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In this study, two types of polyurethane dispersion were applied as surface treatment for 10 types of washed/nonwashed carbon plain woven fabric-reinforced thermosetting and thermoplastic composites. To investigate the effects of surface treatment on the mechanical properties, the impregnation of various laminates was observed by a digital microscope. Dynamic mechanical analysis (DMA) was employed to investigate the interfacial interaction properties. Static tensile test was used to study the mechanical properties of composites. A correlation between the mechanical properties and interfacial interaction of composites was successfully observed. The acoustic emission (AE) from various composites was recorded in order to investigate the initial fracture and failure mechanism. Meanwhile, the knee-point method was also employed to look for initial fracture, which showed a good fit to initial strain detected from AE (amplitude > 80 dB). Furthermore, scanning electron microscopic images of single fiber and fractured carbon fiber bundles confirmed the interfacial properties evaluated by DMA analysis. Finally, remarkable improvement in mechanical properties (≈33.3%) of CF/PA6 laminates is discussed.

For traditional magnetorheological (MR) shock absorbers, the damping force is proportional to the square of the impact velocity. The instantaneous peak value of the damping force can easily cause damage to the load structure or human body, which will reduce the buffering efficiency. The viscous damping force is significantly affected by the size of the gap. Therefore, by changing the flow gap under different buffer strokes by presetting, the damping force can be maintained at a constant output in the full piston stroke, thereby improving the buffer efficiency. That is, a large gap is used at high speed and a small gap is used at low speed. The increase of the magnetic damping force at a small gap is applied to compensate for the decrease of the viscous force at low speed. Only constant current needs to be applied during buffering, which can greatly reduce costs. Based on this idea, a novel MR damper based on axial variable damping gap (MRD-VDG) is proposed. The MRD-VDG design method for the constant value output of the damping force in the full piston stroke is discussed and applied. According to the different requirements of the damping force under different piston displacements, the damping gap of different axial position are preset to realize the constant value output of the damping force during the stroke. The damping force under different damping gaps is analytically derived according to the Bingham-plastic nonlinear flow model with minor losses. Combining with the finite element analysis to obtain magnetic fields at different damping gaps between piston and cylinder. To validate the performance of the proposed design method, the prototype of MRD-VDG is fabricated. Damping characteristic test and impact test are performed to measure the damping characteristics of the MRD-VDG under different excited conditions. The results show that the piston displacement history of the damping force in the experiment is agreed well with the displacement history of the desired F-S curve under the assumed speed. The buffer efficiency of the prototype under designed conditions (the ratio of the corrected theoretical constant damping force to the actual peak damping force) exceeds 90%. This demonstrates the effectiveness of the MRD-VDG design. This design method has significant application prospects under impact condition without complex control (such as gun buffer, landing buffer, etc.)

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