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The distortion in machining aeronautical aluminum alloy parts (AAAPs) is one of the serious challenges in the aviation industry, and the residual stresses produced in multimanufacturing steps are the main cause. In order to get a comprehensive understanding of the problems about residual stresses and distortion in machining AAAPs, the state-of-the-art in several aspects including the generation reasons of residual stresses, the factors influencing distortion during machining, the measurement methods of residual stresses, the prediction and controlling methods of distortion are summarized in this paper. The generation mechanism of the bulk residual stress inner materials and the machining-induced residual stresses, as well as the factors affecting two kinds of residual stresses are stated. Also, the influences of residual stresses and machining process conditions on distortion are analyzed. Furthermore, the common residual stress measurement methods and its application scope are summarized. Significantly, the differences, advantages, and disadvantages of various prediction methods are analyzed. The methods of controlling distortion before and after machining are summarized. Finally, the paper gives out further research on the distortion in machining AAAPs in aeronautical manufacturing.

To accurately obtain the deep in-situ stress state during the construction of deep vertical shafts, laboratory-based Anelastic Strain Recovery (ASR) compliance experiments were conducted. The results revealed that under uniaxial loading conditions, the shear and volumetric modes of ASR compliance tend to stabilize after 48 h of unloading, and the extension of the loading time slows the rate of anelastic recovery. The ASR compliance and its ratio under different stress conditions (0.25 UCS and 0.5 UCS) varied with changes in stress. In-situ stress measurements based on the ASR method, conducted at the Sanshandao deep vertical shaft project site, showed that the ASR compliance under the 0.25 UCS stress condition provided stress values that more closely matched the results obtained from hydraulic fracturing, with the maximum principal stress deviation ranging from 0.14% to 4.1%, and the minimum principal stress deviation ranging from 0.27% to 4.57%. This study confirms that combining the depth of the sampled rock cores with in-situ stress conditions for compliance calibration can improve the accuracy of the ASR method. The findings provide foundational support for in-situ stress evaluation and rock mass stability control in similar deep strata.

The hydraulic fracturing technique (also termed mini-frac test) is commonly used to estimate the in situ stress field. We recently conducted a mini-frac stress measurement campaign in the newly-established Bedretto Underground Laboratory (BedrettoLab) in the Swiss Alps. Four vertical boreholes, dedicated for stress characterization of the granitic rock mass, hosted a total of 19 mini-frac test intervals. Systematic pressure transient analysis was performed to carefully estimate the magnitude of the least principal stress (S3). We compared five different methods (inflection point, bilinear pressure decay rate, tangent, fracture compliance, and jacking pressure) to identify an adequate approach best suited for our test scale and the host rock mass. We found that the methods used to determine the fracture closure pressure underestimate the magnitude of S3, presumably due to the rapid closure of the hydraulic fracture after shut-in. The most consistent results were found using the inflection point and bilinear pressure decay rate method, which both determine the (instantaneous) shut-in pressure as the proxy for the S3 magnitude. The determined shut-in pressure, or S3 magnitude, is 14.6±1.4 MPa from the inflection point method. This allowed us to further estimate the stress environment around the BedrettoLab, which is transitional between normal and strike-slip faulting. The measured local pore pressures from extended shut-in periods are between 2.0 and 5.6 MPa, significantly below hydrostatic. A combination of drainage, cooling, and the excavation damage zone of the tunnel may have significantly perturbed the in situ stress field in the vicinity of the BedrettoLab.

Background Residual stresses exist in many manufactured materials and must be measured and taken into account for safe structural design. Established residual stress measurement methods are either destructive or require substantial material-dependent calibration. Objective The present work is aimed at developing an indentation-based method for measuring residual stress that causes minimal specimen damage, does not require a stress-free reference specimen, and has the capability to identify both the size and direction of the surface residual stresses. In this initial study, the simpler case of equi-biaxial stresses is addressed in preparation for subsequent general stress evaluations. Methods The surface displacements around an indentation made by a conical indenter are measured using digital image correlation. The residual stresses are then identified by comparison to the results of a finite model of the indentation process. Results The proposed method is shown to 2–5 times more sensitive to the presence of residual stresses than other commonly used indentation methods, particularly for materials with low Hollomon exponent n . In example measurements, axi-symmetric residual stresses were determined within 8% of the material yield stress. Conclusions The initial study presented here successfully considered the equal-biaxial stress case. The proposed method is attractive for future development because it gives directional information and therefore can be extended to the general non-equal-biaxial case.

X-ray penetration in magnesium alloys is significant due to the low X-ray mass attenuation coefficient. To measure the surface residual stresses in magnesium alloys, a correction needs to be made to account for penetration depth. The residual stresses in as-received and shot peened AZ31B-H24 rolled sheet samples were measured using two-dimensional X-ray diffraction (2D-XRD) method. The electro-polishing layer removal method was used to find the residual stress pattern at the surface and through the depth. The results show that the corrected residual stresses in a few tens of micrometers layer from the surface differ from the raw stresses. To better estimate the residual stress distribution in the surface, the grazing-incidence X-ray diffraction (GIXD) technique was applied. Additionally, micrographs of the lateral cross-section of the peened specimens confirmed the presence of microcracks in this region, causing the residual stresses to vanish. Due to the low X-ray absorption coefficient of Mg alloys, this study shows how a small uncertainty in a single raw measurement leads to high uncertainty in the corrected residual stresses. The results were corroborated with the hole drilling method of residual stress measurements. The corrected X-ray diffraction (XRD) results are in close agreement with the hole drilling and GIXD results.

Residual stresses in multilayer thin coatings represent a complex multiscale phenomenon arising from the intricate interplay of multiple factors, including the number and thickness of layers, material properties of the layers and substrate, coefficient of thermal expansion (CTE) mismatch, deposition technique and growth mechanism, as well as process parameters and environmental conditions. A multiscale approach to residual stress measurement is essential for a comprehensive understanding of stress distribution in such systems. To investigate this, two AlGaN/GaN multilayer coatings with distinct layer architectures were deposited on sapphire substrates using metalorganic vapor phase epitaxy (MOVPE). High-resolution X-ray diffraction (HRXRD) was employed to confirm their epitaxial growth and structural characteristics. Focused ion beam (FIB) cross-sectioning and transmission electron microscopy (TEM) lamella preparation were performed to analyze the coating structure and determine layer thickness. Residual stresses within the multilayer coatings were evaluated using two complementary techniques: High-Resolution Scanning Transmission Electron Microscopy—Graphical Phase Analysis (HRSTEM-GPA) and Focused Ion Beam—Digital Image Correlation (FIB-DIC). HRSTEM-GPA enables atomic-resolution strain mapping, making it particularly suited for investigating interface-related stresses, while FIB-DIC facilitates microscale stress evaluation. The residual strain values obtained using the FIB-DIC and HRSTEM-GPA methods were −3.2 × 10⁻3 and −4.55 × 10⁻3, respectively. This study confirms that residual stress measurements at different spatial resolutions are both reliable and comparable at the required coating depths and locations, provided that a critical assessment of the characteristic scale of each method is performed.

Reliable in-situ stress information is of great significance for the stability assessment and the large deformation mechanism research of deep soft rock roadways. We characterized the stress field of Jinchuan No. 2 Mine using the hydraulic fracturing stress measurement method. A total of 17 hydraulic fracturing measurements and 7 impression tests were conducted in three boreholes to estimate the stress state and variation characteristics at different locations 1000 m below the surface. The results indicate that the main characteristic of the stress field is S H  >  S h  >  S v , which is a strike-slip faulting regime stress, suggesting that horizontal compressive forces dominate the regional stress field. Based on the compiled hydraulic fracturing measurement data (a total of nine boreholes), we indicate that the maximum ( S H ) and minimum ( S h ) horizontal principal stress magnitudes are 7.10–56.73 MPa and 6.44–24.91 MPa, respectively. The S H is dominantly oriented in the NE–NNE direction, which is consistent with the regional tectonic stress field. Finally, the squeezing large deformation analysis and risk assessment of the deep soft rock roadway in the Jinchuan No. 2 Mine were discussed. Significant squeezing deformation may occur in the sublevel 850 m. The radial strain ε of most roadways is between 2.5 and 10%, and only a few are greater than 10%, suggesting a very severe to extreme squeezing large deformation. The results of this study are of great significance for the study of the large deformation mechanism and the selection of matching support technology for the deep soft rock roadway in the Jinchuan No. 2 Mine in the future. Highlights We conducted 17 high-quality in-situ stress measurements using micro-hydraulic fracturing method in the roadway of Jinchuan No.2 Mine, characterizing the magnitudes and orientations of in-situ stress in the mining area 1000 m below the surface. Compiled of 53 sets of hydraulic fracturing data, we conclude that the deep part of Jinchuan Mine is dominated by strike-slip faulting stress, with the S H direction being NE–NNE, which is compatible with the regional tectonic stress field. Based on the measured stress data, our analysis shows that the radial compression deformation of the deep roadway is very severe, which is supported by the on-site investigation.

Background Hole drilling is a measurement technique used to determine near surface residual stresses and has been codified in ASTM E837-20. In ASTM E837-20, the minimum allowable distance to a free edge is prescribed as 1.5 times the gauge circle diameter. Objective This work examines the effect arising from the distance from a free edge on a hole drilling measurement and provides an approach to determine residual stress for measurements where the edge distance is closer than that currently permitted by ASTM E837-20. Methods Numerical experiments were performed to understand how the compliance matrices change when the distance from a hole drilling measurement to a free edge varies. In addition, a series of hole drilling measurements were performed at various distances from a free edge using a shot peened aluminum plate with a nominally equibiaxial stress state to demonstrate the approach. Results The numerical experiments determined that the use of corrected compliance matrices is appropriate when the edge distance is as small as 0.35 times the gauge circle diameter. Physical measurements supported the use of custom compliance matrices for a given free edge distance and specimen thicknesses.

The core of sustainable mining is the preservation of the ground stability, and in situ stress measurement is crucial as most of the stability issues are directly associated with the in situ and induced stresses. Deformation rate analysis and acoustic emission are reliable and low-cost methods of stress measurement leveraging stress memory in rocks. However, owing to rock heterogeneity and complex geological stress history, the accurate determination of in situ stresses is often challenging. This study proposes a simple, accurate, and improved method for determining the in situ stresses in rocks called the Secant Modulus Method (SMM). The effectiveness of SMM is determined through uniaxial cyclic loading and unloading experiments on different types of soft and hard crystalline rocks. The influence of the loading modes, strain rates, and time delay is also investigated. Additionally, its utility for in situ stress measurement is explored. The SMM method proved effective in determining both applied and in-situ stresses, with no effect from variations in loading conditions, loading rates, and time delays. Moreover, the in situ stresses measured using the SMM were in good agreement with the overcoring method. Highlights A simple technique based on inelastic deformation in rocks in proposed for in situ stress measurement. The technique is applied on six different types of soft and hard crystalline rocks to validate its application under various conditions. The influence of the loading modes, the strain rates, and the time delay on the stress memory is presented, indicating their minimal influence on both stress memory and SMM. In situ stress measurement using the proposed technique is presented, showing good correlation with the overcoring results in the same location.

Stress is linked to health problems, increasing the need for immediate monitoring. Traditional methods like electrocardiograms or contact photoplethysmography require device attachment, causing discomfort, and ultra-short-term stress measurement research remains inadequate. This paper proposes a method for ultra-short-term stress monitoring using remote photoplethysmography (rPPG). Previous predictions of ultra-short-term stress have typically used pulse rate variability (PRV) features derived from time-segmented heart rate data. However, PRV varies at the same stress levels depending on heart rates, necessitating a new method to account for these differences. This study addressed this by segmenting rPPG data based on normal-to-normal intervals (NNIs), converted from peak-to-peak intervals, to predict ultra-short-term stress indices. We used NNI counts corresponding to average durations of 10, 20, and 30 s (13, 26, and 39 NNIs) to extract PRV features, predicting the Baevsky stress index through regressors. The Extra Trees Regressor achieved R 2 scores of 0.6699 for 13 NNIs, 0.8751 for 26 NNIs, and 0.9358 for 39 NNIs, surpassing the time-segmented approach, which yielded 0.4162, 0.6528, and 0.7943 for 10, 20, and 30-s intervals, respectively. These findings demonstrate that using NNI counts for ultra-short-term stress prediction improves accuracy by accounting for individual bio-signal variations. Graphical Abstract