The effect of texture on the low cycle fatigue property of Inconel 718 by selective laser melting

In recent decades, additive manufacturing (AM) technology has shown its great advantages to produce end-use products with complex design and high-added value. However, the AM-specific characters, such as inherent material anomalies (porosity, lack of fusion defects, or inclusions), anisotropy, location-specific properties and residual stresses, prevent AM from widely adoption in safety-critical parts. Therefore, the damage tolerance assessment of AM parts is desperately necessary. In this study, the impact of residual stress and the induced texture (columnar/equiax grain structure) after different heat treatment on the low cycle fatigue (LCF) behavior of Inconel 718 fabricated through selective laser melting (SLM) is investigated. The results showed that the texture of AMed parts can be controlled by suitable heat treatment, based on the residual stress during AM processing acting as the drive force to recrystallization. For SLMed Inconel 718 samples with columnar grains, anisotropic LCF properties exist, while no obvious sensitivity to orientations is shown for samples with equiaxed grains. This work is significantly meaningful to speed up the design-to-product transformation of safety-critical AM parts and optimize the orientation of components for various applications

Multiple Cracks Detection in Pipeline Using Damage Index Matrix Based on Piezoceramic Transducer-Enabled Stress Wave Propagation

Cracks in oil and gas pipelines cause leakage which results in property damage, environmental pollution, and even personal injury or loss of lives. In this paper, an active-sensing approach was conducted to identify the crack damage in pipeline structure using a stress wave propagation approach with piezoceramic transducers. A pipeline segment instrumented with five distributed piezoceramic transducers was used as the testing specimen in this research. Four cracks were artificially cut on the specimen, and each crack had six damage cases corresponding to different crack depths. In this way, cracks at different locations with different damage degrees were simulated. In each damage case, one piezoceramic transducer was used as an actuator to generate a stress wave to propagate along the pipeline specimen, and the other piezoceramic transducers were used as sensors to detect the wave responses. To quantitatively evaluate the crack damage status, a wavelet packet-based damage index matrix was developed. Experimental results show that the proposed method can evaluate the crack severity and estimate the crack location in the pipeline structure based on the proposed damage index matrix. The sensitivity of the proposed method decreases with increasing distance between the crack and the mounted piezoceramic transducers

The effect of texture on the low cycle fatigue property of Inconel 718 by selective laser melting

In recent decades, additive manufacturing (AM) technology has shown its great advantages to produce end-use products with complex design and high-added value. However, the AM-specific characters, such as inherent material anomalies (porosity, lack of fusion defects, or inclusions), anisotropy, location-specific properties and residual stresses, prevent AM from widely adoption in safety-critical parts. Therefore, the damage tolerance assessment of AM parts is desperately necessary. In this study, the impact of residual stress and the induced texture (columnar/equiax grain structure) after different heat treatment on the low cycle fatigue (LCF) behavior of Inconel 718 fabricated through selective laser melting (SLM) is investigated. The results showed that the texture of AMed parts can be controlled by suitable heat treatment, based on the residual stress during AM processing acting as the drive force to recrystallization. For SLMed Inconel 718 samples with columnar grains, anisotropic LCF properties exist, while no obvious sensitivity to orientations is shown for samples with equiaxed grains. This work is significantly meaningful to speed up the design-to-product transformation of safety-critical AM parts and optimize the orientation of components for various applications

Rock Mass and Pore Fluid Response in Deep Mining: A Field Monitoring Study at Inclined Longwalls

The dynamics of stress, deformation and pore pressure in the surrounding strata of underground mines are of fundamental importance to groundwater and gas emission management. Compared to numerous studies on the overlying strata, there are significantly fewer investigations concerning the underlying strata, particularly involving large-scale field monitoring. This paper presents a comprehensive field monitoring study conducted at two longwall panels with a depth of around 800 m and an inclination angle of 21°. The monitoring program focused on the floor strata within 50 m below the mining operation, but also covered the roof strata close to the longwall roadway. The purpose was to characterise the favourable zone for gas extraction from the floor coal seams. A combination of stressmeters, extensometers and piezometers were deployed and installed underground. The monitored results demonstrated that the stress change exhibited a three-stage variation—increase, decrease and recovery—during which the strata deformed and the pore pressure changed correspondingly. Strata expansion in the floor occurred primarily in the region 0–35 m behind the longwall face and vertically to at least 42 m below. Some predictive methods of the depth of the failure zone used in shallow mines were analysed to determine if they were still applicable for mining at a depth of around 800 m

Analysis of the Effect of Ultra-Fine Cement on the Microscopic Pore Structure of Cement Soil in a Peat Soil Environment

Treating peat soil foundations around Dianchi Lake and Erhai Lake in Yunnan is a complex problem in practical engineering projects. Peat soil solely reinforced with ordinary cement (OPC) does not satisfy demand. This study aims to solidify soil to achieve better mechanical properties. The preparation of peat soil incorporates a humic acid (HA) reagent into cohesive soil, and cement and ultra-fine cement (UFC) are mixed by stirring to prepare cement soil samples. They are then immersed in fulvic acid (FA) solution to simulate cement soil in the actual environment. X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and pores and cracks analysis system (PCAS) tests are used to study the impact of the UFC on the microscopic pore structure of cement soil in a peat soil environment. The unconfined compressive strength (UCS) test is used for verification. The microscopic test results indicate that incorporating UFC enhances the specimen’s micropore structure. The XRD test results show the presence of C–S–H, C–A–S–H, and C–A–H. SEM and PCAS tests show that the UFC proportion increases by between 0% and 10%, and the percentage reduction in the macropore volume is the largest, at 38.84%. When the UFC admixture is 30%, the cumulative reduction in the percentage of macropore volume reaches 71.55%. The MIP test results show that the cumulative volume greater than 10 µm in pore size decreases from 7.68% to 0.17% with an increase in the UFC proportion. The UCS test results show that the maximum strength growth of cement soil is 12.99% when the UFC admixture is 0–10%. Incorporating UFC to form a compound curing agent solves the problem of the traditional reinforcement treatment of peat soil foundation being undesirable and decreases the amount of cement. This study provides practical guidance for reducing carbon emissions in actual projects

Dempster-Shafer Multifeature Fusion for Pedestrian Detection

Pedestrian detection is of great importance for ensuring traffic safety. In recent years, many works employing image-based shape features to recognize pedestrians have been reported. However, previous pedestrian detectors were in many cases not sufficient to achieve satisfactory results under complex weather conditions and complex scenarios. As a solution this paper exploits two video-based motion feature descriptors and applies such motion features to the detection task in addition to four classical shape features with the aim of significantly improving the detection performance. Our motion features are defined as the trajectory smoothness degree and motion vector field, which are derived from our proposed point tracking strategy beyond tough target segmentation. And then the appealing Dempster-Shafer theory of evidence (D-S theory) is applied to fuse these features, due to the fact that D-S theory is better than the classical Bayesian approach in handling the information with lack of prior probabilities. The proposed automatic pedestrian detection algorithm is evaluated on real data and in real traffic scenes under various weather conditions. Theoretical analysis and experiment results consistently show that the proposed method outperforms SVM-based multifeature fusion approach for pedestrian detection in terms of recognition ability and robustness in various real traffic scenes