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The difference in microstructure leads to the diversity of shale mechanical properties and bedding fractures distribution patterns. In this paper, the microstructure and mechanical properties of Longmaxi marine shale and Qingshankou continental shale were studied by X-ray diffractometer (XRD), field emission scanning electron microscope (FE-SEM) with mineral analysis system, and nanoindentation. Additionally, the typical bedding layers area was properly stratified using Focused Ion Beam (FIB), and the effects of microstructure and mechanical properties on the distribution patterns of bedding fractures were analyzed. The results show that the Longmaxi marine shale sample contains more clay mineral grains, while the Qingshankou continental shale sample contains more hard brittle mineral grains such as feldspar. For Longmaxi marine shale sample, hard brittle minerals with grain sizes larger than 20 mm is 18.24% and those with grain sizes smaller than 20 mm is 16.22%. For Qingshankou continental shale sample, hard brittle minerals with grain sizes larger than 20 mm is 40.7% and those with grain sizes smaller than 20 mm is 11.82%. In comparison to the Qingshankou continental shale sample, the Longmaxi marine shale sample has a lower modulus, hardness, and heterogeneity. Laminated shales are formed by alternating coarse-grained and fine-grained layers during deposition. The average single-layer thickness of Longmaxi marine shale sample is greater than Qingshankou continental shale sample. The two types of shale have similar bedding fractures distribution patterns and fractures tend to occur in the transition zone from coarse-grained to fine-grained deposition. The orientation of the fracture is usually parallel to the bedding plane and detour occurs in the presence of hard brittle grains. The fracture distribution density of the Longmaxi marine shale sample is lower than that of the Qingshankou continental shale sample due to the strong heterogeneity of the Qingshankou continental shale. The current research provides guidelines for the effective development of shale reservoirs in various sedimentary environments. [ABSTRACT FROM AUTHOR]

Tight reservoirs are typically developed by horizontal wells and multi-stage hydraulic fracturing. The conglomerate reservoir is one type of tight reservoirs, which is different from homogeneous rock, such as tight sandstone. This is because that the existence of gravels makes conglomerate have strong heterogeneity. Thus, it is difficult to grasp the fracture mechanism and the law of fracture propagation of conglomerate, which limits the efficient development of the conglomerate reservoir. In this paper, the fracture characteristics and factors influencing the fracturing of Mahu conglomerate were studied by uniaxial compression, acoustic emission monitoring and X-ray computed tomography (CT) scanning experiments. The results show that the fracture characteristics of conglomerates are influenced by the gravel content and cement. The conglomerate in the study area is mainly divided into carbonate cemented conglomerate and clay cemented conglomerate. The fracture complexity of carbonate cemented conglomerate first increases and then decreases with increasing gravel content. However, for clay cemented conglomerates, the fracture complexity increases over the gravel content. The crack development stress is a significant parameter in the crack assessment of conglomerates. This study is useful to understand the influence of meso-fabric characteristics of conglomerates on their fracturing and crack evolution and guides the design of hydraulic fracturing. [ABSTRACT FROM AUTHOR]

Polyetheretherketone (PEEK) is a kind of nontoxic high-performance thermoplastic widely used for medical applications. Compared with other special engineering plastics, PEEK has many excellent properties, such as high temperature resistance, chemical corrosion resistance, radiation resistance, hydrolysis resistance, excellent mechanical properties, good self-lubrication and easy processing. Although PEEK has been widely used as the replacements of metallic and ceramic implants in medical field, it is biologically inertia, which reduces the fusion with host bone tissue after implantation. In addition, the high friction coefficient and hydrophobicity of PEEK also seriously hinder its applications. In view of these, the studies of PEEK biomaterials have now focused on the improvement of biological activity by various material engineering strategies. In this paper, these recently developed strategies to improve PEEK bioactivity to address clinical orthopedic needs (e.g., anti-inflammation, anti-infection and osteointegration) are reviewed. The advantages and disadvantages of these methods are further analyzed. This review paper may provide more targeted direction for developing multifunctional PEEKbased implants in the future. [ABSTRACT FROM AUTHOR]

Magnesium (Mg) alloys are becoming popular in lightweight manufacturing due to their low density and high specific strength. However, insufficient slip systems result in poor plasticity of Mg alloys at room temperature. Therefore, an ultrasonic energy field combined with thermal field is introduced to assist the deformation of AZ31 Mg alloy to improve its plasticity. Firstly, ultrasonic vibration (UV)-assisted tensile tests at different temperatures (130e150 °C) are conducted to investigate the effect of UV on material behaviour and the activation of dynamic recrystallization (DRX). Then, the influences of UV on the mechanical properties and microstructure of the material at 150 °C are investigated by varying the parameters of ultrasound amplitude, strain rate, and vibration interval. The results reveal that applying UV can activate DRX at a relatively lower temperature compared with that without UV. Superimposing a certain amount of ultrasonic energy on this material at warm conditions reduces flow stress and increases elongation. In the intermittent ultrasonic vibration (IUV) tests, the DRX percentage and elongation first increase and then decrease as the vibration interval increases. The elongation of specimens with appropriate vibration intervals even exceeds that of specimens with continuous ultrasonic vibration (CUV). However, CUV is more effective than IUV in reducing ultimate tensile strength at different amplitudes or strain rate. [ABSTRACT FROM AUTHOR]

The effect of scanning strategy on the microstructure and properties of GH3536 Ni-based superalloy prepared by Laser Powder Bed Fusion was investigated, for the purpose of building high quality hydrocyclone part. The results show that the strength of Z67° (a zone with 67° hatch angle strategy) specimen is the highest among the four scanning strategies (0°, 67°, 90°and Z67°), with yield strength and tensile strength of 681 ​MPa and 837 ​MPa, respectively. Selective orientation of crystals occurs during the forming process because the longitudinal section of the specimen exhibits a high texture strength in (001). As the stretching proceeds, the plastic deformation mechanism of the specimen gradually changes from slip to twin-dominated, a substantial amount of twinning is observed in the region where the deformation of the specimen reaches 80%. The additive manufacturing simulation suite: Ansys Additive is used to simulate the stress and deformation of the part during the process, and the displacement results are consistent with the experimental phenomena. According to the simulation results, the structure design is optimized and the surface quality of the part is improved. The results show that the support of the part is more reasonable when the overhang angle is 45°. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (LPBF) combined with reaction bonding (RB) of Al particles is an effective method for preparing high-performance 3D Al2O3 ceramic foams. However, the indistinct microstructure evolution hinders the regulation of pore features and the improvement of synthetic properties. Herein, the microstructure evolution of the Al2O3 ceramic foams during the LPBF/RB process is clarified by various characterization methods, and the corresponding mechanical property modulation is realized by optimizing LPBF parameters, organic binder (E12 epoxy resin) content, heating rate, sintering time, and coral-like Al2O3 content. The expansion from Al2O3 outward growth and Al granule precipitation counteracts the shrinkage from E12 decomposition and Al2O3 sintering, resulting in an ultra-low shrinkage of 0.94%--3.01%. The pore structures of particle packing pores, hollow spheres, and microporous structures allow a tunable porosity of 52.6%--73.7%. The in-situ formation of multi-scale features including hollow spheres, flaky grains, whiskers, nanofibers, and bond bridges brings about a remarkably high bending strength of 6.5--38.3 MPa. Our findings reveal the relationship between microstructure evolution and property optimization of high-performance ceramic foams, with potential significance for microstructure design and practical application. [ABSTRACT FROM AUTHOR]

The study of high-energy and low-vulnerability propellants is important for the power performance and safety of solid propellant rocket motors. The modified split Hopkinson pressure bar (SHPB) tests are performed on two kinds of propellant with different crosslinking density to study the dynamic mechanical responses and damage-ignition mechanism. SHPB apparatus is equipped with a highperformance infrared camera and high-speed camera to capture the deformation, damage-ignition feature and temperature evolution images in the impact process. The results suggested that the mechanical responses and damage-ignition mechanism of the propellants were affected by the strain rates and crosslinking density. The damage-ignition degree is more intense and the reaction occurs earlier with the increase of strain rates. For propellant 1 with higher crosslinking density, the critical ignition strain rate is 4500 s-1. Two kinds of propellants show different ignition mechanism, i.e. crack generation, propagation and final fracture for propellant 1 while viscous shear flow for propellant 2. Meanwhile, the SEM images also reveal the difference of damage-ignition mechanism of the two kinds of propellants. Finally, the ignition mechanism under different strain rates and critical ignition strain rate of propellants are further explained by the theoretical calculation of temperature variations. [ABSTRACT FROM AUTHOR]

Powder-based laser direct metal deposition (DMD), one of the directed energy deposition, was applied in air and underwater to repair pre-machined NV E690 steel plates. Systematic investigations on the effects of underwater environment and ambient pressures (0.01-0.35 MPa) on the microstructure evolution, phase transformation, and mechanical properties were conducted. The water quenching effect refined the grain size and increased the dislocation density and lath martensite content. The theoretical models of the underwater pressurized nitriding process and the precipitation kinetics of (Ti, V)N particles were established. Moreover, the microstructure evolution and the mechanical properties of other underwater DMD repaired samples did not show obvious relation with the underwater ambient pressures. This investigation not only provides a candidate for the underwater restoration technique but also bridges marine engineering and emerging DMD technology. [ABSTRACT FROM AUTHOR]

The present research introduces a unique concept of scarf joint technique in friction stir welding (FSW) of aluminum alloy AA 6061-T6 plates and an investigation on weld quality. A new joint configuration with two distinct scarf angles (75° and 60°) was considered in this study. The various aspects of welding were compared with contemporary simple square butt (SSB) joint configuration. Welding was carried out at a constant tool rotation speed (TRS), tool traverse speed (TTS) and tool tilt angle of 1100 rpm, 2 mm/s and 2°, respectively. The results are analyzed in terms of force and torque distribution, microstructure, macrostructure, and mechanical property perspective for different joint configurations. The study reveals the minimum amount of force and torque at 60° scarf angle joint configuration compared to that of square butt joint configuration. Macro study shows that all the joints were defect-free, and a prominent onion ring was present in the lower portion of the weld nugget (WN). Fine equiaxed grains with a minimum average grain size diameter of 6.82 mm were obtained in the WN of scarf joint configuration (SJC). The maximum ultimate tensile strength (UTS) and maximum average NZ hardness of 267 MPa and 83.82 HV0.1 were obtained in SJC3 at a scarf angle of 60°. It has been observed from the investigation that the joint efficiency increases from 72.5% (SSB) to 86% (SJC3) at a 60° scarf angle. This unique characteristic may lay an impetus on probable joint strength enhancement technique without increasing the production cost. [ABSTRACT FROM AUTHOR]