Influence Of Stress Ratio Research Articles

Influence of stress ratio on transverse crack initiation in quasi-isotropic CFRP laminates subjected to fatigue loading

Influence of stress ratio on transverse crack initiation in quasi-isotropic CFRP laminates subjected to fatigue loading

Investigation on recycled aggregate concretes exposed to high temperature by biaxial compressive tests

Recycled aggregate concretes (RACs) made of building wastes can achieve good environmental and economic benefits. Since fire is one of the most common disaster in modern high-rise buildings, the strength, deformation and bearing capacity of recycled concrete structures under high temperatures should be carefully studied in design. The mechanical performances of RACs exposed to high temperatures under biaxial compressive actions have been studied in this research. The RAC specimens with three replacement rates (0%, 50%, 100%) exposed to high temperatures (200 °C, 400 °C) have been tested. The influences of stress ratios, replacement rates and high temperatures have been investigated intensively. Failure criterions with improved accuracy have been proposed to describe the strength failure characteristics of the RACs. The results indicate that biaxial compressive strength and peak strain after high temperature show an increase compared with that under normal temperature, and the biaxial compressive strength and peak strain have opposite trend with the variation of replacement rate and temperature. The study can provide a scientific instruction for the design of RACs exposed to high temperature.

Experimental and analytical investigation of the bending behaviour of 3D-printed bio-based sandwich structures composites with auxetic core under cyclic fatigue tests

In the present paper, fatigue behaviour of sandwich composites with auxetic core under various stress ratios and for four different core densities is studied. Experimental and analytical analyses are performed on sandwiches subjected to cyclic bending tests in order to determine the influence of stress ratios on their fatigue properties. Experimental and analytical prediction result show good agreement. The analytical method predicts fatigue life as well as damage parameters of the structures and its reliability is verified by experiments. The acoustic emissions method is also used to monitor damage initiation and propagation up to failure. It is found that sandwiches with low core density present the maximum fatigue life.

The influence of stress ratio on fatigue lifetime of NiTi shape memory alloy

The influence of stress ratio on fatigue lifetime of pseudoelastic NiTi alloy are studied. The stress-, strain- and energy-based criteria were used for analysis under on low-cycle fatigue. Increasing the stress ratio from 0 to 0.5 significantly reduces the fatigue life of the NiTi alloy when used to describe the stress range, strain range and dissipation energy density and increases when using the Odqvist’s parameter. A good agreement between experimental and calculated values of predicted lifetime was obtained. The low–cycle fatigue failure criterion of pseudoelastic NiTi alloy - total elastic strain energy density that takes into account the stress ratio was proposed.

Experimental study on wedge-bonded anchors for CFRP tendons under cyclic loading

This paper is concerned with an experimental study on a wedge-bonded anchor for carbon fibre reinforced polymer (CFRP) tendons under cyclic loading. The adhesive reinforced by quartz sand was tested to be superior as a bonding material for the anchor when compared to the adhesive reinforced by ferrous powder or aluminate powder. Structural responses of the wedge-bonded anchor under cyclic loading were analyzed with regard to system slip, sleeve strain, temperature rise in the anchor zone and residual tensile load capacity. The results indicate that the maximum stress level and stress ratio influence significantly the fatigue performance of wedge-bonded anchors. A cyclic loading with a high stress ratio and low stress level is beneficial due to the synergetic effect of the components in the wedge-bonded anchors. However, enhancing the stress level or lowering the stress ratio leads to a larger slip, greater damage and more loading cycles are needed for the stabilization of wedge-bonded anchors. When the stress ratio exceeds 0.4 and the maximum stress is less than 0.5, damage in anchor zone is initiated and developed in the early stage of cyclic loading, but the anchor becomes stable finally. A large decrease in stress ratio may result in a continuous development of microstructural damage and the eventual failure of the anchor, accompanied by continuously increasing energy dissipation under cyclic loading. The axial strain of sleeve in a wedge-bonded anchor is influenced by the extent of damage evolution and the synergetic effect of anchor assemblies; thereby resulting in different trends in sleeve strain-cycle curves under different stress ratios and stress levels. The temperature rise may be pronounced at a loading frequency of 10 Hz or less, which is related to the stress ratio. The damage development in the wedge-bonded anchor with an infinite fatigue life was analyzed. The mechanism of fatigue damage in wedge-bonded anchors is different from that of adhesively bonded anchors. Moreover, wedge-bonded anchors have a stronger resistance against fatigue due to the interaction between the wedges and the other assemblies.

Influence of stress ratio on functional fatigue of pseudoelastic NiTi alloy

The influence of stress ratio on functional properties of pseudoelastic NiTi alloy are studied. The changes of residual strain, strain ratio and dissipated energy on the stress ratio of shape memory alloy are investigated. The functional fatigue of the NiTi alloy under the stress-controlled cyclic loading is dependent on the stress range and stress ratio. Dissipated energy and strain range are invariant to the loading cycles for stress ratio 0 and 0.5. When stress ratio increases from 0 to 0.5 at the same maximal stress, the strain range and energy dissipation are decreasing. With the change of the stress ratio from 0 to 0.5 the residual strain in the first and next cycles increases significantly even at lower values of maximal stress.

A coupled hydraulic-mechanical-damage geotechnical model for simulation of fracture propagation in geological media during hydraulic fracturing

This paper proposed a coupled hydraulic-mechanical-damage (HMD) geotechnical model for simulating the entire failure process in geological media. In this model, elastic damage mechanics describes the damage process of elements. Darcy's Law and unsteady seepage flow equation describe fluid flow in elements, where compression of fluid and rock are considered. The coupled process is fulfilled by Biot's consolidation theory describing how pore-pressure affects the stress field and the stress/aperture/mesh-dependent permeability that represents the influence of stress on seepage field. The HMD model is implemented in the calculation module of Rock-Failure-Process-Analysis on Petroleum-problems (RFPA-Petrol) codes. The RFPA suite of software codes is based on the idea that the heterogeneity leads to non-linearity and causes progressive failure behavior observed in brittle rock. The capability of RFPA-Petrol simulator is demonstrated by a typical coupled problem related to double fractures propagation during hydraulic fracturing. This simulation successfully reproduces the asynchronous initiation, asymmetric growth and non-equal deflection of fractures in the numerical model. Then this simulator was used to investigate how fracture spacing and horizontal stress ratio influence propagation and reorientation of three hydraulic fractures from a horizontal well. At last, a horizontal well drilled by SHENGLI oilfield is simulated to certificate RFPA-Petrol's ability on field-scale models. It is found that larger fracture spacing and higher initial fracture height will form longer and wider fractured zones. HMD-based RFPA-Petrol is suitable for simulation of laboratory scale and field scale fracture propagation problems.

A stress-based model for fatigue life prediction of high density polyethylene under complicated loading conditions

Fatigue life prediction is crucial to the long-term durability evaluation of high density polyethylene (HDPE) which may experience stress-controlled fatigue or strain-controlled fatigue depending on the external loading conditions. Although abundant studies have been carried out on stress-controlled fatigue, investigations on strain-controlled fatigue are insufficient, and the relationship between these two types of fatigues is unclear. In addition, approaches for strain-controlled fatigue life prediction of HDPE are scarce. The present paper aims at revealing the relationship between strain-controlled fatigue and stress-controlled fatigue and proposing a method for fatigue life prediction. Firstly, the stress-controlled fatigue tests were performed to study the influence of stress ratio on fatigue life, and the strain-controlled fatigue tests were successfully conducted thanks to the application of anti-buckling devices. Furthermore, our results showed that the stress level (i.e. stress amplitude and stress ratio) determined the fatigue life for both stress-controlled test and strain-controlled test. More importantly, a stress-based numerical model was established to predict the fatigue life under complicated loading conditions. The numerical model was built based on the constitutive relation for the computation of the stress response, the Walker method for the evaluation of the stress ratio influence, and the damage accumulation for the calculation of the fatigue life. The proposed numerical method was validated by comparing the predicted fatigue lives with the experimental data of the strain-controlled tests.

Void nucleation in alloys with lamella particles under biaxial loadings

Ductile fracture of alloys is typically a three-stage process, involving void nucleation, growth and coalescence. Understanding the detailed physical mechanisms at micro-structural level for each stage is critical to design alloys with better performance. However, there have been a limited number of micromechanical studies to understand effects of the secondary-phase particle morphology and mechanical property on void nucleation of alloys under biaxial loading conditions. In this work, we carry out mechanical tests on Al–3Cualloys under the biaxial loading with proportional stressing. The pattern of void nucleation is characterized by Scanning Electronic Microscope (SEM) and in situ Transmission Electronic Microscope (TEM). In addition, unit cell analysis has also been performed to explore the influences of stress ratio, volume fraction of the particle and hardening of the Al matrix on the void nucleation. The pattern of void nucleation obtained through numerical simulations is found to be consistent with that given by SEM and TEM characterizations. We find that the void nucleation at the interface between the secondary-phase (Al2Cu) and Al matrix is dominant in most scenarios. Void nucleation in the Al matrix is also observed. The quantity depends on the stress triaxiality. In addition, due to the high aspect ratio of lamella secondary-phase particles, it is difficult to observe the full debonding from these secondary particles or their cracking, which are widely used in previous theoretical studies. Therefore, the classical theory for void nucleation should be modified when dealing with Al–Cu alloys containing high aspect ratio particles.

A Modified Walker Model Dealing with Mean Stress Effect in Fatigue Life Prediction for Aeroengine Disks

Mean stress effect plays an important role in fatigue life prediction, and it is discovered that maximum stress has nonnegligible influence on mean stress effect. Therefore, a modified Walker model is proposed to account for mean stress effect on fatigue life of aeroengine disks, which contains the influence of stress ratio and maximum stress on mean stress effect. Eight sets of fatigue data for standard smooth bars from six kinds of materials commonly used in aeroengine disks as well as two sets of experimental data from simulated specimens of turbine disks were employed to investigate the prediction capability of the proposed model against other candidate mean stress relationships. It is found that Goodman model generates most conservative results, while Morrow model overestimates fatigue life for most cases. SWT model yields similar results to Walker model but with less accuracy. The results of the modified Walker model turn out to be superior to those of any other candidate models for all cases examined, especially for large mean stress ones. Thus, the modified Walker model can be an effective method to predict fatigue lives of aeroengine disks influenced by mean stresses.

Fatigue behavior of high-entropy alloys: A review

Fatigue failures cost approximately 4% of the United States’ gross domestic product (GDP). The design of highly fatigue-resistant materials is always in demand. Different from conventional strategies of alloy design, high-entropy alloys (HEAs) are defined as materials with five or more principal elements, which could be solid solutions. This locally-disordered structure is expected to lead to unique fatigue-resistant properties. In this review, the studies of the fatigue behavior of HEAs during the last five years are summarized. The four-point-bending high-cycle fatigue coupled with statistical modelling, and the fatigue-crack-growth behavior of HEAs, are reviewed. The effects of sample defects and nanotwins-deformation mechanisms on four-point-bending high-cycle fatigue of HEAs are discussed in detail. The influence of stress ratio and temperature on fatigue-crack-growth characteristics of HEAs is also discussed. HEAs could exhibit comparable or greater fatigue properties, relative to conventional materials. Finally, the possible future work regarding the fatigue behavior of HEAs is suggested.

CRACK CLOSURE AND FIBRE BRIDGING CONTRIBUTION IN THE STRESSRATIO EFFECT ON DELAMINATION GROWTH UNDER FATIGUE

The objective of this paper is to investigate the contribution/role of the crack closure and the fibre bridging effects in stress-ratio influence in mode I delamination growth in carbon/epoxy composite laminates. The crack closure effect has been assessed by the identification of the non-linearity in the compliance curve of the double cantilever test specimen after the delamination extension. The effect of fibre bridging was investigated by cutting the bridging fibres during fatigue delamination. The fatigue test data was process using fracture mechanics principles. The delamination growth rate in laminates was characterized using approach of strain energy release rate. The results of the experiments of fatigue delamination growth with bridging fibres and un-bridged fibres have been compared for different fatigue stress-ratios. The results show that crack closure only occurs at lower stress ratios. Fibre bridging does not affect the stress ratio however the crack rate was decreased in this case.

Influence of Stress Ratio on Fatigue Strength of PBO Fiber with Kinking Damage

Influence of Stress Ratio on Fatigue Strength of PBO Fiber with Kinking Damage

Influence of Stress Ratio on Fatigue Fracture Behavior of PBO Fiber with Kinking Damage

Influence of Stress Ratio on Fatigue Fracture Behavior of PBO Fiber with Kinking Damage

Influence of Hold Time and Stress Ratio on Cyclic Creep Properties Under Controlled Tension Loading Cycles of Grade 91 Steel

Abstract Influences of hold time and stress ratio on cyclic creep properties of Grade 91 steel were systemically investigated using a wide range of cyclic creep tests, which were performed with hold times (HTs) of 1 minute, 3 minutes, 5 minutes, 10 minutes, 20 minutes, and 30 minutes and stress ratios (R) of 0.5, 0.8, 0.85, 0.90, and 0.95 under tension loading cycles at 600°C. Under the influence of HT, the rupture time increased to HT = 5 minutes at R = 0.90 and R = 0.95, but there was no influence at R = 0.50, 0.80, and 0.85. The creep rate was constant regardless of an increase in the HT, except for the case of HT = 5 minutes at R = 0.90 and R = 0.95. Under the influence of stress ratio, the rupture time increased with an increase in the stress ratio, but the creep rate decreased. The cyclic creep led to a reduction in the rupture time and an acceleration in the creep rate compared with the case of monotonic creep. Cyclic creep was found to depend dominantly on the stress ratio rather than on the HT. Fracture surfaces displayed transgranular fractures resulting from microvoid coalescence, and the amount of microvoids increased with an increase in the stress ratio. Enhanced coarsening of the precipitates in the cyclic creep test specimens was found under all conditions.

Experimental and numerical investigation of the effects of stacking sequence and stress ratio on fatigue damage of glass/epoxy composites

Abstract In the present paper fatigue behavior of glass/epoxy composite materials under different stress ratios and for various plies orientation angles has been established. Experimental and numerical analysis (Finite Element Method) were performed on various specimens subjected to cyclic tensile tests in order to outline the influences of stress ratios and the stacking sequence ([02/902]s; [902/02]s; [03/90]s; [903/0]s) on glass/epoxy fatigue properties. Static analysis is done experimentally to identify the stress-strain diagrams, strain to failure, Young's modulus and tensile strength for each stacking sequence. Comparison between experimental and numerical prediction show good agreement. The Results of this investigation can lead us to choose the most optimal stacking sequence for giving boundary conditions to achieve the maximum fatigue life.

A finite element study on residual stress stability and fatigue damage in high-frequency mechanical impact (HFMI)-treated welded joint

Fatigue improvement from high-frequency mechanical impact (HFMI) is considered to rely on compressive residual stresses, improved weld toe geometry and localized strain hardening at the weld toe. Of these, the existence of compressive residual stresses is generally assumed critical for the effectiveness of the method. In this study, the influence of stress ratio and peak loads on residual stress relaxation and fatigue damage in as-welded and HFMI-treated S700 transverse attachments was investigated. Elastic-plastic stress-strain response for as-welded and HFMI-treated conditions was simulated considering the effects of initial residual stress distribution, local geometry and local material properties. Relative fatigue damage was estimated using the Smith-Watson-Topper parameter. Full residual stress relaxation was observed for a stress ratio of 0.5 and a compressive overload of 0.6 times the nominal yield strength. The fatigue damage assessment showed benefit from HFMI with respect to the as-welded state for all simulated load conditions. The results are consistent with experimentally observed behaviour. The stepwise analysis indicated that the remaining benefit after residual stress relaxation was due to geometry improvement and strain hardening.

Influence of variable stress ratio during train operation on residual fatigue lifetime of railway axles

Railway axles are subjected to cyclic loading, which could lead to fatigue failure. Therefore, it is desired to know residual fatigue lifetime of railway axles to ensure safe operation of trains. Because of detection of relatively small fatigue cracks is not guaranteed an estimation of residual fatigue lifetime is based on damage tolerance approach. The acting stress ratio is variable due to variable amplitude loading and load caused by existence of press-fitted wheel in the vicinity of assumed crack. The contribution is focused on influence of variable stress ratio in EA4T steel on residual fatigue lifetime of railway axles. The influence of stress intensity factor on fatigue crack propagation rate was experimentally evaluated for three different stress ratios, which correspond to operation conditions. Two different expressions of fatigue crack propagation rate were used and mutually compared to show influence of the stress ratio on residual fatigue lifetime of structure made of EA4T steel. The first expression considers stress intensity factor range (respecting stress ratio R) and the second one uses maximal value of the stress intensity factor. The paper shows ability of both expressions to describe experimental data obtained under different stress ratios and their influence on estimated residual fatigue lifetime values. The results obtained contribute to the better estimation of residual fatigue lifetime of railway axles and generally to the safer rail transportation.

Influence of stress ratio and moisture condition of loose deposit on dynamic parameters and ground response spectrum

Influence of stress ratio and moisture condition of loose deposit on dynamic parameters and ground response spectrum

ショットピーニングによる高強度鋼における疲労強度向上と表面欠陥の無害化 (応力比の影響)

ショットピーニングによる高強度鋼における疲労強度向上と表面欠陥の無害化 (応力比の影響)