The selective laser melting (SLM) process provides a more extensive design space and manufacturability. However, it is still hindered by its inaccuracy in dimension and functionality. The distortion in the SLM process affects the dimensional accuracy of the component and may even hinder the SLM process. Still, the distortion mechanism has not been well explained; specifically, the effects from the process parameters and scan strategies on the distortion have not been sufficiently investigated. In this study, a quantitative model that considers displacements, plastic strains, and thermal strains on each layer is developed to analyze the distortion mechanism. The distortion is found to be induced by a residual stress gradient among the layers. Then, a transient numerical method calculates residual stress, plastic strain, and distortion in the SLM process. Different simulations with various layers, scanning speeds, stiffness of support structures, and scan strategies are performed to study the relationship between process parameters and distortion. It can be found that the distortion decreases as the height increases. The distortion increases with the scanning speed, reaching the maximum at 700 mm/s and then dropping. We concluded that increasing the stiffness of the support structures is beneficial to reduce the distortion and changing the scanning direction among layers is useless to reduce the distortion. This study gives a theoretical model to analyze the distortion and provides guidance for reducing distortions in the SLM process.

In large ports, shipyards, and other places of handling operations, gantry cranes are widely used. As a typical slewing crane, its slewing-bearing large gear ring is prone to tooth breakage problems due to the existence of long-term complex alternating load. This paper presents a new fault analysis method based on the gear position accuracy error. Firstly, the relative displacement relationship between the pinion and large gear ring and the large gear ring gear teeth stress nature were analyzed through the establishment of the rotary table structure, slewing bearing, and cylinder structure assembly finite element model. In addition, a dynamic data acquisition instrument and resistance strain gauge data were separately applied to analyze the pinion and large gear ring displacement along with cylinder structure stress for the test position accuracy error. The final results show that under the frontal load condition, the horizontal displacement deviation of the pinion gear and the large gear ring is approximately 2.9 mm, which leads to an increase of 23% in the stress value of the upper tooth root at the engagement of the large gear ring, causing extrusion and accelerating the fatigue and even fracture of the gear teeth.

In the process of grab dredger dredging, how to ensure the accuracy of flat digging is a key technical question. The accuracy of flat digging is related to the force of grab digging. However, there are limitations in the traditional method of studying the force of grab digging. In this study, based on the Rankine theory, the unit integration method is proposed to calculate the force process of grab excavation. This method determines the shape and position of the failure surface under the action of active pressure $F_B$ and passive pressure $F_E$ and further obtains a functional expression for the relation between digging force and digging parameters. Through the simulation of flat digging force using the discrete element method (DEM), we obtained results consistent with the calculation results of the unit integration method. In addition, this study sought to control the movement distance of the closing wires and the hoist wires through the equation of motion, to carry out the precision calculations of theoretical data, and experimental research into grab flat digging. By comparing theoretical data and test data, the following conclusion was drawn: the deviation of the theoretical flat digging precision from the test data falls within the allowable range, at 3.15%. This study provides technical support for the flat digging process of the grab dredger.

The effect of a biaxial load on brittle fractures of solids under predominantly elastic deformation and mode I loading conditions is studied in this article. A cross-shaped specimen is used in this work, and the variation of T-stress is achieved by changing the load applied to the arm parallel to the crack. In the tests, under a series of different loads parallel to the crack, a series of load values perpendicular to the crack are obtained, and the stress intensity factor is calculated by FEM (Finite Element Analysis). The test data demonstrate that the apparent fracture toughness of the material varies with the load parallel to the crack and the T-stress, since the T-stress is directly related to the load parallel to the crack. If only the first term of the Williams series solution is used to describe the stress field near the crack tip, the variation of KC is unexplained; therefore, more than one term in the Williams series solutions is used to develop the theory of biaxial effect on solid fracture behavior. The fracture criterion based on this consideration is also used to predict crack instability or crack curving under mode I load conditions. Experimental data are presented and compared with the theory.

Stacking of bulk solids in terminals, ships, trains, and other bulk solids storage yards is always challenging, considering the requirements of optimal utilization of storage areas. In this study, stacking shapes of a variety of bulk solids with different particle sizes were tested, and the curved shapes of the stockpiles were extracted to establish the actual three-dimensional models of the bulk solids accordingly. The three-dimensional curved stockpiles were used to design the bulk solids stacking strategy where the bulk stacking locations, the stacking volume, and the stacking flatness were optimized. A modified golden section method with a self-influenced factor was developed to improve the calculation efficiency of the stacking algorithm for bulk solids stacking flatness. Furthermore, the bulk solids stacking strategy and algorithm were verified by experiments. The results showed that the curved three-dimensional models were very close to the actual shapes of the bulk solids stockpiles, while the improved golden section method was more accurate and efficient than the traditional golden section method in determining the optimal values of the stacking volumes in terms of flatness. For the different bulk solids tested, the experiment results showed that good flat stacking can be achieved by using the developed stacking strategy.

Gear meshing stiffness is one of the important causes of noise, and the structure optimization of gears, such as spoke hole structures, has been proven to be an effective method to reduce gear meshing noise. In this paper, the meshing dynamics model of spur gears with spoke structures was established, and the quasi-static dynamics simulation of the meshing process was carried out by ANSYS. The results show that more spoke holes lead to less meshing stiffness and less stiffness fluctuation. The BEM (boundary element method) acoustic simulation of spur gears meshing was accomplished by the LMS Virtual.Lab. It shows that meshing stiffness is the dominate factor for noise and less meshing stiffness will result in louder noise. In summary, having fewer spoke holes causes less noise, and the experiment shows the same trend. This has certain reference significance for gear structure design considering NVH (noise vibration harshness) performance.