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Defects such as pores, slag inclusions, and cracks account for a high proportion of the girth weld defects of wind power towers, which seriously affect the safe operation of wind power towers. Therefore, the strength analysis of the girth welds of wind power towers with typical defects has important engineering application value. Taking a 2 MW wind power tower as the research object, we used regular hollow spheres, semi-cylinders and hollow rectangles to characterize the defects. With the failure criterion based on yield strength, the strength analysis of girth weld defects with different types, sizes and locations under three ultimate load cases was carried out. The research shows that for a single spherical pore defect, with the increase of the pore radius from 2 mm to 8 mm, the maximum equivalent stress of the girth weld of the tower increases, and the closer the pore is to the inner and outer surfaces of the wind turbine tower, the greater the maximum equivalent stress is for crack defects , the maximum equivalent stress increases with the increase of the crack defect length, but when the defect length is greater than 25 mm, the maximum equivalent stress tends to decrease. Under the Fxy, max condition, the yield strength is exceeded, which affects the safety of the wind power tower. This research will provide a theoretical reference for the safety determination of actual wind power towers with welding defects.

The microstructure evolution of boron-bearing high speed steel roll materials after casting and tempering was investigated. The results indicate that as-cast boron-bearing high speed steel consists of martensitic matrix, retained austenite and different borocarbides. The as-cast alloy has a hardness above 64 HRC, and the borocarbides distribute along the grain boundaries. After RE-Mg-Ti compound modification treatment, obvious necking and broken network appear in the grain boundaries. The hardness of boron-bearing high speed steel roll materials reduces gradually with the increase of tempering temperature. Under the same conditions, the toughness of the modified roll material is higher than that of the unmodified roll material. Wear tests show that the wear resistance of boron-bearing high-speed steel modified by RE-Mg-Ti compound modification treatment is better.

Based on Adams software, a multi-rigid-body dynamics model of the spindle transmission system of the peeling machine is established. The key components of the spindle transmission system of the peeler are flexibly processed by ANSYS, and the rigid-flexible coupling model of the spindle transmission system is constructed. The gear engagement process of the spindle transmission system is simulated by simulating the rotating speed of the gears at all levels of the spindle transmission system and setting the contact force parameters of the gears. The transmission ratio of the gears is verified. It is determined that the acceleration fluctuation mainly depends on the excitation frequency. At the same time, the tangential direction of the driving gear-transmission gear and the transmission gear-spindle gear is determined. The simulation values of force and radial force are 3 649.21 N, 1 580.15 N, 3 598.64 N and 1 415.13 N, respectively, which are in good agreement with the theoretical values, and the reliability of the simulation is verified by gear meshing frequency. Finally, 10 nodes with the maximum equivalent stress of three flexible parts in the simulation process are extracted, and the results are lower than the allowable stress of gear material, which can provide theoretical reference for the design and manufacture of the spindle drive system of high-performance peeler in practical application.

In this paper, the effects of different quenching temperatures on the microstructure and properties of Fe–4.0C–35.0Cr–0.5Si (wt.%) low-silicon hypereutectic high-chromium cast iron (LS-HHCCI) was investigated. The effect of quenching temperature on the microstructure of LS-HHCCI was analyzed by optical microscope, scanning electron microscope, and X-ray diffractometer. After quenching at different temperatures, the hardness and wear resistance of LS-HHCCI were tested by Rockwell hardness tester, microhardness tester, and wear testing machine. The results show that the microstructure of as-cast LS-HHCCI is mainly composed of austenite matrix and M7C3 carbides. After quenching, the austenite matrix is transformed into martensite, and M23C6 type secondary carbides are precipitated in the matrix. As the quenching temperature increased from 950 °C to 1100 °C, the eutectic carbides first appeared as fine needles, and then they gather and grow up, showing elongated or lumpy. The hardness and abrasion resistance first increase and then decrease, it reached peak values of 67.2 HRC at the temperature of 1050 °C, while the wear resistance is the best. [ABSTRACT FROM AUTHOR]

The critical points and time-temperature-transformation (TTT) curves of the isothermal transformation diagrams for a high-speed steel casting on a horizontal centrifugal casting machine had been determined experimentally in the study. The effects of quenching temperature on the microstructures and properties of centrifugal casting high speed steel (HSS) roll has been investigated using scanning electron microscopy (SEM), light optical microscopy (LOM) and X-ray diffraction (XRD) as well as using tensile, impact, and hardness tests. The results show that the HSS roll has excellent hardenability and its matrix structure can be transformed into the martensite after being quenched in the sodium silicate solution. The retained austenite in the quenching structure increases and the hardness decreases when the quenching temperature exceeds 1,040℃. The tensile strength and impact toughness of HSS roll increase once the quenching temperature is raised from 980℃ to 1,040℃. However, the tensile strength and impact toughness have no signifi cant change when the quenching temperature exceeds 1,040℃. The HSS roll quenched at 1,040℃ exhibits excellent comprehensive mechanical properties.

Isothermal-compression tests of B4Cp/6063Al composites containing 20 vol.% B4C were performed using a Gleeble-3500 device, at strain rates ranging from 0.001 s−1 to 1 s−1 and deformation temperatures ranging from 723 K to 823 K. The results showed that the high-temperature flow stress of B4Cp/6063Al composites increases with the decrease in deformation temperature or the increase in the strain rate. After friction correction, the friction corrected stress was less than the original experimental stress. At the initial stage of deformation, the difference between the rheological stress after friction correction and the measured rheological stress is small, but with the continuous increase in the strain, the difference between the rheological stress after friction correction and the measured rheological stress is grows. Under the same strain, the difference between the rheological stress before and after friction correction becomes more significant with the decrease in the deformation temperature and the increase in the strain rate. Next, the material constants (i.e., α, β, Q, A, n) of B4Cp/6063Al composites were calibrated based on the experimental data, and a constitutive equation was established based on Arrhenius theory. The experimental values and predicted values of the stress–strain curves are in good agreement with the stress–strain curves of the finite element simulation, and the validity of the constitutive equation was verified. [ABSTRACT FROM AUTHOR]

In order to improve the stable mechanical properties of aluminum matrix composites and avoid failure, the 6061 Al alloy and B4C/6061Al aluminum matrix composites with 10% mass fraction of B4 C were prepared by powder metallurgy method and stir casting method respectively. Then, the composites were heat-treated by T6 process (quenched in warm water after holding at 535 °C for 5. 0 h, and aged at 165 °C for 4. 5 h). Scanning electron microscope (SEM) was used to observe the microstructure and mechanical properties of the two materials, and universal tensile testing machine was used to test their mechanical properties. The results show that the yield strength and tensile strength of 6061 Al alloy after heat treatment are 204 and 210 MPa, respectively; the yield strength and tensile strength of B4C/6061Al composites after heat treatment are 221 and 246 MPa, respectively, which are increased by 66% and 62% compared with those before heat treatment. But the effect of heat treatment on the elongation of the two materials is not obvious. The fracture morphology of the composites after heat treatment shows the ductile fracture of 6061 Al alloy, the interface debonding between the matrix and the boron carbide particles and the fracture phenomenon caused by the particles. [ABSTRACT FROM AUTHOR]

In order to investigate the evolution law of thermal deformation microstructure of B4CP/6061 Al composites and further optimize the properties of the materials, the microstructure characteristics of B4CP/6061 Al composites under different thermal deformation conditions (deformation temperature, strain rate and strain level) were studied by using hot compression tests and control variable method. The research show that with the increase of the deformation temperature, the thermal activation energy inside the 6061 aluminum matrix materials increases, the nucleation efficiency and the grain size of the dynamic recrystallization also increases. The time for dynamic recrystallization of the composite material decreases as the strain rate increases, which restricts the growth of grains and the dynamic recrtystallization of the 6061 aluminum matrix materials. The flow stress of the composite material increases with the increase of strain, which improves the nucleation efficiency of the 6061 aluminum matrix materials dynamic recrystallization. The method that enhances strength and toughness of the composites without damages of the plasticity has important reference significance for improving the plastic forming ability of materials and optimizing the forming process (such as rolling, forging, extrusion, etc.) . [ABSTRACT FROM AUTHOR]

Adding mixed K2TiF6-KBF4 salts into mechanical stirred molten A356 alloy (Al-7Si-0.3Mg) provides a simple method to fabricate in situ TiB2/A356 composites via salts-metal reaction. However, some issues, such as the loss of Mg element in A356 alloy and the clustering of TiB2 particles in the matrix, usually occur during the fabricating process. These issues easily result in the degradation of mechanical properties of composites. In this study, a quantitative analysis revealed that the Mg element was almost consumed after the reaction, and a thermodynamic analysis inferred that the loss of Mg resulted from the reaction between Mg and mixed salts. In order to fabricate in situ TiB2/A356 composites with high strength and good ductility, we proposed a developed approach that consisted of supplementing Mg and using ultrasound stirring during the fabricating process. The introduction of ultrasound into the melt could disperse TiB2 particles uniformly in the matrix, leading to more effective refinement of α-Al grains and modification of Si phase. Compared with the untreated A356, both the strength and ductility of the developed sample were improved significantly, and the coefficient of thermal expansion mismatch strengthening was found as the major contributor to the improvement in the yield strength. [ABSTRACT FROM AUTHOR]