Kevlar fiber–epoxy adhesion and its effect on composite mechanical and fracture properties by plasma and chemical treatment

Kevlar 49 fibers were surface-modified by NH₃-, O₂-, and H₂O-plasma etching and chlo-rosulfonation and subsequent reaction with some reagents (glycine, deionized water, eth-ylendeiamine, and 1-butanol) to improve the adhesion to epoxy resin. After these treatments, the changes in fiber topography, chemical compositions of the fiber surfaces, and the surface functional groups introduced to the surface of fibers were identified by SEM, XPS, and static SIMS. Interlaminar shear strength (ILSS) and T-peel strenght between the fiber and opoxy resin, as measured by the short-beam test and T-peel test, were remarkedly improved by gas plasma and chlorosulfonation (0.1% and 0.25% CISO₃H at 30 s). However, from the results of similar G_IC values of the treated and untreated fiber composites, it is clear that the fiber/matrix interfacial bond strength is only a minor contributor to G_IC. SEM was also used to study the surface topography of the fracture surfaces of composites in T-peel test. It could be seen from SEM observations that the improvement of fiber/matrix interfacial bond strength often accompanied a change in fracture mode from the interface of fiber/epoxy resins to the fiber fibrillation and the resins. © 1996 John Wiley & Sons, Inc.     

Effects of processing conditions on the quality of vacuum‐fried carrot chips

The effects of pretreatment and vacuum frying conditions on the quality of fried carrot chips were studied. The moisture and oil contents of fried carrot chips were significantly (p < 0.05) reduced when blanched carrot slices were pretreated by immersion in fructose solution and freezing prior to vacuum frying. Furthermore, more uniform porosity was observed on the vertical cross‐section of carrot chips when examined by scanning electron microscopy. During vacuum frying, the moisture content, colour and breaking force of carrot chips decreased while the oil content increased with increasing frying temperature and time. However, there was no apparent change in Hunter ΔE with time when the frying temperature was below 100 °C and the frying time was below 25 min. Results of this study suggest that vacuum frying at moderate temperature (90–100 °C) for 20 min can produce carrot chips with lower moisture and oil contents as well as good colour and crispy texture. Copyright © 2005 Society of Chemical Industry     

Spherulitic Growth of Apatite in a MgO─CaO─SiO2─P2O5 Glass

Differential thermal analysis, X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, and transmission electron microscopy were used to study the crystallization of a glass with a composition of 11.2 wt% MgO, 40.5 wt% CaO, 33.3 wt% SiO₂, and 15 wt% P₂O₅. A two-phase "composite," which was composed of apatite and an intermediate phase (H-phase), was formed under appropriate heat-treatment conditions. The spherulitic morphology of apatite phase transformed from "open sheaf" into ellipsoidal as samples were heated to a higher temperature. These phenomena were due to the intermediate H-phase becoming unstable at this temperature so that the retardation effect on the apatite dendritic growth disappeared.     

Statistical energy analysis of non-resonant response of isotropic and orthotropic plates

The conventional SEA model considers only the resonant part of the structural response to an acoustic excitation. Therefore, this study investigates non-resonant responses of isotropic and orthotropic plates to acoustically induced vibrations in a reverberation chamber. A modified SEA model is introduced to predict the non-resonant plate response. The estimated non-resonant and resonant responses are then compared with those obtained experimentally, and good agreement is observed for isotropic and orthotropic plates. For an isotropic plate with a small dissipation loss factor, when the non-resonant part is ignored, the estimated response can lead to significant errors at frequencies near and above the critical frequency, while large errors may occur at frequencies below the critical frequency for an orthotropic plate with a high dissipation loss factor. The experimental study indicates that the non-resonant response component should be included in the estimated responses to enhance predictive accuracy.     

Application of a diffraction grating and position sensitive detectors to the measurement of error motion and angular indexing of an indexing table

In this paper, two systems for the measurement of the error motion and angular indexing of a rotary indexing table have been developed. A laser diode, a laser holder and a position sensitive detector (PSD) are integrated as a simple measuring device for the measurement of the rotary error without using a precision reference artifact (a cylinder or a sphere), multiple probes or error separation methods. The laser diode is assembled in the laser holder and fixed on the rotary table. The PSD is set up above the laser holder to detect the position of an incident laser beam from the laser diode. When the rotary table rotates, the rotary error changes the direction of the incident beam and also the position of the spot on the PSD. For the measurement of the angular indexing, a reflective diffraction grating and two PSDs are integrated as a high-resolution angle measuring device without using an autocollimator or a laser interferometer system. The diffraction grating is set at the center of the rotary table and reflects an incident laser beam into several diffractive rays. Two PSDs were set up for detecting the positions of ±1st-order diffraction rays. A simple algebraic method is used to solve the angular indexing through an optical analysis. The experimental results showed the feasibility of the proposed test devices.     

Synthesis and characterization of biodegradable TPP/genipin co-crosslinked chitosan gel beads

Novel chitosan gel beads were synthesized by a coupled ionic and chemical co-crosslinking mechanism. Tripolyphosphate (TPP) and a naturally occurring crosslinking reagent, genipin, which has been used in herbal medicine, were employed, respectively, as an ionic and a chemical crosslinkers to prepare the chitosan-based networks of gel beads. The competitive crosslinking of chitosan with ionic crosslinker (TPP) and chemical crosslinker (genipin) was characterized by FTIR, UV and EDAX spectroscopy (X-ray energy dispersion) spectroscopy. The variation of characteristic peak of genipin observed from UV spectroscopy and the characteristic peak of tripolyphosphate in crosslinked chitosan-based networks observed from FTIR spectroscopy suggests that the co-crosslinking mechanism is dependent on the pH of TPP/genipin co-crosslinker. The energy profiles of carbon and phosphorus estimated from confirms that chemical crosslinking dominates the co-crosslinking reaction at higher pH condition (pH 7.0 and 9.0) and ionic crosslinking dominates the co-crosslinking reaction at lower pH condition (pH 1.0, 3.0 and 5.0). The pH-dependent ionic/chemical co-crosslinking mechanism shows an obvious effect on the swelling property and enzymatic degradation behavior of prepared chitosan networks. These results reveal that the ionic/chemical co-crosslinked chitosan networks may be suitable for biomedical applications.     

Diffusion bonding/superplastic forming of Ti-6Al-6V-2Sn/SUS 304 stainless steel/Ti-6Al-6V-2Sn

The superplasticity of the Ti- 6Al- 6V- 2Sn alloy for different temperatures was evaluated by single-sheet free blowing. The optimal superplastic temperature for the Ti- 6Al- 6V- 2Sn alloy was found to be 850 °C. Diffusion bonding of Ti- 6Al- 6V- 2Sn and 304 stainless steel was carried out in a vacuum. The interface of both bonded alloys was examined by EPMA. The concentration profile of Ni exhibited a peak at the interlayer and a valley adjacent it, whereas that of Cr exhibited a peak where Ni showed the valley. X- ray diffraction (XRD) analyses showed that the Fe ₂ Ti, NiTi, and CrMn Intermetallic compounds and the Cr element formed at the interface. The thickness profiles of the blown specimens were measured and compared with theoretical calculations.     

Crystallization of MgO-CaO-SiO2-P2O5 Glass

The crystallization behavior of a glass with a composition of 40 wt% 3CaO · P₂O₅−60 wt% CaO · MgO · 2SiO₂ was investigated. The primary crystalline phase was apatite with a dendritic form and ellipsoidal shape. β-(3CaO · P₂O₅) and CaO · MgO · 2SiO₂ were crystallized as samples heated to 990°C, and a three-layer structure was obtained. The development and morphology of this construction were explained by both the surface crystallization of the apatite and CaO · MgO · 2SiO₂ and the bulk crystallization of apatite and the CaO · MgO · 2SiO₂-β-(3CaO · P₂O₅) composite.     

Development of FRP Short-Span Deployable Bridge—Experimental Results

For military and civilian applications, there exists a need for lightweight, inexpensive, short-span bridges that can be easily transported and erected with minimal equipment. Owing to its favorable properties, fiber-reinforced polymer (FRP) has been shown to be feasible for the construction of such bridges. Investigations into the behavior of a short-span bridge structural concept, adapted to the material properties of commercially available glass FRP (GFRP) pultruded products, are presented. A 4.8-m span prototype was built from GFRP sections, bonded throughout to form a tapered box beam, with a width of 1.2?m and a height at midspan of approximately 0.5?m. The box beam represents a single trackway of a double-trackway bridge, whose trackways could be connected by light structural elements. The quasi-static and dynamic behavior of the prototype box beam was investigated in ambient laboratory and field conditions to assess the design and construction techniques used, with a view to designing a full-scale 10-m GFRP bridge. Laboratory testing of the prototype box beam used single and pairs of patch loads to simulate wheel loading. These tests confirmed that the box beam had sufficient stiffness and strength to function effectively as a single trackway of a small span bridge. Field testing of the structure was undertaken using a Bison vehicle (13,000?kg), driven at varying speeds over the structure to establish its response to realistic vehicle loads and the effects of their movement across the span.     

In-situ Mössbauer spectroscopic study of the behaviour of tin(II) chloride during coal hydrogenation

In-situ Mössbauer spectroscopy has been used to study the catalytic role of SnCl₂ and its interaction with the IL6 coal during hydrogenation. The measurements have been recorded under three different atmospheres of nitrogen, hydrogen, and hydrogen in the presence of a heavy distillate solvent SRC-II. The study has shown that both tin and chlorine can enter the coal structure at an early stage of hydrogenation. The presence of chlorine has been shown to cause the cleavage of ether-oxygen linkages in the coal. Tin (II) sulphide is the predominant form of the catalyst after the hydrogenation and is the product of the scavenging of coal sulphur by tin. The study has also shown the formation of FeCl₂ · xH₂0 (x = 1, 2) as a result of the reaction between pyrrhotites (Fe_(1?x)S, formed by the decomposition of FeS₂) and hydrochloric acid in the nitrogen and the hydrogen atmospheres.