Ductile–brittle fatigue and fracture behaviour of aluminium/PMMA bimaterial 3PB specimens

Fracture toughness and fatigue crack growth tests and numerical simulations on 3PB specimens were carried out to study the behaviour of a crack lying perpendicular to the interface in a ductile/brittle bimaterial. Polymethylmethacrylate acrylic (PMMA) and aluminium alloy 2024 T531 were joined together using epoxy resin. A precrack was introduced into the ductile material and tests were carried out to obtain fracture toughness and fatigue properties. The body force method and elastic-plastic finite-element analyses were used to simulate the experimental stress intensity KI and cracking behaviour under monotonic and cyclic loads. It was found that the bimaterial fatigue crack growth rate is higher than that for monolithic aluminium 2024 but lower than the rate for a monolithic PMMA. This agreed with the trend for the fracture toughness values and was consistent with the numerical method results. The initial Mode I stable ductile cracking in the aluminium appears to \u27jump\u27 the interface and continues under mixed fracture Mode (I and II) in the PMMA material up to the final failure. A consistency between the simulation methods has indicated that the bimaterial fatigue crack growth is dominantly elastic with a small plastic zone near the crack tip

Activation and Differentiation of Autoreactive B-1 Cells by Interleukin 10 Induce Autoimmune Hemolytic Anemia in Fas-deficient Antierythrocyte Immunoglobulin Transgenic Mice

The Fas (CD95) gene is among critical genetic factors in some autoimmune diseases, which are characterized by autoantibody (autoAb) productions. In mice, mutations in the Fas gene cause lymphoproliferation (lpr) which predominantly develops glomerulonephritis, whereas the mutations in human cause autoimmune lymphoproliferative syndrome (ALPS) characterized by autoimmune hemolytic anemia (AIHA) and thrombocytopenia. Although the mechanism of antinuclear Ab in Fas-deficient background has been well characterized, that of antierythrocyte Ab production in ALPS has been still unclear. To investigate this mechanism, we developed a mouse line by crossing the antierythrocyte antibody transgenic mice (H+L6 mice) and Fas-deficient mice. Although Fas deficiency did not break tolerance of autoreactive B-2 cells in H+L6 mice, autoreactive B-1 cells in Fas-deficient H+L6 homozygous mice became activated and differentiated into autoAb-producing cells in mesenteric lymph nodes and lamina propria of intestine, resulting in severe anemia. In addition, serum levels of interleukin (IL)-10 significantly increased in Fas−/− × H+L6 homozygous mice and administration of anti–IL-10 Ab prevented exacerbation of autoAb production and AIHA. These results suggest that activation of B-1 cells is responsible for induction of AIHA in Fas-deficient condition and that IL-10 plays a critical role in terminal differentiation of B-1 cells in these mice

An extension of the Equivalent Material Concept applied to fracture of U-notched solids

ABSTRACT: The Equivalent Material Concept is a tool that allows the fracture behavior of notched components in elastoplastic materials to be analyzed by transforming them into fictitious linear elastic ones, defining a fictitious failure stress. The combination of a failure criterion with this approach offers a methodology for predicting the maximum load of notched solids with elastoplastic behavior.The validity limits have been established experimentally by a logistic regression using fracture data of linear elastic, small scale yielding and fully plastic material. This paper also proposes an extension of the Equivalent Material Concept, applying the fictitious transformation in a more complete form to tensile, toughness and notch tests. New magnitudes as the fictitious stress, the fictitious toughness and the fictitious notch stress intensity factors have been defined. The final proposal is a partial application of the fictitious transformation that incorporates all of the experimental data gathered.The authors wish to express their gratitude to the European Union’s H2020 research and innovation program for their financial support under the LightCoce project (No 814632)

B-1 Cell Heterogeneity and the Regulation of Natural and Antigen-Induced IgM Production.

A small subset of B cells, termed B-1 cells, with developmental origins, phenotypes, and functions that are distinct from those of conventional B cells exist in mice. It contributes the vast majority of spontaneously produced "natural" IgM. Natural IgM is constitutively produced, even in the absence of microbiota, and fulfills many distinct functions in tissue homeostasis and host defense. B-1 cells also respond with IgM production to innate signals and pathogen exposure, while maintaining steady-state levels natural IgM. Thus, within the B-1 cell pool, cells of distinct and heterogeneous functionality must exist to facilitate these different functions. This review considers three factors that may contribute to this heterogeneity: first, developmental differences regarding the origins of the precursors, second, tissue-specific signals that may differentially affect B-1 cells in the tissue compartments, and finally responsiveness to self-antigens as well as innate and antigen-specific signals. All three are likely to shape the repertoire and responsiveness of B-1 cells to homeostatic- and antigen-induced signals and thus contribute to the functional heterogeneity among these innate-like B cells

Gradient elasticity: a transformative stress analysis tool to design notched components against uniaxial/multiaxial high-cycle fatigue

This paper investigates the accuracy of gradient elasticity in estimating high-cycle fatigue strength of notched components subjected to both uniaxial and multiaxial fatigue loading. A novel design methodology is formulated by combining Ru and Aifantis’ gradient elasticity with the Theory of Critical Distances and the Modified Wöhler Curve Method. The keyfeature of this innovative design methodology is that, via the Theory of Critical Distances, gradient elasticity’s length scale parameter is directly estimated from conventional material fatigue properties (i.e., the plain fatigue limit and the threshold value of the stress intensity factor). From a stress analysis point of view, the proposed approach directly post-processes the gradient-enriched stress states determined, at the hot-spots, on the surface of the component under investigation (and independently of the sharpness of the stress concentrator being assessed). The accuracy and reliability of this design method was checked by using a large number of experimental results taken from the literature and generated by testing notched metallic samples under uniaxial as well as under multiaxial fatigue loading. This comprehensive validation exercise demonstrates that the systematic usage of this transformative design approach leads to the same level of accuracy as the one which is obtained by applying the classic Theory of Critical Distances. This result is certainly remarkable since the proposed approach is not only very efficient from a computational point of view, but it also allows high-cycle fatigue damage to be assessed by directly postprocessing gradient-enriched stress states determined on the surface of the component being assessed

Interleukin-4 Protects against a Genetically Linked Lupus-like Autoimmune Syndrome

Interleukin-4 (IL-4) provides support for humoral immune responses through upregulation of T helper (Th) type 2 cell differentiation, but it is not known whether IL-4 promotes antibodymediated autoimmune diseases such as systemic lupus erythematosus (SLE). Here, we show that the constitutive expression of an IL-4 transgene by B cells completely prevents the development of lethal lupus-like glomerulonephritis in the (NZW × C57BL/6.Yaa)F1 murine model of SLE. This was associated with marked changes in the serum levels of IgG subclasses, rather than in the total levels of anti-DNA antibodies, with a lack of IgG3, a decrease of IgG2a, and an increase in IgG1 subclasses, and by a strong reduction in the serum levels of gp70-antigp70 immune complexes. This effect of the transgene appears to result from a modulation of the Th1 versus Th2 autoimmune response, since the protected mice displayed comparably modified IgG2a and IgG3 antibody response against exogenous T cell–dependent antigen, but not against T cell–independent antigens. Thus, IL-4 prevents the development of this lupuslike autoimmune disease, most likely by downregulating the appearance of Th1-mediated IgG subclasses of autoantibodies such as the IgG3 autoantibodies which have been shown to be especially nephritogenic