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- Strength of Materialsel febrero 29, 2024 a las 12:00 am
- Size Effect on Tensile Properties of Cold-Rolled ASS-304 Sheets at Various Service Temperaturesel febrero 29, 2024 a las 12:00 am
To investigate the relationship between service temperature ranging from –40~250℃, and size effect on tensile properties of thin ASS-304 sheets with nine different thicknesses (40~500 μm), uniaxial tensile tests were performed on thin ASS-304 sheets of the same average grain size in the present study. Within the thickness range of 40 to 300 μm, corresponding to η = t/d values from 1.1 to 8.1. The ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) of ASS-304 exhibits a dimensional effect of “the thinner, the stronger”. For example, as the η increases from 1.1 to 8.1, the UTS rapidly decreased from 1798.8 to 839.0 MPa at 20℃, from 1703.1 to 526.9 MPa at 150℃, and from 1661.2 to 478.9 MPa at 250℃, attenuation of 53.36, 69.06, and 71.17%, respectively. Meanwhile, the YS at 20℃ are separately 1768.9 to 418.7 MPa with 1695.2 to 343.3 MPa at 150℃ as well as 1645.7 to 330.1 MPa at 250°C, decrease the proportion of 76.33%, 79.75% and 79.94% respectively. Notably, the UTS, YS, and EL at 150 and 250℃ are lower than those at 20℃. The true stress value of ASS-304 was enhanced at –20 and –40℃, and the true strain increases first and then weakens as the thickness increases, the reason is the transformation- induced-plasticity (TRIP) effect of ASS-304 in stretching. The asymptotic function describes the relationship between strength and the values of η, while the Chapman function represents the relationship between elongation and the η. A linear variation exists between service temperature and tensile properties. And relevant empirical equations including T-η- and T-η-tensile properties were established, which can predict the UTS, YS, and EL of thin ASS-304 sheets under different service temperatures.
- Strengthening Riveted Joints of the Grain Rail Car Backstopel febrero 28, 2024 a las 12:00 am
The paper analyzes the current state of the grain transportation freight car fleet. The results of the analysis show that grain rail cars have exhausted their initially assigned service life, which is set by the manufacturer, and have the same type of defects in load-bearing structures in the area of the riveted joint of the backstop of the car hitch to the girder beam. A 3D model of a grain rail car of a typical design was developed. The stress distribution near the holes of the riveted joint of the backstop of the car hitch with the girder beam under the simultaneous action of normative forces was calculated by the finite element method using the SolidWorks program according to the 3rd theory of strength by the established design modes I and III. Implementing the proposed improvement justified the need to conduct relevant research work. These works included the study of the places and causes of cracks, and their result became the basis for the proposed modernization of the car frame.
- Numerical Investigation on Fracture Propagation Mechanism of Pre-Existing Symmetrical Cracks Emanating from the Circular Blast Holesel febrero 28, 2024 a las 12:00 am
The mechanism of fracture propagation from the circular blast holes with two symmetrical cracks in rock blasting operations was investigated by the displacement discontinuity method. The stress intensity factors at the crack tips of the pre-existing cracks were numerically determined using the displacement variations near the crack tips. In this paper, the variation of the displacement discontinuities along pre-existing cracks emanating from blast holes are studied and compared using linear, quadratic, and cubic collocations. For the crack tip behavior, cubic collections are used, and also the special crack tip element is employed to reduce the singularity at the crack tips. The numerical results of the normalized stress intensity factor for linear, quadratic, and cubic collocations of the displacement discontinuities compared with the analytical results. These sets of results are compared with one another, and good agreements have been reached between them.
- Self-Similar Fractal Characteristics of Phosphorus Slag Powder Particles and its Effect on the Mechanical Properties of Cementitious Systemsel febrero 28, 2024 a las 12:00 am
Firstly, this paper used a laser particle size analyzer to test the particle size distribution characteristics of four specific surface areas of phosphate slag powder particles. Then, it used the powder fractal theory to determine the fractal dimension of the different specific surface areas of the phosphate slag powder particle group. Finally, the effect of the fractal dimension of the phosphate slag powder particle group on the mechanical strength and activity index of the phosphate slag powder-cement cementitious system at 3 d, 28 d, and 180 d ages were studied. The results showed that the phosphate slag powder with different specific surface areas has self-similar fractal characteristics; the larger the specific surface area of phosphate slag powder, the higher the fractal dimension, and the fractal dimension of phosphate slag powder particle can characterize the properties of phosphate slag powder’s fineness and particle gradation in the process of grinding and refining. The phosphorus slag powder particle fractal dimension, the mechanical strength, and activity index of the phosphorus slag powder-cement cementitious system have linear correlation characteristics; the larger the fractal dimension, the higher the mechanical strength and activity index of the cementitious system with phosphate slag powder.