Identification of the Elastic–Plastic Behavior of Adhesively Bonded Structures Under Multi-Axial Loadings: Comparison of a Modified Arcan Test and a Tension/Compression–Torsion Test

Structural bonding is nowadays widespread in the industry. However, characterisation methods and 3D modelling of the adhesives need to be improved. The characterisation requires an experimental procedure to obtain a large experimental database under various loading cases, which represents a significant amount of data. The 3D modelling requires advanced models with several parameters to identify and generally uses inverse identification procedures, which can be time expensive. For a good accuracy, the constitutive models need to take into account the dependency on the hydrostatic stress and be written under the non-associated formalism. In this study, the experimental database is obtained via a modified Arcan test that can cover a wide range of loadings between tension, shear, mixed tension–shear, and mixed compression–shear. A second experimental campaign is realized with a tension/compression–torsion (TCT) test that can cover a greater range of loadings: from tension to compression and mixed tension/compression–shear, with an infinite possibility of mixed loadings. The modified Arcan database is used to identify a 3D elastic–plastic Mahnken–Schlimmer type model, according to an inverse identification procedure developed in a previous study. This model identification is validated on the experimental database coming from the TCT test: a numerical/experimental comparison is realized. This allows the validation of the model and emphasizes the benefits of the TCT test. Indeed, it proves that this test is well suited to characterize adhesive joints and presents several capacities that will be really useful for further studies, like an infinite range of non-proportional loadings available.     

Tribological behavior of composites fabricated by reactive SPS sintering in Ti-Si-C system

In this study, wear and friction behavior of two based-composites from the Ti-Si-C system, (40 wt% TiC; 28 wt% Ti₅Si₃; 17 wt% Ti₃SiC₂) and (18 wt% TiC; 26 wt% Ti₅Si₃; 41 wt% Ti₃SiC₂) reinforced by 15 wt% of large size SiC (100-150 µm) particles were investigated. The four-phase composites exhibited approximatively the same friction coefficient (µ ~ 0.9) under high loads (10 N and 7 N). The composite with high Ti₃SiC₂ showed higher wear rate values by one order of magnitude. However, under 1 N, the composite with high TiC content showed a higher running-in period and a lower steady state µ value (0.37 after 1000 m sliding distance). Scanning electron microscopy, Energy Dispersive X-Ray and Raman spectroscopy analysis of the worn surfaces of the two composites revealed that oxidation was the dominant wear mechanism. The oxidation process and the removal kinetics of the oxides during sliding controlled the tribological behavior of the composites. The influence of processing variables on microstructures development and wear mechanisms of the composites is discussed.     

Synthesis of fatty hydroxamic acids catalyzed by the lipase ofMucor miehei

Biotechnological synthesis of a new class of amphiphilic molecules—fatty hydroxamic acids—was carried out using the lipase ofMucor miehei by reacting hydroxyl amine with the fatty acids in their free or methyl ester form. Concurrently with enzymatic synthesis, chemical synthesis of hydroxamic fatty acids has also been developed by adapting methods that already existed for water-soluble acids. Different parameters were studied to determine the optimum operating conditions: temperature, molar ratio of reagents, quantity of biocatalyst and length of reaction. A general method, whatever the type of fatty acids used, is described.     

INFLUENCE OF MATERIAL REMOVAL ON THE DYNAMIC BEHAVIOR OF THIN-WALLED STRUCTURES IN PERIPHERAL MILLING

Machining is a material removal process that alters the dynamic properties during machining operations. The peripheral milling of a thin-walled structure generates vibration of the workpiece and this influences the quality of the machined surface. A reduction of tool life and spindle life can also be experienced when machining is subjected to vibration. In this paper, the linearized stability lobes theory allows us to determine critical and optimal cutting conditions for which vibration is not apparent in the milling of thin-walled workpieces. The evolution of the mechanical parameters of the cutting tool, machine tool and workpiece during the milling operation are not taken into account. The critical and optimal cutting conditions depend on dynamic properties of the workpiece. It is illustrated how the stability lobes theory is used to evaluate the variation of the dynamic properties of the thin-walled workpiece. We use both modal measurement and finite element method to establish a 3D representation of stability lobes. The 3D representation allows us to identify spindle speed values at which the variation of spindle speed is initiated to improve the surface finish of the workpiece.     

Neutronic characterization of the MEGAPIE target

The MEGAPIE project aimed to design, build and operate a liquid metal spallation neutron target of about 1 MW beam power in the SINQ facility at the Paul Scherrer Institut (Villigen, Switzerland). This project is an important step in the roadmap towards the demonstration of the accelerator driven system (ADS) concept and high power liquid metal targets in general. Following the design phase, an experimental program was defined to provide a complete characterization of the facility by performing a “mapping” of the neutron flux at different points, from the center of the target to the beam lines. The neutronic performance of the target was studied using different experimental techniques with the goals of validating the Monte Carlo codes used in the design of the target; additionally, the performance was compared with the solid lead targets used before and after the MEGAPIE experiment.     

Co/SiO2 catalysts prepared from Co2(CO)8 for CO hydrogenation into alcohols and hydrocarbons: characterization by magnetic methods and temperature-programmed hydrogenation

The hydrogenation of carbon monoxide over Co/SiO₂ catalysts obtained by reduction of precursors prepared by the reaction of dicobaltoctacarbonyl with silica gives rise to a mixture of alcohols and hydrocarbons. The chain growth probability for hydrocarbon synthesis is similar to that observed over conventional catalysts prepared by the ammonia method (=0.74) with a comparable metal dispersion (metal particle size 4 nm). Alcohol formation yields a smaller chain growth probability (=0.42). Magnetic measurements have shown that in the latter catalyst, small cobalt clusters (1 nm) are likely to be present together with the cobalt particles (4 nm), this observation reconciles apparently conflicting results from the literature. It has been speculated that alcohol formation might be related to the presence of these clusters according to a concerted mechanism. Furthermore, the observation of large amounts of acetates by temperature-programmed hydrogenation, not detected in hydrocarbon selective catalysts, suggests that they may play a role in ethanol synthesis.     

Proliferative effects of synthetic peptides from β-lactoglobulin and α-lactalbumin on murine splenocytes

Eleven peptides, selected on the basis of physicochemical characteristics and their theoretical release from β-lactoglobulin (β-Lg) and α-lactalbumin (α-La) by trypsin or chymotrypsin, were chemically synthesised to evaluate their immunomodulating properties. Murine splenocyte proliferation in the absence and presence of mitogen and different peptide concentrations were measured after 72–96 h incubations. β-Lg f78–83 had no effect on proliferation; β-Lg f15–20, f55–60, f84–91, f92–105, f139–148, f142–148 and α-La f10–16 stimulated proliferation to different extents; β-Lg f1–8, f102–105 and α-La f104–108 showed a cytotoxic effect. Regression analysis revealed the relationship of positive charge, hydrophobicity and length to the stimulatory proliferative effect. β-Lg f15–20, f55–60 and f139–148 also induced various inhibiting and/or stimulating effects on cytokine secretion. The results confirm that peptides releasable by digestive enzymes from α-La and β-Lg have the potential to influence the specific immune response through the modulation of splenocyte proliferation and cytokine secretion.     

High-resolution full-field optical coherence tomography with a Linnik microscope

We describe an original microscope for high-resolution optical coherence tomography applications. Our system is based on a Linnik interference microscope with high-numerical-aperture objectives. Lock-in detection of the interference signal is achieved in parallel on a CCD by use of a photoelastic birefringence modulator and full-field stroboscopic illumination with an infrared LED. Transverse cross-section (en-face, or XY) images can be obtained in real time with better than 1-microm axial (Z) resolution and 0.5-microm transverse (XY) resolution. A sensitivity of approximately 80 dB is reached at a 1-image/s acquisition rate, which allows tomography in scattering media such as biological tissues.