Applicability of Similarity Principles to Structural Models

A systematic account is given in part I of the use of dimensional analysis in constructing similarity conditions for models and structures. The analysis covers large deflections, buckling, plastic behavior, and materials with nonlinear stress-strain characteristics, as well as the simpler structural problems. (author

Conditions of yield and cyclic plasticity around inclusions

n this paper the stress field in the proximity of a circular (cylindrical) inclusion is considered. The conditions for in-plane plastic flow in the matrix are examined from a classical elasticity solution obtained by Goodier. Elementary cases are considered such as remote loading ranging from pure tensile and pure shear to equibiaxial tension. For proportional loading, it is argued that the upper bound to the shakedown limit is always twice the elastic limit; therefore, within the limits of our assumptions, if the elastic stress concentration for the equivalent stress is greater than two, there is a possibility of cyclic plasticity before bulk yielding, which means that possibly an arbitrarily large plastic strain can cumulate with increasingly high risk of exhaustion of ductility and void nucleation or detachment of the interface Consequently, conditions under which it is possible to reach twice the elastic limit before full-scale yielding are shown in the Dundurs plane representing all possible combinations of elastic parameters. Following these lines, it is shown that there is no possibility of cyclic plasticity under remote shear; there is a limited area of the Dundurs plane for tension, including the hole case; finally, in the equibiaxial limiting case, cyclic plasticity is always possible for any combination of elastic properties

Moiré interferometry applied to fracture in titanium tubes

Despite there being a substantial body of evidence to the contrary, moiré interferometry is often regarded - even by some adherents - as a curiosity of the optics lab. The present work seeks to demonstrate still further that the method can be an effective tool for practical materials research and assessment, in this case, in a novel and challenging experimental application involving fracture testing of heat exchanger tube material, the work being conducted in a conventional materials test laboratory setting. The key to the utility of the present setup lies with the priority given to its optical efficiency. In standard fracture toughness tests, it is axiomatic that standard specimen geometries be used. A dilemma arises when a material's properties are transformed to a substantial degree by the final stages of its process of manufacture, and when the very nature of the finished form dictates that standard geometries cannot be produced. The focus of this investigation was to measure crack-tip opening displacements (CTODs) in thin-walled titanium tubes. Fringe patterns corresponding to in-plane displacement contours were obtained interferometrically and the method for extracting CTODs from these is described. Significant differences in yield, ultimate strength, elongation, and fracture behaviour were observed for different material orientations

Point-loaded discs and blocks applicable to tensile testing of brittle materials

A method of numerically approximating the solutions of plane-stress or plane-strain elasticity problems with boundary conditions consisting of concentrated forces or distributed loads is presented herein. The effect of each concentrated force (commonly termed a point load) that acts on the boundary is represented by a Flamant solution. Usually, the combined effect of these Flamant solutions indicates the presence of distributed loadings or ‘residual stresses’ on some portions of the boundary that are not consistent with the actual boundary conditions. The negatives of these ‘residual stresses’ are used as stress boundary conditions in a singular integral method of numerical analysis that is applicable to plane elasticity problems involving distributed loadings on the boundaries. Since the method presented herein involves only stress boundary conditions, the solutions are valid for both plane stress and plane strain.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Stress Propagation through Frictionless Granular Material

We examine the network of forces to be expected in a static assembly of hard, frictionless spherical beads of random sizes, such as a colloidal glass. Such an assembly is minimally connected: the ratio of constraint equations to contact forces approaches unity for a large assembly. However, the bead positions in a finite subregion of the assembly are underdetermined. Thus to maintain equilibrium, half of the exterior contact forces are determined by the other half. We argue that the transmission of force may be regarded as unidirectional, in contrast to the transmission of force in an elastic material. Specializing to sequentially deposited beads, we show that forces on a given buried bead can be uniquely specified in terms of forces involving more recently added beads. We derive equations for the transmission of stress averaged over scales much larger than a single bead. This derivation requires the Ansatz that statistical fluctuations of the forces are independent of fluctuations of the contact geometry. Under this Ansatz, the $d(d+1)/2$-component stress field can be expressed in terms of a d-component vector field. The procedure may be generalized to non-sequential packings. In two dimensions, the stress propagates according to a wave equation, as postulated in recent work elsewhere. We demonstrate similar wave-like propagation in higher dimensions, assuming that the packing geometry has uniaxial symmetry. In macroscopic granular materials we argue that our approach may be useful even though grains have friction and are not packed sequentially.=17Comment: 15 pages, 4 figures, revised vertion for Phys. Rev.

Ebola virus glycoprotein stimulates IL-18 dependent natural killer cell responses

BACKGROUNDNK cells are activated by innate cytokines and viral ligands to kill virus-infected cells. These functions are enhanced during secondary immune responses and after vaccination by synergy with effector T cells and virus-specific antibodies. In human Ebola virus infection, clinical outcome is strongly associated with the initial innate cytokine response, but the role of NK cells has not been thoroughly examined.METHODSThe novel 2-dose heterologous Adenovirus type 26.ZEBOV (Ad26.ZEBOV) and modified vaccinia Ankara-BN-Filo (MVA-BN-Filo) vaccine regimen is safe and provides specific immunity against Ebola glycoprotein, and is currently in phase 2 and 3 studies. Here, we analyzed NK cell phenotype and function in response to Ad26.ZEBOV, MVA-BN-Filo vaccination regimen and in response to in vitro Ebola glycoprotein stimulation of PBMCs isolated before and after vaccination.RESULTSWe show enhanced NK cell proliferation and activation after vaccination compared with baseline. Ebola glycoprotein-induced activation of NK cells was dependent on accessory cells and TLR-4-dependent innate cytokine secretion (predominantly from CD14+ monocytes) and enriched within less differentiated NK cell subsets. Optimal NK cell responses were dependent on IL-18 and IL-12, whereas IFN-γ secretion was restricted by high concentrations of IL-10.CONCLUSIONThis study demonstrates the induction of NK cell effector functions early after Ad26.ZEBOV, MVA-BN-Filo vaccination and provides a mechanism for the activation and regulation of NK cells by Ebola glycoprotein.TRIAL REGISTRATIONClinicalTrials.gov NCT02313077.FUNDINGUnited Kingdom Medical Research Council Studentship in Vaccine Research, Innovative Medicines Initiative 2 Joint Undertaking, EBOVAC (grant 115861) and Crucell Holland (now Janssen Vaccines and Prevention B.V.), European Union's Horizon 2020 research and innovation programme and European Federation of Pharmaceutical Industries and Associations (EFPIA)

Antibody-Dependent Natural Killer Cell Activation after Ebola Vaccination

BACKGROUND:Antibody Fc-mediated functions, such as antibody-dependent cellular cytotoxicity, contribute to vaccine-induced protection against viral infections. Fc-mediated function of anti-Ebola glycoprotein antibodies suggest that Fc-dependent activation of effector cells, including NK cells, could play a role in vaccination against Ebola virus disease. METHODS:We analysed the effect of anti-Ebola glycoprotein antibody in the serum of U.K.-based volunteers vaccinated with the novel 2-dose heterologous Adenovirus type 26.ZEBOV, Modified Vaccinia Ankara-BN-Filo vaccine regimen, on primary human NK cell activation. RESULTS:We demonstrate primary human NK cell CD107a and IFN-γ expression, combined with downregulation of CD16, in response to recombinant Ebola virus glycoprotein and post-vaccine dose 1 and dose 2 sera. These responses varied significantly with vaccine regimen and NK cell activation was found to correlate with anti-glycoprotein antibody concentration. We also reveal an impact of NK cell differentiation phenotype on antibody-dependent NK cell activation, with highly differentiated CD56dimCD57+ NK cells being the most responsive. CONCLUSIONS:This study thus highlights the dual importance of vaccine-induced antibody concentration and NK cell differentiation status in promoting Fc-mediated activation of NK cells after vaccination, raising a potential role for antibody-mediated NK cell activation in vaccine-induced immune responses