Abstract:

Objective In order to solve the contradiction between the isolation bearing capacity and isolation frequency of linear isolators at low frequencies, a quasi-zero stiffness fabric isolator with this characteristic is designed using diagonal fabric based on the principle of nonlinear stiffness. A sinusoidal excitation signal is applied to the vibration isolator to evaluate its vibration isolation performance through vibration testing.

Method A bending crease model was developed in SolidWorks, and finite element analysis (FEA) was conducted using ABAQUS to simulate the compression behavior of the model. The same bending crease pattern was then applied to the fabric, followed by compression experiments. Two fabric solid elements with different crease curvatures were designed based on the bending crease model. Finite element simulations and experimental compression tests were performed. Vibration isolation performance tests were carried out on different fabric three-dimensional unit arrays to verify the low-frequency vibration isolation performance of the quasi-zero stiffness fabric isolator.

Results Finite element simulation compression was performed on the bending crease model. The simulation results showed that during the compression process of the model, the stress was first concentrated at the creases on both sides with a symmetrical distribution. As the degree of bending increased, the stress was transferred to the middle of the crease. The stress value on the bending surface was always lower than that at the crease throughout the process. The compression force-displacement curve was analyzed to assess the performance. Three different types of stiffness curves were obtained by changing the model parameters (chord height h, folding angle β). When other parameters were held constant, the chord height h was increases from 2.0 mm to 5.5 mm, the stiffness of the model was changed from negative stiffness to quasi-zero stiffness and then to positive stiffness, and the initial compression force value demonstrated a decrease from 30 cN to 21 cN. As the crease angle β varied from 90° to 150°, the model's stiffness was changed from negative stiffness to positive stiffness. Compression experiments were performed on fabric samples using the same bending crease pattern. The compression force displacement curves of the fabric at folding angles β of 110°, 130°, and 150° were highly similar to those obtained from finite element simulation, verifying the correctness of the finite element simulation and jointly elucidating the adjustable mechanism of nonlinear stiffness. Finite element simulation and experimental compression were conducted on fabric units with two different fold curvatures. The correlation coefficients between the simulation results and the experimental results were both above 0.833. Two types of fabric unit arrays were placed on an excitation table. Loads were applied to them to achieve quasi-zero stiffness and positive stiffness, respectively. The experimental results demonstrated that the designed quasi-zero stiffness fabric unit exhibited superior isolation performance compared to the positive stiffness fabric unit in the frequency range of 5-25 Hz.

Conclusion A fabric three-dimensional unit isolator was designed to solve the problem of low-frequency isolation in linear isolators. A bending crease model was proposed, which was subjected to finite element simulation compression and fabric experimental compression. The influence of model parameters on the compression force displacement curve was revealed in two ways. Three distinct stiffness curves were obtained, which elucidate the mechanism of nonlinear stiffness adjustment. Based on this mechanism, two types of fabric three-dimensional units with different bending crease curvatures were designed and simulated and experimentally verified. The experimental compression force-displacement curves of the two fabric units exhibited a strong correlation with the simulation results, with quasi-zero stiffness and positive stiffness demonstrated, respectively. The results show that in the low-frequency range, the vibration transmission of quasi-zero stiffness fabric array is negative, while that of positive stiffness fabric array is positive. The quasi-zero stiffness fabric array exhibits better isolation performance than the positive stiffness fabric array, indicating that the former can be used as a nonlinear isolator.

Key words: bending crease model, vibration isolation performance, adjustable stiffness, fabric unit, fabric vibration isolator