Mechanical glass transition revealed by the fracture toughness of metallic glasses
Abstract not provided
Ketkaew, Jittisa↗
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An Investigation of CO2-Responsive Preformed Particle Gel for Conformance Control of CO2 Flooding in Reservoirs With Fractures or Fracture-Like Channels
Summary Gel treatment is an important technique to solve early CO2 breakthrough and excess–CO2–production problems, caused by the low viscosity and low density of CO2, as well as the heterogeneity of reservoirs with fractures or fracture–like channels. However, there is no reported work on gel that increases its volume after reacting with CO2 (termed CO2–responsive gel) for the conformance control of CO2 flooding. In this paper, the intrinsic properties of a CO2–responsive preformed particle gel (CR–PPG) were evaluated in a water/supercritical–CO2 (scCO2) environment in high–pressure vessels. Continuous scCO2 injection and CR–PPG treatment were conducted in fractured sandstone cores, to probe their plugging performance to scCO2 flow in a high–permeability–contrast system. The volumetric swelling ratio (VSR) of the CR–PPG increased by approximately two times in the presence of scCO2, compared with a sample under similar conditions in the absence of scCO2. The CR–PPG swelling ratio decreased with increasing NaCl concentration. Under the same conditions, the temperature did not have an apparent effect on the swelling ratio after 31 days of swelling. In coreflooding experiments, the placed CR–PPG resisted a considerable pressure up to 617.0 psi before breakthrough. After a shut–in process, CO2–breakthrough pressure was detected at 437.2 psi. It is observed that the shut–in process improved the plugging performance of CR–PPG to CO2 as revealed by the increase in the residual resistance factor. Controlling the shut–in time was found to be effective in augmenting the increase in the residual resistance factor, by increasing the VSR of placed CR–PPG. Resistance of CR–PPG to some real field challenges, including a high pressure gradient and long–term exposure to CO2, was also reported for field–applicability concerns.
Engineering↗
Probabilistic fracture mechanics and optimum fracture control of the solid rocket motor case of the shuttle
Development of a procedure for the reliability analysis of the solid rocket motor case of the space shuttle is described. The analysis is based on probabilistic fracture mechanics and consideration of a probability distribution for the initial flaw sizes. The reliability analysis can be used to select design variables, such as the thickness of the SRM case, projected design life and proof factor, on the basis of minimum expected cost and specified reliability bounds. Effects of fracture control plans such as the non-destructive inspections and the material erosion between missions can also be considered in the developed methodology for selection of design variables. The reliability-based procedure can be easily modified to consider other similar structures and different fracture control plans.
Hanagud, S.↗
Patterns of Fracture and Tidal Stresses Due to Nonsynchronous Rotation: Implications for Fracturing on Europa
Global lineaments on Europa were interpreted as fractures in an icy crust. A variety of lineament types were identified, which appear to form a systematic pattern on the surface. For a synchronously rotating body, the patterns of fractures observed could be produced by a combination of stresses due to orbital recession, orbital eccentricity, and internal contraction. However, it was recently suggested that the forced eccentricity of Europa's orbit may result in nonsynchronous rotation. The hypothesis that fractures in a thin icy crust may have formed in response to stresses resulting from nonsynchronous rotation is studied.
Parmentier, E. M.↗
Determination of interlaminar fracture toughness and fracture mode dependence of composites using the edge delamination test
Edge delamination testing has been conducted in order to determine the mixed mode interlaminar fracture toughness of unnotched (+, -35/0/90)s and (0/+, -35/90)s laminates with graphite fibers and epoxy matrices, with or without elastomer additives. Although the two stacking sequences were chosen so that the total strain energy release rates were equal, the percentages of crack opening and shear mode energy release rates were found to vary widely between the layups. Plots of interlaminar fracture toughness as a function of crack opening energy release rate percentage have been drawn to generate delamination failure criteria which reflect the observed fracture mode dependence.
Obrien, T. K.↗
Prediction of Composite Laminate Fracture: Micromechanics and Progressive Fracture
An investigation is described on the prediction of first-ply failure and fracture in selected composite laminates. The laminates are made from glass fibers and graphite fibers in epoxy matrices. Failure envelopes are generated for combined loading of these laminates on the basis of first-ply failure and laminate fracture. The evaluation is performed by a micromechanics-based theory and progressive fracture.
Gotsis, P. K.↗
Prediction of Composite Laminate Fracture: Micromechanics and Progressive Fracture
An investigation is described on the prediction of first-ply failure and fracture in selected composite laminates. The laminates are made from glass fibers and graphite fibers in epoxy matrices. Failure envelopes are generated for combined loading of these laminates on the basis of first-ply failure and laminate fracture. The evaluation is performed by a micromechanics-based theory and progressive fracture.
Gotsis, P. K.↗
Interface and embedded joint methods for modeling dynamic fracture opening by explosive products [Two methods for modeling dynamic fracture opening by explosive products]
Two computational approaches are proposed in the paper to model dynamic fracture opening by explosive products. The first method assumes that the fractures may be modeled using flow elements embedded along the mesh lines. This method models crack opening in a straightforward way by splitting the nodes of the computational grid. It can account for crack branching; however, the crack directions are constrained by existing mesh faces, which may lead to mesh dependence. Also, the stress in flow elements is calculated explicitly separate from the surrounding solid elements that can impose additional limits on the time step stability condition for explicit integration. The second approach uses embedded flow elements to model the cracks. Typical thickness of the cracks is much smaller than the element size. Therefore, gas pressure in the cracks is assumed to be in stress equilibrium with the element stress. To achieve this, the crack thickness and the state of the gas is updated simultaneously with the state of the solid element which contains the crack. Therefore, the time step is controlled by the explicit solver applied for the solid and does not depend on the thickness of the crack. In conclusion, the main disadvantage of the second approach is due to the complexity of modeling multiple intersecting cracks, which go through the same element. We discuss the areas of possible applications of these 2 methods and the ways to improve and enhance them for future practical applications.
58 GEOSCIENCES↗
Agency Additive Manufacturing (AM) Certification Support Team (AACT) Risk Reduction – Safe Life Category: Fracture Control Framework for Un-inspectable Fracture Critical AM Parts
The NASA Engineering and Safety Center (NESC) was requested to support the development of a governing philosophy to provide a consistent and systematic approach for fracture control certification of additive manufacturing (AM) hardware that cannot be reliably inspected. The overall goal of the NESC assessment was to make progress toward a framework for general certification of un-inspectable fracture critical AM hardware and toward approaches for evaluating risks associated with these components. This report contains the results of the assessment.
Additive Manufacturing↗
Identification of Hip BMD Loss and Fracture Risk Markers Through Population-Based Serum Proteomics: HIP BMD LOSS & FRACTURE RISK MARKERS BY POPULATION-BASED SERUM PROTEOMICS
Accelerated bone loss significantly increases the risk of osteoporosis and fracture. The mechanisms underlying bone loss remain incompletely understood, and there are few available biomarkers. We utilized a novel proteomics approach to identify serum peptides and proteins associated with bone loss in 1967 older men who were randomly chosen from the Osteoporotic Fracture in Men Study (MrOS study) (age ≥ 65 yrs). Men had 2-3 measures of femoral neck BMD over an average follow-up of 4.6 years. Change in BMD was estimated and then categorized into three groups: maintained BMD (n=453), expected loss (n=1185) and accelerated loss (n=237). A liquid chromatography–ion mobility separation-mass spectrometry (LC-IMS-MS) proteomics platform was used to identify and quantify peptides from serum proteins. The whole cohort was randomly divided into discovery (N= 960) and validation (N= 915) sub-cohorts. Linear regression models and a random forest approach were used to discover differentially abundant individual peptides and a proteomic signature that distinguished individuals with accelerated bone loss from those who maintained BMD. Network analyses were performed using the MetaCore knowledgebase. We identified 12 peptides that were associated with BMD loss in both discovery (P< 0.1 FDR) and replication sub-cohorts (P<0.05). Those 12 peptides mapped to the following proteins: ALS, LYVE1, RNAS1, C2, ICOSL, C163A, C7, HEMO, CD14, CERU, CRAC1 and CD59. Meta-analysis of peptidesassociated with bone loss identified 6 additional proteins including GRP78, IGF-2, SHBG, ENPP2, IBP2 and IBP6. We also identified a proteomic signature that was predictive of BMD loss with a discriminative value similar to serum bone marker carboxy-terminal collagen crosslink peptide (CTX). Interestingly, combining the proteomic signature with CTX significantly improved the ability to discriminate men with accelerated loss. In summary, we have identified potential new biomarkers for bone loss that provide a more in depth understanding of its pathophysiology.
59 BASIC BIOLOGICAL SCIENCES↗
Evaluation of inert tracers in a bedrock fracture using ground penetrating radar and thermal sensors
Not provided.
Energy & Fuels↗
Importance of corners in fracture of highly crosslinked polymeric adhesives
In this study, very large molecular dynamics simulations with open ends between two solid adherends have been performed treating tensile deformation of coarse-grained, highly crosslinked polymer networks modeling epoxy systems. The open boundary and the presence of corners dramatically alter the fracture behavior. In contrast to systems with periodic boundaries, the failure strain decreases with increasing system size until a critical size is reached. This decrease greatly reduces the difference in the crack initiation strains between simulation and experiment. In the open geometry, the sides of the polymer network contract inward forming wedge shaped corners. The stress and strain are concentrated in the corners where the shear component is present and large. The nonuniformity of the strain results in accumulation of bond breaking in the corners and crack initiation there. Lastly, t the corner strain is system size dependent, which results in a system size dependence of the failure strain.
36 MATERIALS SCIENCE↗
A Comparative Study of Deep Learning Models for Fracture and Pore Space Segmentation in Synthetic Fractured Digital Rocks
This study focuses on the comparative study of deep learning (DL) models for pore space and discrete fracture networks (DFNs) segmentation in synthetic fractured digital rocks, specifically targeting low-permeability rock formations, such as shale and tight sandstones. Accurate characterization of pore space and DFNs is critical for subsequent property analysis and fluid flow modeling. Four DL models, SegNet, U-Net, U-Net-wide, and nested U-Net (i.e., U-Net++), were trained, validated, and tested using synthetic datasets, including input and label image pairs with varying properties. The model performance was assessed regarding pixel-wise metrics, including the F1 score and pixel-wise difference maps. In addition, the physics-based metrics were considered for further analysis, including sample porosity and absolute permeability. Particularly, We first simulated the permeability of porous media containing only pore space and then simulated the permeability of porous media with DFNs added. The difference between these two values is used to quantify the connectivity of segmented DFNs, which is an important parameter for low-permeability rocks. The pixel-wise metrics showed that the nested U-Net model outperformed the rest of the DL models in pore space and DFNs segmentation, with the SegNet model exhibiting the second-best performance. Particularly, nested U-Net enhanced segmentation accuracy for challenging boundary pixels affected by partial volume effects. The U-Net-wide model achieved improved accuracy compared to the U-Net model, which indicated the influence of parameter numbers. Similarly, nested U-Net has the closest match to the ground truth of physics-based metrics, including the porosity of pore space and DFNs, and the permeability difference quantifying the connectivity of DFNs. The findings highlight the effectiveness of DL models, especially the U-Net++ model with nested architecture and redesigned skip connections, in accurately segmenting pore spaces and DFNs, which are crucial for pore-scale fluid flow and transport simulation in low-permeability rocks.
Wang, Hongsheng↗
Cohesive phase-field fracture and a PDE constrained optimization approach to fracture inverse problems
In recent years there has been a proliferation of modeling techniques for forward predictions of crack propagation in brittle materials, including: phase-field/gradient damage models, peridynamics, cohesive-zone models, and G/XFEM enrichment techniques. However, progress on the corresponding inverse problems has been relatively lacking. Taking advantage of key features of existing modeling approaches, we propose a parabolic regularization of Barenblatt cohesive models which borrows extensively from previous phase-field and gradient damage formulations. An efficient explicit time integration strategy for this type of nonlocal fracture model is then proposed and justified. In addition, we present a C++ computational framework for computing in- put parameter sensitivities efficiently for explicit dynamic problems using the adjoint method. This capability allows for solving inverse problems involving crack propagation to answer interesting engineering questions such as: 1) what is the optimal design topology and material placement for a heterogeneous structure to maximize fracture resistance, 2) what loads must have been applied to a structure for it to have failed in an observed way, 3) what are the existing cracks in a structure given various experimental observations, etc. In this work, we focus on the first of these engineering questions and demonstrate a capability to automatically and efficiently compute optimal designs intended to minimize crack propagation in structures.
97 MATHEMATICS AND COMPUTING↗
Fracture control methods for space vehicles. Volume 2: Assessment of fracture mechanics technology for space shuttle applications
The concepts explored in a state of the art review of those engineering fracture mechanics considered most applicable to the space shuttle vehicle include fracture toughness, precritical flaw growth, failure mechanisms, inspection methods (including proof test logic), and crack growth predictive analysis techniques.
Ehret, R. M.↗
Aspects of fracture mechanics in cryogenic model design. Part 1: Fundamentals of fracture mechanics
The use of fracture mechanics for predicting fracture and fatigue crack growth in metals is presented.
Hudson, C. M.↗
Composite interlaminar fracture - Effect of matrix fracture energy
A major result of the use of the double cantilever beam test to provide a measure of the interlaminar fracture energy in composites subjected to simple Mode I-type loading is the observation that increasing the toughness of the matrix resin by as much as a factor of 20 produced a major (approximately four-fold) increase in interlaminar fracture energy. The data presently analyzed show that, with brittle polymers, resin toughness is fully transferred to the composite, while in the case of tougher polymers the resin toughness is only partially transferred due to the fibers' restriction of the crack tip deformation zone in the polymer, together with their changing of local stress field details. Factors which tend to increase interlaminar toughness are fiber nesting and bridging, as well as fiber breakage and pull-out during crack growth.
Hunston, D. L.↗