Extraction of Mechanical Properties with Second Harmonic Detection for Dynamic Nanoindentation Testing

In this article, a new method based on the detection of the second harmonic of the displacement signal to determine mechanical properties of materials from dynamic nanoindentation testing, is presented. With this technique, the Young’s modulus and hardness of homogeneous materials can be obtained at small penetration depths from the measurement of the second harmonic amplitude. With this innovative method, the measurement of the normal displacement is indirectly used, avoiding the need for very precise contact detection. Moreover, the influence of the tip defect and thermal drift on the measurements are reduced. This method was used for dynamic nanoindentation tests performed on fused silica and on an amorphous polymer (PMMA) because these materials are supposed not to exhibit an indentation size effect at small penetration depths. The amplitude of the second harmonic of the displacement signal was correctly measured at small depths, allowing to calculate the Young’s modulus and the hardness of the tested materials. The mechanical properties calculated with this method are in good agreement with values obtained from classical nanoindentation tests.     

Synthesis of the reported structure of the bisbenzoquinone lanciaquinone, isolated from Maesa lanceolata

Lanciaquinone, isolated from Maesa lanceolata, was originally assigned as a bisbenzoquinone with a C14-chain linking the two quinone rings. A synthesis of the reported structure, in which the key step is a double Claisen rearrangement, suggests that the structure of the natural product needs to be revised.