An elastoplastic three-dimensional homogenization model for particle reinforced composites

A model for the homogenization of the elastoplastic properties of particle reinforced composites is proposed. The microstructure is described by means of a novel technique, consisting of generating particles in a pre-existent constrained Delaunay tetrahedralization of a cubic volume by means of a modified random adsorption algorithm. This technique allows generating models with different amounts of reinforcement by using the same finite element mesh. The obtained particle morphology is similar to that of many ceramic powders often used as reinforcement. Homogenization is carried out for a typical particle reinforced metal matrix composite with reinforcement volume fractions up to 0.25 and the representative volume element size is assessed for both elastic and elastoplastic behaviours. In this latter case the representative volume element size depends on the amount of plastic strain which develops in the matrix material and a criterion to assess the model representativeness is proposed based on the amount of elastic energy stored in the composite. The predictions of the model compare well with pertinent experimental data reported in the literature. (c) 2007 Elsevier B.V. All rights reserved

Interfacial Design for Joining Technologies: An Historical Perspective

This paper gives an historic perspective of the concept of "Interfacial Design” in joined (e.g. soldered, brazed, diffusion bonded) assemblies. During the course of history, the awareness grew that the interface in a material joint can be perceived at different length scales. With the continuing development of joining materials and technologies, it became evident that the performance of assemblies is critically dependent on the structure and composition of the multiple internal interfaces in the material joints. Resulting trends in the microstructural design of soldering, brazing, and other bonding materials by smart engineering of internal interfaces, as driven by increasingly complex technological requirements, are briefly addressed

A Study of the Shear Response of a Lead-Free Composite Solder by Experimental and Homogenization Techniques

The current study proposes a combined experimental and modeling approach to characterize the mechanical response of composite lead-free solders. The influence of the reinforcement volume fraction on the shear response of the solder material in the joint is assessed. A novel optimized geometry for single lap shear specimens is proposed. This design minimizes the effect of plastic strain localization, leading to a significant improvement of the quality of experimental data. The constitutive model of the solder material is numerically identified from the load-displacement response of the joint by using inverse finite element identification. Experimental results for a composite solder with 0.13 reinforcement volume fraction indicate that the presence of the reinforcement leads to a 23% increase of the ultimate stress and a 50% decrease of the ultimate strain. To interpret experimental data and predict the elastoplastic response of the composite solder for varying particle volume fraction, a three-dimensional (3D) homogenization model is employed. The agreement between experiments and homogenization results leads to the conclusion that the increase in the ultimate strength and the decrease in ductility are to be attributed to load sharing between matrix material and particles with the development of a significant triaxial stress state which restricts plastic flow in the matrix

Intranasal nanoemulsion vaccine confers long‐lasting immunomodulation and sustained unresponsiveness in a murine model of milk allergy

BackgroundImmunotherapy for food allergy requires prolonged treatment protocols and, in most cases, does not lead to durable modulation of the allergic immune response. We have demonstrated an intranasal (IN) nanoemulsion adjuvant that redirects allergen‐specific Th2 responses toward Th1 and Th17 immunity, and protects from allergen challenge after only 2‐4 monthly administrations. Here, we investigate the ability of this technology to provide long‐term modulation of allergy in a murine model of cow’s milk allergy.MethodsSix weeks after sensitization to bovine casein, mice received four, monthly IN immunizations with nanoemulsion formulated with casein. Protection from casein challenge was assessed at 4 and 16 weeks after the final vaccine administration.ResultsThe NE vaccine significantly blunted the physiological responses to allergen challenge, and this effect persisted for at least 16 weeks. The protection from challenge was associated with the suppression of casein‐specific Th2 immunity and induced Th1 and Th17 cytokines as well as induction of IL‐10. Of interest, while immunized animals showed significantly decreased Th2 cytokine responses, cow’s milk‐specific IgE remained elevated in the serum at levels associated with reactivity in control sensitized animals. Protection was associated with suppressed mast cell activation and markedly reduced mast cell infiltration into the small intestine.ConclusionThe sustained unresponsiveness of at least 16 weeks after vaccination suggests that the nanoemulsion vaccine alters the allergic phenotype in a persistent manner different from traditional desensitization, and this leads to long‐term suppressive effects on allergic disease without eliminating serum IgE.This study evaluates the ability of an intranasal nanoemulsion‐based vaccine to induce long‐term modulation of allergic reactions in a mouse model of cow’s milk allergy. Intranasal immunization with nanoemulsion adjuvant suppresses Th2 responses and anaphylaxis. The sustained unresponsiveness of at least 16 weeks after vaccination suggests that the nanoemulsion vaccine alters the allergic phenotype.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154959/1/all14064_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154959/2/all14064.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154959/3/all14064-sup-0003-FigS3.pd

A frozen super-Earth orbiting a star at the bottom of the Main Sequence

We observed the microlensing event MOA-2007-BLG-192 at high angular resolution in JHKs with the NACO adaptive optics system on the VLT while the object was still amplified by a factor 1.23 and then at baseline 18 months later. We analyzed and calibrated the NACO photometry in the standard 2MASS system in order to accurately constrain the source and the lens star fluxes. We detect light from the host star of MOA-2007-BLG-192Lb, which significantly reduces the uncertainties in its char- acteristics as compared to earlier analyses. We find that MOA-2007-BLG-192L is most likely a very low mass late type M-dwarf (0.084 [+0.015] [-0.012] M\odot) at a distance of 660 [+100] [-70] pc orbited by a 3.2 [+5.2] [-1.8] M\oplus super-Earth at 0.66 [+0.51] [-0.22] AU. We then discuss the properties of this cold planetary system.Comment: published version A&A 540, A78 (2012) A&A, 10 pages, 7 Figure

Estudio del daño por choque térmico en materiales compuestos de matriz de vidrio reforzados con fibras de carburo de silicio

The development of microstructural damage in silicon carbide fibre (Nicalon™) reinforced glass matrix composite samples subjected to thermal shock was investigated by using a nondestructive forced resonance technique and fibre push out indentation tests. Thermal shock testing involved quenching samples in a water bath maintained at room temperature from a high temperature (650ºC). Changes in the Young's modulus and internal friction of the samples with increasing number of shocks were measured accurately by the forced resonance technique. Fibre push-out tests showed no significant changes in the properties of the fibre-matrix interface, indicating that damage in the composite was concentrated mainly in the development of matrix microcracking. It was also shown that the internal friction is a very sensitive parameter by which to detect the onset and development of such microcracking. A simple semi-empirical model is proposed to correlate the internal friction level with the microcracking density in the glass matrix. Finally, the relevance of detecting nondestructively the existence of microcracks in the glass matrix, before any significant interfacial degradation occurs, is emphasized, in conextion with the possibility of inducing a crack healing process by a thermal treatment (annealing), taking advantage of the viscous flow properties of the glass.El desarrollo de daño microestructural en materiales compuestos de matriz de vidrio reforzados con fibras de carburo de silicio (Nicalon™) sometidos a choque térmico fue investigado mediante la técnica no-destructiva de resonancia forzada y por mediciones de indentación "push-out" de fibras. Los ensayos de choque térmico involucraron el enfriamiento brusco en un baño de agua a temperatura ambiente de las piezas previamente calentadas a una temperatura elevada (650ºC). La técnica de resonancia forzada permitió medir cambios en el módulo de Young de elasticidad y en la fricción interna de las muestras, ocurridos al aumentar el número de choques térmicos como consecuencia del daño microestructural inducido. La investigación del "push-out" de fibras mostró que las propiedades de la interfase fibra/matriz no variaron apreciablemente bajo las condiciones de choque térmico estudiadas. Los resultados demostraron que la única forma de daño microestructural inducido por choque térmico en el material compuesto fue el agrietamiento de la matriz de vidrio. Además se observó que la fricción interna es un parámetro altamente sensible para detectar el inicio y desarrollo de tal agrietamiento. Se presenta un modelo semi-empírico simple, el cual permite correlacionar el nivel de fricción interna medido con la densidad de agrietamiento de la matriz de vidrio. Finalmente, se dedica especial atención a la importancia de detectar en forma no-destructiva la presencia de microgrietas en ¡a matriz de vidrio, en conexión con la posibilidad de inducir un proceso de curado de tales microgrietas mediante un tratamiento térmico, aprovechando el flujo viscoso del vidrio

A Proposed Role for Pro-Inflammatory Cytokines in Damaging Behavior in Pigs

Sickness can change our mood for the worse, leaving us sad, lethargic, grumpy and less socially inclined. This mood change is part of a set of behavioral symptoms called sickness behavior and has features in common with core symptoms of depression. Therefore, the physiological changes induced by immune activation, for example following infection, are in the spotlight for explaining mechanisms behind mental health challenges such as depression. While humans may take a day off and isolate themselves until they feel better, farm animals housed in groups have only limited possibilities for social withdrawal. We suggest that immune activation could be a major factor influencing social interactions in pigs, with outbreaks of damaging behavior such as tail biting as a possible result. The hypothesis presented here is that the effects of several known risk factors for tail biting are mediated by pro-inflammatory cytokines, proteins produced by the immune system, and their effect on neurotransmitter systems. We describe the background for and implications of this hypothesis.Peer reviewe