Study on the Influence and Law of Waterproof System Design Factors on the Typical Stress of Bridge Deck Pavement

To improve the structural design rationality of cement concrete bridge deck pavement systems and reduce diseases such as interlayer displacement and rutting in the early stage of bridge deck use, this paper studies the influence and law of the coupling effect of various factors of the waterproof system on the typical stress of bridge deck pavement and determines the best structure combination for the bridge deck pavement structure. A finite element model was established by using commercial software to simulate the mechanical response of different types of waterproof bonding layer, waterproof leveling layer, and impervious structure layer under different parameters. The simulation results show that when the thickness of the pavement layer was 8 cm, the maximum shear stress of the pavement layer occurred in the middle of the wearing course and the junction between layers. When the pavement layers were continuous, the maximum strain of the waterproof bonding layer with the “rubber asphalt + protective plate” structure in the transverse and longitudinal directions was the largest. When the waterproof leveling layer was cement concrete, the structure bore a large amount of stress and easily produced cracks, resulting in water damage. High-density water-based asphalt concrete with a low permeability coefficient can reduce the interlayer shear stress and effectively ensure the interlayer bonding effect. On this basis, the following bridge deck pavement structure was proposed: waterproof system + multifunctional waterproof layer + load-bearing structure layer + surface functional layer.

Microstructure of Ag Nano Paste Joint and Its Influence on Reliability

In this paper, the microstructure of Ag nano paste joint was investigated in pressure-less sintering conditions, and the influence of the microstructure on the joint’s reliability was studied. Firstly, silver nanoparticles (Ag NPs) were synthesized using the redox reaction method. To tightly stack the Ag NPs in nano paste, Ag NPs with sizes of 30~50 nm and submicron-sized Ag particles were mixed. It was found that increasing the sintering temperature or sintering time can reduce the porosity of the bonding layer and the interfacial crack simultaneously, resulting in higher shear strength. When sintering at a temperature of 250 °C, a complete bonding interface was formed, with a 0.68 μm interdiffusion layer. At a higher temperature (300 °C), the bonding interface reached 1.5 μm, providing 35.9 ± 1.7 MPa of shear strength. The reliability of the die attachment was analyzed under thermal shocking from −65 °C to 150 °C for 50 cycles. As the crack could quickly grow through the interfacial defects, the separation ratio was 85% and 67% when sintered at 150 °C and 200 °C, respectively. Because of the reliable bonding interface between the die and the substrate, the Ag nano paste joint formed a slight crack on the edge of the die when sintering at 250 °C. When the joint was sintered at 300 °C, the small voids became large voids, which featured lower resistance to crack growth. Thus, instead of further improved reliability, the separation ratio increased to 37%.

Two Unexpected Temperature-Induced Supermolecular Isomers from Multi-Topic Carboxylic Acid: Hydrogen Bonding Layer or Helix Tube

Under ambient conditions or 160 °C, two supramolecular isomers, namely [(H4PTTA)(H2O)2(DMF)] and [(H4PTTA)(H2O)3]··Guest (1-L and 1-H, H4PTTA = N-phenyl-N′-phenyl bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxdiimide tetra-carboxylic acid, Guest = DMF and H2O), were obtained through the reaction of H4PTTA in a mixture of H2O and dimethylformamide. The single crystal structures reveal the temperature-dependent supramolecular isomerism derived from the torsion of semi-rigid of H4PTTA. The 1-L prepared at room temperature is a hydrogen bond based achiral layer, while the hydrothermal synthesized 1-H is isomer resulted in an H-bond-based chiral tubes-packed supramolecular framework.

Sn-Aided Joining of Cast Aluminum and Steel Through a Compound Casting Process

Obtaining a strong bond between aluminum and steel is challenging due to poor wettability between aluminum melt and steel and brittle intermetallic phases forming in the interface. In this research, a novel coating method, namely hot dipping of Sn, has been developed to treat the steel insert surfaces. Results show that without preheating the mold or Sn-coated insert, a thin, crack-free, and continuous metallurgical bonding layer was achieved in the A356 aluminum/steel compound castings. Intermetallic structures forming in the interface have been characterized in detail. The Sn-coating layer completely melted and mixed with the liquid aluminum during the casting process. The reaction layer at the aluminum/steel interface is composed of ternary Al–Fe–Si particles and a thin layer of binary Al5Fe2 phase with thickness less than 1 µm. A small fraction of dispersed Sn-rich particles was observed distributing in the reaction layer and adjacent to eutectic Si particles in the A356 alloy. A sessile drop wetting test showed that Sn-coated steel substrates can be well wetted by aluminum melt. The improved wettability between A356 alloy melt and steel was attributed to the penetration and breaking of the aluminum oxide layer at the surface of the aluminum droplets by liquid Sn. Graphic Abstract

Operational Behavior of Graded Diamond Grinding Wheels For End Mill Cutter Machining

The varying related material removal rate during deep grinding of cemented carbide end mill cutters results in an unevenly wear of the grinding wheel. This causes a reduced geometrical precision of the manufactured tools. Consequently, the intervals between dressing steps are reduced and the dressing infeed increases. The aim of this research project is therefore to design a tailored grinding tool with uniform wear behavior. To address this situation, the grinding tool load is determined simulatively along the width of the grinding wheel. From this an equation is derived to adapt the bonding layer properties to the local load differences. First investigations show that two different concentrations zones in the abrasive layer of the grinding wheel improves the wear behavior already. This indicates that a further reduction of the wear difference is possible by a more uniform gradient. A simulation is performed to define a knowledge based gradient with more than two concetration zones. This allows a more precise load optimized adaptation of the grinding layer properties to the geometry to be ground in terms of wear behavior. Grinding tools manufactured on this basis are used for flute grinding of end mill cutters. A reduction of the wear difference over the grindig wheel width of 52% and an improved cutting edge quality of these are demonstrated.

Flexible Neural Probes with Electrochemical Modified Microelectrodes for Artifact-Free Optogenetic Applications

With the rapid increase in the use of optogenetics to investigate nervous systems, there is high demand for neural interfaces that can simultaneously perform optical stimulation and electrophysiological recording. However, high-magnitude stimulation artifacts have prevented experiments from being conducted at a desirably high temporal resolution. Here, a flexible polyimide-based neural probe with polyethylene glycol (PEG) packaged optical fiber and Pt-Black/PEDOT-GO (graphene oxide doped poly(3,4-ethylene-dioxythiophene)) modified microelectrodes was developed to reduce the stimulation artifacts that are induced by photoelectrochemical (PEC) and photovoltaic (PV) effects. The advantages of this design include quick and accurate implantation and high-resolution recording capacities. Firstly, electrochemical performance of the modified microelectrodes is significantly improved due to the large specific surface area of the GO layer. Secondly, good mechanical and electrochemical stability of the modified microelectrodes is obtained by using Pt-Black as bonding layer. Lastly, bench noise recordings revealed that PEC noise amplitude of the modified neural probes could be reduced to less than 50 µV and no PV noise was detected when compared to silicon-based neural probes. The results indicate that this device is a promising optogenetic tool for studying local neural circuits.

Application Modes Affect Two Universal Adhesive Systems’ Nanoleakage Expression and Shear Bond Strength

Objectives. The aim of this study was to evaluate the shear bond strength and the nanoleakage expression of CLEARFIL Universal Bond Quick and Tetric N-Bond adhesive systems bonded to dentin. Materials and Methods. 100 freshly extracted human premolar teeth were utilized. The teeth were sectioned to expose dentin. All dentin specimens were assigned into 4 experimental groups; 2 groups had Universal Bond Quick (Universalself group) and Tetric N-Bond (Tetricself group) applied in the self-etch mode, while 2 groups had Universal Bond Quick (Universaltotal group) and Tetric N-Bond (Tetrictotal group) applied in the total-etch mode. n = 15 for shear bond strength and n = 10 for nanoleakage experiment. One-way ANOVA and Kruskal-Wallis test were utilized to analyze the shear bond strength test and the nanoleakage expression, respectively. Results. The highest significant bond strength value was recorded by the Tetricself specimens ( p < 0.05 ) when compared to the remaining three groups. There were no statistically significant differences between the shear bond strength values recorded in the Tetrictotal, Universalself, and Universaltotal groups ( p < 0.05 ). Both bonding systems applied in the self-etch mode (Universalself, Tetricself) had no silver nitrate deposits in the hybrid layer and the hybrid layer-adhesive interface ( p < 0.001 ); however, both bonding systems applied in the total-etch mode (Universaltotal, Tetrictotal) had silver nitrate deposits in the hybrid layer, the hybrid layer-adhesive interface, and the bonding layer ( p < 0.001 ). Conclusion. Applying the Universal Bond Quick and Tetric N-Bond in the self-etch mode exhibited better results in terms of nanoleakage expression. Universal Bond Quick showed the stability of the shear bond strength to dentin when applied using the total-etch or self-etch modes. Tetric N-Bond showed significant deterioration in bond strength when applied in the total-etch mode and exhibited the highest bond strength when applied in the self-etch mode.