Study and comparison of wear behaviour of Ni-Al2O3 coatings deposited by hot and cold spray

The sliding wear of hot and cold spray nickel-alumina coatings on SA 213-T 91 boiler steel has been evaluated and compared. The investigation was conducted with pin-on-disc apparatus. The wear testing was done by varying normal loads of 30, 40, and 50N at a constant sliding velocity of 1 ms-1. Then another set of experimentation was done at different sliding velocities of 0.5, 1, and 2 ms-1 at a constant normal load of 30 N. This experimentation was designed to study the effect of varying normal loads and sliding velocities on the wear performance of coatings developed with hot and cold spray techniques. The variation of friction coefficient and wear rate with variation in normal loads and sliding velocities were plotted and analyzed. The evaluation of wear mechanisms and characteristics of Ni-Al2O3 coatings is done with the help of weight change measurements and FE-SEM analysis. The wear resistance of hot spray coatings was found better at high normal loads and sliding velocities in comparison to cold sprayed coatings.

Some Aspects of Shear Behavior of Soft Soil–Concrete Interfaces and Its Consequences in Pile Shaft Friction Modeling

This paper examines the stiffness degradation and interface failure load on soft soil–concrete interface. The friction behavior and its variability is investigated. The direct shear tests under constant normal load were used to establish parameters to hyperbolic interface model which provided a good approximation of the data from instrumented piles. Four instrumented piles were used to obtain reference soil–concrete interface behavior. It was found that the variability of the friction characteristics is the highest for organic clays and the lowest for organic silts. The intact samples exhibit lower shear strength than reconstituted ones. The adhesion varies significantly depending on interface and soil type, which can result in high scatter of the skin friction prediction. The analysis of parameters variability can be used to determine the upper and lower bound of friction behavior on the interface at constant normal load condition. The backward shearing results in decrease in shear strength up to 40% of the precedent forward phase but higher initial stiffness by a factor of between 2 and 3. Presented research provides basic shear and stiffness parameters for four soft soils (organic clay, organic silt, peat, and silty loam) and gives information about variability of interface characteristics.

Effects of inert gas environment on the sliding wear behavior of AZ91/B4C surface composites

Tribological characteristics of AZ91/B4C surface composites were studied under air and argon gas environments. Tests were conducted under a constant normal load of 10 N, with a sliding velocity of 0.06 m/s using a linear reciprocating tribometer. Wear tracks and debris were analyzed using scanning electron microscopy, three-dimensional contour topography, and energy-dispersive X-ray spectroscopy in order to understand the wear mechanisms. The wear rate of the specimen tested under the argon environment was found to be lower (∼60%) in comparison with that of the specimen tested under the open-air environment. The value of the friction coefficient was found to be minimum under the argon environment compared with the air environment. In the air environment, the major material loss from the test specimen was attributed to oxidation wear; whereas under the argon environment, strain-hardening effect was dominant, and the material was found to be removed by delamination wear. In addition, the worn surface morphology of the wear tracks and counter surfaces showed the involvement of abrasion and adhesion wear mechanisms. The results of the study pave the pathway for the design of lightweight surface composite material systems such as AZ91/B4C toward an efficient and robust tribo-pair applicability for a controlled environment.

The mechanisms underlying long-term shaft resistance enhancement of energy pile in clays

Although there are several studies indicating that heating increases the long-term shaft resistance of energy piles, the mechanisms by which heating causes this increase have not been adequately evaluated yet. This article aims to perform comprehensive analysis and discussion to assess the important factors contributing to this increase by integrating the findings from three recently published papers studying the thermo-mechanical behavior of clay and clay-pile interface. In these three studies, reconstituted kaolin clay was used, and cyclic and monotonic heat ranging between 24° C and 34°C were applied to the clay and interface. The interface was sheared under two stiffness boundary conditions; Constant Normal Stiffness (CNS) and Constant Normal Load (CNL), where the normal stresses varied between 100 kPa and 300 kPa. The analysis performed in this article reveals that the increase in strength of interface under CNL condition is primarily attributed to clay stiffening at interface. However, the increase in shaft resistance under CNS condition is primarily attributed to the heating-induced increase of effective lateral stress, although clay stiffening at interface also partially contributes to the total increase of shaft resistance.

Fretting Fatigue Design of Subsea Connectors: A Generalised Approach to Testing

In this paper fretting fatigue is addressed as a potential design consideration for wellhead connectors. The study of near-edge relative motion for frictional contacts under constant normal load is described using analytical, numerical and asymptotic methods. Based on published fretting fatigue experimental data an argument is drawn for a generalised fretting fatigue test design. We do this by reducing the parameters responsible for crack nucleation to the smallest number possible and thereby revealing the fretting fatigue strength as a material property independent of geometrical features. Easy to apply recipes are described and thoughts on a potential apparatus are shared with the reader. Commercial potential lies in the wide-ranging applicability of experimental results across many prototypes and loadings once an appropriate amount of fretting fatigue data has been generated for the material in question.