Human Perception-Inspired Grain Segmentation Refinement Using Conditional Random Fields

Accurate segmentation of interconnected line networks, such as grain boundaries in polycrystalline material microstructures, poses a significant challenge due to the fragmented masks produced by conventional computer vision algorithms, including convolutional neural networks. These algorithms struggle with thin masks, often necessitating intricate post-processing for effective contour closure and continuity. Addressing this issue, this paper introduces a fast, high-fidelity post-processing technique, leveraging domain knowledge about grain boundary connectivity and employing conditional random fields and perceptual grouping rules. This approach significantly enhances segmentation mask accuracy, achieving a 79% segment identification accuracy in validation with a U-Net model on electron microscopy images of a polycrystalline oxide. Additionally, a novel grain alignment metric is introduced, showing a 51% improvement in grain alignment, providing a more detailed assessment of segmentation performance for complex microstructures. This method not only enables rapid and accurate segmentation but also facilitates an unprecedented level of data analysis, significantly improving the statistical representation of grain boundary networks, making it suitable for a range of disciplines where precise segmentation of interconnected line networks is essential

Quantitative textural analysis of sedimentary grains and basin subsidence modelling

Part 1: Quantitative textural analysis Shape analysis can provide important information regarding the origin, transport and deposition history of grains. Particle shape measurement has been an active area of research for sedimentologists since the 20th century. However, there is a lack of standardised methodology for quantitative characterisation of grain shapes. The main objective of this work is to develop methodologies that can be used by sedimentologists for quantitative textural analysis of grains such that the results obtained are comparable. A modular suite of code written in the Mathematica environment for the quantitative characterisation of sedimentary grains in 2- dimensions is presented. This image analysis package can be used to analyse consolidated as well as loose sediment samples. Using newly implemented image analysis methods, 20 loose sediment samples from four known depositional environments (beach, aeolian, glacial and fluvial) were analysed. This research aims to identify the most useful shape parameters for textural characterisation of populations of grains and determine the relative importance of the parameters. A key aspect of this study is to determine whether, in a particular sedimentary environment, textural maturity of the samples can be ranked based on their grain shape data. Furthermore, discrimination of sedimentary depositional environments is explored on the basis of grain shape. The available shape parameters suffer from a common shortcoming that particles, which are visually distinct, are not differentiated. To address this issue, the Inverse Radius of Curvature (IRC) plot which can be used to identify corners and measure their sharpness is introduced. Using the IRC plot, four shape parameters are proposed: number of corners, cumulative angularity, sharpest corner and straight fraction. This methodology is applied to a 4000 sand grain dataset. The textural analysis software package developed here allow users to quantitatively characterise large set of grains with a fast, cheap and robust methodology. This study indicate that textural maturity is readily categorised using automated grain shape parameter analysis. However, it is not possible to absolutely discriminate between different depositional environments on the basis of shape parameters alone. The four new shape parameters proposed here based on the IRC plot can be collectively used to quantitatively describe grains shape which correlates closely with visual perceptions. This work opens up the possibility of using detailed quantitative textural dataset of sediment grains along with other standard analyses (mineralogy, bulk composition, isotopic analysis, etc) for diverse sedimentary studies. Part 2: Basin modelling Subsidence modelling is an important part of basin analysis to better understand the tectonic evolution of sedimentary basins. The McKenzie model has been widely applied for subsidence modelling and stretching factor estimation for sedimentary basins formed in an extensional tectonic environment. In this contribution, a numerical model is presented that takes into account the effect of sedimentary cover on stretching factor estimation. Subsidence modelling requires values of physical parameters (crustal thickness, lithospheric thickness, stretching factor, etc.) which may not be always available. With a given subsidence history of a basin estimated using a stratigraphic backstripping method, these parameters can be estimated by quantitatively comparing the known subsidence curve with modelled subsidence curves. In this contribution, a method to compare known and modelled subsidence curves is presented aiming to constrain valid combinations of stretching factor, crustal thickness and lithospheric thickness of a basin. The parameter fitting method presented here is first applied to synthetically generated subsidence curves. Next, a case study using a known subsidence curve from the Campos Basin, offshore Brazil is considered. The range of stretching factors estimated for the Campos basin from this study is in accordance with previous work, with an additional estimate of corresponding lithospheric thickness. This study provides insights into the dependence of subsidence modelling methods on assumptions about input parameters as well as allowing for the estimation of valid combinations of physical lithospheric parameters, where the subsidence history is known

Effects of microstructural features, thermal shocks and strain rate on the mechanical response of granitic rocks

Percussive drilling is regarded as the most effective method for excavation, tunneling, and shallow well boring in the hard rock such as granite. However, its efficiency has been questioned in some specific environments and applications such as drilling for geothermal energy, where bores as deep as 5000 m are needed to reach the desired temperature zone. It is therefore understandable that attempts to drill bores that deep can face significant difficulties, and even though these difficulties have already been overcome by developing new techniques for deep drilling, there still are no replacement for the percussive drilling technique. The reason for this situation can be found in the shortage of technological readiness and in the nature of the rock and its behavior itself. However, in the previous attempts to find a replacement for percussive drilling, not enough of attention has been paid to altering the rock’s properties before drilling for example by using a thermal shock.In this work, the mechanical behavior of the rocks before and after applying heat shocks was studied in quasi-static and dynamic loading conditions. Two different heat shocks were applied on the two studied rocks, one using a flame torch and one using a plasma gun. The heat shocks using the flame torch were applied on the Brazilian disc samples with durations of 10, 30, or 60 seconds. The thermal shocks using the plasma gun were applied on the Brazilian disc samples and on the bulk of the rock for dynamic indentation tests. Three different plasma gun heat shocks were applied on Brazilian disc samples with durations of 0.40, 0.55, or 0.80 second. The heat shocks applied on the bulk of the rock had a duration of 3, 4, and 6 seconds.A methodology was developed to analyze and characterize the damage caused by the heat shocks on the surface of the specimens. In this method, a liquid penetrant was applied on the surface of the samples before and after applying the heat shocks with images taken from the specimens’ surface under an ultraviolet light. Later on, the fractal dimension of the surface crack patterns was calculated using the box counting method. The results indicate that the fractal dimension of the samples increases by increasing the duration of the thermal shock and there is a relationship between the relative increase of the fractal dimension and the mechanical response of the rock material. Even though the fractal dimension analysis is limited to the surface of the samples, the computed tomography results suggest that the effects of the heat shocks are also limited to the very surface of the specimens. Therefore, the fractal dimension analysis provides a fast and accurate enough estimation of the mechanical response of the rock.The mechanical behavior of rock was studied at low and high strain rates using the Brazilian disc samples. The results indicate that by increasing the duration of the thermal shock, increasing the fractal dimension, the strength of the rock decreases in the studied strain rate range. Nonetheless, there are some differences in the rock mechanical behavior at low and high strain rates. The dynamic strength of the rock decreases considerably faster with increase of the fractal dimensions than the quasi-static strength. Therefore, the strain rate sensitivity of the rock decreases with the increasing fractal dimension.The dynamic indentation tests were performed to study the effects of heat shocks in situations similar to percussive drilling. The tests were performed using both single and triple button indenters. Even though the direct measurements of the bit-rock interactions obtained from the stress waves are useful, they do not provide any information about the side chipping and chipping between the indenters. Therefore, optical profilometry was used to study the craters formed during the impacts, and the concept of destruction work was used to characterize the effects of the heat shocks on the material removal during dynamic indentation. The results imply that after applying the heat shock, the extent of material removal increases even though the force levels are not affected much. This means that the efficiency of the indentation processes cannot be evaluated only by using the force-displacement curves but additional analysis such as the ones used in this work are needed