Crack Arrest Research Articles

Measuring Improvement in Fly Ash Based Concrete Impregnated with Glass Fiber

Abstract: In cement and concrete, fly ash has been utilized as a mineral additive. Utilizing it offers a number of benefits, including enhanced workability and strength characteristics as well as environmental advantages linked to waste disposal and lower carbon dioxide emissions. Constantly 1.5%, 2.5%, and 3.5% of the cement's weight is reinforced with alkali-resistant glass Fibers. Glass Fibers improved split and flexural strength without increasing compressive strength and served as an effective crack arrester. For this study, concrete of M30 grade is utilized. Studying fly ash's viability as a mineral additive to replace cement and provide extra glass fibre reinforcement in concrete is the primary goal of this project. Concrete's several structural qualities, such as its compressive, split, and flexural strength, are satisfied by the use of glass Fibers as extra reinforcement and fly ash as a partial substitute for cement. The complete investigation came to the conclusion that the best combination of all the mixes was 10% FA + 3.5% GF, which gave the most tensile strength; 10% FA + 3.5% GF showed greater flexure strength; and 10% FA showed good compressive strength at 28 days compared to standard concrete. After seven days, fly ash blends no longer exhibit improved compressive strength or split tensile strength.

Phase-field modeling of ductile fracture in bioinspired interfaces with dissipative structures

Intrinsic toughening, which occurs during ductile fracture and is motivated by plasticity, plays an important role in the industrial design of biomimetic composites. The interface structure in biomimetic composites can serve as a source of energy dissipation and stress relaxation, thereby achieving the goal of toughening. A new ductile fracture mechanism is proposed considering the influence of accumulated plastic deformation on local fracture toughness in a ductile phase-field model. The inducement to control the toughening mechanism is local energy dissipation, and the possible arrangement and shape of the dissipative structure are designed to capture the corresponding interface toughening mechanism. The channel structures of the barnacle substrate provide great inspiration for the structural toughening of the interface. The toughening mechanisms of weak interfaces are further explored by 3D printing structure specimens. The results indicate that the form of the R-curve is like a mixture of local J shaped and Γ shaped R-curves, which can also be called a periodic alternating mode. The J shaped R-curve represents the dissipation mechanism of the channel shape, while the Γ shaped R-curve represents the periodic crack arrest caused by local deformation of the channel.

Crack Arrest Analysis of Components With Compressive Residual Stress

ABSTRACTA finite element analysis and fracture mechanics methodology for determining the autofrettage pressure required to cause crack arrest in components under varying pressure loading are presented. Superposition of the autofrettage residual stress distribution and working load stress distribution is combined with ANSYS Separating Morphing and Adaptive Remeshing Technology (SMART) to determine the effective stress intensity factor as the crack grows. The condition for crack arrest is identified by comparison with a crack arrest model defining the crack propagation threshold stress intensity factor range for microstructurally short, physically short, and long cracks. The crack propagation threshold models of El Haddad and Chapetti are implemented and applied to fatigue analysis of stainless steel and low carbon steel double notch tensile test specimens with preinduced compressive residual stress. Based on comparison with fatigue test results, the Chapetti model is selected for use in the analysis of a 3D aluminum alloy valve body. The calculated minimum autofrettage pressure required to give crack arrest under a given working load cycle is found to be in good agreement with experimental observations from the literature.

Investigation on crack initiation, propagation, and arrest in thick-walled cylinders under thermal-shock loading

Investigation on crack initiation, propagation, and arrest in thick-walled cylinders under thermal-shock loading

Numerical simulation of ballistic protection performance of circular and hexagonal perforated high nitrogen steel

Abstract The ballistic performance of high nitrogen austenitic stainless steel (HNASS) plates with round and hexagonal perforations was numerically simulated by LS-DYNA software. A systematic analysis was conducted to explore the effects of pore size, hole spacing, impact point, and other variables on the material’s ballistic resistance. It indicate that the failure mechanism of the bullet core penetrating the perforated HNASS plate is dependent on the specific impact point. Additionally, circular perforated plates exhibit superior crack arrest capabilities compared to hexagonal perforated plates. When the width of the steel plate between adjacent holes exceeds the hole radius, there is an increase in core mass loss, both at the center of the hole and at the impact point between two holes. The deflection angle of the bullet core is significantly affected by the impact point, particularly when the width of the steel plate between holes is greater than the hole radius, with a maximum deflection angle of approximately 20°. Factors such as the hole diameter of the perforated plate, the width of the steel plate between holes, and the shape of the perforations all influence the residual velocity of the bullet core. Generally, smaller hole diameters, wider steel plates between holes, and hexagonal perforations result in lower residual velocities of the bullet core. Notably, the hexagonal perforated plates demonstrate a lower residual velocity compared to circular perforated plates, with a maximum average velocity drop that is 43.8% higher. The findings can serve as valuable references for designing additional armor for light armored vehicles.

Effect of strain rates on stress corrosion sensitivity of 7085-T7452 thick-plate friction stir welding joint

The stress corrosion behavior of 7085-T7452 high-strength aluminum alloy base material (BM) and its friction stir welding (FSW) joints under varying strain rates during slow strain rate tensile (SSRT) was investigated. The results show that the stress corrosion sensitivity (ISSRT) of both the BM and FSW joints decreases with the increase of strain rate from 10−7 s−1 to 10−5 s−1. Moreover, the BM demonstrates lower ISSRT than the joints. The cracks in the joints exhibit dendritic paths along grain boundaries, with evidence of crack arrest marking (CAM) at localized areas in 3.5 wt% NaCl solution, suggesting both anodic dissolution and hydrogen-induced cracking simultaneously govern the propagation of stress corrosion cracks. There is the forced more test time in the slower strain rate, and the accumulation of stress corrosion coupling damage accelerates with the time, eventually leading to the greater degradation in the stress corrosion resistance and the higher ISSRT.

Crack arrest characteristics and dynamic fracture parameters of moving cracks encountering double holes under impact loads

Brittle materials such as rock or concrete contain a large number of micro-cracks, voids, and other defects. Under external impacting loads, the interaction between fissures and holes affects the bearing capacity and stability of Engineering structures. To study the interaction mechanism between moving cracks and circular holes, a large-size semi-circular notched with a fissure and double circular hole (SNFDH) specimen was suggested in this research, and the dynamic fracture tests were carried out on the SNFDH specimens with different double circular hole spacing (35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, and 70 mm) using a drop hammer impact test device. Crack propagation gauges were employed to track the time and velocity at which the crack propagated along its trajectory. Dynamic Drucker-Prager yield criterion and cumulative damage failure criterion were used in the numerical simulation of the SNFDH concrete materials. The program AUTODYN was employed to simulate the crack growth characteristics when a crack encounters the double hole. The program ABAQUS was applied to calculate the dynamic fracture parameters of cracks. The test results manifest that the crack propagating trajectory has three different characteristics according to the double hole spacing; the double circular hole has an arresting function for a moving crack; the size of the double hole spacing has a significant effect on the crack propagating velocity, crack propagating length, dynamic stress intensity factor and dynamic energy release rate; the configuration of the SNFDH specimen can be used to investigate the crack arrest mechanism when moving crack encountering double holes.

Impact of elevated loading rates on the shape of the Master Curve (ASTM E1921) for a German RPV steel

The Master Curve Methodology (ASTM E1921) experimentally assesses a materials temperature-dependent fracture toughness, predominantly for quasi-static testing conditions. The treatment of elevated loading rates is described by the annex A1 of ASTM E1921 and A14 of ASTM E1820. This paper presents results of the evaluation of a large and standard-conforming database in order to verify the procedures recommended by the standard for elevated loading rates. Testing involved C(T)- and SEN(B)-specimens of the RPV-steel 22NiMoCr3-7 (A508 Grade 2) for loading rates of 100 MPa√m/s ≤ K̇ ≤ 104 MPa√m/s in the ductile to brittle transition region. While valid T0-values were found, single-temperature T0-values were observed to differ more than expected from multi-temperature T0-values, which cannot be explained by the Master Curve uncertainty. The shape and underlying distribution of the Master Curve show deviations with increased loading rate. The shape factor p is optimized with respect to the individual data, and it increases with K̇, but deviations are not completely overcome. This can be linked to a change in distribution, which was demonstrated by an optimization of minimum fracture toughness Kmin, which increases with temperature. It is argued that the cause for the observations is linked to both heating processes and local crack arrest that severely influence macroscopic fracture behavior. Also, an individual adjustment of p or Kmin is not helpful due to the material-dependency in practice. It is recommended that fracture mechanics testing at elevated loading rates is performed close to or below T0 in order to minimize the influence of dynamic loading conditions on the assessment.

An analytical model for predicting fatigue crack arrest and growth behavior in metal plates strengthened with unbonded prestressed reinforcing strips

Fatigue crack arrest and life extension of metallic structures can be achieved by using prestressed strips for fatigue strengthening. However, the popularization of prestressed strengthening techniques has been limited by lack of versatile analytical methods. In this paper, an analytical method is developed for predicting the fatigue behavior of centrally cracked metal plates after being anchored with prestressed reinforcing strips, based on linear elastic fracture mechanics and the superposition method of stress intensity factors. The force transfer between reinforcing strips and metal cracked plates is modeled using the displacement compatibility principle. The finite-width correction factor for centrally cracked metal plates subjected to four-point concentrated forces is derived, allowing the model to analyze the effect of different anchorage locations on the effectiveness of strengthening. The analytical model is validated through experimental data and finite element analysis. The results show that the model is highly accurate and can be used to analyze how different anchorage locations affect fatigue reinforcement.

A proposal for the combined analysis of bone quantity and quality of human cortical bone by quasi-brittle fracture mechanics

Quasi-brittle fracture mechanics is used to evaluate fracture of human cortical bone in aging. The approach is demonstrated using cortical bone bars extracted from one 92-year-old human male cadaver. In-situ fracture mechanics experiments in a 3D X-ray microscope are conducted. The evolution of the fracture process zone is documented. Fully developed fracture process zone lengths at peak load are found to span about three osteon diameters. Crack deflection and arrest at cement lines is a key process to build extrinsic toughness. Strength and toughness are found as size-dependent, not only for laboratory-scale experimental specimens but also for the whole femur. A scaling law for the length fracture process zone is used. Then, size-independent, tissue fracture properties are calculated. Linear elastic fracture mechanics applied to laboratory beam specimens underestimates the tissue toughness by 60%. Tissue fracture properties are used to predict the load capacity of the femur in bending within the range of documented data. The quasi-brittle fracture mechanics approach allows for the assessment of the combined effect of bone quantity and bone quality on fracture risk. However, further work is needed considering a larger range of subjects and in the model validation at the organ length scale.

A phase field finite element study and evaluation of sulfide stress cracking in DCB specimen testing

The challenges presented by sour environments rich in hydrogen sulfide (H2S) underscore the necessity for a comprehensive understanding of material behavior under such conditions. The cracking susceptibility of metals and alloys used for subsurface equipment in downhole oil and gas exploration operations is particularly concerning. The NACE Double Cantilever Beam (DCB) test has emerged as a widely used quality assurance tool in the petroleum industry, leveraging fracture mechanics principles to assess the environment-assisted cracking (EAC) resistance of metals and alloys. The DCB test evaluates the fracture toughness KISSC of materials in H2S-containing environments via assessment of the crack arrest, which serves as a vital parameter in structural integrity assessments to mitigate the risk of service-related failures from sulfide stress cracking (SSC). However, various studies suggest that different test parameters, such as arm displacement and initial notch, significantly influence KISSC. This work presents a detailed numerical investigation on a comprehensive simulation of the DCB test, examining the effects of different test parameters on KISSC prediction. A coupled deformation-diffusion phase field framework is adopted to simulate SSC in DCB specimens arising from a complex interplay between material deformation, hydrogen diffusion, and fracture. The numerical results show good agreement with experimental results reported in the literature and provide deeper insights into the factors affecting crack growth and arrest in DCB testing.

Tailoring mechanical, microstructural and toughening characteristics of plasma-sprayed graphene-reinforced samarium niobate coatings for extreme environments

Thermal barrier coatings (TBCs) are advanced ceramic layers applied to metal components to provide insulation and protection against high temperatures in extreme operating environments. This study investigated the effects of graphene nanoplatelet (GNP) reinforcement on samarium niobate (SN: SmNbO4) TBCs for extreme environments. Four ceramic top coat compositions were plasma-sprayed onto Inconel 718 substrates: Yttria-stabilized zirconia (YSZ), SmNbO4 (SN), and SN reinforced with 1 and 1.5 wt% GNPs (SN-1GNP, SN-1.5GNP). The research examined microstructural characteristics, phase evolution, mechanical properties and toughening mechanisms. GNP reinforcement significantly improved coating density, with SN-1.5GNP reaching 97.4 ± 1.64% compared to 91.3 ± 1.69% for SN and 86.6 ± 1.47% for YSZ. Hardness and elastic modulus were enhanced by 86.38% and 57.91% for SN-1GNP, and 101.09% and 65.23% for SN-1.5GNP respectively. Moreover, fracture toughness experienced a significant increase from 1.86 ± 0.4 to 5.48 ± 0.7 MPa·m1/2, facilitated by toughening mechanisms, like splat bridging, GNP pull-out, crack arrest and ferroelastic domain switching. Additionally, the SN-1.5GNP coating exhibited a higher adhesion strength of 36.84 MPa, thereby leading to improved layer distribution and lesser chance of delamination. Compared to YSZ, these findings suggest that GNP-reinforced SN coatings offer enhanced performance for extreme environment applications.

Additively manufactured Nb-Ti-Si based alloy: As-built and heat-treated conditions

This work aims to fully characterise the Nb-Ti-Si based alloy (Nb-26Ti-16Si-2.2Al-2Cr), processed by the electron-beam powder-bed-fusion in both as-built and heat-treated conditions, to elucidate the microstructure-property relationships. The as-built condition has [001]-oriented columnar grains of the Nb3Si phase with the Nbss phase dispersed throughout the microstructure. The microhardness is 645.2 ± 6.7 HV0.5, and the indentation fracture toughness shows distinct directionality: 7.7 MPa·m1/2 in the horizontal direction compared to 5.3 MPa·m1/2 in the vertical direction. Both properties are comparable to the cast version. The directionality is attributed to the underlying mechanisms such as crack bridging, arrest, and micro-crack formation. By contrast, in the heat-treated condition, the alloy exhibits a dual-phase microstructure (Nbss and Nb5Si3 phases) with near-equiaxed grain shape due to the Nb3Si phase decomposition. The fracture toughness increases to 12.1 MPa·m1/2, at the expense of a reduced microhardness of 564.4 ± 15.0 HV0.5.

Short Fatigue-Crack Growth from Crack-like Defects under Completely Reversed Loading Predicted Based on Cyclic R-Curve.

Understanding short fatigue-crack propagation behavior is inevitable in the defect-tolerant design of structures. Short cracks propagate differently from long cracks, and the amount of crack closure plays a key role in the propagation behavior of short cracks. In the present paper, the buildup of fatigue-crack closure due to plasticity with crack extension from crack-like defects is simulated with a modified strip yield model, which leaves plastic stretch in the wake of the advancing crack. Crack-like defects are assumed to be closure-free and do not close even under compression. The effect of the size of crack-like defects on the growth and arrest of short cracks was systematically investigated and the cyclic R-curve derived. The cyclic R-curve determined under constant amplitude loading of multiple specimens is confirmed to be independent of the initial defect length. Load-shedding and ΔK-constant loading tests are employed to extend the cyclic R-curve beyond the fatigue limit determined under constant amplitude loading. The initiation stage of cracks is taken into account in R-curves when applied to smooth specimens.

Establishment of a one-dimensional model for CO2 Pipeline rupture process and design recommendations

Pipelines serve as a critical means of transporting CO2 within Carbon Capture, Utilization, and Storage (CCUS) technology. Elevated transport pressures may lead to unforeseen pipeline ruptures. To provide practical recommendations for the design of CO2 pipelines and mitigate the risk of ruptures, this study establishes a one-dimensional Homogeneous Equilibrium Mixture (HEM) model. The model is currently used to predict the decompression behavior in existing pure CO2 rupture tests. Future work will address rupture tests and predictions involving impure CO2. The results indicate that due to differences in pressure reduction caused by decompression waves, the likelihood of long-range ruptures occurring in density CO2 pipelines is lower compared to supercritical CO2 pipelines. The crack propagation velocity and crack arrest pressure of pipelines designed according to ASME B31.3 are calculated using the High Strength Line Pipe Committee (HLP) model. Although the crack propagation velocity is lower than the decompression wave speed, the crack arrest pressure may fall below the rupture pressure, with the pressure at 1.6 m from the rupture point remaining above the crack arrest level for 1 ms post-rupture, a duration that is especially prolonged in larger-diameter pipelines. It is recommended to consider additional thickness beyond the calculated minimum thickness.

Synergic effects of silica aerogel (SA) particles on tensile behavior of cryo-conditioned epoxy: The role of particle morphology and mixing sequence

Cryogenic conditions are of crucial importance for gas storage tanks to provide increased storage density, reduced pressure requirements and minimized energy losses. Incorporation of silica aerogel (SA) particles as a nanostructured material with extremely low density and exceptional thermal insulating properties into epoxy matrices has the potential to facilitate the progress of high performance nanocomposite coatings for advanced cryogenic applications. The objective of this study is therefore to investigate the impacts of particle size, particle content, milling method and mixing sequence on toughness of the cryo-conditioned epoxy coatings. SA particles of varying size (50 μm to 300 μm) were prepared using two different techniques (planetary ball milling vs. 2-blade grinding). Nanocomposite samples were prepared using two distinct mixing sequences, i.e., adding particles (in 0, 0.5, 1 and 1.5%wt.) to epoxy followed by mixing with hardener or adding particles to epoxy/hardener (with 3 or 15 min delay). The nanocomposite samples were subjected to different cryogenic conditions (single 3-h immersion in liquid nitrogen vs. three consecutive 1-h immersions). Mechanical properties of the samples were evaluated by conducting fractography, dynamic mechanical thermal analysis (DMTA) and tensile tests. Large SA particles settled towards the bottom of nanocomposite and resulted in loss of mechanical properties at cryo-conditions. Mixing 1 wt% of optimized SA particles with epoxy/hardener system led to an enhanced tensile strength (26 %), stiffness (3 %) and toughness (71 %) by providing uniform cross-linking reactions and mitigating thermal shock effects at cryo-conditions. Toughening mechanisms included crack deflection, crack pinning, crack arrest and crack branching.

A prediction model of brittle crack arrest toughness in TMCP heavy plates

Micro-alloyed low carbon MnCrNiCuMo steels were proposed to produce heavy plates with a maximum thickness of 100 mm. An integrated industrial route including a thermo-mechanical control process (TMCP) based on a study on continuous cooling transformation was applied in industrial production. Comprehensive mechanical properties tests including the measurement on resistance against crack initiation using crack tip opening displacement (CTOD) approach were conducted. Large scale wide-plate temperature gradient double tension (DT) technique was employed to evaluate the crack arrest toughness Kca in the heavy plates under different conditions. Nil-ductility transition temperature (NDTT) was also tested across the entire thickness section of the plates. The results showed that heavy steel plates were qualified being brittle crack arrest (BCA) products at EH47 grade with yield strength high than 460 MPa. High crack initiation toughness was exhibited by both Charpy-V notch impact property and CTOD values. Crack arrest toughness at −10 °C greater than 253 MPa √m was achieved in a plate even with thickness of 100 mm. The mean value of crack arrest toughness at different temperature measured by the DT approach can be indexed by the highest NDTT in the interior section of the heavy plates leading to an empirical prediction model. Further, fracture mechanics based master curve approach was used to statistically predict crack arrest toughness distribution over a wide range of temperatures showing improved predictability over the empirical model and an existing model in the literature.

Enhancing the fracture resistance of additive manufactured polylactic acid via Morse-code-like architecturing

Additively manufactured poly-lactic acid (PLA) suffers from a limited fracture resistance. In this study, a combination of circular hole (dot) and elliptical hole (dash) architectures inspired from the Morse-Code are incorporated into (PLA) through additive manufacturing (AM) to improve their fracture resistance. The circular hole-like (C) features work as crack arrestors and the elliptical hole-like (E) features work as crack deflectors. A combination of simulations and experiments are performed to quantifiably determine the effect of single feature, double features, and other tailored arrangements of these features on the crack driving force and fracture resistance using elastic-plastic fracture mechanics. All the AM architecture systems show a significantly higher fracture resistance compared to the bulk AM PLA. Amongst the various systems tested, both the initiation work of fracture and total work of fracture are found to be the highest for alternative layers of E-C features. A 1172 % increase is observed from initiation to total work of fracture for the EC architecture, which is reflected in the fracture resistance curve (R-curve). This has important applications in the structural integrity and life of biomedical systems made from PLA. The applicability of work of fracture and conventional fracture mechanics for additively manufactured, architected systems with significant crack tip plasticity is also discussed.

Analysis of properties and microstructure of ASTM 5% Ni steel used for cryogenic pressure vessel

The influence of the QLT (quenching + lamellarizing + tempering) heat treatment process on the structure and properties of ASTM 5% Ni steel is analyzed. Using QLT heat treatment is to improve the cryogenic toughness of steel, which is generally just related to the reversed austenite. The present study deals with the analysis of the role of QLT heat treatment on structure transformation by researching the relationship among QLT, reversed austenite, and cryogenic toughness. After QLT heat treatment, the structure of ASTM 5% Ni steel transforms from coarse F + B to uniform and fine-tempered sorbite. Grain refinement and high dislocation density bring excellent comprehensive mechanical properties. Alloying elements influence the process and results of the phase transformation of austenite and martensite by getting into them to form new segregation structural units. The oscillographic impact results show that unstable crack growth does not occur during the fracture process. The fracture is upper platform type, which indicates that 5% Ni steel has good cryogenic crack arrest performance. Austenite is not found in the structure under X-ray and transmission electron microscope. The results of the electronic probe indicate the condition of creating conversed austenite is not met. So, the good low-temperature toughness is not from austenite but grain refinement and the increase of the ratio of the large angular grain boundary. This study not only provides proof that the QLT process is not the only factor in the forming of reversed austenite, but also gives inspiration that cryogenic toughness should not rely too much on the reversed austenite.

Definitive engineering strength and fracture toughness of graphene through on-chip nanomechanics

Fail-safe design of devices requires robust integrity assessment procedures which are still absent for 2D materials, hence affecting transfer to applications. Here, a combined on-chip tension and cracking method, and associated data reduction scheme have been developed to determine the fracture toughness and strength of monolayer-monodomain-freestanding graphene. Myriads of specimens are generated providing statistical data. The crack arrest tests provide a definitive fracture toughness of 4.4 MPam\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{{{{{{\\rm{m}}}}}}}$$\\end{document}. Tension on-chip provides Young’s modulus of 950 GPa, fracture strain of 11%, and tensile strength up to 110 GPa, reaching a record of stored elastic energy ~6 GJ m−3 as confirmed by thermodynamics and quantized fracture mechanics. A ~ 1.4 nm crack size is often found responsible for graphene failure, connected to 5-7 pair defects. Micron-sized graphene membranes and smaller can be produced defect-free, and design rules can be based on 110 GPa strength. For larger areas, a fail-safe design should be based on a maximum 57 GPa strength.