Dr Mark Cotton, Ms Sheu-Ching Hon, Ms Jill Horsman, Mr Alan Parlane, Dr David Stanley
Economic development and the desire of modern society to travel mean that the number of flights taken worldwide is increasing 8% year on year. As a result, air travel is fast becoming a major contributor to climate change. Flying to Australia and back generates more carbon dioxide than the average driver in one year. 'The trick of keeping hundreds of tonnes of people and machine in the air and transporting them thousands of miles will always have some environmental consequences, the aim is to minimise the impact,' says Phil Withers of the School of Materials at the University of Manchester.
Using state of the art techniques, Phil and his colleagues are working with Rolls-Royce to ensure the safety of new materials and manufacturing processes for the next generation of jet engines. High energy x-rays and neutron beams are used to penetrate deep into engine components, providing images of their structure and maps of the stresses within them, rather like radiographs of the human body, but in 3D. 'In effect we have an engineering body scanner creating a virtual 3D replica of the critical components of a jet engine,' says Phil. 'We have assembled these 3D images into a journey through the jet engine for the Exhibition so that the public can experience how innovative research combined with modern materials, novel manufacturing techniques, and rigorous testing, allows designers to create more environmentally friendly aircraft.'
Key to improving engine efficiency, and thereby reducing environmental impact, is reducing weight and increasing operating temperatures. Superalloy turbine blades are single crystals rather like gemstones, with air channels to cool them and ceramic coatings to protect them so that they can operate in temperatures above their melting point. New superalloys have recently been developed by Rolls-Royce that can operate at even higher temperatures, however they cannot be joined to other components by conventional means. A new technique, known as friction welding, joins them simply by rubbing together. 'Linear friction welding is used to join blades to discs removing at a stroke heavy inefficient slotted joints,' explains Phil. The blade is rubbed back and forth across the disc at high speed and within seconds they become bonded without ever having melted the joint. 'We have a new material, and a new process,' says Phil. 'Our job is to examine the joints, and use our x-ray mapping techniques to engineer the stresses to safe levels.'
The Manchester team are helping Rolls-Royce and the Metal Improvement Company introduce beneficial compressive stresses into the large fan blades you see at the front of engines. In this new method, a laser produces shock waves that introduce compressive stresses deep into the surface. 'These stresses prevent cracks forming and, if they do form, hold them shut so they can't grow,' says Phil. 'We monitor these beneficial stresses to make sure they are stable in-service and therefore can continue to protect the blade from failure.' So the next time you look at an engine before take off, think of the x-ray technology looking after you!