On the Behaviour of Discontinuous Interfaces under Dynamic Loading

Discontinuous interfaces such as bolted connections present a major engineering challenge for the design of mechanical components. While bolted connections are fairly well understood in classical mechanics, understanding of how such interfaces react in high velocity impact scenarios is limited. In particular this poses a major issue for the design of gas turbines, where local velocities can easily exceed hundreds of meters per second (at the blade tips). A greater understanding of the behaviour of these parts can allow for more refined turbine design, reducing weight while maintaining structural integrity.

The proposed research seeks to advance the understanding of the behaviour of discontinuous interfaces when subject to impact loading, such as are present in bolted joints. This will involve a combination of detailed high-rate experimentation and post-test material analysis coupled with numerical modelling. The aim will be to develop an improved understanding of the mechanics of complex interfaces during and after impact events, and to provide validation of numerical modelling approaches. Typical phenomena of interest may include (but not be limited to) dynamic friction, surface finish, frictional heating, static, dynamic and modal response of bolted structures, material/geometric non-linearity. It is also expected that multi-scale effects and their importance in providing full structural understanding will need to be considered. The ultimate destination will be to inform the design of gas turbine engines for load cases such as Fan Blade Off where there is a multiplicity of bolted joints that directly affect the response of the structure and its ultimate integrity.

Specific interface joins of interest include, but are not limited to, bolts and nuts, captive nuts, threaded holes, washers & anti-rotation devices. These features will be tested under various different high velocity impact loading conditions to examine the aforementioned phenomena of interest. By varying test parameters (such as impact velocity, material type, etc.), an understanding of how these factors influence performance will be established. This project will also involve the development of a refined computational model, validated against the large test matrix constructed through this work, for use in commercial finite element codes (e.g. LS-Dyna or Abaqus). This model will be an important aid to predicting the behaviour of discontinuous interfaces in Fan Blade off events as well as other loading scenarios outside of this area, allowing for cost versus fidelity analysis of new blade designs.

One important aspect of this project is the design of a new test platform dedicated to the study of bolted interfaces. This may also involve the development of bespoke fixtures to test bolted connections. The purpose of these fixtures will be to ensure precise pre-loading of the bolted specimen, and the well-controlled application of dynamic loading. Pre-existing gas-driven apparatus may be modified for initial experiments and based on the results of these trials a fully bespoke test rig may be developed.

This project falls within the EPSRC themes of Engineering and Manufacturing the Future and Physical Sciences. This project is being performed in collaboration with Rolls Royce, who have committed to support this for the duration of the DPhil.