Influence Of Compressive Residual Stresses Research Articles

Study on fatigue crack growth property of abrasive waterjet peened aluminum alloy

Abrasive waterjet peening is a favorable surface treatment method for improving the fatigue resistance of metal materials. An insight into the fatigue crack growth properties of AWJ peened specimens is meaningful for obtaining better strengthening performance. In present work, a numerical model of AWJ peening was established and experimentally validated for investigating the fatigue crack growth characteristics of Aluminum specimens. The effect of peening and loading conditions on the fatigue performance was also analyzed. The results indicated that the stress intensity factor at the peened region was enhanced and the crack propagation was significantly inhibited by the compressive residual stress. The influence of compressive residual stress on the effective stress factor range is greater under lower external load and higher loading ratio. The fatigue life for reaching the crack length of 40 mm is increased by 37%, 60% and 98% after peening by using the intensity of 0.6 mmA, 0.8 mmA and 1 mmA, respectively.

An Approach to Predict the Residual Stress-Depth-Profile of Thin Sheet Metal Processed by Laser Shock Peening Without Coating

For conventional laser shock peening, the positive influence of compressive residual stresses on fatigue strength is well understood. To protect the material’s surface from ablation, a sacrificial layer is applied. This, however, leads to an additional process step, which deteriorates its economic efficiency. Thus, laser shock peening without coating (LPwC) is more frequently investigated for industrial applications. However, LPwC increases the thermal impact on the material, which may provoke tensile residual stresses in the surface region. In this regard, understanding the influence of LPwC on the residual stress state and deriving a suitable state, e.g., for subsequent applications or forming operations, result in a design of experiment with numerous residual stress measurements. Residual stress-depth-profiles obtained by X-ray diffraction are time-consuming and cost intensive. Hence, a model is proposed to predict the residual stress-depth-profile of LPwC-processed thin sheets. The analytical model is based on the source stress model and uses experimental results, namely hardness as well as shape change measurements. Sheets made of X5CrNi18-10 and with a thickness of 1 mm are LPwC-processed with a nanosecond fiber laser. In the thermally dominated area where tensile residual stresses are present, the model agrees well with the experimental measurements. Moreover, it is revealed that LPwC leads to a saturation of residual stress level maximum and depth in dependence of pulse energy, repetition rate and number of repetitions. Subsequently, the model is used for tailoring the stress profile of thin sheets by LPwC for subsequent bottom bending.

Influence of local residual stresses on fatigue crack initiation

The aim of the paper is to investigate the influence of compressive residual stresses on the fatigue initiation life (S-Nini) curve of AISI 1141 steel. The analysis has been performed by means of a micro-structurally-based fatigue crack initiation modelling approach. The focus is set on the local (surface) residual stresses typically imposed by a surface treatment technique known as shot -peening. By superimposing such stresses on stresses resulting from outer cyclic loading, it could be shown that an impact on the fatigue curve in the S-Nini diagram can be achieved.

Influence of Compressive Residual Stress Induced by Peening on Contact Fatigue Strength of Case-Hardened Steel Roller

Influence of Compressive Residual Stress Induced by Peening on Contact Fatigue Strength of Case-Hardened Steel Roller

Optimised laser peening strategies for damage tolerant aircraft structures

Simulation models were constructed to explore the influence of compressive residual stress on fatigue crack growth rates in aluminium sheet. Balanced residual stress fields resulting from imposition of compressive stresses in laser peen patches were calculated. Growth rates of cracks approaching, traversing and propagating away from peen patches were calculated using modified superposition models. Effects of patch dimensions and position on residual stress fields, growth rates and life were investigated. Overall life varied widely depending on the balance between retardation and acceleration; many peen arrangements had little or no life benefit. Implications of the results for damage tolerant design are discussed.

Influence of the Thickness of a Nanolayer Composite Coating on Values of Residual Stress and the Nature of Coating Wear

The article discusses the influence of the thickness of the wear-resistant layer of the Zr-ZrN-(Zr,Al,Si)N nanolayer composite coating on the values of residual stress and the nature of coating wear. The study focused on coatings with wear-resistant layer thicknesses of 2.0, 4.3, 5.9, and 8.5 µm, deposited using filtered cathodic vacuum arc deposition (FCVAD) technology. The X-ray diffraction (XRD) method based on the anisotropy of the elasticity modulus was used to find the values of the residual stress. The nature of the formation of interlayer delamination under the influence of residual compressive stress was studied using a scanning electron microscope (SEM). When the wear-resistant layers had a thickness of 2.0–5.9 μm, tensile stress formed, which decreased with an increase in the thickness of the coating. When the thickness of a wear-resistant layer was 8.5 μm, compressive stress formed. Under the action of compressive stress, periodic interlayer delamination formed, with a pitch of about 10 binary nanolayers. A mathematical model is proposed to describe the nature of the formation of interlayer delamination under the influence of compressive residual stress, including in the presence of a microdroplet embedded in the coating structure.

Equivalent constitutive model of steel plate shear wall structures

To accurately and efficiently predict seismic responses of steel plate shear wall structures using simplified strip element models, an improved uniaxial equivalent constitutive model was proposed. Skeleton curves were employed, respectively, to quantify the effect of appreciable cyclic hardening characteristics of different steel materials and to take into account the influence of compressive residual stress. Simplified hysteretic criteria were suggested to capture pinching phenomena, reloading process and unloading process in details. Then, the proposed model was incorporated into the general finite element software ABAQUS as a user defined material (UMAT). Together, the model was validated against a series of typical experimental results. Finally, parametric analyses of the prototypes with a wide range of width-to-thickness ratios and loading patterns were conducted, with focus on the feasibility and applicability of the proposed model. These analyses demonstrated that: the proposed model could better evaluate the hysteretic behavior of steel plate shear wall structures with a wide range of width-to-thickness ratios and different steel materials. Meanwhile, it guarantees both the computational accuracy and efficiency, providing a valuable tool for nonlinear analysis of overall steel plate shear wall structures.

A comparative study between conventional and elevated temperature creep autofrettage

This paper presents a comparative study between conventional hydraulic and elevated temperature autofrettage. For modelling of both methods advanced plasticity and creep material models are used. The main governing equations for the models are presented as well. A beneficial influence of compressive residual stresses induced by both methods is demonstrated on a benchmark problem of cross bored block. The effectiveness and applicability of the two methods are estimated by conduction of compressive residual stress analysis and crack arrest modeling. Numerical simulation of the cyclic plasticity and creep problems are carried out by means of FEM in ANSYS Workbench with FORTRAN user-programmable subroutines for material model incorporating custom equations.

SIMULATION OF ROLLING CONTACT FATIGUE STRENGTH FOR TRACTION DRIVE ELEMENTS

The simulations of the rolling contact fatigue strength for traction drive elements was carried out, and the estimation accuracy of it was verified by comparing with the experimental result. The experiment was carried out by following the 14 S-N testing method. The material of test rollers was carburized JIS SCM420H. The calculated rolling contact fatigue strength in failure rate of 50% at 107 cycles was 750 MPa with a standard deviation of 35.4 MPa. The rolling contact fatigue strength of 1120 MPa with a standard deviation of 50.8 MPa was obtained as a result of experiment. The calculated standard deviation was about equal to the experimental result. Though there was 370 MPa difference between calculated and experimental fatigue strength. Including of the hardening of roller and the influence of compressive residual stress in the simulation and the determination of the depth of failure initiation will decrease above error.

The Crack Initiation and Propagation in threshold regime and S-N curves of High Strength Spring Steels

An integrated fracture mechanics approach is proposed to account for the estimation of the fatigue resistance of component. Applications, estimations and results showed very good agreements with experimental results. The model is simple to apply, accounts for the main geometrical, mechanical and material parameters that define the fatigue resistance, and allows accurate predictions. It offers a change in design philosophy: It could be used for design, while simultaneously dealing with crack propagation thresholds. Furthermore, it allows quantification of the material defect sensitivity. In the case of the set of fatigue tests carried out by rotational bending of specimens without residual stresses, the estimated results showed good agreement and that an initial crack length of 0.5 mm can conservatively explain experimental data. In the case of fatigue tests carried out on the springs at their final condition with bending at R = 0.1 our data shows the influence of compressive residual stresses on fatigue strength. Results also showed that the procedures allow us to analyze the different combinations of initial crack length and residual stress levels, and how much the fatigue resistance can change by changing that configuration. For this set of tests, the fatigue resistance estimated for an initial crack length equal to 0.35 mm, can explain all testing data observed for the springs.

Effects of laser peening on residual stresses and fatigue crack growth properties of Ti–6Al–4V titanium alloy

The effects of laser peening (LP) with different laser peening coverage rates on residual stresses and fatigue crack growth (FCG) properties of Ti–6Al–4V titanium alloy were investigated. Residual stresses after LP and micro-structure with different fatigue striation patterns on fracture cross-sections were analyzed. Compressive residual stresses and dense dislocation arrangements can be obtained in the superficial layer after LP. The influence of compressive residual stresses induced under different LP coverage rates on FCG properties was revealed. LP coverage rate had an apparent influence on FCG properties as confirmed by the fatigue striation spacing on fracture cross-sections. Moreover, FCG rate decreased with the increase of compressive residual stresses perpendicular to the crack growth direction, which indicated that LP had an obvious inhibitory effects on FCG.

Fatigue strength and failure mechanism for the aluminium wrought alloy EN AW 6056 in the VHCF-region and influence of notches and compressive residual stresses

The fatigue strength and the transition of failure mechanism from the high cycle fatigue (HCF) to the very high cycle fatigue regime (VHCF) for EN AW 6056 were investigated at mechanically polished, smooth specimens. Fatigue tests were conducted with a servohydraulic testing machine and a resonant frequency machine at room temperature. Tests run up to a maximum number of cycles N=2⋅108.The results reveal that the fatigue strength decreases with increasing number of cycles, which is known for materials with facecentred cubic lattice. In the very high cycle regime the crack initiation sites of the smooth specimens were internal. Fracture surface and microstructure of the crack initiation sites were investigated by means of scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX), electron back scatter diffraction analysis (EBSD) and metallographic methods. The influence of notches was investigated at slightly notched (Kt=1.75) and sharp notched (screws M10, Kt=4.7) specimens. The influence of compressive residual stresses was investigated by a comparison of precision-turned and shot-peened, slightly notched specimens as well as screws of with thread rolling before heat treatment and thread rolling after heat treatment. The fatigue strength of the specimens without compressive residual stresses decreases with increasing number of cycles. The fatigue strength of the specimens with compressive residual stresses shows a horizontal SN-curve after a point of deflection. The crack initiation sites of the notched specimens were always at the root of the notch independent of the compressive residual stresses and the number of cycles.

Mechanic treatment of fastener holes: The influence of compressive residual stress on the corrosion behaviour of aluminium alloys

AbstractCorrosion has a significant impact on the life cycle cost of military aircraft. Fleet experiences show that structural areas around joining elements (rivets, bolts) and faying surfaces are particularly sensitive to corrosion. During the repair currently performed the corrosion usually is blended out, the surface protection applied, the fastener inserted and a new top coat applied. Blending out corrosion often results in a reduction of fatigue life. To restore fatigue life the induction of compressive stress in the area affected is common practice. It is generally accepted that the induction of compressive residual stress extends fatigue life but its impact on the overall corrosion behaviour of alloys is discussed controversially in the literature. For this reason the influence of compressive residual stress on the corrosion behaviour was investigated in a joint experimental project. The compressive residual stress was introduced in different ways on laboratory scale and the specimens artificially weathered to simulate the effect of corrosion.

Controlled failure design of drillstring threaded connections

ABSTRACTThe threaded connection of the type used in hydrocarbon exploration is a critical component of the drillstring that is highly susceptible to fatigue damage. Fatigue crack growth can either lead to a catastrophic failure of the connection, known as a twist‐off, or can be a non‐critical failure, known as a wash‐out. The design philosophy of Controlled Failure Design has been used in order to promote a ‘friendly’ non‐critical failure in the connection, by the controlled application of compressive residual stresses. The influence of compressive residual stress and its effect on controlling fatigue crack shape has been experimentally investigated with the development of thread root cold rolling equipment. Through the control of the cold rolling process, it has been demonstrated that fatigue crack growth can be controlled to produce a localized, non‐critical failure in the connection.