Civil Engineering May 2021 | Vol 29 No 4

Civil Engineering May 2021 35 is considered a new technology. Conventional sensors including acceler- ometers, strain gauges and inclinometers, among others, are prone to durability and stability failures under specific con- ditions. To overcome these limitations, FOS provide various advantages in com- parison with conventional sensors. These advantages include being lightweight, being immune to electromagnetic interference, and having the ability to operate under harsh conditions. These advantages make FOS an attractive solution for condition monitoring in the railway space. A specific type of FOS, called Fibre Bragg Grating (FBG) sensors, can be used to measure strain and temperature within the rail pad. In grating sensors, the light moves through the optical fibre and the grating serves as a narrow band filter to modulate the range of wavelengths, known as Bragg wavelengths. The varia- tion in the grating period and refractive index corresponds to the deformation of the FBG sensor by strain or temperature. Elastic rail pads are made with rubber or plastics which provide resiliency for the track structure and damping of wheel-induced vibrations and noise. Rail pads are most commonly made from HDPE (high-density polyethylene), EVA (ethylene-vinyl acetate) and TPE (thermopolymer polyester elastomer). 3D printing technology can introduce a new and interesting method of creating rail pads. There are various 3D printing filaments ranging from flexible to hard and brittle plastics. TPU (thermoplastic polyurethane) is a flexible and abrasion resistant thermoplastic that can withstand impacts and serve as an alternative to common rail pad materials. Instrumenting rail pads with smart sensing technology such as FOS is a new and exciting condition monitoring avenue. Rail pads can provide useful information such as load transmission to the substructure when instrumented with load sensing capabilities. An instru- mented rail pad can provide a window into the stresses and strains experienced by a rail pad. Similarly, the South African version of smart rock or smart ballast, namely Kli-pi, uses a miniature battery-powered microprocessor inside a 3D printed ballast stone to measure the deflections, rotations, and vibrations experienced by ballasts during train loading. By combining 3D printed rail pads with smart sensing technology, a cost-effective, small, and lightweight al- ternative to most conventional condition monitoring systems can be provided. CONCLUSIONS The digital railway is all about creating value at new frontiers and creating value in the core business of the railway op- erator. The following acronym, DIGITAL, summarises the main characteristics of the digital railway as touched upon in this paper: Q Q Proactive D ecision making Q Q Contextual I nteractivity Q Q G lobal connectivity Q Q Journey-focused I nnovation Q Q T echnology Q Q Real-time A utomation Q Q L inking people, ideas and things. The technologies of the 4IR are all about people: building foundational digital capabilities, mindsets, and system and data architecture. The digital railway will not be shaped by the binary digits 0 and 1, but will be shaped by people. The investment in technology should be com- plemented by empowering people who will embrace technology, connectivity, and automation. It is here that our institutions of higher learning can and should play a much more significant role. The more digital our rail- ways become, the greater the importance of people skills that cannot be performed by machines. The digital railway has the ability to capture the imagination of a new generation – it is engaging, exciting and transforming our world. The Chair in Railway Engineering at UP invites in- dustry and railway operators into partner- ships that will empower these companies to become digitally enabled and 4IR ready. Our world-class facilities and equipment at Engineering 4.0 are there to serve and advance the railway industry in the Southern African region. Acknowledgments Transnet Freight Rail and the Railway Safety Regulator are gratefully ac- knowledged for sponsoring the Chairs in Railway Engineering and Railway Safety respectively. The NRF National Equipment Programme and the University of Pretoria are also thanked for funding the RRV condition moni- toring project.  Figure 6 3D models of a rail pad and smart ballast (Kli-pi) (left) and 3D printed versions of these track components (right) Smart ballast (Kli-pi) Rail pad Instrumenting rail pads with smart sensing technology such as fibre optic sensors is a new and exciting condition monitoring avenue