ABSTRACT:We examined the molecular and structural variables that govern tensile properties of isotactic polypropylene forming spherulitic morphology. The polypropylenes were crystallized in such a manner as to develop as a wide range as possible in the values of the independent structural variables that describe the solid state. The initial deformations depend strongly on the amorphous regions but are independent of the spherulite size and lamellar thickness. At yield point the lamellae within spherulites were found to be fragmented and replaced by a highly oriented fibrous structure in the post-yield region. [DOI 10.1295/polymj.38.122] KEY WORDS Isotactic Polypropylene / Tensile Properties / Morphology / Spherulite / Semicrystalline polymers such as polyethylene and polypropylene contain both a liquid-like amorphous phase and an ordered crystalline phase. When solidified from the melt, these polymers show spherulitic structure, in which the crystalline lamellae composed of folded chains radiate from its center and the amorphous phases reside in the interlamellar regions in the form of tie chains, loop chains, cilia chains, and floating chains. In addition, the spherulite is filled with the lamellae in such a way that a constant long period is approximately maintained.The tensile properties of semicrystalline polymers showing spherulitic structure have been received a great deal of attention because of their scientific interest as well as practical importance. However, the molecular and structural mechanism underlying the deformation process is not well clarified yet. Essentially mechanical properties of these spherulitic materials are controlled by molecular morphology which depends largely on molecular constitution such as molecular weight and the structural regularity of the chain as well as crystallization conditions.1 The morphology of semicrystalline polymers can be simplified by various levels of hierarchy in structure such as crystalline thickness, amorphous layer thickness, the size of spherulite and the structural organization in the residual amorphous region.2 These diversity and independencies of these structural variables make it difficult to provide a molecular or structural interpretation for tensile behavior as suggested by Mandelkern et al. [2][3][4][5] In order to obtain a better understanding to the tensile behavior of semicrystalline polymers, these variables should be isolated and their individual roles assessed. Recently, this strategy has also been used in studies of tensile deformation of several polyethylenes.3,4 The present work is restricted to isotactic polypropylenes which are one of the most widely used polymers and expected to be further enhanced performance in the future. 5 The objective is to explore the structural variables that govern tensile behavior for isotactic polypropylenes with a high isotacticity. The independent structural variables are widely varied by controlling the molecular constitution and the crystallization conditions. For the purpose, the polymers studied in...
The primary aim of this study is to model and identify vibrations in mechanical systems subject to arbitrary external excitations. We propose a method based on infinite impulse response digital filter technology-termed time-frequency analysis-to analyze transient and steady-state vibrations. First, we introduce the timefrequency analysis procedure and the algorithm that implements it. Second, we analyze typical discrete signal inputs, such as impulse, sinusoidal and swept sine signals, and present time-frequency characteristics for transient and steady-state signals. Third, we apply our analysis method to the mechanical vibration behavior of a single-degree-of-freedom system subjected to various types of external excitations. The results of our analysis for steady-state vibration are verified as being equivalent to those from a Fast Fourier Transform (FFT) analysis. Moreover, the proposed analysis has the advantage over FFT analysis that we can also use it to analyze transient vibration phenomena.
This paper describes a novel energy-efficient, high-speed ADC architecture combining a flash ADC and a TDC. A high conversion rate can be obtained owing to the flash coarse ADC, and low-power dissipation can be attained using the TDC as a fine ADC. Moreover, a capacitive coupled ramp circuit is proposed to achieve high linearity. A test chip was fabricated using 65-nm digital CMOS technology. The test chip demonstrated a high sampling frequency of 500 MHz and a low-power dissipation of 2.0 mW, resulting in a low FOM of 32 fJ/conversion-step.
We are studying a new analysis method for transient responses by using the dlgital filten This paper demonstrates some time − frequency analysis results of responses based on typical differential equations . First , we present the results for the linear 丘ee and fbrced vibration responses of one degree − of − freedom system . Then we consider tho responses based on Duffng ' s equation and it is shown that the dominant frequency change ofthe responses can be visualized in the time − frequency analysis results . And the responses based on Van del Pol and Mathieu equations are analyzed to understand the several dominant frequencies . Finally , we apply the time − frequency analysis to the data ofcar bumping and it is shown that the phenomena may be described by the Duthng ' s equation .
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