Effect Of Dwell Time Research Articles

Effect of dwell time on fatigue properties of wire-arc additively manufactured IN718 alloy

In this research, the effect of inter-layer dwell time and fabrication path strategy on fatigue properties of wire-arc additively manufactured (WAAM) IN718 alloy was studied. Three different dwell times i.e. 10 s, 50 s, and 90 s, and two path strategies i.e. uni-directional and bi-directional, were chosen. The results showed that the bi-directional fabrication strategy resulted in improved mechanical properties than the uni-directional one. Also, the quality of fabricated part i.e. the surface irregularities (roughness), geometrical accuracy, and porosities, was improved with an increase in the dwell times. The mechanical properties were improved as the dwell time increased from 10 s to 90 s: tensile strength by ∼ 18%, yield strength by ∼ 33 %, ductility by ∼ 20 %, and Hardness by ∼ 10%. The fatigue lives were high at higher dwell times and less scattered, owing to the smaller number of porosities. Fractographic investigation revealed either defect-free or defect-induced failures. The observed effect of dwell times and fabrication path strategy was accredited to the reduced heat accumulation, porosities, and residual stresses in the fabricated component at higher dwell times. The results supported by the formulated and validated numerical framework, have been argued in this study.

Neural-fuzzy machine learning approach for the fatigue-creep reliability modeling of SAC305 solder joints

The accuracy of reliability models is one of the most problematic issues that must be considered for the life of electronic assemblies, particularly those used for critical applications. The reliability of electronics is limited by the fatigue life of interconnected solder materials, which is influenced by many factors. This paper provides a method to build a robust machine-learning reliability model to predict the life of solder joints in common applications. The impacts of combined fatigue and creep stresses on solder joints are also investigated in this paper. The common alloy used in solder joint fabrication is SAC305 (Sn–Ag–Cu). The test vehicle includes individual solder joints of SAC305 alloy assembled on a printed circuit board. The effects of testing temperature, stress amplitude, and creep dwell time on the life of solder joints were considered. A two-parameter Weibull distribution was utilized to analyze the fatigue life. Inelastic work and plastic strain were extracted from the stress–strain curves. Then, Artificial Neural Networks (ANNs) were used to build a machine learning model to predict characteristic life obtained from the Weibull analysis. The inelastic work and plastic stains were also considered in the ANN model. Fuzzy logic was used to combine the process parameters and fatigue properties and to construct the final life prediction model. Then a relationship equation between the comprehensive output measure obtained from the fuzzy system and the life was determined using a nonlinear optimizer. The results indicated that increasing the stress level, testing temperature, and creep dwell time decreases reliability. The case of long creep dwell time at elevated temperatures is worst in terms of impact on reliability. Finally, a single robust reliability model was computed as a function of the fatigue properties and process parameters. A significant enhancement of the prediction model was achieved compared to the stress–life equations.

Effect of interlayer dwell time on output quality in wire arc additive manufacturing of low carbon low alloy steel components

Effect of interlayer dwell time on output quality in wire arc additive manufacturing of low carbon low alloy steel components

Friction Stir-Spot Welding of AA5052-H32 Alloy Sheets: Effects of Dwell Time on Mechanical Properties and Microstructural Evolution

Friction stir-spot welding (FSSW) as a solid-state joining process for local welding offers a number of benefits for applications in the automotive, aerospace, and marine industries. In these industries, and from an economic point of view, producing spot welds at a low rotating speed and in a short time is critical for saving energy and enhancing productivity. This investigation helped fill a knowledge gap in the literature about FSSW of 4 mm similar lap joints of AA5052-H32 sheet materials, in which welding takes place over a short time period with a slow tool rotation speed. Consequently, the purpose of this work was to investigate the feasibility of FSSW 2 mm thick AA5052-H32 aluminum alloy sheets to produce 4 mm thick similar spot lap joints at various low dwell times of 1, 2, and 3 s and a constant relatively low tool rotation speed of 500 rpm. The introduced heat input for the friction stir-spot welded (FSSWed) lap joints was calculated based on the applied processing parameters. Joint appearance, cross-section macrostructures, and microstructure features of all the spot welds were evaluated. The mechanical properties (hardness contour maps and maximum tensile shear loads) were also examined. The results show that joining 2 mm sheet thickness AA5052-H32 at a low heat input in defect-free similar lap joints could be successfully achieved. The stir zone (SZ) region became wider as the dwell time increased from 1 to 3 s. The hardness value of the SZ was higher than that attained by the AA5052-H32 base material (BM) for all applied dwell times. Especially at 2 s, the hardness of the SZ was approximately 48% higher than that of the BM. This increase in hardness may be attributed to the high grain refinement of the new dynamically recrystallized grain (4 µm) in the SZ compared to the cold-rolled BM grain size (40 µm). Among the tried FSSW process variables, the dwell time of 2 s at a rotation rate of 500 rpm also produced the maximum tensile shear load of 4330 N. Finally, the locations and features of the fracture surfaces of the FSSWed joints were examined using a scanning electron microscope (SEM) and the obtained results were discussed.

Cross-laminated strand veneer lumber mass timber panels from thermally modified strands

Thin-strand composite panels and subsequent mass timber beams were produced using thermally modified wood strands in a pressurized system. The effects of thermal modification (TM) temperature and dwell time on the mechanical, moisture, and decay performance of panels were studied. TM reduced moisture sorption and increased decay resistance. The thin-strand composites were evaluated in flexure and benchmarked against commercially available structural products. Moreover, the mass timber beams’ out-of-plane bending was accurately predicted with traditionally used laminated beam theory. The study shows that TM, under controlled conditions, enables the production of high-performing wood-strand panels with improved dimensional stability and decay resistance.

Early Elective Replacement of Umbilical Venous Catheter with Peripherally Inserted Central Catheter to Reduce Central Line-Associated Blood Stream Infections in Premature Infants: A Randomized Trial

Background: Central-line umbilical venous catheter (UVC) insertion at birth and replacement later with a peripherally inserted central catheter (PICC) is often required in VLBW infants for medical and nutritional support. A serious complication of central line is associated with bloodstream infections (CLABSIs). There is no consistent evidence about the effect of dwell time of UVC or the time of PICC replacement on the risk of CLABSI in VLBW infants. Objective: To compare the CLABSI rate in VLBW infants when replacing the UVC with the PICC at 72 hours of age versus at seven days. Materials and Methods: VLBW infants with UVC placed at admission and clinically stable for three days were randomly assigned to receive early replacement with PICC at 72 hours of age as the 72-hour group, or at seven days as the 7-day group. The primary outcome was the CLABSI rate. The secondary outcomes were the time from birth to CLABSI and any other complications. Results: Fifty infants in the 72-hour group and 51 infants in the 7-day group were enrolled. The overall incidence of CLABSI was 10% in the 72-hour group and 27.4% in the 7-day group (RR 2.74, p=0.03). There were 4.6 CLABSIs per 1,000 catheter-days in the 72-hour group and 13.4 CLABSIs per 1,000 catheter-days in the 7-day group (p=0.02). The other complications and mortality rates were not significantly different. Conclusion: The early removal of a UVC and replacement with a PICC by 72 hours of age significantly decreased the CLABSI rate compared to the routine replacement of the UVC at seven days of age. Keywords: Very low birth weight; Umbilical venous catheters; Peripherally inserted central catheter; Central venous catheter; Central lineassociated bloodstream infection

Effects of grain size on the electrical properties in the Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics

Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramics are prepared by the conventional solid-state reaction route, and the effect of dwell time on the physical and electrical properties has been investigated. XRD patterns show that morphotropic phase boundaries exist in all BCZT ceramics. BCZT ceramics sintered at 1450 °C for 8 h exhibit the largest grain size (10.5 μm) and highest Curie temperature (T c∼93 °C). BCZT ceramics exhibit the similar relaxor properties to ideal relaxor ferroeletric. Meanwhile, the behavior of diffuse phase transition is weakened with the increase of grain sizes. The fitted activation energy reveals the dominant defects in BCZT ceramics are oxygen vacancies, and the concentration of oxygen vacancies in the region of grain boundaries is higher than that of grains.

Review of Creep-Thermomechanical Fatigue Behavior of Austenitic Stainless Steel

Research on the creep-thermomechanical fatigue (CTMF) behaviors of austenitic stainless steel for nuclear power plant pipelines is reviewed in the present paper. The stress response behavior, the main damage mechanisms, including thermomechanical fatigue, creep, oxidation, and dynamic strain aging (DSA), as well as the effects of strain dwell type, dwell time, and temperature-strain phase angle on fatigue life behavior of austenitic stainless steel under CTMF loading conditions are systematically discussed, and the coupled effects of various damage mechanisms are revealed. It is emphasized that CTMF is closer to the actual service condition of nuclear power plant pipes. It is pointed out that the traditional method of life design based on the isothermal fatigue test data is not conservative. Finally, the research on CTMF behaviors of austenitic stainless steel for nuclear power plant is summarized and prospected.

The synthesis of high purity Ti3AlC2 MAX phase via molten salt method

Many methods have been used to synthesize the Ti3AlC2 MAX phase, but obtaining high-purity (>99.0 %) Ti3AlC2 is still a challenge. In this work, nano/submicro-sized Ti3AlC2 powder was prepared using Ti/Al/C elemental powders by the molten salt method in a vacuum quartz tube system. The effects of reaction temperature and dwell time, mechanical activation, the ratio of flux to reactants, and the ratio of Al on the synthesis of Ti3AlC2 were systematically investigated. The results show that Ti3AlC2 powder with a high purity of up to 99.0 % was prepared using ball milled 3Ti/1.1Al/2C mixture as the reaction material, and NaCl-KCl as the molten salt at 1150 °C for 2 h. The reaction mechanisms of Ti3AlC2 in molten salt have been discussed.

Cold plasma-activated hydrogen peroxide aerosols inactivate Salmonella Typhimurium and Listeria innocua on smooth surfaces and stem scars of tomatoes: Modeling effects of hydrogen peroxide concentration, treatment time and dwell time

This study was conducted to evaluate the effects of hydrogen peroxide (H 2 O 2 ) concentration, treatment time, and dwell time on the efficacy of cold plasma-activated hydrogen peroxide aerosols against bacteria on stem scar and smooth surfaces of tomatoes. Cherry tomatoes inoculated with cocktails of Salmonella Typhimurium and Listeria innocua on the smooth surface and stem scar area were treated for 10, 20 and 30 s followed by 15 and 30 min dwell times in a treatment chamber with cold plasma-activated aerosols generated from 0, 1, 2, 3, 4 and 6% and 7.8% H 2 O 2 . Results showed that the efficacy of the treatments was mostly influenced by the H 2 O 2 concentration and treatment time. The reductions of the two bacteria were modeled as sigmoidal or exponential functions of H 2 O 2 . The models indicated that at H 2 O 2 concentrations ≥4.2%, the treatments reduced populations of L. innocua to non-detectable levels (detection level: 0.70 log CFU/piece) achieving an average 5 log reduction on the smooth surface of tomatoes for all tested treatment times and dwell times. To achieve an average 5-log reduction of Salmonella populations on the smooth surface, H 2 O 2 at concentrations ≥5.7% H 2 O 2 was required. On the stem scar area of tomatoes, populations of Listeria and Salmonella were reduced by less than 2 logs. Our results demonstrated that the efficacy of cold plasma-activated hydrogen peroxide aerosol mainly depended on the concentration of H 2 O 2 , and type and location of inoculated bacteria. • Three main parameters for cold plasma-activated H 2 O 2 process were evaluated. • Non-linear regression models were developed for estimating the efficacy of H 2 O 2 . • Listeria was more sensitive to the activated H 2 O 2 aerosol than Salmonella on tomatoes. • At ≥5.7% H 2 O 2 , both bacteria on the surface of tomatoes were reduced by 5 logs. • Bacteria on stem scar area were more difficult to inactivate than those on surface.

Effect of laser dwell time on pore elimination in powder bed fusion of metal matrix composites: experimentally validated modeling

Many studies have been conducted to better understand the relationship between additive manufacturing (AM) process parameters and the resulting structure and properties of manufactured parts. It is quite clear that defects associated with AM parts are detrimental to part performance and are thus a major concern for a broader application of AM processed parts. In this study, we aim to investigate the influence of process parameters such as laser dwell time in mitigating pore formation during powder bed fusion of AISI 316L austenitic stainless steel (SS316L)-WC composites. Single-track experiments are conducted with varying printing parameters, while discrete element modeling (DEM) is employed for simulating powder-bed packing for composite system. Results show that the filling of the pores between ceramic particles by the molten SS316L is dependent on the laser dwell time, which in turn, depends on the volume fraction of ceramic reinforcement and initial pore sizes between inclusions. Our experiments, in agreement with model analysis, show that with the information of the materials property of the metal phase in a composite system such as viscosity, surface energy and initial pore sizes between ceramic inclusions, the printing parameters can be chosen to yield the appropriate dwell time for pore free composites.

ROI-Finder: machine learning to guide region-of-interest scanning for X-ray fluorescence microscopy.

The microscopy research at the Bionanoprobe (currently at beamline 9-ID and later 2-ID after APS-U) of Argonne National Laboratory focuses on applying synchrotron X-ray fluorescence (XRF) techniques to obtain trace elemental mappings of cryogenic biological samples to gain insights about their role in critical biological activities. The elemental mappings and the morphological aspects of the biological samples, in this instance, the bacterium Escherichia coli (E. Coli), also serve as label-free biological fingerprints to identify E. coli cells that have been treated differently. The key limitations of achieving good identification performance are the extraction of cells from raw XRF measurements via binary conversion, definition of features, noise floor and proportion of cells treated differently in the measurement. Automating cell extraction from raw XRF measurements across different types of chemical treatment and the implementation of machine-learning models to distinguish cells from the background and their differing treatments are described. Principal components are calculated from domain knowledge specific features and clustered to distinguish healthy and poisoned cells from the background without manual annotation. The cells are ranked via fuzzy clustering to recommend regions of interest for automated experimentation. The effects of dwell time and the amount of data required on the usability of the software are also discussed.

The effect of rotational speed and dwell time on Al/SiC/Cu composite made by friction stir spot welding

The effect of rotational speed and dwell time on Al/SiC/Cu composite made by friction stir spot welding

Effect of Tooling Temperature on the Transient Lubricant Behavior in Hot Metal Forming Processes

In hot metal forming processes, the temperature of the forming tool progressively increases under serial production conditions. Water-based two-phase lubricants may be applied to cool the forming tool and moderate temperature, in which the liquid agent would evaporate or decompose rapidly with dry matter deposited on the tooling surface during the dwelling time before the forming process commences. Herein, an interactive friction model for a two-phase lubricant is developed to predict the transient lubricant behaviors, i.e., predicting the effects of tool temperature and dwelling time on the friction coefficient evolution and lubricant breakdown. Friction tests between a warm pin and hot aluminum workpiece are conducted using the advanced friction testing system, TriboMate, to validate the modeling results.

Detection of inorganic elements in single boar spermatozoa by inductively coupled plasma mass spectrometry

Trace elements play an important role in the spermatogenesis, maturation, and fertilization of sperm. Accurate determination of elemental content of sperm cells, especially at the level of single sperm, is of great significance to evaluate the quality of boar semen, which affects the boar's reproductive health and eventually the pig breeding industry. Here we develop a simple method to determine trace elements in single boar's sperm cells by time resolved inductively coupled plasma mass spectrometry (ICP-MS). Effect of dwell time of ICP-MS on the signals of the sperms were investigated and optimized. Signal profiles of single sperm cells and elemental distributions of P, Mg, K, and Zn in normal sperm cells were obtained with dwell time at 0.1 ms. Experimental parameters affecting the adsorption of cisplatin by sperm cells were studied. Interestingly, the incubated Pt in sperm cells shows different signal trends to the endogenous P and Mg under the ultrasonic treatment that separated the sperm's head and tail, indicating elements with variable contents and locations in the sperm cells may be differentiated by the proposed method. The single-cell determination of sperm elements by ICP-MS would be useful for studying sperm signal transduction and relevant physiological topics.

Microstructure and mechanical properties of NbC–Ni cermets prepared by microwave sintering

Abstract This study shows the application of microwave sintering (MS) on preparing NbC–10Ni and NbC–12Ni cermets, as well as the effect of its microstructure, phase formation, and mechanical properties. Results indicated that NbC–Ni cermets with a fine and uniform structure can be obtained by MS in a relatively short time. And the sintering temperature greatly influenced the microstructure and mechanical properties of NbC–Ni cermets, whereas the effect of dwell time is relatively small. With the increase of the sintering temperature, the microstructure of NbC–Ni cermets experienced sintering densification and grain growth. The strength and toughness increased first and then decreased, and the hardness increased with the increase of sintering temperature. According to the comprehensive mechanical properties, the optimized sintering process is 1,390°C and the dwell time is 15 min. At this time, no new phase formed, but the diffraction peak of the Ni phase shifted. Through analysis, it is found that the improvement mechanisms for comprehensive mechanical properties of NbC–Ni cermets mainly include grain refinement, crack deflection and bridging, and energy absorption of the ductile phase of Ni.

Effect of Dwell Time on Fracture Load of Friction Stir Spot Welded Dissimilar Metal Joints

The dissimilar materials joining in heavy structural fabrication industries is tedious work for welding and design engineers, since the weld region’s criticality is encountered by hot cracking and its associated problems. Moreover, dissimilar materials are joined by mechanical locking such as rivets, bolt and nuts, and screws. Nowadays, the fasteners are eliminated by friction stir welding (FSW). The friction stir spot welding (FSSW) is a variant of FSW; it can be avoided by seam welding. Hence, in this investigation, FSSW is used for joining AA6061 aluminum alloy with mild steel using tool rotation speed, plunge depth and rate, and shoulder to pin diameter ratio. The experimental method observed that the joint fabricated with a rotational speed of 1000 rpm, plunge rate of 5 mm/min, plunge depth of 6 mm/min, and shoulder diameter to pin diameter ration of 3.0 yielded highest fracture load The optimum heat input could obtain the improvement in FSSW joint strength. Recrystallized grains and favorable intermetallic compound formation are the primary factors for sound welding.

A comparative study of spark plasma and conventional sintering of undoped SnO2 sputtering targets

SnO2 ceramics were fabricated by spark plasma sintering (SPS) and conventional (pressureless) sintering techniques using undoped submicron SnO2 powders. The effect of sintering temperature and dwell time on the densification behavior, phase evolution, and microstructural development of sintered ceramics were investigated. The relative density of SPSed ceramics increased when dwell time was raised from 1 to 10 min at 950 °C. However, full densification was prevented by the decomposition of SnO2 to Sn. The decomposition started after ∼10 min at 950 °C. In parallel to these observations, as sintering temperature increases, the elemental Sn in agglomerated form increases. On the other hand, the relative densities of conventionally sintered ceramics (at 1200°C-1400 °C) were relatively low (i.e., 63% relative density), and abnormal grain growth was observed due to the shift in sintering mechanisms to evaporation-condensation as a dominant mechanism. Since the undoped SnO2 ceramics, SPSed at 950 °C for 5 min under 30 MPa exhibit 93% relative density, high chemical purity, homogeneous grain size distribution, and smaller average grain size, they demonstrate great potential as sputtering targets for the production of high-quality thin film gas sensors.

Understanding temperature and dwell time dependence of liquid metal embrittlement in austenitic stainless steel by liquid zinc and copper

Austenitic stainless steels are known to be susceptible to LME-induced cracking when exposed to various liquid metals, including zinc and copper. However, the conditions under which LME cracking occurs are only vaguely defined. The effect of temperature and dwell time are investigated in this study using Gleeble hot tensile testing. Liquid zinc embrittlement is most severe at 800 °C and decreases towards lower or higher test temperatures. The lower temperature limit for copper embrittlement is defined by the melting temperature of copper (1085 °C); significant embrittlement is observed up to a test temperature of 1300 °C, at which ductility largely recovers. The observed zinc and copper induced LME behavior in Type 304L austenitic stainless steel are discussed based on the thermodynamics of the 304-Zn and 304-Cu systems which suggest that liquid metal embrittlement occurs in a temperature range where the phase diagrams display a two phase liquid zinc (or copper) + solid region that extends over a wide compositional range. Diffusion calculations across the stainless steel to liquid zinc interface and results from electron microscopy analysis indicate that liquid zinc availability due to isothermal solidification of BCC ferrite at the stainless steel to liquid zinc interface is a limiting factor for LME in the 304-Zn system during Gleeble hot tensile testing.

In-situ and off-line deformations of cylindrical walls manufactured by directed energy deposition with different dwell times

Deformation of directed energy deposition (DED) is an index to reflect the relationship among fabricating quality, parameters and process method. In the present work, Inconel 718 cylindrical walls are manufactured by hybrid additive and subtractive manufacturing (HASM) to investigate the deformation. In-situ and off-line measurements are used to detect the deformation of the cylindrical walls with laser displacement measurement sensor and precision contact probe. The finite element simulation is used to analyze the relationship among the temperature, stress and deformation. The effect of different interlayer dwell times (from 0 to 45 s) on residual stress and deformation are compared. The deformations of different positions and processing parameters are analyzed.