Single-step Tests Research Articles

Lignocellulosic Biomass Conversion by Sequential Combination of Organic Acid and Base Treatments

The present work aims at exploring a new hydrolysis approach using sequential combinations of organic acid [oxalic acid (OA)] and base [tetramethylammonium hydroxide (TMAH)] to convert lignocellulosic biomass at mild conditions (150−215 °C, 1−2 h, and 1 atm N2) using a spruce wood sample in a batch reactor. In the single-step tests, hydrolysis with OA can convert biomass to yield sugars and furanic compounds. Hydrolysis with TMAH mainly depolymerizes lignin to produce phenolic compounds but also converts some polysaccharides in biomass possibly by the peeling reaction and/or alkaline hydrolysis. A sequential combination of OA and TMAH can significantly increase the conversion of the biomass compared to single- or two-step reactions with either the acid or the base. The analysis of liquid products by chemical derivatization followed by gas chromatography equipped with a flame ionization detector (GC−FID) and the characterization of the solid residues by pyrolysis−gas chromatography−mass spectrometry (Py−GC...

Cyclic deformation behavior of a medium carbon steel in the VHCF regime

At the Institute of Materials Science and Engineering an ultrasonic testing facility (UTF) for the fatigue assessment in the very high cycle fatigue (VHCF) regime was developed. The UTF allows to control the test and to measure process parameters like generator power and specimen temperature. In load increase tests (LIT), the critical stress amplitude leading to a first rise of the measured physical values is determined and can be used to identify suitable amplitudes for single step tests in the VHCF regime. The individual design of the UTF allows a defined interruption of the fatigue experiment for detailed microscopic investigations.

A signal amplification assay for HSV type 1 viral DNA detection using nanoparticles and direct acoustic profiling

BackgroundNucleic acid based recognition of viral sequences can be used together with label-free biosensors to provide rapid, accurate confirmation of viral infection. To enhance detection sensitivity, gold nanoparticles can be employed with mass-sensitive acoustic biosensors (such as a quartz crystal microbalance) by either hybridising nanoparticle-oligonucleotide conjugates to complimentary surface-immobilised ssDNA probes on the sensor, or by using biotin-tagged target oligonucleotides bound to avidin-modified nanoparticles on the sensor. We have evaluated and refined these signal amplification assays for the detection from specific DNA sequences of Herpes Simplex Virus (HSV) type 1 and defined detection limits with a 16.5 MHz fundamental frequency thickness shear mode acoustic biosensor.ResultsIn the study the performance of semi-homogeneous and homogeneous assay formats (suited to rapid, single step tests) were evaluated utilising different diameter gold nanoparticles at varying DNA concentrations. Mathematical models were built to understand the effects of mass transport in the flow cell, the binding kinetics of targets to nanoparticles in solution, the packing geometries of targets on the nanoparticle, the packing of nanoparticles on the sensor surface and the effect of surface shear stiffness on the response of the acoustic sensor. This lead to the selection of optimised 15 nm nanoparticles that could be used with a 6 minute total assay time to achieve a limit of detection sensitivity of 5.2 × 10-12 M. Larger diameter nanoparticles gave poorer limits of detection than smaller particles. The limit of detection was three orders of magnitude lower than that observed using a hybridisation assay without nanoparticle signal amplification.ConclusionsAn analytical model was developed to determine optimal nanoparticle diameter, concentration and probe density, which allowed efficient and rapid optimisation of assay parameters. Numerical analysis and subsequent associated experimental data suggests that the response of the mass sensitive biosensor system used in conjunction with captured particles was affected by i) the coupled mass of the particle, ii) the proximal contact area between the particle and the sensor surface and iii) the available capture area on the particle and binding dynamics to this capture area. The latter two effects had more impact on the detection limit of the system than any potential enhancement due to added mass from a larger nanoparticle.

Capability of 11 Antipneumococcal Antibiotics To Select for Resistance by Multistep and Single-Step Methodologies

Testing of 12 pneumococcal strains with differing resistotypes [including tet(M) positive] showed that tigecycline, amoxicillin-clavulanate, imipenem, and ceftriaxone did not select for resistant clones after 50 sequential subcultures. By comparison, azithromycin, clarithromycin, clindamycin, telithromycin, levofloxacin, moxifloxacin, and gemifloxacin did show resistant clones. Tigecycline also yielded a low frequency of resistance in single-step tests compared to all beta-lactams, macrolides/ketolides, and quinolones tested.

Fatigue Life Calculation of Metallic Materials

In stress-controlled load increase and single step tests besides the plastic strain amplitude the changes of the temperature and the electrical resistance caused by cyclic plastic deformation were measured. Temperature and resistance measurements don’t require a defined gage length and can be applied also on components even under service loading to ensure economic and safe operation conditions. On the basis of Morrow and Basquin equations a physically based fatigue life calculation “PHYBAL” was developed. This new short-time procedure allows a rapid and precise calculation of Woehler curves with data of one load increase and two single step tests.

Nonlinear viscoelastic properties of branched polyethylene in reversing flows

Two-step reversing flows are severe tests of constitutive equations for polymer melts and have attracted interest for testing the response of branched polymers. Here we report on single-step and three types (types B, C, and D) of reversing torsional flows on branched and linear polyethylenes (PEs). The responses were analyzed using Kaye–Bernstein–Kearsley–Zapas (K-BKZ) theory. Comparisons between data and theory in type B and C flows for the two branched PEs (LD 103 and LD 146) and a linear HDPE are presented. For the LD 146 material and to strains higher than previously examined, the results agree with prior studies, i.e., the K-BKZ theory provides a good description of the response of branched polymers in reversing flows while the opposite is the case for the linear polymers. Surprisingly, it is found that the other branched polymer (LD 103) behaves more like a linear polymer and not a branched polymer in that it does not follow the K-BKZ theory. In the type D flow, one which was not previously investigated, the K-BKZ theory describes the normal force (NF) responses for branched LD 146 but not for the linear PE. Also, isochronal derivatives of the strain potential function (W1 and W2) were calculated from torque (T) and NF responses in single-step tests. The damping function fits to a modified sigmoidal formula and is close to the BKZ limit as reported by Wagner (2004a) for branched polystyrenes. The normal stress difference ratio and damping function were extracted from W1 and W2. Finally, the Cox–Merz rule was examined for one of the branched PEs.

Cyclic deformation behaviour and lifetime calculation of Al‐3Mg‐Mn

AbstractPlastic strain amplitude, temperature and electrical resistance measurements were performed on the aluminium‐magnesium alloy Al‐3Mg‐Mn (AA5454) in recrystallised condition to describe and evaluate the cyclic deformation behaviour in detail. The endurance limit was estimated in load increase tests (LIT). In stress‐controlled single step tests at ambient temperature the cyclic deformation behaviour is characterised by pronounced cyclic hardening, which leads to a saturation state with a plastic strain amplitude of nearly zero. Due to far‐reaching cross effects of the applied measuring techniques, the plastic strain amplitude, the change of the specimen temperature due to cyclic plastic loading and the change of the electrical resistance show a strong interrelation with the underlying fatigue processes. A new lifetime calculation method “PHYBAL” on the basis of the plastic strain amplitude, the change of the temperature and the change of the electrical resistance yields an excellent accordance with experimentally determined lifetimes. Microstructural details were investigated by light and scanning electron microscopy.

Cyclic deformation behaviour and lifetime calculation of the magnesium die-cast alloys AZ91D, MRI 153M and MRI 230D

Abstract The magnesium alloys AZ91D, MRI 153M and MRI 230D were investigated in the form of die-cast specimens with a cast-skin. The fine-grained microstructure consists of a dendritic magnesium solid solution and interdentritic precipitates. The cyclic deformation behaviour was characterised in stress-controlled load increase and single step tests by means of mechanical stress – strain hysteresis and temperature measurements. Load increase tests allow a reliable short-time estimation of the endurance limit. With the physically based lifetime calculation method “PHYBAL”, the lifetime of the magnesium alloys can be precisely calculated on the basis of the plastic strain amplitude and the change of the specimen temperature due to cyclic plastic deformation with three experiments. Lifetimes calculated according to “PHYBAL” agree excellently with experimentally determined data.

PHYBAL—A new method for lifetime prediction based on strain, temperature and electrical measurements

Stress-controlled fatigue tests with constant and variable amplitudes were performed with quenched and tempered specimens of the steel SAE 4140 (42CrMoS4) and specimens of the railway wheel steel R7 (SAE 1050) specified in standard 812-3V of the International Railway Union UIC on servohydraulic testing systems. In addition to mechanical stress–strain hysteresis measurements, the changes of temperature and electrical resistance were regarded. All measured values depend on microstructural changes due to plastic deformation processes, and therefore, show a clear interaction with the actual fatigue state. Consequently, a physically based lifetime prediction (PHYBAL) according to Morrow and Manson/Coffin can be derived. A new testing procedure was applied allowing hysteresis measurements for the characterization and description of the fatigue behavior under random and even service loading. The basic idea is to combine any kind of load spectrum with constant load sequences using an amplitude below the endurance limit. This offers the possibility to apply lifetime prediction methods on the basis of cyclic deformation data for random or service loading equivalent to single step tests. Scanning and transmission electron microscopy allow to interpret the measured physical data on the basis of microstructural details.

Multiple Comparisons with the Best Control in a One-Way Layout

In many settings, one wishes to show that one or more experimental treatments are better than the best of more than one control or standard treatments in a one-way layout. One-sided, normal theory and distribution-free, single-step and step-down simultaneous testing procedures are developed in this article. These tests are intersection-union tests and hence use existing critical points. The single-step tests are inverted to form simultaneous lower confidence bounds on the amount of improvement that each experimental treatment offers relative to the best control or standard treatment. The single-step, normal theory procedures can be improved if one assumes that the control expectations do not differ by more than a predetermined number of standard deviations.

Characterization of the cyclic deformation behaviour and fatigue crack initiation on titanium in physiological media by electrochemical techniques

Abstract In the present work, the cyclic deformation behaviour as well as fatigue crack initiation processes of commercially pure (cp) titanium grade 2 were characterized in axial single step and stepwise load increase tests by mechanical hystereses, corrosion potential and current measurements. Scanning electron microscopic investigations were used to correlate fatigue induced surface damages with the results of electrochemical investigations. Potential measurements proved to be very sensitive to indicate surface damages in situ at the very beginning. The corrosion potential is strongly related to the development of the plastic strain amplitude. Thus, cyclic softening and hardening processes are represented by a characteristic decrease and increase of the potential curve. Current measurements are less sensitive, but allow a detailed characterization of crack propagation processes.

Deformation behaviour and damage accumulation of cortical bone specimens from the equine tibia under cyclic loading

Despite its clinical importance, the fatigue behaviour of cortical bone has not been examined as widely as its static behaviour. In the present study, specimens from the tibiae of horses have been subjected to load-controlled single step tests. The cyclic deformation behaviour was described by the development of stress–strain hysteresis parameters over the lifetime. The fatigue behaviour of bone is characterised by cyclic softening which is most distinctive towards the end of the lifetime. The microstructural damage accumulated during cyclic loading results in a loss of stiffness, asymmetrical deformation of the bone in tension and compression in cyclic creep. As shown by light and scanning electron microscopy, microcrack formation and growth is the main damage mechanism. The crack growth behaviour is strongly influenced by the microstructure, the stress components and the absolute value of the local stresses. Lower local stresses and/or compressive mean stresses lead to a dominant influence of the shear stress components with shear failure at inner interfaces. With increasing crack length, that is, higher local stress amplitudes, or tensile mean stresses, the microstructure is more and more ignored and failure occurs primarily under the influence of the normal stress components. This can be clearly seen on the fracture and specimen surfaces.

Evaluation of the HCF-behavior of 42CrMoS4 by means of strain, temperature and electrical measurements

Single step tests were performed on quenched and tempered specimens of the steel 42CrMoS4. Strain, temperature and electrical resistance measurements yielded an empirical evaluation of fatigue life according to Coffin [L.F. Coffin, A Study of Cyclic Thermal Stress in a Ductile Metal, Trans. ASME, 76 (1954) 931], Manson [S.S. Manson, Behavior of Materials under Conditions of Thermal Stress, NACA TN-2933, 1953] and Morrow [J. Morrow, Cyclic plastic strain energy and fatigue of metals. In: Internal Friction, Damping and Cyclic Plasticity, ASTM STP 378, 45/87, American Society of Testing and Materials, Philadelphia, PA, 1964]. All the measured values are based on physical processes and therefore show a strong interrelation. A new testing procedure was developed permitting hysteresis measurements to be used for the characterization and description of fatigue behavior under variable amplitude loading. The basic idea is to combine fatigue tests with any kind of load spectrum with single step tests. This offers the possibility to apply lifetime prediction methods normally used for single step tests to those with random or service loading.

Cyclic stress–strain response of the ODS nickel-base, superalloy PM 1000 under variable amplitude loading at high temperatures

The cyclic stress–strain behaviour of the recently developed oxide dispersion-strengthened nickel-base alloy PM 1000 was studied under constant and variable amplitude loading conditions. Single-step tests with a constant total strain amplitude as well as incremental step tests covering the same amplitude range have been carried out at 1123 and 1273 K. The interaction of the dislocations with the fine, homogeneously distributed oxide dispersoids was found to suppress the formation of dislocation cell structures. Rather, networks with dislocations frequently pinned at the particle/matrix interface have been observed by transmission electron microscopy. However, wavy dislocation slip still contributes to the stress–strain response. Despite the similarity of the resulting microstructures, the cyclic stress–strain curve obtained from constant amplitude tests deviates slightly from the one observed in incremental step tests. While non-Masing behaviour was found for constant amplitude testing, the strong influence of the dispersoids on dislocation mobility in combination with the constancy of dislocation arrangement yields Masing behaviour for the incremental step tests.

CYCLIC STRESS‐STRAIN, STRESS‐TEMPERATURE AND STRESS‐ELECTRICAL RESISTANCE RESPONSE OF NiCuMo ALLOYED SINTERED STEEL

Abstract—The influence of sintering temperature on the fatigue behaviour of a NiCuMo alloy was determined. It is common practice to characterize the cyclic deformation behaviour by means of plastic strain amplitudes. For sintered materials the quantity of the plastic strain amplitudes is influenced by microstructural changes as well as crack opening and crack growth effects and does not allow any distinction between these mechanisms. In the present work cyclic stress‐strain, cyclic stress‐temperature and cyclic stress‐electrical resistance measurements were studied simultaneously to get a more comprehensive description of the fatigue behaviour of sintered steels. The temperature is essentially sensitive to the work of plastic deformation during cyclic loading. The electrical resistance responds to microstructural changes, e.g. dislocation rearrangements and void formation as well as to crack initiation and propagation. Beyond that it is shown that continuous stress‐increase tests are a suitable short term testing method to determine cyclic stress‐strain curves which are in a very good agreement with those from single step tests.

Effect of initial ramp loading on fatigue behavior in polycrystalline copper

Understanding the development of fatigue damage in step tests is often complicated by the occurrence of different crack initiation and propagation mechanisms associated with different stress and strain levels. In an attempt to simplify this, ramp loading was used on polycrystalline copper to initiate fatigue tests which were subsequently conducted in stress or strain control; ramp loading encourages strain localization, persistent slip band behavior and transgranular cracking. Results are reported on life behavior, cracking modes and dislocation structures for both single-step and two-step tests, with and without ramp loading. Although ramp loading has a significant benign effect on life (in a limited stress range) in single-step tests, its effect is insignificant in two-step tests for both low-high and high-low sequences. Prolongation of life in low-high step tests is explained by a gradual reduction in strain localization with prolonged cycling, lower extremes of strain localization at lower amplitude and increased slip reversibility with increasing number of cycles.