Deflectometry, a full field slope measurement technique: General perspectives and application to loading identification using the virtual fields method

Abstract

The ability of photographic techniques to quickly record high volumes of scientific data has been understood since the early 1900s. It is only following the advent of digital imaging and data processing systems that so-called full-field optical measurement techniques became sufficiently reliable for performing high spatial density structural vibration measurements. In particular, the deflectometry technique directly provides a spatially and temporally resolved measurement of slope fields on plane structures using a single high-speed camera. The presentation first demonstrates the principles of this technique and explores some direct applications of such full-field measurements. The advantages and drawbacks of deflectometry are compared with other optical techniques like digital image correlation or scanning laser Doppler vibrometry. A key aspect of several engineering domains consists in the identification of dynamic loads acting on structures by inverse methods. It is shown that coupling deflectometry measurements with the virtual fields method enable the reconstruction of stationary and transient excitations without any specific regularization. Experimental reconstruction results on an aluminum panel are presented for two different transient mechanical loadings: instrumented impact hammer and impacting metal marbles (multiple unknown excitations). Finally, the identification of random excitations is considered using a plate and a membrane.The ability of photographic techniques to quickly record high volumes of scientific data has been understood since the early 1900s. It is only following the advent of digital imaging and data processing systems that so-called full-field optical measurement techniques became sufficiently reliable for performing high spatial density structural vibration measurements. In particular, the deflectometry technique directly provides a spatially and temporally resolved measurement of slope fields on plane structures using a single high-speed camera. The presentation first demonstrates the principles of this technique and explores some direct applications of such full-field measurements. The advantages and drawbacks of deflectometry are compared with other optical techniques like digital image correlation or scanning laser Doppler vibrometry. A key aspect of several engineering domains consists in the identification of dynamic loads acting on structures by inverse methods. It is shown that coupling deflectometry me...