Strain-controlled Tests Research Articles

Isothermal low-cycle fatigue, fatigue–creep and thermo-mechanical fatigue of SiMo 4.06 cast iron: Damage mechanisms and life prediction

A series of strain-controlled Low-Cycle Fatigue tests (LCF) and Thermo-Mechanical Fatigue tests (TMF) were performed on silicon-molybdenum ductile cast iron SiMo 4.06. LCF tests were performed for various mechanical strain amplitudes at a high strain rate of 3×10−3/s for various temperatures between 20 °C and 750 °C. In addition, several LCF tests were performed for a low strain rate of 1×10−4/s and as fatigue–creep tests with a tensile strain dwell. TMF tests were performed as out-of-phase and fully constrained between 100 °C and 650 °C. The investigation of the damage mechanisms revealed that the predominant failure mode is a combination of graphite-matrix debonding and transgranular crack propagation through ferritic matrix. Finally, a novel damage model based on the dissipated hysteresis energy is proposed in order to effectively predict the lifetime of SiMo 4.06 under LCF and TMF loading. Creep and fatigue damage are each calculated separately and the oxidation effect is taken into account indirectly.

Effect of particle size on the dynamic properties of tire derived aggregates (TDA)

This paper investigates the dynamic properties of tire derived aggregate (TDA) as a recycled material used in civil engineering applications. The effect of TDA type A particle size on the dynamic response is studied experimentally in detail, and the effects of hysteresis loop asymmetry, shear strain, and confining pressure on the shear modulus and damping ratio are also examined. Undrained strain-controlled cyclic triaxial tests with consolidation stresses ranging from 25 to 200 kPa and shear strains ranging from 0.1 to 10% are used to compare a granulated rubber (GR) specimens and TDA specimens with different maximum particle sizes. The dynamic response of TDA type A differs from that of granulated rubber, because of the larger particle sizes of TDA type A. Although TDA stiffness increases with increasing particle size, the damping ratio is insensitive to TDA particle size in the particle size range considered in this study. However, at all consolidation stresses, the damping capacity of GR is significantly lower than that of TDA. In particular, due to hysteresis loop asymmetry, conventional equations can significantly underestimate the shear modulus and damping ratio of TDA type A. Furthermore, a generalized MKZ model is proposed to estimate the maximum shear modulus at small strains (Gmax) and to predict shear modulus degradation curves for TDA type A with maximum particle sizes ranging from 19.1 mm to 50.8 mm. Comparisons of these shear modulus degradation curves to data reported in the literature and to the experimental results of a TDA sample with a random particle size distribution show that the proposed generalized MKZ model can provide reasonable estimates of the shear modulus of TDA type A.

Cyclic threshold shear strain for pore water pressure generation and stiffness degradation in marine clays at Yangtze estuary

Cyclic threshold shear strain is a fundamental property of saturated soils under cyclic loading. To investigate the cyclic threshold shear strain for pore water pressure generation (γtp) and stiffness degradation (γtd), a series of strain-controlled multistage undrained cyclic triaxial tests were carried out on in-situ saturated marine clay in the Yangtze estuary with different plasticity index Ip. The test results show that both γtp and γtd increase with increasing Ip, and γtp is larger than γtd for the same marine clay tested under the same conditions, with γtp = 0.017 ~ 0.019%, γtd = 0.008 ~ 0.012% for Ip of 17, γtp = 0.033 ~ 0.039%, γtd = 0.020 ~ 0.025% for Ip of 32, and γtp = 0.040 ~ 0.048%, γtd = 0.031 ~ 0.036% for Ip of 40. Moreover, the development of stiffness degradation may not necessarily require the generation of pore water pressure but can be aggravated by it. Furthermore, the γtp and γtd of marine clay are compared with terrestrial soils and marine clays cited from the published literature, the results indicate that the special marine sedimentary environment and the combined action of flow and tidal wave system cause the γtp and γtd of marine clay in the Yangtze estuary to be smaller than that of the terrestrial clays and marine clays in other sea areas.

Rational relationship between the fatigue curves of asphalt mixes obtained from tension/compression and 4-point bending tests

The fatigue properties of asphalt mixes are usually established according to a series of laboratory cyclic loading tests at fixed temperature (θ) and frequency (f). Unfortunately, the results are different when considering different types of tests. This paper proposes a rational method to link the 4-point bending (4PB) and tension/compression (TC) fatigue test results. First a theoretical analysis of the 4PB fatigue test is presented. This analysis allows to introduce a link between the fatigue curves (modulus or damage versus number of cycles) of this type of test with the results from uniform TC tests. The 4PB fatigue curve is superimposed with the TC fatigue curve if the reference strain amplitude is correctly chosen. This amplitude must not be the maximum strain at the boundary fibre of the beam (ε 0max), as usually considered, but a lower proposed value (ε 0h0). Then, the previous approach is extended to the fatigue failure Wöhler’s law, which is a line in the Log–Log plot of the number of cycles at failure versus the loading amplitude (stress or strain). An experimental campaign on a Canadian asphalt concrete (HMAC) validates the developped approach. It is an important output from this research as fatigue life from one type of test can be obtained from the other type of test in the case of strain (or displacement) control tests.

Investigation of Chaboche and Bouc–Wen Parameters of Quenched and Tempered Steel and Comparison of Model Predictive Capabilities

The aim of this paper is to model the elastic–plastic uniaxial behaviour of a quenched and tempered steel. The common Chaboche isotropic kinematic hardening model (CIKH) is introduced, and a physics-based procedure is proposed to determine its parameters. This procedure is based on strain- and stress-controlled tests and is focused on the stabilized cycles. The imposed cycle properties are the hysteresis area, the stress range, the slope at the inversion points, obtained from the stabilized cycles of strain-controlled tests, and the ratcheting rate extracted from a stress-controlled test. The novelty of the algorithm is to determine the hardening parameters from the global properties of the cycle rather than imposing a pointwise fitting, which is also implemented to calculate the parameters for a comparison. The Bouc–Wen model showed great flexibility in describing nonlinear behaviours, corresponding to different physical phenomena, through an appropriate tuning of its parameter values. In this paper, another optimization approach is developed to estimate the Bouc–Wen coefficients and accurately describe the same experimental cycles. The performances of the Bouc–Wen model are compared with the predictions of the Chaboche model, and a discussion comparing the techniques used to reproduce cyclic plastic behaviour is provided.

Strain controlled fatigue behaviour of a wire + arc additive manufactured Ti-6Al-4V

This paper presents the cyclic deformation behaviour and fatigue properties of a wire + arc additive manufactured Ti-6Al-4V alloy in the as built condition under strain-controlled test condition. Higher local energy input used to build the material has resulted in a coarser primary columnar β grain structure along with a coarser α microstructure compared to Ti-6Al-4V alloys produced by other additive manufacture processes. Test specimens were manufactured in horizontal and vertical orientations with respect to the deposited layers. Isotropic fatigue property was observed at lower applied strain values. When the strain amplitude was above 0.6%, the vertical samples, where the loading axis was parallel with the primary columnar β grains, showed marginally higher fatigue life owing to the material being more ductile in this direction. Moreover, higher cyclic softening rate by a factor of two was measured in the vertical samples. No porosity defects were found in the material. Cracks were initiated from either the α laths or α/β interface due to cyclic slip localisation.

Strength performance of soil-fly ash-MSW fine layered system under different controlled loading conditions: A comparative study

The study outlines the interpretation of strain-controlled static triaxial tests on homogenous samples of locally available soil (LS), fly ash (FA), and municipal soil waste fines (MSW fines), as well as layered soil-waste systems. The 2-layered (FA + LS) and 3-layered samples (FA + MSW fines + LS) were arranged according to the increasing density order. The tests were conducted under three controlled conditions, i.e., unconsolidated undrained (UU), consolidated undrained (CU), and consolidated drained (CD) to determine the shear strength parameters required for the design of any structure over similar deposits. Significant improvement in the shear strength parameters of the considered LS can be seen through a soil-waste layered system. The results from the considered example for the strip footing also show maximum improvement in the bearing capacity of LS when considered under a 2-layered system for saturated conditions (CU and CD). The layered soil-waste system not only has a geotechnical application, but also provides a solution to the large environmental problem of the considered wastes.

Assessing the SAC305 Solder Joint Fatigue in Ball Grid Array Assembly Using Strain-Controlled and Stress-Controlled Approaches

Abstract One of the crucial factors in determining the reliability of an electronic device is fatigue failure of the interconnecting solder joints. In most cases, large bulk samples are used to study the fatigue characteristics of the solder materials. Real solder joints often encountered in ball grid array (BGA) components have only been considered in limited investigations. In this study, a specialized sandwich BGA test vehicle with a 3 × 3 solder joint was connected to the two substrates. The alloys were tested at room temperature using an Instron micromechanical tester in both the stress-controlled and strain-controlled methods. The tests were performed at a constant strain rate. Four stresses and four strain levels of the solder alloy Sn-3.0Ag-0.5Cu (SAC305) were examined using organic solderability preservative (OSP) and electroless nickel-immersion silver (ENIG) surface finishes. The work per cycle and plastic strain range was computed based on a systematic recording of the stress–strain (hysteresis) loops of each sample. A novel approach based on inelastic work is developed to calculate the fatigue life of a BGA assembled test vehicle. The results of the stress-controlled and strain-controlled tests indicated that the OSP surface finishes outperformed the ENIG surface finish. Regardless of the testing process and surface finish, the Coffin–Manson and Morrow energy models were acceptable for SAC305.

A Walker-based mean strain correction models for low-cycle fatigue life prediction

A Walker-based mean strain correction model of low-cycle fatigue (LFC) life prediction is proposed for high loaded parts. The model is based on a function depending on the strain range and strain ratio controlled in the strain-controlled LCF test of fatigue specimens and a constant reflecting the material sensitivity to strain ratio. The independence from the stress cycle parameters which can change during the strain-controlled LCF test is an obvious advantage of the model. The model was verified using the results of strain-controlled LCF tests of smooth titanium alloy Ti-6A1-4V ELI and iron-based alloy specimens conducted at room temperature. The proposed model was compared to the Smith - Watson - Topper and Walker models that take into account the mean stress effect. The proposed model provided the best prediction accuracy for titanium alloy. For Iron-based alloys the results obtained by the Walker model and the model proposed are close to each other. A simplified model based on the analysis of model parameters tailing into account the mean strain effect for predicting fatigue life of aeroengine critical parts is developed using a limited amount of experimental data when only the results of Rε = 0 tests are known. A comparison of the predicted life with the number of cycles to failure showed satisfactory results of fatigue life prediction for Ti-6A1-4V ELI and Iron-based alloys specimens.

Influence of Fiber Type and Dosage on Tensile Property of Asphalt Mixture Using Direct Tensile Test.

In engineering practice, fiber addition is a frequently used method to improve the tensile property of asphalt mixture. However, the optimum fiber type and dosage have not been determined by direct tensile tests. In this paper, monotonic tensile tests were conducted on three kinds of stone mastic asphalt (SMA13) mixtures, that is, granular-lignin-fiber-reinforced SMA (GFSMA), flocculent-lignin-fiber-reinforced SMA (FFSMA), and basalt-fiber-reinforced SMA (BFSMA) at different fiber dosages to probe the influence of fiber dosage on their tensile mechanical indexes (tensile strength, ultimate strain, elastic modulus, and strain energy density) and to determine the optimum dosage of each kind of fiber. The results showed that with the elevation of fiber dosage, the tensile strength, elastic modulus, and strain energy density of all three kinds of asphalt mixtures increased first and then decreased, while the ultimate strain increased constantly. The optimum dosage was 0.50 wt%, 0.45 wt%, and 0.50 wt% for granular lignin fiber, flocculent lignin fiber, and basalt fiber, respectively. On this basis, strain-controlled direct tensile fatigue tests were conducted on the three kinds of asphalt mixtures at the corresponding optimum fiber dosage. The results indicated that asphalt mixture reinforced with 0.50 wt% granular lignin fiber exhibited ideal direct tensile fatigue performance with respect to fatigue life and accumulative dissipated energy. Therefore, granular lignin fiber is recommended as the favorable fiber type, and its optimum dosage is 0.50 wt%. Moreover, scanning electron microscopy (SEM) demonstrated that the essence of the impact of fiber dosage and type on the tensile property of SMA is whether the reinforcement effect on the mixture matrix outweighs the negative effect of the defects between fiber and mixture matrix, or whether the reverse applies.

Experimental Study of the Dynamic Shear Modulus of Saturated Coral Sand under Complex Consolidation Conditions

The shear modulus is an essential parameter that reflects the mechanical properties of the soil. However, little is known about the shear modulus of coral sand, especially under complex consolidation conditions. In this paper, we present the results of a multi-stage strain-controlled undrained cyclic shear test on saturated coral sand. The influences of several consolidation state parameters: effective mean principal stress (p0′), consolidation ratio (kc), consolidation direction angle (α0), and coefficient of intermediate principal stress (b) on the maximum shear modulus (G0), the reference shear strain (γr) and the reduction of shear modulus (G) have been investigated. For a specified shear strain level, G will increase with increasing p0′ and kc, but decrease with increasing α0 and b. However, the difference between G for various α0 and b can be reduced by the increase of shear strain amplitude (γa). G0 shows an increasing trend with the increase of p0′ and kc; on the contrary, with the increase of α0 and b, G0 shows a decreasing trend. To quantify the effect of consolidation state parameters on G0, a new index (μG0) with four parameters (λ1, λ2, λ3, λ4) which is related to p0′, kc, α0, b is proposed to modify the prediction model of G0 in literature. Similarly, the values of γr under different consolidation conditions are also evaluated comprehensively by the four parameters, and the related index (μγr) is used to predict γr for various consolidation state parameters. A new finding is that there is an identical relationship between normalized shear modulus G/G0 and normalized shear strain γa/γr for various consolidation state parameters and the Davidenkov model can describe the G/G0–γa/γr curves. By using the prediction model proposed in this paper, an excellent prediction of G can be obtained and the deviation between measured and predicted G is all within ±10%.

Analyses of the model parameters of kinematic-isotropic hardening rule using genetic algorithm approach for predicting cyclic-plasticity of metallic structural materials

Modeling of engineering components under cyclic loading is complex because cyclic-plastic phenomena like the Bauschinger effect, ratcheting, shakedown, and mean stress relaxation are to be considered in the constitutive modeling. This has led to several investigations on modeling the cyclic-plastic behaviour of materials under stress-controlled and strain-controlled testing; but amongst these, Chaboche's isotropic-kinematic hardening (CIKH) model is quite popular and a frequently used one. A new methodology has been recently proposed by some of the present authors to use genetic algorithm towards optimization of the parameters of CIKH modeling with a demonstration of its applicability for a few materials. This investigation aims to elucidate that this approach is applicable to both cyclically stable materials as well as cyclic softening or hardening materials using several examples on structural materials. The considered metallic materials include several aluminum (like AA7075-T6 alloy), iron (like CS-1026and Sa333 C-Mn steel), titanium (like TA16 alloy), zirconium (like Zr-4 alloy)-base alloys or superalloys (like INCONEL718). The merit of the analysis of cyclic plastic deformation behaviour of materials with the current approach is inherent in its achieving higher accuracy of fitting to the experimental data with a single set of material parameters under both strain- and stress-controlled cycling. This has been established with a comparative analysis of the accuracy of fitting by the present approach with the ones available from the existing reports. The parameters obtained using the approach for the different materials are compared to get insights into the mechanism of plastic deformation.

Utilization of Different Additives in Improving Sandy Soil against Liquefaction

One of the main risks in low-densified sandy soils with the presence of water and an external force such as an earthquake is the generation of liquefaction. The influence of several types of reinforcement on liquefaction resistance, such as polypropylene fibers, geofibers, cement and polypropylene fibers with cement is shown in this study. Cyclic stress-controlled triaxial tests and cyclic strain-controlled triaxial tests were performed on saturated samples with and without reinforcements under undrained conditions. Cemented specimens were prepared with cement contents ranging from 0% to 3% by weight of dry sand and then cured for 3 days. The lengths of polypropylene fibers are 10 mm and 20 mm, respectively. The fibers were mixed with dry sand– cement mixes containing 0.50% and 1.00% by weight, respectively. Geofiber specimens were prepared in various arrangements. It was found that the liquefaction improvement factor (LIF) increased when fiber content and fiber length increased. The addition of geofibers increased the liquefaction resistance, as the number of layers increased. The addition of 3%C+1%F provided the best liquefaction resistance in this study compared with other additives. Finally, the reinforcement with cement and fibers is crucial for liquefaction resistanceof bitumen mastic should be considered beside the asphalt mixture performance and the bitumen rheological behavior. KEYWORDS: Liquefaction, Shear modulus, Cyclic stress, Geofiber, Polypropylene fiber.

DYNAMIC PROPERTIES OF SAND FOR EARTHQUAKE RESPONSE ANALYSIS IN THE BAY OF CAMPECHE

The Bay of Campeche is located in a region of moderate to high seismic activity related to the active triple junction between the North American, Caribbean, and Cocos plate boundaries. Therefore, the fixed offshore platforms and subsea structures in the Bay of Campeche must be designed against earthquake loading. A database was developed of classification and index properties tests, in situ measurements of shear wave velocity (Vs) using downhole P-S suspension seismic velocity logging, in situ piezocone penetration tests, resonant column tests to characterize the shear modulus and material damping ratio at small shear strains (10−5 % to about 0.1 %), and strain-controlled cyclic direct simple shear tests to evaluate the decrease of shear modulus and the increase of material damping ratio at large shear strains (0.1 % to about 10 %) performed on sand from the Bay of Campeche, including sands with no carbonate content to 100 % carbonate content, retrieved from the seafloor to a penetration depth of 120 m below seafloor. The database was tailored specifically to develop empirical correlations for the Bay of Campeche sand to determine Vs when in situ measurements of Vs are not available and to develop numerical modeling to predict the variation of the normalized shear modulus (G/Gmax) and material damping ratio (D) as a function of shear strains (g) when dynamic test results are unavailable for all the sand layers. The equations developed to calculate Vs and the curves of G/Gmax-g and D-g of Bay of Campeche sands are recommended for preliminary or perhaps even final seismic site response evaluations.

DYNAMIC PROPERTIES OF CLAY FOR EARTHQUAKE RESPONSE ANALYSIS IN THE BAY OF CAMPECHE

The Bay of Campeche is located in a region of moderate to high seismic activity related to the active triple junction between the North American, Caribbean, and Cocos plate boundaries. Therefore, the fixed offshore platforms and subsea structures in the Bay of Campeche must be designed against earthquake loading. A database was developed of classification and index properties tests, in situ measurements of shear wave velocity using downhole P-S suspension seismic velocity logging, in situ piezocone penetration tests, resonant column tests to characterize the shear modulus and material damping ratio at small shear strains (10−5 % to about 0.1 %), and strain-controlled cyclic direct simple shear tests to evaluate the decrease of shear modulus and the increase of material damping ratio at large shear strains (0.1 % to about 10 %) performed on clays from the Bay of Campeche, including clays with no carbonate content to 100 % carbonate content, retrieved from the seafloor to a penetration depth of 120 m below seafloor. The database was tailored specifically to develop empirical correlations for the Bay of Campeche clay to determine Vs when in situ measurements of Vs are not available and to develop numerical modeling to predict the variation of the normalized shear modulus (G/Gmax) and material damping ratio as a function of shear strains (g) when dynamic test results are unavailable for all the clay layers. The equations developed to calculate Vs and the curves of G/Gmax-g and D-g of Bay of Campeche clays are recommended for preliminary or perhaps even final seismic site response evaluations.

Cyclic Direct Shear Testing of a Sand with Waste Tires

This study investigates the cyclic behavior of sand mixed with waste tires by using a series of strain-controlled cyclic direct shear tests under constant normal load (CNL) conditions. Crushed Stone Sand (CSS) was used in the experimental studies. The sand grains have angular shapes and sizes changing from 1.0 mm to 2.0 mm. Two different types of waste tires were used in the experiments; (i) tire crumb (TC), and (ii) tire buffing (TB). The TC grains have an angular shape and size between 1.0 mm and 2.0 mm, whereas TB grains used were found to be fiber-shaped, with dimensions changing from 1 mm to 9 mm, and an aspect ratio of about 1:5. The tests were carried out under 100 kPa vertical effective stress on the sand with 0%, 2.5%, 5%, 7.5%, and 10% waste tire contents. The testing results were found to be highly dependent on both the type and amount of waste tires in the mixtures. Furthermore, the behavior of the mixtures was estimated by the Bayesian Regularization Neural Network (BRNN) prediction model, for further use by researchers. The performance of the proposed BRNN model was found to provide a quite high correlation coefficient (R2 = 0.96).

Stress-rate dependency of uniaxial compressive strength of hard rock with regard to test procedure standards

The uniaxial compressive strength test of hard rock is one of the most worldwide applied tests for characterization of hard rock in rock engineering and engineering geology. The uniaxial compressive strength as the results of this test is a basic parameter, used, for example, for the design of rock engineering structures. In the commonly applied standards, stress-controlled test procedures using constant stress rates are recommended by a wide range of stress rates varying between 2 and 60 MPa/min and/or a specific minimum test time. Though the effect of stress-rate dependency of hard rock is generally known, most investigation is focused on dynamic action behavior using high stress rates and/or fast actions. Strain-controlled test procedures are often used as well. For stress-controlled test procedures within the recommended range of stress-rates, the data base is rather poor, the effects to the results are reported by only very few researchers. The research described in this paper aims to close this gap and focuses on the stress-rate dependency of uniaxial compressive strength of hard rock. Seven different stress rates varying between 1 and 100 MPa/min on five different types of hard rock (quartzite, granodiorite, gabbro, sandstone, basalt) using five to fifteen single tests per stress rate have been executed. A significant increase of uniaxial compressive strength by increasing stress rates has been stated; the increase may not be ignored in assessing rock strength in rock engineering projects. The effect has to be considered especially when different parties are involved in the site investigation programs.

Natural rubber latex treatment of sand: A novel remediation technique for soil liquefaction

We present a novel method to improve liquefaction resistance in sandy soil by treating it with natural rubber latex (NRL) using a pressurised permeation technique. Sand samples treated with NRL solutions of 10%, 15%, 20%, and 30% concentrations were tested. The liquefaction resistance of the untreated and NRL-treated sand samples was evaluated by performing strain-controlled cyclic triaxial tests with 0.15%, 0.3%, and 0.5% axial strain amplitudes. We find that NRL treatment reduces excess pore pressure development in the sand, thereby increasing liquefaction resistance. Further, this study also explores the effect of NRL treatment on stiffness deterioration in the sand under cyclic loading. NRL-treated sand samples showed resistance to progressive stiffness degradation even after many cycles due to interparticle bonding developed by virtue of the solidified NRL fibres. From a pilot study on the behaviour of treated sand under stress-controlled loading, it was seen that irrespective of the pore pressure development, NRL effectively resist the strain development in sand. Hence, we propose the utilisation of NRL as an environment-friendly soil stabiliser for mitigating liquefaction.

Low cycle fatigue behavior of micro-grain casting K4169 superalloy at room temperature

The strain-controlled low cycle fatigue tests were carried out at 298 ​K for the newly developed micro-grain casting K4169 superalloy, and the cyclic stress response, deformation and fracture behaviors of the alloy were studied. The results show that the fatigue life of the alloy was increased by more than two times compared with other casting K4169 alloys. This can be partly attributed to grain refinement impeding crack initiation and propagation. When the strain amplitude was in plastic range (Δεt/2 ​≥ ​0.5%), the alloy displayed a short period of initial cyclic stability followed by cyclic softening to fracture. By observing dislocation configurations, only a few dislocations moved around grain boundaries at initial cycles, leading to short cyclic stability. Afterwards, dislocations in the slip bands cut γ" phase continuously leading to cyclic softening. When the strain amplitude was in elastic range (Δεt/2 ​≤ ​0.4%), the alloy exhibited elastic deformation and the peak stress kept stable. In addition, the crack initiation site changed from the MC carbides to the persistent slip bands on surface with increasing strain amplitudes.

Creep-fatigue of P92 in service-like tests with combined stress- and strain-controlled dwell times

Complex service-like relaxation- and creep-fatigue tests with strain- and stress-controlled dwells and fatigue cycle durations of approx. 2200 s were performed exemplarily on a grade P92 steel at 620 °C in this study. The results indicate deviations in the prevailing creep mechanisms of long-term relaxation and creep dwells, affecting subsequent dwells, load shifts, and the macroscopic softening behavior quite differently. In addition, fracture surfaces and longitudinal metallographic sections reveal intergranular crack growth for complex loading with stress-controlled dwells, whereas complex strain-controlled tests enhance oxidation and transgranular crack propagation. These findings substantiate the limited transferability of relaxation-fatigue to creep-fatigue conditions.