Preparation of H-bar cross-sectional specimen for in situ TEM straining experiments: A FIB-based method applied to a nitrided Ti-6Al-4V alloy

The in situ tensile straining of cross-sectional specimens inside a TEM is intrinsically very difficult to perform despite its obvious interest to study interfaces of surface treated materials. We have combined a FIB-based method to produce H-bar specimens of a nitrided Ti-6Al-4V alloy and in situ TEM straining stage, to successfully study the plastic deformation mechanisms that are activated close to the nitrided surface in the Ti-based alloy.     

Natural killer cell activity in coeliac disease: effect of in vitro treatment on effector lymphocytes and/or target lymphoblastoid, myeloid and epithelial cell lines with gliadin

BACKGROUND: While there is substantial evidence that psychological stress enhances risk for coronary artery disease, the mechanisms underlying such an influence remain unclear. We examined the effects of short-term psychological stress on serum lipid levels, hemoconcentration, fibrinogen level, and plasma viscosity. METHODS: Forty-four healthy young adults were randomly assigned to perform a distinctly frustrating cognitive task for 20 minutes (stress condition) or to rest quietly for the same period (control condition). RESULTS: Relative to controls, stressed subjects showed significant increases in blood pressure and heart rate; total, low-density, and high-density lipoprotein cholesterol levels; hematocrit; hemoglobin level; and total protein concentration. Stressed subjects also showed significant reductions in plasma volume and increased plasma viscosity and estimated whole-blood viscosity compared with controls. A similar trend in fibrinogen level was not statistically significant. Individual differences in blood pressure and heart rate response to stress correlated highly with changes in total cholesterol levels and hematocrit. CONCLUSIONS: Our investigation provides further evidence that exposure to short-term mental stress elicits hemoconcentration with associated increases in serum lipid concentrations, hemostatic factors, and blood viscosity.     

Investigation of early stage deformation mechanisms in a metastable β titanium alloy showing combined twinning-induced plasticity and transformation-induced plasticity effects

As expected from the alloy design procedure, combined twinning-induced plasticity and transformation-induced plasticity effects are activated in a metastable β Ti–12 wt.% Mo alloy. In situ synchrotron X-ray diffraction, electron backscatter diffraction and transmission electron microscopy observations were carried out to investigate the deformation mechanisms and microstructure evolution sequence. In the early deformation stage, primary strain/stress-induced phase transformations (β → ω and β → α″) and primary mechanical twinning ({3 3 2}〈1 1 3〉 and {1 1 2}〈1 1 1〉) are activated simultaneously. Secondary martensitic phase transformation and secondary mechanical twinning are then triggered in the twinned β zones. The {3 3 2}〈1 1 3〉 twinning and the subsequent secondary mechanisms dominate the early-stage deformation process. The evolution of the deformation microstructure results in a high strain-hardening rate (～2 GPa), bringing about high tensile strength (～1 GPa) and large uniform elongation (>0.38).     

Origin of {112} < 111 > antitwinning in a Ti-24Nb-4Zr-8Sn superelastic single crystal

Journal of Materials Science - $${\left\{112\right\}\langle {111}\rangle }_{\beta }$$ twins are observed in a superelastic β Ti-24Nb-4Zr-8Sn (wt.%) single crystal after tensile test. A careful...     

Superelastic Behavior of Biomedical Metallic Alloys

Metallurgical and Materials Transactions A - In this this work, superelastic NiTi and Ni-free Ti-23Hf-3Mo-4Sn biomedical alloys were investigated by tensile tests in relationship with their...     

Characterization of viscous response of a polymer during fabric IMD injection process by means a spiral mold

Injection molding is a plastic transformation process to produce complex parts; an efficient way of decorating a part is to do it during the molding cycle, introducing decorated film or fabric inside the mold.One of the most important tools to optimize the injection cycle is to make simulations, but the recognized software do not have potential to simulate IMD (In Mold Decoration) process because the behavior of the polymer flowing over fabric is unknown.This article is focused on the design of a methodology to characterize polymer rheological behavior from a macroscopic point of view, in order to estimate a useful viscous model for use in CAE software by means of a spiral mold and pressure sensors located in it, instead of a rheometer. However, the test temperature of polymer is not constant during the test when the spiral mold method is used, and it is necessary to introduce corrections.For authors, this study is a novelty because any author has used a spiral mold to characterize the rheological behavior of polymers injected over fabric, and the exposed methodology will be very useful to adjust IMD pressure drop on computer programs.     

Method to characterization of the overmolded polymer penetration into the fabric

A penetration into the fabric is a typical defect which appears when plastic is injected over textile and it is able to pass through the fabric to reach the aesthetic side of the part. Once that penetration takes place, the faulty piece is rejected and a possible solution to eliminate the defect is the trial and error process, changing successively the injection parameters, and therefore increasing the production costs. For that reason, it is very important to characterize these penetrations in order to anticipate the injection conditions that cause the defect and consequently, to optimize the overmolded injection process, reducing to the maximum the number of rejected pieces. In this article, the work consists of designing a methodology to combine injection parameters and fabric tension that causes the penetration that appears to characterize them. The combination of minimum tension, minimum injection temperature, and minimum injection pressure in the exact point in which defect appears will characterize the penetration. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Direct measurement of the variation in the energy of a dislocation locked in specific orientations

A general method is presented based on transmission electron microscopy observations of the segmented shape of dislocations under stress for measuring the decrease in dislocations’ self-energy when they are locked in specific orientations. The general formulation is given for any direction of locking in any material, and the method is exemplified in the case of the hexagonal phases of an industrially important Ti-based alloy, where a significant in-core rearrangement reduces the energy of screw dislocations by ～16%.     

Dimensional study of thermoplastic parts made using sequential injection molding

As a result of new aesthetical and economical requirements in injection molding, several processes have been developed during last years. In spite of conventional process, sequential injection molding is a versatile technique based on independent control for each gate opening. This procedure allows part filling without weld lines or, at least, these defects can be relocated in suitable positions. A short discussion about sequential principles is made introducing computer simulations. Pressure required for part filling and molding shrinkage were evaluated using experimental procedures with a prototype mold and using conventional and sequential methods. Several setting up parameters were also used to analyze the effect on injection process. Final results show that shrinkage in sequential injection is similar to conventional process but some new effects could be induced by the process asymmetry and should be investigated further. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers