Identification of material properties of composite plate specimens

An indirect identification technique to predict the mechanical properties of composite plate specimens is presented. This technique makes use of experimental eigenfrequencies, the corresponding numerical eigenvalue evaluation, sensitivity analysis and optimization. The laminate analysis is formulated in terms of non-dimensional material parameters and the discrete model is based on the linear shear deformation theory of Mindlin. The constrained minimization of an error functional expressing the difference between measured higher frequencies of a plate specimen and the corresponding numerical ones is then carried out to find the desired optimum parameters. The required sensitivities with respect to changes in the non-dimensional material parameters have the option of being evaluated analytically, semi-analytically or alternatively by finite difference. Results which show the validation of the sensitivities and the limitations of the model to predict the required quantities and its range of application and accuracy are demonstrated through test cases.     

Theory of infrared microspectroscopy for intact fibers

Infrared microspectroscopy is widely used for the chemical analysis of small samples. In particular, spectral properties of small cylindrical samples are important in forensic analysis, understanding relationships between microstructure and mechanical properties in fibers or fiber composites, and development of cosmetics and drugs for hair. The diameters of the constituent cylinders are typically of the order of the central wavelength of light used to probe the sample. Hence, structure and material spectral response are coupled and recorded spectra are usually distorted to the extent of becoming useless for molecular identification. In this paper, we apply rigorous optical theory to predict the spectral distortions observed in IR microspectroscopic data of fibers. The theory is used, first, to compute the changes that are observed for cylinders of various dimensions under different instrument configurations when compared to the bulk spectrum from the same material. We provide a method to recover intrinsic material spectral response from fibers by correcting for distortion introduced by the cylindrical structure. The theory reported here should enable the routine use of IR microspectroscopy and imaging for the molecular analysis of cylindrical domains in complex materials.     

Attenuated total reflection surface-enhanced infrared absorption microspectroscopy for identification of small thin layers on material surfaces

Attenuated total reflection surface-enhanced infrared absorption microspectroscopy (micro-ATR-SEIRA) was developed for the identification of sub-mm size and nm-thick layers on material surfaces by using gold island films deposited on the surface of micro-ATR crystals. A thin layer of triphenyl phosphate (TPP) on a poly(tetrafluoroethylene) (PTFE) membrane filter was used to evaluate the enhancement of the absorption bands. Three types of crystals: diamond, silicon, and germanium, were evaluated. Diamond gave the greatest enhancement with a 12 nm thick gold island film. The enhancement factor was 200 times compared to bare diamond crystal, whereas it was 10 times for germanium crystal. This variation of enhancement factor according to crystal types was presumed to be due to the morphology of the gold films on the crystals. We also obtained an enhanced ATR map over an area of approximately 2 x 6 mm for a thin layer (approximately 1 nm thick) of di-2-ethylhexylphthalate on PTFE using gold-coated hexagonal silicon micro-ATR crystals. This micro-ATR-SEIRA technique has major potential for analyzing small and thin substances on material surfaces.     

Two-dimensional correlation analysis of polyimide films using attenuated total reflection-based dynamic compression modulation step-scan Fourier transform infrared spectroscopy

Attenuated total reflection (ATR)-based dynamic compression modulation two-dimensional (2D) correlation study of poly(p-phenylene biphenyltetracarboximide) film is carried out in combination with spectral simulation analysis by density functional theory (DFT). The dynamic 2D infrared (IR) correlation spectra in the region of imide I (C=O stretching mode) show three distinct correlation peaks located around 1777, 1725, and 1708 cm(-1). The band at 1708 cm(-1) is the lower wavenumber shift component of 1777 or 1735 cm(-1) peaks and is attributed to the results from intermolecular interactions, according to the DFT analysis. The 1708 cm(-1) band also shows the largest dynamic response, suggesting that these intermolecular interactions may enhance the dynamic response. The dynamic 2D IR correlation spectra in the region of imide II (C-N-C axial stretching mode) vibrations also show three correlation peaks located around 1335, 1355, and 1370 cm(-1), although the imide II band is shown to consist substantially of one component by the DFT analysis. These multiple peaks may be attributed to the compression-induced wavenumber shift of the band in the backbone structures. The sequential analysis of 2D correlation data show that, upon applying the dynamic compression, the response of the backbone regions (imide II) occurs first, followed by that of the side-chain regions (imide I, C=O).     

Analysis of latent fingerprint deposits by infrared microspectroscopy

We report the use of infrared (IR) microspectroscopy for the analysis of fingerprint residues. The advantage of using an IR microscope lies in the ability to visualize and obtain spectra of individual particles and droplets that make up fingerprint ridge deposits at a spatial resolution of approximately 10 microm. Our initial results suggest that infrared microspectroscopy in reflection-absorption mode provides reproducible spectral analysis of fingerprint residue. Since infrared microspectroscopy is nondestructive to the sample, we will be able to study the changes in fingerprint ridge deposits as a function of time. The method holds promise for probing the difference between latent fingerprints of adults and children.     

Aleurone cell walls of wheat grain: high spatial resolution investigation using synchrotron infrared microspectroscopy

Infrared microspectroscopy and immunolabeling techniques were employed in order to obtain deeper insight into the biochemical nature of aleurone cell walls of wheat grain. The use of a synchrotron source, thanks to its intrinsic brightness, has provided unprecedented information at the level of a few micrometers and has allowed the discrimination of various polysaccharides in cell walls. The high spectral quality obtained in the small analyzed domain has been beneficial in estimating the relative proportions of beta-glucan and arabinoxylan, through the use of principal component analysis (PCA). The highest amount of beta-glucan is found in periclinal cell walls close to the starchy endosperm. The junction regions between aleurone cells are enriched in arabinoxylan. At the early stage of wheat grain development (271 degrees D), the chemical composition along the cell walls is more heterogeneous than at the mature stage. Both synchrotron infrared microspectroscopy and immunolabeling experiments made it possible to reveal the spatial heterogeneity of the various chemical compositions of aleurone cell walls.     

Characterization of an attenuated total reflection-based sensor for integrated solid-phase extraction and infrared detection

A novel attenuated total reflection (ATR) sensor, which integrates solid-phase extraction (SPE) and infrared detection, is presented. The flow cell, which enables the on-line coupling with a sequential injection system, is the core of the proposed sensor since it allows the continuous delivery of different solutions through the ATR and also the continuous spectrum acquisition. A SPE sorbent material (LiChrolut EN) was located in the sensitive element of the ATR without using any external coating substance, increasing the versatility of the system. A marked sensitivity enhancement was obtained as the analyte was concentrated before detection. The new sensor was qualitatively and quantitatively validated using the determination of caffeine in soft drinks as the model analytical problem. Linearity, precision (RSD = 4%), and sensitivity (LOD = 7 microg/mL) levels have been established. Finally, the main advantages and limitations of the new proposal are presented and compared with existing alternatives.     

Synchrotron infrared microspectroscopy characterization of heterogeneities in solid-state blended polymers

Immiscible polymers, including polystyrene (PS) and polyethylene terephthalate (PET), were blended in the solid state via mechanical attrition, the first step of a near net-shape manufacturing (NNSM) technique. Subsequent analysis via Fourier Transform Infrared Spectroscopy (FT-IR) with synchrotron radiation successfully distinguished between blend components. Characteristic absorbance peaks for each polymer allowed both qualitative and quantitative mapping within prepared samples. Reproducible area maps were created for 50/50 blends of polymethylmethacrylate (PMMA)/PET and PET/PS, which exhibited areas of macroscopic phase separation. Fluctuations in blend concentration were particularly evident for PS/PMMA. However, spatial resolution was shown to limit the detection of heterogeneities. Further modifications with the synchrotron IR apparatus will improve resolution and allow for the direct comparison of NNSM-processed and melt-blended polymers.     

In situ infrared microspectroscopy of approximately 850 million-year-old prokaryotic fossils

In situ infrared (IR) and Raman microspectroscopy have been conducted on Neoproterozoic, organic-walled microfossils (prokaryotic fossils) in doubly polished, petrographic thin sections in order to detect their spectral signatures. The microfossils are very well preserved and occur in black chert from the approximately 850 million-year-old Bitter Springs Formation, Northern Territory, Australia. Raman microspectroscopy on two species of microfossils, one a filament and the other a coccoid, shows disordered peaks (D peak, 1340 cm(-1)) and graphite peaks (G peak, 1600 cm(-1)), indicating that they consist of disordered carbonaceous materials. IR micro-mapping results of the filament reveal that the distributions of peak heights at 2920 cm(-1) (aliphatic CH(2)), 1585 cm(-1) (aromatic C-C), and 1370 cm(-1) (aliphatic CH(3)) match the shape of the filamentous microfossil. These results suggest that IR microspectroscopy can be used for in situ characterization of organic polar signatures that morphologically indicate microfossils embedded in chert by using doubly-polished rock (petrographic) thin section samples. Further, these methods can be applied to controversial microfossil-like structures to test their biogenic nature.     

Evaluating fatigue crack propagation properties using miniature specimens

Standard fatigue crack propagation (FCP) test placed strict requirement on specimen size. FCP rate in subsize specimen was found to be slightly but consistently slower than that in the standard specimens. Based on a critical study on two aluminum alloys and two steels, we found the lower rates can be attributed to the plane stress state in the miniature specimens being different from that in the standard specimens. By taking account of crack closure, the miniature specimen data are brought in line with the standard specimen results and may serve as an upper bound estimate of FCP properties.     

Determination of mechanical strength properties of hemp fibers using near-infrared fourier transform Raman microspectroscopy

Fourier transform near-infrared (FT-NIR) Raman microspectroscopy was adopted for analyzing the micro mechanical tensile deformation behavior of cellulosic plant fibers. Mechanical strength parameters such as tensile strength, failure strain, and Young's modulus of diversified hemp fibers were determined within the range of single fiber cells and fiber filaments. The analysis of fiber deformation at the molecular level was followed by the response of a characteristic Raman signal of fiber cellulose that is sensitive to the tensile load applied. The frequency shift of the Raman signal at 1095 cm(-1) to lower wavenumbers was observed when the fibers were subjected to tensile strain. Microstructural investigations using electron microscopy under environmental conditions supported the discussion of mechanical properties of hemp fibers in relation to several fiber variabilities. Generally, mechanical strength properties of diversified hemp fibers were discussed at the molecular, microstructural, and macroscale level. It was observed that mechanical strength properties of the fibers can be controlled in a broad range by appropriate mercerization parameters such as alkali concentration, fiber shrinkage, and tensile stress applied to the fibers during the alkaline treatments.     

Imaging properties in two-photon excitation microscopy and effects of refractive-index mismatch in thick specimens

The detrimental effects of a refractive-index mismatch on the image formation in a two-photon microscope were investigated. Point-spread functions (PSF's) were recorded with an oil-immersion objective numerical aperture (NA) of 1.3 and a water-immersion objective NA of 1.2 in an aqueous sample at different depths. For the oil-immersion objective the enlargement of the PSF volume with increasing depth yields an axial and a lateral loss in resolution of approximately 380% and 160%, respectively, at a 90-mum depth in the sample. For the water-immersion objective no resolution decrease was found. Measurements on a thick aqueous biofilm sample shows the importance of matching the refractive index between immersion fluid and sample. With a good match, no loss in image resolution is observed.     

Distinction of cervical cancer biopsies by use of infrared microspectroscopy and probabilistic neural networks

Fourier-transform infrared spectroscopy has shown alterations of spectral characteristics of cells and tissues as a result of carcinogenesis. The research reported here focuses on the diagnosis of cancer in formalin-fixed biopsied tissue for which immunochemistry is not possible and when PAP-smear results are to be confirmed. The data from two groups of patients (a control group and a group of patients diagnosed with cervical cancer) were analyzed. It was found that the glucose/phosphate ratio decreases (by 23-49%) and the RNA/DNA ratio increases (by 38-150%) in carcinogenic compared with normal tissue. Fourier-transform microspectroscopy was used to examine these tissues. This type of study in larger populations may help to set standards or classes with which to use treated biopsied tissue to predict the possibility of cancer. Probabilistic neural networks and statistical tests as parts of these biopsies predict the possibility of cancer with a high degree of accuracy (> 95%).     

Methodological aspects of studying dynamic material properties using the Kolsky method

An experimental configuration designed for studying properties of structural materials within the strain-rate range of 5 × 10²−5 × 10³ s⁻¹ is described. The configuration is based on the conventional versions of the dynamic testing methodologies using the split Hopkinson bar (SHB) method and modifications of these methods originally proposed by the authors. Special emphasis is given to discussing the modifications of the Kolsky method that render new possibilities for studying history effects (including those for alternating dynamic loading) and dynamic hardness. Examples are given illustrating the capabilities of the experimental configuration in studying the dynamic properties of some materials.     

Measurement of the material properties of viscous liquids using ultrasonic guided waves

The theoretical basis for a testing tool in the form of a circular waveguide for measuring both the dynamic viscosity and the longitudinal bulk velocity of viscous liquids is presented. It is based on the measurements of the attenuation of the fundamental torsional mode, T(0,1), and the fundamental longitudinal mode, L(0,1), of the waveguide when immersed in the liquid. The modeling techniques to extract the shear viscosity and the longitudinal bulk velocity are explained and experimentally verified. Results for two viscous liquids are presented: good agreement between theory and experiment was obtained.     

High-accuracy standard specimens for the line-focus-beam ultrasonic material characterization system

We prepared standard specimens for the line-focus-beam ultrasonic material characterization system to obtain absolute values of the propagation characteristics (phase velocity and attenuation) of leaky surface acoustic waves (LSAWs). The characterization system is very useful for evaluating and analyzing specimen surfaces. The calibration accuracy of these acoustic parameters depends on the accuracy of acoustical physical constants (elastic constants, piezoelectric constants, dielectric constants, and density) determined for standard specimens. In this paper, we developed substrates of non piezoelectric single crystals (viz., gadolinium gallium garnet [GGG], Si, and Ge) and an isotropic solid (synthetic silica [SiO₂] glass) as standard specimens. These specimens can cover the phase velocity range of 2600 to 5100 m/s for Rayleigh-type LSAWs. To determine the elastic constants with high accuracy, we measured velocities by the complex-mode measurement method and corrected diffraction effects. Measurements of bulk acoustic properties (bulk wave velocity and density) were conducted around 23°C, and bulk wave velocities were obtained with an accuracy of within ±0.004%. We clearly detected differences in acoustic properties by comparing the obtained results with the previously published values; the differences were considered to be due to differences of the specimens used. We also detected differences in acoustic properties among four SiO₂ substrates produced by different manufacturers     

热红外伪装遮障材料的制备

热红外伪装遮障材料的制备是研制超轻型多波段伪装遮障的关键技术之一。阐述了一种优化的制备热红外伪装遮障材料的关键技术、配方与工艺等。采用本体透明型方法制备了绿色和土色低发射率材料。检测结果表明，研制的低发射率防热红外伪装涂层样品具有红外发射率低、红外透明性好、多光谱兼容等特点。     

Measurement of viscoelastic properties of tissue-mimicking material using longitudinal wave excitation

This paper presents an experimental framework for the measurement of the viscoelastic properties of tissuemimicking material. The novelty of the presented framework is in the use of longitudinal wave excitation and the study of the longitudinal wave patterns in finite media for the measurement of the viscoelastic properties. Ultrasound is used to track the longitudinal motions inside a test block. The viscoelastic parameters of the block are then estimated by 2 methods: a wavelength measurement method and a model fitting method. Connections are also made with shear elastography. The viscoelastic parameters are estimated for several homogeneous phantom blocks. The results from the new methods are compared with the conventional rheometry results.