Fracture Analysis Research Articles

On the Application of Non-Linear Rheological Models In Longitudinal Fracture Analysis of Beams Made of Functionally Graded Materials

On the Application of Non-Linear Rheological Models In Longitudinal Fracture Analysis of Beams Made of Functionally Graded Materials

Uticaj varijacija u sadržaju Mn na mehaničke i korozione karakteristike Cu-Al-Mn legura sa memorijom oblika

In this work, the role of Mn on the shape memory effect and mechanical and corrosion behavior of Cu-Al-Mn shape memory alloys was studied. The composition of Al was fixed to 10 wt% while that of Mn was varied from 2 to 10 wt%. The strain recovery by SME was evaluated using the bend test, while the yield and ultimate tensile strength were obtained using the tension test. The corrosion behavior was studied using three different solutions: freshwater, substitute ocean water, and Hank's solution. The yield and ultimate tensile strength of Cu-Al-Mn alloys increased with Mn content up to 6%, which was attributed to grain refinement and precipitation hardening, while the fracture analysis showed mixed mode failure for all alloys. The corrosion behavior of Cu-Al-Mn alloys was modified due to the addition of Mn. With the increase in Mn content, the alloys displayed better corrosion resistance and lower corrosion rates. The corroded surface analysis tested in freshwater showed pitting corrosion, while Cu-Al-Mn alloy with low Mn content was tested in substitute ocean water. Hank's solution showed surface damage with an unstable surface layer.

Avaliação da Influência dos Parâmetros de Processamento na Manufatura Aditiva do Aço VP50IM por PCGTAW

Abstract The wire arc additive manufacturing process or WAAM (Wire Additive Arc Welding) is recognized as a process able of making pieces of high geometric complexity, with mechanical properties comparable to those of the cast material. However, there are significant challenges associated with WAAM, such as undesirable microstructures and mechanical properties, high residual stresses and geometric distortion. This study aims to contribute to the selection of deposition parameters for VP50IM steel using WAAM via pulsed TIG (Tungsten Inert Gas) and characterization of the generated stacking, using the Central Composite Complete methodology, CCC. In this study, the peak (Cp) and base (Cb) current, wire feed speed during peak (Vap), base (Vab) and welding speed (Vs) were varied. The ideal parameter presented was Cp=200A, Cb=100A, Vap=2.9cm/min, Vab=1.2cm/min and Vs=20cm/min. Tensile tests showed up to 15% greater resistance in the samples in the longitudinal section in the welding direction compared to the transverse direction. Hardness tests demonstrated up to 9% less hardness at the center of the stack compared to the top and bottom. The fracture analysis of the specimens showed ductile fracture.

An open-source moose implementation of phase-field modeling of fracture in functionally graded materials

Fracture analysis of functionally graded plates is a challenging problem in materials engineering due to the complex material behavior and the presence of cracks. In this study, we propose an efficient open-source MOOSE implementation of phase field fracture analysis of functionally graded. Automatically oriented exponential finite elements are used to discretize the model, which allows for efficient and accurate computation of the fracture behavior. The functionally graded material properties are modeled using a power law function, which captures the variation of material properties along the thickness direction of the plate. The phase field model is coupled with a finite element solver to simulate the mechanical response of the plate under loading. The proposed implementation is validated using several benchmark problems available in literature. The results show that the proposed MOOSE implementation provides accurate predictions of the crack propagation and fracture behavior of functionally graded plates.

Ductile fracture of high-strength bolts under combined actions at elevated temperatures

Steel bolted connections are critical structural components that can initiate progressive collapse at ambient and elevated temperatures. High-strength bolts are highly vulnerable members due to rapid strength degradation at high temperatures. This paper presents a numerical study on the ductile fracture of the frequently used Grade 8.8 and 10.9 structural bolts under tension, shear, and combined forces at 20–700 °C. True stress–strain curves have been defined up to fracture for both grades. The fracture parameters have been calibrated by a total of four experiments: two tensile and shear tests for each grade. The ductile fracture models with proposed fracture parameters have been further validated by pretensioned shear tests at elevated temperatures. The relationship between equivalent strain and triaxiality was investigated based on the numerical results. In general, equivalent plastic strain values become larger with increasing temperature. The fracture analysis with given ductile fracture parameters estimates the test results with reasonable accuracy under all failure modes. The fracture model can be used in numerical analysis to investigate the ductile failure of the high-strength bolted connections at ambient and elevated temperatures. Furthermore, the influence of displacement at fracture values on the results was investigated by a three-bolted inclined shear test.

Analysis of microstructures and fractures in Ag–In transient liquid phase bonded joints

Silver (Ag) and indium (In) are increasingly investigated as transient liquid phase (TLP) bonding materials for die attachment in next generation power modules. In this study, we systemically investigated the relationship between the microstructural evolution, shear strength, and fracture behavior of Ag–In TLP bonded joints. During bonding, Ag9In4 was the primary phase formed between the solid Ag and liquid In. The Ag9In4 joints exhibited brittle fractures with an intergranular fracture mechanism. The shear strength increased as bonding time and temperature increased (from 26.9 MPa to 53.0 MPa), attributed to the improved cohesiveness of grain boundaries. As the bonding process progressed, ζ (Ag3In) formed and developed between Ag and Ag9In4 owing to the solid–solid interdiffusion. The ζ (Ag3In) joints, obtained from the conditions of 250 °C and 40 min, exhibited the highest shear strength of 82.87 MPa. Here, the ductile fracture was characterized with an intergranular fracture mechanism. This ductility was partially attributed to the relatively low hardness of ζ (Ag3In) (2.1 GPa). The high strength and ductility of ζ (Ag3In) found in this study present differ from the conventional understanding of the inherently brittle intermetallic compounds. Therefore, the study findings form the basis for enhancing the reliability of power modules.

Study of structural characteristics of hydrocarbon reservoir pore space based on X-ray computed tomography images

Digital studies of pore space and internal structure of hydrocarbon reservoir were conducted on the basis of multiscale X-ray computed tomography images and the analysis of heterogeneities, cavernosity, fracturing and bedding in the rock. Main results. 3D models of rock pore space were created on the basis of computed tomography images through segmentation. Porosity estimation based on the digital approach was performed. It was shown that the digitally obtained data are in good agreement with the results of laboratory measurements. Analysis and visualization of the structure of the main filtration channels in the rock were performed. Pore size distributions in the specimen were obtained, and 3D visualization of the largest pore size was shown. Conclusions. The pore space characteristics obtained on the basis of tomographic approach are valuable data for filling reservoir models and can be used in solving the problems of permeability reduction during different kinds of reservoir impacts. Application of the obtained results in combination with geomechanical tests of rocks is intended to expand existing approaches to complex analysis of core material of reservoirs, as well as to supplement and refine mathematical and operational models of the studied objects.

Influence of corrosion-active non-metallic inclusions on the accelerated destruction of the internal surface of the Oplot-M tank barrel

The metallographic features of operational damage to the inner surface of the barrel of the Oplot-M tank were analyzed. It was established that with the movement from the chamber to the cut of the barrel, the number and size of damage decreases, which is related to the distribution of pressures of working gases, temperature and aggressiveness of the environment. It is shown that the damage is placed on the inner surface chaotically and the nature of their destruction is corrosive and corrosive-mechanical in origin. Local analysis of their chemical composition revealed a high oxygen content, which indicates the formation of oxide-hydroxide compounds. The surface layers of the barrel were studied and it was established that a "white" layer with a thickness of ~50 μm and a microhardness of 930 kg/mm2 is formed on the surface, the structure of the inner layer of the steel of the barrel is troostite (HW 225 kg/mm2). 
 The effect of corrosion-active non-metallic inclusions (KANV) on the destruction of the surface of a barrel made of steel 38KHN3MFA was studied. It is shown that more sensitive to changes in the technical state of steel due to degradation are studies of corrosion resistance, microelectrochemical heterogeneity and impact toughness of steel. It was established that the presence of KANV in the steel structure leads to an increase in corrosion currents by 4 times and microelectrochemical heterogeneity, in particular, non-periodic potential peaks of 50-70 and 200-230 mV. Due to the influence of tap water on the surface of the steel, corrosion ulcers of a rounded shape and a size of 50-80 μm were recorded, which contribute to the local corrosion of the steel. The analysis of steel fractures revealed that inclusions of a round shape with a size of 3-5 μm contain impurities of harmful elements Al, Mg, F, which accelerate local corrosion on the surface of the steel of the tank barrel. It is shown that the study of fractures, and not of samples, provides an opportunity to estimate not only the size and density of inclusions, but also their chemical composition.

A C0 scalar field approach for describing sprain variables in finite element analysis of fracture

A new approach is proposed to account for the impact of sprain variables for computational simulation of fracture in quasi-brittle materials. For an isotropic solid, these variables are equal to the Laplacians of the components of the displacement field, and they were introduced in a recent study by Zhang and Bazant to resolve spurious mesh effects for cases involving softening material response. This is possible by establishing localization-resisting forces which are conjugate to the displacements with respect to a sprain energy functional, defined as a function of the sprain variables. To enable the evaluation of the sprain variables in a conventional, C0 continuum finite element approximation, this paper introduces a set of scalar fields, each being weakly equal to the Laplacian of one of the components of the displacement vector field. This leads to a straightforward implementation with standard continuum (solid) elements, eliminating the need for approximations satisfying higher continuity requirements or for ad-hoc, finite-difference algorithms which were adopted in the original pertinent work for the calculation of the sprain variables.

Risk of Falls and Fractures in Individuals With Cataract, Age-Related Macular Degeneration, or Glaucoma

Three leading disease causes of age-related visual loss are cataract, age-related macular degeneration (AMD), and glaucoma. Although all 3 eye diseases have been implicated with falls and fracture risk, evidence is mixed, with the contribution of different eye diseases being uncertain. To examine whether people with cataract, AMD, or glaucoma have higher risks of falls or fractures than those without. This cohort study was a population-based study in England using routinely collected electronic health records from the Clinical Practice Research Datalink (CPRD) GOLD and Aurum primary care databases with linked hospitalization and mortality records from 2007 to 2020. Participants were people with cataract, AMD, or glaucoma matched to comparators (1:5) by age, sex, and general practice. Data were analyzed from May 2021 to June 2023. For each eye disease, we estimated the risk of falls or fractures using separate multivariable Cox proportional hazards regression models. Two primary outcomes were incident falls and incident fractures derived from general practice, hospital, and mortality records. Secondary outcomes were incident fractures of specific body sites. A total of 410 476 people with cataract, 75 622 with AMD, and 90 177 with glaucoma were matched (1:5) to 2 034 194 (no cataract), 375 548 (no AMD), and 448 179 (no glaucoma) comparators. The mean (SD) age was 73.8 (11.0) years, 79.4 (9.4) years, and 69.8 (13.1) years for participants with cataract, AMD, or glaucoma, respectively. Compared with comparators, there was an increased risk of falls in those with cataract (adjusted hazard ratio [HR], 1.36; 95% CI, 1.35-1.38), AMD (HR, 1.25; 95% CI, 1.23-1.27), and glaucoma (HR, 1.38; 95% CI, 1.35-1.41). Likewise for fractures, there were increased risks in all eye diseases, with an HR of 1.28 (95% CI, 1.27-1.30) in the cataract cohort, an HR of 1.18 (95% CI, 1.15-1.21) for AMD, and an HR of 1.31 (95% CI, 1.27-1.35) for glaucoma. Site-specific fracture analyses revealed increases in almost all body sites (including hip, spine, forearm, skull or facial bones, pelvis, ribs or sternum, and lower leg fractures) compared with matched comparators. The results of this study support recognition that people with 1 or more of these eye diseases are at increased risk of both falls and fractures. They may benefit from improved advice, access, and referrals to falls prevention services.

Study on deformation behavior of Ti60 alloy based on multi-physics coupling

Titanium alloys are extensively employed in aerospace due to their superior performance, but their development is constrained by limited formability at room temperature, an electrically assisted forming (EAF) process emerges as a promising solution to reduce flow stress, improve formability, and accelerate material recrystallization. This study focuses on elucidating the interplay between pulse current, temperature, and flow stress in Ti60 alloy under combined electrical, thermal, and stress fields. To this end, electrically assisted tensile (EAT) tests were performed on Ti60 alloy using six different current densities. Currently, there is no unified theory for electro-plasticity in metal materials, and the absence of a suitable model hinders finite element simulation in EAF. The investigation encompasses four key areas: the impact of multi-physics coupling on temperature variations, the stress-strain curve characteristics, the microstructural analysis of tensile fractures, and the modification of the Johnson-Cook (MJC) model. Notably, temperature distribution proves more uniform across the width than the length. Tensile elongation initially rises and then falls with increasing current density, peaking at a critical current density (J=30 A/mm2). Higher current densities lead to a transition in fracture features, with deep, numerous dimples and tiny voids supplanting tearing ridges and facets. Despite this, brittle fracture remains the dominant mode, accompanied by granular oxide formation at J= 35, 40 A/mm2. The MJC model aligns closely with experimental outcomes, showing R and EAARE values of 92.7% and 7.15%, respectively. This model accurately predicts Ti60 alloy's deformation under multi-physics conditions, marking a significant advancement in integrating electro-plasticity into constitutive modeling.

Treatment of 2-part, 3-part, and 4-part proximal humerus fractures from 2016 to 2020: A nationally-representative database

IntroductionComplex proximal humerus fractures pose challenges in elderly patients, as this common scenario can lead to unpredictable outcomes, regardless of treatment method. Given the evolving nature of the treatment for 3-and-4-part proximal humerus fractures, an epidemiological analysis offers a way to minimize the gap between appropriate understanding and effective intervention. As such, we aimed to i) evaluate the trends of nonoperative and operative management; and ii) compare the complication rates of ORIF to conversion ORIF (to RTSA). MethodsWe utilized a national, all-payer database to include patients who underwent open reduction and internal fixation for 2-part (n = 2783), 3-part (n = 2170), 4-part (n = 1087) proximal humerus fractures between April 2016 to December 2022. Patients who failed ORIF to RTSA included n = 108 for 2-part fractures, n = 123 for 3-part fractures, and n = 128 for 4-part fractures. We collected demographic and postoperative medical and surgical complications at 90-days, in addition to time-interval between ORIF and RTSA. ResultsThe malunion and nonunion rates for ORIF between different types of proximal humerus fractures were similar (2-part fractures: 1.8 %, 4.7 %; 3-part fractures: 1.8 %, 3.5 %; 4-part fractures: 2.4 %, 3.7 %). The conversion rates of failed ORIF to RTSA were 1.9 %, 2.8 %, and 5.9 % for 2-part, 3-part, and 4-part fractures, respectively. The time interval from failed ORIF to RTSA was 190 days for 2-part fractures, 169 days for 3-part fractures, and 129 for 4-part fractures. ConclusionAn epidemiological analysis of proximal humerus fractures by fracture type demonstrated an increase in RTSA for 2-part, 3-part, and 4-part fractures while nonoperative treatment showed no change from 2016 to 2020. Additional research is needed to determine which fractures are best treated operatively while maximizing outcomes. In the setting of complex proximal humerus fractures, several options seem feasible depending on patient demographic characteristics.

Peridynamics-based analysis on fracture behaviors of a turbine blade shroud

Fracture analysis of turbine blades is a critical aspect of turbomachinery design. However, direct numerical analysis of fractures on blades is limited by the complexity of blade structures and discontinuity-induced singularities it meets. Peridynamics (PD) methods are applied to describe discontinuous problems and thus promising for simulating blade fractures. In this paper, a PD method is used to numerically analyze a blade whose shroud is fractured. The established model effectively describes the cracking process and predicts the cracking path. Besides, corrosion-accelerated cracking behaviors are numerically examined, highlighting the ability of PD to solve multi-physical cracking problems in complex structures.

Mixed-Mode Fracture behaviour of Si-C-N coatings

Micro-electro-mechanical systems (MEMS) technology has made it possible for the semiconductor industry to construct systems and devices on silicon substrates. Nanocomposite Si-C-N coatings must have reliable characteristics for MEMS as well as in the form of protective coatings for heavy-duty industries like aerospace, automobiles, reactors, etc. Vickers indentation was used to study the fracture response of Si-C-N coatings that were deposited on silicon substrates. Images of the fractured regions which consisted of different types of cracks were analyzed and used for qualitative fracture analysis. The Drucker-Prager (DP) model and subsurface layer distributions were used to evaluate the fractured zones. Microscopic evaluation and supporting image analysis were used to study the growth nature of the coatings.

Nanomechanical, mechanical and microstructural characterization of electron beam welded Al2219-T6 tempered aerospace grade alloy: A comprehensive study

As compared to traditional fusion welding processes, electron beam welding (EBW) is known to produce structurally robust microstructures and narrow heat-affected zone (HAZ) in metals. The process becomes more significant for the tempered alloys vulnerable to heat exposure. In the present investigation, Al 2219-T6 alloy was joined using the EBW process. The microstructural, mechanical, and nanomechanical characteristics of the resulting joint were investigated. EBW resulted in a narrow HAZ (22 μm) with a 430 mm fusion zone (FZ). A dendritic structure was observed in the FZ zone, while second-phase particles were absent indicating their dissolution during welding and interesting formation of Al2Cu mixture around the dendrites. The limited content of Cu in the base metal (BM) resulted in the formation of a solid solution in the FZ, along with the presence of fine equiaxed grains in the HAZ and equiaxed dendritic grains in the FZ zone. The X-ray diffraction analysis confirmed the absence of peaks corresponding to incoherent phases in the FZ. Compared to the BM, micro-hardness measurements revealed a 12.7 % increase in the hardness in the HAZ, while a significant decrease of approximately 19 % was observed in the FZ. The joint exhibited reduced tensile strength, ultimate strength by 42.2 %, and yield strength by 47.3 % when compared to the BM. The fracture analysis indicated a ductile failure mode with the presence of microvoids. Nano-indentation tests at various loads demonstrated a decrease in the nanohardness from the BM to the HAZ and FZ regions. Atomic force microscopy (AFM) analysis revealed significant pile-ups in the FZ, indicating the occurrence of plastic deformation during the welding process. The presented findings are valuable for the joint and structure design of Al −2219T6 alloy in particular and other Al alloys in general.

Assessment of Fracture Density Distribution from Image Logs for Sensitivity Analysis in the Asmari Fractured Reservoir

Characterizing fracture properties in naturally fractured reservoirs poses a significant challenge. While welltesting remains valuable, it often fails to provide precise descriptions of these properties. Bridging this gap requires the integration of geological expertise to enhance fracture assessment. This study addresses the limitations of well-test analysis and explores the application of Conventional Image Logs in structural, fracture, and geomechanical analysis. However, effectively combining these applications with well-test analysis on a field scale reveals a substantial knowledge gap. A critical challenge in this context is the absence of a defined procedure for calculating the variable "σ," a crucial parameter for simulating fractured carbonate reservoirs using image log fracture density. Integrating geological knowledge is essential to reduce uncertainties associated with well-test analysis and provide more accurate characterizations of fracture properties. Image log data processing emerges as a valuable avenue for gaining insights into the static attributes of naturally fractured reservoirs. This study focuses on Characterizing fractures using data from ten image logs and Developing a more accurate simulation model through the interpretation of images, with a particular emphasis on OBM imaging. The main goals of this fracture study revolve around establishing correlations between fracture densities well by well within the simulation and enhancing the accuracy of the simulation model by incorporating fracture data from image logs. Borehole imaging tools such as FMI/FMS and OBMI-UBI play a pivotal role in identifying significant structural features, including faults, fractures, and bedding. Fine-tuning fracture parameters during the history matching process, while potentially time-consuming, significantly impacts other historical match parameters. Consequently, the reliability of reservoir simulation results, predictions, and recovery enhancement strategies hinges on the precision of fracture properties and their distribution within the model. Recent advances in interpretation techniques have expanded the horizons of image interpretation, enabling the creation of more accurate simulation models for fractured reservoirs using fracture data obtained from image logs. The overarching goal of this project is to comprehensively evaluate a fractured reservoir field by integrating data from ten individual wells.

Prediction of graphene's mechanical and fracture properties via peridynamics

Although graphene is believed to be the strongest material, many properties of this material are still worth exploring and discovering, especially the influence of inevitable defects in its preparation on the mechanical and fracture properties which are of high significance. This work provides a new feasible way to study the mechanical and fracture properties of graphene. The novelties of this study are threefold: (1) A novel peridynamic (PD) model is proposed for polycrystalline graphene in which grains of large size exist; (2) The coupling effect of the pre-crack length and the grain size on the inverse pseudo Hall-Petch relation is revealed; (3) The results confirm the applicability of classical Griffith theory in brittle fracture analysis of graphene. Based on the proposed PD model, dependence of the mechanical and fracture properties on the grain size which changes from a few to hundreds of nanometers is investigated in this study. The fracture forms of graphene are consistent with the experimental observations. Based on the Griffith theory, the obtained fracture toughness such as Kc (i.e. 3.8MPam - 6.3MPam) or Gc (i.e. 14.0 J/m2 – 40.9 J/m2) is comparable with previously reported theoretical and experimental values, which proves the validity of the proposed PD model. Besides, the fracture toughness can be greatly enhanced by the blunt pre-crack tip. This work presents insights into mechanical failure of graphene and guidance on fragmentation of graphene for its practical use.

Analysis of aperture values of stratabound fractures in bedded rock: Use of the maximum likelihood method in studying a truncated data set

In this study, a truncated data set of aperture values of stratabound joints in carbonate rocks, already studied in a previous work and in which sampling of smallest fractures was problematic, has been reanalysed through regression analysis by means of Maximum Likelihood Estimation (MLE). This analysis criterion has been tested through Monte Carlo simulations, which demonstrated that MLE is able to correct the measurement bias due to truncation. The statistics corroborate as the median joint aperture value is mainly controlled by mechanical bed thickness, according to a linear regression law with non-zero intercept. The achieved results are of interest (i) from the viewpoint of statistical methodology as well as (ii) for the purpose of characterizing stratabound joint sets. With reference to point (i), the proposed method is significantly more reliable than the Least Squares Method (LSM). Therefore, it may be routinely employed in fracture analysis and potentially adapted also for other cases in which there is an analogue bias at lower limits of the sampling range. Regarding point (ii), these results provide a step ahead in characterizing and modeling of stratabound joint networks based on bed thickness data, which is relevant to identify pathways and storage systems in oil reservoir study, in hydrogeology and in all environmental problems involving ground fluids.

Improving traumatic fracture detection on radiographs with artificial intelligence support: a multi-reader study.

The aim of this study was to evaluate the diagnostic performance of nonspecialist readers with and without the use of an artificial intelligence (AI) support tool to detect traumatic fractures on radiographs of the appendicular skeleton. The design was a retrospective, fully crossed multi-reader, multi-case study on a balanced dataset of patients (≥2 years of age) with an AI tool as a diagnostic intervention. Fifteen readers assessed 340 radiographic exams, with and without the AI tool in 2 different sessions and the time spent was automatically recorded. Reference standard was established by 3 consultant radiologists. Sensitivity, specificity, and false positives per patient were calculated. Patient-wise sensitivity increased from 72% to 80% (P < .05) and patient-wise specificity increased from 81% to 85% (P < .05) in exams aided by the AI tool compared to the unaided exams. The increase in sensitivity resulted in a relative reduction of missed fractures of 29%. The average rate of false positives per patient decreased from 0.16 to 0.14, corresponding to a relative reduction of 21%. There was no significant difference in average reading time spent per exam. The largest gain in fracture detection performance, with AI support, across all readers, was on nonobvious fractures with a significant increase in sensitivity of 11 percentage points (pp) (60%-71%). The diagnostic performance for detection of traumatic fractures on radiographs of the appendicular skeleton improved among nonspecialist readers tested AI fracture detection support tool showed an overall reader improvement in sensitivity and specificity when supported by an AI tool. Improvement was seen in both sensitivity and specificity without negatively affecting the interpretation time. The division and analysis of obvious and nonobvious fractures are novel in AI reader comparison studies like this.

Maximum Likelihood Instead of Least Squares in Fracture Analysis by Means of a Simple Excel Sheet with VBA Macro

This technical note illustrates a linear regression algorithm based on the Maximum Likelihood Estimation (MLE), with a related Excel spreadsheet and VBA program, adapted to the case of fracture aperture data sets in which sampling of the smallest values is problematic. The method has been tested by means of Monte Carlo simulations and exhibits significantly better convergence against Least Squares criterion (LSM). As the method is conceptually simple and, following the indications illustrated here, the relative spreadsheet can be easily designed, it may be routinely used, instead of the Least Squares, in fracture analysis. Furthermore, the proposed method, with the appropriate modifications, might be potentially extended to other cases in geology and geophysics, in which significant biases at the lower limits of the sampling scale occur.