Flexible porous materials generally switch their structures in response to guest removal or incorporation. However, the design of porous materials with empty shape-switchable pores remains a formidable challenge. Here, we demonstrate that the structural transition between an empty orthorhombic phase and an empty tetragonal phase in a flexible porous dodecatuple intercatenated supramolecular organic framework can be controlled cooperatively through guest incorporation and thermal treatment, thus inducing empty shape-memory nanopores. Moreover, the empty orthorhombic phase was observed to exhibit superior thermoelasticity, and the molecular-scale structural mobility could be transmitted to a macroscopic crystal shape change. The driving force of the shape-memory behaviour was elucidated in terms of potential energy. These two interconvertible empty phases with different pore shapes, that is, the orthorhombic phase with rectangular pores and the tetragonal phase with square pores, completely reject or weakly adsorb N2 at 77 K, respectively.
Network structures based on Star-of-David catenanes with multiple superior functionalities have been so far elusive, although numerous topologically interesting networks are synthesized. Here, a metal-organic framework featuring fused Star-of-David catenanes is reported. Two triangular metallacycles with opposite handedness are triply intertwined forming a Star-of-David catenane. Each catenane fuses with its six neighbors to generate a porous twofold intercatenated gyroid framework. The compound possesses exceptional stability and exhibits multiple functionalities including highly selective CO capture, high proton conductivity, and coexistence of slow magnetic relaxation and long-range ordering.
In this article, novel thermal gas sensors with newly designed diffusion gas channels are proposed to reduce the flow-rate disturbance. Simulation studies suggest that by lowering the gas flow velocity near the hot film, the maximum normalized temperature changes caused by flow-rate variations in the two new designs (Type-H and Type-U) are decreased to only 1.22% and 0.02%, which is much smaller than in the traditional straight design (Type-I) of 20.16%. Experiment results are in agreement with the simulations that the maximum normalized flow-rate interferences in Type-H and Type-U are only 1.51% and 1.65%, compared to 24.91% in Type-I. As the introduced CO2 flow varied from 1 to 20 sccm, the normalized output deviations in Type-H and Type-U are 0.38% and 0.02%, respectively, which are 2 and 3 orders of magnitude lower than in Type-I of 10.20%. In addition, the recovery time is almost the same in all these sensors. These results indicate that the principle of decreasing the flow velocity near the hot film caused by the two novel diffusion designs can enhance the flow-rate independence and improve the accuracy of the thermal conductivity as well as the gas detection.
In order to evaluate the flow stress of dual phase high strength steel in warm forming processes, the flow stress behaviours of dual phase steel were investigated at different temperatures and strain rates. A mathematical model is proposed to predict the stress–strain curves of dual phase steel during warm tension by employing the hyperbolic sine function of Zener–Hollomon parameter, which can describe the relationship among temperature, strain rate and flow stress under warm tensile deformation correctly. Material constants in the equation are expressed in polynomial form of strain. Parameters in the polynomials were obtained by least square method. The predicted stress–strain curves are in good agreement with experimental results, which confirms that the proposed model is accurate.
Based on empirical analysis and FEA modeling of multi-stage sheet metal stamping, the optimal sheet metal stamping process can be supplied. Concurrently, the effects of process parameters on formability are found by numerical simulation. Taking an example of deep drawing part, the results got from the numerical simulation are compared with experimental results, which proves that finite element analysis (FEA) is effective and accurate in optimizing the process design of multi-stage sheet metal progressive stamping.
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