Dynamic Crack Growth Research Articles

Investigation of IG-SCC Growth Kinetics in Al-Mg Alloys in Thin Film Environments

The effect of thin film environments on the intergranular stress corrosion cracking (IG-SCC) behavior of AA5083-H131 was investigated using fracture mechanics-based testing, high-fidelity monitoring of crack growth, and electrochemical potential measurements. A protocol for conducting thin film IG-SCC fracture mechanics experiments with anodized aluminum oxide membranes is developed and the ability to maintain films of specific thicknesses without impeding oxygen diffusion during testing is validated via electrochemical impedance spectroscopy testing and computational modeling. The IG-SCC susceptibility was found to increase once a critical thin film thickness of 82 μm was achieved; above this thickness a duality in IG-SCC susceptibility behavior was observed. These results are analyzed in the context of a coupled anodic dissolution and hydrogen (H) embrittlement mechanism, where susceptibility is found to scale with the cathodic limitation of the governing IG-SCC mechanism. Specifically, thinner film thicknesses led to limitations on the amount of cathodic current availability, which caused a decrease in the dissolution at the crack tip, a less aggressive crack chemistry development, and thus lower levels of H production. A close correlation between the open-circuit potential of the bulk surface and the crack growth kinetics was also observed, consistent with trends reported in previous IG-SCC studies on this alloy.

Analysis of cracks development in rock massif with the use of dynamic destruction resistance

The object of research: the process of development of main cracks in the massif of rocks under the action of a wave impulse taking into account the dynamic destruction resistance.
 Investigated problem: Description of the dynamics of crack development in the impulse mode of increasing their size, as well as the transition to an unstable mode of crack growth.
 The main scientific results: In the present article uses an approach based on the principle of least action and N-characteristic of dynamic crack growth resistance. This allowed to obtain analytical equations of the crack growth trajectory in the rock massif and the main characteristics of the process.
 The area of practical use of the research results: The considered approach allows to predict the formation of the shear surface in quarries and natural slopes. This approach also allows to set a time-varying probability of their steady state and adjust, if necessary, the parameters of blasting.
 Innovative technological product: Analytical regularities for the driving force of the crack and dynamic destruction resistance are obtained, which take into account the velocity and acceleration of the crack, as well as the time and nonstationarity of the impulse load.
 Scope of the innovative technological product: The proposed approach can be used in the design of blasting operations in quarries and in the calculation of the probabilities of the steady state of natural massifs under the influence of impulse loads.

Modeling and calculation of the fatigue crack growth life in structural steels

The kinetics of fatigue crack growth has been studied in tensile testing of compact steel tensile specimens (S(T)-type) in the middle section of the kinetic diagram of fatigue fracture (fatigue crack growth diagram) under regular and irregular loading with different asymmetry and maximum load values. The samples were tested on a BISS Nano-25kN servo-hydraulic machine. Standard loading spectra typical for different technical objects exposed to alternating loading during operation were used. The values of the crack growth rate per cycle in the loading block were obtained. Parameters for assessing the character of irregular loading and crack closure, namely, the irregularity factor and crack closure coefficient were proposed. When calculating the effective value of the range of the stress intensity factor (SIF) at the crack mouth, we propose also to take into account the loading irregularity in addition to the closure coefficient. With this approach, the obtained fatigue crack growth diagrams can be grouped into one equivalent curve, which is characteristic of regular loading with R = 0. Moreover, grouping of the fatigue crack growth diagrams provided the use of unified parameters when calculating the crack growth kinetics, regardless of the type and parameters of loading, which rather simplified the crack growth determination. The fatigue crack growth life was predicted taking into account the crack «closure» and the nature of loading according both to the approach developed by the authors and by cyclic calculation method (cycle-by-cycle). All the data obtained are tabulated and classed according to the type of loading. The calculation results and experimental data showed good convergence, which was confirmed by the high values of the correlation coefficient.

Fatigue damage prognosis of steel bridges under traffic loading using a time-based crack growth method

Traditionally, the fatigue damage assessment of steel bridges is conducted using cycle-based methods. Cycle-based methods require stress time history be transformed to cycle history first before fatigue analysis can be performed. However, well-defined cycle history does not exist for the traffic-induced stress time history of bridges as it contains numerous large and small cycles with random stress ranges embedded together. To address this inherent difficulty, a time-based fatigue crack growth (FCG) model is proposed for fatigue damage prognosis of steel bridges under traffic loading. The time-based FCG method describes the crack growth in the time domain through a crack growth kinetics function derived based on the physical mechanism of fatigue crack propagation. To demonstrate the proposed method, numerical simulations are first performed using full-scale coupled vehicle-bridge interaction framework to generate stress time histories of a typical steel bridge under traffic loading. Then, FCG analysis is performed using the time-based method and the effects of road surface roughness and vehicle weight on the FCG are studied. Finally, a case study on the I-10 Twin Span Bridge is presented to demonstrate the time-based FCG method for fatigue damage prognosis using in situ monitoring data. The results show that the proposed method can be used to directly predict the FCG of steel bridges in the time domain using stress time histories obtained either from stress analysis or in situ monitoring.

Stochastic Study on Discontinuous Slow Crack Growth Kinetics from an Arbitrarily Located Defect of Polyethylene Based on the Crack Layer Theory

The major failure aspect of high-density polyethylene pipes under the service condition is the discontinuous slow crack growth (DSCG) from the initial defects inside the pipe wall. In this study, the DSCG kinetics for an internal eccentric crack is theoretically simulated by developing a crack-layer growth model for an eccentric crack. The present model precisely mimics the experimental DSCG kinetics for the eccentric crack, and it also estimates the final failure time accurately. Furthermore, to investigate the reliability of the DSCG-dominated failure concerning the uncertainties related to the initial crack, a stochastic study on the lifetime distribution due to the probabilistic distribution of the initial crack size is performed. Additionally, lifetime distribution fitting using the Birnbaum–Saunders (B-S) distribution function and the maximum likelihood estimation method is conducted for various initial crack locations, sizes, and applied stresses. The B-S function accurately describes the simulated lifetime distribution, and the equations for estimating the scale and shape parameters of the B-S function with regard to the initial crack distributions at various crack locations and remote stress levels are presented.

Experimental study of crack propagation and failure around a horseshoe tunnel during nearby blasting

To investigate the effects of nearby blasting on a horseshoe tunnel and to analyze dynamic response and crack growth with different loading directions, five laboratory experiments were performed using granite specimens of a rectangle plate containing a blast hole and horseshoe tunnel structure. HS photography and digital image correlation (DIC) methods were used to visualize the highly transient process of crack propagation in the surrounding rocks when the sidewall, spandrel, vault, corner, and bottom floor were selected as the front blasting faces. According to the experimental results, the shock wave attenuated to stress wave when the wave arrived at the front blasting face of the tunnel, and the radial fracturing played a significant role around the tunnel. The radial cracks originated from the borehole and merged with the cracks which from the tunnel. The central damage area between the borehole and the tunnel were similar for different loading directions. The initial stress wave became weak when it arrived at the tunnel back blasting face, the combined action of the reflected and diffracted stress waves played an important role in the crack growth. The side cracks were more easily generated in the orthogonal corner, and their growth was strongly influenced by the loading direction. Therefore, the reinforcement of the existing tunnel was valuable along the connection direction and corners.

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.

Численная оценка кинетических параметров докритического роста трещин в конструкционных клеевых соединениях при длительном статическом нагружении с использованием модели когезионной зоны и экспериментальных данных

The article proposes a numerical method for modeling and calculating the kinetics of subcritical crack growth and creating kinetic G-V diagrams for structural adhesive joints under prolonged static loading. The load was set by the global subcritical crack opening according to mode I. Modeling and calculations were carried out using a cohesive zone model implanted into the finite element method in the ANSYS software package. The parameters of the cohesive zone law and the kinetics of subcritical crack growth were experimentally determined for samples in the form of a double cantilever beam made of aluminum alloy plates glued with industrial grade epoxy glue. Comparison of the calculated and experimental data showed a good correlation.

Elucidating the loading rate dependence of hydrogen environment-assisted cracking in a Ni-Cu superalloy

The effect of loading rate (dK/dt) on the hydrogen environment-assisted cracking (HEAC) behavior of Monel K-500 immersed in 0.6 M NaCl and polarized to −950 and −1200 mVSCE was assessed via a slow-rising stress intensity (K) testing framework at dK/dt ranging from 0.2 to 20 MPa√m/hr. Comparative testing on Monel K-500 in an inert environment (dry N2 with RH < 5%) at dK/dt ranging from 0.1 to 4 MPa√m/hr revealed a clear dK/dt-dependence of local plasticity effects on the direct current potential difference (dcPD) signal. A method for decoupling this “false” signal caused by local plasticity from the ‘true’ crack growth kinetics is presented. Analysis of the corrected data showed that the threshold stress intensity for the onset of HEAC (KTH) was nominally invariant with dK/dt. The HEAC growth rates (da/dt) were only mildly dependent on dK/dt under severe environmental conditions (−1200 mVSCE). However, for moderate conditions (−950 mVSCE), a strong influence of dK/dt on HEAC growth rates (da/dt) was observed. For this latter testing environment, two characteristic regimes of behavior were noted depending on the applied dK/dt: (1) a ‘plateau’ regime where da/dt is independent of dK/dt was observed for dK/dt > 8 MPa√m/hr and (2) a ‘linear’ regime where log(da/dt) linearly scales with log(dK/dt) was observed for dK/dt < 8 MPa√m/hr. These trends are interpreted using resistance curves calculated from the measured da/dt vs. KJ data. The results of this analysis demonstrate that diffusion-mediated crack growth is only observed for dK/dt > 10 MPa√m/hr at −950 mVSCE and all evaluated dK/dt at −1200 mVSCE, while mechanics-based factors govern the da/dt response for dK/dt < 10 MPa√m/hr at −950 mVSCE. The influence of dK/dt is considered in the context of current testing standards for evaluating HEAC susceptibility; specifically, rising K-based frameworks consistently yield conservative HEAC metrics.

Damage tolerance-based methodology for fatigue lifetime estimation of a structural component produced by material extrusion-based additive manufacturing

Abstract While additive manufacturing of polymers, especially material extrusion-based methods such as fused filament fabrication, has become increasingly popular for design studies, rapid prototyping and the production of non-critical spare parts, its application in structurally loaded components is still scarce. One of the reasons for this might be scepticism of engineers due to the lack of knowledge regarding the expected lifetime and reliability of these components under stress. Therefore, it is necessary to find fast, easy and reliable ways to determine the expected lifetime of a component without the need to apply expensive full-scale component testing for every new part. To realise this, finite element analysis combined with fracture mechanical lifetime calculations can be applied. In this paper, crack growth kinetics of the commonly used material poly(lactic acid) have been utilised to estimate the lifetime of a component under complex loading conditions, namely fatigue and friction. The calculated lifetime, based on a damage tolerant fracture mechanics approach, was found to be in good agreement to the results of full-scale component tests, proving the applicability of the chosen approach. Applying this knowledge can vastly decrease the necessary time during component design and encourage the additive manufacturing community towards applying their components also in structurally loaded applications.

Methodical Approach to Studying Growth Kinetics for Short and Long Fatigue Cracks in Irradiated Reactor Materials: Part 1. Problem Definition. The Effect of Initial Notch Acuity on the Fatigue Crack Rate in Small-Sized Samples

The main methodological features of the studies on the kinetics of fatigue crack growth in the course of testing of irradiated small-sized samples are considered. The effect of the initial notch acuity on the long crack growth rate is studied. On the basis of experimental studies, the size of stress concentration zone is estimated depending on the notch type in the small-sized samples. A brief literature review of the main problems in the studies on the growth kinetics for short fatigue cracks is performed. The tasks for further research are formulated.

Assessing surface fatigue crack growth in railway wheelset axle

Purpose: The aim of the proposed research is to create a calculation model of surface fatigue crack growth at the axle of railway wheelset working under operational loads. Design/methodology/approach: The energy approach of the fracture mechanics was used to formulate the calculation model of fatigue crack propagation at the wheelset axle surface. The method of least squares was used to determine the investigated material mechanical constants that the kinetic equations of the calculation model contain. The system of differential equations of crack growth kinetics was solved numerically using the Runge-Kutta method. Findings: On the basis of the energy approach of the fracture mechanics the calculation model of fatigue macrocrack growth in three-dimensional elastic-plastic body in case of a mixed-mode I+II+III macromechanism of fracture has been built. On the basis of the created calculation model, the kinetics of the growth of fatigue cracks was investigated both in the middle part of the wheelset axle and in the axle journal. Research limitations/implications: The results obtained on laboratory specimens should be tested during a real railway wheelset axle investigation. Practical implications: The created calculation model can be used in practice to formulate method of residual lifetime estimation of railway wheelset axle. Originality/value: It was shown, that surface crack kinetics depends not only on the crack initial area but also significantly depends on the crack edge geometry and comparatively small crack-like defects at the wheelset axle surface can reach critical sizes in comparatively short run. It has been found that mechanical shear stresses caused by the weight of the loaded railway wagon in the cross section of the wheelset axle journal can significantly accelerate the growth of the transverse fatigue crack at the axle surface, reducing the period of crack subcritical growth by about 20%.

Actuation-Induced stable crack growth in near-equiatomic nickel-titanium shape memory alloys: Experimental and numerical analysis

Shape Memory Alloy (SMA) actuation technology requires a thorough understanding of the failure response of these alloys under loading that involves thermal variations, termed “actuation” loading. In this paper, the experimental observation of stable crack growth in SMA compact tension specimens during temperature changes under constant bias loads is reported for the first time. The intrinsic damage mechanisms that promote crack advance are those reported in literature for nominally isothermal overload fracture, i.e., cleavage assisted by ductile void growth. Moreover, a numerical analysis is employed, and the resulting simulations are compared with the experimental data with the purpose of building confidence in the insight provided on the role of extrinsic mechanisms that further promote or impede crack advance. It is concluded that phase transformation plays a dual role on the crack growth kinetics by promoting crack growth when occurring in a fan in front of the crack tip and providing the toughness enhancement that results in stable crack growth when left in the wake of the advancing crack. While the latter is well known as transformation-induced toughness enhancement, the former has just been recently observed experimentally and is characteristic of SMAs subjected to actuation loading conditions.

A Time Dependent Process Zone Model for Slow Crack Growth of Polyethylene Pipe Material

Polyethylene (PE) pipe is widely used in water supply and gas transportation engineering. Its fracture behavior is very important for the safe operation of the pipeline. The objective of this work is to simulate the slow crack growth (SCG) process of PE pipe material via a time dependent crack-tip process zone model. To achieve this end, the crazing damage caused by stress concentration at crack tip of PE material is taken into account, the stress on the bulk/craze interface layer is supposed to be uniformly distributed due to the micro necking mechanism of the layer, and a linear crack growth kinetics is used. In order to describe the delay characteristics of the fracture process of PE materials, the fracture surface energy is considered as an exponential decay function of time, which is attributed to the creep damage of the craze fibrils. A simulation algorithm of the proposed process zone model is suggested using iterative method. The model is verified by comparing the simulation with the discontinuous SCG behavior reported in the literature.

Subcritical Crack Growth in Cementitious Materials Subject to Chemomechanical Deterioration: Numerical Analysis Based on Lattice Model

AbstractThe kinetics of subcritical crack growth (SCG) in hardened cement pastes attacked simultaneously by mechanical damage and calcium leaching was experimentally investigated by a novel test ap...

Parameter interdependence of dynamic self-similar crack with distance-weakening friction

SUMMARY In several analytical and numerical studies, the slip rate function and energy release rate for dynamic self-similar crack growth have been investigated, and the results obtained have contributed to a theoretical understanding and estimation of on-fault energetics. However, the relationships among physical parameters, including stress state, process zone size, rupture velocity, peak slip rate and energy release rate, are still unclear. Therefore, the aim of this study is to derive an analytical solution of the slip rate distribution of antiplane self-similar crack growth under distance-weakening friction that mimics slip-weakening friction. To satisfy the condition that the slip rate starts from zero at the rupture front, a trade-off relationship among rupture velocity, process zone size and breakdown stress-to-stress drop ratio is proposed. The peak slip rate, slip-weakening distance and fracture energy obtained using the proposed model provide a possible mechanism for the determination of the rupture velocity and the estimation of the fracture energy of the self-similar crack growth, based on the seismic observables.

Determination of fracture toughness for carbon fiber reinforced plastics free of the crack initiator using the acoustic microscopy

The fracture toughness which reflects change in the elastic deformation energy of the structural element with an increase in the crack area per unit at the onset of straining is one of the crack resistance parameters of carbon fiber plastics (CFRPs). When studying the fracture toughness, the position of the crack front is determined: both the initial one and that obtained as a result of crack growth. Currently existing test standards (STO TsAGI, ASTM D7905) determine the viscosity by the shear mode GIIc using the samples with a crack initiator. However, the method does not reflect the real conditions of crack initiation in CFRPs structures and can lead to a decrease in the accuracy of determining the load of crack initiation. A new technique of the fracture viscosity determination free of the standard delamination initiator has been developed in TsAGI. We present the results of developing the proposed methodology. The GIIc values were determined for a shear crack under three-point bending conditions after wedging. To determine the position and shape of the crack front, as well as to assess the dynamics of its propagation under subsequent loads, we used ultrasonic methods — ultrasonic flaw detection (ultrasonic NDT) and acoustic microscopy instead of the standard visual observation of the crack boundaries from the end surface of the samples. It is shown that acoustic microscopy at a frequency of 50 MHz provides determination of the crack front position in CFRP samples at a depth of 3.0 – 3.5 mm with a high resolution about 100 μm. The features of the crack growth under shear conditions are discussed. The results of the study show that high accuracy of acoustic microscopy in comparison with traditional ultrasonic NDT diagnostics is strongly sought for determining the shape of the cracks, as well as for analyzing the dynamics of crack growth and revealing the mechanisms of interlayer crack propagation in a composite material.

Dynamic crack growth characteristics of half-circular disk PMMA specimens with prefabricated penetration defects under impact loading

In this paper, the dynamic fracture experiment of half-circular disk PMMA specimens with prefabricated penetration defects under impact loading was carried out on the digital laser dynamic caustics experimental system (DLDC), the law of crack initiation, growth and traversing under different tilt angles (30°, 45°, 60°) was examined, and the variations of crack growth trajectory, velocity and DSIF at crack tip were compared for analysis. In addition, the discrete lattice spring method (DLSM) as a new development was employed to simulate how the dynamic cracks grew in PMMA specimens with defects, it was found that the numerical model can reproduce the experiment phenomenon. On the basis, the effect of the elastic modulus of the penetration defect medium on crack growth was analyzed. Referring to the experiment and numerical results, it was thus concluded that the angle and the elastic modulus of penetration defect would dramatically influence the crack growth characteristics.

An analytical model for the coupled-field dynamic fatigue crack growth in a metallic beam under chaotic excitations

Dynamic fatigue crack growth (FCG) under chaotic excitations has not yet received due attentions. The current paper presents an analytical model for predicting the FCG in a metallic notched beam subject to external chaotic excitations. The proposed stand-alone analytical model only requires the physical properties of the cracked beam; initial crack conditions; the material constants for the Paris power law; and the time series of the external chaotic excitation. The validity of the analytical model proposed is verified using relevant experimental results from other researchers.The validated model is employed to conduct parametric studies on the coupled field FCG in a notched metallic beam vibrating under external chaotic excitations. The fatigue lives obtained under a group of statistically similar chaotic excitations significantly disperse. The ratio between the maximum and minimum fatigue lives is around 5.2. The ratio remains as high as 2.4, even when only the initial conditions in the chaotic excitations vary.The common practice Palmgren-Miner rule is also used to estimate the fatigue life under chaotic excitations. These predictions differ, by several times, from those provided by the current validated analytical model. Similar shortcomings were noticed in a previous experimental study, where the Palmgren-Miner rule, reportedly, considerably overestimated the fatigue damage under chaotic excitations. In the current study, both under and over-predictions are noted.

Setup for studying the kinetics of crack growth in cyclic bending tests

The goal of the study is analysis of the features of fatigue cyclic fracture of steels. An installation has been designed to induce fatigue cracks and to study the kinetics of fatigue crack development. Crack growth is recorded by the method of potential difference. The data on the crack growth kinetics were processed on a computer using LGraph2 programs and Excel spreadsheets. When studying the kinetics of the fatigue crack development, the electrodes were soldered to the edges of the initial notch of the sample and time dependence of the potential difference was recorded on a computer during crack growth. To interpret the experimental data, a calibration chart in the coordinates «potential difference (U) – the crack length (Lcr)» constructed on the basis of the millivoltmeter readings was used, with due regard for the size of the sample section, current flow and length of the fatigue crack. Cyclic loading of the sample resulted in a stepwise character of the crack growth: first occurred zone of plastic deformation of the metal is then followed by accumulation of stresses of a certain size, their relaxation in the form of a crack and sudden crack growth. An abrupt crack growth is clearly visible on a graph of the fatigue crack growth rate obtained upon computer processing of experimental data. Using a graphical editor KOMPAS, a graph was constructed which characterized the growth of the fatigue crack against the number of cycles of fatigue tests for bending. The experimental setup provides the possibility of fatigue crack formation for impact tests, determination of the work of crack propagation, as well as studying of the kinetics of crack development and computer processing of experimental data.