Early Crack Growth

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J. Tong - One of the best experts on this subject based on the ideXlab platform.

  • characterisation of foreign object damage fod and Early fatigue Crack Growth in laser shock peened ti 6al 4v aerofoil specimens
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011
    Co-Authors: S. Spanrad, J. Tong
    Abstract:

    Abstract Foreign object damage (FOD) has been identified as one of the primary life limiting factors for fan and compressor blades, with the leading edge of aerofoils particularly susceptible to such damage. In this study, a generic aerofoil specimen of Ti–6Al–4V alloy was used. The specimens were treated by laser shock peening (LSP) to generate compressive residual stresses in the leading edge region prior to impact. FOD was simulated by firing a cubical projectile at the leading edge using a laboratory gas gun at 200 m/s, head-on; and at 250 m/s, at an angle of 45°. The specimens were then subjected to 4-point bend fatigue testing under high cycle (HCF), low cycle (LCF) and combined LCF and HCF loading conditions. Scanning electron microscopy (SEM) was used to characterise the damage features due to FOD. Crack initiation and Early Crack Growth due to FOD and subsequent fatigue Growth were examined in detail. The results were compared between the two impact conditions; and with those from samples without LSP treatment as well as those impacted with spherical projectiles. The results seem to suggest that LSP has improved the Crack Growth resistance post FOD. Delayed onset of Crack initiation was observed in LSPed samples compared to those without LSP under similar loading conditions. Damage features depend on the geometry of the projectile, the impact angle as well as the impact velocity.

  • Characterisation of foreign object damage (FOD) and Early fatigue Crack Growth in laser shock peened Ti–6Al–4V aerofoil specimens
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010
    Co-Authors: S. Spanrad, J. Tong
    Abstract:

    Abstract Foreign object damage (FOD) has been identified as one of the primary life limiting factors for fan and compressor blades, with the leading edge of aerofoils particularly susceptible to such damage. In this study, a generic aerofoil specimen of Ti–6Al–4V alloy was used. The specimens were treated by laser shock peening (LSP) to generate compressive residual stresses in the leading edge region prior to impact. FOD was simulated by firing a cubical projectile at the leading edge using a laboratory gas gun at 200 m/s, head-on; and at 250 m/s, at an angle of 45°. The specimens were then subjected to 4-point bend fatigue testing under high cycle (HCF), low cycle (LCF) and combined LCF and HCF loading conditions. Scanning electron microscopy (SEM) was used to characterise the damage features due to FOD. Crack initiation and Early Crack Growth due to FOD and subsequent fatigue Growth were examined in detail. The results were compared between the two impact conditions; and with those from samples without LSP treatment as well as those impacted with spherical projectiles. The results seem to suggest that LSP has improved the Crack Growth resistance post FOD. Delayed onset of Crack initiation was observed in LSPed samples compared to those without LSP under similar loading conditions. Damage features depend on the geometry of the projectile, the impact angle as well as the impact velocity.

  • Characterization of foreign object damage (FOD) and Early fatigue Crack Growth in laser shock peened Ti-6AL-4V aerofoil specimens
    Procedia Engineering, 2010
    Co-Authors: S. Spanrad, J. Tong
    Abstract:

    Abstract Foreign object damage (FOD) has been identified as one of the primary life limiting factors for fan and compressor blades, with the leading edge of aerofoils particularly susceptible to such damage. In this study, a typical aerofoil specimen of Ti-6Al-4V alloy was used. The leading edge of the specimen is representative of a generic aerofoil geometry. The specimens were treated by laser shock peening (LSP) to generate protective residual stresses in the leading edge region prior to impact. FOD was simulated by firing a cubical projectile at 250 m/s head-on at the leading edge using a laboratory gas gun. The specimens were then subjected to fatigue testing under high cycle (HCF), low cycle (LCF) and combined LCF and HCF loading conditions. Scanning electron microscopy (SEM) was used to characterise the damage features due to FOD. Crack initiation and Early Crack Growth due to FOD and subsequent fatigue loading were examined in detail. An analysis with a backscatter electron (BSE) detector was also carried out to investigate the microstructual deformation due to FOD, LSP, as well as the Early fatigue Crack Growth mechanism in a complex residual stress field.

S. Spanrad - One of the best experts on this subject based on the ideXlab platform.

  • characterisation of foreign object damage fod and Early fatigue Crack Growth in laser shock peened ti 6al 4v aerofoil specimens
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011
    Co-Authors: S. Spanrad, J. Tong
    Abstract:

    Abstract Foreign object damage (FOD) has been identified as one of the primary life limiting factors for fan and compressor blades, with the leading edge of aerofoils particularly susceptible to such damage. In this study, a generic aerofoil specimen of Ti–6Al–4V alloy was used. The specimens were treated by laser shock peening (LSP) to generate compressive residual stresses in the leading edge region prior to impact. FOD was simulated by firing a cubical projectile at the leading edge using a laboratory gas gun at 200 m/s, head-on; and at 250 m/s, at an angle of 45°. The specimens were then subjected to 4-point bend fatigue testing under high cycle (HCF), low cycle (LCF) and combined LCF and HCF loading conditions. Scanning electron microscopy (SEM) was used to characterise the damage features due to FOD. Crack initiation and Early Crack Growth due to FOD and subsequent fatigue Growth were examined in detail. The results were compared between the two impact conditions; and with those from samples without LSP treatment as well as those impacted with spherical projectiles. The results seem to suggest that LSP has improved the Crack Growth resistance post FOD. Delayed onset of Crack initiation was observed in LSPed samples compared to those without LSP under similar loading conditions. Damage features depend on the geometry of the projectile, the impact angle as well as the impact velocity.

  • Characterisation of foreign object damage (FOD) and Early fatigue Crack Growth in laser shock peened Ti–6Al–4V aerofoil specimens
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010
    Co-Authors: S. Spanrad, J. Tong
    Abstract:

    Abstract Foreign object damage (FOD) has been identified as one of the primary life limiting factors for fan and compressor blades, with the leading edge of aerofoils particularly susceptible to such damage. In this study, a generic aerofoil specimen of Ti–6Al–4V alloy was used. The specimens were treated by laser shock peening (LSP) to generate compressive residual stresses in the leading edge region prior to impact. FOD was simulated by firing a cubical projectile at the leading edge using a laboratory gas gun at 200 m/s, head-on; and at 250 m/s, at an angle of 45°. The specimens were then subjected to 4-point bend fatigue testing under high cycle (HCF), low cycle (LCF) and combined LCF and HCF loading conditions. Scanning electron microscopy (SEM) was used to characterise the damage features due to FOD. Crack initiation and Early Crack Growth due to FOD and subsequent fatigue Growth were examined in detail. The results were compared between the two impact conditions; and with those from samples without LSP treatment as well as those impacted with spherical projectiles. The results seem to suggest that LSP has improved the Crack Growth resistance post FOD. Delayed onset of Crack initiation was observed in LSPed samples compared to those without LSP under similar loading conditions. Damage features depend on the geometry of the projectile, the impact angle as well as the impact velocity.

  • Characterization of foreign object damage (FOD) and Early fatigue Crack Growth in laser shock peened Ti-6AL-4V aerofoil specimens
    Procedia Engineering, 2010
    Co-Authors: S. Spanrad, J. Tong
    Abstract:

    Abstract Foreign object damage (FOD) has been identified as one of the primary life limiting factors for fan and compressor blades, with the leading edge of aerofoils particularly susceptible to such damage. In this study, a typical aerofoil specimen of Ti-6Al-4V alloy was used. The leading edge of the specimen is representative of a generic aerofoil geometry. The specimens were treated by laser shock peening (LSP) to generate protective residual stresses in the leading edge region prior to impact. FOD was simulated by firing a cubical projectile at 250 m/s head-on at the leading edge using a laboratory gas gun. The specimens were then subjected to fatigue testing under high cycle (HCF), low cycle (LCF) and combined LCF and HCF loading conditions. Scanning electron microscopy (SEM) was used to characterise the damage features due to FOD. Crack initiation and Early Crack Growth due to FOD and subsequent fatigue loading were examined in detail. An analysis with a backscatter electron (BSE) detector was also carried out to investigate the microstructual deformation due to FOD, LSP, as well as the Early fatigue Crack Growth mechanism in a complex residual stress field.

Yanyao Jiang - One of the best experts on this subject based on the ideXlab platform.

  • An experimental study of the orientation effect on fatigue Crack propagation in rolled AZ31B magnesium alloy
    Materials Science and Engineering: A, 2016
    Co-Authors: Culbertson, Yanyao Jiang
    Abstract:

    Abstract Mode I fatigue Crack Growth (FCG) experiments were performed using compact tension (CT) specimens made of rolled AZ31B magnesium alloy in ambient laboratory air. The testing specimens were made with respect to two material orientations: a Crack surface perpendicular to the rolled direction (R-T) and a Crack perpendicular to the thickness or normal direction (N-T). The constant amplitude load experiments were performed at three load (R) ratios (minimum load over maximum load in a loading cycle) of 0.1, 0.5, and 0.75, respectively. Material orientation was found to affect the Early Crack Growth stage more than the later stable Growth stage. For each R-ratio, the threshold stress intensity factor range for the R-T specimens was less than that for the N-T specimens. Three sub-stages of steady Crack Growth were observed following the threshold stage: a low Paris law slope for the first sub-stage, a second sub-stage with a very high slope, and an intermediate slope during the third sub-stage. The R-T specimens exhibited an overall typical Mode I Cracking direction, with occasional local deviation from the horizontal Crack path. The N-T specimens displayed a general Mode I Cracking with irregular Crack pathing into the specimen away from the observation surface. Transgranular Cracking was the primary Cracking mode for both specimen orientations. Slip induced cleavage dominated Cracking in both orientations. Few residual twins were found in the plastic zone area surrounding the Crack tip, and no evidence of twin boundary Cracking was found.

  • A study of fatigue damage development in extruded Mg–Gd–Y magnesium alloy
    Materials Science and Engineering: A, 2014
    Co-Authors: Fenghua Wang, Jie Dong, Miaolin Feng, Jie Sun, Wenjiang Ding, Yanyao Jiang
    Abstract:

    Abstract Fatigue damage development through a surface Crack observation of an extruded rare-earth Mg–8.0Gd–3.0Y–0.5Zr (GW83) magnesium (Mg) alloy was experimentally studied by conducting strain-controlled tension–compression experiments along the extrusion direction. Companion specimens were tested at three strain amplitudes of 1.2%, 0.75%, and 0.5%, correspondingly. The GW83 alloy has a weak texture and displays concave-down hysteresis stress–strain loops due to the slip dominant plastic deformation for all the three strain amplitudes studied. At a higher strain amplitude, Cracks are mainly initiated at the grain boundaries (GBs) and propagate predominately intergranularly. Twin boundary (TB) Cracks are seldom found although a few tension twins are detected. Final fatigue failure is due to both continuous Crack initiation and microCrack coalescence. When the strain amplitude is low, Cracks are found to initiate at the persistent slip bands (PSBs) as well as GBs, and Early Crack Growth is mainly transgranular. Final fatigue failure is due to continuous accumulation of distributed microCracks. During a majority of the fatigue lives at the three strain amplitudes studied, the Crack initiation and Early Crack Growth do not significantly influence the cyclic stress–strain response of the material.

  • An Experimental Study of the Crack Growth Behavior of 16MnR Pressure Vessel Steel
    Journal of Pressure Vessel Technology, 2008
    Co-Authors: Xiao Gui Wang, Zeng Liang Gao, Tianwen Zhao, Yanyao Jiang
    Abstract:

    An experimental investigation was conducted on the Crack Growth behavior of a pressure vessel steel, 16MnR, in ambient air. Standard compact tension specimens were subjected to Mode I loading with several R-ratios and loading amplitudes. Three circular notch sizes ranging from very sharp notch to blunt notch were used. In addition to constant amplitude loading, experiments were conducted to study the influences of overload and loading sequence on Crack Growth. The results show that the R-ratio has an insignificant influence on the Crack Growth of the material. The size of the notch together with the R-ratio and loading amplitude has a great influence on the Early Crack Growth from the notch. A single tensile overload during a constant amplitude loading experiment retards the Crack Growth significantly. Right after the application of an overload, the Crack Growth rate is higher than that of the stable Crack Growth observed in the constant amplitude loading. The Crack Growth rate decreases and reaches a minimum value before it gradually increases and reaches the stable Crack Growth curve. In high-low sequence loading with the maximum load in the second step lower than that of the first loading step, the preceding higher constant amplitude loading results in a significant Crack Growth retardation in the second loading step. This phenomenon is similar to the effect of a single tensile overload on the constant amplitude loading. An existing model making use of the stress intensity factor is discussed with respect to its capability to describe the observed Crack Growth behavior with the influence of overload and sequence loading.

  • An Experimental Investigation of the Fatigue Crack Growth Behavior of a Pressure Vessel Material
    Volume 6: Materials and Fabrication, 2006
    Co-Authors: Xiao Gui Wang, Zeng Liang Gao, Tianwen Zhao, Fei Ding, Yanyao Jiang
    Abstract:

    An experimental investigation was conducted on 16MnR, a pressure vessel material widely used in China. Standard compact specimens were subjected to several different R-ratios (the ratio of the minimum load over the maximum load in a loading cycle) and loading amplitudes. Three different notch sizes ranging from very sharp notch to blunt notch were used. In addition to constant amplitude load, experiments were conducted with overloads being applied at different Crack lengths. Two-step high-low sequence loading experiments were conducted to study the influence of the loading sequence. The experimental results show that the R-ratio has an insignificant influence on Crack Growth of the material. A single overload at the start of Crack Growth from a notch results in a Crack arrest. The application of an overload during a constant amplitude loading experiment retards the Crack Growth significantly. A higher constant amplitude loading history has a great influence on the Crack Growth in the subsequent lower constant amplitude loading. The size of the notch together with the R-ratio has a great influence on the Early Crack Growth from the notch.Copyright © 2006 by ASME

David L. Mcdowell - One of the best experts on this subject based on the ideXlab platform.

  • Assessment of small fatigue Crack Growth driving forces in single crystals with and without slip bands
    International Journal of Fracture, 2012
    Co-Authors: Gustavo M. Castelluccio, David L. Mcdowell
    Abstract:

    Strain localization under low amplitude cyclic loading is a manifestation of plastic irreversible deformation associated with Early Crack Growth. However, traditional constitutive models cannot usually reproduce strain localization in smooth single crystals, which can affect Crack Growth predictions for crystallographic fatigue Cracks. This work analyzes the influence of bands of localized plastic shear strain on the cyclic Crack tip displacement and on a fatigue indicator parameter by making special provision of a Crack along the interface of a deformation band. Furthermore, the quality of local and volume-averaged fatigue indicator parameters are assessed using finite element models of a Cu single crystal cycled to induce plastic deformation under multiple loading conditions.

  • microstructure sensitive probabilistic modeling of hcf Crack initiation and Early Crack Growth in ni base superalloy in100 notched components
    International Journal of Fatigue, 2012
    Co-Authors: William D Musinski, David L. Mcdowell
    Abstract:

    Abstract Microstructure-sensitive simulation-based strategies for modeling fatigue life reduction in cyclically loaded notched components offer a means to augment costly experiments and to project performance of microstructures not yet processed. To advance design tools for notch fatigue resistance in aircraft gas turbine engine components, we present a formulation that links microstructure heterogeneity (grain size distribution) to size effects and fatigue scatter in notched polycrystalline Ni-base superalloy IN100 specimens. Simulated double-edged notched specimens with various notch radii are subjected to completely-reversed, quasistatic, isothermal (650 °C), strain-controlled loading at three different strain amplitudes. Polycrystal plasticity and experimentally-calibrated Crack formation/Growth laws are used to correlate cyclic plastic slip to the probability of forming and propagating a Crack from grain scale to a transition Crack length at which LEFM is applicable. Probabilistic strain-life and cumulative distribution function (CDF) plots show that larger notch sizes display a larger notch size effect and fatigue knock-down effect. The proposed CDF can be determined for any failure probability and number of cycles, which has implications for minimum fatigue life design of aircraft gas turbine engine components.

  • Damage Mechanics and Metal Fatigue: A Discriminating Perspective:
    International Journal of Damage Mechanics, 1999
    Co-Authors: David L. Mcdowell
    Abstract:

    The effects of microstructure on the development and Growth of small fatigue Cracks in structural components play a strong role in dictating the class of mechanics approaches which are most viable in their treatment. The development of multiple small Crack embryos associated with distributed cyclic plastic strain processes motivates a Continuum Damage Mechanics (CDM) description rather than a fracture mechanics treatment. The influence of material heterogeneity and the proximity to the free surface on the fatigue process in wrought alloys is significant and must be addressed in CDM. Sequential processes of Early Crack Growth past heterogeneously distributed microstructural barriers, small Crack coalescence and propagation of a dominant flow must be addressed through a consistent scheme which identifies damage driving forces as well as accessible propagation paths through the microstructure. Size effects in fatigue are related to the accessibility of low resistance microstructure paths to formation and pro...

Tom Lassen - One of the best experts on this subject based on the ideXlab platform.

  • Fatigue Crack initiation and subsequent Crack Growth in fillet welded steel joints
    International Journal of Fatigue, 2019
    Co-Authors: Zbigniew Mikulski, Tom Lassen
    Abstract:

    Abstract The fatigue damage evolution in fillet welded steel joints where Cracks are emanating from the weld toe is investigated. Based on existing experimental data for as-welded joints including Crack depth measurements of the Early Crack Growth it is proposed to make a distinction between the Crack initiation phase and the subsequent Crack Growth phase. The welded detail in question is an F class detail with plate thickness 25 mm made of medium strength carbon steel. It is found that the Crack initiation phase defined at a Crack depth of 0.1 mm is close to 25% of the fatigue life even at a relatively high constant stress range of 150 MPa. At lower stress ranges it is concluded that the initiation phase is the dominating part of the fatigue life. The present work is focusing on the Crack propagation phase that is defined from a Crack depth of 0.1 mm to final failure of the detail. It is demonstrated that the recommendation given in rules and recommendations (DNVGL and BS 7910) for applying Linear Elastic Fracture Mechanics (LEFM) for the Crack propagation phase is valid for the propagation of such small surface breaking Cracks. A model based on the rule-based formulas for the Stress Intensity Factor Range (SIFR) and the Growth parameters C and m in Paris law agree well the with the measured Crack Growth curves. For these small semi-elliptical Cracks at the weld toe notch important topics like the existence of a threshold limit for the SIFR and the influence of the stress ratio R are discussed. Due to the inherent scatter in the variables characterizing the fatigue damage evolution stochastic approaches are applied for the analyses. Observations and measurements are presented by descriptive statistics and simulations are carried out using Monte Carlo techniques.

  • A fracture mechanics approach for the Crack Growth in welded joints with reference to bs 7910
    2013
    Co-Authors: P. Darcis, D. Santarosa, Naman Recho, Tom Lassen
    Abstract:

    The fatigue process in welded joints is discussed and modeled. A fracture mechanics model has been proposed to describe the entire fatigue process. The model is calibrated to fit the Crack Growth measurements carried out on fillet welded joints. The objective is to establish a unified approach which is consistent with rules and regulation both based on the S-N approach (Eurocode 3) and applied fracture mechanics (BS 7910). Emphasis is put on how to choose Growth parameters in conjunction with a fictitious initial Crack size to obtain both reliable Crack Growth paths and predictions of the entire fatigue life. If the Growth rate parameters given in BS 7910 for a single linear relationship between log da/dN and log ∆K are used in conjunction with initial Crack depths near 0.015 mm the model fits both measured Crack histories and S-N fatigue life estimates at various stress levels. Introduction and objectifs In the present paper the fatigue process in fillet-welded joints where Cracks emanate from the weld toe is studied and modelled. The objective is to establish a model that strikes the balance between simplicity and accuracy in order to provide a tool for the practising engineer. The model should be useful for both durability analysis and inspection planning. Although several investigations have proven the existence of a Crack initiation phase in welded joints, it may be argued that a fracture mechanics model, although lacking a firm footing for the Early Crack Growth, is good enough for all practical purposes. The information needed is usually: • Prediction of time to failure. • Predictions of likely Crack Growth histories leading to the failure. The first criterion is obvious from a fatigue durability point of view; we require a reliable estimate for the entire fatigue life. This estimate must be compared with planned service life and proper dimensions for the joint must be chosen to obtain a safety margin. Hence, our model should be corroborated by S-N data for the joint in question when these are available. The second criterion is essential if in-service inspections are to be planned; we must know what Crack sizes to look for at different times before final failure. This will make the scheduled inspection more efficient and economical. Hence, our model should predict a Crack evolution that coincides with measured Crack Growth histories before