The development of advanced creep constitutive equations for high chromium steel P91 at low stress range

Diffusion dominates the creep deformation at low stress range for high chromium steel P91. Brittle creep fracture is caused by cavity nucleation, growth and coalescence of cavities and large precipitates (Laves phase and M23C6) at grain boundary under low stress range. At low stress range, a linear relation between strain at failure and different stresses has been described. Moreover, the minimum strain rate is also proportional to the different stresses

Analyzing the characteristics of the cavity nucleation, growth and coalescence mechanism of 9Cr-1Mo-VNb steel (P91) steel

Creep damage is one of the serious problems for the high temperature industries and computational approach (such as continuum damage mechanics) has been developed and used, complementary to the experimental approach, to assist safe operation. However, there are no ready creep damage constitutive equations to be used for predicting the lifetime for this type of alloy, particularly for low stress. This paper presents an analysis of the cavity nucleation, growth and coalescence mechanism of 9Cr-1Mo-VNb steel (P91 type) under high and low stress levels and multi-axial stress state

Review of creep deformation and rupture mechanism of P91 alloy for the development of creep damage constitutive equations under low stress level

This paper presents a review of creep deformation and rupture mechanism of P91 alloy for the development of its creep damage constitutive equations under lower stress level. Creep damage is one of the serious problems for the high temperature industries and computational approach (such as continuum damage mechanics) has been developed and used, complementary to the experimental approach, to assist safe operation. However, there are no ready creep damage constitutive equations to be used for prediction the lifetime for this type of alloy, partially under low stress. The paper reports a critical review on the deformation and damage evolution characteristics of this alloy, particularly under low stress, to form the physical base for the development of creep damage constitutive equations. It covers the influence of the stress level, states of stress, and the failure criterion

Review on the current state of developing of advanced Creep Damage Constitutive Equations for high Chromium Alloy

This paper presents a review of developing of creep damage constitutive equations for high chromium alloy (such as P91 alloy). Firstly, it briefly introduces the background of creep damage for P91 materials. Then, it summarizes the typical creep damage constitutive equations developed and applied for P91 alloy, and the main deficiencies of KRH (Kachanov-Robatnov-Hayhurst) type and Xus type constitutive equations. Finally it suggests the directions for future work. This paper contributes to the knowledge for the developing creep damage constitutive equations for the specific material

Preliminary analysing of experimental data for the development of high Cr Alloy Creep damage Constitutive Equations

This conference paper presents the current research of preliminary analysing of experimental data for the development of high Cr Alloy Creep damage Constitutive Equations (such as P91 alloy). Firstly, it briefly introduces the background of general creep deformation, rupture and continuum damage mechanics. Secondly, it illustrates the constitutive equations used for P91 alloy or its weldment, especially of the form and deficiencies of two kinds of most widely used typical creep damage constitutive equations Kachanov-Rabotnov-Hayhurst (KRH) and Xu’s formations. And then, the methodology for development of new set constitutive equation proposed by Xu (2004) has been followed in this research. Fourthly, there is a critically analysis of the specific experiment data for P91 alloy and its weldment. Afterwards, the specific requirements for developing a new set constitutive equation have been reported

The development of advanced creep constitutive equations for high chromium alloy steel (P91) at transition stress range

Creep damage is a time-dependent deformation in metals under a constant stress at high temperature condition. Since the 1980s, high chromium alloy steel P91 (9%Cr-1%Mo-0.25%V) is highly demanded in high temperature industries (Saha, 2003). Continuum damage mechanism is becoming a generic life assessment tool to predict the lifetime of materials at creep condition. The consitutive equations were proposed to predict the lifetime and creep behaviours of materials. The most widely used constitutive equations are simply called Kachanov-Rabotnov-Hayhurst (KRH) in the current research. The lifetime of high chromium alloy steel P91 has been overestimated by the extrapolation method from short-term creep tests (high stress) to long-term creep tests (lower stress). The definition of stress ranges depends on different materials and temperatures. The current researcher classifies the stress ranges into high stress range, transition stress range and low stress range with stress exponen

Inhibitory effect of HIV-specific neutralizing IgA on mucosal transmission of HIV in humanized mice

HIV-1 infections are generally initiated at mucosal sites. Thus, IgA antibody, which plays pivotal roles in mucosal immunity, might efficiently prevent HIV infection. However, mounting a highly effective HIV-specific mucosal IgA response by conventional immunization has been challenging and the potency of HIV-specific IgA against infection needs to be addressed in vivo. Here we show that the polymeric IgA form of anti-HIV antibody inhibits HIV mucosal transmission more effectively than the monomeric IgA or IgG1 form in a comparable range of concentrations in humanized mice. To deliver anti-HIV IgA in a continual manner, we devised a hematopoietic stem/progenitor cell (HSPC)–based genetic approach using an IgA gene. We transplanted human HSPCs transduced with a lentiviral construct encoding a class-switched anti-HIV IgA (b12-IgA) into the humanized bone marrow-liver-thymus (BLT) mice. The transgene was expressed specifically in B cells and plasma cells in lymphoid organs and mucosal sites. After vaginal HIV-1 challenge, mucosal CD4^+ T cells in the b12-IgA–producing mice were protected from virus-mediated depletion. Similar results were also obtained in a second humanized model, “human immune system mice.” Our study demonstrates the potential of anti-HIV IgA in immunoprophylaxis in vivo, emphasizing the importance of the mucosal IgA response in defense against HIV/AIDS