ABSTRACT:For some polymers such as PTFE, the crystallization is so rapid that it is difficult to observe isothermal crystallization by differential scanning calorimetry (DSC). In this investigation, first, isothermal crystallization kinetics of PTFE was followed by DSC and the results were analyzed by the Avrami method, which showed that PTFE crystallizes one-dimensionally from preexisting nuclei, presumably impurities. Furthermore, the crystallization activation energy, the equilibrium melting point, and the nucleation rate parameter K g were calculated in the isothermal crystallization. Second, nonisothermal crystallization was also studied and the result was in accordance with the results of isothermal crystallization. Then, the Kissinger method was used to investigate the activation energy of PTFE in the nonisothermal crystallization. Third, the effect of glass fiber (used as filling) was investigated on crystallization of PTFE matrix.

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Recently, there is interest in triggering shape recovery of shape-memory polymers(SMPs) by novel non-external heating. In this paper, many hard works have been carried out to make SMP induced by solution. The main challenge in the development of such polymer systems is the conversion of solution-induced effects at the molecular level to macroscopic movement of working pieces. This paper presents a systematic study on the effects of solution on the glass transition temperature (Tg). The results reveal that the hydrogen bonding of shape memory polymer (SMP) was aroused by the absorbed solution that significantly reduces Tg of polymer. The mechanism behind it is solution firstly intenerates polymeric materials till the Tg of polymer lowered down to the temperature of ambient, then hydrogen bonding interaction improves the flexibility of polymeric macro-molecular chains. Thus, the shape memory effect (SME) can undergo solution-driven shape recovery. In addition, it provides a new approach that the SMP can be induced by applying non-energy stimulus. The Dynamic Mechanical Analyzer (DMA) results reveal that the modulus of polymer was softened gradually with immersion time increasing. The experimental result is approximate to the theory.

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This work presents an investigation on the damage and high-speed impact deformation mechanisms at elevated temperatures in honeycomb sandwich panels made from PM1000 and PM2000 alloys. The impact temperatures ranged from 22°C to 866°C. The investigation was performed experimentally using a custom-made gas gun rig, and by using Finite Element and developing a phenomenological analytical model to predict the residual velocity and ballistic limit equations for the case in which the diameter of the projectile is close or smaller to the honeycomb cell length. The sizes of the holes have been also evaluated by carrying out numerical thermal loading simulations on honeycomb sandwich specimen models impacted at high speed. The predictions provided by the Finite Elements and the analytical model give a good agreement with the results from the experimental tests. The hole diameters for the two idealized normal impact cases, in which the projectile hits the cell core and at the triple-wall intersection of the core, were also presented as a function of the projectile diameter and velocity in this paper.