Subjects: Mechanics >> Applied Mechanics submitted time 2023-03-20 Cooperative journals: 《应用力学学报》
Abstract： As a new surface treatment technology , cold spraying is widely used in additive manufacturingand parts repair. To investigate the fatigue crack propagation law of the cold-sprayed Q355B steelsubstrate , two groups of standard single notched 3-point bending specimens were processed by coldspraying that pure Al and A5052 aluminum alloy coatings were deposited on the smooth Q355B steelsubstrate surface , respectively.Then a fatigue test was performed on the cold sprayed specimens and agroup of unsprayed polished specimens to obtain and compare the relation curves between the crack tipopening displacement and crack length , the crack propagation rate and load cycles. The results show thatthe crack tip opening displacements of cold-sprayed specimens and unsprayed specimens are close when the crack growth length is the same , and the crack tip opening displacement increases rapidly with thegradual fatigue crack growth. In a certain range of crack tip opening displacement , cold spraying canreduce the fatigue crack growth rate. It is accurate and reasonable to use the crack tip opening displace-ment as a fatigue crack growth control parameter to judge the fatigue crack growth law of cold sprayedspecimens , and the crack tip opening displacement is easily obtained through test and can meet thecondition of both the crack tip elasticity and plasticity.
Subjects: Mechanics >> Applied Mechanics submitted time 2023-03-20 Cooperative journals: 《应用力学学报》
Abstract： With the rise of microwave heating technology , this technology is widely used in rock crushing.In this paper, basalt is used to analyze the heating characteristics , temperature and thermal stress fields,and intermal damage emergence of rock under multi-source microwave irradiation.Basalt samples were irra-diated by industrial microwave oven with common experimental frequency. SEM was used to analyze the e-volution law of microcracks in rock samples before and after microwave irradiation.Combined with COM-SOI5. 5 ,a rock uniform model was established to analyze the heating rate of rock surface in microwavefield.A rock two-phase mineral model was established to analyze the internal temperature , temperature gra-dient and thermal stress distribution of rock. The damage of rock caused by microwave heating was evaluated by temperature field and stress field.The results show that in the microwave field ,the heating rate ofrock surface increases at first and then decreases at the same power level.SEM images confirm that micro-wave irradiation can accelerate the propagation of microcracks in rock , and strong wave-absorbing mineralsare melted and destroyed after microwave irradiation.'The average heating rate of the upper surface calcu-lated by the rock homogeneous model is consistent with the results of microwave heating,and the intermalthermal stress calculated by the rock two-phase mineral model reaches the maximum at the mineral inter-face.The experimental results show that microwave irradiation can accelerate the thermal damage andcrack propagation of basalt.
Subjects: Mechanics >> Applied Mechanics submitted time 2023-03-20 Cooperative journals: 《应用力学学报》
Abstract： The time delay of rockburst in deep tumnels is closely related to the creep mechanical propertiesof hard and brittle surrounding rocks.Therefore, the time-delayed mechanism and laws of rockburst wereanalyzed and discussed by combining the theoretical approach ( including elastoplastic model for deep tun-nel and brittle creep failure model for rocks) and the numerical simulation. The results show that after theexcavation and unloading of the deep tunnel , the damage accumulation occurs inside the surrounding rockdue to the generation and development of micro-defects , which easily triggers time-delayed rockburst in ashort period without timely support. 'The surrounding rock is more inclined to creep failure in the plasticzone and the failure duration increases with the distance from the excavation boundary. 'The surroundingrock presents more instability in the strong excavation damaged zone , needing to be supported in time toavoid a secondary rockburst. As the excavation radius of the tunnel increases , both the delayed failureduration of sumounding rocks and the scope of the excavation damaged zone increase. Futhermore , theresearch results provide some reference and enlightenment for exploring the mechanism , disaster prediction and prevention of time-delayed rockburst.
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