Yanmeng Xu

Acoustic emission study on WC–Co thermal sprayed coatings

Thermally sprayed coatings contain residual stresses that are produced in the spraying process. These may reduce the coating lifetime. In order to determine the optimum spraying conditions with respect to the residual stress level present, the acoustic emission (AE) during four-point bend tests on tungsten carbide–cobalt coatings sprayed onto mild steel substrates was investigated. Samples tested at different levels of deformation were studied by means of scanning electron microscopy and AE in order to understand the cracking mechanisms. Relationships between the number and amplitude of AE events detected and the type of cracking processes occurring were established. It has been possible to compare the residual stresses caused by the effect of different spraying parameters, such as coating thickness, spraying distance and high velocity oxy-fuel gun.

The effect of fillers on the wear resistance of thermoplastic polymeric coatings

Abstract Thermoplastic polymer matrix composites are used as coating materials for the bore of downhole tubulars used as water injectors in the oil industry. These coatings are primarily employed for corrosion resistance but must also resist mechanical damage from the inspection tools lowered at speed down the tubing. This mechanical damage is produced by the wearing action of the supporting wire against the coating (wireline wear) and by direct impact of the tool against the coating. Filler materials are added to these polymeric coatings and these additions are known to affect the wear resistance of the coating. In this study, three types of thermoplastic polymeric coatings were subjected to wear tests. Both abrasive wear tests — using silicon carbide papers as the abrasive, and wireline wear tests, utilising a true tribocouple consisting of the coating and a length of “slickline” wire on a modified pin on disc apparatus — were carried out to study the wear resistance of these three coatings. Detailed scanning electron microscopy was performed on the wear tracks produced to elucidate the wear mechanism and in particular the role of fillers. In abrasive wear a polymer with a brittle filler has a higher wear rate than an unfilled polymer due to the fact that the brittle fillers can be easily fractured and detached from the polymer matrix. In general, the weak bond between the filler and a thermoplastic polymer matrix leads to the filler particles detaching from the matrix causing enhanced wear. In wireline wear the presence of voids and unmelted particles is particularly deleterious.

Measurement of 9 mm cartridge case external temperatures and its forensic application

The external temperature of the cartridge cases of 9 mm parabellum ammunition during the firing sequence was measured by a series of methods. Using a thermal imaging camera was the most successful method and showed that aluminium alloy cases reached higher temperatures than did brass cases. Peak temperatures for brass cases were 336 K at the case mouth after 1.2 ms and 331 K at the case base after 2 ms. Corresponding temperatures for aluminium alloy cases were 363 K at the mouth after 0.8 ms and 372 K at the base after 1.2 ms. These times at temperature would not be sufficient to destroy any DNA residues left on the case. Measurement of the DNA of fired cartridges showed that DNA deposited on the cartridge case before firing was not affected by the temperatures reached during the firing sequence. Estimates of temperatures to be found in pure aluminium and mild steel cases were made, these indicating that pure aluminium would give higher temperatures than aluminium alloy and steel a lower temperature than for brass.

Study on the characteristics of Magneto-Electrolytic-Abrasive Polishing by using the newly developed nonwoven-abrasive pads

Abstract Recently, advanced technologies in general industry demand that the production of precision parts is much more precise and efficient. However, most of the precision finishing technologies cannot satisfy both the finishing efficiency and surface finishing at the same time. Magneto-Electrolytic-Abrasive Polishing (MEAP) is a new ultra precision machining technology, which combined many kinds of energy, has been deeply investigated under this urgent demand and its effect has been much improved. The method of MEAP for those difficult-to-cut materials has become an important technique in the precision machining field. In particular, the nonwoven abrasive pad, which is a kind efficient matching polishing material used in MEAP system, has been developed. Because nonwoven abrasive pads can cut off the oxide membrane which appears during electrolytic polishing process without time delay and there are no scratches left on workpiece surface, it has been proved that it is a high efficiency and economic polishing material. In this study, the basic properties of nonwoven abrasive pads have been explained and the developed processes for SiC and Al 2 O 3 nonwoven abrasive pads have also been described. Their polishing abilities on difficult-to-cut materials of Cr-coated rollers have been tested according to different kinds of pad. Through using the life test experiment, their economic benefits in Magneto-Electrolytic-Abrasive Polishing systems will be discussed.

A comparative study of the wear resistance of thermoplastic and thermoset coatings

Abstract Thermoset and thermoplastic polymeric materials are used as coatings on the bore of downhole tubulars such as water injectors in the oil industry. Previous work has indicated that such coatings can fail by impact damage and by abrasion from the wire used to lower inspection tools down the tubular. The wire is commonly called “slickline” and the type of wear is called “wireline wear”. However, the different wear mechanisms of thermoset and thermoplastic polymeric coatings under wireline wear conditions have not been clarified. Filler materials such as calcium silicate, calcium fluoride and alumina are often added to polymeric coatings to enhance the mechanical properties of the matrix materials; nevertheless, fillers can improve the wear resistance or exacerbate the wear rate of polymeric coatings depending on the characteristics of the filler material such as its shape, concentration, and the boundary condition between the filler and the matrix material. In this study, two types of thermoset polymeric coatings, a modified novolac containing calcium silicate fillers and a modified epoxy containing alumina as the filler, and one type of thermoplastic coating, a fluoropolymer with 2% calcium fluoride filler, were selected for wear tests. The disc specimen in a pin-on-disc (POD) apparatus was modified to enable embedding a circular loop of wire into its surface. That arrangement was used to study the effect of normal force and sliding distance on wireline wear of the three polymeric coatings. Detailed scanning electron microscopy (SEM) was carried out on the wear tracks produced to investigate the wear mechanisms. Energy dispersive X-ray (EDX) spectroscopy was used to X-ray map the wear scars so as to quantify the amount and size distribution of filler present in the wear scar compared to that in the bulk material and thus elucidate the role of fillers in the wear mechanism.

Deterring gun crime materially using forensic coatings

Surface coatings that can help deter and solve gun crime are described. These nanoengineered coatings have been applied and evaluated on brass cartridge cases, where they increase associative forensic evidence through nanotag donation to the handler and the retention of handlers DNA. In future we expect this approach to be used for other surfaces and conditions.

Design and manufacture of surface textures on gun cartridge cases to trap DNA material

Abstract US and Australian work has shown that the effectiveness of extracting deoxyribonucleic acid (DNA) from standard gun cartridges is low and so analysis costs are high (www.cci.gov/Reference/LpDNACtg_files). The presence of greater than 1 ng of trapped bio-material would increase the success rates of DNA profiling and facilitate cheaper DNA analysis. The aim of this work is to increase the amount of recoverable DNA from a gun user deposited on fired cartridges, using microtextured surfaces as DNA receptors. Success would increase the probability of identifying perpetrators of gun crime through DNA matching. Various textures have been applied to flat surfaces of cartridge case material and the effects of those surface textures on trapping skin materials have been evaluated. In addition to treated/patterned surfaces, standard emery abrasive paper was adopted as a control medium. From the different surfaces tested, the emery abrasive paper was found to be most effective at trapping skin debris. Rough surfaces with pyramid textures, which are similar to features on emery paper, were subsequently manufactured on cartridge rims by a standard knurling process. Scratch tests were carried out to simulate the process of handling and loading these cartridges during the use of firearms. DNA test results of the knurled cartridges after firing, showed a high success rate of DNA profiling and high matching percentage to the donors DNA profile.

A study of 3D printed flexible supercapacitors onto silicone rubber substrates

The rapid development of flexible energy storage devices is crucial for various electronics industries. Highly flexible electrochemical double layer capacitors (EDLCs) can be manufactured by 3D printing technology. It was a great challenge to fabricate multiple material layers of the EDLC in one rapid and accurate deposition event. The fabricated structures were composed of twelve electrodes which could be configured in a number of different ways in one block module. This work aims to investigate the performance of the flexible EDLCs manufactured by 3D printing in a honeycomb pattern. The EDLC cells were fabricated using a slurry made from commercial activated carbon (AC) and a gel electrolyte deposited on a transparent silicone substrate. The flexible EDLCs structures can be used in flexible electronics with different patterns and sizes using 3D printer and can be applied to many applications such as wearable technology.

Fabrication and characterization of smart fabric using energy storage fibres

Fibre supercapacitors were designed and manufactured using a dip-coating method. Their electrochemical properties were characterized using a VersaSTAT 3 workstation. Chinese ink with a fine dispersion of carbon and binder was coated as the electrode material. The specific capacitance per unit length of a copper fibre supercapacitor with the length of 41 cm reached 34.5 mF/cm. When this fibre supercapacitor was bent on rods with a diameter of 10.5 cm, the specific capacitance per length was 93% of the original value (without bending). It showed that these fibre supercapacitors have good flexibility and energy storage capacity. Furthermore, the fibre supercapacitor in the fabric showed the same capacitance before and after weaving.

Development of 3D printing technology for the manufacture of flexible electric double-layer capacitors

ABSTRACT This study presents a novel process and manufacturing system for the fabrication of Electric Double-Layer Capacitors (EDLCs) as energy storage devices. It shows an approach for printing multilayer EDLC components using 3D printing technology. This process allows layers of activated carbon (AC) slurry, gel electrolyte, and composite solid filaments to be printed with high precision. The study describes the detailed process of deposition of the AC and gel electrolyte using the dual nozzle system. The performance of the flexible EDLCs manufactured by 3D printing in a rectilinear infill pattern has been investigated. It describes the energy storage performance of the printed supercapacitors in relation to the differences in thickness of the AC printed layers and the differences in density of gel electrolyte. A supercapacitor based on printed AC and composite materials displays a specific capacitance of 38.5 mF g−1 when measured at a potential rate change of 20 mV s−1 and a current density of 0.136 A g−1. The highest energy density value for the flexible EDLC was 0.019 Wh kg−1 and power density of 165.0 W kg−1 in 1.6 M H2SO4/PVA gel electrolyte.