptible to SCG at 800°C. The strength-probability-time ( SPT) diagram is constructed for design proposes. The stress for a lifetime of 40 years should not exceed 27.21 MPa at RT or 4.53 MPa at 800°C to assure a failure probability below 1%. [ABSTRACT FROM AUTHOR]

The present study evaluates the fracture strengths and the Weibull modulus of Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3−δ (BSCF) oxygen transport membranes by means of biaxial and uniaxial bending tests at both room temperature (RT) and 800 °C. The fracture strengths obtained from the biaxial bending tests are much lower than those obtained from the uniaxial bending tests while Weibull moduli (m) are similar. By utilising Weibull statistics the uniaxial strengths can be predicted from the biaxial values at both RT and 800 °C. Fracture surfaces at both RT and 800 °C show only a transgranular fracture mode. Failure origins are also determined by scanning electron microscope (SEM) based on the fractographic principles. Most defects determining the fracture strength of this particular material are found to be pores with a relatively large size. [ABSTRACT FROM AUTHOR]