Finite element analysis of effect of interfacial bubbles on performance of epoxy coatings under alternating hydrostatic pressure

The stresses around bubbles formed on a coating/substrate interface under hydrostatic pressure(HP)and alternating hydrostatic pressure(AHP)were calculated using the finite element method.The results reveal that HP promotes coating failure but does not mechanically destroy the interface,whereas AHP can provide tensile stress on bubbles formed at the interface and accelerate disbonding of the coating.Because of water resistance,a lag time exists for the coating that serves in an AHP environment.The coating can have a better protective performance if the lag time suits the AHP to minimize the impact of the AHP on the interface.     

等静压力诱导的PMN-PT单晶介电弛豫特性研究

研究了不同等静压力下的PMN-PT单晶的介电常数(εr)与温度(T)的关系,以及常温下介电常数(εr)及损耗(tanδ)与压力(p)之间的关系.发现了PMN-PT单晶在压力作用下出现明显的介电频率弥散现象.当等静压力增大到一定压力时,PMN-PT单晶的介电常数值迅速降低,介电频率弥散更加显著,且出现弛豫特性,介电损耗的弛豫特征更加明显.随着频率的增加,介电损耗峰对应的峰值压力向高压方向移动.其根本原因是压力诱导的介电-压力弛豫特性导致的.     

Reliability-based load and resistance factor design of composite pressure vessel under external hydrostatic pressure

A reliability-based load and resistance factor design procedure for subsea composite pressure vessel subjected to external hydrostatic pressure is presented. The failure criterion for defining the performance function is considered as buckling. A sensitivity analysis is conducted to research influences of statistical characteristics of variables on the partial safety factors and the thickness of pressure vessel. The results shows the longitudinal modulus, inside radius of composite layers, unsupported length and external pressure significantly affect the design results, whereas transversal modulus, Poisson’s ratio, shear modulus and winding angle have little effects. In order to validate the design results, a filament-wound composite pressure vessel is manufactured, and the buckling test is performed. It is observed that when the applied external hydrostatic pressure is a little more than the designed critical buckling pressure, the buckling and subsequent burst behaviours occur, which shows a good agreement between the experimental and analytical results.     

静水压力下高分子材料黏弹性动力学参数测量

提出测量静压下高分子材料黏弹性动力学参数方法。分别制作均匀实心覆盖层及圆柱空腔覆盖层样品,测量实心覆盖层复反射系数计算复纵波波数,测量圆柱空腔覆盖层复反射系数,结合圆柱空腔结构变形,利用圆柱管中轴对称波特征方程计算复剪切波波数,综合复纵波波数与复剪切波波数计算静压下复杨氏模量及复泊松比。对橡胶材料进行声管测试,分析、总结静压对黏弹性动力学参数影响规律。测量某吸声覆盖层静压下反射系数,并与用实测材料参数计算的反射系数进行比较,验证方法的可靠性。     

Use of material grading for enhanced buckling design of thin-walled composite rings/long cylinders under external pressure

This paper presents a mathematical model for enhancing the buckling stability of composite, thin-walled rings/long cylinders under external pressure using radial material grading concept. The main structure to be analyzed is built of multi-angle fibrous laminated lay-ups having different volume fractions of the constituent materials within the individual plies. This leads to a piecewise grading of the material in the radial direction. The objective is to maximize the critical buckling pressure while preserving the total structural mass at a constant value equal to that of a baseline design. The fiber volume fractions are included among the standard design variables such as fiber orientation angles and ply thicknesses, which are used by many investigators in the field. The model employs the classical lamination theory, where an analytical solution that accounts for the effective axial and flexural stiffness separately is given. The critical buckling pressure contours subject to the mass equality constraint are given for several types of anisotropic rings/long cylinders showing the functional dependence of the constrained objective function on the selected design variables. It is shown that material grading can have significant contribution to the whole optimization process in achieving the required structural designs with enhanced stability limits.     

Preparation of carbon nanotube/epoxy composite films with high tensile strength and electrical conductivity by impregnation under pressure

Based on the production of a carbon nanotube (CNT) assembly, a new technique is developed for preparing CNT/epoxy (EP) composite films with high tensile strength and electrical conductivity. CNTs are synthesized by floating catalyst spray pyrolysis. After self-assembling into a hollow cylindrical assembly, CNTs are drawn and wound on a rotating drum to form a uniform CNT film. EP resin solutions of different concentrations are used to fill into the pores within the film under different pressures and form composite films after hot-press curing. The permeability of the EP resin and thus the interfacial bonding between the CNT and the EP resin are studied by varying the concentration of the EP resin solution and the pressure used for impregnation. Under optimal preparation conditions, the composite film contains CNTs of a high content of 59 wt.%, and shows a high tensile strength of 1.4 GPa and a high electrical conductivity of 1.4x10^5 S·m^-1, 159% and 309% higher than those of the neat CNT film, respectively.     

Evolution of silicon nanoclusters and hydrogen in SiNx:H films: Influence of high hydrostatic pressure under annealing

Hydrogenated silicon-rich nitride (SRN) films of various stoichiometry (SiN_x:H, 0.7 < x ≤ 1.3) were deposited on single-crystalline Si substrates with the use of plasma enhanced chemical vapor deposition at a temperature of 100 °С. Furnace annealing for 5 h in ambient Ar at 1130 °С under atmospheric and enhanced hydrostatic pressure (HP — 11 kbar, 1.1 GPa) was applied to modify the structure of the films. The properties of as-deposited and annealed films were studied using ellipsometry, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, photoluminescence (PL), as well as high-resolution transmittance electron microscopy (HRTEM). According to the Raman data, the as-deposited film, in which the stoichiometry parameter x is below 1.0, contains amorphous silicon nanoclusters. Furnace annealing leads to crystallization of the nanoclusters. From the HRTEM and Raman data, the average size of the Si nanocrystals in the annealed films was 6-7 nm. No silicon nanoclusters were observed in the as-deposited films with relatively low concentration of excessive silicon atoms (the case of SiN_x:H, x > 1); furnace annealing leads to segregation of the Si and Si₃N₄ phases, so, the amorphous Si clusters were observed in annealed films according to Raman data. Surprisingly, after annealing with such high thermal budget, according to the FTIR data, the SRN film with parameter x close to that of the stoichiometric silicon nitride contains hydrogen in the form of SiH bonds. From analysis of the FTIR data of the SiN bond vibrations one can conclude that silicon nitride is partly crystallized in the films with x > 1 after annealing for 5 h. No influence of HP on the structure of Si nanoclusters was observed in the case of SRN films with x ≤ 1.1. Dramatic changes in the PL spectra of the SRN films with the x parameter close to that of the stoichiometric silicon nitride (x ≈ 1.3), annealed under atmospheric pressure and HP, were observed. HP stimulates the formation of very small hydrogenated amorphous nanoclusters. The size of amorphous Si nanoclusters determined from the quantum size effect model describing the PL spectra, should be 2-4 nm in this case.     

Evaluation of a laboratory‐scale pressure differential (force/decay) system for non‐destructive leak detection of flexible and semi‐rigid packaging

This study evaluated the capabilities of a bench‐top non‐destructive pressure differential leak tester using 355 ml polyethylene terephthalate/ethylene vinyl alcohol/polypropylene (PET/EVOH/PP) trays. This evaluation was done by monitoring the equipment's force/decay responses to leaks, changes in the package headspace volume and differences in the seal strength of 986 sample trays. Leak detection evaluation was done using artificially created channel leaks (10–200 µm) in the sealing areas and pinholes (5–50 µm) in the lids of the polymeric trays. Seal strength evaluation included the ability of the equipment to identify non‐leaking but weak seals and the extent to which the pressure differential unit affected good seals during a normal test run. The results showed that the equipment had a detection limit of 40 µm for channel leaks 6 mm in length and 15 µm for pinholes. The results also showed that the pressure differential unit caused a 9% reduction in the seal strength of the tested packages. However, peel strength analysis and distribution testing showed that this reduction in seal strength did not compromise the integrity of 99% of the packages tested. Results showed that the equipment could also detect weak but non‐leaking seals that had potential to lose integrity during transportation and retail handling. The results of this study could be used to determine the capabilities and limitations of a non‐destructive pressure differential bench‐top leak testing device intended for food packaging quality control. Copyright © 2002 John Wiley & Sons, Ltd.