Search results

Based on the mechanical model of typical shear tests, this study aims to propose the test principle and method of freshwater/seawater ice adhesion shear strength of carbon ceramic brake pads for amphibious aircraft, designs and builds the test equipment, prepares the freshwater/seawater ice samples and completes the tests.

This study examines the influence of the icing process, mechanism, temperature and freshwater/seawater on ice adhesion shear strength of carbon ceramic brake pads and puts forward a test method for the freshwater/seawater ice adhesion shear strength of amphibious aircraft brake pads.

The obtained results examine the influence of the icing process, mechanism, temperature and freshwater/seawater on ice adhesion shear strength of carbon ceramic brake pads. The adhesion shear strength of frozen freshwater and of the seawater of Dalian, Qingdao, Fuzhou and Zhuhai on the surface of aircraft brake pads is measured at –10 to –50°C. It is found that the shear strength of freshwater increases first and then decreases with the decrease of temperature. The adhesion shear strength of seawater; however, increases mainly linear with the decrease of temperature.

The value of this paper is that the test method proposed and test results for the freshwater/seawater ice adhesion shear strength of amphibious aircraft brake pads provide technical support for the anti-icing design of amphibious aircraft brake devices.

This paper presents results on adding silane coupling agents to the underfill encapsulant to enhance the rheology and wetting of the underfill. These results include rheology measurements, contact angle measurements, and in situ flows using a simulated test chip on an FR4 with solder mask substrate. Three properties of the underfill encapsulant that can affect the mechanical reliability of the die and substrate assembly are: CTE; elastic modulus; and adhesion to the die and substrate surfaces. The approach taken in this paper is to add silane coupling agents with different chemistries to the underfill encapsulant to provide interfacial coupling of the underfill material to different die and substrate materials. This paper presents results on the enhancement of the adhesion of underfill encapsulant to silicon (Si), silicon nitride (SiN) die passivation, benzocyclobutene (BCB) die passivation, and solder mask surfaces. The adhesion strength was measured by die shear testing.

The paper aims to present the original and easy for application methods of mechanical strength and electrical properties examination of conductive adhesives and adhesive joints at room as well as at liquid nitrogen temperatures.

The Epoxy Technology EPO‐TEK E4110 and EPO‐TEK H20E adhesives were investigated both in the form of the loose rod and as the printed layers on alumina substrates. Additionally, the mechanical and electrical properties of adhesive joints in low temperatures were investigated, where their characteristics depended on the physical properties of joined elements.

The results indicate the substantial influence of the substrate material on the adhesive resistivity. The joints samples were exposed to multiple thermal shocks in the range from room down to liquid nitrogen temperatures and it was observed that the joints strength and resistance stability could be reached in determined curing conditions of the adhesive.

It is generally stated that tested adhesives can be fully suitable for work in low temperatures. However, it should be underlined that these adhesives' properties change after cooling them down to the liquid nitrogen temperature – the strength growths and the resistance diminishes (about few times).

The paper examines mechanical strength and electrical properties of conductive adhesives and adhesive joints at various temperatures.

This paper provides a comprehensive review of the literature concerning the various causes of failures of external wall tile finishes.

A 4×3 matrix hierarchy framework is developed for a systematic analysis of the literature reviewed.

The findings from this paper indicate the importance of environmental effects, movement joints, and adhesive on the performance of external wall tile finishes. Thermal and moisture effects induce movement of tiles, and the failure of the tiling system depends very much on the adhesive strength and the provision of movement joints. Workmanship is also a key factor affecting the performance of external wall tile finishes and should not be overlooked.

Various studies have been carried out on the causes of defects in external finishes in the past. However, many of them were case‐oriented and were not supported by laboratory findings. The hierarchical framework developed in this paper serves as a basis for further laboratory and field studies on this issue.

The framework is conducive to the diagnosis of external wall tile delamination.

This paper reviews systematically and comprehensively the literature on the causes of external wall tile delamination.

Sprayed metal coatings are an alternative means of effectively protecting steel structures and equipment exposed to severe environments where other coatings, such as paint, are unsuitable or provide only temporary protection. Selecting the most suitable material for a given application is a very important step in achieving success. For resistance to corrosive environments, zinc and aluminium are the most successful and widely used coatings, both being anodic to iron and steel. The performance of sprayed metal coatings is a function of the environment, coating thickness, adhesion, density and the type of sealer used. The mechanism of adhesion is mainly mechanical, the bond strength being dependent on the application process chosen and standard of surface preparation. This paper describes the results of research work associated with hot sprayed aluminium applied by combustion flame and electric arc processes using compressed air and argon carrier gases. Studies included ductility and adhesion tests, scanning electron microscopy of surfaces and cross sections, and Auger surface analyses.

To evaluate the mechanical properties of cured epoxy modified with amine terminated poly (ethylene glycol) benzoate (ATPEGB) along with the comparison of results with change in chain length of ATPEGB.

ATPEGB prepared from poly (ethylene glycol) (PEG) of different molecular weights (200, 400 and 600) were used as modifiers for epoxy resin here. For effective toughening, different compositions were made by adding various concentration of each ATPEGB to epoxy. The impact, adhesive, tensile and flexural strengths of modified and unmodified epoxy were characterised and compared for each ATPEGB.

Modification of epoxy resin using each ATPEGB showed significant enhancement of mechanical strengths over unmodified epoxy. The modification caused a chemical linking between ATPEGB and resin which led not only to a phase separation but also to ensuring their intrinsically strong chemical bonds across the ATPEGB phase/resin matrix interface and this was the main cause to the improved mechanical strengths. The optimum results were obtained at 12.5 phr (parts per hundred parts of epoxy resin) concentration of each modifier.

The modifiers, ATPEGB, used in the present context were synthesised from PEG of molecular weight 200, 400 and 600. Besides, it could be synthesised from PEG of molecular weight 4,000 and 20,000, etc. and modification of epoxy resin could also be studied effectively by using these.

The method for enhanced toughness of cured epoxy was novel and could find numerous applications as surface coating and adhesive onto an intricate structure.

The purpose of this paper is to deal with the tribological study on the brake pads developed using various purity-based graphitized graphite.

This paper deals with developing copper-free brake pads by using graphite as a key lubricant produced using a graphitization process with purity percentages (85, 90 and 95%). The brake pads were developed using traditional manufacturing processes and evaluated for their physical, chemical, thermal and mechanical properties as per industrial standards. Fade and recovery characteristics were analyzed using a full-scale inertia brake dynamometer as per JASO-C-406. The scanning electron microscope was used to analyze the worn surfaces of the brake pads.

The testing findings reveal that the brake pads with 95% graphitized graphite showed better shear strength with good adhesion levels and lesser density, hardness, acetone extract value, loss on ignition and higher porosity. Effectiveness studies of brake pads with graphite (95% graphitized) showed better results at higher pressure speed conditions than others because of better plateau formation and adequate lubrication.

This paper discusses graphitized graphite of different purity influences brake pad's tribological performance by modifying tribo-films and reducing friction undulations.

Additive manufacturing (AM) is a promising alternative to the conventional production methods (i.e., machining), providing the developers with great geometrical and topological freedom during the design and immediate prototyping customizability. However, frictional characteristics of the AM surfaces are yet to be fully explored, making the control and manufacturing of precise assembly manufactured mechanisms (i.e., robots) challenging. The purpose of this paper is to understand the tribological behavior of fused deposition modeling (FDM) manufactured surfaces and test the accuracy of existing mathematical models such as Amontons–Coulomb, Tabor–Bowden, and variations of Hertz Contact model against empirical data.

Conventional frictional models Amontons–Coulomb and Tabor–Bowden are developed for the parabolic surface topography of FDM surfaces using variations of Hertz contact models. Experiments are implemented to measure the friction between two flat FDM surfaces at different speeds, normal forces, and surface configuration, including the relative direction of printing stripes and sliding direction and the surface area. The global maximum measured force is considered as static friction, and the average of the local maxima during the stick-slip phase is assumed as kinematic friction. Spectral analysis has been used to inspect the relationship between the chaos of vertical wobbling versus sliding speed.

It is observed that the friction between the two FDM planes is linearly proportional to the normal force. However, in contrast to the viscous frictional model (i.e., Stribeck), the friction reduces asymptotically at higher speeds, which can be attributed to the transition from harmonic to normal chaotic vibrations. The phase shift is investigated through spectral analysis; dominant frequencies are presented at different pulling speeds, normal forces, and surface areas. It is hypothesized that higher speeds lead to smaller dwell-time, reducing creep and adhesive friction consequently. Furthermore, no monotonic relationship between surface area and friction force is observed.

Due to the high number of experimental parameters, the research is implemented for a limited range of surface areas, which should be expanded in future research. Furthermore, the pulling position of the jaws is different from the sliding distance of the surfaces due to the compliance involved in the contact and the pulling cable. This issue could be alleviated using a non-contact position measurement method such as LASER or image processing. Another major issue of the experiments is the planar orientation of the pulling object with respect to the sliding direction and occasional swinging in the tangential plane.

Given the results of this study, one can predict the frictional behavior of FDM manufactured surfaces at different normal forces, sliding speeds, and surface configurations. This will help to have better predictive and model-based control algorithms for fully AM manufactured mechanisms and optimization of the assembly manufactured systems. By adjusting the clearances and printing direction, one can reduce or moderate the frictional forces to minimize stick-slip or optimize energy efficiency in FDM manufactured joints. Knowing the harmonic to chaotic phase shift at higher sliding speeds, one can apply certain speed control algorithms to sustain optimal mechanical performance.

In this study, theoretical tribological models are developed for the specific topography of the FDM manufactured surfaces. Experiments have been implemented for an extensive range of boundary conditions, including normal force, sliding speed, and contact configuration. Frictional behavior between flat square FDM surfaces is studied and measured using a Zwick tensile machine. Spectral analysis, auto-correlation, and other methods have been developed to study the oscillations during the stick-slip phase, finding local maxima (kinematic friction) and dominant periodicity of the friction force versus sliding distance. Precise static and kinematic frictional coefficients are provided for different contact configurations and sliding directions.

Liquid encapsulation techniques have been used extensively in advanced semiconductor packaging, including applications of underfilling, cavity‐filling, and glob top encapsulation. Because of the advanced encapsulation materials and the automatic liquid dispensing equipment involved, it is very important to understand the encapsulation material characteristics, equipment characteristics, encapsulation process development techniques in order to achieve the encapsulation quality and reliability. In this paper, the authors will examine the various considerations in liquid encapsulation applications and address the concerns on material characterization, automatic liquid dispensing equipment/process characterization and the encapsulation quality and reliability. The discussions will be helpful for future material and process development of semiconductor packages.

Protecting off‐shore splash zones from corrosion presents special problems, not the least of which is the task of applying coatings in‐situ. The hazards include: