Smarter dynamic testing of critical structures

• Main Author: Daborn, Philip Matthew
• Published: University of Bristol 2014
• Subjects: 629.1
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.683391

Critical structures, such as are found in many aerospace applications, are those whose failure in service could be catastrophic, leading to multiple loss of life and/ or unacceptable financial and reputational damage. The safety and performance of these structures are regularly qualified using laboratory-based environmental tests, the aim of which is to simulate the in-service environments. The methodology behind these environmental tests was developed during the 1960s and 1970s and with only minor advances since then, there is a wealth of anecdotal evidence that suggests this situation leads to serious limitations with current practice. The aims of this research are (i) to conduct an objective assessment of current environmental test practice, (ii) to reveal any deficiencies and (iii) to propose a new technology which could offer significant enhancements. Numerical and practical case studies are presented which highlight that current practice often leads to tests which offer poor simulations of the intended environment. This results from inadequate matching of the boundary conditions, ignorance of the load-path and the prevalence of single-axis excitation techniques. The structure is often' over-tested' to such a degree that unrealistic failures occur in the laboratory, resulting in lengthy and costly delays to certification programmes. Equally, the research found clear examples of significant under-testing and revealed an alarming characteristic of current practice - namely, a wholly unjustifiable perceived conservatism. A new technology has been developed as part of this research - specifically, the Impedance-Matched Multi-Axis Test (IMMAT) technology - which has been designed to overcome the issues identified with current practice. The IMMAT technology offers far superior tests and can help to ensure that critical structures are subjected to realistic excitation conditions in the laboratory. It is hoped that industry will embrace it, thereby ensuring critical structures are adequately qualified in future certification programmes in a scientific and efficient manner.