Statistical tolerance analysis of a hyperstatic mechanism,using system reliability methods

The quality level of a mechanism can be evaluated a posteriori after several months by following the number of warranty returns. However, it is more interesting to evaluate a predicted quality level in the design stage: this is one of the aims of statistical tolerance analysis. A possible method consists of computing the defect probability (P_D) expressed in ppm. It represents the probability that a functional requirement will not be satisfied in mass production. For assembly reasons, many hyperstatic mechanisms require gaps, which their functional requirements depend on. The defect probability assessment of such mechanisms is not straightforward, and requires advanced numerical methods. This problem particularly interests the VALEO W.S. company, which experiences problems with an assembly containing gaps. This paper proposes an innovative methodology to formulate and compute the defect probability of hyperstatic mechanisms with gaps in two steps. First, a complex feasibility problem is converted into a simpler problem. Then the defect probability is efficiently computed thanks to system reliability methods and the m-dimensional multivariate normal distribution Φ_m. Finally, a sensitivity analysis is provided to improve the original design. The whole approach is illustrated with an industrial case study, but can be adapted to other similar problems.     

Investigation of the effects of recycled engine oil bottoms on asphalt field performance following an oxidation modeling approach

This work investigates the effects of recycled engine oil bottoms (REOBs) on asphalt field performance by comparing asphalts with and without REOBs in terms of the asphalt properties required for pavement oxidation modeling. Specifically, oxidation reaction kinetics parameters, dynamic shear rheometer (DSR) function (DSRFn) hardening susceptibility (HS), and low sheer viscosity (LSV) HS are determined and compared for base binder, 5 wt.% REOBs, and 15 wt.% REOBs blends. At the higher percentage, addition of REOBs appears to increase the initial oxidation rate at field temperatures and significantly increases LSV HS, but does not significantly increase the DSRFn HS. A field modeling example elucidates the effects.     

Application of real/mixed μ computational techniques to an H∞ missile autopilot

A multivariable missile autopilot is synthesized using an H_∞ approach. A tradeoff is achieved between performance, actuators solicitation and uncertainties in the actuators and bending modes dynamics. Robust stability and performance of the control law are then studied in the face of large real parametric aerodynamic uncertainties: computational techniques for real and mixed μ analysis (namely De Gaston and Safonov's, Dailey's, Jones’, Young and Doyle's, Fan, Tits and Doyle's and Safonov and Lee's methods) are briefly reviewed before being used to compute either the exact value, or an interval of the structured singular value (SSV). For small amounts of parameters, the upper and lower bounds provided by these methods are compared to the exact value, computed by De Gaston and Safonov's method. For larger amounts of parameters, NP hardness of the problem prohibits the use of algorithms which compute the exact value: these algorithms are indeed necessarily exponential-time. As an alternative in this case, the use of polynomial-time methods for computing upper and lower bounds leads in our examples to accurate approximates of the real and mixed structured singular values.     

Activatable Peptides for Rapid and Simple Visualization of Protease Activity Secreted in Living Cells

Activity-based monitoring of cell-secreted proteases has gained significant interest due to the implication of these substances in diverse cellular functions. Here, we demonstrated a cell-based method of monitoring protease activity using fluorescent cell-permeable peptides. The activatable peptide consists of anionic (EEEE), cleavable, and cationic sequences (RRRR) that enable intracellular delivery by matrix metalloproteinase-2 (MMP2), which is secreted by living cancer cells. Compared to HT-29 cells (MMP2-negative), HT-1080 cells (MMP2-positive) showed a strong fluorescence response to the short fluorescent peptide via cell-secreted protease activation. Our approach is expected to find applications for the rapid visualization of protease activity in living cells.     

Subtle variations in the structure of crosslinked epoxy networks and the impact upon mechanical and thermal properties

Presented here is an investigation of the structure–property relationships of crosslinked networks using three bi-functional glycidyl ether aromatic epoxy resins, two bi-aryl and one tri-aryl, cured with bi- and tri-aryl amines. Subtle changes to the monomer chemistry including changing aromatic substitution patterns from meta to para, methylene to isopropyl and isopropyl to ether were explored. Changing an epoxy resin backbone from methylene to isopropyl enhances backbone rigidity thus increasing glass transition temperature (T_g), yield strength, and strain despite reducing modulus. Changing meta-substitution to para increases T_g and yield strain while leaving strength unaffected and reducing modulus. Changing isopropyl linkages to ether reduces modulus, strength, T_g, and yield strain reflecting increased molecular flexibility. Using three instead of two aromatic rings increases the molecular weight between crosslinks thereby decreasing T_g and yield strain while increasing modulus and strength. Despite the complexities of multiple systems for varying epoxy resins and amine hardeners, the effect upon network properties is explained in terms of short- and long-range molecular and segmental mobility, crosslink density, and equilibrium packing density. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48874.     

Magnetoelectric sensor for microtesla magnetic-fields based on (Fe80Co20)78Si12B10/PZT laminates

The magnetoelectric sensor based on (Fe₈₀Co₂₀)₇₈Si₁₂B₁₀/PZT laminates is designed, fabricated and characterized for determining dc and ac magnetic-field strengths as well as field orientations. At low dc magnetic-fields, a ME-voltage response (dV_ME/dH) as high as 2 mV/Oe is achieved. The linear relation V_ME(h_ac) with a slope of dV_ME/dh_ac of 17 mV/Oe shows a great ability to self-powered detecting low ac magnetic-fields. The field orientation can be detected by using the sinusoidal dependence of the magnetoelectric voltage. The sensor is promising not only for microtesla magnetic-field sensing but also for magnetic biosensor applications.     

Synthesis of optical quality ZnO nanowires utilizing ultrasonic spray pyrolysis

ZnO nanowires were grown by an ultrasonic spray pyrolysis technique. The aspect ratio and size of the wire were dependent mainly on the pH value of a precursor solution and the growth temperature. By high-resolution transmission electron microscopic analysis and photoluminescence measurements, it was confirmed that the nanowires are monocrystalline with good optical quality.     

Achievement of 100% Removal of Oil from Feathers Employing Magnetic Particle Technology

Iron powder has previously been demonstrated to be a potential dry cleansing agent for oiled feathers, whereby both the oil ad(b)sorbing particles and the contaminant may be harvested magnetically. Previous studies on feather clusters have only been able to achieve 97.4% removal. While impressive, this is not considered to be entirely satisfactory for wildlife rehabilitation in practice. Reported in this Technical Note is a series of experiments designed to establish whether a grade of iron powder can be identified that is capable of achieving 100% removal and to identify those characteristics responsible for such improvement. To this end, the abilities of nine different grades of iron powder to remove four different contaminants (three crude oils and a crude oil/seawater emulsion) from feather clusters have been compared, as have the relative physical characteristics of the different iron powders. It has been established that the efficiency of remediation is indeed related to certain physical attributes of the particles (the “grade”). Specifically, a spongy superfine iron powder has been identified that is capable of achieving 100% removal (within experimental error) for all four contaminants tested. This represents an important proof of principle that makes the development of a practical field device a real possibility.