This paper presents a novel flexible tactile sensor for triaxial force dynamic measurement based on piezoelectric elastomer. The piezoelectric elastomer is flexible composite of polyvinylidene fluoride (PVDF) terpolymer and polydimethylsiloxane (PDMS), and multi-wall carbon nanotubes (MWCNTs) are added into the elastomer to improve the piezoelectricity. The elastomer is placed under a PDMS bump and divided into four sensing units by attaching separated copper electrodes. Electrical charges generated by the sensing units are corresponding to the triaxial contact force and the amplitudes of the component forces in three directions could be obtained via the charge outputs of the proposed sensor. Prototype sensors were validated through dynamic tests and the results showed that the sensitivity of the sensor could be improved by adjusting the content of PVDF (10% to 30%) and MWCNTs (0% to 4%). Specifically, the sensitivity in normal direction would increase by 85% as the content of PVDF increases and increase by over 150% as the content of the MWCNTs increases. Accordingly, the sensitivity in shear direction would increase by 45% and 85%, respectively.

Thermography is widely used to detect delamination defects in carbon fiber reinforced plastics (CFRP). This paper proposes a model to detect defects automatically by extracting the thermal signal characteristics of CFRP materials. An optically excited thermography system is constructed for pulsed and lock-in thermography experiments to compare thermal signal data sets in different excitation modes. A multi-task joint loss function is defined to train the model for defect detection and depth prediction. The effects of different attention modules (AM) are analyzed to improve the model performance. By comparing the effects of traditional thermography processing methods and methods based on Convolutional Neural Network (CNN), it is found that the proposed model can detect defects with minimum aspect ratio (ratio of short side to depth) of 2.5, and the relative error percentage in depth prediction is below 10%.

In this study, the performance of braided composite tubes under low-velocity transverse impact loading at mid-span was investigated using both numerical and experimental methods. Three types of braided composite tubes with different braiding angles (30°, 45°, and 60°) were manufactured. The transverse punch behavior of the tubes was examined on a low-velocity imspact test bench. A meso-level finite element model of the composite tube was also established for identifying the damage initiation and development. The numerical results showed a good correlation with the experimental data. The mechanical response including force–time histories, force–displacement histories, and fracture morphologies was compared between three types of composite tubes for analyzing the influence of braiding angle on the impact response and failure mode. Although suffering from the low bending stiffness depends on fiber volume fraction at initial impact stage, the braided tube with 30° angle engaged more portion to resist impact loading in subsequent process and thus presented higher peak loading than the one with large angle. In addition, there are distinct different failure modes between composite tubes with various braiding angles. Shear yarn breakage underneath the punch was prone to occur in 30° sample because the braiding yarn was closer to the axial direction of tube. In contrast, the resin was deboned severely from the braiding yarn and then the braiding yarn exhibits plastic deformation in 60° sample due to the stress concentration caused by the large braiding angle.