Strength of Materials

Underwater vehicles have a great deal of tactical significance in the future sea warfare, and their structural forms are mostly cylindrical shells: underwater vehicles. It may be attacked by underwater weapons. Its payload forms include hydrostatic pressure and localized impact. This article uses finite element analysis software ABAQUS to study the dynamic response of thin-walled cylindrical shells under local impact loading and circumferential pressure effect of cylindrical shell under coupling effect of pressure and local shock. Study shows that under impact load alone, the time of action, the maximum deflection at the point of application of the timing is linear with the peak value of the impact load. When the impact load peak is less than 40MPa, the coupling 30% reduction in critical collapse pressure of columnar crucibles due to cooperative use than cumulative ones, and impact load crest satisfy a certain function form and fit the results of this study to get the functional relationship.

Using the created experimental equipment for testing metals by the method of instrumented indentation, a procedure for determining Brinell hardness during the nondestructive testing of structural elements has been developed. In contrast to the conventional method, the hardness is determined by the proposed procedure using the proportionality parameter of plastic indentation, a, which is equal to the slope of the instrumented indentation diagram in the coordinates maximum force of cycle Fmax – residual indentation depth hp after removing the test load of this cycle. Based on the results of a series of tests by the method of instrumented indentation of hardness standards, a linear correlation dependence was obtained between the Brinell hardness value and the proportionality parameter of plastic indentation in a wide range of measured hardness values of 110–650 HBW. The peculiarities of using this procedure and its limitations are analyzed on a number of structural carbon, heat-resistant, and high-strength steels. It is shown that the Brinell hardness measurement results, obtained by the improved procedure, agree within the permissible error with the results of the conventional DSTU ISO 6506-1:2019 method. The difference between their values does not exceed 3.9%. The presented improved procedure can be used in the laboratories of research and educational institutes, central factory laboratories and specialized divisions of various subordination, and other organizations involved in monitoring the condition of the operating critical equipment and setting its further service life both in the laboratory and in the field.

In the present research, the Al-Si-Fe hypereutectic alloys with different Ti addition were prepared and the electric field treatment was performed on the alloys to regulate the phase morphology. The microstructure and mechanical properties of the alloys were characterized by OM, SEM, TEM, EPMA and tensile test. The results reveal that the Al-Si-Fe hypereutectic alloy prepared by conventional casting is mainly composed cubic β-Si phase, long rod-like and needle-like β-Al5FeSi phases. In addition, there are stacking faults in the β-Al5FeSi phase. Minor Ti addition in Al-Si-Fe hypereutectic alloy could change the needle-like phase into eutectic structure, decrease the size of β-Al5FeSi phase and homogenize the β-Si phase size. The more Ti addition tends to coarsen the β-Al5FeSi and β-Si phases, and moreover the needle-like phase precipitate again. The electric field treatment promotes the coarsening of β-Al5FeSi and β-Si phases in the Al-Si-Fe hypereutectic alloy with 0-1.0 wt.% Ti addition, but results in the refinement of β-Al5FeSi and β-Si phases in 1.5 wt.% Ti doped Al-Si-Fe hypereutectic alloy. Furthermore, the needle-like phase has been transformed into small-size eutectic structure in the 1.0 and 1.5 wt.% Ti doped Al-Si-Fe hypereutectic alloys. With the synergistical effect of Ti addition and electric field treatment, the 1.5 wt.% Ti doped Al-Si-Fe hypereutectic alloy obtains yield strength of 100 MPa and ultimate tensile strength of 113 MPa, which is about 26% and 37% higher than the conventional-cast Al-Si-Fe hypereutectic alloy.

The rock-breaking force of the disk cutter is affected by many factors. The greater the rock-breaking force applied to the disk cutter, the higher the breakage efficiency and removal in the rock masses, thereby speeding up the excavation speed and improving construction efficiency. The elastic-plasticity of rock materials will greatly affect the disk cutter rock-breaking force, thereby affecting the efficiency and speed of the TBM excavation process. The commercial finite element software LS-DYNA was performed to simulate the rock breakage mechanism by disk cutter, and the influence of three rock behavior models of elastic-plastic, plastic, and elastic models on the rock-breaking force by disk cutter was studied. Finally, the elastic model with the least influencing parameters was selected to study the effects of rock elastic modulus and disk-cutting depth on rock-breaking force.