Multiple-step Test Research Articles

Austenitic Stainless Steel EBF Subjected to Low and Extremely Low Cycle Fatigue

AbstractDissipative zones buildings, in which plastic hinges or plastic strains occur during, for instance, seismic episodes, have been studied for many different types of steel fuse elements. Stainless steel (SS), has attracted attention in this regard due to its high ductility and further studies are needed to determine its performance and usefulness as fuses.The use of SS in the construction industry has represented an advance due to its already known anticorrosive properties in addition to its strength and ductility. However, recent research on cyclic plasticity shows that SS has significant hardening properties, which can be exploited in the use of this material in structural elements to support cyclic loads, such as those occurring during earthquakes.The cyclic plasticity models in SS have been studied with some applications (fatigue, low‐cycle fatigue and extremely low cycle fatigue). Several studies carried out cyclic tests to obtain experimental data, which have been used for numerical models with the utilisation of a combined numerical model of kinematic/isotropic hardening. These studies recommend models to simulate the behaviour of SS under a cyclic load.This work presents an experimental study of the cyclic behaviour of SS when subject to low and extremely low cycle fatigue. Several protocols on tests such as companion, multiple step and arbitrary tests were carried out. The results inferred from the experimental program provide hardening parameters used to study one example of dissipative zones of eccentrically braced frames (EBFs).

Tuneable material properties of Organosolv lignin biocomposites in response to heat and shear forces

Lignin as a renewable biomacromolecule is considered as a sustainable feedstock for the generation of bioplastics and bioplastic composites. However, during thermoplastic processing, high temperature and mechanical forces are known to promote destructive bond-cleavage in a vast majority of macromolecules due to overheating and internal friction between molecular constituents. This study demonstrates that several material properties (e.g. thermal stability, mechanical properties) of biocomposites with a high Organosolv lignin content (≥50w%) can be tuned by carefully selecting thermal and mechanical energy input during compounding. Organosolv lignin obtained from ensiled grass was shown to undergo in-situ coupling reactions at temperatures below the main degradation point (<200 °C) resulting in an up to 6-fold increase in molecular weight (Mw). The results from Fourier Transform Infrared (FTIR) spectroscopy suggested the formation of ester bonds, which was ascribed to direct esterification reactions, which occur due to energy transfer in the melt phase. When subjecting the extracted lignin to prolonged compounding times, it was shown that higher coupling degrees resulted in a lignin biocomposite with increased stiffness and ultimate tensile stress of about 1800% and 40%, respectively. Temperature was shown to have the highest effect on coupling reactions, whereas the energy transfer by mechanical forces during compounding was lower and followed a non-linear behaviour. In tensile stress–strain curves, biocomposites with high energy input revealed a distinct yield point (16 MPa). Ultra-micro-hardness tests confirmed that the biocomposite became significantly stiffer in response to shear and thermal forces with a reduction in indentation creep Cit of 2.0% to a value of up to 8.5%. Organosolv lignin biocomposites obtained at higher specific energy input (EIN) through thermal energy input and shear forces showed an increased dynamic stiffness Cdyn up to 100%, which was observed by multiple step tests (MST).

Monotonic and Fatigue Behavior of EBM Manufactured Ti-6Al-4V Solid Samples: Experimental, Analytical and Numerical Investigations

The present study aims to carry out an experimental, analytical and numerical investigation of the monotonic and fatigue performance of electron beam melted Ti-6Al-4V structures. Therefore, tensile tests, multiple step tests and strain-life tests were performed on machined EBM Ti-6Al-4V solid samples. An elastic-plastic material model in combination with a numerical damage model was examined according to the experimental tensile tests. Analytical models proposed by Ramberg and Osgood, as well as Coffin and Manson were obtained to describe the cyclic stress-strain curves and strain-life curves, respectively. The fracture surfaces of the tested samples and the influence of different build directions were analyzed. A prediction of the static and fatigue material properties is of particular importance, e.g., for the safe application of additively manufactured load-bearing implant structures. Based on the determined analytical and numerical models, the material and product behavior of complex electron beam melted structures under cyclic loading and fatigue life determination can be investigated in the early stages of the product development process.

Group Testing with Homophily to Curb Epidemics with Asymptomatic Carriers

Contagion happens through heterogeneous interpersonal relations (homophily) which induce contamination clusters. Group testing is increasingly recognized as necessary to fight the asymptomatic transmission of the COVID-19. Still, it is plagued by false negatives. Homophily can be taken into account to design test pools that encompass potential contamination clusters. I show that this makes it possible to overcome the usual information-theoretic limits of group testing, which are based on an implicit homogeneity assumption. Even more interestingly, a multiple-step testing strategy combining this approach with advanced complementary exams for all individuals in pools identified as positive identifies asymptomatic carriers who would be missed even by costly exhaustive individual tests. Recent advances in group testing have brought large gains in efficiency, but within the bounds of the above cited information-theoretic limits, and without tackling the false negatives issue which is crucial for COVID-19. Homophily has been considered in the contagion literature already, but not in order to improve group testing.

Failure behaviour of metal inserts embedded in CFRP subsequent to thermal, mechanical and cyclic pre-damage

One of the most efficient implementations of lightweight design is the use of carbon fibre reinforced plastics due to their outstanding specific mechanical properties. With respect to multi-material-design, carbon fibre reinforced plastic parts have to be joined to other components such as load frames or functional elements. The use of embedded metal elements, so called inserts, is favoured to avoid drilling of composites. The fibre continuity is ensured and no local bearing stresses occur. In the work at hand the influence of impact damage on the quasi-static and cyclic strength was evaluated by pre-damaging the components by various impact energies. The components show only a minor reduction of the mechanical properties for impact energies up to 12 J. For impact energies between 12 J and 16 J, a loss in the mechanical properties is evident but final failure only occurred for impact energies above 16 J.Another aim of this study was to derive service-life-prognosis using multiple step tests and to validate these with experimentally determined S-N curves. Due to different damage mechanisms occurring under quasi-static and cyclic loads, a service-life-prognosis based on the multiple step tests was not feasible, however, a service-life-prognosis based on the experimental data is given.

Fatigue properties of tungsten from two different processing routes

Fatigue failure is a distinct possibility in spallation targets like tungsten, subjected to cyclic thermo-mechanical loading caused by beam trips and beam pulses. In this study, the tensile and fatigue properties of pure tungsten from two different processing routes have been determined at room temperature. The specimens tested were sintered, rolled and annealed (RA), as well as sintered and HIPed tungsten (SH).Tensile tests showed low total strain (∼0.25%) and negligible plastic strain for both specimens. However, the UTS for rolled specimens (∼1 GPa) was much higher relative to the HIPed material (567 MPa).As tungsten is very brittle, fatigue testing was done primarily under stress-control, using the staircase method and a near zero stress ratio. For the rolled and HIPed materials, fatigue limits (no specimen failure up to 2⋅106 load cycles) were determined to be 350 MPa and 180 MPa, respectively. In addition, results from strain-controlled multiple-step testing (strain ratio ∼0) indicated a slight relaxation in stress for the HIPed material while the rolled specimens showed a purely elastic response.The implication of fatigue test results for spallation target design is discussed.

Comparative characterization of quasi-static and cyclic deformation behavior of glass fiber-reinforced polyurethane (GFR-PU) and epoxy (GFR-EP)

Abstract Glass fiber-reinforced polymers (GFRP) are highly suitable for use in transportation industry in order to achieve the targets of energy and resource efficiency. In this context, due to its high specific strength, GFR-epoxy (GFR-EP) has already been implemented in a wide range of applications. However, in cases of energy efficiency and damage tolerance, GFR-EP shows disadvantages compared to GFR-polyurethane (GFR-PU). The aim of this study is the comparative characterization of the quasi-static and cyclic deformation behavior of GFR-PU and GFR-EP with similar layer setup. The mechanical properties have been investigated in instrumented tensile, interlaminar shear strength and compression after impact tests. In addition, the tests were combined with varying temperatures (−30 °C, RT, +70 °C) with respect to aerospace applications to determine the material property development under low and elevated temperatures. In cyclic investigations, the fatigue properties have been estimated by resource-efficient multiple step tests and validated in constant amplitude tests. Hysteresis and temperature measurements were applied in order to investigate the damage processes. It could be shown that polyurethane exhibits improved damage tolerance by significantly reducing delamination area under impact loading, whereas epoxy leads to optimized properties under elevated temperature. Furthermore, epoxy generally underlines higher capabilities under cyclic loading, which is due to void content of polyurethane.

Influence of the production process on the deformation and fatigue performance of friction drilled internal threads in the aluminum alloy 6060*

Aluminum alloys are used for enhancement of dynamic range, resource optimization and emission reduction in many fields of traffic engineering, whereby aluminum components are manufactured by means of welded, adhesive and screw joints. Friction drilling, as forming process with subsequent manufacturing of threads, offers the opportunity to produce an internal thread in lightweight profiles with a usable thread depth larger than the profile thickness, making use of local material expansion. Moreover, the direct manufacturing offers a huge potential for time and cost saving in comparison to conventional thread machining. Microstructural characterization of mechanical properties of EN AW-6060 internal threads, both in profile and bulk material specimens, was carried out using tensile tests and fatigue tests in the tensile loading range. A comparison was made between the manufacturing techniques tapping, thread forming and thread milling. The maximum tolerable loads of the profile specimens are about 50 % lower in the quasi-static range and about 25 % lower in the cyclic range in comparison to bulk material specimens. Formed threads show the best and cut threads the worst mechanical properties which were correlated with the production-related profile qualities and changes in microstructure. Multiple step tests prove that the fatigue limit of aluminum internal threads, validated in single step tests until 107 cycles, can be reliably estimated by means of plastic strain.

Mechanical response of HEMA gel under cyclic deformation: Viscoplasticity and swelling-induced recovery

Observations are reported on poly(2-hydroxyethyl methacrylate) (HEMA) gels with various degrees of swelling in uniaxial tensile tests, relaxation tests, cyclic tests with a strain-controlled program, and multiple-step tests where cyclic deformation is alternated with periods of re-swelling. Constitutive equations are derived for solvent transport and the viscoplastic response of a hydrogel under an arbitrary deformation with finite strains. Adjustable parameters in the stress-strain relations are found by fitting the experimental data. Special attention is focused on the self-recovery phenomenon: a decay in plastic deformation under swelling of a preloaded sample.

Analysis of the Effective and Internal Cyclic Stress Components in the Inconel Superalloy Fatigued at Elevated Temperature

Cyclic multiple step test in strain control have been performed on cylindrical specimens of cast polycrystalline Inconel 738LC and 792-5A superalloys at 800 °C in laboratory atmosphere. Hysteresis loops were analyzed according to the statistical theory of hysteresis loop. The effective and internal stress components were evaluated. The effective stress of γ´ precipitate has significant influence on the stress-strain response both materials. The stress amplitude in IN 792-5A is higher than in IN 738LC at approximately same total strain amplitude due to significantly higher effective stress of γ´ phase. Cyclic hardening/softening curves and cyclic stress-strain curves using short-cut procedure were obtained. Cyclic hardening/softening behavior depends both on temperature and strain amplitude. Low amplitude straining is characterized by the saturation of the stress amplitude. In high amplitude straining slight softening was found. The cyclic stress-strain curves for both materials can be fitted by power law. Cyclic stress-strain response in terms of internal and effective stress components is discussed in relation to microstructural parameters of the materials. The observation of surface relief revealed the presence of persistent slip markings.

Effect of Temperature on the Cyclic Stress Components of Gamma - TiAl Based Alloy with Niobium Alloying

Cyclic strain controlled multiple step tests have been performed on cylindrical specimens of cast -TiAl based alloy with 2 at.% of Nb with nearly lamellar microstructure at 23 and 750 °C in laboratory atmosphere with the aim to study the effect of temperature on the internal and effective cyclic stress components. At these temperatures, the evolution of the effective and internal stress components and the effective elastic moduli were derived from the hysteresis loops analyzed according to the statistical theory of hysteresis loop. Cyclic hardening/softening curves and cyclic stress-strain curves were obtained at both temperatures. Cyclic stress–strain curves measured using short-cut procedure coincide with the basic cyclic stress-strain curve. They are shifted to lower stresses with increasing temperature. Cyclic stress-strain response at both temperatures was compared and discussed in relation to changes of internal and effective stress components and dislocation modes referred in literature concerning this class of the material.

Comparative evaluation of AMPLICOR HPV PCR and Linear Array assays on SurePath liquid-based Pap samples for the detection of high-risk HPV genotypes

Background Persistent cervical infection with high-risk [HR] HPV is a causative factor for cancer. Liquid-based [L-Pap] Pap samples are convenient for HPV testing and SurePath samples have been least studied. Most HPV tests have multiple step protocols and testing laboratories experience large volumes of samples. Objectives Using SurePath L-Pap residual samples the objectives were as follows: [1] to test the performance of AMP-HPV and LA-HPV. [2] To perform an agreement study between two laboratories for the AMP-HPV test and [3] to compare agreement of results between AMP-HPV and LA-HPV and HC2. Study design Samples from 657 women were tested for Pap cytology then assayed for HR-HPV using AMP-HPV and LA-HPV tests. AMP-HPV performance was compared between 2 laboratories and agreement studies were conducted between AMP-HPV, LA-HPV and HC2. Results HR-HPV genotypes were associated with L-Pap readings as follows: HSIL 92% [23/25], LSIL 73.6% [162/220], ASCUS 70.4% [131/186], normal 31.9% [72/226]. More women less than 30 were infected with HR-HPV and multiple genotypes regardless of the L-Pap reading. AMP-HPV and LA-HPV testing had an overall raw agreement with each other of 84.2% [Kappa 0.66] and each had agreement of 94% with HC2 testing of 133 samples [Kappa 0.86/0.87]. AMP-HPV agreement between two laboratories was better at 93% [Kappa 0.84] compared to 76.1% [Kappa 0.40] when extraction was standardized. Conclusion It is feasible to perform AMP-HPV and LA-HPV on SurePath samples to detect HR-HPV genotypes. HC2, AMP-HPV and LA-HPV showed strong agreement. The extraction component of the AMP-HPV assay needs careful attention to yield consistent results.

Cyclic Stress in 316L Austenitic Stainless Steel at Low Temperatures

Austenitic stainless steel was cycled at a series of temperatures in the interval from 296 K to 113 K. Constant plastic strain amplitude loading at different levels of plastic strain amplitude and testing similar to multiple step test method were applied at different temperatures. The stress amplitude was continually recorded and selected hysteresis loops were stored and later analyzed using statistical theory of the hysteresis loop. Effective stress component and probability density function as a function of temperature were evaluated. The results were discussed in terms of the temperature dependence of the cyclic yield stress and its sources.

Effect of two work practice changes on the microbial contamination rates of pharmacy-compounded sterile preparations

Using a multiple-step testing medium-risk-level compounding test procedure, the evaluation of two work-practice changes to determine if the changes could effectively reduce the potential for contamination occurrence was conducted. Along with training and evaluation of aseptic sterile compounding techniques, each individual pharmacist and pharmacy technician at M. D. Anderson Cancer Center must successfully demonstrate aseptic preparation competency annually by performing the complicated multistep aseptic transfers of growth medium with no resulting growth of microorganisms. The multistep aseptic transfers are designed to simulate manual compounding of the most complicated medium-risk-level preparations anticipated as specified in the United States Pharmacopeia's chapter 797. An evaluation of two modest and simple work-practice changes was conducted: The use of bare hands and nonsterile gloves with only initial disinfection with 70% isopropyl alcohol (IPA) during years 1 and 2 (group A) was compared with the use of nonsterile chemotherapy gloves with initial and repeated disinfection with IPA for year 3 (group B) and the use of sterile gloves with initial and repeated disinfection with IPA for year 4 (group C). The process involved multiple discrete manipulations, including reconstitution of dry-growth medium; transfers of growth medium from vials and ampules using syringes, needles, a dispensing pin, and a filter straw; and transfers to an empty plastic i.v. bag. For groups B and C, significant reductions in contaminated samples were found compared with group A. The use of protective chemotherapy gloves that were repeatedly disinfected with IPA decreased the contamination rate of pharmacy-compounded sterile preparations.

A Slip-Based Model for Strength Evolution During Cyclic Loading

Motivated by the strong dependence of strain-hardening processes on slip system activity, a slip system hardening formulation that explicitly employs accumulated slip system shear strains and net crystal shearing rates is introduced within a polycrystal plasticity modeling formulation for predicting material response during cyclic deformation. The model, which is a slight modification of the Voce hardening model commonly employed for large strain forming simulations, was employed to model the behavior of 304L stainless steel subjected to uniaxial and multiaxial nonproportional multiple-step experiments and multiaxial multiple-phase angle experiments. The model successfully captured the pseudosaturation response that is common during the multiple-step tests and captured many of the loop-shape and stress-level features of the multiple-phase angle experiments.

Influence of prestraining on cyclic deformation behaviour and microstructure of a single-phase Ni-base superalloy

The influence of a monotonic predeformation at room temperature on the cyclic deformation behaviour of single-phase Ni-base superalloy Nimonic 75 was studied at various plastic strain amplitudes and temperatures from room temperature to 800°C. For all test parameters, Nimonic 75 shows a pronounced cyclic saturation behaviour. At intermediate temperatures, dynamic strain ageing effects occur. The planar slip character observed was found to prevail under all test conditions applied and leads to a cyclic stress–strain curve, which is rather independent of the testing mode used (single step test, multiple step test, incremental step test). Predeformation leads to a characteristic change in the dislocation arrangement and affects cyclic stress–strain response. In general, the influence of a predeformation on the macroscopic mechanical behaviour and the microstructure of Nimonic 75 decreases with increasing temperature and increasing loading amplitude.

Cyclic stress–strain behaviour of circumferentially notched cylindrical bars at high temperature

Cyclic stress–strain tests were undertaken at temperatures between 550°C and 820°C on plain and doubly-notched specimens of three alloy steels: 20Cr/25Ni/Nb, 316 and 1CrMoV respectively. Integrated axial ‘strains’ were measured between the minimum sections of the (semi-circular) notches using a longitudinal extensometer, while surface hoop strains were measured on one notch by means of a diametral extensometer. Cyclic hardening occurred in plain specimens of 316 steel, cyclic softening occurred in the 1CrMoV steel and the 20Cr/25Ni/Nb alloy showed stable behaviour. These effects were also demonstrated in notched specimens, although to a lesser degree. From hysteresis loops determined during multiple step tests, the cyclic deformation response of the notched regions was expressed in terms of an ‘equivalent gauge length’. Comparison was also made between the equivalent (von Mises) stress–strain curves deduced at a representative (skeletal) point in the minimum section with stress–strain data obtained from uniaxial (plain) specimens. The equivalent curves calculated from standard relations were found to be lower than the uniaxial curves and possible reasons for this are suggested.

Plasma cortisol concentration in Thorougbred horses during and after standardized exercise tests on a treadmill and effect of conditioning on basal cortisol values

The behaviour of cortisol concentration in plasma of clinically normal horses performing two different exercise tests on a treadmill was investigated to study the possible value of measuring cortisol for performance diagnosis. In addition, the horses were exercised with different conditioning programmes and their effect on basal plasma cortisol concentration was measured. Finally, the repeatability of the cortisol values measured before and after exercise were examined. Horses were always exercised on a treadmill. The multiple step exercise test consisted of five gallop workouts lasting five minutes each. The velocity in the first step was 6.0 m/s. Each consecutive step velocity was increased by 0.5 m/s. The two-speed exercise test consisted of two runs. In the first run horses were galloped over 1,200 m at a constant velocity of 10, 10.5 or 11 m/s. Thereafter horses were walked for 30 minutes. The second run over 1,200 m was conducted at speeds of 13, 13.5 or 14 m/s. Each conditioning programme examined consisted of eleven repetitions of exercise of 5, 15 or 25 minutes duration at a velocity at which, mathematically, horses had a blood lactate concentration of 2.5 or 4 mmol/l. During the multiple step test the mean cortisol concentration in plasma showed a tendency to increase (p = 0.07). The mean peak of the cortisol concentration in plasma was measured 10 minutes after the test. Thereafter mean cortisol concentration continuously decreased and the day after the test values were similar to those before the test. After the first run of the two-speed test mean plasma cortisol concentration tended to increase (p = 0.08), while significant changes were registered after the second run (p < 0.01): It decreased up to the fifth minute after exercise (p < 0.05) and increased threreafter reaching a plateau between the 15th and 45th minute after exercise (p < 0.05). The morning after the test mean plasma cortisol concentration had returned to the values measured the morning before the test. None of the conditioning programmes had an effect on the mean plasma concentration of cortisol in the horses at rest. The mean coefficient of variation of plasma cortisol concentration in five horses before exercise was 34.1% and 36.4% after exercise. The large individual variability of plasma cortisol concentrations before and after exercise does not allow a good repeatability of results, and enforces the need for multiple blood sampling during exercise. The multiple step exercise test as well as the two-speed exercise test induced increases of the plasma cortisol concentration after exercise. The changes measured supply a basis for studies on treadmills on the value of monitoring the plasma cortisol concentration of sport horses for performance diagnosis.

Cyclic deformation behavior of non-isoaxial copper tricrystals and bicrystals

The cyclic hardening and saturation behaviors of copper tricrystals and bicrystals were investigated in strain-controlled multiple step tests. The results show that, for the inclined grain boundary (GB) bicrystal with single slip components, the cyclic stress strain (CSS) curve exhibits a plateau or quasi-plateau region, while the CSS curve of tricrystals shows no plateau. Observations of surface morphologies indicated that owing to the strain incompatibility of three grains, at lower strain amplitude the triple junction (TJ) retards obviously the primary slip in grains and makes deformation near it smaller than that near the bicrystal GB, while at higher strain amplitude slip can be distributed near the TJ homogeneously. The probability of crack initiation at the same TJ is closely related to the loading direction. The saturation dislocation structures of tricrystal specimens under the strain amplitude of the last step were explored by the electron channeling contrast technique in SEM (ECC-SEM). Loop patches with persistent slip band (PSB) ladders embedded were found even in the TJ vicinity for all grains. Dislocation-free zones (DFZ) occurred in the vicinity of TJ and GB, and the difference in shapes between them is due to the difference in internal stress field. Misoriented cell structure and dislocation wall structure were found near the crack tip, and the formation of them is associated with the cooperative action of crack tip, GB, grain orientation and the applied strain amplitude.

Observations of Low Cycle Fatigue of Al Thin Films for Mems Applications

AbstractThis paper addresses tension-tension (R=0) low cycle fatigue behavior of thin film Al structures released from a substrate. Al beam specimens 2 µm thick, 50 µm wide and 500 µm long (gauge length) were micromachined over a window in a Si substrate. Cyclic load-displacement behavior was investigated using a multiple step test method, in which each specimen was cycled with several blocks of constant maximum displacement amplitude. Load, displacement and temperature were recorded continuously. A load drop and a corresponding stabilized state were observed for each displacement block. Monotonic tension tests to failure were also performed for comparison. Evidence of cyclic creep was observed. SEM images revealed fatigue markings on cyclically loaded specimens but not on monotonically loaded beams.