The Influence of Pantograph Carbon–Metal Composite Slider Thermal Properties on the Railroad Wire Temperature

This article presents the methodology, description, and results of experimental studies aimed at determining the impact of the copper concentration in a carbon–metal composite contact strip on the maximum temperature of the copper contact wire during a contact event when used for operation in the railway industry in Europe. Based on these tests, we determined the minimum percentage of copper that is required for the composite to meet the normative requirements for current loads. In addition to experimental research, a 3D FEM numerical model was also developed in which the contact strip and contact wire geometry were mapped, along with imposed loads resulting from the test for current loads mentioned above. Fifteen simulation variants were carried out for the established model, where the value of the thermal conductivity coefficient and the specific heat coefficient were varied. On this basis, we analyzed the sensitivity of thermal coefficients to the contact wire temperature and determined the minimum conductivity coefficient value, which allowed the maximum copper contact wire temperature of 120 °C to be obtained during the verification tests.

The Influence of Mechanical Alloying and Plastic Consolidation on the Resistance to Arc Erosion of the Ag–Re Composite Contact Material

The article presents the influence of mechanical alloying and plastic consolidation on the resistance to arc erosion of the composite Ag–Re material against the selected contact materials. The following composites were selected for the tests: Ag90Re10, Ag95Re5, Ag99Re1 (bulk chemical composition). Ag–Re materials were made using two methods. In the first, the materials were obtained by mixing powders, pressing, sintering, extrusion, drawing, and die forging, whereas, in the second, the process of mechanical alloying was additionally used. The widely available Ag(SnO2)10 and AgNi10 contact materials were used as reference materials. The reference AgNi10 material was made by powder metallurgy in the process of mixing, pressing, sintering, extrusion, drawing, and die forging, while the Ag(SnO2)10 composite was obtained by spraying AgSniBi alloy with water, and then the powder was pressed, oxidized internally, sintered, extruded into wire, and drawn and die forged. The tests of electric arc resistance were carried out for loads with direct current (DC) and alternating current (AC). For alternating current (I = 60 A, U = 230 V), 15,000 switching cycles were made, while, for constant current 50,000 (I = 10 A, U = 550 V). A positive effect of the mechanical alloying process and the addition of a small amount of rhenium (1% by mass) on the spark erosion properties of the Ag–Re contact material was found. When DC current of 10 A was used, AgRe1 composite was found to be more resistant than commonly used contact materials (AgNi10 and Ag(SnO2)10).

Evaluation of Sampling Methods for Detection of Pathogens from Steel Surfaces; Contact Plates, Foam Swabs, and Flocked Swabs

Background: Contaminated healthcare surfaces can serve as reservoirs for the transmission of pathogens. Sensitive sampling methods are needed to investigate sources of pathogens for implementing effective disinfection strategies and thereby preventing environmental transmission. Conventional approaches employ swabs to sample environmental surfaces. Contact plates represent an alternative approach for sampling healthcare surfaces that does not require lab processing, though little is known about their performance. A contact plate is an agar plate that is overfilled with selective or nonselective media. It can be gently applied to the surface, then simply incubated at a temperature optimal for target organism (s), thus saving time and resources. Methods: In this study, contact plates containing trypticase soy agar with 5% sheep blood (TSAII), foam swabs, and flocked swabs were evaluated for their ability to recover 4 pathogens that persist on healthcare surfaces. Stainless-steel coupons (4 in2) were inoculated with the following pathogens (102 CFU): Acinetobacter baumannii (AB, strain type 12), carbapenemase-producing KPC+ Klebsiella pneumoniae (KP; ATCC BAA-1705); methicillin-resistant Staphylococcus aureus (MRSA; ATCC 43300); and vancomycin-resistant Enterococcus faecalis (VRE; Van A + 256). The plates were allowed to dry 1 hour. Sampling with CPs was performed in 2 ways; (1) a single contact plate was used to sample 1 stainless-steel surface and (2) a composite was collected by 3 sequential contact-plate samplings of the same stainless-steel surface. The contact plates were then incubated at 351C. Foam and flocked swabs were premoistened with phosphate-buffered saline + 0.02% polysorbate 80 (PBST) and were used to sample the stainless-steel coupons. Swabs were held for 1 hour and processed by sonication and vortexing in 5 mL of PBST, then the eluent was cultured and CFU counted. Mean percentage recoveries (%R) relative to the inoculum were calculated and compared. Results: When the %R for all 4 pathogens were pooled, the composite contact-plate sampling method yielded the highest, (P < .05) (66.0%; SD, 0.22), followed by the single contact plate method (39.7%; SD, 0.12), foam swab (32.9%; SD, 0.18), and flocked swab (20.3%; SD, 0.20). The composite contact plate method yielded the highest %R for VRE (102.1 %; SD, 0.17), and the lowest %R was observed when using flocked swabs to recover KP (6.3%; SD, 0.05). Conclusions: The contact-plate composite method may provide investigators with minimal environmental microbiology capacity an alternative method for environmental sampling and detection of organisms from surface areas (4 in 2) with low bioburden.Funding: NoneDisclosures: None

Impact of Fiber Metal Laminates - Literature Research

The paper refers the general idea of composite materials especially Fiber Metal Laminates (FMLs) with respect to low-velocity impact incidents. This phenomenon was characterized by basic parameters and energy dissipation mechanisms. Further considerations are matched with analytical procedures with reference to linearized spring-mass models, impact characteristics divided into energy correlations (global flexure, delamination, tensile fracture and petaling absorbed energies) and set of motion second order differential equations. Experimental tests were based on analytical solutions for different types of FML - GLARE type plates and were held in accordance to ASTM standards. The structure model reveals plenty of dependences related to strain rate effect, deflection represented by the correlations among plate and intender deformation, separate flexure characteristics for aluminium and composite, contact definition based on intender end-radius shape stress analysis supported by FSDT, von Karman strains as well as CLT. Failure criteria were conformed to layers specifications with respect to von Misses stress-strain criterion for aluminium matched with Tsai-Hill or Puck criterion for unidirectional laminate. At the final stage numerical simulation were made in FEM programs such as ABAQUS and ANSYS. Future prospects were based on the experiments held over 3D-fiberglass (3DFG) FMLs with magnesium alloy layers which covers more favorable mechanical properties than FMLs.

Transient Contact Opening Forces in a MEMS Switch Using Au/MWCNT Composite

Most failures in micro electromechanical system (MEMS) switches can be attributed to the degradation of contact surfaces and sticking contacts. A wear-tolerant composite contact material, composed of a Au film supported by multi walled carbon nanotubes (Au/MWCNT), has been engineered to provide wear resistance and enhanced switching lifetime with conductive properties close to pure Au. Switching lifetimes of billions of cycles have been demonstrated, representing greatly increased performance over thin film Au. Below the arcing threshold (~12 V) the wear mechanism has been shown to be a combination of the fine transfer of contact material by the molten metal bridge (MMB) phenomenon and a delamination of the Au. In this study, the composite contact is hot switched at low current DC conditions (4 V DC and 20 mA) while the contact force is measured at the micro Newton scale in nanosecond resolution. The characteristic voltage waveform associated with the MMB is observed with forces detected as the contact softens, melts, and separates. The presence of a delamination event (DE) is also observed, where the contact opens abruptly with no MMB phenomenon apparent. The DE contact openings are associated with a transient peak force of 21.6 ± 2.3 µN while the MMBs are linked to a lower peak force of 18.1 ± 2.5 µN.