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41.
Two Lock-in InfraRed Thermography (LIRT) techniques were developed and applied to detect interfacial defects in a ceramic coated steel plate deposited by plasma spraying technology. Stimulations were performed either by electromagnetic waves (lamps) or by high power ultrasonic waves (sonotrode). The first one is based on remote optical heating of the area of interest; while the second technique is based on the mechanical loss angle effect, occurring locally and for particular defects such as cracks and delaminations. The potential of these two techniques was evaluated against artificial (calibrated holes) and real (disbonding) interfacial defects. The results show success and also some limitations of both LIRT techniques in function of sizes and depths of ceramic coating interfacial defects. 相似文献
42.
T. K. Chaki 《Materials Science and Engineering: A》1995,190(1-2):109-116
A model is proposed to explain on a unified basis the role of boron in enhancing ductility and reducing environmental embrittlement in polycrystalline Ni3Al. The grain boundaries in strongly ordered Ni3Al have a porous structure with crack-like microcavities, which can open up under small stresses. Furthermore, atomic hydrogen, generated by the reaction of environmental moisture with Al, can diffuse to the tips of the microcavities under stress and can cause embrittlement. It is argued that strong bonding between interstitial B atoms and Ni atoms in B-doped Ni3Al reduces the strength of directional bonding between Ni and Al atoms in the interior of the grains. When two such grains with weakened Ni---Al bonding meet each other, the atoms near the grain boundary can relax easily and close up the microcavities. As a result, the ductility is enhanced in B-doped Ni3Al. The environmental embrittlement is also reduced, because a small amount of environmental hydrogen cannot nucleate microcracks. Numerous experimental observations have been explained with the proposed mechanism. 相似文献
43.
Powder of lanthanum-modified lead zirconate titanate (PLZT) with the composition La/Zr/Ti=8/65/35, was synthesized from aqueous
nitrate solutions. A single-phase PLZT was obtained at ∼550 °C. The reactivity of the powder during low-temperature heating
was determined using X-ray diffraction and various thermal analysis techniques. The dielectric properties of the compound
were also studied at 1 and 10 kHz frequency from room temperature to 200 °C. Diffuse phase transition (DPT) in the material
was observed around 136 °C at 1 kHz. An increase in peak-permittivity temperature (i.e. the transition temperature) with increasing
frequency (a characteristic of relaxor ferroelectrics) was also observed. 相似文献
44.
Akimoto T. Murai I. Kato S. Chaki S. Shoji I. Ogawa Y. 《IEEE transactions on nuclear science》1990,37(5):1594-1598
The design and feasibility of a simple and practical system for measuring two-parameter signals is reported. A dual-parameter multichannel pulse-height analyzer (MCA) which uses two central processing units (CPUs) is developed and designed. One computer (master computer) controls the other computer (slave computer), and also displays, records, and analyzes the data. The slave computer controls two analog-to-digital converters (ADCs), collects the dual-parameter data, and transfers the collected data to the master computer. Three methods of data transfer between the two CPUs are examined and discussed. The count capacity at the data collection by the slave computer is 216-1/ch (2-B-long data), and this is expanded to 232-a/ch (4-B-long data) at the master computer. The data are analyzed and at any time stored in the storage apparatus by the dual CPU system. The system demonstrates stable operation over long measurement periods 相似文献
45.
Michael R. Van De Mark Ameya M. Natu Sagar V. Gade Minghang Chen Catherine Hancock Cynthia Riddles 《Journal of Coatings Technology and Research》2014,11(2):111-122
The formation of colloidal unimolecular polymer (CUP) particles from single polymer strands was investigated as a function of molecular weight. The CUP particle size was correlated with the absolute molecular weight and its distribution. The characteristics of the particles were evaluated with respect to viscosity, acid number, size distribution, and stability. The particle size varied from less than 3 nm to above 8 nm representing polymers with molecular weight in the range of 3000–153,000. Lower molecular weight polymers were found to be unstable. Particle size measurements using dynamic light scattering technique indicated a normal distribution which corresponded to the molecular weight distribution of the copolymer. The statistical distribution of the acid groups in the polymer chains played a significant role in the stability of low molecular weight polymers. 相似文献
46.
In this paper, the Gurson–Tvergaard–Needleman (GTN) fracture model has been implemented in a 3D nonlinear finite element framework to investigate ductile failure. The simulation consists of both model parameter calibrations and predictions based on the experimental configurations that were described in the Sandia fracture challenge in 2012. The goal is to test the robustness of the GTN model in predicting crack initiation and propagation in a ductile structural stainless steel (15-5 PH). It has been observed that the predicted load drops at crack initiation agree well with the experimental data. Both the simulation and experiments reveal that cracks always initiate in the subsurface. The observed crack path in the experiments, however, is not unique and is strongly influenced by the geometric variations in the specimen introduced in the fabrication process. The crack path is quite sensitive to the relative location of pre-existing features (notch and holes) in this challenge problem, and a very small variation can potentially lead to different path, hence affecting the ductile failure pattern significantly. Variations in the crack path are also observed in the simulation with different choices of GTN model parameters that control the void nucleation and growth behavior. 相似文献
47.
The conductive composites were prepared using two different types of conductive black (Conductex and Printex XE2) filled in
matrices like EVA and NBR and their different blends. The electromagnetic interference shielding effectiveness (EMI SE) of
all composites was measured in the X band frequency range 8–12 GHz. Both conductivity and EMI SE increase with filler loading.
However, Printex black shows higher conductivity and better EMI SE at the same loading compared to Conductex black, and this
can be used as a material having high EMI shielding effectiveness value. The conductivity of different blends with same filler
loading generally found to increase slightly with the increase in NBR concentration. However, EMI SE has some dependency on
blend composition. EMI SE increases linearly with thickness of the sample. EMI SE versus conductivity yields two master curves
for two different fillers. EMI SE depends on formation of closed packed conductive network in insulating matrix, and Printex
black is better than Conductex black in this respect. Some of the composites show appreciably high EMI SE (>45 dB). 相似文献
48.
Shreedatta Hegde Ravindrachary Vasachar Rohan Nandeesh Sagar Ismayil Ganesh Sanjeev 《应用聚合物科学杂志》2024,141(19):e55349
In the present study, solid polymer electrolytes (SPEs) based on poly (vinyl alcohol) (PVA) doped with lithium bromide (LiBr) were prepared by solution casting method. Fourier transform infrared spectroscopy results affirm the complexation of LiBr with PVA. X-ray diffraction results exhibit the increase of amorphous nature of the polymer electrolytes, which is also observed in scanning electron microscopy images and atomic force microscopy topographs. Thermogravimetric analysis thermographs endorse the increase of thermal stability of the polymer due to doping. Dielectric studies exhibit non-Debye nature of the polymer electrolytes. Conductivity spectra reveal the maximum ionic conductivity (1.15 × 10−4 S/cm) for 20 wt% LiBr/PVA electrolyte at ambient temperature. Impedance analysis reveals the decrease of ionic relaxation in the polymer electrolytes and the studied transport properties of the electrolyte show that the major contribution to the conduction in this polymer electrolyte is ions. 相似文献
49.
Real-time embedded systems (RTESs) operating in safety-critical domains have to satisfy strict performance requirements in terms of task deadlines, response time, and CPU usage. Two of the main factors affecting the satisfaction of these requirements are the configuration parameters regulating how the system interacts with hardware devices, and the external events triggering the system tasks. In particular, it is necessary to carefully tune the parameters in order to ensure a satisfactory trade-off between responsiveness and usage of computational resources, and also to stress test the system with worst-case inputs likely to violate the requirements. Performance tuning and stress testing are usually manual, time-consuming, and error-prone processes, because the system parameters and input values range in a large domain, and their impact over performance is hard to predict without executing the system. In this paper, we provide an approach, based on UML/MARTE, to support the generation of system configurations predicted to achieve a satisfactory trade-off between response time and CPU usage, and stress test cases that push the system tasks to violate their deadlines. First, we devise a conceptual model that specifies the abstractions required for analyzing task deadlines, response time, and CPU usage, and provide a mapping between these abstractions and UML/MARTE. Then, we prune the UML/MARTE metamodel to only contain a purpose-specific subset of entities needed to support performance tuning and stress testing. The pruned version is a supertype of UML/MARTE, which ensures that all instances of the pruned metamodel are also instances of UML/MARTE. Finally, we cast the generation of configurations and stress test cases as two constrained optimization problems (COPs) over our conceptual model. The input data for these COPs in automatically generated via a model-to-text (M2T) transformation from models specified in the pruned UML/MARTE metamodel to the Optimization Programming Language. We validate our approach in a safety-critical RTES from the maritime and energy domain, showing that (1) our conceptual model can be applied in an industrial setting with reasonable effort, and (2) the optimization problems effectively identify configurations predicted to minimize response time and CPU usage, and stress test cases that maximize deadline misses. Based on our experience, we highlight challenges and potential issues to be aware of when using UML/MARTE to support performance tuning and stress testing in an industrial context. 相似文献
50.