Crack Growth In Steel Research Articles

Experimental study on slow tensile, fatigue, and impact on X42 steel and #20 carburizing steel

Hydrogen embrittlement is a common phenomenon in high-strength steels and presents a significant challenge in the research and development process. This study aims to analyze the mechanism of hydrogen embrittlement, investigate the causes of crack growth in steel, and conduct experiments at mesoscopic and microscopic scales to gain a deep understanding of the relationship between hydrogen embrittlement and defects in high-strength steels. The research includes a slow tensile test to study the shrinkage and ductility of X42 steel and 20# carburizing steel under air and hydrogen environments. Furthermore, fatigue testing is conducted to comparatively investigate the crack growth of CT specimens in nitrogen and hydrogen environments at different pressures. Additionally, impact testing is performed to examine the fracture of V-notched specimens in air and hydrogen at different pressures. The findings reveal that 20# carburizing steel exhibits better fracture toughness than X42 steel during the slow tensile process, and its hydrogen embrittlement sensitivity is lower. Moreover, the fatigue crack growth process of 20# carburizing steel is less affected by hydrogen embrittlement, resulting in better fatigue rupture resistance compared to X42 steel. Furthermore, the impact toughness value of 20# carburizing steel is higher than that of X42 steel in the impact toughness test. Both steels show varying effects on crack growth under different hydrogenation pressures. Importantly, the impact toughness of both steels is less affected by different hydrogenation pressures.

Experimental and XFEM modelling of high cycle fatigue crack growth in steel welded T-joints

The current paper reports the results of a series of high cycle fatigue (HCF) experiments on steel welded T-joints, tested under constant amplitude three-point bending. The eXtended Finite Element Method (XFEM) was then implemented to simulate the experiments. The crack and its growth were characterised by means of level set functions to eliminate the need for re-meshing. The study can be viewed as a first-of-its-kind in XFEM fatigue simulation of butt welded steel T-joints; where the crack geometry and growth is essentially three dimensional, making the problem particularly acute. The XFEM/fatigue crack growth (FCG) procedure employed in the study was first validated against constant amplitude HCF experiments on notched steel plates from other researchers. The same modelling procedure was then used for simulating the fatigue tests conducted on steel welded T-joints. It was found that the XFEM predictions for the crack growth, the growth rate, number of cycles to failure, crack shape and final crack size were satisfactorily comparable to those obtained in the experiments. Mean errors in the XFEM predictions for the fatigue life ranged from -20.7% to +0.9%. The morphology of the fracture surface from the numerical model, in general, had a good agreement with the corresponding experimental morphology.

Modeling of Nonlinear Crack Growth in Steel and Aluminum Alloys by the Element Free Galerkin Method

In this study, the modelling and simulation of the nonlinear fatigue crack growth phenomenon in steel and aluminium alloys has been carried out by employing the element free Galerkin method. The primary variable is approximated by the moving least square shape functions. For the consideration of the effect of various discontinuities present in the domain, appropriate enrichment functions have been added to the standard EFGM approximation. In order to keep track of the various discontinuities, the standard level set method is used. The present study includes the material and geometric nonlinearities in the mathematical formulations. The geometric nonlinearity has been modelled by employing the updated Lagrangian approach. The isotropic hardening has been used with the Ramberg-Osgood model to obtain the elasto-plastic behaviour of the material. Finally, several numerical problems have been solved by the element free Galerkin method to investigate fatigue crack growth in steel and aluminium alloys.

A Method to Decompose the Streamed Acoustic Emission Signals for Detecting Embedded Fatigue Crack Signals

The data collection of Acoustic Emission (AE) method is typically based on threshold-dependent approach, where the AE system acquires data when the output of AE sensor is above the pre-defined threshold. However, this approach fails to detect flaws in noisy environment, as the signal level of noise may overcome the signal level of AE from flaws, and saturate the AE system. Time-dependent approach is based on streaming waveforms and extracting features at every pre-defined time interval. It is hypothesized that the relevant AE signals representing active flaws are embedded into the streamed signals. In this study, a decomposition method of the streamed AE signals to separate noise signal and crack signal is demonstrated. The AE signals representing fatigue crack growth in steel are obtained from the laboratory scale testing. The streamed AE signals in a noisy operational condition are obtained from the gearbox testing at the Naval Air Systems Command (NAVAIR) facility. The signal addition and decomposition is achieved to determine the minimum detectable signal to noise ratio that is embedded into the streamed AE signals. The developed decomposition approach is demonstrated on detecting burst signals embedded into the streamed signals recorded in the spline testing of the helicopter gearbox test rig located at the NAVAIR facility.

Hydrogen-enhanced fatigue crack growth in steels and its frequency dependence.

In the context of the fatigue life design of components, particularly those destined for use in hydrogen refuelling stations and fuel cell vehicles, it is important to understand the hydrogen-induced, fatigue crack growth (FCG) acceleration in steels. As such, the mechanisms for acceleration and its influencing factors are reviewed and discussed in this paper, with a special focus on the peculiar frequency dependence of the hydrogen-induced FCG acceleration. Further, this frequency dependence is debated by introducing some potentially responsible elements, along with new experimental data obtained by the authors.This article is part of the themed issue 'The challenges of hydrogen and metals'.

2013 Bower Award and Prize for Achievement in Science presented to Kenichi Iga, Tokyo Institute of Technology, Tokyo, Japan

The mechanical behavior of materials can be modeled and evaluated across multiple scales that encompass: atomic and molecular rearrangements to create incipient defect nuclei; combination or growth of such nuclei to form micro-scale and subsequently macro-scale defects; and finally development of critical flaw sizes that result in final failure of engineering structures. Through an understanding of the mechanisms governing these processes, which depend on the loading conditions and the specific materials, new or modified materials systems designs can be integrated with advanced structural concepts to advance our energy, civil, transportation and healthcare infrastructures, among others.Subra Suresh׳s research includes development of novel experimental techniques and the discovery of new mechanistic processes that are broadly applicable to essentially every major class of natural and synthetic materials, including metals, ceramics, polymers, composites, biomolecules and biological cells. Beginning in the 1970s, he elucidated mechanisms of near-threshold fatigue crack growth in steels and aluminum alloys, contributing to improved alloy design for nuclear pressure vessels, fossil plants, offshore structures and aircraft. Subsequent work identified mechanisms for toughening brittle ceramics against fatigue crack growth under cyclic compressive loads. Turning to the microscale and the study of thin films, he developed new methods for extracting elastoplastic and functional properties of materials from small-volume contact probing. This led to new theories, computation and experiments on material and surface design through controlled gradients in composition and properties, and applications to coatings. At the nanoscale, he experimentally discovered nanocrystallization of bulk amorphous alloys during nanoindentation, and also showed how nanoscale twins could optimize the strength and ductility of fine grained metals. Most recently, he is noted for demonstrating the effects of disease-induced changes to human red blood cell deformability and biorheology, and for linking these changes to human diseases such as malaria.

2013 Benjamin Franklin Medal in Mechanical Engineering presented to Subra Suresh

The mechanical behavior of materials can be modeled and evaluated across multiple scales that encompass: atomic and molecular rearrangements to create incipient defect nuclei; combination or growth of such nuclei to form micro-scale and subsequently macro-scale defects; and finally development of critical flaw sizes that result in final failure of engineering structures. Through an understanding of the mechanisms governing these processes, which depend on the loading conditions and the specific materials, new or modified materials systems designs can be integrated with advanced structural concepts to advance our energy, civil, transportation and healthcare infrastructures, among others.Subra Suresh׳s research includes development of novel experimental techniques and the discovery of new mechanistic processes that are broadly applicable to essentially every major class of natural and synthetic materials, including metals, ceramics, polymers, composites, biomolecules and biological cells. Beginning in the 1970s, he elucidated mechanisms of near-threshold fatigue crack growth in steels and aluminum alloys, contributing to improved alloy design for nuclear pressure vessels, fossil plants, offshore structures and aircraft. Subsequent work identified mechanisms for toughening brittle ceramics against fatigue crack growth under cyclic compressive loads. Turning to the microscale and the study of thin films, he developed new methods for extracting elastoplastic and functional properties of materials from small-volume contact probing. This led to new theories, computation and experiments on material and surface design through controlled gradients in composition and properties, and applications to coatings. At the nanoscale, he experimentally discovered nanocrystallization of bulk amorphous alloys during nanoindentation, and also showed how nanoscale twins could optimize the strength and ductility of fine grained metals. Most recently, he is noted for demonstrating the effects of disease-induced changes to human red blood cell deformability and biorheology, and for linking these changes to human diseases such as malaria.

Time-variant flexural reliability of RC beams with externally bonded CFRP under combined fatigue-corrosion actions

Time-variant reliability analysis of RC highway bridges strengthened with carbon fibre reinforced polymer CFRP laminates under four possible competing damage modes (concrete crushing, steel rupture after yielding, CFRP rupture and FRP plate debonding) and three degradation factors is analyzed in terms of reliability index β using FORM. The first degradation factor is chloride-attack corrosion which induces reduction in steel area and concrete cover cracking at characteristic key times (corrosion initiation, severe surface cover cracking). The second degradation factor considered is fatigue which leads to damage in concrete and steel rebar. Interaction between corrosion and fatigue crack growth in steel reinforcing bars is implemented. The third degradation phenomenon is the CFRP properties deterioration due to aging. Considering these three degradation factors, the time-dependent flexural reliability profile of a typical simple 15m-span intermediate girder of a RC highway bridge is constructed under various traffic volumes and under different corrosion environments. The bridge design options follow AASHTO-LRFD specifications. Results of the study have shown that the reliability is very sensitive to factors governing the corrosion. Concrete damage due to fatigue slightly affects reliability profile of non-strengthened section, while service life after strengthening is strongly related to fatigue damage in concrete.

Thermally activated processes of fatigue crack growth in steels

Fatigue crack growth rates in steels at high and low temperatures have been investigated using Paris curves. The fatigue crack growth rates at high temperatures are quite different from those at low temperatures. Arrhenius plots between fatigue crack growth rate (da/dN) and test temperatures at constant stress intensity factor range (ΔKI) indicate a difference of the rate-controlling process for fatigue crack growth with temperature. Slip deformation at the crack tip governs fatigue crack growth at high temperatures, while hydrogen diffusion is associated with crack growth at low temperatures.

Fracture Modelling of Crack Propagation in Steel

In the present study, an interface element with softening and hardening series springs is used to model crack growth in steel. These series spring elements are developed to obtain the strain energy release rates based on the virtual crack closure technique (VCCT). Two nonlinear springs are proposed to be placed between interfacial node pairs. A spring element with softening behaviour and another spring element with hardening behaviour are placed in series at the crack tip between two nodes to calculate the internal forces. Therefore, with these springs, strain energy release rates can be calculated directly. Also, with the implementation of fracture criteria, crack growth can be also analyzed. The model decreases computational time and complexity for analysing discrete cracks. The model is easy, accurate, and independent of the mesh size.

Growth Retardation of Fatigue Crack by Cold Expanded with Ring Indented Method for AISI 304 Stainless Steel

Drilled, cold expanded with ring indented method was employed for crack-tip on the both sides and front side of the specimens, thus build up the residual compressive stresses, strain hardening and plasticity induced closure, and lead toward crack growth retardation. The compact tension specimens of AISI 304 stainless steel were used drilled, cold expanded with ring indented in the fatigue test. The experimental methods were drilled (Φ=2mm ) and cold expanded (Φ=2.074mm) and both sides at 2mm and 1mm position of the crack-tip in the specimen, then apply 0kN, 6KN, and 9kN test loads, respectively. The experimental results showed that, for the same test position, the number of delay cycles result from cold expanded than that of drilled and the number of delay cycles are 220798. For the same position, the stronger test load is, the greater crack growth retardation effect is. And, This study proposed some useful information on utilizing cold expanded with ring indented method for AISI 304 Stainless Steel crack growth retardation.

Modeling of Crack Growth in Steels

The paper discusses issues related to the damage accumulation and cracking in steels. Special attention is paid to the selection of appropriate methods in the modeling of progressive damage development. In special cases, the accumulation of damage and crack propagation may lead to the brutal destruction of machine parts. In addition, some attention was drawn to the conditions that can lead to this brutal destruction.

The influence of plasticity in creep crack growth in steels

Much of the reported work on assessing time-dependent (creep) crack growth has focussed on creep ductile materials, with the deformation conditions ranging from small-scale creep to extensive steady state creep. This previous research on crack initiation and growth has been mainly concerned with characterising creep crack growth rates using the C ∗ parameter. In this paper we interpret recent experimental results by exploring the contributions from elastic, plastic and creep deformation processes prior to and during crack growth. To assess the contribution of each component we use displacement partitioning. Elastic compliance functions are used to determine the elastic contribution. A key curve analysis is presented to determine the plastic contribution. The creep displacements are found by subtracting the sum of the elastic and plastic displacements from the total displacements. This approach is employed to explore the behaviour of a Carbon–Manganese (C–Mn) steel. Results show that after onset of crack growth the contribution of creep displacements is relatively minor for short-term laboratory tests, e.g. tests less than 2000 h. However, for longer-term tests it is evident that there is a greater contribution from creep. The implications of these findings are discussed in terms of using the C ∗ parameter. A simpler approach presented in this paper is to provide, irrespective of test duration, material resistance curves whereby material toughness is a function of time.

Effect of Grain Size on the Fatigue Crack Growth in Steels at Temperatures 295 and 77 K

Fatigue crack growth (FCG) and threshold stress intensity in low carbon and HSLA steels with remarkably different ferrite grain sizes (d f ) at room temperature and temperature of liquid nitrogen were investigated. The FCG rates were found to decrease with decreasing temperature for all investigated microstructural states and the influence of temperature decrease was the most significant in coarse grain microstructures. The threshold values of the stress intensity factor, (ΔK th ), below which cracks do not propagate, decreased by between 29.1 % (d f =2.7μm) and 49.3 % (d f =88.4μm) when specimens were tested at the cryogenic temperature. A general relationship between the FCG rate, the effects of grain boundary blocking on the plastic zone size and/or the crack-tip opening displacement and the effect of changing temperature, is discussed. Furthermore, the concept of a functional relation between tensile and fatigue data at cryogenic temperatures was also investigated. It was shown that the ratio of ΔK th at 77 K to ΔK th at 295 K is proportional to the second root of the ratio of the tensile strength values at these temperatures i.e. ΔK th77K /ΔK th295K (σ u77K /σ u295K ) 1/2 .

On the dependence of the rate of fatigue crack growth on the σ na(2 a) parameter

An empirical fatigue crack growth law, d(2 a)/d N= Cσ n a(2 a), where σ a is the stress amplitude, n is a material-dependent exponent, N is the number of cycles and 2 a is the length of a surface crack, has been used to describe the rate of fatigue crack growth in steels in the physically short-crack, elastic—plastic range. The present paper demonstrates that the rate of fatigue crack growth can also be predicted by a more physically based, modified linear-elastic approach. The modifications involve: a material constant that provides a transition from stress control of fatigue crack growth for small cracks to stress intensity factor control for large cracks, a plastic zone size correction, and consideration of crack closure in the wake of a newly formed crack. The modified linear-elastic fracture mechanics approach also predicts that in the very early stages of crack growth, i.e., up to a crack size of 300 μm for the steels investigated, the empirical relation cited above is not valid.

Stress Corrosion Crack Rate of STS 304 Stainless Steel in High Temperature Water

Sensitized STS 304 stainless steel crack growth rate(CGR) in high temperature water was investigated under trapezoidal wave loading test using fracture mechanics techniques. The CGR, due to stress corrosion cracking(SCC), were systematically measured as a function of the stress intensity factor and stress. holding time under trapezoidal wave loading. In high temperature water, CGR was enhanced by a synergistic effects in combination with an aggressive environment and mechanical damage. The CGR, was basically described as a summation of the environmentally assisted crack growth rate , and fatigue crack growth rate in air $(da/dN)air,. The CGR, , increased linearly with increasing stress holding time. The CGR, decreased linearly with increasing stress holding time. Fracture surface mode varied from trans-granular cracking to inter-granular cracking with increasing stress holding time.

Inclusion induced anisotropy of short fatigue crack growth in steel

In this study, the growth behaviour of short fatigue cracks in En7A steel with a high content of elongated MnS inclusions was investigated by generating and evaluating the short crack data under different loading conditions for the six principal specimen orientations. Short cracks showed a strong anisotropic behaviour in which they grew muchfaster in the transverse and short transverse orientations than in the longitudinal orientations in all fatigue processes. This was due to the relatively high content of the elongated inclusions. Inclusion induced anisotropy is also observed in the percentages of fatigue life of the initiation and growth periods of short cracks which may result in inaccurate fatigue life predictions. Inclusion induced anisotropy was the result of strain intensification at the matrix/inclusion interface.MST/3250A

Inclusion induced anisotropy of short fatigue crack growth in steel

In this study, the growth behaviour of short fatigue cracks in En7A steel with a high content of elongated MnS inclusions was investigated by generating and evaluating the short crack data under different loading conditions for the six principal specimen orientations. Short cracks showed a strong anisotropic behaviour in which they grew muchfaster in the transverse and short transverse orientations than in the longitudinal orientations in all fatigue processes. This was due to the relatively high content of the elongated inclusions. Inclusion induced anisotropy is also observed in the percentages of fatigue life of the initiation and growth periods of short cracks which may result in inaccurate fatigue life predictions. Inclusion induced anisotropy was the result of strain intensification at the matrix/inclusion interface.MST/3250A

A comparison of short and long fatigue crack growth in steel

In this study, the growth behaviour of short fatigue cracks in En7A steel with a high content of elongated MnS inclusions has been investigated by generating and evaluating short crack growth data for the six principal specimen orientations. The anomalous initiation and growth behaviour of short cracks was also compared with that of long crack data for the same material and loading conditions determined before. This comparison revealed the sub-threshold initiation and faster growth rate of short cracks compared with long cracks under the same stress intensity factor range. In order to simulate this discrepancy between short and long cracks, a crack closure model for long crack data was used.

Effect of a Microdefect ahead of a Main Crack on Strength of Solids. 3rd Report. Main Crack-Slip Band Interaction Model and Its Application to Microcrack Growth.

In the present paper, in order to elucidate micromechanically the crack length dependence of threshold stress for no crack growth in steel, we propose a main crack-slip band interaction model which consists of a main crack, a dislocation free zone, and a slip band. Analyzing the above model by the method based on the continuously distributed theory of dislocations, we obtain the distribution functions and the stress intensity factors K both at the tip of the main crack and the slip band in a closed form. Using these K values, we can elucidate the effective range of the above interaction model and the crack shielding effect by a slip band. Furthermore, the analytical expression for the crack length dependence of threshold stress for no crack growth, which involves the effect of the crack length and grain size, can be obtained successfully by using the present model.