Bond Quality Research Articles

Junction growth in ultrasonic spot welding and ultrasonic additive manufacturing

The processes of ultrasonic spot welding and ultrasonic additive manufacturing are modelled by approximating the weld interface as rough metallic surfaces in sliding contact. It is assumed that bonding is due to athermal plastic deformation of surface asperities and the associated growth of metallic junctions along the weld interface. To link the process variables and the extent of junction growth, an expression for the real contact area at the weld interface is combined with process-specific frictional heating models developed here. The resulting framework is validated by comparing its predictions of the weld strength with data from the ultrasonic welding literature. The close agreement between the framework's predictions and the experimental data demonstrates that the surface asperities soften due to frictional heating, while acoustic softening effects are insignificant. The junction growth model is used to identify parameter sets for ultrasonic spot welding and ultrasonic additive manufacturing that maximize the weld strength while simultaneously minimizing the thermal excursion at the weld interface. It is found that in ultrasonic spot welding, certain processing conditions can cause interfacial melting, although melting is not required to form strong bonds. It is also shown that in ultrasonic additive manufacturing, the deposition rate is highest when the positions of the peak temperature and complete interfacial bonding coincide underneath the sonotrode. If the position of complete interfacial bonding leads the position of the peak temperature, there is excessive heating of the build, and the sonotrode velocity can be increased without degrading bond quality.

A Comparison of the Inertia Friction Welding Behavior of Similar and Dissimilar Ni-Based Superalloys

The inertia friction welding behavior of similar (LSHR to LSHR or Mar-M247 to Mar-M247) and dissimilar (LSHR to Mar-M247) alloy pairs was determined. The relationships between the IFW process parameters and welding response, such as the kinetics and efficiency of the transformation of the mechanical energy of the flywheel into heat of joining samples, weld duration, kinetics of flash formation, and bond quality were identified. Conditions resulting in sound welding were determined. It was found that the mechanistic behavior of each of the alloys during dissimilar welding can be approximated by the behavior of the respective alloy during similar welding. By contrast, the microstructure, microhardness and the thickness of the heat affected zone depended on the type of the alloy pair used during IFW.

Surface Activated Bonding of LiNbO3 and GaN at Room Temperature

Lithium niobate (LiNbO3: LN) is a unique ferroelectric material with excellent electro-optical (EO), non-linear optical (NLO), acousto-optical, piezo-electrical, and pyro-electrical characteristics, in addition to a wide transmission curve ranging from the ultraviolet to the mid-infrared. Thus, it is widely utilized for numerous applications, including ultra-fast optical modulators, wavelength convertors, surface acoustic wave filter, and pyro-imaging devices. At the same time, Gallium Nitride (GaN) film is a direct widegap semiconductor commonly used for light emitting diode light, power devices, and radio frequency components. Therefore, wafer bonding of LN and GaN has the potential for creating a new platform capable of realizing multi-functional micodevices that can fully exploit the unique properties mentioned above. Generally, a GaN sample is prepared as a structure of an as-grown GaN film on a sapphire. The coefficient thermal expansion (CTE) of LN is 14.4 (a-, b-axes)-7.5 (c-axis) × 10-6/K at room temperature, whereas that of GaN is 5.59 (a-axis)-3,17 (c-axis) × 10-6/K and that of sapphire is 5 × 10-6/K. Therefore, it is desirable for low-temperature bonding of LN and as-grown GaN film for overcoming the large CTE mismatch. Conventional plasma activated bonding requires relatively high temperature annealing process at above 200 °C to achieve a high bond strength. The high-temperature process causes a large thermal stress, which may often generate cracks. Surface activated bonding (SAB) is a powerful method for low temperature bonding of dissimilar materials. By a surface activation process with argon (Ar) fast atom beam (FAB) or ion beam bombardment, a high bond strength can be achieved at room temperature due to the strong attractive forces between atomically cleaned surfaces. Recently, room-temperature bonding of a GaN and a Si has been demonstrated using ion beam bombardment [F. Mu et al., Applied Surface Science, 2017]. It is interesting to apply the SAB to bond a LN wafer and a GaN. To date, little work has focused on the application of the SAB method to the direct bonding of LN and GaN. In this paper, we report surface activated bonding of a LN and a GaN at room temperature. In this experiment, we prepared a commercially available 3-inch LN (Z-cut) wafers and a 2 inch as-grown GaN wafer which is a 2-μm-thick GaN epitaxial layer grown on a 430-μm-thick sapphire wafer. In direct bonding, sub-nm RMS roughness of the bonding surface is typically required to achieve strong bonding at room temperature. Using atomic force microscopy, the measured RMS roughness of LN and GaN epitaxial layer was approximately 0.1 nm and 0.3 nm, respectively. For surface activation process, Ar FAB bombardment on each bonding surface was performed. Figure 1 (a) shows a schematic diagram of our SAB process. When the background pressure fell below 1×10-5 Pa, the two wafers were activated by Ar FAB bombardment. After that, the surfaces of LN and GaN epitaxial layer were brought into contact with an applied load at room temperature. The Ar FAB bombardment time was 60 s, and the applied load was approximately 10 MPa. Figure 1 (b) shows the photograph of the bonded LN and GaN wafers at room temperature. As shown, LN/GaN hybrid structure without generating serious cracks was demonstrated in wafer scale. The void was formed by particle contaminations and non-bonding at the peripheral area may be responsible for the thickness distribution of the GaN epitaxial layer. In this presentation, we will discuss the bond quality and the bonding interface state in details. The authors would like to acknowledge Mitsubishi Heavy Industries Machine Tool Co., Ltd. for assisting with surface-activated bonding experiment. This study was supported in part by JSPS KAKENHI Grant Number JP17H04925. Figure 1

Measuring the propagation of financial distress with Granger-causality tail risk networks

Using the test of Granger-causality in tail of Hong et al. (2009), we define and construct Granger-causality tail risk networks between 33 systemically important banks (G-SIBs) and 36 sovereign bonds worldwide. Our purpose is to exploit the structure of the Granger-causality tail risk networks to identify periods of distress in financial markets and possible channels of systemic risk propagation. Combining measures of connectedness of these networks with the ratings of the sovereign bonds, we propose a flight-to-quality indicator to identify periods of turbulence in the market. Our measure clearly peaks at the onset of the European sovereign debt crisis, signaling the instability of the financial system. Finally, we use the connectedness measures of the networks to forecast the quality of sovereign bonds. We find that connectedness is a significant predictor of the cross-section of bond quality.

Improving the Mode-II interlaminar fracture toughness of polymeric matrix composites through additive manufacturing

Delamination is a common failure mode observed in fiber reinforced polymeric composites subjected to thermo-mechanical loads. Reinforcements at the interlaminar regions or in the through-thickness direction have been previously shown to improve the damage resistance and durability of these composites. In particular additive manufacturing (AM), also called 3D printing, has been shown to increase the interlaminar shear strength when used for custom printing of polymer reinforcements over carbon fiber prepreg prior to the layup process of layered composites. In this paper, printing of interlaminar polymer reinforcements using fused deposition modeling (FDM) technique within AM is proposed for improving the interlaminar fracture toughness of carbon fiber laminates. The rationale behind this improvement in the interlaminar fracture toughness values due to printed polymer reinforcements (PPR) is investigated by elucidating the influence of varying the process parameters, such as print speed, spacing, and dimensions. An in-depth understanding of the bond quality between the prepregs and the printed polymers as well as the interlaminar fracture surfaces formed on the Mode-II fracture toughness values are established by developing an experimentally validated thermo-chemical finite element modeling framework.

Interlayer adhesion and fracture resistance of polymers printed through melt extrusion additive manufacturing process

This study aims to establish the relationships between the process parameters, mesostructural features (interlayer neck and void sizes), and the fracture resistance of 3D printed parts. The proposed method enables the decoupling of bond quality and mesostructure effects on the overall fracture behavior. Double cantilever beam specimens of acrylonitrile butadiene styrene (ABS) were designed, printed, and fracture tested. The apparent fracture resistance (Jc,a), the interlayer fracture resistance (Jc,i), and the microstructure were characterized. The fracture results and the microscopic examinations indicate that Jc,a is strongly correlated with the process parameters through both the interlayer adhesion as well as the mesostructure. Nozzle and bed temperatures and layer height were found to have significant effects on the fracture behavior. For instance, the Jc,a increased by 38% with a 20 °C increase in the nozzle temperature. This originated from 15% increase in the interlayer fracture resistance and 23% increase in the actual fracture surface area (interlayer neck size). The quality of interlayer bond was explained in terms of temperature, pressure, and time of the process. This work quantifies the relationships between the printing process and the fracture behavior and provides novel tools and insights in the design and analysis of printed materials.

Reformation as an Inspiration for Reforms of the Eastern Churches in the Polish-Lithuanian Commonwealth

The Reformation was a phenomenon influencing transformations of the Orthodox Church and the Uniate Church in the multi-denominational Polish-Lithuanian state. In response to a particularly severe lack of education compounded by the influence of the Reformation in the Easter Churches, certain educational initiatives were undertaken, translation of the Bible and liturgical texts into the Old Orthodox Church Slavonic language, acquainting people with new forms and ways of religious apologetics. Ideas initiated by the Reformation were developed in the 16th century by Piotr Mohyła. Under the influence of the Reformation a new quality of relationships and social bonds was created in the Orthodox Church society of the Polish-Lithuanian Commonwealth. The activities of laymen and Orthodox Church fraternities became more intensified. The ideas of the Reformation on soteriological subjects became an inspiration for part of Orthodox Church elites to enter into union with the Papacy.

Effect of the Mould Rotational Speed on the Quality of Bimetallic Pipe Fabricated by Centrifugal Casting Process

Bimetallic pipes have found a wide range of applications in the present market scenario. It is due to the fact that they possess really impressive mechanical properties like high corrosion resistance at elevated temperatures, high strength, high toughness, etc. The bimetal pipes can be made by using several combinations of metals depending on the requirements like Al-Cu, Al-Ni, etc. Bimetallic pipes are manufactured by the principle of cladding where one metal is made to clad over another one. They have found their applications in steam condenser, heat exchangers, water supply, industrial applications, etc. These pipes are manufactured using the centrifugal casting process. This paper deals with the effect of the various mould rotational speeds on the quality of the bond produced in the Al-Cu bimetallic pipe while fabricating through the centrifugal casting process. The vertical centrifugal casting setup is used for the process. The detailed analysis of the bond quality is done using Scanning Electron Microscope (SEM). Furthermore, the chemical composition of the bond is studied by using Energy Dispersive X-Ray Spectroscopy (EDS). The strength and quality of the Al-Cu bimetallic bond is studied at varying rotational speeds of the mould and finally the observations are taken. The conclusion is framed accordingly based on the observations.

Study of Channeling Mechanism between Sections and Anti-Channeling Methods for Horizontal Well Multi-Stage Fracturing

During multi-stage fracturing of horizontal well, the key to successfully stimulating formation and improving fracturing effectiveness is ensuring no channeling between sections. Channeling frequently occur which decreases fracturing effectiveness. Cracks propagating mechanics model basing on cementing sheath second interface failure was established according to fracturing mechanics, and second interface failure length calculating model was established. Channeling conditions of different sections were calculated by using the model according to parameters of a certain multi-stage fracturing horizontal well. Calculated channeling conditions were same with actual ones, which prove that the model is reasonable and effective, and can be used to accurately calculate channeling conditions. Anti-channeling methods such as increasing Young's modulus and Poisson's ratio of cement sheath, improving cementing interface bond quality were proposed. The research achievements can provide theoretical basis for reasonable designing section interval and improving multi-stage fracturing effectiveness.

The execution quality of corporate bonds

This paper investigates execution quality issues in corporate bond trading. Using an extensive sample of bond trades by insurance companies, we find that an insurance company entering a trade of similar size and on the same side for the same bond on the same day with the same dealer will receive a better price if the insurance company is a more active trader than if it is a less active trader. Trading with the dominant dealer or underwriter worsens these differentials, while greater transparency and smaller trading networks lessens these effects. Our results provide strong evidence that execution quality differences remain pervasive in corporate bond trading.

Bonding technology for bamboo-based fiber reinforced composites with Phyllostachys bambusoides f. shouzhu Yi

The objective of this study was to investigate the mechanical and physical properties of bamboo-based fiber reinforced composites (BFRC) that were formed by using loose bamboo bundles (LBB) and phenol formaldehyde (PF) adhesive. Three resin content levels (10%, 14%, and 18%) and seven different assembly patterns were selected when the bundles were glued together. Board performance testing showed that the bond quality was improved by increasing the resin content. The board face layers impregnated with 18% resin content and core layers impregnated with 14% resin content had the best mechanical properties, and the boards impregnated with 18% resin content had the best dimensional stability properties. The mechanical and physical properties increased with increasing resin content and were affected by the assembly pattern. Various performance indices of the BFRC met the requirements of the China national standard GB/T 20241 (2006).

Influence of concrete-reinforcement bond quality on the process of fracture due to uniaxial compression. Fracture detection

ABSTRACTMechanical behaviour of reinforced structures to a great extent depends on the quality of the concrete-reinforcement bond. This article studies the influence of concrete-reinforcement bond quality on the process of fracture due to uniaxial compression. The relationship between the characteristics of the concrete-reinforcement interface and the distribution of internal stresses under compressive load has been studied based on physical and computational simulation. A good agreement between experimental and theoretical results has been shown. Consistent patterns of the influence of the concrete-reinforcement bond quality on the parameters of the electric response to mechanical impact during a gradual increase in the external compressive load have been established. Criteria for evaluating the concrete-reinforcement bond quality and predicting the reinforced concrete fracture have been proposed.

Evaluation of Bonding Quality in the Carbon Fiber--Reinforced Polymer (CFRP) Composite Laminates by Measurements of Local Vibration Nonlinearity

ABSTRACTA new approach to monitoring the quality of adhesive bonding in the carbon fiber--reinforced polymer (CFRP) is developed by using a local nonlinear response of the laminate. It is shown that a degraded (contaminated) boundary layer of the adhesive contributes to an overall nonlinear response of the laminate that enables to evaluate and quantify bonding quality caused by various types and levels of single contaminations. In the context of aviation applications, two typical stages during the life of a structural part for which the adhesive properties of a bonding joint could be degraded were considered: the production process and the maintenance/repair scenario. All kinds of single contaminations studied result in enhancement of the nonlinear response of the CFRP laminate, which is an indication of deterioration of the bonding quality. The effect of multiple contaminations confirms a cumulative decline of adhesion caused by increase of the contents of single contamination components.

Effect of Thermal Treatment on CFRP Parts Before and After Adhesive Bonding

Numerous non-destructive techniques are being investigated for assuring quality of the adhesive bonds. The research presented here is focused on non-destructive assessment of carbon fibre reinforced polymer (CFRP) parts. The surface condition directly influences the performance of adhesive bonds. The structural joints should ensure safe usage of a structure. However, some modifications of the surface may lead to weak bond that cannot carry the desired load. This is why there is a search for methods of surface assessment before bonding. Moreover, reliable techniques are required to allow to verify the integrity of the adhesive bond after manufacturing or bonded repair. We focus on the laser induced fluorescence (LIF) method for assessing the surface state. The LIF is a non-contact measurement method. In the context of adhesive bond assessment the electromechanical impedance (EMI) method is studied. The EMI uses surface bonded piezoelectric sensors for excitation and sensing. The investigated samples were made of CFRP layers. The samples were treated at elevated temperatures. The influence of the thermal treatment was studied using LIF. The thermal treatment at 220℃ could be clearly distinguishedrom the rest of the considered samples. The thermally treated plates were bonded to untreated plate and then they were measured with the EMI method to study the influence of the treatment on the adhesive bond. The changes of EMI spectra were significant for the treatment at 280℃ and for some thermally treated samples that were later contaminated with de-icing fluid.

Interface microstructure and bond strength of 1420/7B04 composite sheets prepared by diffusion bonding

The effect of temperature on interface microstructure and shear strength of 1420 Al–Li alloy and 7B04 Al alloy composite plates prepared by diffusion bonding were investigated. The results indicate the optimum temperature for bonding the composite plates is 520 °C, a sound bonding interface without continuous intermetallic compound layers and interfacial voids is obtained, and the shear strength value of bond joints can be as high as 190 MPa. An interfacial transition zone is formed due to the alloying elements mutual diffusion during the bonding process. Meanwhile, the effect of temperature on diffusion of alloying elements and interface reaction were discussed in detail, the results show that the higher temperature can increase the diffusion of alloying elements fluxes across the bonding interface, which can accelerate the closure of interfacial voids; meanwhile, when Mg atoms diffuse across the bonding interface, it can react with and break up the surface oxide films into discrete particles, and the removal of interface oxides increases the metal to metal bond areas and improves the bond quality.

Analisis Penambahan Coupling Agent terhadap Sifat Tarik Biokomposit Kulit Waru (Hibiscus Tiliaceus)-Polyester

The aim of this research is to investigate the effect addition of silane coupling agents of Waru bast-polyester composite on tensile strength. Biocomposite is an innovation in material engineering made from the environment-friendly and potentially-developed bast fibers of Waru tree. Waru bast fibers, as reinforcement, were prepared by alkali procces employing using 6% NaOH solution for 120 minutes and then were added coupling agent with variation of 0%, 0.25%, 0.5%, 0.75% and 1.0%. The biocomposite was formed by continuous fiber arrangement using 60:40 fiber-matrix mass fractions with vacuum pressure resin infusion method. Tensile test specimens were formulated base ASTM D638-03 standard. Biocomposite investigation was performed by tensile test, while bond quality observation utilized use micro photo. The results of the study show that the highest strength of biocomposite was 401,368 Mpa on the silane coupling agent addition0.75%

Mechanical performance and crack pattern analysis of aged Carbon Fabric Cementitious Matrix (CFRCM) composites

We discuss the effect of environmental exposure on mechanical performance of impregnated Carbon Fabric Reinforced Cementitious Matrix (CFRCM) composite. Following the recently published ICC-ES AC434 guidelines, mechanical performance of prismatic composite specimens is determined on the basis of tensile uni-axial tests. Exposure to saline and alkaline aqueous solutions is considered at 28- as well as 60-day curing time. Special emphasis is placed on crack pattern evaluation as a mean to gain better insight into matrix/fabric bond quality. To this aim, the evolution of the average crack spacing and of the average crack width is determined as a function of strain for all test environments and curing times. It is found that curing time plays a significant role in mitigating the detrimental effect of aggressive environments. Furthermore, the average crack spacing provides a very reliable measure of matrix/fabric bond degradation at all test stages.

Influence of processing parameters and wood properties on the edge gluing of green Eucalyptus grandis with a one-component PUR adhesive

The predominant plantation hardwood species in South Africa Eucalyptus grandis is, despite relatively good strength and stiffness properties, seldom used for lumber production due to low dimensional stability, splitting, and cracking of the wood. As critical defects often develop or aggravate during the drying process, the edge gluing of Eucalyptus grandis lumber in its wet state, before kiln-drying, was considered a potential inhibiting factor for this behaviour. The objective of this study was to determine how certain material and processing variables influence the bond quality of unseasoned, edge-glued, Eucalyptus grandis, using a moisture-curing one-component polyurethane adhesive. The study considered the effect of four parameters, namely wood density, moisture content, adhesive spread rate and pressure, on the shear strength of bondlines. Micro computed tomography scanning was used to observe adhesive penetration behaviour. Overall, the bonding quality was satisfactory proving the feasibility of edge gluing of this wood in the wet state. Multiple ANOVA showed that generally better results were obtained for samples with a higher moisture content of roughly 60% compared to specimens with lower moisture content around fibre saturation point. Results indicated that the lower spread rate tested (150 g m−2) should be preferred to the higher one (250 g m−2), since it will likely give more stable shear strength results and it would be preferable from an economic point of view. Increasing pressure did not increase the shear strength significantly.

Electrochemical Investigation of Stainless Steel Cladded Carbon Steel Manufactured Via Powder Bed Selective Laser Melting

This study aims to investigate the electrochemical and corrosion properties of 316L-stainless steel cladded carbon steel manufactured using powder bed the selective laser melting (PB-SLM) technique in various environments. The PB-SLM technique involves localized melting of a thin layer of 316L-SS powder bed with Yb - fiber laser. Main parameters of the PB-SLM process such as particle size, particle size distribution, laser power, laser-scanning speed and layer thickness were selected to optimize the density of the cladded layer and the quality of metallurgical bond to the substrate. Using the optimized process parameters, carbon steel substrates were cladded with stainless steel of various thicknesses. Several mechanical and microscopic tests (viz. nano-indentation, X-ray diffraction, Scanning electron microscopy) were performed to characterize both the bulk properties of the stainless steel layer and the interface between the cladding and the substrate. Electrochemical and corrosion properties were tested via. open-circuit potential monitoring, electrochemical impedance spectroscopy (EIS) and cyclic polarization (CP) in electrolytes with acidic to alkaline pH range and with increasing levels of chloride, simulating different application conditions. Scanning vibrating electrode technique was employed to study the galvanic corrosion properties of the stainless steel and carbon steel at the clad-substrate interface.

Bondline shear strength and wood failure of European and tropical hardwood glulams

The study reports on block shear investigations with bondlines of face-glued laminations and matched solid wood specimens from hardwood glulam (GLT) beams produced industrially from eight technically and stand volume-wise important species. The European hardwoods comprised oak, beech, sweet chestnut and ash and the tropical species were teak, keruing, melangangai and light red meranti. The adhesives were phenol-resorcinol and melamine-urea. When combining all species in one sample, a rather strong linear relationship of bond and wood shear strength was observed. The ratio of bond vs. wood shear strength was for all species on the mean value level ≥ 0.9, and likewise (with one exception) for the respective strengths’ 5%-quantiles. Consistent with literature, the test results showed no significant correlations between bond shear strength and density, wood shear strength and wood failure percentage of individual species, respectively. The investigations render the methodological basics of some international standards on bond quality verification as being inappropriate. New, empirically validated hardwood GLT bond requirements are proposed for discussion and implementation at the CEN and ISO levels. The strength ratio specifications reflect respective ANSI provisions, yet the reference quantity wood shear strength is now determined in an unbiased manner from matched GLT specimens. The wood failure verification proposal is based on the 10%-quantile and mean level for initial type testing and factory production control. The requirements further account for the pronounced difference observed in scatter of wood failure between European and tropical species.