Fatigue crack growth rate of AISI 4140 low alloy steel treated via shot peening and plasma nitriding

Very limited comparative research has been conducted on microstructure evolution induced by different peening methods. Herein, the 2024T351 aluminium alloy was subjected to conventional shot peening (CSP) and ultrasonic shot peening (USP) under the identical Almen height to investigate the differences in surface roughness, residual stress and microhardness. The results demonstrated that under the same Almen height, the CSP treatment resulted in a rougher surface with higher surface roughness and more surface defects, and higher surface and maximum compressive residual stress (CRS) than the USP treatment. In contrast, the CRS depth was relatively lower for the CSP treated samples. In addition, the USP treatment produced more significant microhardness and hardened layer than the CSP treatment.

Residual stress and microhardness evolution induced by conventional and ultrasonic shot peening

Effect of shot peening on high cycle and very high cycle fatigue properties of Ni-based superalloys

Vibration fatigue performance improvement in 2024-T351 aluminum alloy by ultrasonic-assisted laser shock peening

Strengthening mechanism in thermomechanical fatigue properties of Ti6Al4V titanium alloy by laser shock peening

Effects of shot peening with different coverage on surface integrity and fatigue crack growth properties of 7B50-T7751 aluminum alloy

• Two different laser shock peening pulse energy (10 J and 20 J) with square spots are used to treat the surface of the specimen. • Laser shock peening treatment reduced the fatigue life of specimens, tensile residual stresses were induced inside the specimens and they promote fatigue crack initiation and crack growth. • After LSP treatment of the specimen, fatigue cracks mostly initiated inside the specimen under the very high cycle fatigue range, and under the high cycle fatigue range, cracks initiated in the second phase particles on the material surface. Laser shock peening (LSP) as an emerging surface peening technology that is widely used in aerospace manufacturing. The effect of laser shock peening on surface integrity and high cycle fatigue (HCF) and very high cycle fatigue (VHCF) properties of 2024-T351 aluminum alloy was investigated in this study. Accordingly, the surface roughness, surface topography, microstructural, microhardness and residual stress of specimens treated with two different LSP pulse energy levels (10 J and 20 J) were analyzed. Additionally, the HCF and VHCF test was performed by ultrasonic fatigue test system. The results showed that surface roughness R a value and microhardness of LSP treated specimens increased by a maximum of 89.37% and 16.3% comparing to the untreated specimen, respectively. X-ray diffraction analysis also showed that subgrain sizes were refined to the nanoscale. Furthermore, high-level compressive residual stresses (the maximum value about −210 MPa with 700 μm thickness) were introduced to the surface layer of the specimens. The S-N curve results showed that LSP treatment reduced the fatigue life of specimens, and the higher the laser pulse energy, the more obvious the effect of reduction. The fatigue fracture of specimens was analyzed via scanning electron microscope and residual stress distribution map. It is observed that fatigue cracks are predominantly initiated at fractured secondary phase particle locations in a VHCF range for untreated specimens. However, for LSP specimens, surface and internal crack initiation mechanisms were both observed. Under low and intermediate stress levels, the tensile residual stresses (which coexists with the compressive residual stresses) initiated fatigue cracks from the interior of the specimens; under high-stress levels, fatigue cracks were initiated at the material surface. 

The effect of laser shock peening on surface integrity and high and very high cycle fatigue properties of 2024-T351 aluminum alloy

Rainstorm-induced large-scale landslides in Northeastern Chongqing, China, August 31 to September 2, 2014

Underground mining activity in the karst mountain in southwestern China has induced several large-scale rocky landslides and has caused serious casualties. At present, there is a lack of systematic research on the formation mechanism of landslides in this area using multi-method fusion technology. First, the orthophoto images of the landslide area obtained by UAV photography were used to analyze the deformation characteristics of the landslide. Second, the failure characteristics of the strata overlying the goaf were analyzed by geophysical detection. Finally, the deformation response characteristics of the mountain under underground mining were analyzed by UDEC numerical simulation. The results revealed that during the underground mining, the failure process of the mountain occurred in four stages: fracture expansion, subsidence and collapse, shear sliding, and multi-level sliding. Gently dipping soft–hard alternant strata and a blocky rock mass structure formed the geological foundation of the landslides. Underground mining accelerated the fracturing of the overlying strata and the formation of a stepped penetrating sliding surface. Tensile movement of the structural planes of hard sandstone in the free face, and shear sliding of the weak mudstone layer, were the main causes of the landslides. The slope instability mode was tension-shear fracturing, shear sliding, back toppling, and compressive shear failure. In addition, the fracture propagation in the overlying strata and damaged geological structure revealed by the geophysical detection were consistent with the simulation results. This study provides ideas for the precise countermeasures of disaster prevention and mitigation for similar landslides in this area.

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Han Zhang

Papers

Effects of shot peening with different coverage on surface integrity and fatigue crack growth properties of 7B50-T7751 aluminum alloy

The effect of laser shock peening on surface integrity and high and very high cycle fatigue properties of 2024-T351 aluminum alloy

Effect of shot peening on high cycle and very high cycle fatigue properties of Ni-based superalloys

Rainstorm-induced large-scale landslides in Northeastern Chongqing, China, August 31 to September 2, 2014

Failure Mechanism Analysis of Mining-Induced Landslide Based on Geophysical Investigation and Numerical Modelling Using Distinct Element Method