Non-woven carbon tissue (NWCT) with different fiber lengths was prepared with a simple surfactant-assistant dispersion and filtration method and used as interleaving to enhance both delamination resistance and electrical conductivity of carbon fiber reinforced plastics (CFRPs) laminates. The toughing effect of NWCT on both Mode I and Mode II interlaminar fracture of CFRPs laminate is dependent on length of fibers, where the shorter carbon fibers (0.8 mm) perform better on Mode I interlaminar fracture toughness improvement whereas longer carbon fibers (4.3 mm) give more contribution to the Mode II interlaminar fracture toughness increase, comparing with the baseline composites, and the toughness increase was achieved without compromising of flexural mechanical properties. More interestingly, comparing with the baseline composites, the electrical conductivity of the interleaved composites exhibited a significant enhancement with in-plane and through-the-thickness direction, respectively. Microscopy analysis of the carbon tissue interleaving area in the laminate indicated that carbon fibers with shorter length can form into a 3D network with more fibers aligned along through-the-thickness direction compared with longer ones. The shorter fibers thus potentially provide more effective fiber bridges, pull-out and matrix deformation during the crack propagation and improve the electric conductivity significantly in through-the-thickness direction.

An analytical model was developed to study the interlaminar fracture behaviour of polymer composite reinforced by carbon fibres grafted with carbon nanotubes. Delamination properties, such as load with displacement or crack (R-curve) and toughness with crack (G_R-curve), can be obtained from this model. The bridging laws presented, based on the CNT pullout mechanism (CNT pullout from polymer matrix) and the CNT sword-in-sheath mechanism (CNT breakage), were incorporated into the proposed analytical model to investigate the influence of the structure of CNT growth onto CFs (CNT@CFs) on delamination properties. The numerical results showed that different toughening mechanisms led to different features of G_R-curves, R-curves, and load with displacement curves. Parametric study demonstrated that strengthening the CNT@CF interface resulted in significant improvement in toughness. Further, it was found that elastic deformation of CNTs played an important role in the toughness improvement in the CNT sword-in-sheath mechanism, but no such role was evident in the CNT pullout mechanism.

At the current stage, there is an urgent need for new techniques to dynamically calibrate advanced wide-range (up to 10⁴ N~10⁵ N) triaxial force transducers. Based on this background, this paper proposes a novel impact calibration method, specifically for the triaxial force transducer, with a wide range and high-frequency response. In this method, the Hopkinson bar, which is typically used to test the dynamic mechanical properties of materials, was used as a generator to generate reference input force for the transducer. In addition, unlike conventional methods, the transverse sensitivities of the transducer were given necessary importance in the proposed method. The calibration result of the triaxial force transducer was expressed in a sensitivity matrix, containing three main sensitivity coefficients and six transverse sensitivity coefficients. The least squares method (LSM) was used to fit the sensitivity matrix linearly. Calibration experiments were performed on a typical triaxial force transducer. Several key issues, involving the validity and the test range, of the method were further investigated numerically. The feasibility and validity of the method were eventually confirmed. The test range of the method can be up to 10⁶ N.

At present, the split Hopkinson tensile bar (SHTB) is widely used to determine the dynamic tensile properties of materials under high strain rates, in which sheet specimen with dogbone-shaped structure is commonly adopted. However, the geometry dimensions of the specimens used in different literatures vary widely and no uniform criterion has been formulated. In order to obtain the optimal specimen geometry associated with the best measurement accuracy in SHTB experiments, the specimen geometry influence on the measurement accuracy of SHTB experiments is investigated by using the finite element (FE) method, and several key indicators which can characterize the measurement accuracy of specimen are proposed based on simulation analysis. Orthogonal tests are designed to generate training samples for BP (back propagation) neural network, and the complex and highly nonlinear mapping between the structure parameters and measurement accuracy indicators of specimen is fitted by BP and then utilized for the fitness function design of genetic algorithm (GA). Finally, the optimal geometry as well dimensions of the SHTB sheet specimen are determined using GA. Meantime, the finite element simulations are carried out in further to verify the effectiveness of the optimized geometry of specimen. The results of this investigation will provide a recommendation for specimen geometry design and a basis for data reliability analysis in SHTB experiments.

Synchronous calibration for the triaxial accelerometers with non-ultra-high (~10kHz) frequency response requires synchronous shocks with high amplitudes and wide pulse widths (narrower band). However, the generation of high-energy shocks with both large widths and high amplitudes is challenging at this stage, especially for the shocks requiring synchronization in three dimensions. This paper then focuses on the method investigation for the generation of synchronous shocks with wide pulse widths and its application in triaxial accelerometer calibration. A device capable of generating three-dimensional synchronous shocks with amplitude of 10 ² g and pulse width of 3.5~4ms, or amplitude of 10 ³ g and pulse width of 0.85~1.1ms, was developed based on a high-energy vertical shock device and a shock amplification technique. It complements the amplitude and pulse width ranges that cannot be covered by the common Hopkinson bar method. A synchronous calibration method for triaxial accelerometers was then proposed based on the shocks generating method. The sensitivity of the triaxial accelerometer was mathematically characterized as an exploitation and sensitivity matrix using the least-square method. Calibration experiments were carried out on a typical high-g triaxial accelerometer using the newly proposed synchronous method and the conventional asynchronous method, respectively. Results show that the developed synchronous shocks generating method is feasible and effective for triaxial accelerometer calibration. And synchronous calibration methods ought to be given priority for triaxial accelerometers, because they can significantly improve the measurement accuracy. At last, several key issues regarding to the application of the proposed shocks generating method in triaxial accelerometer calibration were discussed.