基于内聚力模型的某传动机构涂层失效分析

硬质涂层具有耐磨性好,接触疲劳寿命高的优点,广泛应用于航天航空领域。然而在重载工况下,涂层基底的界面处可能会发生脱层失效,影响机械零件的可靠性。近年来涂层失效机理及增强涂层结合能力的研究逐渐受到关注。采用内聚力的理论模型,结合有限元模拟的方法,对涂层基体的界面分层失效行为进行分析。研究结果表明,基于内聚力理论模型的仿真分析结果与试验结果对比吻合程度高。在此基础上,讨论了不同因素对涂层结合能力大小的影响。增加涂层厚度和提高涂层弹性模量均可以提高界面的结合能力,增加零件的承载范围。     

复合材料胶接强度分析

以Von Mises屈服准则为胶层失效判据及基于应力分布的三维Hashin失效准则为复合材料层合板失效判据,采用材料刚度退化的方法,在ANSYS中建立了考虑复合材料层合板和胶层失效的复合材料胶接强度分析模型;利用该模型对复合材料胶接强度进行了准确预测.重点研究了胶层厚度和胶接长度两个设计参数对复合材料胶接强度的影响,结果表明:胶接强度在一定范围内随着胶层厚度和胶接长度的增大而增大,呈非线性关系.     

胶接技术在工程中的应用

简要介绍了胶接剂的组成及其在工程中的选用原则。对实际应用中通常采用的胶接原理作了定量的说明,在此基础上对胶接前构件的表面处理工艺及表面涂胶方式进行了叙述;同时对胶接技术的使用场合及性能特点也作了说明。     

碳纤维管与铝合金的胶接强度试验研究

根据赛车轻量化设计的需要,对碳纤维管与铝合金接头的胶接工艺进行了试验研究。分析了胶接强度的影响因素,设计了因素水平;通过正交试验和分析,确定了胶层厚度、铝合金表面粗糙度和表面化学处理方式。试验结果为胶接工艺的实施提供了试验依据。     

不同胶接参数对CFRP层合板单搭胶接结构强度的影响及优化设计

对于碳纤维增强基复合材料(Carbon fibre-reinforced polymer,CFRP)层合板单搭胶接结构的优化问题,首先利用连续损伤力学模型、三维Hashin准则和内聚力模型研究不同胶接参数对CFRP层压板单搭胶接结构力学性能的影响,其次采用拉丁超立方试验设计方法和响应面法构建了拉伸强度代理模型,最后基于...     

一种复合材料层合板分层扩展的修正内聚力模型

针对复合材料的分层现象,考虑初始断裂韧性和裂尖材料损伤的影响,提出了一种修正内聚力模型,并给出了内聚力模型参数确定的方法.根据相关试验,采用该方法,获得了考虑初始断裂韧性和裂尖材料损伤的内聚力模型,基于该内聚力模型对试验进行了仿真分析.结果 表明,与仅考虑初始断裂韧性获取的内聚力模型相比,考虑初始断裂韧性和裂尖材料损伤的内聚力模型,可以更加准确地模拟复合材料的分层现象.     

考虑汽车车身涂装工艺影响的非平衡胶接接头强度

汽车轻量化的发展要求汽车采用更多的轻型材料取代传统的金属材料,而异种材料的连接就为结构胶接技术的应用提供平台。通过模拟汽车车身涂装工艺中环境温度和相对湿度的变化,采用韧性和脆性两种结构胶粘剂,分别对钢/铝和钢/碳纤维增强复合材料非平衡胶接接头的剪切强度进行环境影响研究。试验结果表明,汽车涂装环境对结构胶接接头的性能有着显著的影响,并且与胶粘剂自身性质有关。通过对不同工况接头的失效模式分析和对胶层的内聚力单元数值二维建模仿真,得到两种胶粘剂在涂装工况影响下胶层宏观力学属性和内部应力分布情况的变化趋势,并对碳纤维增强复合材料与相应胶粘剂材料表面参数的匹配问题进行研究。采用扫描电镜法对胶层失效表面进行样貌分析,探究相应宏观试验结果产生的微观原因。     

基于内聚力模型的夹层玻璃冲击破坏仿真分析

夹层玻璃冲击破坏特性的研究对于风挡玻璃设计、行人保护及交通事故再现具有重要意义。针对传统有限元方法不能有效描述脆性材料冲击破坏的问题,在介绍双线性内聚力模型基本理论的基础上,建立适用于夹层玻璃冲击破坏现象的有限元模型,使用已嵌入内聚力模型的有限元软件LS-DYNA仿真分析夹层玻璃的冲击破坏过程。同时,设计简易夹层玻璃板落锤试验装置,以评价仿真分析结果。夹层玻璃板的裂纹分布和冲击加速度的仿真与试验结果的良好一致性,验证了内聚力模型与仿真分析方法的有效性。     

不锈钢夹层复合板的胶接强度

为了提高不锈钢夹层复合板的胶接强度,研究了表面处理、胶粘剂对不锈钢夹层复合板(铝蜂窝夹芯)胶接强度的影响.结果表明:不锈钢基材的表面处理是影响夹层复合板胶接强度的主要因素,盐酸-甲醛法处理的不锈钢板胶接强度最优,相同条件下,国产环氧胶膜夹层复合板胶接性能相对较好,最大胶接强度达到4.63 kN·m-1.     

胶接技术在工程中的应用

简要介绍胶接技术，在实例的基础上详细阐述它的特性，以及在现代工程中的应用和未来发展前景。     

Comparison of microtensile bond strength and resin–dentin interfaces of two self‐adhesive flowable composite resins by using different universal adhesives: Scanning electron microscope study

The aim of this in‐vitro study was to evaluate microtensile bond strength (μTBS) of two different self‐adhesive composites (SACs) on the permanent dentin by applying five different universal adhesive systems. In this study, two different SACs [Vertise Flow (VF), Fusio Liquid Dentin (FLD)] and five different bonding systems [Clearfil Universal Bond Quick (CUB), Single Bond Universal (SBU), All Bond Universal (ABU), Prime Bond Universal (PBU), Futurabond U (FBU)] were used. A total of 22 groups were created in which SACs were applied without adhesive and with five different universal bonding agents in total‐etch (TE) and self‐etch (SE) modes. Two hundred and forty test sticks were obtained using 48 healthy human molar teeth in total with groups having 10 samples each. The μTBS test was applied to each sample in the Universal test device and the data obtained were analyzed statistically by variance analysis and Tukey HSD test. In addition, the resin–dentin interface and fractures modes in the groups were examined by SEM. Upon examining the μTBS results, the highest values were seen in the use of SBU adhesive in TE mode in VF group, while the lowest values were seen in the FLD control group. The difference between the control and experimental groups was found statistically significant (p < .05). Upon comparing the control groups with each other, it was seen that VF group had higher μTBS values than FLD group and the difference between the groups was found statistically significant (p < .05). The μTBS results and SEM images of the study showed that the use of SACs with universal adhesive systems provides a more effective bond strength.     

Effect of adhesive layer properties on the shear strength of single-lap structures of dissimilar materials based on the cohesive zone model

Journal of Mechanical Science and Technology - An analysis method for improving the shear strength for the single-lap joints of dissimilar materials based on the cohesive zone model (CZM) is...     

Dentin bond strength and nanoleakage of the adhesive interface after intracoronal bleaching

This study evaluated dentin bond strength (BS) and nanoleakage of non‐ and pre‐etched dentin immediately (T₀,), 7 days (T₇), and 14 days (T₁₄) after bleaching. Bovine incisors (150) were selected and half of them submitted to intrapulpal dentin etching (e). Non‐ and pre‐etched dentin were subjected to the following (n = 15): no bleaching/control (C); 35% carbamide peroxide (CP); 35% hydrogen peroxide (35% HP); 25% hydrogen peroxide (25% HP); and sodium perborate (SP). Bleaching agents were applied to the pulp chamber four times within a 72‐h interval. Afterwards, pulp chamber dentin was prepared for the BS test at different evaluation times (n = 5): T₀, T₇, and T₁₄. Composite blocks were built on pulp chamber and sectioned in slices. Slices were reduced to an hour‐glass shape with a cross‐sectional area of 0.8 mm² and submitted to microtensile BS test. Two additional specimens for each group were prepared for nanoleakage evaluation by transmission electron microscopy (TEM). Results were analyzed by ANOVA (two‐way) and Dunnett's test (p < .05). BS decreased immediately after intracoronal bleaching for both sound and pre‐etched dentin (p < .05). At T₁₄, the BS of non‐etched bleached dentin increased for all groups, whereas the pre‐etched SPe group presented BS similar to the Ce. Nanoleakage within the hybrid layer was perceptible immediately after bleaching, although a decrease in nanoleakage was observed for all groups at T₁₄. Adhesive restorations should be performed 7–14 days after bleaching, according to the bleaching agent used. Intracoronal bleaching should be performed preferably with sodium perborate if previous dentin etching is applied.     

Shear bond strength and ultrastructural interface analysis of different adhesive systems to bleached dentin

Background: It remains unclear as to whether or not dental bleaching affects the bond strength of dentin/resin restoration. Purpose: To evaluated the bond strength of adhesive systems to dentin submitted to bleaching with 38% hydrogen peroxide (HP) activated by LED‐laser and to assess the adhesive/dentin interfaces by means of SEM. Study design: Sixty fragments of dentin (25 mm²) were included and divided into two groups: bleached and unbleached. HP was applied for 20 s and photoactivated for 45 s. Groups were subdivided according to the adhesive systems (n = 10): (1) two‐steps conventional system (Adper Single Bond), (2) two‐steps self‐etching system (Clearfil standard error (SE) Bond), and (3) one‐step self‐etching system (Prompt L‐Pop). The specimens received the Z250 resin and, after 24 h, were submitted to the bond strength test. Additional 30 dentin fragments (n = 5) received the same surface treatments and were prepared for SEM. Data were analyzed by ANOVA and Tukey's test (α = 0.05). Results: There was significant strength reduction in bleached group when compared to unbleached group (P < 0.05). Higher bond strength was observed for Prompt. Single Bond and Clearfil presented the smallest values when used in bleached dentin. SEM analysis of the unbleached specimens revealed long tags and uniform hybrid layer for all adhesives. In bleached dentin, Single Bond provided open tubules and with few tags, Clearfil determined the absence of tags and hybrid layer, and Prompt promoted a regular hybrid layer with some tags. Conclusions: Prompt promoted higher shear bond strength, regardless of the bleaching treatment and allowed the formation of a regular and fine hybrid layer with less deep tags, when compared to Single Bond and Clearfil. Microsc. Res. Tech., 2010. © 2010 Wiley‐Liss, Inc.     

The effect of different nanoparticles and open time on bonding strength of poly (vinyl acetate) adhesive

Nanotechnology is one of the major technologies through in this century. Nano particles are an important part of this technology. Properties of many traditional materials can be changed by using the nanoparticles. Open time is one of key processing parameters for adhesive applications. Many adhesion failures are caused by exceeding of the open time. The main objective of this study is to improve the adhesion performance of PVAc adhesive by increasing open time through application of nanoparticles, specifically silicium dioxide (SiO₂) and titanium dioxide (TiO₂). For this reason, nano SiO₂ and nano TiO₂ were blended with PVAc at the open time 0, 5, 10 and 15 min. Effect of the nanoparticles and open time was determined by lap shear joint strength tests. Tests were carried out according to DIN EN 302-1. The results indicate that nanoparticles can considerably improve the bonding strength of PVAc at open-time of 5 and 10 min.     

Fatigue strength estimation of adhesively bonded tubular joint using genetic algorithm approach

The bonding strength of adhesives is influenced by many factors such as, the surface roughness, bonding clearances, interference fit, temperature, and material of the joining parts, etc. Since all these factors affect the strength of the adhesively joined parts, the effects of these parameters need to be investigated. The present paper describes the use of stochastic search process that is the basis of Genetic Algorithm (GA), in developing fatigue strength estimation of adhesively bonded cylindrical components. Nonlinear estimation models are developed using GA. Developed models are validated with experimental data. Genetic Algorithm Fatigue Strength Estimation Model (GAFSEM) is developed to estimate the fatigue strength of the adhesively bonded tubular joint using several adherent materials, such as steel, bronze and aluminum materials.     

The role of spatial frequency analysis in correlating atomic force microscopy and optical profilometry with self‐etch adhesive enamel bond fatigue durability

The purpose of this study was to: (a) evaluate the role of enamel surface roughness on bond fatigue durability and (b) evaluate statistical differences in roughness values based on measurement technique, including the use of spatial filtering for optical profilometry (OP). OptiBond XTR (Kerr Corp), Prime & Bond elect (DENTSPLY Caulk), Scotchbond Universal (3 M Oral Care), and XTR pre‐etched with Ultra‐Etch phosphoric acid (35%) (Ultradent) self‐etch adhesives were used to treat enamel. A flat ground enamel surface was included as a control. Atomic force microscopy (AFM) and OP were used to measure the surface topography of each enamel surface following the application of adhesives. AFM, OP, and filtered OP (FOP) roughness values, where FOP was designed to only include the lateral spatial resolution consistent with AFM roughness values, were collected. Spatial resolution filtering with OriginPro was used to compare line scans from the two imaging techniques and generate the FOP group. These micro‐ versus nanoscale lateral roughness values were correlated with shear bond and shear fatigue strengths of the adhesives bonded to enamel. Roughness values showed differences based on measurement technique and strong correlations with bond and fatigue strength. The filtered OP group demonstrated the importance of careful usage and reporting of atomic force microscopy and OP metrics in adhesive dentistry. Best practices for surface roughness analysis were also discussed.     

Adhesive interface and bond strength of endodontic sealers to root canal dentine after immersion in phosphate‐buffered saline

This study evaluated the bond strength (BS) and the adhesive interface of four endodontic sealers to root canal dentine, before, and after immersion in phosphate buffered saline (PBS) to simulate an in vivo environment. Eighty roots were instrumented using ProTaper rotatory files, under irrigation with 17% EDTA and 1% NaOCl. Posteriorly were divided into four groups (n = 20) according to the sealer used: Endofill, AH Plus, Sealapex, and MTA Fillapex. Each group was divided into two subgroups (n = 10) and stored at 37°C immersed in water for 7 days and in PBS for 60 days. From each subgroup, 1 mm thick sections were obtained. One section of each region (coronal, middle, and apical) was submitted to the push‐out test and failures were observed. Twelve sections of each subgroup (four from each region) were evaluated under SEM. Three‐way ANOVA evaluation for BS showed significant differences between groups and regions (P < 0.0001), but not between subgroups (P > 0.05). AH Plus had significantly higher BS than the others sealers, regardless of the analyzed subgroup (Tukey's test, P < 0.5). The most common failures were adhesive to dentine and cohesive of the sealer. The SEM evaluation (Kruskal–Wallis, Mann–Whitney) showed homogeneous adhesive interface formed and sealer tags in all groups with significant statistical differences with AH Plus, regardless of PBS immersion. AH Plus was superior to the other sealers for both BS and quality of interface formation. Immersion in PBS did not interfere on BS or adhesive interface of the sealers tested. Microsc. Res. Tech. 77:1015–1022, 2014. © 2014 Wiley Periodicals, Inc.