The feasibility of an absolute ultrasonic measurement of the tightening force in bolts was investigated. For this purpose, we used both longitudinal and transverse ultrasonic waves (bi-wave method) to remove the time-of-flight measurement of waves in the unstressed state. To avoid the systematic calibration tests (generally carried out before tightening control), an experimental method has been applied. This method allows determination of the effective length under stress and the difference between longitudinal and transverse acoustoelastic coefficients of a tightened bolt. The results show that the proposed method can provide absolute measurement of the tightening force without either loosening the bolt or performing systematically calibration tests with an uncertainty estimated on the order of ±10% at 95% reliability.

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International audienceThe general subject concerns the non destructive testing of prestressed structures in civil engineering. In this topic we are interested in the feasibility of stress evaluation in concrete by ultrasonic methods. To do that, we use the acoustoelasticity theory which exploits the nonlinear behaviour of media to establish the link between stress and ultrasonic velocity. This theory has been validated in homogeneous media and used in steel (to evaluated stresses in steel bolt for example). Concrete is a heterogeneous medium where the ultrasonic velocity measurement is more difficult than in steel. The scattered waves induce uncertainty in the measured values but the nonlinear behaviour of concrete is more important than the one of steel. We show an application in high performance concrete submitted to uniaxial compression. We measure velocities of longitudinal and transversal transmitted ultrasonic waves in the direction and perpendicularly to the stress at different level of the stress test. The sensibility of the different velocities is observed and the potential to evaluate stress in concrete is shown. Prospects particularly concern extension of tested formulations and in situ measurements. This study is supported by ANR‐ACTENA, a French research program

International audienceThe in‐service inspection (ISI) of internal structures in future liquid sodium‐cooled fast reactors is studied in‐depth by the CEA. Among the different options available, ultrasounds from outside the sodium circuit can be used for this purpose. The need to propagate the maximum energy possible orientated the study towards Lamb waves. This study aims at controlling ultrasonic propagation in these multilayered structures in order to determine the best conditions for the NDT of a plate behind n screens

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