Analysis of Slope Stability and Disaster Law under Heavy Rainfall

Based on this, the slope stability and disaster law under the condition of heavy rainfall are studied. With the slope of Shangge Village as the background, the slope stability under the condition of heavy rainfall is deeply studied through theoretical analysis, laboratory physical model experiment, and numerical simulation. Results showed that due to the heavy rainfall within 2 h, the deformation of the slope is not obvious in the rain 2 h~7 h period, first of all in the position of slope toe of slope stress raiser; As the rainfall continued, the infiltration of rainwater led to weakening of the rock mass strength, and the cracks in the slope fracture zone further expanded and extended to the top of the slope. After 7 hours of rainfall, the slope formed a sliding surface. The physical model experiment and the numerical simulation results are in good agreement, which can provide the basis for slope reinforcement under heavy rainfall conditions and have important scientific significance and social value for the reasonable site selection of housing construction, transportation network, and disaster prevention and mitigation in coastal areas.

TESTING THE HYPOTHESIS OF THE COSINE DISTRIBUTION OF STRESSES IN THE SHAFT-HOLE CONTACT

One of the most common connection types in mechanical engineering and construction is the shaft-hole connection. The mechanical stresses caused by its loading are distributed in the contact zone of the loaded parts of the joint. In some cases, they can lead to destruction. Therefore, while designing, it is important to analyze the mechanical stresses in the contact zone. Traditionally, calculations assume that the contact stresses are distributed according to the cosine law. However, this is not entirely true, especially with diff erent shaft and hole diameters. The authors examined theoretical studies of the contact zone of the shaft and the hole (including the cases of diff erent diameters) and the stress distribution in the contact zone. Based on the studies, they performed numerical calculations in the APMWinMachine environment to determine the stresses in the volume of the shaft and the plate with a hole when loading the shaft-hole connection. The analyses were performed for the two-dimensional case by the fi nite element method in the APMStructure program. The results show that when the diameters in the connection are equal, the stress distribution is close to the cosine law. In this case, only one stress raiser occurs in the contact zone, which is located on the line of action of the loading force. However, if there is a slight discrepancy in the shaft and hole diameters, there are three stress raisers in which the connection may break – the central zone and two side zones. The angular distance between them can be determined based on the known theoretical formulas. The authors made an experiment with a plexiglass model, which qualitatively confi rmed the correctness of the analysis performed.

Effect of Altering the Sequence of Chempolishing and Electropolishing on Surface Properties of Additively Manufactured (AM) 316 Steel Components

The surface roughness of as produced additively manufactured (AM) components is very high and may lead to component failure and undesirable coefficients of friction. In rough surfaces, small cracks form at regions of high surface roughness acting as a stress raiser or crack nucleation sites. Likewise, rough surfaces impact both static and kinetic friction that can impede desired motion and oppose desired mechanical forces. For using these components in many applications, it is necessary to reduce surface deviations drastically during postprocessing. For parts with complex geometries and enormous internal surface areas, this reduction presents a complex engineering problem. We have explored chempolishing (C) and electropolishing (E) to reduce the external and internal surface roughness of stainless-steel components in our previous studies. Chempolishing is an electroless etching process that can uniformly smoothen the accessible surfaces of complex AM components. Electropolishing can produce an extremely smooth surface to sub-micrometer level roughness. Our prior work showed that chempolishing and electropolishing produced very distinct surface microstructures. It is quite possible that in future surface finishing, chempolishing and electropolishing may be applied on the same AM component to reduce the surface roughness of complex AM components. The resulting microstructure after the sequential application of chempolishing and electropolishing may be quite different as compared to that of after chempolishing or electropolishing alone. Here, we report the application of altering the sequence of chempolishing and electropolishing to reduce the external and internal surface roughness of 316 steel components. It is unknown what will be the impact of manipulating the sequence of electropolishing and chemical polishing on surface roughness and microstructure of AM materials. This paper focuses on the post-process sequencing of chempolishing, followed by electropolishing (CE) and vice versa (EC). We found chempolishing followed by electropolishing reduced internal surface roughness by as much as 12 micrometers. Whereas the electropolishing followed by chempolishing reduced external surface roughness by an average of ∼15 micrometers. The structure and properties of the surface finished pieces were examined using: Scanning Electron Microscopy (SEM), Surface Profilometry, and Water Contact Angle Measurement. SEM provided direct insight that CE and EC process produced significantly different microstructures from each other and also from chempolished and electropolished processes. Water contact angle measurements performed on CE, and EC treated AM samples showed that surface energy was quite different. Hence, CE and EC are expected to perform quite differently under a corrosive environment and also yield various adhesion quality for the protective coatings. Confirmation of structural changes provided in this experiment shed light on the capabilities of postprocessing improvements we can make to materials performance.

Corrosion Behaviour of SMAW and GMAW Welded Mild Steel Attacked by Hydrochloride Acid

Corrosion is described as material’s destruction or deterioration because of reaction with its surrounding environment. This type of degradation represents a tremendous economic loss since so much value of loss being described. Mostly, in petroleum industry, mild steel are still the most commonly used metal to build structures. However, acid which is hydrochloric acid has been used as acidizing operation since its advantage over other mineral acid. This may cause mild steel structure susceptible to corrosion. This project is about the study of the rate of corrosion on SMAW and GMAW welded mild steel with different time of exposure. The comparison of f these two type of welded joint were subjected for microstructure analysis using SEM/EDX. Welded mild steel were prepared using SMAW and GMAW process with dimension of 100mm x 50mm x 6mm. Then, samples were inspected using NDT technique using magnetic particle testing. After that, the samples were immersed in 6 mol of HCl acid. Then, the corroded samples were cross-sectioned and were examined using SEM/EDX. The results show that, the rate of corrosion on SMAWwelded mild steel is higher compared to the GMAW welded mild steel. As the duration of exposure increase, the weight loss also increased as well as the value of the corrosion rate. This results were supported by the MPT showing that the flaws and defects on the SMAWwelded mild steel might be the cause that act as a stress raiser and thus, enhancing the corrosion degradation.

Effect of Laser Shock Peening on Fatigue Life at Stress Raiser Regions of a High-Speed Micro Gas Turbine Shaft: A Simulation Based Study

Fatigue failure due to stress raiser regions on critical rotating components in gas turbine engines, such as the shaft, is a crucial aspect. Methods to reduce these stresses and improve fatigue life are a source of ongoing research. Laser shock peening is a method where compressive residual stresses are imparted on the stress raisers of such components. However, numerical based studies on multiple laser shock peening applied to stress raisers is under-researched. Hence, this study will attempt to predict the fatigue life at fillet radii step induced stress raiser regions on a high-speed gas turbine engine shaft by utilization of laser shock peening. The objective of this study was achieved by developing a more computational efficient finite element model to mimic the laser shock peening process on the fillet radii step induced stress raiser regions of a shaft. A modified laser shock peening simulation method for effective prediction of the residual stress field was introduced. Furthermore, the fatigue life improvement due to laser shock peening was predicted by employing Fe-safe fatigue software. From the results, the modified laser shock peening simulation method provided accurate prediction of the residual stress field with a reduced computational time of over 68% compared to conventional methods. The fatigue life revealed an improvement of 553% due to laser shock peening, which is comparable to similar findings in the literature. Hence, from the findings and results achieved, the developed finite element model can be an appropriate tool to assist in the fatigue life estimation of laser shock peening applied to stress raisers.

Fatigue Life Behavior of Laser Shock Peened Duplex Stainless Steel with Different Samples Geometry

Two different stress raiser geometries (fillets and notched) were treated by laser shock peening (LSP) in order to analyze the effect of sample geometry on fatigue behavior of 2205 duplex stainless steel (DSS). The LSP treatment was carried through Nd : YAG pulsed laser with 1064 nm wavelength, 10 Hz frequency, and 0.85 J/pulse. Experimental and MEF simulation results of residual stress distribution after LSP were assessed by hole drilling method and ABAQUS/EXPLICIT software, respectively. The fatigue tests (tensile-tensile axial stress) were realized with stress ratio of R = 0.1 and 20 Hz. A good comparison of residual stress simulation and experimental data was observed. The results reveal that the fatigue life is increased by LSP treatment in the notched samples, while it decreases in the fillet samples. This is related to the residual stress distribution after LSP that is generated in each geometry type. In addition, the fatigue crack growth direction is changed according to geometry type. Both the propagation direction of fatigue crack and the anisotropy of this steel results detrimental in fillet samples, decreasing the number of cycles to the fatigue crack initiation. It is demonstrated that the LSP effect on fatigue performance is influenced by the specimen geometry.