Fiber Welding Research Articles

Sensitivity-enhanced optical fiber sensor based on the Vernier effect for detection of ammonia in water

A sensitivity-enhanced optical fiber sensor for the detection of dissolved ammonia in water based on the Vernier effect is proposed and demonstrated. The sensor comprises a sensing Fabry-Perot interferometer (S-FPI) and a reference Fabry-Perot interferometer (R-FPI) in parallel. The S-FPI is an open cavity fabricated by the dislocation welding of single-mode fiber(SMF), which is filled with a mixture of ultraviolet-curable resin NOA 170 and Oxazine 170 perchlorate (O17). The R-FPI is a sealed cavity, which is constructed by fusion splicing of SMF and hollow core fiber (HCF). The proposed sensor is based on the chemical reaction between the dissolved ammonia and O17. This chemical reaction alters the refractive index (RI) of the S-FPI, resulting in a wavelength shift of the reflected spectrum. The two interferometers exhibit a nearly identical free spectral range (FSR), thereby enabling the generation of the Vernier effect, which markedly enhances the ammonia sensitivity of the sensor. Experimental results indicate that the sensor sensitivity is 0.34 nm/ppm in the dissolved ammonia range of 5-40 ppm, which is approximately 9.1 times that of the single S-FPI. The proposed sensor exhibits both good repeatability and a short response time, in addition to selectivity for the detection of ammonia.

Ultrasonic welding of continuous carbon fiber reinforced PEEK with embossed energy directors

Ultrasonic plastic welding (UPW) is an efficient and environmentally friendly method for joining carbon fiber reinforced thermoplastic (CFRTP). A crucial aspect of UPW is the design of the energy director (ED). In this study, ultrasonic embossing technology was used to process flat EDs to obtain a new type of ED, named embossed ED. The effect of embossed EDs on the joint formation in ultrasonic welding of continuous carbon fiber reinforced PEEK was investigated in terms of tensile shear properties, macro and micro-morphologies, and fracture morphology. The results show that the use of embossed EDs makes a more homogeneous temperature distribution at the welding interface which significantly reduces defects in the joint. The use of embossed EDs increases the failure load of welded joints by about 50 % (up to 39.6 MPa) and reduces the variation of the joint quality compared with the use of flat EDs. In the optimal condition, the joints made with embossed EDs experiences interlaminar failure of the base material.

Study on pore behavior of laser welding process between steel and CFRP based on numerical simulation

In order to understand the pore behavior during laser welding of metal and polymer, the laser welding of steel and carbon fiber reinforced plastics (CFRP) was studied. A three-dimensional transient model of multi-physical field couple with heat, flow and force was constructed to simulate the temperature distribution, fluid flow, stress change and solidification under the thermal decomposition of CFRP based on the experiments. The formation, function and evolution mechanism of pores in welded joints were discussed, and the relationship between heat input and pore morphology at the interface was clarified. The results show that the model error is lower than 9 %, and the model is reliable. In laser welding process, bubbles generate, expand and fuse in the center of CFRP molten pool, which changes the local flow velocity and direction, but most of the fluid still flows to the molten pool edge under the action of temperature gradient, and forms pores of stable size with the cooling process. When the heat input is high, the large pores are formed at the interface due to the violent thermal decomposition of CFRP and big stress difference. When the heat input is low, there is still a large stress gradient in the center of the interface, and it is difficult for the insufficiently melted polymer to provide sufficient resistance to deformation, resulting in obvious pore phenomenon in the center of the interface.

Underwater dissimilar friction stir lap welding of aluminum alloy and CFRTP

With the rapid development of the transportation and electronic equipment industries, the demand for robust joining technology for metal/polymer has become imperative, especially in the pursuit of lightweight solutions. Underwater welding is one of the methods to reduce the formation of holes and other welding defects, which is conducive to improve the quality and strength of joints. In this study, the underwater friction stir lap welding (UFSLW) of 6061-T6 Al alloy and carbon fiber reinforced thermoplastic (CFRTP) joints is investigated. The welds are evaluated by optical microscope (OM) image, scanning electron microscope (SEM), and energy dispersive X-ray spectrometer (EDS) of the fracture, tensile, and hardness analysis. Research reveals that the presence of cracks and tunnel defects similar to those in air FSLW (AFSLW) is reduced in the underwater welding process. From the microscopic result analysis, the rapid dissipation of frictional heat and substrate viscosity in the cooling medium of circulating water in the stirring zone reduces the interaction between Al alloy and molten CFRTP, which leads to the rapid transformation of the plasticized material into a solid state and reduces the formation of thick stacked layer. In addition, finer Al alloy fragments are obtained in the welding zone due to the fast cooling rate. Ultimately, the maximum tensile strength of 32.12 MPa is achieved, which is 10.76% higher than that of the same welding parameters in air. Based on UFSLW technology, the joint strength of this study is 69% higher than that of Al alloy and polymer joints, which demonstrates enormous application potential and opens up new prospects for the joining technology of dissimilar materials.

Fiber welded EDTA-modified cellulose for remediation of heavy metal ions

Ethylenediaminetetraacetic acid (EDTA) is a well-known metal chelator and an attractive ligand for covalently modifying adsorbents for bioremediation. Cellulose, a naturally occurring biopolymer, has immense potential as an inexpensive, earth abundant, biocompatible scaffold for EDTA-facilitated environmental remediation; however, pretreatment of the material is required to achieve sufficient degrees of chemical modification. In this study, Natural Fiber Welding (NFW) is used to prepare commercial cotton Aida cloth for EDTA functionalization. Following NFW, the cotton scaffold was covalently modified with up to 0.56 mmol of EDTA per gram of adsorbent, a nearly 2.5-fold increase over native material. The welded EDTA-modified substrates were tested qualitatively against cobalt and quantitatively against nickel, reaching equilibrium binding capacities (qe) of up to 46 mg metal per g of adsorbent, on par with capacities reported from past work on EDTA-modified cellulose. In addition, adsorbent material could be regenerated using mild acid treatment with no significant loss in qe. Unlike the controls, the fiber-welded EDTA-Aida did not fray even after 3 chelation cycles, indicating enhanced textile robustness afforded through NFW treatment. Overall, NFW offers a new approach to converting commercially available, sustainable biomaterials into robust adsorbents for environmental remediation.

Effect of the Energy Director Material on the Structure and Properties of Ultrasonic Welded Lap Joints of PEI Plates with CF Fabric/PEI Prepreg

To estimate the possibility of using both low-melting TecaPEI and neat PEI films as energy directors (EDs) for ultrasonic welding (USW) of carbon fiber (CF) fabric–polyetherimide (PEI) laminates, some patterns of structure formation and mechanical properties of their lap joints were investigated by varying the process parameters. The experiment was planned by the Taguchi method with the L9 orthogonal matrix. Based on the obtained results, USW parameters were optimized accounting for maintaining the structural integrity of the joined components and improving their functional characteristics. The use of the low-melting EDTecaPEI film enabled US-welding the laminates with minimal damage to the fusion zone, and the achieved lap shear strength (LSS) values of ~7.6 MPa were low. The use of EDSolverPEI excluded thermal degradation of the components as well as damage to the fusion zone, and improved LSS values to 21 MPa. With the use of digital image correlation (DIC) and computed tomography (CT) techniques, the structural factors affecting the deformation behavior of the USW lap joints were justified. A scheme was proposed that established the relationship between structural factors and the deformation response of the USW lap joints under static tension. The TecaPEI film can be used in USW procedures when very high interlayer adhesion properties are not on demand.

Effects of different heating strategies on the joint properties during infrared welding of glass fiber reinforced polyamide 6

In infrared welding, the heating phase is the phase offering the highest flexibility of choice regarding the process parameters. In this phase, the process parameters such as the heating time, emitter power, and emitter-component distance can be individually selected and combined with each other. The defined heating phases have a different influence on the joining components. In this work, the effects of four heating strategies and their influence on the resulting temperature distribution over the joining surface, the possible thermal material degradation, the morphology of the joining zone, and the short-term tensile strength of the welded samples are investigated. In order to investigate the morphology, microsections are prepared which enable transmitted light microscopy of the black PA6 GF50 used. In summary, it can be concluded that different heating strategies have a different influence on the material even if the generated melt layer thickness is kept the same. Three of the four strategies result in material degradation on the joining surface. However, this has almost no effect on the resulting short-term strength of the weld. The results allow the interpretation that a high joining pressure compensates for the influence of the material damage by pressing the damaged material into the bead.

Multifactor optimization for induction welding of carbon fiber reinforced thermoplastic composites based on response surface methodology

AbstractInduction welding of thermoplastic (CFRP) composites is one of the most promising welding techniques due to its high efficiency, flexibility, and selectivity of the heat area. However, the nonuniformity of the temperature field in the welding area poses a challenge to welding quality. In this paper, a multifactor optimization method devoted to the quality and efficient bonding of carbon fiber‐reinforced polycarbonate (CF/PC) composites was presented. A transient three‐dimensional finite element model was developed and validated to analyze the heating characteristics during the welding process. The mapping relationship between process parameters—equilibrium temperature and relative effective area were established to optimize the weld quality applying the response surface method. The single lap shear experiment was carried out to evaluate the mechanical properties of the welded joints, focusing on micro appearances and welding defects. The results show that the optimal process parameters are a current of 100A and a coil distance from the surface of 3.6 mm. Under the process parameter, the effective welding area is 0.3823 with an error of 4.25%.Highlights The transient three‐dimensional finite element (FE) model was established. The evaluation indicators for welding quality were proposed. The multifactor optimization method for process parameters was developed. The mechanical property and welding defects of welded joints is evaluated.

Interrogating the Latent Porosity Within Natural Fiber Welded Composites.

Seemingly nonporous biopolymer composites prepared by natural fiber welding (NFW) possess latent pores that can be exfoliated by conscientious solvation. We present a seminal demonstration of this concept for cellulose and explore the impact of latent pores on the manufacture and commercialization of NFW products.

Infrared-thermography measurement of temperature distribution in carbon fiber–reinforced polypropylene during ultrasonic welding

Herein, the temperature distribution during ultrasonic welding of carbon fiber–reinforced polypropylene (CF/PP) was investigated. The temperature distribution was assessed using a thermographic camera that specifically targeted the lateral aspect of the welded section of the adherend in the lap joint. In addition, single lap shear tests were performed on the resulting welded joints. The welding experiments confirmed that the amplitude of the sonotrode impacts both the temperature distribution during welding and the quality of the joint, eventually affecting the mode of failure. By applying the half-width method to the measured temperature distribution in the thickness direction of the adherend, we assessed the spread of the high-temperature region centered on the welding interface. In this study, at a small amplitude (36 μm), the half-width of the maximum temperature showed approximately twice higher slope than at other amplitudes, indicating a wider high-temperature range even at the same interface temperature.

Simulation of temperature and weld growth mechanism in ultrasonic welding of carbon fiber reinforced polyamide 66 composite: Employing the high frequency real-time horn vibration

Ultrasonic welding (UW) of carbon fiber reinforced polyamide 66 (CF/PA 66) composite is a very promising process for assembly of automobile component. Simulation of the temperature distribution and weld growth in UW process remains a difficulty issue. In this study, a high frequency sensor is equipped in the welder to collect the real-time horn vibration during UW. Then the real-time horn vibration is applied on tip of the horn and integrated into the finite element model in Abaqus. The simulation results are validated with experimental tests of temperature and weld evolution in UW of CF/PA 66. Results showed the ultrasonically welded CF/PA 66 joint made with a weld time of 2.7 s consisted of five distinct stages and the characteristics in stage 3 determined the quality of the weld. An index Q based on the amplitude and duration of T3 was proposed to evaluate the joint quality. The accuracy of Q was also verified through extensive experiments.

Friction stir welding of lapped low-melt polyaryletherketone carbon fiber reinforced thermoplastic laminate

Carbon fiber reinforced thermoplastics (CFRTP) have increasing use in aerospace structures due to improved process-ability and weldability. In this study, lap joints between carbon fiber reinforced low-meltpolyaryletherketone (LMPAEK) are formed by friction stir welding (FSW). This study presents novelty by applying FSW to continuous carbon fiber composites in woven laminate form. FSW disrupts the fibers in the weld zone and distributes fragments as small as several microns in length. Thermal analysis shows that the weld zones degrade at 40°C cooler temperatures than the base laminate material due to enhanced polymer mobility surrounding the disrupted carbon fibers. Though optimized joints have regions of over 9% porosity, tensile strengths of up to 73.8 MPa retains up to 50% joint efficiency of a comparable short carbon fiber reinforced composite. CFRTP also requires lower processing forces during FSW than metals, and the power consumption of 67 W during the traverse period for strength optimized welds retains energy efficient characteristics.

Investigation of the weldability of PA6 and CF/PA6 based on a servo-driven ultrasonic welder without using energy director

For ultrasonic welding (USW) of fiber reinforced thermoplastic composites without energy director (ED), the special contact surface and interphase structures due to the addition of fibers have strong relation to the weld quality. In this study, through the servo-driven USW experiments and the corresponding mini-anisotropy modeling for PA6 and CF/PA6 composites welding without ED, the fusion phenomena and weldability of the materials are addressed. The results show that as compared to pure PA6, CF/PA6 has the higher loss modulus and lower specific capacity, leading to more viscoelastic heat generation during USW. As the CF/PA6 surface has the higher roughness, the more significant local stress and energy concentrations occur around the initial contact area, leading to the increased welding area; while more pores are observed within the joints of composites due to the poor liquidity and air trap from larger contact gap. Due to the interphase structure between CF and PA6, the high strain and high temperature occur around the fibers, where pores form due to thermal decomposition.

Study on YB-laser welding applied on aluminum/polymer composites

In the present study, an anodizing process was applied to aluminum alloy (AA2024-T3) to enhance interlocking in dissimilar joints with glass fiber-reinforced polyetherimide (GF/PEI) composite, using ytterbium-doped laser fiber welding as a heat source. A factorial Central Composite Design (CCD) was conducted to determine the most appropriate processing and optimization parameters, with lap shear strength (LSS) as the response variable. The obtained and fractured joints were characterized. Anodizing effectively improved the interlocking between dissimilar joints, resulting in LSS values of around 16 MPa. Surface impressions were observed in joints with lower shear values, likely due to the ineffective heat distribution in the processed joint. In the AA2024-T3 alloy, the annealing process occurred, beginning with the segregation of the alloy elements at the grain boundaries and subsequently reducing its hardness. The SEM analysis of the laminate in the best welding condition revealed a well-established fracture surface, with cusps, fibers covered by the polymer matrix, and river marks, indicating good consolidation of the process applied to the metal/polymer junction, which is consistent with the highest shear values obtained. These findings have important implications for future research and industrial applications and can help advance the understanding of these materials and processes.

Ultrasonic welding of banana fiber based HDPE composites with energy directors

Joints are an integral element of any product and a source of failure under different loading environments. The current experimental investigation explores in detail the ultrasonic welding behavior of banana fiber/HDPE composites. The effect of fiber loading, type of energy directors and process parameters has been investigated on the mechanical and thermal behavior of the welded joints. The comparative assessment has been supported by the results of the dynamic mechanical analysis and the thermal conductivity of the fibers and HDPE. The mechanism of heat generation during welding process has been discussed. The TGA, DTG, DSC and FESEM analysis has been performed to substantiate the results. Composite adherends welded at optimum level of welding parameters with cross energy director profile depicted better load bearing characteristics. The short fibers also participated in the diffusion mechanism during welding. TGA and DTG results showed no significant effect on thermal stability of composites post welding.

Laser Welding of Fiber and Quartz Glass Ferrule.

Optical fiber sensors fabricated by bonding have several limitations. To address these limitations, a CO2 laser welding process for an optical fiber and quartz glass ferrule is proposed in this study. A deep penetration welding method with optimal penetration (penetrating the base material only) is presented to weld a workpiece according to the requirements of the optical fiber light transmission, size characteristics of the optical fiber, and the keyhole effect of the deep penetration laser welding. Moreover, the influence of laser action time on the keyhole penetration is studied. Finally, laser welding is performed with a frequency of 24 kHz, power of 60 W, and duty cycle of 80% for 0.9 s. Subsequently, the optical fiber is subjected to out-of-focus annealing (0.83 mm, 20% duty cycle). The results show that deep penetration welding produces a perfect welding spot and has good quality; the hole generated from deep penetration welding has a smooth surface; the fiber can bear a maximum tensile force of 1.766 N. The performance of the optical fiber sensor is stable, and the maximum pressure deviation corresponding to the cavity length fluctuation is about 7.2 Pa. Additionally, the linear correlation coefficient R of the sensor is 0.99998.

Resistance welding of thermoplastic composites via a novel carbon nanofilm implant

A novel composite heating element constructed by carbon nanotube film and stainless steel meshes was used to resistance welding of carbon fiber reinforced polyetherimide (CF/PEI) laminates. The microstructure and mechanical property of the resistance welding joints under different t w were respectively investigated by scanning electron microscopy (SEM) and tensile test. The failure interface and failure model matched the mechanical properties were analyzed in detail, and the characteristic area shown a strong correlation with morphological changes of CNT film.

Tunable porosity of cotton xerogels via ionic liquid-based natural fiber welding

Tunable porosity of cotton xerogels via ionic liquid-based natural fiber welding

Time-Dependent Development of Mesoporosity in Ionic Liquid Treated Cellulosic Materials

Natural Fiber Welding (NFW) is process that leverages the unique solvating power of ionic liquids (IL) to mobilize a natural fiber’s outermost polymer strands and enable these mobile polymers to reconfigure and interact with mobilized polymers of adjacent fibers. Upon removal of the ionic liquid via a solvent exchange and drying process, the biopolymer material is welded into a new matrix while still maintaining the vast majority of its native structural hierarchy. Recent work in our laboratory has shown relatively simple modifications to the NFW process can drastically impact the modified matrix morphology, particularly regarding surface structure. Changes in polarity during the solvent exchange process, for instance, can be used to very the surface area over a 1000-fold and produce high surface are materials with tunable mesoporosity. In the present work we investigate the impact of variable ionic liquid treatment time on the development of mesoporosity in fiber welded cotton substrates. Nitrogen gas adsorption/desorption measurements were employed to evaluate changes in surface area and pore size with ionic liquid treatment time. Raman spectroscopy was carried out on epoxy potted material cross sections to assess the impact of treatment time on cellulose decrystallization, and epoxy penetration measured by Raman spectroscopy was used to evaluate the continuity of the mesoporous regions and further asses material porosity.

Incorporation of Functional Extraneous Cellulose in the Natural Fiber Welding Process

The efficient and non-derivatizing dissolution of natural biopolymers by ionic liquids (ILs) is poised to redefine the application of these ubiquitous and structurally robust materials on a grand industrial scale. In concert with this idea is Natural Fiber Welding (NFW), a technique which exploits the solvating properties of ionic liquids to partially dissociate the outer biopolymer layers in strands of fibrous thread, followed by solvent removal to collapse the structures in a reconfigured and entangled hydrogen bonding network. For cotton, this welding produces a layered motif of mesoporous cellulose atop a core of unmodified crystalline cellulose, creating a hierarchical structure which retains a semblance of the native biomaterial. Aggressive welding conditions increase the thickness and surface area of the mesoporous layer, though excessive welding leads to full dissolution of the crystalline core creating a tradeoff between an increase in surface area with loss of product integrity. In the present work, we seek to subvert aggressive welding conditions by supplementing dissolved cellulose as an additive in the welding solution. We will demonstrate how this extraneous cellulose can coat and weld to the underlying cotton substrate to increase the size of the amorphous shell around the crystalline core and, ultimately, bolster the mesoporous network and enhance the overall surface area. In addition, we will discuss how Raman-sensitive functionalization can be used to identify inclusion depth of the extraneous material and as a way to probe the potential for layer-by-layer deposition of functional cellulose during the NFW process.