Surface treatment for adhesive-bonded joints by excimer laser

In this work a treatment for surface preparation to improve mechanical resistance in adhesive bonding of plastic composites reinforced with fibres and metallic material, has been performed using an excimer laser. The following couplings have been selected to reproduce joints commonly used in the aerospace and automotive industry: CFC (carbon fibre composite) with CFC, CFC with Al 2024T3, Al 99% with Al 99%, GFC (glass fibre composite) with zinc-coated sheet in low carbon steel FeP01. The surfaces have been prepared using an excimer laser, adopting several values of laser parameters. The obtained surfaces have been examined by optical and scanning electron microscope: comparative measures of wetting and roughness have been performed to obtain an accurate characterisation and to select the proper finishes suitable to improve the mechanical resistance of the joints. The results obtained show that laser treatment always improves the final resistance of the joint; notable increases, and no significant surface damages have been highlighted. Better results have been obtained with the Al 99% with Al 99% joints which, with a low number of pulses treatment, have shown an increase of mechanical resistance up to the 70%.     

EXCIMER LASER ABLATION OF GLASS FIBER IN REINFORCED POLYMER

In excimer laser ablation of glass fiber reinforced polymer, the fibers were found to be acting as refocusing lenses and caused partial fiber removal within the fiber. An analytical analysis based on Snell's law of refraction was used to calculate the laser intensity within the fiber, and the results of which were able to explain the partial removal phenomenon.     

Analysis on effect of electroless coated SiCp on mechanical properties of polymer matrix composites

ABSTRACT

The versatility of polymer matrix composites in industrial applications has gained reputation and adaptability among advanced materials. Still, treatment of reinforcement for these composites has emerged as a vital domain to be explored. With a continuance to this fact, the present paper aims to analyze the effect of reinforced electroless coated silicon carbide particulates on mechanical properties of composites. The composite is developed using epoxy polymer as matrix and glass fibers as primary reinforcement. The electroless coated and uncoated silicon carbide particulates were used as secondary reinforcement. The phase identification of copper on secondary reinforcement was identified using X-ray powder diffraction technique. Fracture analysis during tensile testing and bonding behavior between matrix and reinforcement is examined using field emission scanning electron microscopy with energy dispersive spectroscopy. The presence of copper particles on secondary reinforcement results in improved interfacial bonding and resistance against fracture during loading.     

硅烷偶联剂对玻璃织物/水泥复合材料界面行为的影响

本文通过织物抽拔试验和抽拔试验后残留在水泥基体中的纤维表面形貌扫描电镜照片分析,研究了在玻璃纤维织物表面涂覆硅烷偶联剂或涂蜡,对它增强的水泥基复合材料界面行为的影响.实验结果表明:在玻璃纤维织物表面涂覆硅烷偶联剂有利于它与水泥基体间的界面粘结,改善它们间的界面行为,在玻璃纤维织物表面涂蜡则不利于它与水泥基体间的界面粘结.     

基于激光三维雕刻的CFRP多梯层挖补胶接接头加工技术研究

在航空飞行器的碳纤维复合材料(CFRP)结构件损伤修复时,挖补胶接技术是获得高性能的CFRP层合板接头的理想工艺.本文提出一种CFRP层合板的多梯层挖补胶接接头设计策略,设计了挖补胶接接头阴阳膜构建和分层切片激光三维雕刻扫描工艺代码生成算法,探索了CFRP梯层界面的激光烧蚀成型工艺规律和粘结性能改善机理,验证了胶接接头...     

Comprehensive study of pulsed UV-laser modified polyamide fibers

Polyamide fibers (nylon 6) are modified by UV-radiation using a pulsed excimer laser with different treatment parameters. The treated samples are characterized by using a scanning electron microscopy (SEM), tapping mode atomic force microscopy (TM-AFM), x-ray photoelectron spectroscopy (XPS), and chemical force microscopy (CFM). Depending on the conditions during the irradiation, different surface modifications are obtained which can generally be distinguished as high-fluence (above the ablation threshold) and low-fluence (below the ablation threshold). Topographical results indicate that ripple-like structures of micrometer size are developed under high-fluence laser irradiation. On the contrary, smaller sub-micron structures are formed by low-fluence treatment. XPS results show that bond scission occurs on the polymer surface under the action of high-fluence while low-fluence modifies the sample by an oxidative process. Changes in surface chemical properties of the laser-irradiated polyamide are supported by chemical force microscopy experiments with gold-coated AFM tips modified with -COOH terminated self-assembled alkanethiol monolayers (SAMs).     

A biodegradable composite material based on polyhydroxybutyrate (PHB) and carnauba fibers

In this investigation, carnauba fibers obtained from the leaves of the carnauba palm tree were chemically modified and their potential for the development of a biodegradable composite was evaluated. Fiber treatments to improve interfacial bonding were carried out by alkali, peroxide, potassium permanganate and acetylation. Biodegradable composites were prepared using carnauba fibers and polyhydroxybutyrate (PHB) as matrix. Mechanical properties of the composites prepared with 10 wt.% of short carnauba fibers were investigated and related to fiber treatment. According to the results, the tensile strength of the composites made from peroxide treated fibers was superior to those using untreated fibers or any other fiber treatment. SEM observations on the fracture surface of the composites suggest improved fiber–matrix adhesion after peroxide treatment. This surface modification of the fibers was found to contribute to the enhancement of the mechanical properties of the composites, even though the tensile strength of the fibers was slightly reduced. Dynamic mechanical thermal analyses suggested improvement in storage modulus of the composites reinforced with carnauba fibers at higher temperatures as compared to the neat polymer.     

Joining of natural fiber reinforced composites using microwave energy: Experimental and finite element study

The development of natural fiber reinforced polymer composites has received widespread attention due to their environment friendly characteristics over the synthetic fiber based polymer composites. Although, different categories of natural fiber reinforced composites have been developed, their joining has not been explored extensively. In the current article, natural fibers (nettle and grewia optiva) reinforced polylactic acid green composites and polypropylene based partially biodegradable composites have been developed. These composites have been joined with an innovative microwave heating process in the presence of suitable susceptor. Samples have also been joined with the well known adhesive bonding technique for comparison purposes. Joint strength has been evaluated in each case as per standard procedures and results showed that microwave joining provides higher joint strength as compared to adhesive bonding. Microwave heating process has also been simulated with standard multiphysics finite element (FE) software to analyze the microwave heating mechanism. The results of the experimental study are in close agreement with the finite element investigation.     

Reusing recycled fibers in high-value fiber-reinforced polymer composites: Improving bending strength by surface cleaning

Glass fiber-reinforced polymer (GFRP) composites and carbon fiber-reinforced polymer (CFRP) composites were recycled using superheated steam. Recycled glass fibers (R-GFs) and recycled carbon fibers (R-CFs) were surface treated for reuse as fiber-reinforced polymer (FRP) composites. Treated R-GFs (TR-GFs) and treated R-CFs (TR-CFs) were characterized by scanning electron microscopy (SEM) and remanufactured by vacuum-assisted resin transfer molding (VARTM). Most residual resin impurities were removed by surface treatment. Analysis indicated no adverse effect of surface treatment on bending strength. The mechanical properties of the TR-GF reinforced polymer (TR-GFRP) and TR-CF reinforced polymer (TR-CFRP) composites were determined and compared with those of R-GF reinforced polymer (R-GFRP) and R-CF reinforced polymer (R-CFRP). The bending strengths of R-GFRP (26%) and R-CFRP (49%) were very low, compared to that of virgin glass fiber-reinforced polymer (V-GFRP) and that of virgin carbon fiber-reinforced polymer (V-CFRP). The bending strength of TR-GFRP composites was improved to about 90% of that of V-GFRP, and the bending strength of TR-CFRP composites was improved to about 80% of that of V-CFRP.     

非晶态合金带增强聚合物基复合材料的研究

本文研究了超高强的非晶态合金带增强高性能聚合物的复合材料.通过对非晶态合金带进行合适的表面化学处理,可以提高其复合材料的粘结强度:同时本文应用复合材料的剪切强度来研究非晶态合金带增强复合材料的粘结性能.用扫描电镜(SEM)微观分析技术分析研究了经过表面处理前后的非晶态合金带增强的复合材料的表面和界面.     

纳秒激光调控CFRP复合材料表面润湿性及其对胶接性能的影响

采用纳秒激光对碳纤维增强树脂基(CFRP)复合材料进行表面预处理,调控其表面成分、粗糙度和表面润湿性,然后采用SEM、接触角测量仪、光学轮廓仪、XPS等表征CFRP复合材料的表面微观形貌、接触角、粗糙度和化学成分,并通过拉伸剪切实验评价和分析激光表面处理对CFRP复合材料胶接强度的影响规律和机制。结果表明:优化激光表面处理参数,可以去除CFRP复合材料表面的环氧树脂胶,调控其表面成分、粗糙度和表面润湿性;与未处理的CFRP复合材料相比,激光表面处理后的CFRP复合材料表面化学成分改变,表面粗糙度有所增加,润湿性提高,胶接强度也增大;与未处理CFRP复合材料相比,激光离焦量分别为5 mm、10 mm和15 mm时,处理后的CFRP复合材料胶接强度分别提高了129.41%、112.13%和105.88%;激光表面处理CFRP复合材料的表面润湿性和表面粗糙度均高于机械处理CFRP复合材料,但激光处理导致的热损伤对胶接强度提高有负面影响。      

协同处理对湿热环境下木粉/聚乙烯复合材料表面性质演变的影响

采用硅烷偶联剂涂覆与等离子体放电协同处理的方法处理木粉/聚乙烯(WP/PE)复合材料表面,以改善其胶接性能。利用胶接强度测试、FTIR和X射线光电子能谱研究了硅烷偶联剂涂覆和等离子体放电的协同表面处理对WP/PE湿热环境下表面性质演变的影响,探究协同处理的WP/PE胶接接头湿热环境下的胶接耐久性。结果表明,协同处理后,WP/PE表面有含氧极性基团生成,且在偶联剂与材料表面之间形成了化学键接,胶接性能大为改善。湿热环境下,虽然处理试样的表面没有新的化学基团产生,但表面元素的化学环境发生了改变。WP/PE表面在湿热环境下的性质演变会直接影响其胶接接头的耐久性。协同表面处理能够降低湿热环境下WP/PE表面性质的改变程度,从而提高WP/PE的胶接性能,尤其是湿热环境下的胶接耐久性能。     

Microstructuring of UV-transparent functionalised films on glass by excimer laser irradiation

KrF excimer laser irradiation was used to remove organic moieties from UV-transparent films of organosilanes on borosilicate glass. High-resolution patterns with different functional groups on glass were obtained by a combination of laser modification and silanisation steps. The local material modification near the ablation threshold of glass was investigated by white light interference microscopy. Change in chemical properties of irradiated surface areas were studied by fluorescence microscopy after an appropriate dying of exposed samples. From the results, the domination of thermo-chemical effects induced by the laser irradiation is derived. Finally, an example is given how the patterned organosilane films can be applied to influence cell growth on glass.     

Study of chemical and mechanical properties of Dharbai fiber reinforced polyester composites

This investigation is focused on identifying a new variety of natural fiber (Dharbai fiber) for reinforcement in polymer matrix composites. An investigation on extraction procedure of Dharbai fibers has been undertaken. The chemical properties of Dharbai fibers were determined experimentally as per TAPPI standards. The FT-IR Spectroscopy was used to study the chemical structure of Dharbai fibers and the tensile properties of these fibers were studied using single filament test. The fibers extracted were reinforced in polyester matrix by varying the fabrication parameters namely fiber weight content (%) and fiber length (mm). The effect of fiber weight content and fiber length on the mechanical properties of Dharbai fiber-polyester composites were evaluated as per ASTM standards. Scanning electron microscope was used to characterize the interfacial bonding between Dharbai fibers and polyester matrix. This study confirmed that, the Dharbai fibers could be used as an effective reinforcement material for making low load bearing polymer composites.     

Photomodification of polymer microchannels induced by static and dynamic excimer ablation: effect on the electroosmotic flow

This paper presents a study of polymer surfaces modified by laser ablation using poly(ethylene terephthalate) (PET) as a model system. The surface properties induced by static and dynamic ablation with the 193-nm pulsed radiation of an ArF excimer laser (4 x 10(7) W/cm2) in air have been successfully used to control the electroosmotic flow (EOF) in photoablated PET microchannels. Through the creation of well-defined static ablation patterns onto the walls of a trapezoidal channel, it was found that the resulting reduction in the EOF could be controlled. For example, a reduction of 25% in the EOF was observed in 42-microm-deep microchannels when using a static ablation pattern treating 50% of the total wall surface area. A numerical study describing the fluidic behavior induced by a static pattern is also presented. Moreover, X-ray photoelectron spectroscopy has been used to point out surface changes between static and dynamic ablation, thereby demonstrating an ability to create new functionalities in microchannels by laser treatment.     

Using silane-functionalized graphene oxides for enhancing the interfacial bonding strength of carbon/epoxy composites

Silane-functionalized graphene oxides (sGOs) were fabricated with four different self-assembled monolayers (SAMs) to reinforce an epoxy adhesive, with the aim of improving the bonding strength of carbon/epoxy composites. The oxygen-containing groups on the surface of graphene oxide (GO) were converted by the SAMs to amine, epoxy, or alkyl groups. The successful reaction between the silane molecules of the SAMs and functional groups of GO was evidenced by the results of different characterization methods such as Fourier transform infrared spectroscopy. It was found that the average thickness of the sGO flakes was higher than that of GO flakes. The bonding strength of a carbon fiber/epoxy composite, tested with a single lap joint bonded with an epoxy adhesive, was increased by 53% after the addition of a sGO that contained amine groups. These results show that sGOs, especially those containing amine functional groups, can strengthen the interfacial bonding between the carbon fibers and epoxy adhesive.     

Enhancement of ceramic-to-metal adhesive bonding by excimer laser surface treatment

A silicon nitride (Si₃N₄) based ceramic cutting material and a structural alloy steel (SAE 4340) were surface-treated using a 800 mJ KrF excimer laser with an aim to improve the ceramic-to-metal bond strength. For these two materials, the effects of laser energy density and the number of pulses upon the surface morphologies of the laser-treated surfaces to be joined were examined. Conical surface microstructures were generally observed on the laser-treated surfaces of the Si₃N₄ material, and the number of conical features was found to be significantly influenced by the laser energy density. Moreover, the results of XPS have shown that the surface chemistry of the ceramic was altered after being laser treated. On the other hand, excimer laser treatment had caused the alloy steel surfaces be melted and resulted in some “beach-mark” features. However, the laser energy density has little effect on the overall surface morphology and the roughness of the treated surfaces. Shear tests were performed on adhesive bonded samples of the laser-treated ceramic and alloy steel. Significant improvement in adhesion shear strength was obtained for the laser-treated samples as compared with those tested in the as-received and mechanically abraded conditions. The required laser operation condition for achieving good shear joint strength was discussed.     

服役低温老化对铝合金-玄武岩纤维增强树脂复合材料粘接接头力学性能的影响及失效预测

为了给铝合金-玄武岩纤维增强树脂(BFRP)复合材料粘接结构在汽车工业中的应用提供参考和指导,加工了铝合金-BFRP复合材料粘接接头。结合汽车服役中的温度区间,选取?10℃和?40℃的低温老化环境,对接头进行0、10、20、30天的老化。对老化后的粘接接头进行准静态拉伸试验和剪切试验,得到不同老化时间下铝合金-BFRP粘接接头的准静态失效强度。结合DSC和FTIR分析低温老化对BFRP复合材料的影响,并对粘接接头的失效断面进行宏观分析和SEM分析。结果表明:在低温老化环境中,胶粘剂与BFRP复合材料的化学性质受低温老化作用影响不大,BFRP中的官能团与玻璃化转变温度(T_g)没有发生明显的变化,接头的失效强度和失效模式主要受胶粘剂与粘接基材的热应力影响。对于拉伸接头,随着低温老化时间的增加,BFRP复合材料纤维与树脂基体间的结合力降低,铝合金-BFRP复合材料接头的失效断面中纤维撕裂的比例逐渐减少,拉伸接头失效强度逐渐下降。老化后剪切接头仍为内聚失效,BFRP复合材料的低温老化对铝合金-BFRP复合材料剪切接头的失效强度几乎没有影响,剪切接头失效强度的下降主要是胶粘剂与粘接基材热膨胀系数不一致引起的热应力的影响。采用二次应力准则公式对?10℃和?40℃低温环境下,拉应力、剪应力值随老化时间的变化规律进行了拟合,在此失效准则的基础上,根据响应面原理,建立接头失效强度随老化时间变化的三维曲面,为粘接技术在车身结构中的工程应用提供参考。      

Short-aramid-fiber toughening of epoxy adhesive joint between carbon fiber composites and metal substrates with different surface morphology

Carbon-fiber epoxy composites were bonded to four different types of aluminum substrates with different surface roughness and finish. The four aluminum substrates considered in this study have the following surface conditions: two solid aluminum substrates polished with two different grades of sandpapers, and two porous aluminum foams with two different as-received surface conditions, one with a patterned surface finish and one with rough pore structures. Moreover, the thin epoxy adhesive joints between the carbon-fiber face sheets and aluminum substrates were reinforced by adding short aramid fibers. During the fabrication process of the hybrid laminar, sparsely-distributed short aramid fibers were inserted between the fiber-metal interface to promote bridged fibers for tougher and stronger adhesive bonding, while at the same time to minimize any significant change in the thickness of the adhesive joint. Measurements of the critical energy release rate showed that the toughening effects of the low-density short aramid fibers were influenced by the metal-substrate surface roughness and finish. Further comparison indicated that the interfacial fracture toughness of aramid-fiber interleave adhesive joints increased via increase of surface roughness of metal substrates. The surface-roughness effect of metal substrate mainly depends on whether the free fiber ends of the short aramid fibers were pressed and embedded into the surface cavities of aluminum substrates according to scanning electron microscopy observations. The results indicated that the properties and performances of aramid-fiber interleaved adhesive joints between the carbon-fiber face sheets and aluminum substrates could be improved by surface treatments on the aluminum substrates to achieve appropriately surface roughness.     

Influence of filler/reinforcing agent and post-curing on the flexural properties of woven and unidirectional glass fiber-reinforced composites

The aim of this study is to investigate the reinforcing effect of woven and unidirectional glass fibers and the effect of post-curing on the flexural strength and flexural modulus of glass fiber-reinforced composites. A series of composites containing 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)-phenyl]propane and triethyleneglycol dimethacrylate matrices and different reinforcements of unidirectional or woven glass fibers were prepared. The samples, 25 × 2 × 2 mm, were cured with a halogen curing lamp, followed by additional curing by thermal treatment at 135 ± 5 °C temperature and 60 psi pressure. Samples were tested before and after post-curing in order to determine the flexural strength and flexural modulus. The degree of reinforcement with glass fibers was varied between 14 and 57 wt% or 7.64 and 38.44 vol% by changing the number of unidirectional bundles or woven glass fiber bands in the composites, respectively. The obtained flexural strength values were in the range of 95.20–552.31 Mpa; the flexural modulus ranged between 2.17 and 14.7 GPa. The highest flexural strength and flexural modulus values were recorded for samples with unidirectional glass fibers. The mechanical qualities of the glass fibers-reinforced composites increased after post-curing treatment. Increasing of the glass fiber amount in the experimental composites improves both flexural strength and modulus. SEM micrographs of fractured composites indicate a strong interfacial interaction between the glass fibers and the polymer matrix.