Mechanical Properties of Matrix Hybrid Thick-Composites

For the purpose of more safety boats, the large thickness of outer plates is required to increase flexural stiffness, strength and impact properties. Some problems in mechanical properties are generated by increasing in thickness because the effect of interlaminar shearing of Thick-composites on whole mechanical properties is greater than that of thin-composites. We have investigated the matrix hybrid composite with two kinds of unsaturated polyester, one was hard type resin with low toughness and the other was flexible type resin with low modulus and high toughness. In this study, matrix hybrid composite was focused and applied to Thick-composites. First, the flexural properties were investigated and the micro fracture progress was precisely observed with in-situ observation using replica method. Then, impact properties of the Thick-composites were examined and the availability of matrix hybrid composite was investigated. It was concluded that the matrix hybrid composite achieved high performance in both static and impact load.

Failure Identification Methodology for Woven Composites Incorporating Sensor Degradation

The long-term goal of this project is the development of embedded, optimally distributed, multi-scale sensing methodologies that can be integrated into material systems for failure identification in structural systems. The coupling of sensor data fusion with a three-dimensional predictive framework will provide insight and understanding of events that are difficult, if not impossible, in any experimental study, such as subsurface damage and crack nucleation in structural systems. The current work presents an experimental study of the survivability and degradation behavior of an optical fiber Bragg grating sensor, surface mounted on a woven fiber composite material system during multiple low velocity impacts. The results reveal that as sensor degradation occurs, additional coupling phenomena other than Bragg reflection are observed in the grating sensor. From these additional modes, information on the sensor/host bond and fiber degradation is obtained.

The Theoretical and Experimental Evaluation of Gas-Particle Flow in Laser Cladding Repairing of Three Dimensions

In this paper, the powders transportation in laser cladding repairing during the coaxial powder-feeding was evaluated. The theoretical evaluation is based on a two-fluid approach in which both the gas and particulate phase is treated each phase separately, and the only link between the phases is through the drag force in the momentum equations. The particles velocities are calculated with changes of the gas flow and mass flow rate. This is important for the coaxial nozzle and the carrier-gas powder transportation equipment characteristics determined. An experimentally of the influence of carrying gas on the powder stream was set up. The gas-particles flowing from the nozzle was illuminated by a 2D sheet of light. A typical image from the CCD camera is captured. The axial velocity and cross section were described. According to the results, it was found that: (1) Different mass flow rate Mp=0.5g/s, 0.67g/s, 0.83g/s, 1g/s, the powder stream luminance intensity and distribution will change. (2) The distribution of powder concentration at longitudinal axis from the nozzle exit is shown. The faster particulates stream has the less density per unit volume for a given mass flow rate. (3) The gas velocity for transportation is the most important parameter.

Microstructure Evolution During Alternating-Current-Induced Fatigue

Subjecting electronic interconnect lines to high-density, low-frequency alternating current creates cyclic thermomechanical stresses that eventually cause electrical failure. A detailed understanding of the failure process could contribute to both prevention and diagnostics. We tested unpassivated Al-1Si traces on the NIST-2 test chip; these are 3.5 μm wide by 0.5 μm thick by 800 μm long, with a strong (111) as-deposited fiber texture and an initial average grain diameter of approximately 1 μm. We applied rms current densities of 11.7 to 13.2 MA/cm2 at 100 Hz. Resistance changes in the lines indicated that such current densities produce temperature cycles at 200 Hz with amplitude exceeding 100 K. Open circuits occurred in under 10 minutes, with substantial surface damage seen after only one minute. A few failures initiated at lithography defects initially present in the lines, but most were produced by the current alone. In one detailed example presented in this paper, we monitored the damage process by interrupting the current at 10, 20, 40, 80, 160, and 320 s in order to characterize an entire line by scanning electron microscopy and automated electron backscatter diffraction (EBSD); failure took place after 697 s. Results are described in terms of deformation, grain growth, and orientation changes.

Processing of Composite Cathode and YSZ Coatings for Solid Oxide Fuel Cells

In our research, composite cathodes of strontium-doped lanthanum manganite (LSM) and yttria-stabilized zirconia (YSZ) were produced by using slurry casting and sintering procedures. The slurry was prepared using ball milling. The time of ball milling was studied in terms of particle size and homogeneity of the powder in the slurry. The effect of the composition of the slurry on the microstructure was studied to obtain cathodes with desired porosity. The sintering process was also optimized to compromise the porosity, grain size, and strength of the cathodes. The YSZ coating was implemented using electrophoretic deposition in liquid phase. Different charging methods of the YSZ powder in the suspension was used and their results were compared. The microstructures of cathodes and YSZ coatings were characterized using scanning electron microscope (SEM).

Micromechanics-Based Elastoplastic and Damage Modeling of Particle Reinforced Composites

A micromechanical damage model is proposed to predict the effective elastoplastic behavior of ductile composites containing randomly dispersed particles. The interfacial debonding between particles and the matrix is considered as the primary micromechanical damage mechanism. The debonded isotropic elastic reinforcements are replaced by equivalent anisotropic elastic inclusions. The interfacial debonding process is simulated by three-dimensional debonding angles. After the local stress field in the matrix is calculated, the homogenization averaging procedure is employed to estimate the effective elastic stiffness and yield function of the composites. The associative plastic flow rule and the isotropic hardening law are postulated based on the continuum plasticity theory. As applications, the overall elastoplastic and damage constitutive behavior of the composites under various loading conditions is numerically simulated and compared with available experimental results.

Characterization of Magnesium/Carbon Nanotubes Composites Synthesized Using an Innovative Solidification Method

In the study reported in this paper, carbon nanotubes of up to two per cent by weight were added as reinforcement to the pure magnesium. A disintegrated melt deposition technology was employed as the solidification method and the ingots produced were subsequently hot extruded at a temperature of 350 °C and extrusion ratio of 20:1. The thermo-mechanical analysis showed a reduction in the coefficient of thermal expansion due to the presence of the carbon nanotubes. Examination of the mechanical properties indicated that with increasing amount of carbon nanotubes reinforcement added, there was a significant improvement in the performance of pure magnesium. An attempt is made to correlate the weight fraction of the carbon nanotubes with the properties of the resulting magnesium nanocomposite material.

Growth of Microcellular Foams in Viscoelastic Mediums

The growing of the critical bubble by diffusion process in visco-elastic medium was treated by an integral method for the concentration boundary layer. In this study, we obtained a set of the first order time dependent equations to obtain bubble radius and gas pressure inside the bubble simultaneously. The calculated final cell sizes depending on the initial saturation pressure are in close agreement with the observed ones. The governing equations developed in this study may be used in polymer processing of microcellular foams.

Study on Unstable Brittle Crack Arrest Toughness of Extremely-Low Carbon Bainitic Steel Plates

The extremely-low carbon bainitic steel (ELCB steel) is a high strength steel with about 0.02 mass% or less carbon. In this research, unstable brittle crack arrest toughness of ELCB steel plates was investigated by temperature-gradient ESSO tests, compared with that of conventional TMCP steel plates. Both of ELCB and TMCP steel plates without pre-straining had sufficient crack-arrest toughness at 0°C. After 10% prestraining, the TMCP steel plate had not sufficient crack-arrest toughness at 0 °C . The ELCB steel plates, however, maintained high crack arrest toughness at 0°C. even after 10% pre-straining. ELCB steel were also different from TMCP steels in the correlation between transition temperature of crack arrest toughness and fracture appearance transition temperature (vTrs) obtained by Charpy impact test. When the vTrs of an ELCB steel and that of a TMCP steel were the same value, crack arrest toughness of an ELCB steel was higher than that of a TMCP steel. In the cross section of the ESSO test piece of the ELCB steels, many sub-cracks and micro-crack branching were observed. However, in the cross section of the ESSO test piece of the conventional TMCP steels, there were few subcracks and branching. Initiation of sub-cracks and branching around the main crack tip reduces the stress intensity factor of the main crack. It was considered that the above features of the ELCB steel were caused by initiation of sub-cracks and branching at the tip of the main brittle crack.

Elongation Variability of AM60 Die Cast Specimens

Tensile properties of die cast magnesium AM60 were investigated by testing tensile bar specimens obtained from three sources. The first series of tensile bars were cut from eight locations from multiple copies of a die cast magnesium AM60 automotive instrument panel beam. The second series were cut from six-inch square AM60 die cast plates in both the parallel and perpendicular to the flow direction. The last series of specimens were die cast AM60 tensile bars. The measured yield stress did not significantly depend on the specimen source and matched published values. However, the elongation as determined by the engineering strain at break in the tensile test varied significantly for samples cut from the automotive instrument panel beams and those cut from the six-inch by six-inch plates. The elongation remained constant for the cast tensile bars. Statistic General Linear Models were used to study the effect of casting conditions on both the yield stress and the strain at break. Sample location within the beams was the main factor for the material property variation.