Fracture Speed Research Articles

Omega and CTOA for dynamic steady-state fracture propagation and their dependency to fracture speed

Dynamic ductile fracture in pressure vessels is an increasingly important topic. Recent catastrophic pressurised pipeline failures highlighted the critical needs of reliable pipeline infrastructures. The ability for line pipe steels to resist fracture is a critical design factor for governing the severity level of fracture failures given that it determines if fracture propagates for several kilometres or is arrested quickly. Developing a reliable fracture toughness test to systematically evaluate new steel products’ quality is therefore important. In the current work, a novel small-scale fracture toughness parameter Omega was implemented and compared to the well-established parameter CTOA, with respect to their performance of characterizing steady-state fracture propagation and their dependencies to Fracture Speed. The current experimental data were collected from a 3-point bend dynamic Drop Weight Tear Test (DWTT) for 9 line pipe steels with different thicknesses and impact conditions. It was found that the Omega gives significantly better description for steady-state fracture propagation; and it is found to be independent of the Fracture Speed. The current study confirmed that in DWTT, CTOA values decrease with increasing Fracture Speed. Finally, a simple analytical model is proposed to describe this dependency (CTOA-Fracture Speed) from a geometrical standpoint.

Fracture toughness of 3D printed denture teeth.

Advances in digital dentistry lead to use of three-dimensional (3D) printed resin denture teeth. Fracture toughness of these teeth must be assessed. This study aimed to compare the chipping and indirect tensile fracture resistance of denture teeth fabricated by 3D printing technique with traditionally fabricated resin denture teeth. Four groups (Gr) were made (n= 50/group): Gr-1 3D printed denture teeth (denture teeth; Formlabs Inc., Somerville, MA, USA), Gr-2 SR-Orthosit-PE (Ivoclar Vivadent AG), Gr-3 Portrait IPN (Dentsply Sirona), Gr-4 Pala Premium 8 (Heraeus Kulzer GmbH). Stereolithography 3D printing was used to create the methacrylate-based photopolymerized resin teeth models and remaining group teeth were collected commercially. A 1 mm/min chipping and indirect tensile fracture speed tests were carried out till fracture occurred. The data so obtained were statistically analysed using one-way analysis of variance with Tukey's honestly significant difference multiple comparisons test (p< 0.05). At the end of the test, the fractured areas of the specimens were evaluated by the chief researcher to assess the fracture pattern of the teeth. The indirect tensile fracture values of the 3D printed teeth were more than that of Pala Premium-8 and SR-Orthosit-PE but it was lower than that of Portrait IPN teeth. In chipping test, buccal chipping of the loaded cusp was seen in 3D printed resin without distortion and in indirect tensile test in 3D printed resin teeth, line of fracture emerges near the loading point propagates from the inner incline of both cusps and extends cervically, unlike in other groups where first deformation occurs then fracture. Prosthetic teeth fabricated by the 3D printing technique using printable resin material provide adequate fracture resistance as denture teeth.

Failure energy evolution of coal–rock combination with different inclinations

In this paper, in the deformation and damage process under different confining pressures, the energy evolution characteristics and damage mechanism of coal–rock combinations with different inclination angles are studied. Based on the brittleness indexes of coal rock combinations, the evolution rules between brittleness indexes and the inclination are explored, as well as the confining pressure of coal rock combinations; then, the influence mechanism of the inclination angle of coal rock combinations on the plastic yielding degree, energy dissipation level, crack extension and fracture speed in the pre-peak stage is revealed. The composite specimens are mainly damaged due to oblique shear and accompanied by tensile damage; In the deformation and damage, various energies of coal rock composites are distributed as a negative exponential function of the inclination angle, which is significantly affected by the change of the confining pressure.

Sliding Friction and Wear Characteristics of Wire Rope Contact with Sheave under Long-Distance Transmission Conditions.

Wire rope has different degrees of surface wear under long-distance transmission conditions, which leads to performance degradation and greatly threatens its safety and reliability in service. In this paper, friction and wear tests between the transmission wire rope and sheave under different sliding velocities (from 0.8 m/s to 1.6 m/s) were carried out using a homemade test rig. The material of the steel wires was low carbon steel, and pulley material was ASTM A36 steel plate. The sliding friction coefficient (COF), friction temperature rise, wear characteristic parameters and wear mechanisms of the wire rope were analyzed. Additionally, the effect of different wear on the fracture behavior of the wire rope was investigated by a breaking tensile test. The results show that the average COF in the relatively stable stage decreased from approximately 0.58 to 0.51 with the increase of sliding velocity. The temperature rise of the wire rope increased rapidly with an increase of sliding velocity, from approximately 52.7 °C to 116.2 °C. The maximum wear width was the smallest when the sliding velocity was 1.2 m/s (approximately 1.5 mm). The surface wear was characterized by spalling, furrowing and plastic deformation, which are strongly affected by the sliding velocity. The wear mechanisms of the wire rope were mainly adhesive wear and abrasive wear. Surface wear changes the fracture morphology of the wire rope and accelerates its fracture speed.

Fatigue Fracture Analysis on 2524 Aluminum Alloy with the Influence of Creep-Aging Forming Processes.

The different creep-aging forming processes of 2524 aluminum alloy were taken as the research object, and the effects of creep-aging temperature and creep stress on the fatigue-crack propagation properties of the alloy were studied. The research results showed the following under the same sintering time of 9 h, at creep-aging temperatures of 100 °C, 130 °C, 160 °C, and 180 °C, respectively, with an increase in creep-aging temperature: the fatigue-crack propagation rate was promoted, the spacing of fatigue striations increased, and the sizes of dimples decreased while the number was enlarged; this proves that the fatigue property of the alloy was weakened. Compared with the specimens with creep deformation radii of 1000 mm and 1500 mm, the creep deformation stress was the smallest when the forming radius was 1800 mm, with a higher threshold value of fatigue-crack growth in the near-threshold region of fatigue-crack propagation (ΔK ≤ 8 MPa·m1/2). Under the same fatigue cycle, the specimens under the action of larger creep stress endured a longer fatigue stable-propagation time and a faster fracture speed. Comparing the effect of creep-aging temperature and creep stress, the creep-aging temperature plays a dominant role in the fatigue-crack propagation of creep-aged 2524 aluminum alloy.

The whole fatigue crack propagation life prediction of Ni-based single crystal super-alloy specimen with single hole based on EIFS and ‘Fish-eye’ theory

In this work, based on the ‘Fish-eye’ theory and EIFS method, a prediction model of the whole fatigue crack propagation life of the predictable structure under multi-axial stress fatigue is proposed. Then, the fatigue crack propagation life of single-hole nickel-based single crystal superalloy samples under nine working conditions was predicted and verified by finite element simulation. Finally, the effects of three loads and three initial crack lengths on the fatigue crack propagation life of single-hole nickel-based single crystal superalloy were discussed by finite element simulation. The results show that the analysis results of the theoretical model and the finite element model proposed in this work are basically consistent under certain conditions. It is found that the fatigue crack propagation life of the initial crack stage, short crack stage and long crack stage accounts for 2%, 6%–10% and 90% of the whole crack propagation fatigue crack propagation life, respectively. Under the same loading stress condition, the higher the proportion of short crack stage in crack propagation is, the faster the fracture speed of the sample is. At the same time, the progressive crack propagation process of single hole specimen under fatigue load can be seen through the calculation results of finite element model. The above conclusions provide a good theoretical reference for the design and fatigue crack propagation life prediction of nickel-based single crystal superalloy turbine blades with cooling film holes.

Damage mechanisms and energy absorption of aluminosilicate glass under compression/tensile loading

The transparent laminated structures having annealed and tempered glass layer with adjoining interlayer are used increasingly in aircrafts, high-speed trains, and important installations. In a pursuit to realize the fracture initiation, propagation, speed, path, and catastrophic failure to dynamic impact event in brittle materials like (annealed and tempered) silicate glass are experimentally analyzed in this research article undergoing tensile and compression loading. The Kolsky bar system linked with high-speed framing camera is applied to record the deformation images of glass samples for compression/tensile dynamic loading. The captured images are studied to identify the damage development and final rupture of silicate glass specimens. The stress-time history curves were related with recorded high-speed stills to enlighten the load-bearing capacity and damage accumulation in glass specimens. The stress–strain relations from two types of loading were used to envisage the energy absorption capability of annealed and tempered glass. The collected debris after test suggested that both glass types are loading-rate sensitive and the tempered glass dices in fine particles than annealed glass. In compression, and tensile loading mode the maximum energy was absorbed in by tempered glass which supports the use of this type of glass in impact resistant transparent laminated structures. The microscopic and scan electron microscope (SEM) pictures of collected fragments were also analyze to observe the failure mechanism and fracture surfaces in two types of glasses.

Dynamic characteristics of deposit fracture and impacts of operating pressure during sootblowing in the radiant syngas cooler

AbstractDuring the operation of entrained‐flow gasifiers, the ash deposits located on the wall tubes in the radiant syngas coolers (RSC) reduce the heat transfer efficiency. Syngas sootblowing is an effective method to remove the slag deposits in the RSC. In this study, a 3D numerical model was developed by combining the cohesive zone method (CZM) and the coupled Eulerian–Lagrangian analysis to investigate the deposit fracture process in RSC during sootblowing. The quasi‐static analysis using ABAQUS obtained the stress–strain curve of the slag sample, which agreed well with the experimental tests and provided the detailed mechanical parameters to the CZM model. The dynamic characteristics of deposit fracture were discovered. The main fracture occurred between 1.0 and 1.5 ms, and the shape of the fracture area was not round but elliptical. The RSC operating pressure (P) was also investigated. The study found that higher pressure led to lower fracture speed, longer sootblowing time, and more syngas consumption. Based on the same extent of deposit fracture, syngas consumption increased when P &lt; 3.5 MPa, and the density of syngas (ρsyngas) has a more significant influence on the syngas consumption than the velocity of sootblowing syngas flow (vavg), especially when the sootblowing time is small.

Dynamic crack growth along heterogeneous planar interfaces: Interaction with unidimensional strips

We examine theoretically and numerically fast propagation of a tensile crack along unidimensional strips with periodically evolving toughness. In such dynamic fracture regimes, crack front waves form and transport front disturbances along the crack edge at speed less than the Rayleigh wave speed and depending on the crack speed. In this configuration, standing front waves dictate the spatiotemporal evolution of the local crack front speed, which takes a specific scaling form. Analytical examination of both the short-time and long-time limits of the problem reveals the parameter dependency with strip wavelength, toughness contrast and overall fracture speed. Implications and generalization to unidimensional strips of arbitrary shape are lastly discussed.

Case study of hydraulic fracture monitoring using multiwell integrated analysis based on low-frequency DAS data

Distributed acoustic sensing (DAS) is an effective technique for hydraulic fracture monitoring. It can potentially constrain fracture propagation direction and time while monitoring strain perturbation, such as stress shadowing. In this study, we acquired passive DAS and distributed temperature sensing (DTS) data throughout the entire fracturing operations of adjacent production wells with varying offset lengths from the fiber-optic cable in the Montney tight gas area. We applied data processing techniques to the DAS data to extract low-frequency components (less than 0.5 Hz) and to construct the strain rate and cumulative strain maps for detecting responses related to fracture hits along the fiber-optic cable. We used low-frequency DAS (LF-DAS) results to estimate the fracture hit position and time, and in certain cases, to additionally estimate the fracture connection. By integrating LF-DAS results with DTS results, we detected the temperature changes around the compression response near the fracture hit position and time. Furthermore, we observed that timing of the fracture hit can be constrained more precisely by using high-frequency DAS data (greater than 10 Hz). We estimated the fracture propagation direction and speed from the estimated fracture hit position and time. The fracture propagation direction deviated slightly from a perpendicular line to the fiber direction. In addition, as estimated from the first fracture hit time, the fracture length and fluid injection volume had a proportional relationship. Due to challenges associated with the data, it is important to design data acquisition geometry and fracturing operations on the premise of acquiring LF-DAS data. It is also important to apply an additional noise reduction process to the data.

Features of formation of karst falls on the earth’s surface

Karst manifestations are widespread in many regions and pose a significant danger to residence and economic activity. Failing funnels arise during the collapse of rocks over underground voids (caves, workings, etc.), formed during karst formation or in the process of anthropogenic doing in the rock massive. However, not every karst or technogenic cavity gives rise to a failure of the earth’s surface, and as a rule, its occurrence is unexpected. In this work, we consider the dynamics of the formation of dips of the earth’s surface in the form of a collapse pipe. To do this, the geomechanical problem is solved by the meshless code Smoothed Particle Hydrodynamics (SPH). The method allows to obtain a solution to the problem taking into account large deformations and possible discontinuities in the process of changing the stress-strain state. The Drucker-Prager fracture criterion is used, the parameters of which change over time in accordance with the accumulation of damage, which determines the temporary development of the fracture process, its beginning and speed. Various options for the formation of a vertical dip are considered depending on the geometrical parameters of the initial cavity, its depth and materials composing the rock mass, as well as the features of the destruction of various materials composing the mass during the formation of the dip. Relations are obtained that relate the depth of the cavity, the horizontal size of the hole, the strength properties of the rocks (adhesion, angle of internal friction), the coefficient of lateral pressure in the array. The features of wave processes generated by the formation of a dip are considered, for which a velocity field is obtained near the fracture zone at various time points in the fracture process.

Spinal sagittal balance associated with age, vertebral fracture, and functional disability in patients with rheumatoid arthritis: A cross-sectional study

Objectives: The purpose of this study was to assess the relationships between spinal sagittal balance and functional ability of Japanese patients with rheumatoid arthritis.Methods: A total of 491 patients with rheumatoid arthritis who underwent the measurement of sagittal vertical axis for the assessment of spinal sagittal balance were enrolled. Factors associated with sagittal vertical axis were analyzed by categorizing patients according to sagittal vertical axis (<4 cm, 4–9.5 cm, and >9.5 cm). In addition, univariate and multivariate regression analysis were performed to identify factors associated with Health Assessment Questionnaire Disability Index (HAQ-DI) in different age groups.Results: The percentage of patients with sagittal vertical axis <4 cm, 4–9.5 cm, and >9.5 cm was 61.1%, 32.4%, and 6.5%, respectively. Age, vertebral fracture, and gait speed were associated with sagittal vertical axis. Sagittal vertical axis was associated with HAQ-DI in the 80–90 years age group.Conclusion: Sagittal balance was associated with age, vertebral fracture, and gait speed. In super-aged patients with rheumatoid arthritis, HAQ-DI was affected by sagittal balance. Management of super-aged patients with rheumatoid arthritis should include evaluation of joints as well as spinal alignment.

Control of bacterial attachment by fracture topography

In the biomedical arena, bacterial fouling is a precursor to complications such as implant infection and nosocomial infection. These complications are further compounded by biochemical mechanisms of resistance that threaten the action of traditional antibacterial strategies. Accordingly, antibacterial property by physical, not biochemical, mechanisms of action is becoming increasingly popular and promising. The present work falls in line with this paradigm shift. Here, microtextured Ti-6Al-4V surfaces were manufactured by destructive tension at three different cross-head speeds, probed with scanning electron microscopy (SEM) and multifocus optical microscopy, and treated with Staphylococcus aureus to study bacterial attachment. The fractographic study revealed the presence of dual-mode fracture, typical of Ti-6Al-4V, comprising  regions of both ductile, microvoid coalescence and brittle, cleavage faceting. Based on load-extension curves, quantitative roughness data, and qualitative SEM visualisation, it was evident that cross-head speed modulated fracture behaviour such that increased speed produced more brittle fracture whilst lower speeds produced more ductile fracture. The topography associated with ductile fracture was found to possess notable antibiofouling property due to geometric constrains imposed by the coalesced microvoids. Accordingly, fracture at low cross-head speeds (1 mm/min and 10 mm/min) yielded significant reduction in bacterial attachment, whilst fracture at high cross-head speeds (100 mm/min) did not. The greatest reduction (~72%) was achieved at a cross-head speed of 1 mm/min. These findings suggest that antibiofouling property can be elicited by fracture and further ‘tuned’ by fracture speed. Discovery of this novel, albeit simple, avenue for topography-mediated antibacterial property calls for further research into alternate techniques for the manufacture of ‘physical antibacterial surfaces’.

Study on Fracture-Split Performance of 36MnVS4 and Analysis of Fracture-Split Easily-Induced Defects

The material 36MnVS4 is the second generation of connecting rod fracture-split material. However, it generates more quality defects during the fracture-split process. To investigate the causes of defects that occurred, the material properties and fracture-split performance of the 36MnVS4 are researched and compared with C70S6. The fracture-split easily-induced defects are also analyzed. By finite element simulation and experimental analysis, the results show that the 36MnVS4 has lower carbon content and more ferrite, therefore the fracture surface of the 36MnVS4 connecting rod is more prone to tears and the plastic deformation range is greater. The fracture speed of the 36MnVS4 connecting rod is 20% lower than that of the C70S6 connecting rod. The slower fracture separation rate increases the possibility of defects generation. The crack initiation position of the 36MnVS4 connecting rod is random, scattered, and unstable, and the 36MnVS4 has higher gap sensitivity. Therefore, the 36MnVS4 connecting rod is more prone to produce quality defects in the fracture-split process. By changing the cross-section design, the outer edge of the joint surface is changed to arc-shaped, which can improve the fracture-split process of the 36MnVS4 connecting rod and reduce the processing defects.

A fracture-propagation-control model for pipelines transporting [formula omitted]-rich mixtures including a new method for material-model calibration

This work considers a predictive numerical modelling approach for fracture-propagation control in CO2-transport pipelines, an area where current engineering tools do not work. Fluid–structure interaction model simulations are compared with three published medium-scale crack-arrest experiments with CO2-rich mixtures. The fluid flow is calculated by a one-dimensional homogeneous equilibrium model, and the thermodynamic properties of CO2 are modelled using the Span–Wagner and the Peng–Robinson equation of state. The pipe material is represented by a finite-element model taking into account large deformations and fracture propagation. Material data commonly found in the literature for steel pipes in crack-arrest experiments is not sufficient to directly calibrate the material model used here. A novel three-step calibration procedure is proposed to fill the information gap in the material data. The resulting material model is based on J2 plasticity and a phenomenological ductile fracture criterion. It is shown that the numerical model provides good predictions of the pressure along the pipe, the ductile fracture speed and a conservative estimate of the final crack length. An approximately plane-strain stress state ahead of crack tip implies that a fracture criterion accounting for a wide range of stress states is not necessary.

Transient wave in a transformable periodic flexural structure

The analysis of a transition wave propagating in a finite heterogeneous discrete beam strip, composed of periodically placed masses and subjected to a harmonic load is presented. The load is assumed to be located sufficiently far away from the transition front. As waves propagate inside the structure, connections are broken and we investigate how this process evolves from the transient regime to the steady-state regime. It is found that the steady-state speed of this transition process, in the averaged sense, coincides with the predicted phase speed of the transition wave. For a given heterogeneity, we show that a transition wave can propagate steadily if the load amplitude and frequency are situated in a parameter subdomain. The steady-state regime does not exist outside of this domain. At a given load frequency, it is demonstrated that the average speed of fracture is independent of the load amplitude within a given steady-state domain and the number of such domains depends on the load frequency and structural heterogeneity. During the transition process, we identify several dynamic effects, including regimes where waves can be transmitted ahead of the front into the structure and the development of an inclination that follows the transition front in the steady-state regime. The occurrence of such effects and their behaviour also correspond to predictions from the theory. We show although the theoretical steady-state fracture regimes are realised globally, locally the fracture speed always behaves in a regular fashion.

Determination of two key parameters of a cohesive zone model for pipeline steels based on uniaxial stress-strain curve

It is widely believed that maximum traction of traction-separation law (TSL) and cohesive energy are the two key parameters of cohesive zone model (CZM). A method is presented in this paper to determine the two key CZM parameters for pipeline steels. The maximum traction of TSL is given by the critical stress defined based on damage at fracture point from the true stress-strain curve. And the other key parameter, cohesive energy defined as the area under the curve of TSL and usually considered as the critical J-integral, is estimated from a simple tensile test simulation. The two key CZM parameters obtained by the present method are validated for dynamic fracture of pipeline steels. Both load-displacement curves and crack tip opening angle (CTOA)-fracture speed curves showed that the two key CZM parameters determined by the present method are reasonable, and dynamic fracture behavior predicted based on the two predicted key CZM parameters well agree with some known test data and previous work.

Application of peridynamic stress intensity factors to dynamic fracture initiation and propagation

A non-local formulation of the classical continuum mechanics theory called peridynamics is used to study initiation and propagation of dynamic fractures. The purpose of this study is twofold. First, we introduce a new post-processing technique to estimate stress intensity factors using peridynamic data. Second, the peridynamic stress intensity factors are used to study the influence of loading rate on key aspects of dynamic fracture. In particular attention is focused on examining the influence of loading rate and material properties on time to fracture and the local stress state at the fracture tip during initiation and propagation. In the first part of the paper emphasis is placed on using stress intensity factors to verify the numerical method. Simulations are performed on simplified test cases and the results are compared to relevant experimental and numerical studies found in the literature. Peridynamic stress intensity factors are then used to demonstrate the influence of loading rate on fracture initiation and propagation. To this end simulations are performed by partially loading the internal surfaces of a notch at various loading rates and monitoring the stress intensity at the tip of the notch. For each loading rate, the stress intensity factor increases smoothly to a value above the input fracture toughness at which point initiation occurs. After initiation, the stress intensity factor remains nearly constant in time. It is shown that the stress intensity factor at initiation and the time to fracture depend on the loading rate. Predictions show that the critical stress intensity is insensitive to loading rate when the fracture initiation time is below a material-dependent characteristic time scale. As loading rate increases, the time to fracture decreases and stress intensity at initiation increases markedly. The characteristic time-scale is shown to be only dependent on the material stiffness and independent of the strength of the singularity at the fracture tip. In our simulations, increasing the loading rate resulted in fracture branching. Also, the fracture speed increases with loading rate. However, the dynamic stress intensity factor of a propagating fracture is shown to be independent of loading conditions for a linear peridynamic solid with rate-independent input fracture toughness.

High-precision deformation and damage development assessment of composite materials by high-speed camera, high-frequency impulse and digital image correlation techniques

Abstract Although composite materials like wood, vulcanized fiber and carbon reinforced plastic (CFRP) are already investigated by means of their mechanical properties, the abrupt fracture mechanism as well as the deformation behavior right before and after fracture has not been investigated. However, it is marginally investigated for CFRP because of the quite high fracture speed. The knowledge about the damage evolution as the crack start and propagation can help to improve the strength and sensitivity to fracture by improving the materials structure and to utilize these materials for structural applications. For the investigated materials, fracture happens abruptly as it is the nature of composites and the detailed fracture mechanisms could not be detected by conventional measurement techniques. Therefore, an innovative combination of testing devices is presented which is able to fill this gap. Tensile tests were performed to receive conventional stress-strain curves. At the fracture stage, a high-speed camera recorded the fracture process. This information could be combined with digital image correlation (DIC) to visualize the deformation behavior. At the same time acoustic emission (AE) was used to detect the spectrum of mechanical vibrations which gives information about the released energy due to fracture. The challenging triggering of the high-speed camera was solved for each material individually. By using improved light sources, the recording speed could be set up to 2 million frames per second (Mfps). The investigations show different fracture mechanisms for each composite. Wood and vulcanized fiber were also investigated in different directions due to their anisotropy.

Analyze the Seismic Attributes in HSX Volcanic Fracture Based on Forward Modeling

This paper uses the Hassan Carboniferous fractured reservoirs as the goal, firstly it analyses the reservoir characteristics of the cracks. On this basis, it uses two-dimensional random fractured media modeling method to build three different fracture models with different fracture parameters (fracture density, dip and speed). Then it uses finite difference wave equation forward and pre-stack depth migration processing of these models, and analyses seismic attribute of the migrated data, finally it finds a variety of seismic attributes sensitive to cracks, lays the foundation for fracture prediction with the seismic multi-attributes.