Effect Of Stress Redistribution Research Articles

Study on the effect of stress redistribution in different notched specimens of DD6 on the life of combined high and low cycle fatigue under high temperature

Under combined high and low cycle fatigue (CCF) loading, the multi-axial stress state induced by geometric discontinuities of different notch forms under the same stress amplitude can result in significant differences in fatigue performance of DD6 alloy. Therefore, it is of great importance to study the CCF behavior of Ni-base single-crystal alloy samples with differing notch geometries at the high temperatures. In order to obtain an approximate CCF lifespan, different stress amplitudes need to be applied to DD6 specimens with different notch forms. In this study, two kinds of notched DD6 plate specimens with [001] orientation were studied by CCF test at 760 °C, and the amplitudes of stresses were acquired under the same service life level. The effect of stress redistribution, in particular stress triaxiality, was evaluated on CCF lifetime of the DD6 specimens. A damage model with anisotropy considering stress triaxiality effect was suggested. The results indicated that the conventional stress–strain variables could not reflect the trend of CCF lifetime for different geometrical notched DD6 specimens, whereas the stress triaxiality at the CCF load peak could. A modified Basquin model was introduced for predicting CCF life according to the stress triaxiality at the peak loading. It can accurately and efficiently estimate the CCF life of two kinds of notched DD6 plate specimens, and the life prediction results fall within a scatter band of ±3 times of fatigue life.

The Effect of Stress Redistribution in a Thick-Walled Sphere Made of Shape Memory Alloy at Direct Phase Transformation under Constant Pressure

The coupled problems of changing the stress-strain and phase state in a thick-walled spherical shell made of a shape memory alloy, the material of which undergoes a direct thermoelastic phase transformation associated with a decrease in temperature uniformly distributed over the entire volume of the material under the action of constant internal or external pressure, are solved. The effects of significant overstressing of the body layers adjacent to the inner boundary and significant unloading of the layers adjacent to the outer boundary associated with the movement of the phase transition completion front through the material were found.

Proposal of a Creep-Experiment Method and Superficial Creep Coefficient Model of CFT Considering a Stress-Redistribution Effect

Existing concrete creep coefficient prediction models have the limitation of not considering the structural characteristics of CFT. For this reason, these models tend to overestimate the creep deformation of CFT. Therefore, in order to overcome the limitations of existing CFT creep experiments, this study proposes a creep-experiment method involving the use of CFT that passively changes the load applied to a single concrete specimen by calculating the stress redistribution between the concrete and a steel tube in CFT based on a step-by-step method. Furthermore, by actually applying the proposed experimental method, a creep experiment of CFT lasting for approximately 163 days was performed and a superficial creep coefficient model of CFT was proposed based on long-term strain data from the experiment. In order to verify the proposed superficial creep coefficient model, it was compared with two design criteria (CEB-FIP and ACI) based on the experimental results of this study and references. As a result, compared to the existing design criteria, the value predicted by the proposed superficial creep coefficient model showed good agreement with the experimental results of this study and the references, proving that the proposed creep-experiment method of CFT and superficial creep coefficient model are reasonable.

Lignin-polylactic acid biopolymer blends for advanced applications – Effect of impact modifier

In this study, lignin underwent chemical modification via acetylation of hydroxyl groups to enhance its interfacial connection with poly (lactic acid) (PLA). Further enhancement of the blend was attained by adding an impact modifier, Biomax Strong. Incorporating Biomax Strong into PLA-lignin blends resulted in improvements in material characteristics, particularly in impact strength and thermal stability. This blend exhibited a unique set of mechanical properties, characterized by a reduction in tensile modulus as well as an increase in ductility. This will allow a more versatile use of PLA in various applications. The observed improved impact strength highlights the synergistic effect of stress redistribution within the PLA matrix contributing to widespread applications of PLA based composites. This can clearly be observed for the compound containing PLA and 15 wt.% lignin, where the impact strength was approximately 15 kJ/m2. With the addition of 5 wt.% impact modifier, the impact strength increased by 60 %, reaching approximately 25 kJ/m2. This synergy effect reinforces the overall structure, improving the impact toughness behavior. The combination of Biomax Strong and lignin not only address the limitations of PLA but also introduces new opportunities for applications requiring a balance of impact strength, ductility, and thermal stability. These advancements indicate a promising future for composite materials in various applications.

Significantly improved interfacial mechanical properties in boron nitride nanosheet/Ti composite via nano-configuration: A molecular dynamics study

Boron nitride nanosheets (BNNSs) reinforced titanium (Ti) matrix composites possess a combination of high strength and ductility due to the in-situ synthesized nano-configurations consisting of BNNSs, titanium boride (TiB) and titanium diboride (TiB2). The mechanisms for the outstanding properties, however, are yet fully unraveled. In this study, BNNSs/Ti composites with various nano-configurations are investigated by molecular dynamics (MD) simulation. Results show that the tensile strength and ductility of the composites increase with the number and length of titanium borides (TiBx). The excellent ductility is attributed to the crack-blocking and internal stress redistribution effects of the well-bonded TiBx nanophases. The strength enhancement mainly arises from the improved dislocation strengthening and load-transfer efficiency brought by the nano-interlocking structure. This work can benefit the optimization of BNNSs/Ti composites for fulfilling the strengthening and toughening potential of BNNS.

Seepage Law of Nearly Flat Coal Seam Based on Three-Dimensional Structure of Borehole and the Deep Soft Rock Roadway Intersection

Exploring the evolution characteristics of gas seepage between boreholes during the drainage process is critical for the borehole’s layout and high-efficiency gas drainage. Based on the dual-porous medium assumption and considering the effect of stress redistribution on coal seam gas seepage characteristics, a coal seam gas seepage model with a three-dimensional roadway and borehole crossing structure has been established and numerically calculated, concluding that the coal seam is between the drainage boreholes. The temporal and spatial evolution characteristics of gas pressure and permeability help elucidate the gas seepage law of the nearly flat coal seam associated with the deep soft rock roadway and borehole intersection model. The results indicate that: (1) The roadway excavation results in localized stress in some areas of the surrounding rock, reducing the strength of the coal body, increasing the expansion stress, and increasing the adsorption of gas by the coal body. (2) Along the direction of the coal seam, the permeability decreases initially and then increases. The gas pressure in the coal seam area in the middle of the borehole is higher than the pressure in the coal seam around the borehole, and the expansion stress and deformation increase, reducing the permeability of the coal body; when near the next borehole, the greater the negative pressure, the faster the desorption of the gas attracts the matrix shrinkage effect and causes the coal seam permeability rate to keep increasing. (3) The improvement of gas drainage with the overlapping arrangement of two boreholes firstly increases and then decreases as time goes on. (4) When the field test results and numerical simulation of the effective area of gas extraction are compared, the effectiveness of the model is verified. Taking the change of the porosity and the permeability into the model, it is able to calculate the radius of gas drainage more accurately.

Press-braked stainless steel channel sections under major-axis combined loading: Tests, simulations and design

This paper reports an experimental and numerical investigation into the cross-section behaviour and resistances of press-braked stainless steel channel sections under combined compression and major-axis bending moment. A testing programme was firstly conducted, including initial local geometric imperfection measurements and major-axis eccentric compression tests on ten press-braked stainless steel channel section stub column specimens. Following the testing programme, a numerical modelling programme was performed, where finite element models were developed and validated against the test results and then adopted to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and initial loading eccentricities. Based on the obtained test and numerical data, the existing design interaction curves, as given in the European code, American specification and Australian/New Zealand standard, were assessed and shown to result in conservative cross-section resistance predictions for press-braked stainless steel channel sections under major-axis combined loading. The conservatism of the codified design interaction curves stems from the conservative end points (i.e. cross-section resistances under pure compression and pure bending), which are determined without considering the effect of material strain hardening, and the inefficient linear shape, which ignores the effect of stress redistribution. Improved design interaction curves were proposed through the adoption of (i) more accurate end points, which are calculated with a rational exploitation of material strain hardening by continuous strength method and (ii) more efficient nonlinear shape, which allows for the stress redistribution. The proposed design interaction curves were shown to result in substantially more accurate resistance predictions for press-braked stainless steel channel sections under major-axis combined loading than their codified counterparts. The reliability of the proposed design interaction curves was confirmed by means of statistical analyses.

Backward earthquake ruptures far ahead of fluid invasion: Insights from dynamic earthquake-sequence simulations

The 2011 M9 Tohoku-Oki earthquake caused widespread seismicity including that associated with upward fluid migration within the overriding plate. Such fluid-driven earthquake sequences have a peculiar behavior whereby the ruptures of individual small earthquakes propagate in the opposite direction to the direction of pore pressure invasion. This backward rupture propagation is not predicted by the conventional fluid-driven seismicity model that only considers the evolution of pore pressure on the fault, thus ignoring the effect of stress redistribution. Here, we investigated the characteristics of earthquakes under the influence of upward fluid invasion using numerical simulations considering realistic frictional behavior and fault creep. Specifically, we examined the slip behavior of a fault governed by rate-and-state dependent friction when imposing upward pore pressure diffusion. We assumed multiple velocity-weakening patches on an otherwise velocity-strengthening fault. Our results show that the seismicity front can migrate much faster than predicted by the conventional model because of the redistribution of shear stress on the fault. The recurrence of earthquakes and the directions of ruptures are controlled by the brittleness, β, i.e., the patch size divided by the critical nucleation size. When β > 1, earthquakes repeatedly occur at the same patches, and the swarm activity expands with time. The first rupture at each patch propagates updip, while the directions of subsequent ruptures are variable. When β < 1, earthquakes occur only once in each patch, followed by repeating slow slip events, and the source region migrates rather than expands. In this case, individual earthquake ruptures propagate downdip in the opposite direction to the pore pressure invasion, explaining the observed peculiar rupture characteristic. The consistency obtained between the simulated β < 1 characteristics and the observed ones suggests that the fluid-driven seismicity following the Tohoku-Oki earthquake was only a fraction of the total deformation in which aseismic slips were dominant.

Numerical Analysis of Shallow Foundations Resting on Granular Columns Embedded in Liquefiable Soil

Shallow footings are the most preferred foundations for buildings due to low cost and ease of construction. However, under seismic loads, these foundations may suffer excessive settlements, particularly when there is a risk of soil liquefaction. This paper explores the effectiveness of granular columns in mitigating the liquefaction-induced ground deformations under shallow foundations, using FLAC2D program. PM4Sand, a critical state-based bounding surface plasticity model is used to simulate the stress–strain response of sand to cyclic loading. The responses of granular columns are also simulated using the same soil model. Validation of the numerical model is presented against the experimental results of mildly sloping ground. The application of granular column groups resulted in maximum reduction of the settlement of footing by 60% when soil densification is included along with drainage and stress redistribution effects. Though excess pore water pressure is relatively low in treated deposit compared to the untreated deposit, its contribution to the reduction in settlement of footing is found to be minimal.

Coupled Modeling of Sedimentary Basin and Geomechanics: A Modified Drucker–Prager Cap Model to Describe Rock Compaction in Tectonic Context

The aim of basin modeling is to characterise fluids and rocks in a basin considering its history and data partly describing its present state. In usual basin simulators, only a simplified description of geomechanics based on the hypothesis of oedometric strain is used. To both enhance the modeling of basin history and to characterise actual in situ stresses, the effect of stress redistribution, horizontal stresses, and strain variations during basin history should be considered. To address this point, a coupled basin-geomechanics framework based on a new constitutive law is proposed in this paper using the prototype simulator $$\mathrm{A}^{2}$$ . This framework has been built to provide relevant results for various kinds of basin cases including tectonic loading. A finite strain poromechanical approach is considered along with an modified Drucker–Prager Cap model to describe rock compaction under natural sedimentation, erosion, and tectonics. The constitutive model can be seen as a tensorial extension of the compaction models of Athy or Schneider as it allows to recover the same behaviour in oedometric context. Simple test cases are modeled considering typical sand or shale properties, emphasizing the effect of tectonic loading on the present-day pore pressures and in situ stresses. It appears that even relatively moderate tectonic loading ( $$5\%$$ of horizontal strain) can lead to overpressures of several hundreds of bars and to a complete change in in situ stress regime for deeply buried layers (above a depth of 2000 m).

Design of statically indeterminate reinforced glass beams: accounting for system action

ABSTRACTTransparency has become a trend in architecture. In the near future, the scale of application of structural glass will grow from elements (beams, columns, etc.) to entire systems (floors, roofs, façades, frames, etc.). Especially beams, being one of the most important and common building components, will be combined into load‐carrying systems (e. g. a supporting grid for floors and roofs). However, this scale‐up cannot be realized without incorporating structural safety and robustness on an element and system level, as required by modern building codes. For glass beams, research resulted in the concept of hybrid glass beams, in which a glass web is combined with flanges or reinforced with another material that provides post‐fracture strength and ductility, hence providing structural element safety and robustness. Especially the stainless steel reinforced glass beam, based on the principle of reinforced concrete, proved satisfactory. To investigate the feasibility of applying this concept in innovative beam systems, experimental five‐point bending tests on 3.0 m beams and membrane action tests on 4.3 m beams were performed, resulting in satisfactory load‐carrying behaviour with significant stress redistribution due to plastic hinge formation and membrane action, both compressive and tensile. Both features/mechanisms resulted in significant increases in the post‐fracture capacity of the beam systems. For the latter's design, focusing only on glass fracture is insufficient, as the element and system safety requirements should also be satisfied. Therefore, post‐fracture capacity and ductility should be incorporated in design. The latter requires an amount of reinforcing material, which decreases the beam's overall transparency. Therefore it is important that design aims at achieving maximum capacity and ductility with as little reinforcing material as possible. This paper investigates the effect of stress redistribution and membrane action on the achievable capacity of a reinforced glass beam system. It is concluded that both features/mechanisms, and especially membrane action can make a significant contribution to the ultimate capacity and ductility of the beam system. This paper also considers the incorporation of these mechanisms in design, resulting in optimal (i.e. minimal) usage of materials. Compared to statically determinate beams, a decrease in reinforcing material is possible, resulting in ever more transparent structures.

Effect of stress redistribution during thermal actuation of shape memory alloys in notched cylindrical bars

Shape memory alloys present a unique ability to undergo a solid-to-solid, diffusionless, reversible phase transformation. The forward phase transformation is commonly associated with transforming from the austenitic phase to the martensitic phase, while the reverse transformation is defined by going from the martensitic phase to the austenitic phase. In thermal actuation loading paths, forward transformation is generally associated with cooling, while reverse transformation is commonly associated with heating. In this article, however, it is shown that reverse transformation may occur during cooling of notched cylindrical shape memory alloy bars. The reversal in phase transformation is associated with the redistribution of stress in the shape memory alloy due to the phase transformation.

Finite element simulation of the influence of fretting wear on fretting crack initiation in press-fitted shaft under rotating bending

A Finite element based methodology for fretting wear and fretting fatigue prediction in press-fitted shaft is developed. This methodology integrates wear modelling with fretting fatigue analysis to quantitatively predict of the effects of stress redistribution and material removal induced by the fretting wear on fretting crack initiation properties. The fretting wear-induced evolutions of mean normal stress, a mean correction multiaxial damage parameter and accumulated fatigue damage are predicted by this methodology. The results show that the fretting crack initiation at the contact edge is significantly suppressed by the severe fretting wear, since the server stress concentration is relieved and the surface material with high accumulated fatigue damage is grinded off. While, the fretting crack initiation at the inner surface of the contact area is greatly promoted by the slight wear by introducing the large stress concentration near the edge of fretted wear scar.

Stress Redistribution Explains Anti-correlated Subglacial Pressure Variations

We used a finite element model to interpret anti-correlated pressure variations at the base of a glacier to show the importance of stress redistribution in the basal ice. Two pairs of load cells are installed 20 m apart at the base of the 210 m thick Engabreen glacier in Northern Norway. Pressurisation of a subglacial channel located over one pair led to anti-correlation in pressure between them. A full Stokes 3D model of a 210 m thick and 25-200 m wide glacier with a pressurised subglacial channel represented as a pressure boundary condition was used to investigate the anti-correlated response at the bed. The model reproduced the anti-correlated pressure response at the glacier bed and variations in pressure of the same order of magnitude as the load cell observations. The anti-correlation pattern was shown to depend on the bed/surface slope such that the anti-correlated pressure variations were reproduced at a distance greater than 10-20 m from the channel when the bed slope was zero, whereas anti-correlation occurred within 10 m of the channel when the bed was inclined by 5 degrees. Pressurisation of the channel led to lateral or vertical ice flow away from the channel, support of the overlying ice and reduction of the normal stress on the bed. If the modelled cross-section was laterally constrained and the bed flat, the resulting bridging effect diverted some of the normal forces acting on the bed to the sides. In contrast, if the bed was inclined, then channel support was vertical only. The model showed that the effect of stress redistribution depends on the slope as well as the geometry of the subglacial channel and glacier, and can lead to an opposite response in pressure at the same distance from the channel.

A numerical study of the effects of shot peening on the short crack growth behaviour in notched geometries under bending fatigue tests

The current paper presents a numerical analysis of the effects of shot peening on short crack growth in a low pressure (LP) steam turbine material, FV448. The fatigue behaviour of this material has been experimentally evaluated using a U-notched specimen (representing the fir tree root geometry of the turbine blade) under 3-point bend tests. Two different shot peening intensities were considered in this study: an industrially applied shot peening process and a less intense shot peening process.In the modelling work, a 2-D finite element (FE) model with static short cracks has been developed, incorporating both compressive residual stress and strain hardening distribution effects caused by shot peening. Both linear-elastic (LEFM) and elasto-plastic (EPFM) fracture mechanics were used to characterise the crack driving force in the un-peened and shot-peened conditions, taking into account the effects of stress redistribution caused by residual stress relaxation and crack opening. The stress intensity factor used in the LEFM approach was calculated using the weight function method, and the equivalent stress intensity factor used in the EPFM approach was calculated from the J-integral, which was evaluated using the cracked FE model. These results could explain the mechanism of (experimentally observed) retardation of crack growth through the shot-peening-affected layer and also quantified this influence on fatigue life. The relative contributions of compressive residual stresses and strain hardening were assessed by investigating them separately. The sub-surface compressive residual stress distribution produced by shot peening could effectively reduce crack propagation but the strain hardening distribution, in contrast, can accelerate it. However, strain hardening is expected to hinder the crack initiation process by restricting the plastic deformation during cyclic loading. Predictions of the fatigue life of the shot-peened notched specimens were made based on this numerical analysis. Acceptable results were obtained using both the LEFM and EPFM approaches and the difference between them is discussed.

Stress redistribution and fracture propagation during restimulation of gas shale reservoirs

Restimulation of previously hydraulically-fractured wells can restore productivity to near original levels. Understanding the stress state resulting from the original hydraulic fracturing and subsequent depletion is vital for a successful refracuring treatment. The stress obliquity in the vicinity of the wellbore, due to production from a previously introduced hydraulic fracture, promotes a new concept – that of altered-stress refracuring which allows fractures to propagate into previously unstimulated or understimulated areas and therefore enhancing recovery. In this study, a coupled poromechanical model is used to define stress redistribution and to define optimal refrac timing as defined by maximizing the size of the stress reversal region. Key factors include the time dependency of the stress reorientation, the threshold stress ratio σhmax/σhmin and the influences of permeability anisotropy/heterogeneity, pressure drawdown and rock-fluid properties. The results show that stress reorientation develops immediately as the reservoir begins to produce. This stress reversal region extends to a maximum extent before retreating as the direction of the maximum principal stress gradually returns to the initial state. The optimal refrac timing and the size of the stress reversal region are positively correlated with pressure drawdown and Biot coefficient, negatively correlated with stress ratio σhmax/σhmin ratio and Poisson’s ratio and ambiguously correlated with permeability anisotropy. Permeability magnitude and porosity have no influence on the size of the resulting zone but are negatively and positively correlated to the timing, respectively. Permeability heterogeneity has no influence on the size nor the timing. Coupled fluid flow and damage-mechanics simulations follow fracture propagation under the effect of stress redistribution during refracturing treatments. These results define the evolving path of secondary refracture as it extends perpendicular to the initial hydrofracture and ultimately turns parallel to the hydrofracture as it extends beyond the stress-reversal region. This discrete model confirms the broader findings of the continuum model.

The influence of traffic moving speed on shakedown limits of flexible pavements

ABSTRACTShakedown theory is often used to analyse elastic–plastic responses of structures subjected to variable or repeated loads. In pavement engineering, it has been used to predict the maximum admissible load (termed as ‘shakedown limit’) against excessive rutting in flexible pavements. Pavement shakedown analysis, which involves the calculation of the pavement shakedown limit, usually utilised elastic stresses induced by a static wheel load and therefore neglected any possible dynamic responses. This paper will, for the first time, evaluate the dynamic effect of the moving load on the shakedown limit of flexible pavement. A numerical approach is developed based on a recent lower bound method for solving the pavement shakedown problem. The dynamic responses of elastic stresses to the moving traffic loads are computed using finite element method in which infinite elements are used for boundaries. Shakedown limits for a single subgrade layer and a pavement-subgrade system under traffic loads at various speeds are investigated. It is found that the shakedown limit is consistent with the static solution when the load moving speed is very low and it is reduced as the load moving speed is changed towards the speed of Rayleigh wave propagation. In the layered system, the shakedown limit increases with rising strength ratio and layer thickness until a maximum value is reached. The rise of stiffness modulus ratio can either increase or decrease the shakedown limit of the first layer due to the negative effect of stress redistribution and the positive effect of rising Rayleigh speed. When the stiffness modulus ratio is relatively small, the latter effect overwhelms the former one, or vice versa.

Time-dependent redistribution behavior of residual stress after repair welding

Welding is one of the main technological operations in shipbuilding and it is used in all ship manufacture steps, from joining plates to the unions of sub-blocks and blocks during the final stage of ship assembly. The correction of dimensional discrepancies in ship blocks during assembly involves an additional welding operation named repair welding, which introduces new residual stresses in the structural elements of the ship. Being an emergency operation in manufacture, repair welding becomes a standard operation in ship maintenance. This paper presents an experimental study of residual stress caused by repair welding. The state of the residual stress was monitored using a magnetic method, and the stress values were measured using X-ray diffraction techniques. The experimental results show that the residual stress distribution varies significantly after the welding process within a period of 2 weeks. This phenomenon was not previously reported in the literature. The authors name it the welding stress redistribution effect. The same phenomenon was also observed for repair welding specimen with the shot peening treatment to relieve residual stresses.

Coring damage mechanism of the Yan-tang group marble: combined effect of stress redistribution and rock structure

Micro-cracks induced by the coring process in rock samples retrieved from high in situ stress conditions may seriously influence the evaluation of rock properties. This paper presents work performed to study the coring damage mechanism of marble samples containing a kind of inclined grey (or brown) ribbon-like stripes, whose mineral components are calcite and dolomite. These samples were obtained from the Jin-ping Second Stage Hydropower Station (JPII) in China, and the coring site is located in the strata of the 5th layer of the Yan-tang group marble in the Middle Triassic system (T 2y 5 ). A special stress-relief coring scheme was carried out to collect rock samples under different stress levels at one position, then the coring damage in these samples was examined by sonic wave testing and acoustic emission monitoring under uniaxial loading conditions, and a numerical simulation was also conducted to investigate the stress path experienced by a rock core during sampling. The results indicate that for the specific Jin-ping Yan-tang group marble (T 2y 5 ) sample, the coring damage can be attributed to two kinds of micro-cracks: horizontal micro-cracks induced by stress redistribution, and vertical or sub-vertical micro-cracks mainly derived along the special rock structure. The horizontal cracks, generated by the tensile stress induced during coring, are mostly trans-granular ones, and can be regarded as the main reason for coring damage. In contrast, the vertical (or sub-vertical) micro-cracks are mainly caused by the combined effect of coring-induced high deviatoric stress and the inclined grey-brown ribbons, and it usually occurs along grain boundaries. At a relatively low stress level, the shear failure may preferentially occur along special rock structures. However, the impact of the micro-structure on cracking reduces significantly with the increase of stress level, and then the induced tensile stress may become the dominant factor leading to horizontal cracks or disking.

Fatigue crack growth behaviour in the LCF regime in a shot peened steam turbine blade material

In this study, short fatigue crack initiation and early growth behaviour under low cycle fatigue conditions was investigated in a shot peened low pressure steam turbine blade material. Four different surface conditions of notched samples have been considered: polished, ground, T0 (industry applied shot peened process) and T1 (a less intense shot peened process). Fatigue crack aspect ratio (a/c) evolution in the early stages of crack growth in polished and shot peened cases was found to be quite different: the former was more microstructure dependent (e.g. stringer initiation) while the crack morphology in the shot peened cases was more related to the shot peening process (i.e. surface roughness, position with respect to the compressive stress and strain hardening profiles). Under similar strain range conditions, the beneficial effect of shot peening (in the T0 condition) was retained even at a high strain level (Δε11=0.68%), Nf,ground<Nf,T1<Nf,polished<Nf,T0. The a/c evolution effects were incorporated in K-evaluations and used in calculating da/dN from surface replica data. Apparent residual stress (based on crack driving force ΔK difference) was applied to describe the benefit of shot peening and was seen to extend significantly below the measured residual stress profile, indicating the importance of the strain hardening layer and stress redistribution effects during crack growth.