Range Of Stress Ratios Research Articles

Fatigue delamination damage analysis in composite materials through a rule of mixtures approach

The present study investigates delamination damage initiation and propagation within a homogenization theory of mixtures, using the concept of virtual layers and virtual interfaces. It eliminates spatial discretization of layers, introducing a resultant damage variable to capture structure’s bulk response under both monotonic and cyclic loads. Fatigue-induced deterioration is classified into sub-critical, critical, and over-critical stages based on interfacial stresses. Calibration is conducted employing the widely-available Wöhler curves for each loading mode independently. An advance-in-time strategy is included in the model to enhance the simulation speed. The reliability of the approach is assessed for crack initiation and propagation separately through standard test coupons, showing good correlation with experimental data in mode I, mode II, and mixed-mode loading conditions. Depending on the calibration procedure adopted, the model is applicable to a wide range of stress ratios. In addition, it could be integrated into any standard finite element framework using the desired number of elements through the thickness regardless of the physical amount of layers. This allows easy modification of stacking sequences or the number of layers within the constitutive law without mesh structure changes, facilitating simulation of large-scale composite laminates with minimal accuracy loss and reduced computational costs.

A new method for predicting the fatigue strength at various stress ratios based on damage of metallic materials

AbstractThe prediction of fatigue strength for metallic materials in a wide range of stress ratios is a crucial engineering challenge. To pursue a more accurate method, the dependence of fatigue strength on stress ratio for 35CrMo steel and other materials was investigated in detail. It was found that as the stress ratio increases, the damage mechanism changes, and the errors of the conventional models in predicting the fatigue strength increase. The reason is that those models fail to describe the fatigue damage evolution of metallic materials under some special conditions. Based on the variational fatigue damage, a new prediction method was proposed by introducing the damage parameter. Through the validation with fatigue strength covering a variety of metallic materials and loading conditions, the method exhibits higher universality. And then the corresponding parameter of the formula is further analyzed to elucidate the influences of various loading conditions on fatigue damage of materials.

Continuum damage mechanics-based fatigue life prediction of L-PBF Ti-6Al-4V

The fatigue behavior and life of additively manufactured Ti-6Al-4V are very dependent on its heterogeneous microstructure, which in turn results from its fabrication process. In this paper, a fatigue damage model based on continuum damage mechanics was proposed to predict the high-cycle and very-high-cycle fatigue life at various stress ratios of Ti-6Al-4V fabricated by laser powder bed fusion (L-PBF). Model predictions were found to be in good agreement with experimental results for the different stress ratios considered. The model was found to be sufficiently robust to predict the fatigue life of other titanium alloys over a range of mean stress. The primary novelty is the incorporation of a tensorial formulation for anisotropic fatigue properties and the nonlinear effect of mean stress, which extended the model applicability to a wide range of stress ratio from -1 to 0.5. The results provide new insight into mean stress effects on fatigue of L-PBF Ti-6Al-4V up to the very-high-cycle fatigue regime.

Fatigue behavior of copper thin films

In this study, to investigate the mean stress effect on fatigue life of a 12 μm thick copper thin film, fatigue tests were performed at four maximum stress levels for a wide range of stress ratios. Tensile and creep tests were also performed to obtain the reference mechanical properties of the copper thin film tested. The fatigue behavior of copper thin films depended on the regions of the stress ratio and the modified Goodman and Gerber equations could not describe the mean stress effect on fatigue life well. The Haigh diagram was constructed using stress vs. life curve data obtained in this study, and the constant life curve was approximated by three straight lines. The Haigh diagram for copper thin films can be classified into three regimes: fatigue, fatigue-creep, and creep, depending on the fracture mode. The fatigue life can be well described with the equivalent stress amplitude calculated from the constant life curve, regardless of stress ratio.

Assessing fatigue crack growth thresholds for a Ti-6Al-4V (STOA) alloy using two experimental methods

Fatigue crack growth rate behavior in the threshold and near-threshold regimes for a Ti-6Al-4V solution-treated and over-aged (STOA) alloy was investigated using two test procedures: i) accelerated load reduction (ALR) utilizing faster load-shed rates than recommended in the ASTM standard E647 load-reduction (LR) test procedure, and ii) compression pre-cracking constant-amplitude (CPCA) or load-increasing (CPLI) and load-reduction (CPLR). Fatigue crack growth tests were conducted on compact, C(T), specimens (B = 6.35 mm) with two different widths (W = 51 and 76 mm) at two stress ratios (R = 0.1 and 0.7). The crack-growth-rate test data were compared to previous test data produced from the same batch of material using the ASTM LR and CPCA test procedures that were tested on C(T) specimens (W = 25, 51 and 76 mm) over a wide range in stress ratios (R = 0.1, 0.4, and 0.7).Although none of the load-reduction test procedures provided a good representation of the threshold value (ΔKth) at low R, the CPCA test procedure was the most promising. The LR, ALR, and CPLR test procedures were influenced by prior loading history, leading to higher ΔKth values and slower crack growth rates in the threshold regime due to a rise in the crack-opening loads. The LR and ALR tests at R = 0.1 and shed rates of −0.08, −0.32, and −0.95 mm−1 yielded ΔKth values that were 15 to 38 % higher than the estimated threshold stress-intensity factor range (ΔK*th)R=0.1 based on the crack-closure model (FASTRAN). The compression pre–cracking test procedures are more accurate alternatives for developing threshold and near-threshold fatigue crack growth rates. Specifically, the CPLR test procedure produced a ΔKth value that was 8–18 % higher than (ΔK*th)R=0.1. Additionally, LR and ALR tests produced different ΔKth values as a function of the specimen width for a given load ratio, which violates classical fracture mechanics principles. In addition, the spread in the ΔK-rate data in the low-rate regime was larger than the spread in the mid-rate regime as a function of R, a term referred to as “fanning”. In contrast, the CPCA test procedure produced consistent crack growth rates over the same range of ΔK values examined, independent of the specimen width and these data did not exhibit “fanning” with R. Further research is necessary to develop standard test procedures capable of providing a more definitive representation of the ΔKth value in the threshold regime. However, FASTRAN can serve as a crucial tool in aligning the actual ΔKth values with those obtained through CP testing, thereby bridging the gap and enhancing the reliability of the results.

Fatigue Crack Growth on Several Materials under Single-Spike Overloads and Aircraft Spectra during Constraint-Loss Behavior

Abstract The phenomenon of flat-to-slant crack growth has been studied by many in the fracture mechanics community. At low stress-intensity factors, a fatigue-crack surface is flat (tensile mode) and the crack-front region is under plane-strain conditions (high constraint). As the crack grows with higher stress-intensity factors, a 45° shear lip occurs through the thickness of the sheet or plate. This behavior is the shear mode, which is under low constraint or plane-stress conditions. In 1966, Schijve found that the transition from flat-to-slant crack growth on a 2024-T3 Alclad aluminum alloy over a wide range in stress ratios (R) occurred at a “constant” crack-growth rate. Also, Newman and Hudson showed the same behavior on 7075-Temper-6 and Ti–8Al–1Mo–1V alloys, validating Schijve’s observation that crack-growth rate was the key parameter for flat-to-slant crack-growth behavior. The materials considered herein are 2024-T3, 7075-T6, and 9310 steel. Crack-growth behavior during single-spike overloads and simulated aircraft spectrum loading are presented. The fatigue structural analysis (FASTRAN) crack-closure based life-prediction code was used to correlate the constant-amplitude (CA) crack-growth-rate data over a wide range in stress ratios (R = Smin/Smax) and rates from threshold to near fracture, and to calculate or predict the crack-growth behavior on single-spike overload tests. Crack-closure behavior is strongly dependent upon the level of constraint. The main objective was to see if the constraint-loss region is the primary reason for crack-growth delays after single-spike overloads. Also, crack-growth analyses are presented on tests that were conducted by Wanhill on 2024-T3 Alclad aluminum alloy under the transport wing standard (TWIST) spectrum. Crack-growth analyses using crack-closure theory without constraint loss was “unable” to predict crack growth under spike overloads or simulated aircraft spectra. However, predicted crack length against cycles with constraint-loss behavior compared reasonably well with all tests.

Fatigue Crack Growth Analysis in Modified Compact Tension Specimen with Varying Stress Ratios: A Finite Element Study

In this study, the primary objective is to analyze fatigue crack propagation in linear elastic fracture mechanics using the SMART crack growth module in the ANSYS Workbench, employing the finite element method. The investigation encompasses several crucial steps, including the computation of stress intensity factors (SIFs), determination of crack paths, and estimation of remaining fatigue life. To thoroughly understand crack behavior under various loading conditions, a wide range of stress ratios, ranging from R = 0.1 to R = 0.9, is considered. The research findings highlight the significant impact of the stress ratio on the equivalent range of SIFs, fatigue life cycles, and distribution of deformation. As the stress ratio increases, there is a consistent reduction in the magnitude of the equivalent range of stress intensity factor. Additionally, a reciprocal relationship is observed between the level of X-directional deformation and the number of cycles to failure. This indicates that components experiencing lower levels of deformation tend to exhibit longer fatigue life cycles, as evidenced by the specimens studied. To verify the findings, the computational results are matched with the crack paths and fatigue life data obtained from both experimental and numerical sources available in the open literature. The extensive comparison carried out reveals a remarkable level of agreement between the computed outcomes and both the experimental and numerical results.

Investigation on the Fatigue Behaviors of Maraging Steel at Different Stress Ratios

Herein, the high‐cycle fatigue behaviors of 18Ni maraging steel with different tensile strength in the stress ratio range from 0.1 to 0.5 are investigated, and compared with those at the stress ratio of −1. It is found that the relationship between the fatigue strength at the stress ratios of −1 and 0.1 and tensile strength is nonmonotonic, while the fatigue strength at the stress ratio of 0.5 improves as the tensile strength heightens. The tensile strength corresponding to the optimal fatigue strength state would change with the variation of the stress ratio, which is related to the alteration of key factors affecting the fatigue damage. Moreover, it is found that the Walker equation: σaR = σ−1 ⋅ [(1 − R)/2]β gives reasonable results for the influence of stress ratio on the fatigue strength of 18Ni maraging steel.

Experimental study on bending fatigue strength of adhesively bonded joints

This paper focuses on the establishment of repair or strengthening method of steel structures by externally bonded patch plates. The bending static tests and bending fatigue tests of adhesively bonded joints were conducted and the fatigue life is evaluated. The Konishi E258R is used as an adhesive, and the bending fatigue tests were conducted, varying the applied stress ranges and the stress ratio, the ratio of minimum and maximum stress of fatigue test. The result indicates that the fatigue life of adhesively bonded joints can be evaluated in the function of principal stress ratio, the ratio of principal stress range against principal stress at debonding by the bending test, with constant linearity regardless of the stress ratio.

A new mixed type crack propagation criterion in shale reservoirs

Hydraulic fracturing is a mainstream technology for unconventional oil and gas reservoirs development all over the world. How to use this technology to achieve high-level oil and gas resource extraction and how to form complex fracture networks as hydrocarbon transportation channels in tight reservoirs, which depends to a large extent on the interaction between hydraulic and pre-existing cracks. For hydraulic fracturing of fractured reservoirs, the impact of natural fractures, perforation direction, stress disturbances, faults and other influencing factors will produce a mixed Ⅰ&Ⅱ mode hydraulic fracture. To forecast whether hydraulic fractures cross pre-existing fractures, according to elastic mechanics and fracture mechanics, a stress state of cracks under the combination of tensile (Ⅰ) and shear (Ⅱ) is presented. A simple mixed-mode Ⅰ&Ⅱ hydraulic fracture's crossing judgment criterion is established, and the propagation of hydraulic fractures after encountering natural fractures is analyzed. The results show that for a given approaching angle there exists a certain range of stress ratio when crossing occurs. Under high approaching angle and large stress ratio, it is likely that hydraulic cracks will go directly through pre-existing cracks. The reinitiated angle is always controlled within the range of approximately 30° among the main direction of penetration.

Research on process modeling and simulation of spent lead paste desulfurization enhanced reactor

In the reaction process of carbonate desulfurization lead paste, the produced PbCO3 is easily wrapped in the outer periphery of PbSO4 to form a product layer, hindering the mass transfer process. Therefore, it is necessary to break the PbCO3 product layer. In this work, the rotor stator-reinforced reactor was selected as the enhanced desulfurization reactor for the purpose of breaking the PbCO3 product layer and promoting mass transfer. The breakage process of the PbCO3 product layer generated during the PbSO4 desulfurization was modeled. Computational fluid dynamics simulation to the rotation conditions was carried out to theoretically analyze the fluid flow characteristics of PbSO4 slurry and the wall shear stress affecting the breakage of PbCO3 product layer. By optimizing the rotation conditions, the distribution ratio of effective rotor wall shear stress range achieved 96.1%, and the stator wall shear stress range reached 99.15% under a rotation of 2000 r·min−1. The research work provides a reference for analysis of the mechanism of product layer breakage in the PbSO4 desulfurization process, and gives a clear and intuitive systematic study on the fluid flow characteristics and wall shear stress of the desulfurization reactor.

Creation of a Life Prediction Model for Combined High-Cycle Fatigue and Creep

Abstract While industrial gas turbine blades are commonly designed to resist creep and high-cycle fatigue (HCF) failure, the combination of these two loading conditions is seldom considered. The effect of creep damage elicited prior or concurrent to HCF loading is not well established and can significantly reduce the HCF lifetime of these critical components. A comprehensive life prediction model capable of capturing these superimposed effects is needed to ensure current reliability standards are maintained when designing aggressively loaded, next-generation industrial gas turbine blades. The consequence of combined HCF and creep loading to the lifetime a Ni-base superalloy is characterized and modeled in this study. Composition and calibration of the model are carried out using data from HCF tests conducted on virgin and pre-crept specimens at 750 °C and 850 °C. The experimental data encompass a wide range of stress ratios and pre-creep strains to mimic to the expansive set of potential turbine blade loading conditions. The proposed microstructurally informed model is based on existing principles and relies on test data and information gathered from a comprehensive failure analysis of the tested samples.

Data-driven prediction of the fatigue performance of corroded high-strength steel wires

Corrosion damage determines the fatigue performance and intensifies the fatigue lifespan scatter of high-strength steel wires. Many experimental studies have been performed on corroded wires to quantify the correlation between fatigue life and corrosion. However, accurate analysis and fatigue performance prediction of various types of corrosion are still insufficient. This study proposes a predictive machine learning-based model to explore the quantitative influence of corrosion degree, stress ranges, loading ratio, loading frequency and other factors on the fatigue life of corroded high-strength steel wires. The proposed model is trained using the adaptive boosting algorithm on the basis of a collected database containing 323 samples from corrosion fatigue tests. A cross-validation method with the grid-search approach is applied to accelerate the optimisation of the hyperparameters. The performance of model is thoroughly compared with the empirical models and the common utilized machine learning algorithms. The prediction performance of the proposed model is considerably good, with a coefficient of determination of 0.96. The generalisation ability of the proposed model is superior to that of two common machine learning algorithms. Additionally, the physical meaning of the model is proven to be reasonable through a weight analysis of the input features. The stress range, corrosion rate and loading stress ratio dominate the fatigue performance of corroded high-strength steel wires.

On the modeling of deformation mechanisms in a Mg-3Al-1Zn alloy under biaxial tension

Although the {10-12} twinning behavior of Mg alloys under uniaxial tension and compression has been extensively investigated, the simulations of {10-12} twinning behavior under biaxial tension have rarely been reported. In this work, the EVPSC-TDT model is first employed to systematically investigate the deformation behavior of a Mg alloy AZ31 plate under biaxial tension in the RD-TD and ND-TD planes. The RD, TD and ND refer to the rolling direction, transverse direction, and normal direction of the hot rolled plate. The measured stress-strain curves and texture evolutions are well predicted and the contours of plastic work under biaxial tension are also constructed for comparison with experiments. The plastic response has been interpreted in terms of relative activities of various deformation modes. For biaxial tension in the RD-TD plane, basal and pyramidal slips mainly contribute to the plastic deformation for stress ratios of σRD:σTD= 1:2 to 2:1. Prismatic slip becomes more active for σRD:σTD=1:4 and 4:1. Compression twinning could be activated and so cause texture reorientation at large strains, especially for σRD:σTD=1:1. The six-fold feature of {10-10} pole figure could still be observed forσRD:σTD=1:4 and 4:1 at large strain. For biaxial tension in the ND-TD plane, tensile twinning plays an important role for σND:σTD≥1:2, while prismatic slip contributes to plastic deformation for the other cases. With the increase of stress ratio from σND:σTD≥1:1 to 1:0, the predicted twin volume fractions (VFs) at a specific strain along the ND, εND, almost linearly decrease, however, it is seen that the experimental ones at given strains along the ND do not follow such a trend with the measured twin VFs within the range of stress ratios, 2:1≤σND:σTD≤6:1, clearly being overestimated, and the difference between experiments and simulations becomes most obvious at the relatively small strain of εND=0.015. The possible reasons for the observed difference are discussed.

Creep behavior of Grade 10.9 high-strength bolts under and after fire

• Experiments were conducted on creep behaviour of Grade 10.9 high-strength bolts under and after fire. • The Field & Field model is calibrated for simulating creep behavior of high-strength bolts at elevated temperatures. • The temperature, load ratio and loading duration are key factors affecting the creep behavior of T -stub connections. • High-strength bolts have more obvious creep deformation at high temperatures than high-strength steels. • A reduction factor is recommended to consider the creep effect on determining strength of T -stub connections in Eurocode 3. High-strength bolts are widely used in beam-column connections of high-rise steel framed buildings. At the event of a fire, high-strength bolts may experience significant creep in a state of both high stress and high temperature, leading to fracture of connections and even progressive collapse of structures . This paper experimentally and numerically investigates the creep behavior of Grade 10.9 high-strength bolts under and after fire. The creep strain–time curves at different temperatures and stress ratios are obtained using DIC systems. The micromorphology and failure mechanism of high-strength bolts is examined by SEM. The Field & Field creep model is calibrated against test results, and parametric studies are conducted on creep behavior of T -stub connections. The experimental results show that the creep deformation of high-strength bolts is significant at high temperatures, and the creep strain is positively correlated with temperatures and stress ratios. While the creep effect of high-strength bolts after fire can be ignored. The creep-induced fracture of high-strength bolts under fire is in a ductile manner, and that after fire is in a brittle manner. High-strength bolts have more obvious creep phenomenon at high temperatures than high-strength steels, and it is unsafe to directly apply creep data of high-strength steels to high-strength bolts. The numerical results show that the Field & Field model is suitable for characterizing the creep behavior of high-strength bolts under fire with an applicable temperature range of 20–600 °C and stress ratio range of 0.4–0.8. The temperature, load ratio and loading duration significantly affect the creep behavior of T -stub connections under fire conditions. A reduction factor of 0.8 for 500 °C and 0.6 for 600 °C is recommended to consider the effect of creep on the strength of bolts in determining bearing capacity of T -stub connections in Eurocode 3. It is necessary to consider the effect of creep for predicting the fire behavior of high-strength bolts and steel connections, ensuring a safe design.

Empirijski pristup sveobuhvatnoj funkciji napona koja je ekvivalentna zamornom oštećenju

This paper develops an empirical damage-equivalent stress function for fatigue. Classical analysis methods are used to 'fit' an equation to a number of S-N curves for various grades of carbon steel. The resulting equivalent-damage stress function is applicable to steels subjected to a wide range of heat treatments, from normalised up to hardened and tempered to 1900MPa. It is also applicable to a wide range of stress concentrations, unnotched up to Kt = 5.0 and typical of screw threads. A range of stress ratios and mean stresses are also considered. The function overcomes some of the limitations of existing methods of 'correcting' for mean stress. Existing methods are limited in that, while they may give good results over a range of conditions, there are some circumstances where the results are highly inaccurate. The damage-equivalent stress function is suitable for use in automated calculation procedures such as spreadsheets, MathCAD ©, and SMathStudio ©.

INFORMATIVE BOUNDS OF NEURAL NETWORKS PREDICTION FOR COMPOSITE FATIGUE LIFE UNDER VARIABLE AMPLITUDE LOADING

In this study, the informative bounds of neural networks (NN) prediction with respect to the utilization of less fatigue data for fatigue life assessment of composite material covering a wide range of stress ratios R was examined and investigated. Fiberglass reinforced polyester of [90/0/±45/0] S lay-up with fatigue data of various stress ratios ( R = 0.1, 0.5, 0.7, 0.8, 0.9, -0.5, -1, -2 and 10) was examined in the present paper. Multi-layer Perceptrons (MLP) trained with Levenberg-Marquardt algorithm was utilized to result in fast and efficient NN model and Bayesian regularization technique was incorporated to deal with limited training data chosen for the model. The developed NN model was trained with fatigue data from only two stress ratios, where three sets of two stress ratio values were formed and used as the training sets, namely R = 0.1 and 0.5, R = 0.1 and -1, and R = 0.1 and 10, respectively. It was obtained that fatigue data from R = 10 produced the widest bounds of prediction, namely having the highest estimated standard deviation value from the fatigue lives predicted. Furthermore, it is revealed in the current study knowing the fact that fatigue data from R = 10 have the highest estimated standard deviation and subsequently including the fatigue data as one of the training data set, the NN model trained could produce the lowest mean squared error (MSE) value for the results of fatigue life prediction. This is justifying also the selection of training set of R = 0.1 and 10 as best training set in the previous study, which is based on the stress ratios’ better relative positions in the corresponding constant life diagram (CLD). Finally, taking the highest estimated standard deviation value from fatigue data of R = 10 as the conservative estimated bounds of NN prediction, it was shown that for the NN prediction of fatigue life whose noticeable discrepancies with the experimental data, the discrepancies were well confined within the conservative bounds of prediction.

Calibration of Paris law constants for crack propagation analysis of damaged steel plates strengthened with prestressed CFRP

Paris law constants, C and m, are two vital parameters of the Paris law for fatigue crack propagation of steel structures. Traditionally, the constants are determined through a linear regression of experimental crack growth curve under tension-to-tension cyclic loading. However, the direct linear regression would provide the value of C with larger error under negative stress ratios (tension-to-compression cyclic loading) probably caused by prestress. This study firstly proposed a reverse-reasoning methodology to obtain and calibrate Paris law constants based on the notched specimens with non– and prestressed CFRP (Carbon Fiber-reinforced Polymer) reinforcement under a wider range of stress ratios. Finite element (FE) modeling was then performed using a combination of the programs FRANC3D and ANSYS to compute the stress intensity factors (SIF) as well as crack tip shape evolution of the respective specimens. A sensitivity analysis was also made to investigate the variety of the constants affected by crucial factors. The comparison of experimental and theoretical results confirms excellent accuracy of the proposed method. The results indicated that the constant m is stable around 3.15 and prestress effect is significant not only on reduction of effective SIF range but also on change of the constant C. Moreover, the suggested value of m and C are 3.15 and 1.08E-12 for prestressed CFRP reinforced steel structures under negative stress ratio (R ≤ 0), and are 3.15 and 2.17E-13 for the positive stress ratio (R > 0) in the unit of mm and MPa, respectively.

Mean and residual stress effects on fatigue behavior in a pre-strained corner of stainless steel sheet

There are many thin-walled corners in the components of automobiles, machines, and structures. It is essential to elucidate their fatigue properties and influence factors. Parameters for stress–strain behavior of ferritic stainless plane sheet and pre-strained sheet were obtained under tensile, bending, and cyclic bending loads using the Ramberg–Osgood model. The parameters were integrally used as the fundamental characteristics of bending fatigue behavior for obtaining the mean stress and crack initiation stress amplitude from the measured strains in the curved portion of corner specimens. Bending fatigue tests of pre-strained corner specimens were carried out, and the relationships between the crack initiation strain amplitudes and the mean strains were verified. The strain amplitude ratios of the curved inside to outside portion were analyzed. The residual stress and hardness were measured, and work hardening effect on the inside was higher than that on the outside for improving fatigue strength. The fatigue limit of the corner specimen with the radius ratio of 1.3 was 23% higher than the unworked plane sheet. The effects of mean stress and residual stress on the fatigue strength were analyzed using the fatigue limit–static stress relation equations, indicating that the Gerber parabola can be used for fatigue limit predictions in the stress ratio range of R < –0.5 and that the Goodman line can be used after the point of R = –0.5. The SWT function can be used to accurately predict the fatigue lives in various conditions of stress amplitudes combined with static stresses.

Damage accumulation near a hole under low cycle fatigue proceeding from measurements of local deformation response

A new destructive method for quantitative determination of the damage accumulation in the vicinity of a stress concentrator has been proposed and verified. Increase of damage degree in local area with a high level of the strain gradient was achieved through preliminary low-cycle pull-push loading of plane specimens with central open holes. The above procedure is performed for three programs at the same stress range (333.3 MPa) and different stress ratio values 0.33, – 0.66 and – 1.0, and vice versa for two programs at the same stress ratio – 0.33 and different stress range 333.3 and 233.3 MPa. This process offers a set of the objects to be considered with different degree of accumulated fatigue damages. The key point of the developed approach consists in the fact that plane specimens with open holes are tested under real operation conditions without a preliminary notching of the specimen initiating the fatigue crack growth. The measured parameters necessary for a quantitative description of the damage accumulation process were obtained by removing the local volume of the material in the form of a sequence of narrow notches at a constant level of external tensile stress. External load can be considered an amplifier enhancing a useful signal responsible for revealing the material damage. The notch is intended for assessing the level of fatigue damage, just as probe holes are used to release residual stress energy in the hole drilling method. Measurements of the deformation response caused by local removing of the material are carried out by electronic speckle-pattern interferometry at different stages of low-cycle fatigue. The transition from measured in-plane displacements to the values of the stress intensity factor (SIF) and the T-stress was carried out on the basis of the relations of linear fracture mechanics. It was shown that the normalized dependences of the stress intensity factor on the durability percentage for the first notch (constructed for four programs of cyclic loading with different parameters), reflect the effect of the stress ratio and stress range of the loading cycle on the rate of damage accumulation. The data were used to obtain the explicit form of the damage accumulation function that quantitatively describes damage accumulation process. The functions were constructed for different stress ratios and stress ranges.