Adhesion to zirconia as a function of primers/silane coupling agents,luting cement types,aging and test methods

This study evaluated the adhesion of resin cements to zirconia with different primers/silane coupling agents using two test methods with and without aging. Zirconia discs (Cercon) (N = 900, n = 15 per group) were ground finished to 2000 grit silicone carbide and randomly divided into seven groups: (a) C: No treatment (Control), (b) SG: Signum, (c) CL: Clearfil Ceramic Primer, (d) AP: Alloy Primer, (e) Monobond Plus, (f) ES-R: ESPE-Sil after Rocatec and (g) ES-C: ESPE-Sil after CoJet. Methacrylate (Variolink II-VL) and MDP based (Panavia F2.0-PN) dual-polymerized and self-adhesive resin cements (RelyX Unicem-RX) were adhered and polymerized accordingly. The specimens were further randomly divided into two groups to be tested after (a) 24-h dry storage at 37 °C and (b) thermocycling (×5000, 5–55 °C). Macroshear (MSB) and macrotensile bond tests (MTB) were conducted in an universal testing machine (crosshead speed: 1 mm/min) and failure types were analyzed after debonding. Data were analyzed using Univariate analysis and Tukey’s tests (α = 0.05). Two-parameter Weibull modulus, scale (m) and shape (0) were calculated. While primer/silane (p < 0.001), cement type (p < 0.001) and aging (p < 0.001) significantly affected the bond results, test method did not show significant difference (p = 0.237). In MSB test, Weilbul moduli were more favorable for MP-VL (4.2) and AP-PN (6) combinations and after aging for MP-VL (4.2) and AP-PN (5.66). In MTB test, after aging, Weilbul moduli were more favorable for AP-PN (5.41). Bond strength results mostly decreased with SG (24–92%) after aging. Cohesive failures in the cement were more frequent with PN (252) compared to VL (83).     

Mode-l Fracture Behaviour of Adhesive Joints. Part I. Relationship Between Fracture Energy and Bond Thickness

The fracture properties of adhesive joints of aluminium were investigated using a rubber-modified tough epoxy resin system (G_IC = 2.76 kJ/m²) as adhesive material. Compact tension (CT) adhesive joints were manufactured for a wide range of bond thickness t (from 0.05mm to 10mm) and fracture tests conducted under static load. Scanning electron microscopy (SEM) was used to examine the fracture surface morphology. A large deformation elastic- plastic finite element model was developed to evaluate the J-integral value for different bond thickness. The fracture energy, J_c , was found to be highly dependent on the bond thickness and was lower than that of the bulk adhesive. As the bond thickness was increased J_c also increased, though not monotonically, towards the fracture energy of the bulk adhesive. This result was caused by the complicated interactions between the stress and strain fields, plastic deformation of the adhesive around the crack tip, constraint from the adherends and the failure path. It was shown that values of J_c as a function of bond thickness correlated well with the variation of plastic zone height. Scanning electron micrographs from the fracture surfaces of the CT adhesive joints illustrated that the failure path was mainly cohesive through the centre-plane of the adhesive layer. Brittle fracture mechanisms were observed for thin bonds (0.04mm < t< 0.5 mm) but tough fracture mechanisms were identified for thick bonds (t > 1 mm).     

Adhesive bond strength and compressive strength of a novel bulk fill composite with zirconia nano-hybrid filler

The aim of the study was to investigate the adhesive bond and compressive strength of novel bulk fill resin composite with zirconia (Zr) nano-hybrid filler. Sixty molars were mounted in acrylic resin with flat occlusal surface. Half of the specimen (n = 30) were bonded using total etch (TE) and the other half with self-etch (SE) technique. Specimens treated with SE (n = 30) and TE (n = 30) bonding protocol were divided into three groups, based on the type of bulk fill build-up materials (ZC–ZirconCore, MC–MulticCore Flow and LC–Luxacore Dual), resulting in six study groups [MC-TE, MC-SE, LC-TE, LC-SE, ZC-TE, ZC-SE]. Cylindrical (3 × 3 mm) build-ups were performed followed by shear bond strength testing (crosshead speed-1 mm/min). Ten specimens for each bulk fill build-up material (MC, LC and ZC) were prepared for compressive strength testing. All specimens were tested for maximum failure loads (crosshead speed?0.5 cm/min). Analysis of variance and paired t-test were performed to statistically analyze the data. TE technique showed significantly higher bond strength values as compared to SE technique (p < 0.001) for all three materials (MC, LC and ZC). Shear bond strength for MC [TE,17.88(2.00)-SE,9.43(0.98)] and LC [TE,18.91(2.57)-SE,6.35(1.12)] groups were significantly higher than ZC group [TE,13.99(1.09)-SE,4.61(0.84)]. Specimens in ZC group (266.73 ± 9.76) showed significantly higher compressive strength in comparison to MC (247.66 ± 9.72) (p = 0.004) and LC (249.87 ± 13.17) (p < 0.001) groups. Zirconia nano-hybrid filler resin bulk fill material has comparatively high compressive strength and low bond strength making them suitable for clinical applications in the posterior region with favorable conditions for adhesive bonding.     

Numerical analysis and experimental tests for long-term strength of adhesive bonds

This paper presents selected numerical analysis results on static strength of adhesive layers which were subjected to long-term loads. The numerical calculations involved modelling the properties of the adhesive layer using the Burger's model. The coefficients of the Burger's model components were determined on the basis of the creep curves of the adhesive. Some results were verified experimentally. It was ascertained that it is possible to examine the problems of long-term strength of adhesive bonds using numerical analysis under certain limitations. Numerical tests should reduce the need for time-consuming experiments. The investigations pointed out adhesive joints long-term strength dependence on creep curves of adhesives. The long-term strength of adhesive joints increased by reinforcement of the adhesive layer with glass fabric.     

Dispersion of phosphovanadates on silica gel chemically modified with silane coupling agents having an amino group and their catalytic activities for methanol oxidation

Phosphotetradecavanadate (PV14) was dispersed on a silica gel chemically modified with a silane coupling agent (AnPS-SiO₂) by an equilibrium adsorption method. The PV14 contents approximately correlated with the V(IV) spin contents by ESR. PV14 dispersed on AnPS-SiO₂ resulted in a quite high selectivity for formaldehyde such as 97% in methanol oxidation.     

硅烷偶联剂对氢氧化镁表面改性及其在聚丙烯中的应用

选用具有相同亲水基团的4种硅烷偶联剂对工业级氢氧化镁进行常温湿法表面改性,并与聚丙烯(PP)熔融混合制得掺杂氢氧化镁质量分数为35%的复合材料,以SEM,FT-IR等手段对氢氧化镁及复合材料进行表征,考察了不同硅烷对复合材料阻燃性能和力学性能的影响。结果表明,硅烷偶联剂湿法改性可以提高氢氧化镁的分散性和与材料的相容性,改善氢氧化镁/PP的力学性能,但对阻燃性能影响不大;十二烷基三甲氧基硅烷在水相中稳定性好,可以较多地包覆于氢氧化镁表面,改性后材料的悬臂梁缺口冲击强度提高50%,断裂伸长率提高6倍,达到很好的改性效果。     

表面活性剂和硅烷偶联剂有机复合改性蒙脱土的制备及性能表征

为增加蒙脱土与有机物的相容性,采用十六烷基三甲基溴化铵(CTAB)与硅烷偶联剂(KH-560)对蒙脱土进行了有机复合改性。X-射线衍射和红外光谱的结果表明,CTAB已插入蒙脱土片层,平均层间距离从1.54 nm增大到3.98 nm和2.08 nm,而KH-560未插入蒙脱土片层,只是覆盖在蒙脱土表面,未改变蒙脱土的插层结构;分散性实验表明,表面活性剂和硅烷偶联剂有机复合改性的蒙脱土在苯乙烯、液体石蜡中的分散性好于其他改性蒙脱土;有机复合改性不仅增大了蒙脱土层间距,且改善了蒙脱土与聚氯乙烯的界面效果,提高了蒙脱土在聚氯乙烯基体中的分散均匀性,从而使聚氯乙烯/蒙脱土复合材料玻璃化转变温度的提高和力学性能的改善更明显。     

Fracture resistance of endodontically treated molars restored with polyethylene fiber and different posts

The purpose of this study was to compare the fracture strength and mode of teeth restored with fiber/titanium post, polyethylene fiber, and adhesive composite. The mesial, distal, and palatal walls of human maxillary molar teeth were removed, so that only the buccal wall remained. Group 1, with caries-free maxillary molars, was used as a positive control group and the remaining groups were restored as follows: group 2, with only adhesive composite; group 3, with polyethylene fiber and adhesive composite; group 4, with fiber post and adhesive composite; group 5, with fiber post, polyethylene fiber, and adhesive composite; group 6, with titanium post and adhesive composite; and group 7, with titanium post, polyethylene fiber, and adhesive composite. A universal testing machine was used for fracture tests. Compressive loads were applied at an angle of 90 degrees on the occlusal surface of the specimens at crosshead speed of 1?mm/min until fracture occurred. Kruskal–Wallis and Mann–Whitney U tests were adopted for statistical analysis. The study shows that, based on the fracture strength, the group of teeth that were restored with glass fiber post, polyethylene fiber, and adhesive composite has the most significant improvement over all the other teeth groups. Based on the fracture mode, the teeth groups restored with only glass fiber post, adhesive composite, polyethylene fiber, and adhesive composite have relatively more restorable fractures observed.     

Physical properties of a bisphenol-F epoxy containing a silica filler treated with silane coupling agents

A model epoxy system consisting of a diglycidyl ether of bisphenol-F epoxy resin, 1,4-butanediol, and cured with 4-methyl-2-phenylimidazole has been investigated. Thermal analysis indicated that 3 parts per hundred resin (phr) is the optimum amount of curing agent for this system. The influence of silane-treated amorphous fumed silica fillers on properties of the cured epoxy was also examined. Silica particles were treated with 3-aminopropyldiethoxymethylsilane (APDS) and3-aminopropyltriethoxysilane (APTS) coupling agents. No change in glass transition temperatures was observed with the addition of the filler (with or without coupling agents) to the epoxy. Addition of the filler led to a slight increase in the activation energy for the glass transition; however, no change in activation energy was observed when using the coupling agent. Addition of either coupling agent to the filler surface led to an increase in cooperativity. Fumed silica also did not significantly affect moisture diffusion properties, but a small decrease was observed in the moisture saturation mass with the addition of silica particles treated with APDS.     

废热锅炉管板结构应力分析与强度评定

应用ANSYS有限元软件对温度与压力载荷共同作用下的废热锅炉结构进行3D建模与热-结构耦合的数值模拟,得到了整个模型的应力分布云图。在最大应力位置附近或沿管板厚度方向选取不同路径,并对路径上的应力值进行线性化处理,根据JB 4732—1995《钢制压力容器-分析设计标准》对整体模型和管板结构分别进行了应力强度评定。应力分析与强度评定的结果表明,管板的结构设计能够满足强度要求。     

二氧化硅表面修饰硅烷偶联剂APTS的过程和机制

二氧化硅表面经过硅烷偶联剂γ-氨丙基三乙氧基硅烷（APTS）修饰后,在橡胶、塑料、催化剂、色谱柱、吸附剂、生物和医药等领域中具有独特的应用性能,大量文献结合特定应用体系研究二氧化硅表面修饰APTS的基本规律,以实现理想可控的修饰效果。总结这些分散性研究结果,有利于在新的基础上有效地促进研究的深入。在分析文献的基础上,系统地阐述了二氧化硅表面修饰APTS的反应机理、修饰工艺、反应动力学、修饰层稳定性和结构形貌等方面的研究进展,提出了目前研究还存在的问题和进一步的研究方向。     

一种木材粘合剂胶接强度新型试验装置的研制

设计了一种由基础框架、加载液压千斤顶、测力弹簧、读数百分表和试样夹具组成的木材粘合剂胶接强度试验装置。有限元数值分析与通用材料试验机的测试比较结果表明：该装置可满足JIS K6852标准的要求，且具有结构简单、体积小、测量可靠和便捷的特点。     

On the Use of Laminated Beams for the Determination of Pure and Mixed-Mode Fracture Properties of Structural Adhesives

The use of cracked laminated beam specimens is proposed for determining fracture properties of structural adhesives. Slight variations in specimen geometry and loading are used to produce pure mode I and II conditions as well as an intermediate mode-mix. Bounds are established for proper use of the specimens and mixed-mode fracture criteria are examined.     

On the Use of Laminated Beams for the Determination of Pure and Mixed-Mode Fracture Properties of Structural Adhesives

The use of cracked laminated beam specimens is proposed for determining fracture properties of structural adhesives. Slight variations in specimen geometry and loading are used to produce pure mode I and II conditions as well as an intermediate mode-mix. Bounds are established for proper use of the specimens and mixed-mode fracture criteria are examined.     

Experimental and numerical investigation on the strength of polymer-metal hybrid with laser assisted metal surface treatment

The aim of this study was to evaluate the effect of laser assisted treating metal surface on the strength of polymer-metal hybrid. The oxide film on the metal surface was removed by caustic soda and nitric acid solution. After that, the metal surface was treated by fiber laser, and the hot pressing connection between polymer and metal was completed by plate vulcanizing machine. And then, the tensile strength was obtained by using universal testing machine. The effect of different laser power, different scanning line width and different scanning speed on the bonding strength of polymer-metal hybrid was investigated. The correlation between the characteristics of metal surface and the bonding strength of polymer-metal hybrid was analyzed based on the micro structure morphology and scanning electron microscope (SEM). The results show that the bonding strength of polymer-metal hybrid increases first and then decreases with the increase of laser power. With the increase of scanning line width, the strength of polymer-metal hybrid increases. When the scanning speed is 500?mm/s, the strength of polymer-metal hybrid is the lowest. Based on the experiment, a simplified model is established and analyzed. Through using ABAQUS to conduct the numerical simulations, the results are consistent with the theoretical analysis and experimental data.     

PTFE薄膜横向拉伸变形行为及其有限元分析

采用分步位移加载和弹塑性材料模型,在应力应变曲线及材料基本参数的基础上,对PTFE薄膜横向拉伸过程进行了实验研究和有限元分析,得到了均匀横向拉伸和横向拉伸过程中薄膜的应力和位移变形分布状态及规律。实验和模拟结果表明,由于PTFE薄膜在低应力下易发生塑性变形,在横向拉伸过程中存在明显的应力和位移分布不匀,并导致薄膜在面内发生弓曲变形。研究结果对通过扩幅实现双向拉伸薄膜的非均匀变形控制具有参考价值。     

Synthesis and characterization of epoxy resin modified with γ‐thiopropyl triethoxy silane

Organic/inorganic hybrids with 1 to 7% silica contents were synthesized from bisphenol‐A and epichlorohydrin by utilizing γ‐thiopropyl triethoxy silane (KH580). The reactive coupling agent KH580 was introduced to epoxy resin to obtain high adhesive strength material for engineering industry. It was hypothesized that the multiple reactive functional silanol group Si? OH of KH580 after hydrolyzing reacted with epoxy resin to increase the shear strength and toughness of epoxy resin. IR spectra indicated that bonded stationary phase was formed. Shear strength of epoxy resin–based composite increased and then decreased after SiO₂ content reached 5 wt %; the optimal value was 24.78 MPa. SEM analysis showed that toughness of SiO₂/epoxy resin–based composite also increased and then decreased when the content of SiO₂ is more than 5 wt %. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Elastoplastic finite element stress analysis and strength evaluation of adhesive lap joints of hollow shafts subjected to tensile loads

The stress distributions in adhesive lap joints of dissimilar hollow shafts subjected to tensile loads have been analyzed by the elastoplastic finite element method, taking the nonlinear behaviors of the adhesive and the hollow shafts into consideration. A prediction method for the joint strength has been proposed based on the Mises equivalent stress distribution in the adhesive and the frictional resistance between the adhesive and the shaft after rupture of the adhesive. In the experiments, three different kinds of adhesive lap joints were made, i.e. the inner and outer hollow shafts were aluminum alloy/aluminum alloy, steel/steel, and steel/aluminum alloy combinations, and the tensile strength of each joint was measured. From the numerical calculations, in the case of the two hollow shafts made of the same material, the tensile strength increases with an increase of Young's modulus of the shaft and in the case of the two hollow shafts made of different materials, the tensile strength increases when the inner hollow shaft of larger Young's modulus is bonded to the outer one of smaller Young's modulus. Also, the effects of the overlap length and the inner diameter of the inner shaft on the tensile strength of the joint are discussed. By comparing the predicted values of the tensile strength with the experimental results, it was shown that the proposed prediction method could estimate the tensile strength of the adhesive lap joints of hollow shafts within an error of about 15%.     

Mode-l Fracture Behaviour of Adhesive Joints. Part II. Stress Analysis and Constraint Parameters

The constraint effect on the fracture behaviour of a rubber-modified epoxy was investigated using compact tension (CT) adhesive joints. An elastic-plastic finite element analysis was conducted to evaluate the stress distribution ahead of the crack tip in the bulk adhesive and adhesive joints of different bond thickness. The models with sharp and finite radius crack tips were evaluated in the analyses. The constraint effect of adherends on the stress triaxiality ahead of the crack tip in the adhesive joints were discussed. The constraint parameters were investigated using the J-Q theory and the J-CTOD relationship. It was found that as the adhesive thickness was increased, the stress triaxiality ahead of the crack tip was relieved by the remarkable deformation of the adhesive material. Similarly, the crack tip constraint was reduced with increasing bond thickness so that the fracture energy increased towards the value of the bulk adhesive. A higher constraint was associated with a lower fracture energy and vice versa. Furthermore, the J-integral did not have a unique relationship with the crack-tip opening displacement (CTOD) for different adhesive bond thickness, as this depends on the constraint around the crack tip. The results of this study will help improve reliability assessment of adhesive joints in engineering applications.     

Biomechanical three-dimensional finite element analysis of monolithic zirconia crown with different cement thickness

Limited information is available on the optimal cement thickness of monolithic zirconia crowns. This study was designed to evaluate the stress distribution in the posterior monolithic zirconia crowns with different cement thicknesses under masticatory force and maximum bite force using three-dimensional finite element analysis. The prepared and unprepared mandibular right first molar models were scanned and exported to the computer-aided design system. Solid models of monolithic zirconia crowns, which were cemented on prepared teeth were generated. Four models were fabricated applying different cement thicknesses (100 µm, 200 µm, 400 µm, and 600 µm). The solid models were imported into the finite element analysis software and meshed into tetrahedral elements. Four three-dimensional finite element models were simulated under masticatory force and maximum bite force: vertical (axial), angular (45°) and horizontal loads of 280 N at 5 points; vertical load of 700 N at 8 points were loaded, respectively. The stress distribution varied with the different cement thicknesses and directions of applied loads. The monolithic zirconia crowns with cement thicknesses exceeding 200 µm had wider distributions of peak maximum principal stress under the same loading conditions. Monolithic zirconia crowns have more stress concentrations on the occlusal surfaces, while the cement layers have more stress concentrations on the cervical areas. Thicker cement layers were associated with more concentrated stresses on the buccal and lingual cervical areas. The test results show that the cement thickness plays an essential role in the success of monolithic zirconia restorations in terms of reducing cement wash-out. Cement thickness of 100 µm is recommended for monolithic zirconia crowns.