On-line studies of structural and morphological changes during the heating and drawing process of isotactic polypropylene (iPP) fiber were carried out using synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques. A unique image analysis method was used to deconvolute the two-dimensional (2D) WAXD patterns into quantitative fractions of crystal, mesomorphic, and amorphous phases. Results showed that the R-form crystals were quite defective in the initial iPP fibers and were converted into the mesomorphic modification by drawing at room temperature. Corresponding 2D SAXS patterns showed that there was no obvious long period (i.e., no lamellar structure) in the mesophase of the iPP fiber. We postulate that the constituents of the mesophase in iPP fibers include oriented bundles of helical chains with random helical hands and perhaps oriented chains with no helical structures; both have only partial packing ordering. The formation of the mesophase is through the destruction of the lamellar crystalline phase probably by pulling chains out from crystals. The R-form crystals were not converted into the mesophase by drawing at high temperatures. At higher temperatures, the R-form crystals became perfect and the crystallinity increased when the fiber was drawn. However, the draw ratio showed an inverse effect. The increase in draw ratio had a minimal effect on the crystallinity, but the transformation from the amorphous phase to the mesophase became dominant.

The surface composition and surface chain conformation of a series of random aspecific poly(ethylene-copropylene) rubber copolymers (aEPR) was quantified by sum frequency generation surface vibrational spectroscopy (SFG). All of the copolymers are found to preferentially orient side-branch methyl groups out of the surface. As the ethylene content of the copolymer increases, the number of methyl groups contributing to the sum frequency signal decreases. However, the percentage of methyl groups oriented out of the surface, relative to the bulk concentration of methyl groups, increases. This surface excess of oriented methyl groups is proposed to be a result of decreased steric hindrances between adjacent methyl groups in ethylene-rich copolymers. Additionally, analysis of the CH 2 bands in the SFG spectra suggests that the CH 2 units at the surface become more oriented toward the surface normal and adopt a trans configuration as the ethylene content increases.

The morphology and properties of high modulus polypropylenes (PP) are characterized over a wide range of material variables. These variables include the tacticity, room temperature xylene solubles (XSRT), molecular weight, melt flow rate (MFR), and polydispersity index (PI). Flexural modulus in quench‐cooled compression moldings of propylene homopolymer can be correlated to the volume fraction crystallinity, ϕc, by an empirical logarithmic dependence. The quantitative zero orientation results for the quench‐cooled compression moldings provide an approximate crystallinity normalization for oriented moldings. WAXS analyses of crystalline orientation were determined over a range of melt temperatures and mold locations and correlated to the skin area fraction by optical microscopy. WAXS analysis of the balance of orientations for the crystallographic axes suggest that the orientation balance is primarily determined by the “melt orientability” of the resin type. An empirical description of flexural modulus in injection molded PP is developed for the range of material variables and molding conditions studied. This description is represented as a function of crystallinity‐normalized modulus vs. the frozen‐in crystalline orientation.

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This article describes a new system for high-speed and noncontact rail integrity evaluation being developed at the University of California at San Diego. A prototype using an ultrasonic air-coupled guided wave signal generation and aircoupled signal detection has been tested at the University of California at San Diego Rail Defect Farm. In addition to a real-time statistical analysis algorithm, the prototype uses a specialized filtering approach due to the inherently poor signal-to-noise ratio of the air-coupled ultrasonic measurements in rail steel. The laboratory results indicate that the prototype is able to detect internal rail defects with a high reliability. Extensions of the system are planned to add rail surface characterization to the internal rail defect detection. In addition to the description of the prototype and test results, numerical analyses of ultrasonic guided wave propagation in rails have been performed using a Local Interaction Simulation Approach algorithm and some of these results are shown. The numerical analysis has helped designing various aspects of the prototype for maximizing its sensitivity to defects.

The surface composition profiles of bulk miscible and immiscible blends of atactic polypropylene (aPP) with aspecific poly(ethylene-co-propylene) rubber (aEPR) were studied by differential scanning calorimetry (DSC), sum frequency generation surface vibrational spectroscopy (SFG), and X-ray photoelectron spectroscopy (XPS). SFG spectra of blends of aPP and aEPR show that aPP preferentially segregates to the air/polymer interface, for both the bulk miscible and immiscible systems. The SFG spectra also indicate that methyl side branches assume a preferred configuration at the air/polymer interface, which may play a role in the high surface activity of aPP. Bulk miscibility is shown to control the thickness of the surface enrichment layer, with thicker enrichment layers detected by XPS on bulk immiscible blends. The thickness of the surface enrichment layer measured in the bulk miscible systems is in agreement with the thickness calculated using existing depth profiling models based on Flory-Huggins energy of mixing.

Structure and morphology development during the isothermal crystallization and subsequent melting of syndiotactic polypropylene (sPP) was studied with differential scanning calorimetry (DSC), time-resolved simultaneous small-angle X-ray scattering (SAXS), and wide-angle X-ray diffraction (WAXD) methods with synchrotron radiation. The morphology of sPP isothermally crystallized at 100°C for 3 h was also characterized with transmission electron microscopy (TEM). Time-and temperature-dependent parameters such as the long period (L), crystal lamellar thickness (l c ), amorphous layer thickness (l a ), scattering invariant (Q), crystallinity (X c ), lateral crystal sizes (L 200 and L 010 ), and unit cell dimensions (a and b) were extracted from the SAXS and WAXD data. Results indicate that the decreases in L and l c with time are probably due to the formation of thinner crystal lamellae, and the decreases in a and b are due to crystal perfection. The changes in the morphological parameters (Q, X c , L, and l c ) during subsequent melting exhibited a twostage process that was consistent with the multiple melting peaks observed in DSC. The two high-temperature peaks can be attributed to the melting of primary lamellae (at lower temperatures) and recrystallized lamellae (at higher temperatures). An additional minor peak, located at the lowest temperature, was also visible and was related to the melting of thin and defective secondary lamellae. TEM results are consistent with the SAXS data, which supports the assignment of the larger value (l 1 ) from the correlation function analysis as l c . WAXD showed that the thermal expansion was greater along the b axis than the a axis during melting.

Recent train accidents have reaffirmed the need for developing a rail defect detection system more effective than that currently used. One of the most promising techniques in rail inspection is the use of ultrasonic guided waves and noncontact probes. A rail inspection prototype based on these concepts and devoted to the automatic damage detection of defects in rail head is the focus of this paper. The prototype includes an algorithm based on wavelet transform and outlier analysis. The discrete wavelet transform is utilized to denoise ultrasonic signals and to generate a set of relevant damage sensitive data. These data are combined into a damage index vector fed to an unsupervised learning algorithm based on outlier analysis that determines the anomalous conditions of the rail. The first part of the paper shows the prototype in action on a railroad track mock-up built at the University of California, San Diego. The mock-up contained surface and internal defects. The results from three experiments are presented. The importance of feature selection to maximize the sensitivity of the inspection system is demonstrated here. The second part of the paper shows the results of field testing conducted in south east Pennsylvania under the auspices of the U.S. Federal Railroad Administration.