Subcritical crack growth behavior of a perovskite‐structured Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ oxygen transport membrane

Abstract

This paper herein studies subcritical crack growth (SCG) behaviour of a perovskite-structured Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) as an oxygen transport membrane material. The SCG behaviour 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%.

Mechanical reliability of Ce0.8Gd0.2O2−δ‐FeCo2O4 dual phase membranes synthesized by one‐step solid‐state reaction

“…A strength‐probability‐time (SPT) diagram was constructed to express the relationship between stress, failure probability and lifetime 54‐56,58 . Since low Weibull modulus and low characteristic strength indicate high failure probabilities at low stresses, the lower uncertainty limit of an SPT line at a given lifetime () was obtained using the lower confidence bound of Weibull modulus () and the lower uncertainty limit of characteristic strength ().…”

“…A strength-probability-time (SPT) diagram was constructed to express the relationship between stress, failure probability and lifetime. [54][55][56]58 Since low Weibull modulus and low characteristic strength indicate high failure probabilities at low stresses, the lower uncertainty limit of an SPT line at a given lifetime (t) was obtained using the lower confidence bound of Weibull modulus (m) and the lower uncertainty limit of characteristic strength ( t ). Correspondingly, the upper uncertainty limit of an SPT line at a given lifetime (t) was derived by using the upper confidence bound of Weibull modulus and the upper uncertainty limit of characteristic strength ( t ).…”

“…The subcritical crack growth behavior of dual phase membranes, though, has not yet been studied. In fact, long‐term mechanical reliability of ceramic materials only allows limited subcritical crack growth, 54‐57 since a fast degradation of fracture strength with increasing service time can be expected for ceramics that are susceptible to subcritical crack growth 55 . Such dependence of strength on service time can be predicted utilizing a lifetime assessing model based on failure probability analysis, that is, Weibull analysis, and parameterized subcritical crack growth behavior 58 …”

“…In fact, long-term mechanical reliability of ceramic materials only allows limited subcritical crack growth, [54][55][56][57] since a fast degradation of fracture strength with increasing service time can be expected for ceramics that are susceptible to subcritical crack growth. 55 Such dependence of strength on service time can be predicted utilizing a lifetime assessing model based on failure probability analysis, that is, Weibull analysis, and parameterized subcritical crack growth behavior. 58 In this work, we are comparing the mechanical reliability of Ce 0.8 Gd 0.2 O 2−δ :FeCo 2 O 4 composites with two different compositions.…”