Strength of Materials

Numerical results are presented for the low-temperature serrated deformation process in tension induced by a suspended load of 03Kh20N16AG6 austenitic steel and AMg5 aluminum alloy specimens in liquid helium at 4 K. In practice, large loads at cryogenic temperatures are met with liquefied gas tanks, in particular in hydrogen tanks of launch vehicles. The local one-dimensional multiparametric nonlinear mathematical model of the low-temperature serrated metal deformation process was constructed, with its adequate display and quantitative estimates based on mechanical material properties and loading system characteristics. This effect manifests the local thermomechanical metal deformation instability under adiabatic conditions. The mathematical problem was formulated as a nonlinear differential equation of second order with certain initial and other conditions. It represents the dynamic equilibrium of the specimen-loading device system and describes the process of serrated specimen deformation as the system motion. The model is specified for 03Kh20N16AG6 steel and AMg5 aluminum alloy specimens creep-tested in liquid helium. The numerical experiment demonstrated adequate accuracy with the computational method. The qualitative similarity of the process was revealed for the materials of different classes, with the strain levels achieved differing markedly. Comparative computations established that potential energy of the gravitational field induced a much larger localized deformation of the specimen than potential elastic energy, even in combination with additional factors, viz operation of an electric or hydraulic drive, when the deformation rate is two orders of magnitude higher than the standard one for static metal tests in tension. A very large strain arising and localized under slow loading relaxation inevitably fails before the serrated process is complete.

In the process of use and manufacture, carbon fiber foam sandwich structures were often damaged by low-energy impact, resulting in performance degradation. Therefore, it was necessary to study the damage caused by the low-speed impact of composite sandwich structures. Based on the Hashin failure criterion, this paper established an equivalent finite element model of carbon fiber foam sandwich panels under low-velocity impact. The model was used to simulate the damage of the foam sandwich panel with [±45°/±45°/(core)/±45°/±45°] ply structure under the impact energy of 10.58, 21.17, 31.75, and 42.34 J. The simulation results of impact damage depth were compared with the experimental results. The error was less than 10%, which proved the rationality of the impact equivalent model. The model was used to predict and analyze the damage of foam sandwich panels with [±45°/(core)/±45°], [±45°/ (0°, 90°)/(core)/±45°], and [±45°/(0°, 90°)(core)/(0°, 90°)/±45°] ply structures under 21.17J impact energy. The low energy impact resistance was analyzed by comparing and analyzing the damage situation, impact force response time, and impact velocity response time. The results showed that increasing the number of ply layers [±45°] can reduce the impact damage degree and improve the bearing capacity of sandwich panels.

The most common defect in the axles of wheelsets of railroad cars of the RU1Sh type is damage or wear of M20 threaded holes for bolts for fixing the locking strips of roller bearings. It is proposed that such threaded holes be repaired by cladding them with a restoring sleeve and then cutting a new thread. Fatigue tests of the repaired threaded holes showed that their durability practically corresponds to the basic values for new axles. The repair technology was tested on two full-scale axles mounted on a railcar bogie and subjected to route tests. The railcar with repaired axles traveled 35,000 km without damaging or wearing the restored threaded holes.

This paper evaluates and modifies the direct strength method (DSM) in AS/NZS 4600:2018 for cold- formed channel purlins based on the nonlinear analysis of Strand7 software. Initially, the original DSM curves from the THIN-WALL program are investigated for each buckling mode. Then the nonlinear analysis is performed using the finite element method (FEM). Next, the accuracy and reliability of the original and modified DSM curves are examined and analyzed based on the FEM results. In analyzing the results, the differences, mean and standard deviation between DSM and FEM results are compared. The percentage error ε is reasonable with the width-to-thickness ratios of 40 ≤ b/t ≤ 75, while in the distortional buckling mode, the acceptable range of the width-to-thickness ratio would be 32 ≤ b/t ≤ 63. Most sections have reasonable error values for different slenderness ratios λl (or λd). The results show that the modified DSM results are more accurate and reliable than the original ones, and the dispersion and calculation error of the test data will be smaller after the modification. However, the study’s limitations would be the interference of the buckling modes and the sample size. The results of this research will provide structural engineers with a more comprehensive analysis of design methods and can be used as a reference for engineering design.

Underground engineering has led to the rapid development of tunnel boring machines (TBM), which have been used in practical projects such as transportation, municipalities, water, and electricity in recent years due to advantages such as excavation speed. Excavation speed, high safety, and good construction quality greatly affect the life of the hobs (disc cutters of TBMs). The rock-breaking process for rock crushing under the forces of TBM hobs was numerically performed using LS-DYNA software based on the finite element method. A full-section model with five hobs was used to simulate the rock-breaking process of hobs. In addition, an analysis was performed on the internal and kinetic energy involved in the rock-cutting and breaking processes under TBM hobs. The results show that the vertical force plays a major role in the rock-breaking process of the hob, and the values of the lateral force and the rolling force are small and do not affect it. The results obtained from this simulation can be used as boundary conditions for bearing analysis. Numerical and theoretical results were compared to verify the reasonability of the constructed constitutive model.