A new structure with a bidirectional negative stiffness (BNS) value utilizing buckling phenomena (often called bi-stable or snap-through) and a mechanical diode are presented with regard to mechanical metamaterial applications. The need for cost and mass efficient vibration isolation parts within the modern aerospace, automotive, and civil industries has been the subject of many interesting studies in the last several decades. With conventional materials in nature, many innovative approaches have been proposed, but with some limitations for vibration suppression. To cope with these difficulties, it was possible to employ a man-made material with a negative density or negative stiffness, not existing in nature. Recently metamaterials, i.e., man-made repeating structures with negative densities or/and stiffness values, have been proposed and their applications have been reported. This research presents a new man-made structure with a BNS, using the help of bi-stable mechanisms and a mechanical diode. With regard to the metamaterial application of this phenomenon, the dispersion nature of a 1D bi-stable mechanism has been studied and a new novel structure having BNS with a mechanical diode is presented. The effects of states of snap-through were highlighted and quantified experimentally.

We propose and demonstrate a coating-enhanced dual-microspheric structure fiber sensor that measures temperature and refractive index simultaneously. The claddings of the two microspheric structured fibers are spliced together and the ends of the fibers are coated with a layer of gold film to increase reflection, thereby forming a dual-microspheric structure sensor head. Our experimental results show that the temperature sensitivity and the refractive index can reach 65.77 pm °C−1 and −19.7879 nm RIU −1 , respectively. Compared with the uncoated sensor, the refractive index sensitivity is significantly improved by the gold film. This work suggests a low-cost, high-resolution and convenient fiber-based method to achieve multifunctional sensing applications.

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To qualitatively understand the deformation processes and damages in the human body caused by high-speed impact, we conducted experimental and computational investigations for bullet penetration into viscoelastic ballistic gelatin blocks. Because it is difficult to measure the strain rate-dependent material properties of viscoelastic gelatin blocks during high-speed impact, the material properties that are indirectly defined by the stress relaxation test were used for the computational simulation. We also conducted some firing experiments and analyzed the deformation processes of the structures. In particular, the passing through times and the shapes of the temporary and permanent cavities inside the ballistic gelatin blocks were analyzed and compared. This data reveals that the employed material models, with some modifications for the FE simulation, are sufficient for predicting the high-speed impact behaviors. To investigate the shapes of the permanent cavities and fragments made by bullets inside the gelatin blocks, two-dimensional sectional images were taken by an industrial CT scanner and a three-dimensional CAD model was constructed based on these images.

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