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.

With the rapid advancement in the design and manufacturing of fibre-reinforced polymer composites, the limited research on the high-rate dynamic flexural behaviour restricts the effective use of these materials in high-performance load-bearing applications. Sustainable composites made from intralaminar-hybridised basalt-flax fibres, along with their hybrids incorporating carbon fibres, were fabricated using vacuum assisted resin infusion technique. A modified Split-Hopkinson Pressure Bar technique was employed for the high-rate three-point bending tests, while the quasi-static flexural behaviour was assessed with an electromechanical universal testing machine. In-situ damage characterisation for the dynamic testing was analysed with the aid of high-speed camera footages. The strain rate effect and energy absorption capability were also analysed. The novel basalt-flax/carbon fibre-reinforced epoxy composite achieved an ultimate flexural strength exceeding 2000 MPa at a loading velocity of 30.5 m/s, which represents a 21% improvement over its pure carbon fibre-reinforced counterpart and a 93% improvement surpassing its carbon/basalt fibre-reinforced counterpart. Their superior dynamic flexural properties demonstrate great applicability of basalt and flax fibres as sustainable reinforcing fibres in high-velocity impact applications, especially in the automotive and aerospace industries. Graphical Abstract

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.