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Investigations on ultrasonic welding of thermoplastic composites always focus on carbon fibre-reinforced thermoplastics so far. This study marks the first attempt at joining glass fibre-reinforced polyphenylene sulphide (GF/PPS) using ultrasonic welding. Attributed to the high observability of the glass fibre-reinforced thermoplastic, new discoveries on bonding formation and mechanism of void defect evolution were acquired. A special pattern of alternating high and low heat input regions was revealed, which was independent of welding energy variations and presented an inherent characteristic of ultrasonic welded GF/PPS joints. Squeeze-out and thermal degradation of matrix induced two primary defect types: larger voids with a size of approximately 100 μm were formed in the matrix between fibre bundles at the joint edge at lower welding energies and were diminished at excessive welding energy; smaller microvoids within 10 μm were formed within the fibre bundles at moderate welding energies and were increased in prevalence with higher energy levels. The research identified four distinct fracture modes that are strongly influenced by the welding energy and closely linked to the lap shear strength (LSS) of the joint. The GF/PPS joint achieved a maximum LSS of 22.6 MPa, which is the state-of-the-art welding joints, typically resulting from fracturing in the welded adherend. These findings provide valuable insights for refining the ultrasonic welding process of thermoplastic composites. [Display omitted] [ABSTRACT FROM AUTHOR]

Resistance welding, a favored method for joining thermoplastic composites, often faces the challenge of nonuniform bonding which leads to weak bonding at the overlap edge and compromises joint integrity. This study proposes a novel modification to traditional resistance welding by incorporating ultrasonic during the final stage of the process. We employed various durations of resistance welding and ultrasonic to join the GF/PPS composites, which yielded significant improvements in bonding strength and welding efficiency. Applying ultrasonic introduced a self-adaptive temperature compensation mechanism, enhancing the temperature at the overlap edge while diminishing the temperature difference between the center and edge of the overlap. This method also improved fusion bonding by encouraging resin flow along the unfused interface at the overlap edge, thereby expanding the bonding area. Notably, the introduction of ultrasonic revealed a new bonding mechanism involving the interaction between molten PPS and unmelted PPS, which was thoroughly examined. The results revealed a 19% increase in lap shear strength and a 40% reduction in welding time for joints with ultrasonic compared to those without ultrasonic. [ABSTRACT FROM AUTHOR]

Among the constraint-handling techniques (CHTs) in constrained multiobjective optimization, constrained dominance principle (CDP) is simple, flexible, nonparametric, and easy to be embedded into multiobjective evolutionary algorithms. However, CDP always prefers constraints to objectives, which tends to cause premature convergence. To overcome this drawback, we propose a new CHT on the basis of CDP. In our CHT, the fitness function of each solution is defined as the weighted sum of two rankings: one is the solution’s ranking based on CDP and the other is the solution’s ranking based on Pareto dominance (i.e., without considering any constraints). It is evident that these two rankings favor the “feasibility” and “optimality” of each solution, respectively. More importantly, the weight employed in the fitness function is related to the proportion of feasible solutions in the current population, enabling the population to adaptively balance constraints and objectives in the evolutionary process. The effectiveness of our CHT is evaluated on three test suites and the experimental results demonstrate that our CHT shows better or highly competitive performance compared with other representative CHTs. [ABSTRACT FROM AUTHOR]

Ti6Al4V and 6061-T6 Al alloys were joined by ultrasonic-assisted friction stir welding (UAFSW) at different rotational velocities and pin offsets to explore the influencing mechanisms of the ultrasonic. Results indicate that the positive or negative influence of ultrasonic depends on the welding condition. Applying ultrasonic increases the joint tensile strength at 450 rpm ~ 850 rpm rotational velocity and 1.2 mm pin offset because it does not only decreases the void defect and the size of Ti6Al4V fragments but also promotes the diffusion bonding at Al/Ti interface. When a large pin offset of 1.6 mm is used, a thick intermetallic compounds (IMCs) layer is formed at the Al/Ti interface and large Ti6Al4V fragments appear in the stir zone. Applying ultrasonic at the large pin offset induces cracks initiating in the thick IMCs layer and the formation of large void defect in the stir zone. This investigation provides a reference for the reasonable application of UAFSW technique. [ABSTRACT FROM AUTHOR]

The potential impact of elevated intra-abdominal pressure (IAP) on residual renal function (RRF) has not been determined. The objective of this study was to investigate the relationship between IAP and the rate of RRF decline in newly initiated peritoneal dialysis (PD) patients, and to identify the optimal IAP threshold value for delaying the deterioration of RRF. A cohort of 62 newly initiated PD patients who completed both 6- and 12-month follow-up evaluations was obtained using the Durand method. A logistic regression model was used to identify variables associated with a rapid decline in RRF. Receiver operating characteristic (ROC) curves were generated to determine the optimal threshold value. Another retrospective cohort analysis was performed to validate the identified critical value. For each 1 cmH2O increase in IAP, the risk of a rapid decline in the RRF increased by a factor of 1.679. Subsequent analysis revealed that patients in the high IAP group had more significant decreases in residual renal estimated glomerular filtration rate (eGFR) (Z = −3.694, p < 0.001) and urine volume (Z = −3.121, p < 0.001) than did those in the non-high IAP group. Furthermore, an IAP ≥15.65 cmH2O was a robust discriminator for the prediction of the rate of RRF decline. Patients in the high IAP group experienced a more rapid decline in RRF. Additionally, an optimal critical pressure of 15.65 cmH2O was identified for predicting the rate of RRF decline. IAP, as one of the factors contributing to the rapid decline in RRF in the first year of PD, should be given due attention. [ABSTRACT FROM AUTHOR]

The bonding of thick Cu and AlN is necessary in power modules with the development of high‐frequency communication technology. In this work, 2 mm‐thick Cu was successfully bonded with AlN by using Sn9Zn solder with the assistance of ultrasonication at 230°C. Results showed that an AlN/Sn9Zn/Cu joint without crack was manufactured with a cooling rate of 7°C/min. Nonreactive wetting was realized between AlN and Sn9Zn, forming an amorphous transition layer. CuZn2 and CuZn were formed at the Sn9Zn/Cu interface. A joint with the highest bonding strength of 30.07 MPa was obtained, in which the AlN/Sn9Zn interface was no longer the weakest location. This work provides a low‐temperature manufacturing method for thick Cu/AlN joints. [ABSTRACT FROM AUTHOR]

The metallization of the SiC ceramic was realized with Sn0.5Zn at a relatively low temperature of 250 °C with the assistance of ultrasonication. This process avoided the use of high temperature, vacuum, or long holding time in traditional metallization methods. Results indicate that fine metallization without defects can be completed under ultrasonication excitation for 20 s. The bonding mechanism was forming a nano-scale layer of non-uniform but continuous amorphous zinc suboxide (ZnO 1-x) (even when the Zn was only 0.5 (wt%)), which acted as a transition region from the SiC ceramic substrate to the Sn0.5Zn metal layer. The tensile strength between the Sn0.5Zn layer and the SiC was 12.3 MPa. The acoustic pressure in the liquid Sn0.5Zn pool was calculated via COMSOL Multiphysics software. The simulation results show that alternating positive and negative acoustic pressure existed in the liquid Sn0.5Zn metal, with the highest amplitude of more than 107 Pa, thereby generating the cavitation effect. The collapse of cavitation bubbles resulted in micro-jets, hot spots, and a high cooling rate, promoting the movement of Zn atoms toward the SiC surface and the formation of ZnO 1-x. [ABSTRACT FROM AUTHOR]

Aiming at slippage and belt breakage of large mechanical conveyor belts, a new type of water-cooled permanent magnet brake (WPMB) is proposed. In order to determine the braking performance of WPMB, a multi-physics coupling model and analysis method of magneto-thermal-structure are built. The braking torque and temperature characteristics of WPMB under different working conditions are obtained. Based on the magnetic vector potential equation, an electromagnetic eddy current model is established, and the variation trend of braking torque with speed is predicted. The temperature field model is built based on the equivalent thermal network method. Using multi-field coupling analysis method and 3-D FEM, the influence factors of WPMB braking torque are analyzed. Two test prototypes with rated speed of 78 rpm, braking torque of 3000 N⋅m are designed and developed. Braking torque characteristic tests and magnetic shielding characteristic tests at different speeds and continuous braking characteristic test are carried out. Experiments show that the proposed method provides very practical results to ensure the continuous and stable operation of WPMB. [ABSTRACT FROM AUTHOR]

Ultrasonic vibration was applied when soldering carbon fiber-reinforced aluminum composites (C f /Al) in this work. The effects of ultrasonic action time on joint formation, carbon fiber distribution, and mechanical properties of the joints were studied. Results show that, with the assistance of ultrasonic vibration, inactive solder can wet the carbon fiber within dozens of seconds at low temperature (250 °C). Short ultrasonic action time leads to minor erosion of aluminum substrate, thereby restricting the movement of carbon fibers into joint. Extensive erosion of the aluminum occurs with prolonged ultrasonic action time. A uniform distribution of carbon fibers in joint is achieved at 60 s. Wetting of carbon fiber is characterized by amorphous-nanocrystalline oxides on its surface, which can be attributed to the elevated temperature and pressure induced by the cavitation of the solder. Extending ultrasonic time enhances the hardness and the shear strength of the joint. The failure cracks propagate through the substrate when ultrasonic time exceeds 15 s. This work provides referential value when soldering materials with low surface energies. [Display omitted] • Ultrasonic time of 60 s produces a fully carbon fiber reinforced joint. • Carbon fiber is rapidly wetted by inactive SnZn solder under ultrasonication. • Carbon fibers flowing into the joint strengthen the joint seam. [ABSTRACT FROM AUTHOR]

Mg/Ti dissimilar alloys were lap welded by friction stir lap welding (FSLW) with the tool pin slightly penetrating into the bottom Ti alloy during the welding process. The joint microstructure, mechanical properties and fracture behavior were systematically investigated. The metallurgical bonding associated with an Al enrichment layer and the mechanical interlocking bonding relying on the pin marks on the bottom Ti alloy surface were formed at the lap interface. Decreasing the welding speed was beneficial to increasing the interfacial bonding strength due to the widened Al enrichment layer and the improved mechanical interlocking resulting from the denser pin marks. When the welding speed decreased to 80 mm/min from 120 mm/min, the fracture location transferred to the upper Mg alloy from the lap interface. The maximum joint tensile-shear strength was 424 N/mm and the joint efficiency reached 89.2 % with respect to the base Mg alloy. FSLW technique provides an effective method to acquire a high-quality joint of Mg/Ti dissimilar alloys. [ABSTRACT FROM AUTHOR]

Joint seam is always the weak region of the welded joint. The soldered/brazed ceramic joint always fails through the joint seam due to lower strength of the solder/braze. In this work, to fabricate ceramic joint stronger than its substrate, ultrasonic vibration was used when brazing porous Si 3 N 4 ceramics. Results show that the brazing can be directly realized at 450 °C in air because ultrasonic cavitation can break the oxide layers of braze. Under ultrasonication, high acoustic pressure is obtained in braze, thus it rapidly infiltrates into the porous ceramics. Then, tight bond is realized between the ceramic and braze within several seconds because of the cavitation phenomenon. The transmission electron microscope results show that the main bonding medium at the ceramic/braze interface is an amorphous Al 2 O 3 layer. Shear test reveals that long ultrasonic time is beneficial to the shear strength of the joint. Wetting times longer than 10 s produce joint stronger than the ceramic substrate. This work provides a new insight when joining other porous materials. • Porous Si 3 N 4 ceramics joints stronger than the substrate was fabricated by ultrasonic brazing. • Short ultrasonic time of 10 s and low temperature of 450 °C produce joint stronger than the ceramic substrate. • The wetting interface is characterized by amorphous Al 2 O 3. [ABSTRACT FROM AUTHOR]

• C f /Al is joined via ultrasonic soldering in air. • The continuity of carbon fibers in joint is maintained after soldering. • Carbon fibers can be wetted by the ZnAl filler within 5 s. Ultrasonic assistance was utilized during the soldering of carbon fiber-reinforced aluminum composites (C f /Al) using ZnAl solder to enhance joint strength. The results indicated that carbon fibers migrated into the joint seam after Al substrate was eroded and the solder was expelled, effectively maintaining the continuity of the carbon fibers. A joint fully reinforced by carbon fibers was achieved with an ultrasonic application time of 60 s. Transmission electron microscopy revealed rapid wetting of the carbon fibers facilitated by ultrasound, characterized by an amorphous/nanocrystalline interface. The maximum joint strength reached 23.5 MPa, which is equivalent to 77.5 % of the C f /Al. [ABSTRACT FROM AUTHOR]

AlN ceramic was successfully wetted and then joined with nonactive Sn9Zn eutectic solder assisted by ultrasonication in air. The effect of ultrasonic time on the formation of joint was studied. Results indicated that the defect-free joint can be obtained at an ultrasonic time of 5 s. Two regions, namely, AlN/Sn (s,_s) and AlN/Zn (s,_s), were found in the bonding interface. Zn and O accumulated in the AlN/Sn (s,_s) interface. An amorphous and nanocrystalline layer of ZnO formed in the hard-wet AlN surface. And Zn (s,_s) directly bonded with AlN. The low temperature and fast bonding of the AlN was attributed to the high pressure and temperature caused by cavitation effect. The shear strength of the joint increased from 10.6 MPa to 30.7 MPa when the ultrasonic treatment time increased from 5 s to 150 s. With the prolongation of ultrasonic time, more AlN ceramic particles entered the solder and acted as the reinforcing phase. • AlN ceramic was rapidly wetted with a nonactive solder (Sn9Zn) in 5 s assisted by ultrasonication at 230 °C. • Wetting was realized by an amorphous and nanocrystalline ZnO at AlN/Sn interface, and Zn directly bonded with AlN. • The shear strength of the joint was 30.7 MPa with a short wetting time of 150 s. • The triggering mechanism of acoustic cavitation on wetting was analyzed through finite element simulation and calculation. [ABSTRACT FROM AUTHOR]

The hook structure in friction stir lap welding (FSLW) joint is an undesirable structure due to its detrimental effect on tensile lap-shear strength (TLSS). For this reason, a friction stir diffusion welding (FSDW) technique realized by a series of specially designed tools with a turbo-like pin was put forward. 2024-T4 Al alloy with an alclad layer on the surface was chosen as the researched material. Different from the conventional FSLW joint, a basin-like stir zone and a flat bonding interface without hook structure are formed in the FSDW joint. A"turbocharging effect"is formed in the center region of the turbo-like pin, which promotes the material to flow downward and enhances the diffusion bonding at the lap interface. Two diffusion bonding mechanisms, including the heat affected zone bonding and the thermo-mechanically affected zone bonding, are formed at the lap interface. Adjusting the blade number and the plunge depth enables the transformation of these two bonding mechanisms. The joint fabricated by the turbo-like pin with four blades at the plunge depth of 1.3 mm has the maximum TLSS of 12.21 kN and fractures at the SZ edge of top sheet. The FSDW realized by the novel tool provides a new approach to acquiring a high-quality lap welding joint. [ABSTRACT FROM AUTHOR]

A new approach was adopted to improve the corrosion behavior of the chromium nitride (CrNx) hard coating through magnetron sputtering deposition at different nitrogen flow rates. The influence of the nitrogen flow rates on the chemical composition, microstructure, mechanical property and corrosion behavior in artificial seawater of the CrNx coatings was investigated. The results show that with the increase of the nitrogen flow rates, the growth structure of the coatings varied from dense granular growth to coarse columnar growth. Increasing the nitrogen flow rates was helpful to decrease the Cr/N ratio and induce the phase transforming from mixed hexagonal Cr2N and face-centered cubic CrN to single CrN. However, the coatings under different nitrogen flow rates significantly improved the corrosion resistance and hardness of the steel substrate. Furthermore, at high nitrogen flow rate, the coating had high corrosion velocity and low protective capability against the substrate corrosion due to the fast corrosion channels acted by the columnar grain boundaries. While at the middle nitrogen flow rate, the coating with CrN phase, densely granular growth structure and moderate grain size resulted in excellent corrosion resistance and highest hardness. [ABSTRACT FROM AUTHOR]

• Cavitation characteristics of GaIn melt during the ultrasonic-induced spreading process are studied in situ by high-speed photography. • The cavitation cloud, single cavitation bubble, stable cavitation bubble, their sizes and life periods are identified. • The bubble density decreases with the spreading of the droplet, which is explained by acoustic pressure. • A non-cavitation region showing increasing width as the droplet spreads consistently appears at the spreading front due to the acoustic pressure loss. • A cavitation threshold measuring method is proposed, and the cavitation threshold of eutectic GaIn alloy is identified to be approximately 0.65 MPa. Cavitation is widely used in many fields, but the nature of cavitation, especially in metallic liquids, remains unclear. In this work, the cavitation bubble characteristics during the spreading of eutectic GaIn liquid droplet subjected to ultrasonication were studied in-situ by high-speed photography. The types, diameters, variations, and life cycles of cavitation bubbles were identified. Results show that the bubble density gradually decreases during the droplet spreading process because of the decreased acoustic pressure inside the thinned liquid. The cavitation presents strong/weak change characteristics with a period of dozens of acoustic periods (T, 50 µs). Cavitation clouds with large sizes and long lifetimes are observed at the early-spreading stage. Tiny cavitation bubbles emerging and collapsing within 1 T dominate the cavitation field in the late-spreading stage. Stable cavitation bubble showing continuous nucleation and collapse but minimal changes in its position is also observed. A non-cavitation region consistently appears at the spreading front because the acoustic pressure is below the cavitation threshold. The width of the non-cavitation region gradually increased as the size of the spreading area increased. A cavitation threshold measuring method is proposed based on the cavitation observation and simulation and the cavitation threshold of eutectic GaIn alloy is identified to be approximately 0.65 MPa. The cavitation bubble dynamics result shows that the cavitation bubbles with different nucleation diameters have different life periods the same growth velocity. [Display omitted] [ABSTRACT FROM AUTHOR]

Brazing is a commonly used method to join porous Si 3 N 4 ceramics; it requires high temperature, long holding time, and vacuum environment. In this work, given the phenomena of sonocapillary and increased cavitation in narrow channels, ultrasonic-assisted soldering was successfully used to join porous Si 3 N 4 ceramics at low temperature of 230 °C in the air within a short period. The effect of ultrasonic time on the microstructure and mechanical properties of the soldered joints was studied. The bonding mechanism of solder to ceramic was studied by scanning electron microscope, electron probe microanalyzer, and transmission electron microscope (TEM). Results showed that the Sn9Zn solder can infiltrate the microchannels of the porous Si 3 N 4 ceramics through sonocapillary within a short ultrasonic time of 3 s. Prolonged ultrasonic time resulted in better wetting of solder to ceramic and wider infiltration layer. The infiltrated solder tightly bonded with the ceramic rod without pores and cracks. The TEM results showed that Zn and O were the main bonding elements. The bonding interface was characterized by nanocrystalline and amorphous ZnO. The shear tests revealed that prolonged ultrasonic time enhanced the joint strength. • Porous Si 3 N 4 ceramics are directly soldered in the air with the assistance of ultrasonic. • Solder is driven by sonocapillary to infiltrate the ceramics, thereby leading to the improvement of the joint strength • The bonding of the solder to ceramic is realized by the formation of nanocrystalline and amorphous ZnO oxide. • Prolonged ultrasonic time results in longer infiltration distance and higher joint strength. [ABSTRACT FROM AUTHOR]

• The acoustic pressure of the solder was increased by four times when the width of the lap clearance was reduced from 0.8 mm to 0.2 mm. • Higher ultrasonic intensity gave rise of more eroded Al spots and grain refinements in the joint and produced stronger joint. • The rapid ultrasonic soldering process was discussed from the viewpoint of the effect of the collapse of cavitation bubbles. To avoid substrate softness, AA7075 were rapidly soldered using a Sn-9Zn solder at 200 °C under ultrasonication. The effect of acoustic intensity on the microstructure and mechanical properties of the soldered joint was studied. The acoustic intensity inside the solder was improved by decreasing the lap width without increasing the input ultrasonic power. Results showed that the softness of the substrate was almost avoided with minimal hardness decrease. The acoustic intensity increased by four times when the width of the lap clearance was reduced from 0.8 mm to 0.2 mm. Pronounced erosion of the substrate occurred under high acoustic intensity. Thus, the content of Al in the joint seam increased from 3.35% to 10.84% after reducing the lap width from 0.8 mm to 0.2 mm. The joint seam was characterized by interlaced fine/coarse Sn-Zn eutectic. The Sn and Zn grains had average sizes of 2.31 and 0.31 μm in the fine eutectic and 3.03 and 0.41 μm in the coarse eutectic. Increasing the acoustic intensity during soldering can effectively increase joint strength. The maximum shear strength of 65.4 MPa and hardness of 29.5 HV were obtained in the joint soldered at 0.2 mm. The cavitation bubble with a nucleation diameter of 10 μm had a large liquid velocity of 7653 m/s, a temperature over 1800 K, and a pressure of 4 × 1012 Pa during its collapse. [ABSTRACT FROM AUTHOR]

[Display omitted] • The cavitation characteristics of Sn melt during ultrasonic-assisted spreading are studied through high-speed photography. • The bubble density decreases with the spreading of the droplet, which is correlated by acoustic pressure simulation. • A noncavitation region at spreading front is responsible for the phenomenon that the oxide layer is difficult to remove. • A method of measuring the cavitation threshold of liquid metals through experiment and numerical simulation is proposed. • The cavitation threshold of pure Sn is first identified, which is 1.26 MPa at 250 °C. The cavitation characteristics during the spreading of a pure Sn liquid droplet subjected to ultrasonication were studied for the first time through high-speed photography to reveal the wetting mechanism. Ultrasonic vibration realized the spreading of Sn droplet on the nonwetting pure Al substrate. However, the oxide layer of the substrate at the spreading front is difficult to remove. The high-speed photography result shows that a noncavitation region consistently appears at the spreading front, because the acoustic pressure is below the cavitation threshold of 1.26 MPa. In particular, the width of the noncavitation region gradually increases as the size of the spreading area increases. Such a result accounts for the condition wherein the oxide layer at the spreading front is difficult to remove. Furthermore, the bubble density during spreading gradually decreases due to the decreased acoustic pressure of the thinned liquid. Finally, the bubble dynamics were calculated to verify the wetting mechanism. [ABSTRACT FROM AUTHOR]