The Non-destructive Testing of Adhesively Bonded Structure: A Review

The types of defect encountered in adhesive joints and the non-destructive testing techniques available to detect them are reviewed. Three types of defect: complete voids or dis-bonds, poor cohesive strength of the adhesive layer and poor adhesion between the adhesive layer and adherend are commonly present. It is shown that a variety of techniques is available for dis-bond and void detection, ultrasonics and sonic vibration being the most commonly used. The detection of poor cohesive and adhesive properties, however, is much more difficult than void and dis-bond detection and is the subject of current research. At present there is only one commercially available instrument which claims to predict cohesive strength. There is no reliable non-destructive test to detect poor adhesion.     

Use of acrylate‐based liquid rubbers as toughening agents and adhesive property modifiers of epoxy resin

Carboxyl‐randomized poly(2‐ethyl hexyl acrylate) (CRPEHA) and epoxy‐randomized poly(2‐ethylhexyl acrylate) (ERPEHA) were synthesized by solution polymerization technique in the form of liquid rubbers. The liquid rubbers were characterized by IR and ¹H‐NMR spectroscopic analysis, nonaqueous titration, and GPC. The liquid rubbers were pre‐reacted with the epoxy resin and the modified epoxy networks were made by curing with an ambient temperature curing agent. The modified epoxy networks containing different concentrations of CRPEHA (A‐1) and ERPEHA (B‐1) were evaluated with respect to their thermal and impact properties. The optimum properties were obtained at 10‐phr concentration of a (1 : 1) mixture of CRPEHA and ERPEHA. Fracture surface analysis by scanning electron microcopy indicated the presence of a two‐phase microstructure. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3814–3821, 2004     

Yttria-stabilized zirconia-based composites with adaptive thermal conductivity

Thermal conductivity trends in a “chameleon coating” thin film were characterized with a time-domain thermoreflectance (TDTR) technique. A yttria-stabilized zirconia (YSZ)-based nanocomposite material containing ∼21 vol.% silver (Ag) was employed for this study. The thermal conductivity (k) of the as-deposited composite film was measured with TDTR and found to have a value of 7.4 ± 1.4 W m⁻¹ K⁻¹. The film was then annealed at 500 °C for 1 h to stimulate Ag flow from within the composite to the surface via diffusion. The Ag that coalesced on the surface during annealing was removed to expose the underlying porous YSZ matrix, and the sample was reexamined with the TDTR technique. The thermal conductivity of the porous nanocomposite YSZ material was then measured to be 1.6 ± 0.2 W m⁻¹ K⁻¹, which is significantly lower than a fully dense control sample of pure nanocrystalline YSZ (2.0 ± 0.1 W m⁻¹ K⁻¹). The annealed film displayed a 20% reduction in thermal conductivity as compared to the control sample and a 4–5-fold reduction in thermal conductivity as compared to the as-deposited material. The experiments demonstrate temperature triggering of a composite material, resulting in self-modifying thermal conductivity and diffusion-controlled porosity. These aspects can be used to enhance or restrict thermal transport (i.e., a thermal switch). The applicability of the TDTR technique to measurements of thin, nanoporous film materials is also demonstrated.     

Dose and Temperature Dependence of Void Swelling in Electron Irradiated Stainless Steel

In a high voltage electron microscope, solution treated Type 316 stainless steel was electron-irradiated at temperatures in the range of 370–630°C to a dose of about 30 dpa. The swelling (ΔV/V) induced by the irradiation beyond about 5 dpa is well described by an empirical equation, ΔV/V=A(dpa) ⁿ , under constant void and dislocation densities. With increasing irradiation temperature, the fluence exponent n increases and the pre-exponent term A decreases. At 550°C irradiation, the fluence exponent takes the value of 1.5 due to the diffusion-limited void growth. The value of n larger than 1.5 at higher temperature (>550°C) is attributable to the surface reaction-limited void growth. The smaller value of n for the low temperature (?500°C) irradiation appears to arise from the dislocation assisted vacancy diffusion. The peak swelling temperature of the specimen irradiated to 30 dpa is about 570°C, which shifts to a higher temperature with increase in electron dose.     

Void Swelling and Precipitation in Ti-Modified Austenitic Fe-Ni-Cr Alloys

Irradiation temperature dependence of void swelling, and the effects of aging before irradiation on void swelling and on precipitation were examined in three Ti-modified austenitic steels called No. 1 (Fe-14Ni-16Cr-1.8Mn-2.4Mo-0.1Nb-0.1Ti-0.9Si-0.07C), No. 2 (Fe-14Ni-15Cr-1.6Mn-2.6Mo-0.24Ti-1.0Si-0.06C) and No. 3 (Fe-25Ni-15Cr-1.6Mn-2.4Mo-0.4Ti-1.0Si-0.06C). After irradiation to 10 dpa with 150–200 keV proton, the cold worked No. 1 showed swelling peak of 0.4% at 823 K, the cold worked No. 2 0.15% at 773 K and the cold worked No. 3 0.08% at 723 K. Sample Nos. 2 and 3 which were aged at 923 K for 5.4 Ms (1,500 h) showed larger void swelling because of higher void number density than the unaged ones after the irradiation to 20–40 dpa at 923 K. The amount of intragranular TiC precipitates in the irradiated specimens did not vary significantly with preirradiation treatments. Voids were mostly attached to eta (M₆C) phase which was produced during irradiation. The number density of eta phase produced during the irradiation in aged specimens was much higher than that in unaged ones. This is thought to give a main reason why void swelling in aged specimens was larger than that in unaged ones.     

Influence of unsaturated acid monomer on the morphology of latex particles in the preparation of hollow latex via the alkali post‐treatment

Multistage hydrophilic core/hydrophobic shell latexes containing carboxyl groups were prepared via multistep seeded emulsion copolymerization, and particles with different morphologies were obtained after alkali post‐treatment. Influences of the type and content of unsaturated acid monomer on the polymerization and the particle morphology were investigated based on conductometric titration and TEM observation. Results showed that the hydrophilic core/hydrophobic shell particles could be easily formed using methacrylic acid (MAA) instead of acrylic acid. When MAA was 12.2 wt % in the core latex preparation, only fine pores existed inside the alkali‐treated particles. With MAA increased from 20.0 to 30.0 wt %, the alkali‐treated particle morphology evolved from porous, hollow to collapse structure. When MAA further increased to 40.0 wt %, it was difficult to prepare uniform multistage particles and distinct morphologies including solid, deficient swelling, hollow and collapse structure were coexistent in the alkali‐treated particles. Moreover, the forming mechanism of different morphologies was proposed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Characterization of nanosilica‐filled epoxy composites for electrical and insulation applications

We report in this article the results of nanosilica (SiO₂)‐filled epoxy composites with different loadings and their electrical, thermal, mechanical, and free‐volume properties characterized with different techniques. The morphological features were studied by transmission electron microscopy, and differential scanning calorimetry was used to investigate the glass‐transition temperature (T_g) of the nanocomposites. The properties of the nanocomposites showed that the electrical resistivity (ρ), ultimate tensile strength, and hardness of the composites increased with SiO₂ weight fraction up to 10 wt % and decreased thereafter; this suggested that the beneficial properties occurred up to this weight fraction. The temperature and seawater aging had a negative influence on ρ; that is, ρ decreased with increases in the temperature and aging. The free‐volume changes (microstructural) in the composite systems correlated with seawater aging but did not correlate so well with the mechanical properties. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

不均匀背景下芯片焊接气泡的X射线检测

针对X射线不均匀透视图像背景下的芯片焊接气泡检测问题,为了准确提取焊接气泡,特别是小气泡,提出了基于二维集合经验模式分解和基于灰度形态滤波的两种气泡检测算法.以大功率三极管芯片焊接气泡检测为案例,运用两种方法进行不均匀背景下气泡检测分析.结果表明,两种方法均能准确提取不均匀图像背景下的芯片气泡,而基于二维集合经验模式分...     

85 MeV ~(19)F离子辐照α-Al_2O_3热退火产生的空洞研究

:采用正电子湮没寿命技术研究了注量为 5 2 8× 10 16 cm- 2 的 85MeV 19F离子辐照后α Al2 O3热退火产生的空洞。实验结果表明 :辐照后的α Al2 O3经 4 50℃退火开始出现空洞 ;550～ 750℃时 ,空洞半径达到 0 37nm ,且其大小不变而浓度则随温度迅速增加 ;高于 80 0℃ ,退火温度升高 ,空洞增大 ;10 50℃退火 ,形成了半径为 1 0 2nm的空洞     

450℃高能电子辐照对CLAM钢微观结构的影响

为了研究低活化马氏体CLAM钢的抗辐照肿胀性能,在450℃下对CLAM钢进行大剂量高能电子辐照的原位动态实验.利用超高压透射电子显微镜观察发现,CLAM钢中产生了大量的间隙原子型位错环和多面体形状的辐照空洞.分析了它们的形核和长大规律以及相关机制.计算表明,CLAM钢在高能电子辐照下的最大肿胀率为0.26%,具有较好的抗辐照肿胀性能.