Manabu Enoki

Quantized Folding of Plasmid DNA Condensed with Block Catiomer into Characteristic Rod Structures Promoting Transgene Efficacy

Highly regulated folding of plasmid DNA (pDNA) through polyion complexation with the synthetic block catiomer, poly(ethylene glycol)-block-poly(L-lysine) (PEG-PLys), was found to occur in such a way that rod structures are formed with a quantized length of 1/2(n + 1) of the original pDNA length folding by n times. The folding process of pDNA was elucidated with regard to rigidity of the double-stranded DNA structure and topological restriction of the supercoiled closed-circular form, and a mechanism based on Eulers buckling theory was proposed. Folded pDNA exhibited higher gene expression efficiency compared to naked pDNA in a cell-free transcription/translation assay system, indicating that the packaging of pDNA into a polyion complex core surrounded by a PEG palisade is a promising strategy for constructing nonviral gene carrier systems. Extension of this finding may provide a reasonable model to further understand the packaging mechanism of supercoiled DNA structures in nature.

New automatic localization technique of acoustic emission signals in thin metal plates.

In acoustic emission (AE) measurement, the information of the arrival time is very important for event location, event identification and source mechanism analysis. Manual picks are time-consuming and sometimes subjective, especially in the case of large volumes of digital data. Various techniques have been presented in the literature and are routinely used in practice such as amplitude threshold, analysis of the long-term average/short-term average (LTA/STA), high-order statistics or artificial neural networks. A new automatic determination technique of the first arrival times of AE signals is presented for thin metal plates. Based on Akaikes information criterion, proposed algorithm of the first arrival detection uses a specific characteristic function, which is sensitive to change of frequency in contrast to others such as envelope of the signal. The approach is applied to data sets of three different tests. Reliable results show the potential of our approach.

Fracture mechanism and toughness of the welding heat-affected zone in structural steel under static and dynamic loading

Due to the influence of the welding thermal cycle, the toughness of structural steel generally degenerates. Recently, the intercritically reheated coarse-grained heat-affected zone (IC CG HAZ) was found to demonstrate the worst toughness in welded joint, which was associated with its fracture mechanism. In this article, two IC CG HAZs of a structural steel were prepared by welding thermal-cycle simulation techniques. For the two IC CG HAZs, the static and dynamic fracture toughness were evaluated; the fracture mechanism was also studied. Under both static and dynamic loading, cracks in the IC CG HAZ were found to initiate at the intersection of bainitic ferrite αB/0 packets with different orientations, followed by propagation in cleavage. In some crack propagation regions, adjacent cleavage facets are connected by shear, thus producing dimple zones. Though the brittle fracture initiation mechanism remains unchanged, the cleavage facet size, the proportion of the dimple zones between facets, and the distance from the cracking initiation site to the crack tip vary with loading speed and welding conditions. These changes were found to be related to the variations caused by strain rate and welding conditions in fracture toughness for the IC CG HAZs.

A study on fracture behavior of particle reinforced metal matrix composites by using acoustic emission source characterization

Abstract A one directional acoustic emission (AE) source characterization has been used during a three point bending fracture toughness test on 6061 aluminum matrix composites with Al2O3 particle reinforcements of 5 and 10 μm sizes, in order to evaluate the dynamic process of micro-fracture in these materials. Different acoustic emission sources are characterized and, as a result, two types of AE events are distinguished. It is observed that at very low strain levels void nucleation is the main source for acoustic emission. At higher levels, the micro pop-in of primary voids and their eventual coalescence results in a different type of acoustic emission. In fine particle reinforced materials, when the amplitude of AE events in void nucleation at fine particles is not high enough to be detected, the main source of AE events is only the void coalescence. By increasing the particle size, the number of detectable events during void nucleation is increased.

Non-contact measurement of acoustic emission in materials by laser interferometry

Abstract The non-contact measuring system of acoustic emission (AE) by laser interferometry was developed to detect AE signals and analyze microfracture quantitatively during materials testing. The capability of this system was estimated by comparison between simulated AE signals due to glass capillary breaking and calculations using the finite element method. The systemcould measure AE signals during practical tensile tests of carbon fiber reinforced plastics. This technique was also applied to the thermal cycle test of ceramic/metal coatings, and AE signals during cooling were successfully detected and analyzed by a deconvolution method to evaluate quantitatively the microfracture process.

Microstructural analysis and mechanical properties of in situ Nb/Nb-aluminide layered materials

Abstract Thin foil hot press process has been developed for manufacturing metal/intermetallic compound laminate composites to induce self-propagating high-temperature synthesis (SHS) reaction between different pure metal sheets. In the present work, Nb/Nb-aluminide laminate composites were manufactured with pure Nb and Al sheets, which consist of fine Nb/Nb2Al/NbAl3 or Nb/Nb3Al/Nb2Al/NbAl3 layer structure. Microvickers hardness test and energy dispersive X-ray spectroscopy (EDS) analysis in the intermetallic compound layer demonstrate the formation of various phases, and the microvickers hardness values decrease with increasing Al/Nb atomic ratio. Although the tensile strength of laminate composites is similar to pure Nb, ductility and fracture toughness are significantly improved due to plastic deformation in Nb layer.

Effect of second phase on mechanical properties and toughening of Al2O3 based ceramic composites

Abstract This work considers the fabrication of Al 2 O 3 - based composites with three different types of microstructure: nano composites with the nano-dispersed second phase, hybrid composites with both micro- and nano-sized dispersed second phase, and elongated composites with needle-like in situ dispersed second phases. Methods for improving the mechanical properties of Al 2 O 3 ceramics were investigated using Al 2 O 3 /5 vol% SiC composites fabricated by hot-pressing. Very fine SiC particles were dispersed uniformly in an Al 2 O 3 matrix. However, larger SiC particulates existed in grain-boundaries of alumina. The flexural strength was inversely proportional to the square root of the matrix grain size. TEM observation indicated that propagating cracks were deflected by the dispersed SiC particulates. High density Al 2 O 3 /SiC/YAG hybrid composites having an equiaxed second phase were fabricated in the temperature range from 1000 to 1800°C using SiC and Y 2 O 3 powders as additives. YAG (yttrium aluminum garnet, Y 3 Al 5 O 12 ) was formed as the second phase from the reaction between Al 2 O 3 and Y 2 O 3 above 1400°C. Also, Al 2 O 3 /LaAl 11 O 18 (lanthanum-β-alumina) composites, having an elongated second phase, were successfully fabricated using La 2 O 3 powder as additives. Microstructural observation of the hot-pressed samples were done by SEM + TEM; the planes were analyzed by XRD. Mechanical properties such as the flexural strength and the fracture toughness of the composites were investigated and exceeded the mechanical properties of the monolithic Al 2 O 3 . Additionally, the composites having elongated grains showed higher toughness, due to grain bridging, than the composites having an equiaxed second phase.

In situ monitoring of microfracture during plasma spray coating by laser AE technique

Abstract Atmosphere plasma spray coating materials include many pores and lamellar boundaries formed by flattened particles during spraying process although high reliability are required in ceramic coatings for turbines. These boundaries become an origin of the microcracks and following crack growth. As it is known that spraying parameters strongly affect the microstructure and strength of coating, it is expected to establish in situ monitoring technique for coating process. However, there is a limit to apply the existing non-destructive evaluation techniques to real-time monitoring at elevated temperature. We have investigated a non-contact measuring system to detect acoustic emission (AE) signals due to microfractures using a laser interferometer, and applied this technique for understanding microfracture process of ceramic coating at elevated temperature. In this paper, we evaluated the effect of several spraying parameters on the initiation and growth process of microcrack by detecting AE signals during coating process using a non-contact laser AE technique.

Simulation of fracture behavior in particle-dispersed ceramic composites

Abstract A two-dimensional crack path is simulated in particle-dispersed ceramic composites along with the related variation of fracture resistance with crack extension. The direction of crack propagation is influenced by the geometrical crack shape and localized residual stresses due to the thermal expansion mismatch between particle and matrix. The simulation is conducted for both a SiC matrix composite dispersed with Al 2 O 3 particles and an Al 2 O 3 matrix composite dispersed with SiC particles, under an assumption of hard particles. In the SiCAl 2 O 3 (p) composite, a crack propagating near the Al 2 O 3 particles has a tendency to be repelled due to the residual tensile stress in the radial direction around the particles, and the entire fracture resistance shows a lower value than the matrix toughness. In the Al 2 O 3 SiC (p) composite, a crack is attracted by the SiC particles. Due to the residual compressive stress in the radial direction around the SiC particles, the fracture resistance increases up to five times the matrix toughness when the crack propagates along the interface. The apparent fracture resistance of the Al 2 O 3 SiC (p) composite shows a higher value than the matrix toughness, and an increasing R -curve behavior with crack extension is predicted. The approximately estimated two-dimensional fracture toughness of the Al 2 O 3 SiC (p) composite increases with the volume fraction of particles, while it decreases in the SiCAl 2 O 3 (p) composite.

Effect of rate on the fracture mechanism of TiAl

Abstract This study investigated the effect of microfracture mechanisms on the fracture toughness of both fully lamellar and duplex TiAl. It is known that the static fracture toughness of TiAl is improved by a lamellar microstructure and also depends on the grain size. The effect of loading rate on the fracture toughness is very important. In this paper, we measured the static fracture toughness of TiAl with different grain sizes of lamellae and various volume fractions of γ phase, and also estimated the effect of loading rate on the fracture toughness. The static fracture toughness increased with an increase in grain size of the lamellae and with a decrease in volume fraction of γ phase. Many acoustic emission (AE) signals were detected before the final fracture, and microcracking was observed. The toughening due to microcracking and sequential shear ligaments was demonstrated to be a major mechanism for improvement of the toughness, which was confirmed by our toughening model. Our advanced AE technique also demonstrated that it took several microseconds to generate microfracture. The dynamic fracture toughness decreased with an increase in grain size of the lamellae and with a decrease in volume fraction of γ phase. It was concluded that the toughening mechanism under static conditions could not occur under dynamic conditions and that another toughening mechanism operates under dynamic conditions.