Cyclic Stress Tests Research Articles

Electrochemical hydrogen permeation measurement during cyclic stress testing of a ferritic chromium steel

AbstractIn the present work, the hydrogen diffusion during cyclic stress testing in the ferritic chromium steel 1.4521 (X2CrMoTi18‐2) is investigated. Therefore, electrochemical hydrogen permeation measurements are carried out on a hollow cylinder geometry. Simultaneously an alternating stress is applied using a stress ratio of R=‐1. At low stress amplitudes, no influence on the diffusion behaviour of hydrogen is found. At a higher stress amplitude, close to the macroscopic yield strength, a delayed hydrogen permeation by a factor of two is observed. It is postulated that this observation is a result of the nucleation of new hydrogen traps during the measurement. Hydrogen content measurements using carrier gas hot extraction support this hypothesis.

Insight into the effect of applied potential on the passive behavior of commercially pure titanium in a simulated proton exchange membrane water electrolysis environment: Stable and operational fluctuating potential

The correlation between applied potentials and the passive films of commercially pure titanium (CP-Ti) in a simulated proton exchange membrane water electrolysis (PEMWE) environment was investigated. In the first passive region, the passive film formed at 1 V exhibited superior overall performance. The values of ND were positively correlated with the applied potentials. The oxygen vacancy diffusivities were determined to be on the order of 10–17 cm2 s−1. The average valences of the passive films were positively linear with the applied potentials. As further increasing the potential, due to the intense OER and consequent growth, the oxide ratios and average valences of the passive films increased. The corrosion induced by accelerated stress cycle (ASC) tests was slight and crystallographically oriented. After increasing the frequency of potential change, the total Ti oxides were slightly less than those of 2.5 V.

Microbiological quality and efficacy of preservatives in marigold-based skin care products

<p>The microbiological stability of cosmetic products is crucial, especially in products with high water content, such as creams. Therefore, preservatives are used in order to protect consumers from harmful pathogens that would otherwise invade the cosmetics. Despite their function, the addition of preservatives can be considered controversial in the cosmetics industry. Parabens are frequently used synthetic preservatives in various industries. According to regulatory directives concerning cosmetics (Cosmetic Directive by the European Commission) usage of some parabens (methylparaben, propylparaben, butylparaben, and ethylparaben) is safe and permitted in allowed concentrations. On the other hand, the European Commission prohibited the use of isopropylparaben, isobutylparaben, phenylparaben, benzylparaben and pentylparaben. Therefore, a comprehensive stability study was conducted to evaluate the influence of paraben-based preservative (Gujsol-1<sup>®</sup>, INCI name: Phenoxyethanol, Methylparaben, Ethylparaben, Propylparaben, Butylparaben) and potassium sorbate in order to preserve plant extracts-based skin-care products, Day and Night creams with marigold extract. Previously, mentioned skin-care products were preserved with the preservative Dekaben C<sup>®</sup>, which contained paraben mixture with banned isobutylparaben. All tested formulations showed favorable texture and sensory characteristics, desirable mild acidic pH values, satisfactory physical stability and appropriate microbiological quality at the initial point, as well as after storage at elevated temperature or at cyclic stress test conditions and at room temperature during two years. In addition, both preservatives significantly reduced the number of inoculated microorganisms during the challenge test. It can be concluded that potassium sorbate in plant-based creams could be an efficient alternative to paraben-based preservatives.</p>

The Harpers THMC flow bench: A triaxial multi-reactor setup for the investigation of long-term coupled thermo-hydro-mechanical-chemical fluid-rock interaction.

The scientific analysis and interpretation of coupled thermo-hydro-mechanical-chemical (THMC) processes in rocks requires complex and diverse instrumentation. In this study, we introduce the "Harpers THMC Flow Bench," a multi-cell, flow-through reactor system that allows long-term testing on rock plugs and powdered samples. The setup consists of four small triaxial cells that can hold confining and pore pressure of up to 20 MPa and an axial load of up to 300 MPa. Axial deformation of the samples is measured with linear variable differential transducers. The cells can be heated to 90 °C, and effluents (gas, water, and brine) can be sampled for compositional analysis. An additional Hastelloy-autoclave enables fluid mixing and saturation with gas prior to injection into the samples. Each cell can be operated individually, allowing independent experiments over long testing periods. The sample holders were designed such that they are transparent for X-rays during X-ray computer tomography, minimizing sample handling effects on the imaging results. To demonstrate examples of the capabilities of the flow bench, we present case studies on Carnmenellis granite (Cornwall, UK) and Castlegate sandstone (Utah, USA) samples. Permeability measurements are shown using fractured granite undergoing periodic loading of effective pressure. To demonstrate chemical measurement capabilities, we used deionized water to leach elements from granite powders. We then analyzed effluent compositions using inductively coupled plasma optical emission spectroscopy. Finally, we conducted a strength test and a cyclic differential stress test on sandstone to demonstrate the mechanical testing capabilities of the setup.

Thermal fatigue and cracking behaviors of asphalt mixtures under different temperature variations

Thermal cracking is one of the most annoying distresses in asphalt pavements. The cracking of asphalt pavements caused by extremely low temperature and the damage of thermal fatigue caused by repeated temperature variations are particularly pronounced. The service condition of asphalt pavements has been affected significantly. Laboratory experiments with cyclic loads simulating the actions caused by repeated temperature variations on pavements have been conducted in many previous studies to investigate the thermal fatigue characteristics of asphalt mixtures. In those studies, an equivalent cyclic mechanical stress that can be applied by an actuator was mostly used to replace the cyclic thermal stress induced by a temperature variation. It could simplify the experimental process but could not consider the performances of asphalt mixtures varying as a function of temperature. In the present study, the thermal fatigue properties and cracking behaviors of asphalt mixtures were comprehensively investigated through a modified thermal stress restrained specimen test (TSRST) and the numerical analysis. Various temperature ranges (-20 to −10 °C, −10 to 0 °C), cyclic cooling rates (10 °C/h, 20 °C/h), low-temperature performance cooling rates (10 °C/h, 8 °C/h, 6 °C/h, 4 °C/h, 2 °C/h) and pre-crack dimensions were considered for the study to address the influences of those parameters on the analysis results. Based on the testing and simulation results, it was found that the effects of thermal fatigue on asphalt mixtures under different temperature variations and cooling rates were quantified, and the damage characteristics of the asphalt mixtures were also explored. The results showed that under the low-temperature performance state, the thermal stress of asphalt mixtures increases with a uniform cooling rate and it could be obtained that the faster the cooling rate, the larger the thermal stress generated. In the cyclic thermal stress test, due to the viscoelastic properties of asphalt mixtures, the thermal stress showed significant stress relaxation phenomena under the temperature variations. The magnitude of thermal stress decreased gradually within each cycle. It demonstrates that under the same temperature variation, the thermal stress decreases continuously with the increasing thermal cycles. Through the numerical simulation, it was clear that under different temperature ranges and cooling rates, the magnitude of thermal stress increased with the temperature range decreased, whereas the magnitude of thermal stress increased with an acceleration of the cooling rate. The lower temperature range induced a larger stress intensity factor (KI), which implies a faster cracking evolution. Analyzing the effects of different pre-crack dimensions on the number of temperature cycles, the height of pre-crack showed significant effects on the number of temperature cycles than width.

Seismic Resilience Study of Piers Enhanced by Ultrahigh-Performance Concrete Jackets Based on Cyclic Loading Test and Static Push-Over Curves

The efficiency of novel retrofitting of constructed reinforced concrete piers with ultra-high performance concrete (UHPC) jackets was investigated. Pier specimens were subjected to a series of cyclic quasi-static stress tests, whereby two tests employed UHPC jackets with a single width (UHPC-W), while the other two used UHPC jackets with several narrow widths (UHPC-N). The seismic responses were compared in terms of energy dissipation, ductility, hysteresis curves, and skeleton curves. The seismic capability of reinforced concrete piers is increased by both W-type and N-type UHPC jackets by reducing concrete damage. Reinforced concrete piers with a UHPC-W jacket offer greater lateral strength but are more vulnerable to plastic hinge movement. On the other hand, the UHPC-N jacket increases the ductility of concrete and conceals concrete damage. However, construction quality was critical to ensure tight contact between the multiple strips and the reinforced concrete shaft. Based on the implicit method, a 3D finite element model is recommended for nonlinear static elasticplastic analysis. The nonlinear reinforcement model, bond-slip behavior, and concrete damage plastic model are all included in the finite element model. In order to assess the seismic susceptibility of the retrofitted piers, various limit states were defined, and fragility curves unique to the particular structure were produced.

Experimental study on the damage process of marble under true triaxial pre-peak unloading conditions

Stress-induced instability is associated with rock damage. Here, the progressive brittle fracturing process in Jinping marble is studied by introducing two types of true triaxial pre-peak unloading tests, namely, the incrementally cyclic loading-unloading minimum principal stress test (ICM test) and the incrementally cyclic loading-unloading maximum and minimum principal stress test (ICMM test). By comprehensively analysing the irreversible strains, dissipated energy, acoustic emission (AE) characteristics and scanning electron microscopy (SEM) results, the rock damage evolution can be quantified and divided into two distinctive damage stages. At the boundary point, the irreversible strain increments reach their minimum values. In the gentle damage stage, the normalized irreversible strains increase linearly, and this process is associated with a small number of AE hits with low amplitude. The rapid damage stage is characterized by a nonlinear increase in the normalized irreversible strains, and this process is associated with a large number of AE hits with high amplitude. The dissipated energy mainly increases in the rapid damage stage. In addition, the rapid damage stage in the ICMM test mainly occurs in the last five cycles, due to the differences in the deviatoric stresses in each cycle. In both of these tests, the failure mode is principally characterized by tensile failure. Moreover, the precursory signals of rock fracturing and the influence of the loading paths on the strength are discussed.

Research on the Mechanical Characteristics of Cyclic Loading and Unloading of Rock Based on Infrared Thermal Image Analysis

In the operations of underground rock engineering, such as mining, the formation of goafs is often accompanied by unloading and energy effects. In this study, a cyclic loading and unloading stress test is carried out to analyze the strength characteristics of the loaded samples under different loading and unloading ranges as well as different numbers of cycles. The rock force is accompanied by substantial energy changes. To better fit the energy analysis under cyclic loading and unloading conditions, thermal infrared radiation characteristic analysis is performed during rock loading and unloading. An infrared radiation camera is adopted to detect the infrared characteristics of the rock force process after cyclic loading and unloading. Multiangle detection is implemented on the temperature, temperature field, and frequency histogram. The analysis shows that cyclic loading and unloading first strengthen and then weaken the rock. Moreover, the failure caused by the local stress concentration leads to a sharp increase in the temperature. There are significant temperature fluctuations before and after failure, and the temperature field after failure can be divided into three zones, namely, the normal temperature zone, heating zone, and mutational temperature zone, to comprehensively reflect that rock compression failure which is accompanied by the process of energy accumulation and release. On the basis of infrared energy analysis, the index of the energy release rate is introduced, and the loading and unloading analysis model is constructed. The research results reveal that rock failure is accompanied by the process of energy accumulation and release, which provides evidence for the analysis of the spatial stability of the rock mass under cyclic loading and unloading conditions and engineering excavation.

Determination Method of Elasto-Plastic Correction Factor of TA16 Titanium Alloy Based on RCC-M Code Methodology

Abstract In the code for nuclear equipment, the elasto-plastic correction factor KE is a correction factor when the stress range exceeds the yield limit for simplified elasto-plastic fatigue analysis. The parameters and expressions of KE for commonly used materials (such as austenitic stainless steel) are given in the RCC-M and ASME codes, but the parameters of KE for titanium alloy materials are lacking. Based on the cyclic elasto-plastic constitutive model of Z2CND18.12 (nitrogen control) and KE parameters of austenitic stainless steel given in the code, considering various sensitive factors, a numerical calculation method for determining KE correlation coefficient is established. The elasto-plastic constitutive model of TA16 alloy with nonlinear kinematic hardening was established by the uniaxial tension, strain, and stress cycling tests of TA16 titanium alloy. Based on the numerical calculation method of KE and the constitutive model of TA16 titanium alloy, the expression and correlation coefficient of KE for TA16 titanium alloy were determined.

Study on Near‐Adiabatic Performance of Electric Vehicles' Lithium Battery at Low Temperature

In recent years, electric vehicles have developed rapidly. However, as the power source of electric vehicles, lithium battery has poor performance at low temperature, and has some problems such as reduced capacity and increased internal resistance. In this paper, two thermal environments, including natural convection condition and near‐adiabatic condition, are established, and discharge capacity test and cyclic dynamic stress test (DST) are conducted for lithium iron phosphate batteries. The actual effect of near‐adiabatic conditions is analyzed from three perspectives: battery surface temperature, terminal voltage and EIS. The results show that the near‐adiabatic working condition has almost no effect on the discharge capacity at the standard discharge current (0.5 °C) under the same temperature conditions, ranging from −15 to 25 °C. In the low‐temperature − 10 and − 15 °C cyclic dynamic stress test, compared with the natural convection working condition, the near‐adiabatic condition has a rapid rise in terminal voltage one cycle earlier, causing the cycle to stop. Also, the polarization impedance increases at least twice after the cycle under the near‐adiabatic condition. Finally, according to the analysis of variance (ANOVA), the near‐adiabatic condition has a significant effect on voltage and polarization resistance at low temperatures. Still, it has almost no effect on ohmic resistance and discharge capacity. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Reliability estimation for one-shot devices under cyclic accelerated life-testing

A one-shot device, like an automobile airbag, is a product or an equipment that can be used only once. Better quality and longer lifetime of one-shot devices nowadays increase the cost of life test experiment under normal operating condition. Cyclic stress test, adopted in life-testing experiments by increasing stress levels to induce more failures, has been used to investigate the reliability analysis of one-shot devices based on Coffin–Manson principle. However, the Coffin–Manson model only considers temperature change in each cycle. Moreover, it assumes that the reliability is independent of the cycling frequency, which may not be a realistic assumption in practice. Birnbaum–Saunders distribution, originally developed to model fatigue failure under cyclic loading, has been used widely to model lifetime data. As the Norris–Landzberg model is proposed for modeling fatigue life due to cyclic temperature fluctuation, it is used in this work together with Birnbaum–Saunders distribution for modeling lifetimes of one-shot devices under accelerated life-tests with different cyclic temperature fluctuations. It contains the Coffin–Manson model as a special case. Inferential methods for model parameters, reliability and mean lifetime are developed in this paper. Simulation study and model discrimination are carried out to evaluate the performance of the proposed model and inferential methods. Finally, an example is presented to illustrate the model and the inferential results developed here.

Study on characteristics of fatigue strength of ARALL composite in constructive elements

Due to Fatigue Testing fatigue life of specimens made of various materials and with various flange types was estimated. Specimens with dish-shaped and ring-shape flanges were tested. Specimens were made of aluminum alloy D16chATV sheets (thickness 1.2 mm) and of ARALL with a thickness of 1.2 mm based on aluminum layers of 0.5 mm thickness. Specimens were tested under 3 levels of cyclic stress: σmax=120, 100, 80 MPa with minimum stress of σmin=20 MPa. Some of ARALL specimens were tested only under σmax=100 MPa stress level. Under each stress level were tested 5 – 6 specimens. According to the results of all specimen tests the authors plotted plotted fatigue curves. Using the Finite Element Method the stress state of specimens during cyclic stress tests was analyzed. Calculations of fatigue life of specimens were made on the basis of the offered method. Full-element and numerical experiments revealed that fatigue resistance of monolithic alloy specimens with dish-shaped flange under all stress levels is higher than of specimens with a ring-shaped flange. ARALL specimens with dish-shaped and ring-shaped flanges both according to test results have a higher fatigue resistance than monolithic alloy specimens.

An Approach to Drug Stability Studies and Shelf-life Determination

The main objective of carrying out stability studies of the drug product is to establish shelf life of drug during storage. Stability of drug is defined as “The capability of a particular formulation in a specific container/closed system, to remain within its physical, chemical, microbiological, therapeutic, and toxicological specifications throughout its shelf life”. As mentioned in the International Conference on Harmonization (ICH) guideline Q1A (R2), stability studies are commonly the activity on the critical path to regulatory filing and approval. Stability studies are of different types and different methods are useful for the determination of stability like real-time stability testing, accelerated stability testing, retained sample stability testing and cyclic temperature stress testing. pH and temperature are the main factors influencing the stability of the drug. The pH-rate profile (log(k)vs pH) is the pH dependence of the specific rate constant of degradation of compounds. Forced degradation includes deterioration of new drug substances and products at more severe conditions than the accelerated conditions and it indicates the accuracy of stability-indicating methods. The different conditions applied during the forced degradation include hydrolytic, oxidation, photolytic and thermal stress etc. The techniques utilized for evaluation of stability studies can be LC-MS/MS, HPLC-DAD, HPLC-MS, HPLC-UV, HPTLC, TLC, LC-NMR etc. amongst them some techniques shows high sensitivity and resolution power to establish more effective stability-indicating method while for shelf life estimation of drugs and products the different methods mentioned are FDA’s method, the direct method, inverse method, simulation results and Garret and Carper method. Thus stability testing of pharmaceutical products inputs specific scheme in the evolution of a new drug as well as new formulation.

Deformation and Fatigue Behaviour of A356-T7 Cast Aluminium Alloys Used in High Specific Power IC Engines.

The continuous drive towards higher specific power and lower displacement engines in recent years place increasingly higher loads on the internal combustion engine materials. This necessitates a more robust collection of reliable material data for computational fatigue life prediction to develop reliable engines and reduce developmental costs. Monotonic tensile testing and cyclic stress and strain-controlled testing of A356-T7 + 0.5 wt.% Cu cast aluminium alloys have been performed. The uniaxial tests were performed on polished test bars extracted from highly loaded areas of cast cylinder heads. The monotonic deformation tests indicate that the material has an elastic-plastic monotonic response with plastic hardening. The strain controlled uniaxial low cycle fatigue tests were run at multiple load levels to capture the cyclic deformation behaviour and the corresponding fatigue lives. The equivalent stress-controlled fatigue tests were performed to study the influence of the loading mode on the cyclic deformation and fatigue lives. The two types of tests exhibit similar fatigue lives and stress-strain responses indicating minimal influence of the mode of loading in fatigue testing of A356 + T7 alloys. The material exhibits a non-linear deformation behaviour with a mixed isotropic and kinematic hardening behaviour that saturates after the initial few cycles. There exists significant scatter in the tested replicas for both monotonic and cyclic loading.

Cyclic stress responses of a newly developed nickel-base superalloy at elevated temperatures

Total strain-controlled low cycle fatigue tests were conducted on the newly designed nickel-base superalloy M951G under different testing conditions; the relationship among cyclic stress responses, microstructural degradations, deformation mechanisms and testing conditions has been established. Results show that both the cyclic hardening and softening behaviors are dependent on the testing temperature and strain amplitude. As the strain amplitude increases both at 900 and 1000 °C, M951G alloy exhibits cyclic hardening under low strain amplitudes and cyclic softening under higher strain amplitudes. At 900 °C, the initial cyclic hardening is related to the coherent γ/γ′ interface, parallel dislocation arrays and dislocation bypassing the tiny γ′ particles. At higher strain amplitudes, the initial cyclic softening is due to the higher density of shearing dislocations in γ′ precipitates. At 1000 °C, plenty of parallel dislocation arrays present in γ channels, which reduces the possibility of dislocation interactions from different slip systems and results in initial cyclic hardening. Under higher strain amplitudes, apart from microstructural degradations, dislocations shearing into γ′ precipitates and formation of dislocation networks, the dislocation annihilation and partial loss of coherency of γ′ precipitates are also responsible for the initial cyclic softening at 1000 °C.

Variation of the Corrosion Behavior Prior to Crack Initiation of E690 Steel Fatigued in Simulated Seawater with Various Cyclic Stress Levels

The electrochemical process and corrosion behavior prior to crack initiation of E690 steel fatigued in simulated seawater are investigated under different cyclic stress levels by methods of electrochemical impedance spectroscopy, cyclic current response, electrochemical noise and morphology observation. The results show that the electrochemical behavior changes with the peak stress of cyclic loading and the corrosion behavior transforms as the peak stress increases over the proof strength. The charge transfer resistance (Rct) decreases with elevated peak stress. Continuous decreasing Rct with cycling number under peak stress of 1.02 σp0.2 indicates that continuous fresh metal induced by work-softening is exposed to the seawater, which is also proved by cyclic current response induced by cyclic stress and contact angle test. As a result, the corrosion type of E690 steel changes from general corrosion to pitting corrosion with the peak stress close to and above the proof strength. That induces the corrosion fatigue crack initiation mechanism to change correspondingly.

Hydrogen behavior in high strength steels during various stress applications corresponding to different hydrogen embrittlement testing methods

Atomic scale phenomena during various types of hydrogen embrittlement testing were examined by investigating hydrogen desorption during the tests using tempered martensitic steel and cold-drawn pearlitic steel specimens. Hydrogen desorption increased in the elastic stage of constant stress/strain and cyclic stress testing, implying hydrogen transportation by dislocations. In contrast, hydrogen desorption increased in the elastic stage but turned downward near proof stress and finally deceased to less than that before stress application. This implies that hydrogen-enhanced strain-induced lattice defects such as dislocations and vacancies formed in addition to hydrogen accumulation by mobile dislocations. These results suggest that one of the reasons for the high hydrogen embrittlement susceptibility of high strength steels is hydrogen accumulation on the grain boundaries and cementite interfaces due to hydrogen transportation by mobile dislocations under elastic deformation.

Fatigue fracture assessment of high strength steel using thermographic analysis

Fatigue behaviour is most commonly evaluated in uni-axial cyclic stress tests using standardised dog-bone samples. When components are sharply bent into shape and subjected to cyclic loading, the fatigue damage will accumulate at the inside of the bend. This paper reports on an experimental investigation about the feasibility of infrared thermographic techniques to monitor fatigue damage initiation and accumulation. By monitoring spectral components of the thermal response, the fatigue limit, the onset of crack initiation and the ratio of initiation to propagation lifetime can all be determined. Also the effect of surface treatments on initiation properties is investigated. Most results are consistent with expected behaviour based on a previous study, indicating that thermographic techniques have a greater sensitivity and can be used to reduce the number of samples and time required for fatigue characterisation.

Predicting Linear Elongation With Conductive Thread-Based Sensors

Conductive thread-based sensors have the potential to offer ambulatory measurement of body movement and posture. While such sensors have been previously described in terms of their overall correlation with existing measurement modalities, the ability of thread-based sensors to predict linear elongation has yet to be investigated. We constructed multiple stitched sensors, 20 cm in length, using two silver-coated nylon threads and seven different types of stitches, including cover and overlock stitches. Stitched sensors underwent elongation and cyclic stress tests while sensor resistance was recorded. Optimal predictive functions were derived for each sensor such that the range-normalized error was minimized. Responses were found to be governed by the combination of stitch geometry and physical properties of the threads. The average error in predicting elongation was 14% of the usable sensor range, suggesting that the stitched sensors are perhaps better suited to intermittent detection of stretched versus unstretched states rather than continuous prediction of absolute elongation. Nonetheless, coverstitches were generally superior to overlock stitches in terms of minimizing range-normalized error. The path of the conductive looper thread and the presence of stabilizing needle threads were important determinants of the sensor’s prediction capability and repeatability. Stress tests revealed a systematic upward drift of the resistance response curve for all sensors over repeated trials, suggesting that these stitched sensors require adequate recovery time between measurements. Given the possibility of applying stitched sensors non-destructively to existing garments, further study of these sensors—particularly those comprising multiple independent stitches in novel stitch geometries—remains worthwhile.

Cyclic behavior of Q345GJ steel used in energy dissipation shear links

The cyclic behavior of Q345GJ steel was explored by strain cycle tests, stress cycle tests and uniaxial tension tests. The results of strain cycle tests confirmed that Q345GJ steel has no cyclic hardening, and it had rare strain amplitude effect or strain history effect. The stress cycle tests confirmed that the cumulative plastic strain goes up stably under eccentric stress with increasing loading loops. Thus, it can be concluded that the hardening characteristics of Q345GJ coincide with kinematic hardening, having almost no isotropic hardening. The superposition of four nonlinear kinematic hardening model based on Chaboche’s constitutive model was used to predict the hardening characteristics of Q345GJ steel, and the parameters of the constitutive model were calibrated based on the test results. The numerical validation of the constitutive model confirmed that the proposed parameters can give good simulation for strain cycle behavior and stress cycle behavior of Q345GJ steel.