Better sandwich structures for the transport sector
Composites combine two or more materials whose individual structures remain intact (they are not mixed) in order to benefit from the properties of the individual members. In the transport industry where greater weight means higher fuel consumption and more emissions, sandwich structures with light weight and high strength are very popular. However, they are subject to cracking and delamination from low-velocity impact loading. With EU support of the IMPACTSMART SANDWICH(opens in new window) (Active control of impact response of smart sandwich structures) project scientists developed a feedback control algorithm to minimise low-velocity impact effects. The team modelled the sandwich structure with a small number of discrete layers to efficiently predict stress at interfaces with low computational load. Advanced mathematical methods enable prediction of temporal variations of impact force, displacements, electric potential, velocities, strains and stresses. The methodology uses about 1 % of the computational resources of the solution for a conventional full impactor-target system model. Reduced computational load is meaningless if the results are inaccurate. IMPACTSMART SANDWICH scientists confirmed the value of their methodology through comparison with published numerical and experimental results and with their own experimental measurements using their tailor-made test configuration. Using the impact mechanics model and constrained optimisation algorithms, scientists developed an impact identification technique. It identifies all parameters associated with the impact and then calculates the global and local impact response, and can determine if there is delamination or core crushing damage. An active impact feedback control algorithm then activates a surface-attached piezoelectric ceramic layer that minimises the impact force through a shape morphing system. The team has also quantified the energy stored in the piezoelectric transducers during the impact event with an eye on exploitation of energy harvesting. Results have been described in four peer-reviewed scientific journal publications and three conference publications. The technology will make an important contribution to the competitiveness of the EU composites manufacturing industry, improving both the designs of composites and their monitoring and inspection when in service.
