Search

This paper presents the development of the multiple linear regression approach based on the stress ratio and applied load that was assessed using entropy generation. The energy dissipation is associated with material degradation to determine the fatigue life with consideration to the irreversible thermodynamic framework. This relationship was developed by predicting a complete entropy generation using a statistical approach, where a constant amplitude loading was applied to evaluate the fatigue life. By conducting compact tension tests, different stress ratios were applied to the specimen. During the tests, the temperature change was observed. The lowest entropy generation was 2.536 MJm-3 K-1 when 3,000N load with a stress ratio of 0.7 was applied to the specimen. The assumptions of the models were considered through graphical residual analysis. As a result, the predicted regression model based on the applied load and stress ratio was found to agree with the results of the experiment, with only 9.3% from the actual experiment. Therefore, the entropy generation can be predicted to access the dissipated energy as an irreversible degradation of a metallic material, subjected to cyclic elastic-plastic loading. Thermodynamic entropy is shown to play an important role in the fatigue process to trace the fatigue life.

In the present investigation the high cycle fatigue behavior of Al6061-T6 aluminum alloy has been investigated at different frequencies. Fatigue tests were conducted at a frequency of 33 Hz and 50 Hz. A constant amplitude rotating bending fatigue experiment was performed at room temperature at a stress ratio of −1. The fatigue limit was tested using the staircase method at 107 cycles. At greater number of cycles, the S–N curve has shown its downward trend compared with the earlier member of cycles. The crack initiation point, crack propagation and sudden failure points were seen on the fractured surfaces. The fractured surfaces also shown uniform spacing of striations.

Earthquakes or cyclic loadings cause significant changes in the strength characteristics of soil. These changes, especially for sliding zone soil, can lead to catastrophic landslides. Taking into account this characteristic, this paper investigates the effects of prior cyclic loading on the consolidated undrained triaxial compression strength of sliding zone soil with the KTL triaxial automated system. Our experimental results indicate that the prior cyclic loading has a significant effect on the strength behaviour of saturated sliding zone soil. Under different confining pressures, cycle periods, and number of cycles, the samples exhibit the characteristics of strain-hardening. Deviatoric stress under cyclic loading condition is smaller than that with monotonic loading condition under different confining pressures, cycle periods, and number of cycles. As the confining pressure and cycle period increase, the failure stress ratio decreases. The axial strain exhibits a steep rise first and then stays stable under a cycle period of 90 s, while the axial strain shows a linear increase with an increase in the number of cycles under a cycle period of 10 s under confining pressures of 100 kPa and 400 kPa, respectively. The logarithmic relation correlates well with the failure stress ratio in the cyclic loading tests, which preliminary validates the applicability of logarithmic relation for sliding zone soil influenced by prior cyclic loading, providing a theoretical basis and guidance for the further understanding of strength characteristics of sliding zone soil.

This paper presents an analytical approach to predict the behaviours of geosynthetic-encased stone column (GESC)-supported embankments. The soil arching in the embankment and the nonlinear behaviours of stone columns are considered. Based on nonlinear elastic and elastoplastic constitutive models of stone columns, the nonlinear behaviours of GESCs, including settlement and radial deformation, are analysed. The deformations of GESCs, the surrounding soil, and the overlying embankment fill are compatible by applying stress continuity and volume deformation continuity at the bottom of the embankment fill. This method is verified via comparison with literature data and numerical analysis. The influences of parameters of the GESC, including encasement stiffness and column friction, on the performance of the embankment are investigated. Without considering the nonlinear behaviours of the column, the column-soil stress ratio is overestimated. It is more appropriate that the nonlinear characters of the column be considered in the analysis of GESC-supported embankments.

To study the seismic behavior of reinforced concrete (RC) columns serviced in coastal areas and strengthened with textile-reinforced concrete (TRC) after a dry-wet cycle coupled with a sustained load, low cycle loading testing was performed with six RC columns strengthened with TRC and one control column without TRC. The sustained stress ratio of the control column during the dry-wet cycle was 0.4 while those of the others strengthened with TRC were 0, 0.2, 0.4 and 0.6. The results show that although chloride dry-wet cycles decrease the ductility and energy dissipation capacity of strengthened columns, compared with the control column, TRC could still delay stiffness degradation and increase the ductility of strengthened columns to a certain extent. Additionally, with an increase in the sustained stress ratio, the energy dissipation capacity of the specimens decreases. The peak loads of the specimens gradually decrease with increasing sustained stress ratio during loading in the forward direction, and the variation in the peak load is irregular during loading in the negative direction. Besides, a reasonable proportion of the vertical load could improve the seismic capacity of unstrengthened specimens under chloride corrosion.

The fatigue analyses of AlSi7 closed-cell aluminium foam were performed using a real porous model and three different homogenised material models: crushable foam model, isotropic hardening model and kinematic hardening model. The numerical analysis using all three homogenised material models is based on the available experimental results previously determined from fatigue tests under oscillating tensile loading with the stress ratio R=0.1. The obtained computational results have shown that both isotropic and kinematic hardening models are suitable to analyse the fatigue behaviour of closed-cell aluminium foam. Besides, the kinematic hardening material model has demonstrated significantly shorter simulation time if compared to the isotropic hardening material model. On the other hand, the crushable foam model is recognized as an inappropriate approach for the fatigue analyses under tension loading conditions.

The fatigue crack initiation and growth characteristics in 7050-T7451 aluminum alloy butt joints subjected to different stress ratios and owing to friction stir welding (FSW) were investigated using fatigue tests for stress ratios of 0.1, 0.3, and 0.5. The difference between the fatigue crack initiation in the base material (BM) and FSW joints, related to coarse secondary phases, was explored using scanning electron microscopy (SEM). Accordingly, Al23CuFe4, Al7Cu2Fe, and Al2Mg3Zn3 were the preferred joint crack initiation locations, whereas Mg2Si was the major fracture initiation point of the parent material, and cracks tended to propagate along dense, coarse secondary phases, becoming more pronounced for larger cracks. In addition, as the stress ratio increased, non-Mg2Si phase fracture initiation points appeared in the BM. Meanwhile, the quantity of non-Mg2Si phases in the joints continued to increase, and the crack initiation sites became increasingly concentrated in the TMAZ-HAZ region.

Creep behavior is an important parameter of the material properties of cold-formed steel (CFS) at elevated temperatures and the corresponding investigation is still very limited. In this paper, an experimental study with the creep duration of 4 h was performed for 1.0 mm thick G550 CFS. Forty-one test conditions were selected. The results showed that the creep curves of G550 CFS were distinctly different from that of Q550 and Q690 hot-rolled high-strength steel at elevated temperatures. In addition, the G550 CFS coupon specimens which demonstrated tertiary creep during the experiments would experience creep rupture. For the fire safety of steel structures, a critical temperature of G550 CFS which represented the onset of tertiary creep was given. When the stress ratio was less than 0.7, the critical temperature was lower than the temperature corresponding to the high-temperature yield strength of G550 CFS. Furthermore, a steady-state creep rate expression of G550 CFS was proposed. When the primary creep stage of G550 CFS was insignificant, the proposed expression could be used to give the estimation of the high-temperature creep curves of G550 CFS. Finally, the transient-state test strain of G550 CFS at 500 °C was predicted and compared with previous experimental results. It was shown that the creep strain was an essential part of the total strain of G550 CFS under transient-state conditions, and also a key factor leading to the difference of strain results between the transient-state and steady-state tests.

This study experimentally investigated the whole-life ratcheting behavior of sintered copper joints with consideration of the effects of stress rate, stress amplitude, mean stress, maximum stress, and stress ratio. Deformation of joints under cyclic load was measured by a noncontact displacement detecting system. In these joints, ratcheting strain and ratcheting strain rate were found to be sensitive to loading factors. For example, strain decreased as mean stress and stress amplitude decreased, and also as stress ratio and stress rate increased. Meanwhile, larger stress amplitude or mean stress reduced ratcheting fatigue life, while increasing stress ratio and stress rate increased fatigue life. The results indicate the modified Goodman model accounting for the effects of mean stress can usefully predict the ratcheting fatigue life of sintered copper joints at room temperature.

Crack size prediction under variable amplitude loading is a very complex process, which is also important for life prediction in engineering. A crack growth model considering different stress ratio for fatigue remaining life prediction is proposed in this paper. The model utilizes stress ratio to describe the variable loading sequences, which makes the calculation greatly simplified. The rain-flow method is utilized to characterize the load sequence effects under variable amplitude loading. In addition, particle filter is utilized to estimate the model parameters describing the crack growth. Finally, case study indicates that the proposed approach is efficient in predicting crack growth and fatigue remaining life.

Influence of contact pressure and maximum cyclic stress (σmax) on the fretting fatigue behavior of modified 9Cr-1Mo steel has been studied using contact pads made of the same steel. The contact pressure was varied from 50 to 200 MPa using σmax of 400 and 500 MPa at a stress ratio (R) of 0.1. The fatigue life was observed to decrease in the presence of fretting action. For a given σmax the fretting fatigue life of the steel decreased with an increase in contact pressure up to 100 MPa beyond which saturation was observed. The ratio of slip to stick area increased with the contact pressure. This is in agreement with the increased depth of the fretting-induced debris and roughness.

To study the influence of consolidation stress ratio and stress history on 1-D consolidation permeability of saturated clay, one-dimensional consolidation permeability tests were carried out with GDS triaxial device. The results indicated that the permeability coefficient and void ratio of normally and overconsolidated saturated clay decreased with the increase of consolidation stress ratio under different consolidation stress ratios but the same stress history. And the amount of final sample’s compression increased with the increase of the consolidation stress ratio. Under the condition of the same consolidation stress ratio but different stress history, the amount of final compression of the overconsolidated saturated clay was smaller than that of the normally consolidated saturated clay. Besides, the stress difference σdv between consolidation pressure σ and gravity stress σ c z was fitted to the amount of the final sample’s compression, and a good linear relationship between the stress difference σ d v and the amount of the final sample’s compression under each consolidation pressure was obtained. The results showed that it is necessary to consider the influence of consolidation stress ratio and stress history simultaneously on 1-D consolidation permeability of saturated clay. Meanwhile, it can accurately predict the amount of the final sample’s compression after knowing the gravity stress. Moreover, a model prediction analysis was conducted on the saturated clay and recommended to use the modified Kozeny-Carman’s equation to predict the permeability coefficient of Luochuan saturated clay during one-dimensional consolidation.

The formation of optical dark area (ODA) on high-cycle fatigue fracture surface of Al alloys at atmosphere is very common and questionable in the engineering fields. Herein, we discovered that the oxygen induced inner friction causes the serious Cu element segregation in the form of nanoparticles on the fatigue fracture surface at atmosphere, which forms the ODA in Al–Cu–Mg alloy. By increasing stress ratio or applying Vaseline coatings fatigue tests, the ODA can be absolutely eliminated simultaneously with a significant extension of their fatigue lives.

Biocement as an alternative to cement for soil improvement has been studied for the past decade. A comparative study on the cementation effect on the mechanical behavior of sand by biocement and Portland cement is presented. Drained triaxial tests were carried out on both cement- and biocement-treated sand. The yielding of cemented sand is largely associated with the breakage of bonding. Bonding ratio is defined in this paper to quantify the bonding effect. The bonding provided by biocement is stronger than that by cement, and as a result, the stress ratio at yielding for biocement-treated sand is higher than that for cement-treated sand given the other conditions the same. The shear resistance of cemented sand consists of bonding, dilation and friction. The stress–dilatancy relationship of biocement-treated sand is different from that of cement-treated sand or the Rowe’s stress–dilatancy equation. The increase in stress ratio with dilatancy ratio (1 − δev/δe1) is higher for biocement-treated sand.

The novel destructive method, which is based on enlarging of initial cold-expanded hole diameter, is developed for quantitative assessment of fatigue damage accumulation. The secondary hole diameter increments in principal strain directions are measured at different stages of low-cycle fatigue. These data offer construction of normalized dependencies of principal residual strains, related to the secondary hole diameter, against of lifetime percentage, thus providing a explicit form of the damage accumulation function. These functions are obtained for mandrel entrance and exit side. Obtained information reveals peculiarities of damage accumulation depending on residual stress level. The results also demonstrate how stress ratio influences on the damage accumulation process under low-cycle fatigue conditions.

The stability of underground excavations has become an important issue in order to extend underground mining operations and extract deeper deposits. The increasing demand for Tin-Tungsten (Sn-W) for industry and its market price has created a motivation for mining companies to extract deep-seated Sn-W ore deposits in Myanmar. Thus, this paper aims to investigate the stability of underground openings, especially, the stope with considering the mining methods. To meet the objective, FLAC3D 5.0 simulation was used for the assessment of stope under different stress ratios, 0.5, 1.0, and 1.5 for two types of underground mines; Open stoping and Cut and Fill stoping. The results show that the risk of instability of stope is high under the stress ratio of K = 0.5 than that of K = 1.0 and K = 1.5 in both mining methods. However, the stability of the stope in open stope method is lower than that of cut-and-fill method obviously. This result shows that the appropriate mining method has to be selected for extraction of Sn-W deposit carefully in terms of the balance of safety and cost.

This study mainly investigates the Fatigue Crack Growth Rate (FCGR) of 10CrNi3MoV high strength steel and its welded joints used in modern marine environment considering the stress ratio and strength mismatch. To reflect the strength mismatch of weldment, two kinds of weld filler material are selected to obtain Even-Matched (EM) and Under-Matched (UM) marine Ni-Cr-Mo-V steel welded joints. The Fatigue Crack Growth (FCG) rates of base metal and related welded joints are investigated considering load ratio (0.1, 0.4, 0.7) and post-welding heat treatment. The experimental FCG trends for base metal and weldments have been compared with the trends available in standards. The FCG rate (da/dN) results show fatigue crack propagation resistance under post welded heat treatment (PWHT) is lower than the as-welded state for both EM and UM welded joints.

Modified version of the crack compliance method is used for determination of stress intensity factor (SIF) related to narrow notches emanating from cold-expanded holes. These notches are inserted at different stages of low-cycle fatigue under constant external load. It is shown how residual SIF values, generated by residual stress field influence, can be separated from total experimental SIF values. Residual SIF values, obtained at different stage of low-cycle fatigue with the same stress range Δσ = 350 MPa but different stress R = –0.4 and R = –1.0, provide quantitative description of residual stress evolution near cold-expanded hole. It shown that maximal residual stress relaxation of order 20 per cent occurs at 95 lifetime per cent for both loading programs.

The "Ribnica" landfill of the "Vrtlište" surface mine bordered the river Ribnica until during 2017, a landslide was started and the river Ribnica was interrupted, and a water reservoir was formed. After the completion of the tunnel that diverted the river Ribnica, its previously interrupted riverbed in the downstream part is planned for continuation of the disposal of masses from the surface mine "Vrtlište" by making an earth dam. The dam has the role of retaining large waters in case of exceeding the maximum tunnel flow, as well as in cases of monitoring and construction work in the tunnel.The requirement to use landfill material for the construction of the dam poses a significant risk due to the lack of data on its shear strength. This paper presents the results of research on the shear strength of materials in the conditions of dam construction, under optimal moisture conditions and maximum compaction and analyzes the obtained results, which should define the behavior of the tested materials in the conditions of dam construction. The conducted research represents the first phase of the research, which will be followed by research into the shear strength of completely saturated materials, which will determine the behavior of deposited materials in the dam body and the final slopes.

To obtain high strength and excellent deformability for ferrite/bainite dual-phase (F/B DP) pipeline steel for gas pipelines based on strain-based design, the volume fractions of ferrite and bainite should be considered first. In this work, abstract representative volume elements (RVE) of finite element models (FEMs) of mesostructure for F/B DP pipeline steel with volume fractions of bainite between 30% and 58% were established, and the effects of volume fraction of bainite on the tensile properties and deformation compatibility were studied. Results show that the stress and strain in the mesostructure were primarily distributed in the bainite and ferrite, respectively, and strain concentration occurs at the ferrite/bainite interface. With increasing volume fractions of bainite, the strain localization factor (SLF) and strain ratio of ferrite with bainite ( ε F / ε B ) decrease, which can improve the deformation compatibility of the F/B DP pipeline steel. However, the stress ratio of bainite with ferrite ( σ B / σ F ) and the contributions of bainite to stress and strain sequentially increase, and, as a result, the strength increases and the ductility decreases. Therefore, a balance of strength and deformability can be obtained when the optimal volume fraction of bainite is in the range of 40% to 48%.

In this paper, the tests under biaxial compression were conducted on five kinds of recycled aggregate concrete (RAC) by stress ratios (0:−1, −0.1:−1, −0.25:−1, −0.5:−1, −0.75:−1, and −1:−1) at the strain rates of 10–5/s, 10–4/s, 10–3/s, and 10–2/s. This study was accomplished in the servo-hydraulic multi-axial testing system, which was carried at Dalian University of Technology. The experimental phenomena of RAC under biaxial compression are described, and the experimental results of biaxial compressive strength of RAC are analyzed. The effects of strain rate, stress ratio, and substitution percentages of recycled coarse aggregate (RCA) on the biaxial compressive strength of RAC were studied. During the experiments, the failure modes of concrete have not been changed because of the increased impact of the RCA on RAC. The strength of RAC is improved with the increase in strain rates. With the increase in stress ratios, the biaxial compressive strength increases at first. However, the strength then decreases. Based on the strength theory of common concrete and analysis of experimental data, this paper built a new dynamic strength criterion. The biaxial compressive strength criterion describes the characteristics of structural RAC at different stress ratios and strain rates. This strength criterion can provide theoretical foundation for future concrete multi-axis dynamic tests and the design specification with the considerations of multi-axis dynamic strength and nonlinear analysis. The feature of the model is that it can take into account the influence of strain rates.

Resilient modulus of soil is crucial for the design of a structure on a foundation subjected to a cyclic loading (e.g., traffic load or machine vibration load). This paper conducted a series of dynamic triaxial tests of saturated silty clay, considering the influence of the factors of cyclic stress ratio (CSR), static deviatoric stress ratio (SDR), and overconsolidation ratio (OCR) on the resilient modulus and dynamic damping ratio of the soil. A cyclic loading with a form of half sine wave was used to model the traffic loading. The results showed that the soil was prone to failure under a higher SDR, even though the applied CSR was less than the critical CSR. The saturated silty clay performed a strain softening behavior and its dynamic properties deteriorated significantly when higher CSR and SDR and lower OCR were involved. Based on the test results, an empirical method with a form of exponential function was proposed to evaluate the resilient modulus of the soil, considering the combined effects of CSR and SDR and OCR. The proposed method was verified through a comparison with the test results in this study and from literatures, and some recommendations for its application were offered.

The Finite Element Method [FEM] used to replicate the products and systems. In this method, the abnormality estimation of the spine has developed and presented in this paper. Spine injury found on vertebrae L1–L5 and its corresponding inter-vertebral disk. Different types of filters used to eliminate obtained noise, starting the MRI image at different levels. The noiseless image was segmented using differing Edge Detection Algorithm (EDA) such as Canny Edge Detection Algorithm (CEDA), Prewitt, Sobel, and Robert from the applied segmentation algorithm the best EDA identified and the 3D model for lumbar spine was created. After the segmentation algorithm, the FEA method utilized for examining images of the 3D human lumbar spine on different loads. The experiment conducted with the stress–strain relationship and Modal Analysis on Natural Frequency (NF) calculated. The entire analysis accomplished by real-time simulation software called ANSYS.

A series of laboratory tests are performed to determine the energy evolution and fatigue behavior of sandstone subjected to cyclic loading, as well as the influence of the upper stress level on the fatigue life. The test results show a nearly linear negative correlation between the rock fatigue life and the upper stress ratio. The evolution of the dissipated energy and the elastic energy can be classified into three stages: a fatigue hardening stage (I), a steady development stage (II) and a steep destruction stage (III). This observation is used to develop a three-stage fatigue damage model for sandstone based on the energy dissipation. The initial rock damage is incorporated into the damage model with the dissipated energy as the damage variable. The proposed model is validated by comparing the predicted and test results.

Earthquakes occur frequently in the Loess Plateau area, which result in damage to loess due to the disturbance of multiple cyclic loading. In this paper, the historical earthquake process is simulated by pre-dynamic loading treatment on undisturbed loess samples. Then cyclic tests are carried out on these treated samples to study the later liquefaction responses with different initial water content. The undisturbed sample is relative to the remold sample instead of the samples without disturbance. Results show that the axial deformation and pore pressure ratio of treated loess samples with initial water content of 5% are larger than those without treatment. For samples with initial water content of 10% and 15%, the cycle number required for liquefaction increases after treatment, but pore pressure ratio is between 0.18 and 0.36, which is less than the 5% water content samples. It means that liquefaction will have been formed before the excess pore pressure increases to large values. Combined with microstructural analysis, it is found that pre-dynamic treatment causes earthquake damage zone in loess with water content of 5%, which results in lower liquefaction stress ratio than non-treated ones. As for samples with water content of 10% and 15%, the internal voids become smaller and fine particles move into the gaps between large particles after treatment, resulting in denser structure which is hard to be liquefied. However, the increasing dynamic stress will aggravate the deterioration of loess at the water content from 5 to 15%. The changes of microstructure of loess samples are vulnerable to the dynamic stress amplitude and water sensitivity.

Investigations on engineering structures show that residual stresses in combination with external loads can cause failure in loads that are less than the design threshold. Due to the applicability of austenitic steel in important industries (such as oil pipelines), accurate measurement of residual stress in this material is very important. Indentation is a new method for estimating residual stress. In this paper, by performing a large number of finite element simulations, the accuracy of residual stress measurements in austenitic stainless steels using indentation was studied by performing a large number of finite element simulations. Three different models (Suresh's, Wang's and Lee and Kwon's model) were investigated and it was found that the Lee and Kwon's model has a more accurate prediction of residual stress values in austenitic steels. Based on these numerical simulations and by studying how the residual stress measurement error of Lee and Kwon's model changes according the stress ratio, a method is suggested to correct this error and calculate the real amount of non-equibiaxial residual stresses in austenitic steels. The procedure is significantly reducing the error of residual stress measurement (from about 50% to less than 10%) and has been verified by conducting experimental test on a sample made from austenitic steel.

The fatigue strength deterioration in Ti–6Al–4V specimens impacted by steel sphere was experimentally investigated. Based on the test data of Peterson’s formula and the fatigue notch factor, the relationships linking the fatigue notch factor, fatigue strength, injury notch size, and stress ratio were derived. The effect of the notch dimension, residual stress, and stress ratio on the fatigue strength is discussed. The main conclusion is that the impact damage-induced reduction of the fatigue strength depends on the ratio between notch depth and notch radius: the greater the ratio, the more pronounced the reduction. Furthermore, the greater the stress ratio, the less id the reduction. These findings have a certain reference value for blade protection design against foreign object damage, the standard-setting, and maintenance guidelines.

Practices show that the triaxial stress change of mining-disturbed coal deeply affects its failure and permeability characteristics and easily cause the coal and rock dynamic disasters during deep underground mining process. The combined mechanic-damage-permeability experiments of gas-bearing coal were carried out under the mechanical paths of conventional triaxial compression (CTC), fixing axial pressure and unloading confining pressure (FAPUCP) and loading axial pressure and unloading confining pressure (LAPUCP). Then the effects of the deviatoric stress ratio (DSR) on the damage and permeability characteristics of coal were analyzed. The results proved that the distinguishing deformation and strength characteristics of coal were showed due to the different mechanical paths and the coal specimens were converted from brittle deformation to plastic deformation with the effect of higher confining pressure. The coal specimens of the three mechanical paths generated the main shear failure, tensile-shear failure and ‘X’ conjugate shear failure, respectively, and the fracture angles decreased in order. The damage and permeability of coal specimens could be more and more severe in the order of CTC, FAPUCP and LAPUCP paths, which was due to the different DSR. Thus, the deep mining-disturbed coal of lager DSR is seriously prone to cause the coal and rock dynamic disasters. The corresponding measures should be taken to reduce the DSR of mining-disturbed coal and then avoid the dynamic disasters.

In the design of 2G superconducting magnets and coils, both the yield strength and the irreversible stress limit for critical current ( I c ) degradation of coated conductor (CC) tapes under various environmental conditions have been investigated. Equally important and yet often discounted are the reliability tests to evaluate the I c degradation induced by the fatigue loading expected during operation. Because I c degradation at the stress level below the reversible stress limit of the CC tapes is possible (e.g., under a static fatigue load), in this study, the procedures for evaluating the reliability of 2G CC tapes using characteristic limit values obtained through a series of electromechanical properties evaluations are introduced. I c behaviors were obtained at 77 K through specified loading against the elapsed time in a static fatigue test, while electromechanical fatigue limits of CC tapes were determined at a stress ratio (R) of 0.1 in a high-cycle fatigue test. The determination of electromechanical properties through uniaxial tensile and fatigue tests was established, and its long-term reliability was examined.

In fatigue test, the fatigue life of metal components is affected by many factors, such as test temperature, stress ratio and loading frequency. In order to study the influence of temperature on fatigue life of bolted joints, thermal stress and fast coefficient are introduced. A numerical method of fatigue crack initiation life is proposed based on Manson-Coffin strain fatigue formula. The crack initiation life of 2024 aluminum alloy at different temperatures can be obtained by this method, which provides a theoretical basis for the fatigue life prediction of metals. Then, the stress severity factor SSF is introduced to calculate fatigue life of plane bolted joints. The data obtained from the model show that the crack initiation life of aluminum alloy specimen decreases significantly with test temperature rises, the same as the fatigue life of bolted joints.

The fatigue test was carried out by simplified lifting method, and the fatigue characteristic curve of X12Cr13 stainless steel at stress ratio of R = 0.1 was plotted at a single point, with the result that the fatigue strength is about 0.5 times the tensile strength. The normal stress ratio R has significant effects on the fatigue life of X12Cr13 stainless steel. As the stress ratio R increases, the fatigue life of the material increases significantly. At the same stress ratio R, the type of fracture morphology of the fatigue specimens is not significantly influenced by the variation of the maximum load. Under the same maximum load condition, larger stress ratio R leads to finer and smoother fatigue fracture surface.

Asymmetric stress occurs in shallow buried highways and railway tunnels. Due to asymmetricalloading, the design process of the tunnel is different from a regular tunnel. Chinese code for designing railway tunnel contains empirical values for different grounding rock to facilitate engineering judgement of asymmetrical loading tunnels based on the slope angle of surface and the burial depth of the tunnel. However, when calculating the asymmetric stress, there seem to be no quantitative criteria for estimating the asymmetric stress. Thus, in this work we create a numerical model to better evaluate the asymmetric stress ratios in different rock types. Our results demonstrate for surrounding rocks of grade V with poor stability, an asymmetrical loading conditions should be considered specifically when the stress ratio at the spandrel is higher than unity. For surrounding rock with grade IV in which stability slightly increases we found that the tunnel is asymmetrical once the stress ratio at the spandrel reaches to above 2 − 3. For the grade IV with a higher stability, an asymmetrical loading should be considered in the design when the stress ratio reaches to 3 − 4. For rock with grade III with the maximum stability only when the stress ratio is higher than 7 − 8, the asymmetrical loading conditions should be considered. We found that for grades III, IV, and V, the stress ratio of sidewall is about unity under various slope angles and burial depth. Importantly, we show that the stress ratio at the sidewall cannot be used to make judgements on whether the shallow buried tunnels are asymmetrical loading conditions. Our results have practical implications in design, safety, and risk analyses of tunnels.

Investigations into engineering structures show that residual stresses in combination with external loads can cause failure in loads which are below the design threshold. As a result, the exact study of the magnitude and distribution of these stresses is an important topic in mechanical engineering. Indentation is a new method for estimating residual stress. To measure non-equibiaxial residual stresses, there is only one reliable method presented by Lee et al. In this paper, the effect of yield stress and different values of residual stress on the accuracy of residual stress measurements in steels with similar work hardening behavior was studied by performing a large number of finite element simulations. Based on these numerical simulations and by studying how the residual stress measurement error of Lee and Kwon’s model changes according the stress ratio and the yield strain, a method is suggested to correct this error and calculate the real amount of non-equibiaxial residual stresses. The procedure is significantly reduces the error of residual stress measurement (from more than 100% to less than 10%) and has been verified by conducting experimental indentation.

Fatigue failure is one of the primary mode of failure in cemented materials. Traditionally fatigue models are developed using the pavement response parameters such as strain or stress (stress ratio) to evaluate the fatigue performance of different cemented materials. These models are mostly empirical in nature and does not explain the variability associated with the fatigue life even at the same value of the response parameter. An attempt has been made in this paper to evaluate the fatigue characteristics of two different cement stabilized materials using dissipated energy concept. It was observed that being fundamental in nature, dissipated energy based fatigue model predicts the fatigue life better than the traditional approaches.

The improvement in adhesion technology for joining different types of materials has led to expectations of weight reduction in cars and commercial vehicles. Various levels of stress and stress rati...

Post-peak flow instability of six sands notably different in terms of average particle shape characteristics, gradation, and mineralogy was investigated. Tests were carried out under constant volume condition using a NGI-type direct simple shear apparatus. The testing program covers wide ranges of initial void ratios and vertical effective stresses. Experimental findings confirm that the critical state parameters of the test sands depend strongly on the average particle morphologic characteristic factors. For specimens in loose state, it is shown that stress ratio at the onset of flow instability, normalized constant volume peak shear strength, brittleness index, and the normalized pore water pressure of the tested sands are interrelated with the particles’ morphologic factors.

The intricacy in Lekhnitskii’s available single power series solution for stress distribution around hole edge for both circular and noncircular holes represented by a hole shape parameter ε is decoupled by introducing a new technique. Unknown coefficients in the power series in ε are solved by an iterative technique. Full field stress distribution is obtained by following an available method on Fourier solution. The present analytical solution for reinforced square hole in an orthotropic infinite plate is derived by completely eliminating stress singularity that depends on the concept of stress ratio. The region of validity of the present analytical solution on reinforcement area is arrived at based on a comparison with the finite element analysis. The present study will also be useful for deriving analytical solution for orthotropic shell with reinforced noncircular holes.

Convergence of the rotational hardening variable α used in the anisotropic models of clay plasticity, with a constitutively defined attractor/bound αb(η), function of the stress ratio η, under fixed η loading, is analytically investigated. It is analytically shown that depending on various parameters of the rate equation of the evolution of α, such convergence may or may not occur despite the apparent necessity of convergence stemming from the form of the evolution equation of α.

The accurate prediction of fatigue performance is of great engineering significance for the safe and reliable service of components. However, due to the complexity of influencing factors on fatigue behavior and the incomplete understanding of the fatigue failure mechanism, it is difficult to correlate well the influence of various factors on fatigue performance. Machine learning could be used to deal with the association or influence of complex factors due to its good nonlinear approximation and multi-variable learning ability. In this paper, the gradient boosting regression tree model, the long short-term memory model and the polynomial regression model with ridge regularization in machine learning are used to predict the fatigue strength of a nickel-based superalloy GH4169 under different temperatures, stress ratios and fatigue life in the literature. By dividing different training and testing sets, the influence of the composition of data in the training set on the predictive ability of the machine learning method is investigated. The results indicate that the machine learning method shows great potential in the fatigue strength prediction through learning and training limited data, which could provide a new means for the prediction of fatigue performance incorporating complex influencing factors. However, the predicted results are closely related to the data in the training set. More abundant data in the training set is necessary to achieve a better predictive capability of the machine learning model. For example, it is hard to give good predictions for the anomalous data if the anomalous data are absent in the training set.

Flash drought is characterized by a period of rapid drought intensification with impacts on agriculture, water resources, ecosystems, and the human environment. Addressing these challenges requires a fundamental understanding of flash drought occurrence. This study identifies global hotspots for flash drought from 1980–2015 via anomalies in evaporative stress and the standardized evaporative stress ratio. Flash drought hotspots exist over Brazil, the Sahel, the Great Rift Valley, and India, with notable local hotspots over the central United States, southwestern Russia, and northeastern China. Six of the fifteen study regions experienced a statistically significant increase in flash drought during 1980–2015. In contrast, three study regions witnessed a significant decline in flash drought frequency. Finally, the results illustrate that multiple pathways of research are needed to further our understanding of the regional drivers of flash drought and the complex interactions between flash drought and socioeconomic impacts., Flash droughts can have devastating impacts but are notoriously difficult to predict. This study identifies global hotspots of flash drought, driven by evaporative demand and precipitation deficits across varying geographic regions and crop-type, providing a framework for flash drought prediction.

This paper examined the stiffness of expanded polystyrene foam (EPS) with monotonic and cyclic loading under different stress states. The test program was performed for monotonic loading and cyclic loading. The stiffness of geofoam subjected to monotonic loading increased with increasing density. The solid skeleton empirical equation was proposed to predict the geofoam modulus with different densities. The distortional ratio of the EPS decreased with reduced density and increased stress ratio and substantially decreased when the stress was above the elastic limit. The dynamic modulus was higher than the initial modulus with a low stress ratio and began lower than the initial modulus when the stress ratio was over 0.9. The dynamic modulus of the geofoam substantially increased with increasing density and slightly decreased with increasing stress ratio and decreasing load frequency. The proposed empirical equation can reasonably predict the dynamic EPS stiffness with varying densities, stress ratios and loading frequencies.

In this study, the fatigue behavior of composite reinforced cracked aluminum 1050 plates is investigated experimentally and numerically. The tests are conducted in four different stress ratios betw...

A new destructive method of damage accumulation quantifying in the stress concentration zone has been proposed and verified. Damage accumulation in the vicinity of the hole was created by means of preliminary low-cycle fatigue loading of specimens with holes. The damage accumulation functions for different stress ratio and stress range are expressed in an explicit form proceeding from distributions of the normalized stress intensity factor as a function of number of cycles.

Fretting is a damage mechanism which occurs between two tightly clamped components when these two components are subjected to very small amplitude of relative motion. Design and fabrication of fretting rig is essential to conduct fretting tests. The fretting rig has been used to clamp the pads onto the specimen. While conducting the fretting experiments, the normal load was applied through the pads and frictional force was generated at the contact interface between the pad and the specimen. Fretting experiments were conducted with a cyclic load which involves a stress ratio (‘R’ ratio). To decide ‘R’ ratio, we need to understand the load transfer ratio (LTR). LTR is the ratio between the load transferred to the top of the specimen and the load applied to the bottom of the specimen. LTR value should be optimum to conduct fretting experiments. So, the fretting rig which produces least LTR value (close to 50%) can be used as rig in fretting experiments. To ensure this condition, initially eleven cases of simple one-dimensional (1-D) fretting rig models have been designed and Finite Element (FE) analysis of these models was carried out. Afterwards four more different fretting rig models have been designed and analyzed with the inclusion of machine constraints and its results are also presented here. Among these models, the finite element model with optimum LTR was selected to conduct fretting experiments and the detailed three-dimensional (3-D) finite element study of the selected model has been performed and its results were validated with one-dimensional finite element analysis results.

The various advantages of CFC composite materials have lead to its application in lots of area especially in aerospace industry for structural applications. This paper highlights the effect of external damage and its location on the fatigue life of CFC composites. The introduction of the crack of 1 mm width at an angle of 45° was created on the specimens. All the tests were performed using a computer controlled 250 KN servo-hydraulic test system in load mode at room temperature, on one crack and two crack composite specimens. The fatigue strength degradation was monitored through stiffness measurement, which was done using load displacement data obtained during the fatigue loading. The CFC specimens with one inclined crack at the center and two inclined cracks at ends were subjected to constant amplitude loading for stress ratio R = 0.5. The CFC specimens with one crack showed a significant reduction in fatigue life. The fatigue properties for both cracked specimens were evaluated. Fatigue life for one crack specimen was much lower than the two crack specimen. A considerable reduction in stiffness was also observed for both one crack and two cracks specimen.

Highway pavements need to withstand repeated and varying traffic loads due to which they may fail at a stress level lower than their strength called fatigue. Fatigue is the progressive damage due to propagation of cracks and is considered to be the primary cause of structural failure in concrete pavement. The propagation of cracks in concrete is resisted by the fracture toughness, which is a material property. Stress intensity factor is used to express the fracture toughness which depends upon the present state of crack tip stress, strength and geometry of the structural component. Material fracture toughness and the applied stress ratio influence the progressive damage and the fatigue life of concrete. This paper investigates analytically the progressive damage of concrete due to cyclic loading based on a stress intensity factor based fatigue damage prediction model. The effects of material property and specimen size have found to affect the propagation of cracks and the incremental damage. The varying sequence of cyclic loading has found to influence the progressive damage and fatigue life of concrete significantly.

The present research work has been carried out to investigate the ratcheting behavior at different stress ratios under constant maximum stress and changes in post-ratcheting tensile properties of commercially pure (99.97%) polycrystalline Copper. All the ratcheting tests were done at room temperature upto 25% true ratcheting strain accumulation. After ratcheting deformation tensile tests were performed on ratcheted specimens at strain rate of 10−3 s−1 up to complete fracture. Post-ratcheting hardening behaviors were analyzed by the variation of plastic strain amplitude and hardening factors with respect to number of cycles. It is observed that the number of cycles over which a constant amount of ratcheting deformation occurs exponentially increases with increase of stress ratio. It is also observed that post ratcheting tensile properties of annealed copper linearly increases with increase of stress ratio. Such observations of post-ratcheting hardening behavior have been successfully justified by the variation of hardening coefficient and hardening factor.