Review of top of rail friction modifier tribology

© 2016 Informa UK Limited, trading as Taylor & Francis Group.The aim of this paper was to review the current state of research for top of rail friction modifiers (TORFM). In the railway industry, friction modifiers is a catch all term for a wide range of products applied for different purposes which has led to confusion. It is hoped that recently published definitions will aid industry to a better understanding of the different products and how they function. The benefits of friction modifiers are well understood with a large body of research supporting the benefits. Comparatively, there is a lot less knowledge of the optimum amount of product to achieve the benefits or how far down the track from an application site the benefit will be seen. Modelling of the products is another area where there is little research, with most of the modelling papers found focussing on dry wheel–rail contact due to the complexity of introducing a third-body layer to a friction force model. Furthermore, only one paper was found which relates how friction modifiers are affected by contaminants or other applied products such as lubricants. With many different products applied to wheels and rail for different purposes, understanding their interaction is key. At the time of this review, there are currently no standards that prescribe how TORFM should behave although the European Committee for Standardisation is currently developing them at the moment. This review has also attempted to appraise the research against a set of criteria. Depending on how many of the criteria the piece of research filled, it was categorised as A, B or C. It was found that most of the research was of category, this was mainly due to only one test method being used or the scale presented. Category A research incorporated modelling or multiple test-scales to support the results presented

Melting, Solidification, and Crystallization of a Thermoplastic Polyurethane as a Function of Hard Segment Content

Thermoplastic polyurethanes (TPU) with varying hard segment contents (HSC) are monitored during melting and solidifying (20 K/min , Tmax = 220 ° C) by small-angle and wide-angle X-ray scattering (WAXS and SAXS). Hard segments: MDI/BD. Soft segments: PTHF1000. The neat materials are injection-molded, having small amorphous hard domains (chord length d⎯⎯h ∼ 35% show sharp Bragg peaks and larger hard domains ( d⎯⎯h > 7 nm ). When heated, small domains melt, but crystallization in the remaining large domains is not detected. Upon cooling, large agglomerates segregate first, which crystallize immediately. Segregation starts for HSC = 42% at 160 °C and for HSC = 75% at 210 °C. When HSC ≤ 30%, the morphologies before and after are similar, but afterward, many hard blocks are dissolved in the soft phase at the expense of the hard domain fraction. In heating and cooling the melts, multiple homogenization and segregation processes are observed, which are explained by the agglomeration of hard blocks of different lengths in the colloidal fluid

Uncovering three-dimensional gradients in fibrillar orientation in an impact-resistant biological armour

The complex hierarchical structure in biological and synthetic fibrous nanocomposites entails considerable difficulties in the interpretation of the crystallographic texture from diffraction data. Here, we present a novel reconstruction method to obtain the 3D distribution of fibres in such systems. An analytical expression is derived for the diffraction intensity from fibres, explaining the azimuthal intensity distribution in terms of the angles of the three dimensional fibre orientation distributions. The telson of stomatopod (mantis shrimp) serves as an example of natural biological armour whose high impact resistance property is believed to arise from the hierarchical organization of alpha chitin nanofibrils into fibres and twisted plywood (Bouligand) structures at the sub-micron and micron scale. Synchrotron microfocus scanning X-ray diffraction data on stomatopod telson were used as a test case to map the 3D fibre orientation across the entire tissue section. The method is applicable to a range of biological and biomimetic structures with graded 3D fibre texture at the sub-micron and micron length scales

Tensile Deformation of Oriented Poly(ε-caprolactone) and Its Miscible Blends with Poly(vinyl methyl ether)

The structural evolution of micromolded poly(ε-caprolactone) (PCL) and its miscible blends with noncrystallizable poly(vinyl methyl ether) (PVME) at the nanoscale was investigated as a function of deformation ratio and blend composition using in situ synchrotron smallangle X-ray scattering (SAXS) and scanning SAXS techniques. It was found that the deformation mechanism of the oriented samples shows a general scheme for the process of tensile deformation: crystal block slips within the lamellae occur at small deformations followed by a stressinduced fragmentation and recrystallization process along the drawing direction at a critical strain where the average thickness of the crystalline lamellae remains essentially constant during stretching. The value of the critical strain depends on the amount of the amorphous component incorporated in the blends, which could be traced back to the lower modulus of the entangled amorphous phase and, therefore, the reduced network stress acting on the crystallites upon addition of PVME. When stretching beyond the critical strain the slippage of the fibrils (stacks of newly formed lamellae) past each other takes place resulting in a relaxation of stretched interlamellar amorphous chains. Because of deformation-induced introduction of the amorphous PVME into the interfibrillar regions in the highly oriented blends, the interactions between fibrils becomes stronger upon further deformation and thus impeding sliding of the fibrils to some extent leading finally to less contraction of the interlamellar amorphous layers compared to the pure PCLNational Natural Science Foundation of China (21204088 and 21134006). This work is within the framework of the RCUK/EPSRC Science Bridges China project of UK−China Advanced Materials Research Institute (AMRI)