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The Super Tau-Charm Facility (STCF) is a significant initiative for accelerator-based particle physics in China. Electromagnetic Calorimeter (ECAL) is one of the important detectors of STCF, which is tasked with the accurate measurement of photons. STCF ECAL employs pure Cesium iodide (pCsI) as its scintillation crystal and uses a large-area avalanche photodiode (APD) as a photoelectric conversion device. High luminosity of STCF results in significant background levels, leading to pileups challenging conventional signal processing. In this paper, a pile-up correction algorithm called “pipeline optimal filtering” is proposed, and a background simulation platform is built to verify the measurement effect of the algorithm on energy and time. [ABSTRACT FROM AUTHOR]

CUORE Upgrade with Particle IDentification (CUPID) is a foreseen ton-scale array of Li2MoO4 (LMO) cryogenic calorimeters with double readout of heat and light signals. Its scientific goal is to fully explore the inverted hierarchy of neutrino masses in the search for neutrinoless double beta decay of 100Mo. Pile-up of standard double beta decay of the candidate isotope is a relevant background. We generate pile-up heat events via injection of Joule heater pulses with a programmable waveform generator in a small array of LMO crystals operated underground in the Laboratori Nazionali del Gran Sasso, Italy. This allows to label pile-up pulses and control both time difference and underlying amplitudes of individual heat pulses in the data. We present the performance of supervised learning classifiers on data and the attained pile-up rejection efficiency.

The use of lasers in various precise material removal processes has emerged as a viable and efficient alternative to traditional mechanical methods. However, the laser ablation of materials is a complex, multi-parameter process where scanning paths need to be repeated multiple times. This repetition causes changes in the absorption and temperature distribution along the scanning path, thereby affecting the accuracy of the ablation. Therefore, it is crucial to thoroughly study these phenomena. This article presents an experimental and numerical study on the laser ablation of bronze (DIN: 1705) in a multi-track ablation process. Specifically, six consecutive passes using a ns laser at three different energy densities were conducted. After each pass, measurements of the ablation depth and pile-up height were taken at three distinct points along the track (start, middle, and end) to evaluate the efficiency and quality of the process. To gain a deeper understanding of the underlying physical mechanisms, a numerical simulation model based on the Finite Element Method (FEM) was developed. The effective absorptivity was defined through reverse engineering, and the material's cooling rates were also estimated. This study's findings provide significant insights into the influence of machining parameters on the ablation process and its progression with varying numbers of consecutive repetitions. A primarily linear correlation was deduced between the ablation depth, energy density, and number of repetitions, while the relationship with the pile-up height appeared to be more ambiguous and nonlinear. The estimated cooling rates ranged from 106 to 1010 [K/s]. Additionally, a heat accumulation phenomenon and a gradual temperature increase resulting from consecutive laser scans were also observed. A good agreement between the simulation results and experiments for the ablation depths was observed. [ABSTRACT FROM AUTHOR]

Context: The mechanical characteristics and deformation behavior of Cu material under the nanoscratching through a diamond tooltip on the workpiece are studied using molecular dynamics (MD) simulation. Effects of scratching velocity, scratching depth, workpiece temperature, and grain size on the total force, shear strain, pile-up, shear stress, workpiece temperature, and phase transformation are investigated. The results reveal that increasing the scratching velocity leads to higher oscillation in total force, greater shear strain and shear stress, higher pile-up on the workpiece surface, and higher workpiece temperatures. The effect of the scratching velocity on phase transformation shows that most of the dislocation is a transformation structure from the FCC structure to the HCP, BCC, and other structures in all workpieces during the nanoscratching process. In addition, with increasing the scratching depth, material pile-up becomes more prominent, consequently elevating the contact area between the diamond tooltip and the workpiece, which simultaneously leads to an increase in total force, shear strain, pile-up, shear stress, and workpiece temperature. The MD simulation results revealed that the subsurface region of nanoscratched Cu single-crystal experiences the formation of stacking faults, vacancy defects, and cluster vacancies. In studying the effect of workpiece temperature, the results show that higher temperatures lead to the decline of scratching force, high plastic deformation, increased shear strain and stress, lower pile-up height, and high transition from the FCC structure to both other and BCC structures. For polycrystalline structures, the force curves occur in the oscillation state in all cases of different grain sizes because of the dislocation deformation during the cutting process. The maximum force decreases with diminishing grain size, attributed to the inverse Hall-Petch relation. As the grain size increases, leading to a decrease in the shear strain, stress, and an uneven pile up; also, the HCP structure rises with decreasing grain boundary and the partial dislocation and stacking fault mobilize inside grains. Methods: By using molecular dynamics (MD) simulation based on the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) software, all molecular interactions were described by the Lennard-Jones (LJ) and embedded atom method (EAM) potentials. In order to mitigate the effects of temperature fluctuations, the system employs an isothermal and isobaric (NPT) ensemble for precise temperature control. The temperature was set as 300 K and the time step was 1 fs (femtosecond). [ABSTRACT FROM AUTHOR]

The Instrumented Indentation Test (IIT) mechanically characterizes materials from the nano to the macro scale, enabling the evaluation of microstructure and ultra-thin coatings. IIT is a non-conventional technique applied in strategic sectors, e.g., automotive, aerospace and physics, to foster the development of innovative materials and manufacturing processes. However, material plasticity at the indentation edge biases the characterization results. Correcting such effects is extremely challenging, and several methods have been proposed in the literature. However, comparisons of these available methods are rare, often limited in scope, and neglect metrological performance of the different methods. After reviewing the main available methods, this work innovatively proposes a performance comparison within a metrological framework currently missing in the literature. The proposed framework for performance comparison is applied to some available methods, i.e., work-based, topographical measurement of the indentation to evaluate the area and the volume of the pile-up, Nix–Gao model and the electrical contact resistance (ECR) approach. The accuracy and measurement uncertainty of the correction methods is compared considering calibrated reference materials to establish traceability of the comparison. Results, also discussed in light of the practical convenience of the methods, show that the most accurate method is the Nix–Gao approach (accuracy of 0.28 GPa, expanded uncertainty of 0.57 GPa), while the most precise is the ECR (accuracy of 0.33 GPa, expanded uncertainty of 0.37 GPa), which also allows for in-line and real-time corrections. [ABSTRACT FROM AUTHOR]

n the present study, a semi-empirical modeling of the mechanical response in pile-up mode is obtained by deriving the load-depth relationship during the indentation loading cycle. The advantage compared to the relations previously used is that this new expression is a function of the predictable criterion of the mode of deformation, (hf/hm), which makes it possible to distinguish the sink-in mode from the pile-up mode. A comparison between the proposed expression and the results of the instrumented indentation tests shows excellent agreement

While pileups involving only two vehicles showcase obvious liability among the drivers, the assessment of liabilities is much more complex in chain collisions. In this work we propose an analytical indicator, named xEES, which easily allows to assess the correct liabilities among drivers. The name is mutated by the concept of energy equivalent speed (EES), which is the vehicle speed equivalent to the energy consumed to cause the vehicle deformation: xEES is indeed a dimensionless parameter related to the expected EES at the front of the first vehicle requested for a chain reaction car accident and that is energetically coherent with the damages of the hit vehicles. The proposed model needs only the information concerning the damages of the vehicles and does not require any information concerning the accident scene. The model has been tested on real pileups and validated by the software PC-Crash: the analysis has shown how the use of the coefficient xEES leads the engineer to assess the correct liabilities in pileups. Three intervals of variation are defined for xEES, which set apart, with due statistical confidence, chain reaction car accidents from collisions involving a column of moving vehicles.

The use of lasers in various precise material removal processes has emerged as a viable and efficient alternative to traditional mechanical methods. However, the laser ablation of materials is a complex, multi-parameter process where scanning paths need to be repeated multiple times. This repetition causes changes in the absorption and temperature distribution along the scanning path, thereby affecting the accuracy of the ablation. Therefore, it is crucial to thoroughly study these phenomena. This article presents an experimental and numerical study on the laser ablation of bronze (DIN: 1705) in a multi-track ablation process. Specifically, six consecutive passes using a ns laser at three different energy densities were conducted. After each pass, measurements of the ablation depth and pile-up height were taken at three distinct points along the track (start, middle, and end) to evaluate the efficiency and quality of the process. To gain a deeper understanding of the underlying physical mechanisms, a numerical simulation model based on the Finite Element Method (FEM) was developed. The effective absorptivity was defined through reverse engineering, and the material’s cooling rates were also estimated. This study’s findings provide significant insights into the influence of machining parameters on the ablation process and its progression with varying numbers of consecutive repetitions. A primarily linear correlation was deduced between the ablation depth, energy density, and number of repetitions, while the relationship with the pile-up height appeared to be more ambiguous and nonlinear. The estimated cooling rates ranged from 106 to 1010 [K/s]. Additionally, a heat accumulation phenomenon and a gradual temperature increase resulting from consecutive laser scans were also observed. A good agreement between the simulation results and experiments for the ablation depths was observed.

Although cross-slip strongly affects the deformation of polycrystalline materials, the phenomenon is rarely studied in twinned face centered cubic (FCC) metals. Here we performed in-situ TEM nanoindentation on a twinned nickel bi-crystal. Multiple pile-ups were generated, with the first dislocations pinned at a coherent twin boundary (CTB) and multiple following dislocations cross-slipping within the matrix. Stress calculation revealed that the cross-slip events are made possible by the CTB, the first dislocations, and the favorable shear stress created jointly by external stress and dislocation interaction. These cross-slip events reduce tip stress and soften the material until inter-grain plasticity is eventually activated.IMPACT STATEMENTIn-situ TEM nanoindentation reveals the characteristics of dislocation pinning, pile-ups and cross-slip along the twinning boundary in a twinned FCC metal for the first time.

Pile-up is an unavoidable complication for cryogenic detectors with relatively large heat capacities and slow rise time, such as systems for decay energy spectroscopy employing large Au absorbers. We have simulated the spectral response of such slow cryogenic detectors using Monte-Carlo algorithms to investigate the effects of pile-up on absolute and relative activity measurements. We focus on the impact of non-distinguishable pile-up that occurs when the rising edges of two waveforms originating from different events overlap in time and are interpreted as a single event. This effect can not be readily identified and corrected in experimental data. We investigated two representative cases of absolute decay counting and plutonium isotopic analysis and find that pile-up can distort the reconstruction of both the absolute and relative activities. This Monte-Carlo methodology quantifies of pile-up effects and provides a systematic methodology for calculating corrective factors. [ABSTRACT FROM AUTHOR]

In this article, the characteristic curves of microindentation measured on Cu99 were analyzed on the basis of the analytical expression proposed by Habibi et al. (J. Mater. Res, 2021, 36 (15): 3074-3085). The ratio of applied load to square displacement, P/(h+h0)2, was discovered to be non-constant during the loading segment of the microindentation test. An empirical expression for the determination of Martens hardness as a function of indentation load, contact stiffness, and reduced modulus of elasticity by analyzing indentation load curves has been proposed for pile-up mode strain with the corrections imposed by the tip defect, the compliance of the instrument, and the axial axisymmetry coefficient of the Vickers indenter. The results from microindentation tests on this examined ductile material show excellent agreement.

The adoption of machine learning approaches for gamma-ray spectroscopy has received considerable attention in the literature. Many studies have investigated the deployment of various algorithm architectures to a specific task. However, little attention has been afforded to the development of the datasets leveraged to train the models. Such training datasets typically span a set of environmental or detector parameters to encompass a problem space of interest to a user. Variations in these measurement parameters will also induce fluctuations in the detector response, including expected pile-up and ground scatter effects. Fundamental to this work is the understanding that 1) the underlying spectral shape varies as the measurement parameters change and 2) the statistical uncertainties associated with two spectra impact their level of similarity. While previous studies attribute some arbitrary discretization to the measurement parameters for the generation of their synthetic training data, this work introduces a principled methodology for efficient spectral-based discretization of a problem space. A signal-to-noise ratio (SNR) respective spectral comparison measure and a Gaussian Process Regression (GPR) model are used to predict the spectral similarity across a range of measurement parameters. This innovative approach effectively showcased its capability by dividing a problem space, ranging from 5 cm to 100 cm standoff distances and 5 μCi–100 μCi of 137Cs, into three unique combinations of measurement parameters. The findings from this work will aid in creating more robust datasets, which incorporate many possible measurement scenarios, reduce the number of required experimental test set measurements, and possibly enable experimental training data collection for gamma-ray spectroscopy. [ABSTRACT FROM AUTHOR]

In the present study, a semi-empirical modeling of the mechanical response in pile-up mode is obtained by deriving the load-depth relationship during the indentation loading cycle. The advantage compared to the relations previously used is that this new expression is a function of the predictable criterion of the mode of deformation, (hf/hm), which makes it possible to distinguish the sink-in mode from the pile-up mode. A comparison between the proposed expression and the results of the instrumented indentation tests shows excellent agreement. [ABSTRACT FROM AUTHOR]

For the specific case of a spherical diamond nanoparticle with 10 nm radius rolling over a planar Fe surface, we employ molecular dynamics simulation to study the processes of indentation and scratching. The particle is rotating (rolling). We focus on the influence of the adhesion force between the nanoparticle and the surface on the damage mechanisms on the surface; the adhesion is modeled by a pair potential with arbitrarily prescribed value of the adhesion strength. With increasing adhesion, the following effects are observed. The load needed for indentation decreases and so does the effective material hardness; this effect is considerably more pronounced than for a non-rotating particle. During scratching, the tangential force, and hence the friction coefficient, increase. The torque needed to keep the particle rolling adds to the total work for scratching; however, for a particle rolling without slip on the surface the total work is minimum. In this sense, a rolling particle induces the most efficient scratching process. For both indentation and scratching, the length of the dislocation network generated in the substrate reduces. After leaving the surface, the particle is (partially) covered with substrate atoms and the scratch groove is roughened. We demonstrate that these effects are based on substrate atom transport under the rotating particle from the front towards the rear; this transport already occurs for a repulsive particle but is severely intensified by adhesion. [ABSTRACT FROM AUTHOR]

The Instrumented Indentation Test (IIT) mechanically characterizes materials from the nano to the macro scale, enabling the evaluation of microstructure and ultra-thin coatings. IIT is a non-conventional technique applied in strategic sectors, e.g., automotive, aerospace and physics, to foster the development of innovative materials and manufacturing processes. However, material plasticity at the indentation edge biases the characterization results. Correcting such effects is extremely challenging, and several methods have been proposed in the literature. However, comparisons of these available methods are rare, often limited in scope, and neglect metrological performance of the different methods. After reviewing the main available methods, this work innovatively proposes a performance comparison within a metrological framework currently missing in the literature. The proposed framework for performance comparison is applied to some available methods, i.e., work-based, topographical measurement of the indentation to evaluate the area and the volume of the pile-up, Nix–Gao model and the electrical contact resistance (ECR) approach. The accuracy and measurement uncertainty of the correction methods is compared considering calibrated reference materials to establish traceability of the comparison. Results, also discussed in light of the practical convenience of the methods, show that the most accurate method is the Nix–Gao approach (accuracy of 0.28 GPa, expanded uncertainty of 0.57 GPa), while the most precise is the ECR (accuracy of 0.33 GPa, expanded uncertainty of 0.37 GPa), which also allows for in-line and real-time corrections.

Although cross-slip strongly affects the deformation of polycrystalline materials, the phenomenon is rarely studied in twinned face centered cubic (FCC) metals. Here we performed in-situ TEM nanoindentation on a twinned nickel bi-crystal. Multiple pile-ups were generated, with the first dislocations pinned at a coherent twin boundary (CTB) and multiple following dislocations cross-slipping within the matrix. Stress calculation revealed that the cross-slip events are made possible by the CTB, the first dislocations, and the favorable shear stress created jointly by external stress and dislocation interaction. These cross-slip events reduce tip stress and soften the material until inter-grain plasticity is eventually activated. IMPACT STATEMENT In-situ TEM nanoindentation reveals the characteristics of dislocation pinning, pile-ups and cross-slip along the twinning boundary in a twinned FCC metal for the first time. [ABSTRACT FROM AUTHOR]

The effect of pulse pile-up on neutron count rates is a persistent challenge in photon active interrogation. During active interrogation, the neutron signatures from illicit special nuclear material (SNM) can provide a characteristic signal; however, the intense radiation environment can cause pulse pile-up in detectors. Organic scintillator detectors are favorable in active interrogation due to their fast neutron efficiency and fast timing characteristics and rely upon pulse shape discrimination to compare pulse shapes and classify detection events. Pile-up events are typically rejected during the analysis process because the pile-up events result in pulses with relatively large tail integrals, which appear similar to single neutron pulses. Pile-up events can be identified and removed in postprocessing, but in photon active interrogation scenarios, pile-up rejection algorithms can degrade due to the high pile-up rates, leading to erroneously high neutron count rates. Thus, it is essential that pulse pile-up events are minimized to produce accurate results. In this work, we compare the performance of a pair of 6-mm trans-stilbene cubes to a 5.08-cm-diameter, 5.08-cm-height trans-stilbene cylindrical detector during photon active interrogation. We use a Varex electron linear accelerator (linac) to produce an interrogation beam of bremsstrahlung photons up to 9 MeV in energy, which induces photofission and photodisintegration in depleted uranium (DU). We first optimize the pulse shape parameters for the 6-mm stilbene cubes using 137Cs and 252Cf sources and deploy the detectors in an active interrogation environment. As expected, the smaller detectors experience significantly less pile-up than the 5.08-cm stilbene cylindrical detector due to the reduction in detection volume. The 6-mm stilbene detectors observe a 250 ± 24 s−1 net neutron count rate and could determine the presence of the $\approx 2.8$ -kg DU in less than 3 min of measurement time, in stark contrast to the 5.08-cm stilbene detectors that failed to identify a net increase in neutron count rate due to the significantly high proportion of pile-up pulses. This work demonstrates that small detectors are robust against pile-up in photon active interrogation scenarios while maintaining a satisfactory neutron detection efficiency. [ABSTRACT FROM AUTHOR]

In this paper, we propose a device simulation method that quantitatively represents the film profile characteristics. We simulated device characteristics according to pile‐up size and quantitatively confirmed relationship between film profile and device performance. We checked the device characteristics by changing the ratio of the pile‐up area to the planar area in units of pixels and changing the pile‐up stacking thickness. As a result, when ratio of the flat area in active area is 80% or more and the thickness difference is less than 10%, we obtained device efficiency of 90% and more compared to the ideal device (perfectly flat device) for red, green and blue devices. We could also confirm the reliability of the simulation method through device fabrication. And we expect that this study can contribute to improving the characteristics of the panel and device of solution processed OLED. [ABSTRACT FROM AUTHOR]

One of the critical aspects for the accurate determination of neutron capture cross sections when combining time-of-flight and total energy detector techniques is the characterization and control of systematic uncertainties associated to the measuring devices. In this work we explore the most conspicuous effects associated to harsh count rate conditions: dead-time and pile-up effects. Both effects, when not properly treated, can lead to large systematic uncertainties and bias in the determination of neutron cross sections. In the majority of neutron capture measurements carried out at the CERN n_TOF facility, the detectors of choice are the C 6 D 6 liquid-based either in form of large-volume cells or recently commissioned sTED detector array, consisting of much smaller-volume modules. To account for the aforementioned effects, we introduce a Monte Carlo model for these detectors mimicking harsh count rate conditions similar to those happening at the CERN n_TOF 20 m flight path vertical measuring station. The model parameters are extracted by comparison with the experimental data taken at the same facility during 2022 experimental campaign. We propose a novel methodology to consider both, dead-time and pile-up effects simultaneously for these fast detectors and check the applicability to experimental data from 197Au(n , γ), including the saturated 4.9 eV resonance which is an important component of normalization for neutron cross section measurements. [ABSTRACT FROM AUTHOR]

Precise measurement under high counting rates has been a major challenge for γ -ray spectroscopy, where signals generally pile up with each other and their characteristic values are deeply coupled. An off-line pile-up pulse recovery algorithm based on template matching is developed for LaBr 3 scintillation detectors and has been applied to data from China Spallation Neutron Source (CSNS) Back-n white neutron beamline. As an improvement to the traditional Template Matching methods, the predetermined template shape is associated with pulse amplitudes, which is found crucial to achieve the best fitting results. Moreover, a universal strategy of setting the initial values of fitting allows to resolve signals that are separated in time by less than the characteristic rise time. Processing of simulated pulses demonstrates that the lower limit of interval to distinguish successive events is 10 ns, which is a significant improvement to the previous works. The algorithm performs well under a counting rate of 6 × 1 0 7 s−1, and is still effective up to 1 0 8 s−1. Analysis of experimental data indicates that this algorithm recovers over 98% count yield under a counting rates of no more than 4 × 1 0 6 s−1 in this work, providing a more reliable approach to deduce neutron-induced reaction cross sections. [ABSTRACT FROM AUTHOR]

A High Granularity Timing Detector (HGTD) has been proposed for the ATLAS Phase-II upgrade to mitigate the pile-up effects at the High-Luminosity Large Hadron Collider (HL-LHC). The HGTD is based on silicon devices, Low Gain Avalanche Detectors (LGAD), aiming to provide 30–50 ps time resolution per track. Significant progress has been made in the development of various detector components, particularly the radiation-resistant sensor and readout chip. This proceeding concisely summarizes the project overview and current status of the HGTD project. [ABSTRACT FROM AUTHOR]

Fast fluorescence lifetime (FL) determination is a major factor for studying dynamic processes. To achieve a required precision and accuracy a certain number of photon counts must be detected. FL methods based on single-photon counting have strongly limited count rates because of the detector's pile-up issue and are suffering from long measurement times in the order of tens of seconds. Here, we present an experimental and Monte Carlo simulation-based study of how this limitation can be overcome using array detectors based on single-photon avalanche diodes (SPADs). We investigated the maximum count rate per pixel to determine FL with a certain precision and accuracy before pile-up occurs. Based on that, we derived an analytical expression to calculate the total measurement time which is proportional to the FL and inversely proportional to the number of pixels. However, a higher number of pixels drastically increases data rate. This can be counteracted by lowering the time resolution. We found that even with a time resolution of four times the FL, an accuracy of 10% can be achieved. Taken all together, FLs between 10 ns and 3 ns can be determined with a 300-pixel SPAD array detector with a measurement time and data rate less than 1 µs and 700 Mbit/s, respectively. This shows the enormous potential of SPAD array detector for high-speed applications requiring continuous data read out. [ABSTRACT FROM AUTHOR]

In this article, the characteristic curves of microindentation measured on Cu99 were analyzed on the basis of the analytical expression proposed by Habibi et al. (J. Mater. Res, 2021, 36 (15): 3074-3085). The ratio of applied load to square displacement, P/(h+h0)2, was discovered to be nonconstant during the loading segment of the microindentation test. An empirical expression for the determination of Martens hardness as a function of indentation load, contact stiffness, and reduced modulus of elasticity by analyzing indentation load curves has been proposed for pile-up mode strain with the corrections imposed by the tip defect, the compliance of the instrument, and the axial axisymmetry coefficient of the Vickers indenter. The results from microindentation tests on this examined ductile material show excellent agreement. [ABSTRACT FROM AUTHOR]

Purpose: While X-ray photon-counting detectors (PCDs) promise to revolutionize medical imaging, theoretical frameworks to evaluate them are commonly limited to incident fluence rates sufficiently low that the detector response can be considered linear. However, typical clinical operating conditions lead to a significant level of pile-up, invalidating this assumption of a linear response. Here, we present a framework that aims to evaluate PCDs, taking into account their non-linear behavior., Approach: We employ small-signal analysis to study the behavior of PCDs under pile-up conditions. The response is approximated as linear around a given operating point, determined by the incident spectrum and fluence rate. The detector response is subsequently described by the proposed perturbation point spread function (pPSF). We demonstrate this approach using Monte-Carlo simulations of idealized direct- and indirect-conversion PCDs., Results: The pPSFs of two PCDs are calculated. It is then shown how the pPSF allows to determine the sensitivity of the detector signal to an arbitrary lesion. This example illustrates the detrimental influence of pile-up, which may cause non-intuitive effects such as contrast/contrast-to-noise ratio inversion or cancellation between/within energy bins., Conclusions: The proposed framework permits quantifying the spectral and spatial performance of PCDs under clinically realistic conditions at a given operating point. The presented example illustrates why PCDs should not be analyzed assuming that they are linear systems. The framework can, for example, be used to guide the development of PCDs and PCD-based systems. Furthermore, it can be applied to adapt commonly used measures, such as the modulation transfer function, to non-linear PCDs., (© 2024 The Authors.)

The present study shows that effect of impact load on microstructural feature in 27Cr white cast iron alloy, which is destabilized at 1150°C for 3 hour holding. The specimen is received with a microstructure consisting of ductile matrix (57% retained austenite) and amount of dispersed secondary. The residual stresses distribution in the alloy as a function of the impact load, they localized around the eutectic carbides and eutectic carbides, at defect positions. This distribution tends to decrease in the impact loading direction. The dislocations are formed in alloy as a result of the concentration stress, which caused by impact load. High stress concentration promotes the interaction between dislocations and these dislocations tend to pile-up at grain boundaries. In this study, the helical dislocations are observed in the stress concentration areas. The voids are formed by the pile-up of dislocations. The diameter of voids can be from several tens nanometers to 500 nanometers and depending on the applied load. When the voids expand (exceed 500nm diameter), the ligament around void is thinner and leads to an increase in the deformation region between voids. As a consequence, the voids coalesce by formation the necking of the ligament between two voids to form a micro-crack. [ABSTRACT FROM AUTHOR]

A technique for computing the strains and stresses arising at the stage of developed plastic flow and the axial residual stresses after unloading is proposed. The technique has the following assumptions: the indentor is perfectly rigid, the temperature effects are ignored, and the half-space is rigid-plastic and incompressible. The calculation data are presented. [ABSTRACT FROM AUTHOR]

Fast fluorescence lifetime (FL) determination is a major factor for studying dynamic processes. To achieve a required precision and accuracy a certain number of photon counts must be detected. FL methods based on single-photon counting have strongly limited count rates because of the detector’s pile-up issue and are suffering from long measurement times in the order of tens of seconds. Here, we present an experimental and Monte Carlo simulation-based study of how this limitation can be overcome using array detectors based on single-photon avalanche diodes (SPADs). We investigated the maximum count rate per pixel to determine FL with a certain precision and accuracy before pile-up occurs. Based on that, we derived an analytical expression to calculate the total measurement time which is proportional to the FL and inversely proportional to the number of pixels. However, a higher number of pixels drastically increases data rate. This can be counteracted by lowering the time resolution. We found that even with a time resolution of four times the FL, an accuracy of 10% can be achieved. Taken all together, FLs between 10 ns and 3 ns can be determined with a 300-pixel SPAD array detector with a measurement time and data rate less than 1 µs and 700 Mbit/s, respectively. This shows the enormous potential of SPAD array detector for high-speed applications requiring continuous data read out.

Nanolaminates are extensively studied due to their unique properties, such as impact resistance, high fracture toughness, high strength, and resistance to radiation damage. Varieties of nanolaminates are being fabricated to achieve high strength and fracture toughness. In this study, one such nanolaminate fabricated through accumulative roll bonding (Cu(16)/Nb(16) ARB nanolaminate, where 16 nm is the layer thickness) was used as a test material. Cu(16)/Nb(16) ARB nanolaminate exhibits crystallographic anisotropy due to the existence of distinct interfaces along the rolling direction (RD) and the transverse direction (TD). Nanoindentation was executed using a Berkovich tip, with the main axis oriented either along TD or RD of the Cu(16)/Nb(16) ARB nanolaminate. Subsequently, height profiles were obtained along the main axis of the Berkovich indent for both TD and RD using scanning probe microscopy (SPM), which was later used to estimate the pile-up along the RD and TD. The RD exhibited more pile-up than the TD due to the anisotropy of the Cu(16)/Nb(16) ARB interface and the material plasticity along the TD and RD. An axisymmetric 2D finite element analysis (FEA) was also performed to compare/validate nanoindentation data, such as load vs. displacement curves and pile-up. The FEA simulated load vs. displacement curves matched relatively well with the experimentally generated load–displacement curves, while qualitative agreement was found between the simulated pile-up data and the experimentally obtained pile-up data. The authors believe that pile-up characterization during indentation is of great importance to documenting anisotropy in nanolaminates.

Flow curves of 15Kh2MFA, Sv 08Kh19N10G2B and 08Kh18N10T steels used for fabrication of WWER-440 nuclear reactor pressure vessel and core internals were obtained using the automated ball indentation (ABI) test technique and compared with flow curves evaluated from the same measured load-displacement data and widely used Oliver-Pharr method. Differences in results obtained by both studied methods do not exceed 12% and are attributed to the amount of material pile-up. [ABSTRACT FROM AUTHOR]

The post spacing of slit dams is a key parameter that controls the trapping efficiency of these open-type countermeasures. In this study we conduct flume experiments of quasi-monodisperse spherical particles passing through slits to investigate the relationship between the trapping efficiency and the pile-up geometry, as well as the impact of the latter on the interaction between granular flows and slit dams. The ratio of the slit width relative to the particle size b / d is varied while the flume inclination is held constant. Tests reveal that at a critical ratio b / d ∼ 2.3 trapping is most unstable. The trapping efficiency influences the geometry of the granular pile-up that deposits behind the dam after it has been jammed. When >52 % of the granular mass is trapped (occurring at b / d ≤ 2.3), the height of the final deposit changes with the trapping efficiency, whereas below this threshold value (when b / d ≥ 3.1) the flow-wise length becomes more sensitive to the trapping. Impact force measurements further shed light on the mechanisms relating the trapping efficiency and the geometry and their effect on the total force fluctuations. • Flume experiments of granular materials impacting slit dams reveal a critical relative post spacing of b / d ∼ 2.3 at which the trapping is considered most unstable. • The deposit geometry depends on the trapping efficiency. When the efficiency is >52 %, deposit height is sensitive to it but below this threshold only the flow-wise length changes. • The total impact force reflects the pile-up process and geometry. The trapping efficiency influences the magnitude of the impact force and its evolution as particles exit from the slits. [ABSTRACT FROM AUTHOR]

Instrumented nanoindentation tests have reached an effective level of theoretical and practical knowledge to become an interesting and useful tool for determining hardness, H, and local elasticity (reduced Young’s modulus), Er, of a variety of materials, from coatings and thin films to bulk metallic materials. Nanoindentation instruments are equipped with analysis software for raw data for hardness and reduced Young’s modulus evaluation, generally based on the Oliver and Pharr analysis method. On the other hand, it is widely known and recognized that prior data acquisition, a tip-dependent calibration procedure of compliance, and area function are needed. With this in view, an accurate and sound calibration protocol is here reported. Hardness and local elastic modulus is measured on different bulk metallic materials, showing the distinctive strengths of using nanoindentation. Finally, a local elastic-plastic phenomenon mostly induced by the nanoindentation tip on ductile metallic material (i.e., pile-up) is also reported and modelled. This manuscript is thus intended to favor and account for the importance of using the instrumented nanoindentation tests for H and Er measurements of metallic materials.

• The elastic displacement and stress fields induced by a dislocation loop of polygonal shape within an anisotropic homogeneous half-space with general boundary conditions are obtained employing the corresponding Green's functions due to Pan, one of the authors. • Then, the distribution dislocation loop model for nanoindentation is further improved to imitate the friction between the indenter and the indented single crystal by the obtained elastic fields. • A stronger boundary condition is found to correspond to the smaller amount of elastic recovery and larger residual stresses. The elastic displacement and stress fields induced by a dislocation loop of polygonal shape within an anisotropic homogeneous half-space with general boundary conditions on the flat surface z = 0 are obtained by employing the corresponding point-force Green's functions. We first study in detail the effects of the eight sets of boundary conditions on the elastic fields of dislocation loops. We then identify the elastic fields of dislocation loops corresponding to three of the eight sets of boundary conditions. These are the traction-free, completely, and partially sticking contact between the indenter and the indented single crystals, which are employed to establish the distribution dislocation loop model for simulating nanoindentation of single crystals. It is the first time that significant differences in the magnitude of sink-in and pile-up of the indented profile, and of the residual stress components, corresponding to different frictional boundary conditions, are observed, which could serve as benchmark in future nanoindentation study. [ABSTRACT FROM AUTHOR]

Scratch tests are useful techniques to gain insight into the material removal mechanism of abrasive machining processes. In most of the scratch tests, uncut chip thickness value is either constant or varies from zero to maximum. However, in abrasive machining processes, uncut chip thickness value ranges from either zero to maximum or vice versa. Moreover, regular scratch tests are conducted at very low speeds, in which either the indenter or the workpiece is stationary. Because of these limitations, the knowledge obtained from the existing scratch test results is not valid for most of the abrasive processes. Hence, in this paper, the influence of chip thickness variation, speed ratio, and depth of cut on the pile-up behaviour of AISI 1015 steel and 2017A-T4 aluminium alloy surfaces were investigated. The workpiece having the comparable thermal diffusivity value with the grit has shown a significant difference in its pile-up behaviour. Through a better understanding of chip thickness influence on pile-up ratio, a mathematical model was developed for kinematic simulations. Using the developed model, kinematic simulations were done to visualise the scratch surface topography and material pile-up by considering the grit trajectory path and chip thickness variation. Finally, simulated surfaces were compared with the experimental results to show the proposed method applicability. [ABSTRACT FROM AUTHOR]

Dual phase (DP) steels are broadly deployed by the automotive industry to enhance strength and ductility for light weighting. As DPs micro-constituents' grain size is frequently on the same order of sizes probed with nanoindentation, an inverse technique was combined with nanoindentation load-depth curves to extract the stress-strain behavior of ferrite and martensite in DP1180. Determining the appropriate depth to evaluate the properties of the micro-constituent phases enabled computation of the flow behavior of each individual phase. Post indentation microscopy correlated the microstructure to the spatially resolved indentation arrays. The post-indentation impression was characterized to eliminate indentation size effects and probe bluntness influences. The yield strength of ferrite, martensite and DP1180 were determined to be 370, 948 and 836 MPa respectively while the corresponding strain hardening exponents (n) were computed via an inverse method as 0.175, 0.025 and 0.11. Mechanical properties obtained from the indentation method exhibited good agreement with the experimentally measured macroscopic yield stress (922 MPa) and hardening exponent (0.11) of DP1180. [ABSTRACT FROM AUTHOR]

Amorphous silicon oxycarbide (SiOC) films, fabricated by magnetron sputtering, were irradiated at room temperature with 3.5 MeV Fe ions to damage levels of 10, 20, and 50 displacements per atom (dpa). Irradiation-induced changes in the nature of the atomic bonds were studied using Raman spectroscopy and X-ray photoelectron spectroscopy. The chemical composition of the surfaces of the films remained relatively unchanged after ion irradiation. Surface topography of the films was studied by atomic force microscopy and it was found that ordered topographic patterns were formed on the surface of the irradiated films. Deformation behavior of the films was studied by a combination of nanoscratch experiments and in-situ scanning probe microscopy. No signs of cracks or chipping were observed around the scratches on the as-deposited and irradiated films. Furthermore, microindentation experiments with a Vickers indenter were performed on selected films and the impressions were studied by scanning electron microscopy. The film irradiated to 20 dpa showed an increased resistance to indentation cracking compared to the as-deposited film. The study demonstrates that amorphous SiOC, with desirable structural stability and mechanical properties, can be a promising candidate for irradiation tolerant materials. [ABSTRACT FROM AUTHOR]

Abstract Polymer thin films are gaining significant attention these days because of its wide range of applications. Optoelectronics, microelectronics, touch screen panels, wrinkled surfaces, stimuli-responsive films, polymer micro and nanopillars for energy storage and contact lenses are some of the applications of these polymer thin films. In most of these applications, the measurement of mechanical properties of thin films is extremely critical. Pile-up is one of the parameters that significantly affect the measurement of mechanical properties during nanoindentation, nanoscratching, and nano-dynamic mechanical analysis (nano-DMA). These pile-up behavior for thin films are different from their bulk counterparts owing to their confinement in the growth direction. In this research work, static and dynamic loads were applied to study the pile-up response of polymer thin films and most importantly the related mechanisms. Influence of substrate, interface properties, film thickness, indenter shape and the magnitude of the load on the pile-up behaviour is investigated. Nanoindentation (at different loads starting from 40 μN to 500 μN), nanoscratch (at various depths ranging from 80 nm to 300 nm) and nano-DMA (at different frequency range starting from 10 Hz to 200 Hz) experiments were performed to pursue the objective. The effect of pile-up on the measured mechanical properties, such as, elastic modulus, hardness are estimated. Highlights • Pile-up response of polymer thin films was examined. • Scanning probe image analysis has been carried out to quantify the pile-up. • Influence of various parameters on the pile-up behaviour is investigated. • The effect of pile-up on the measured mechanical properties are estimated. [ABSTRACT FROM AUTHOR]

Abstract In counting experiments associated with pulsed sources, a high data collection rate can lead to considerably large counting losses, especially in the case of spallation Time-of-Flight facilities equipped with medium and short flight paths where the research interest is focused on higher neutron energies where counting losses can be quite large due to the higher neutron flux, the more compressed time frame compared to the one on lower energies and the higher cross-section depending on the reaction. Examples of such measurements are the neutron induced fission experiments at the new experimental area EAR-2 at the n_TOF facility at CERN. Although analytical expressions to account for this inefficiency exist in literature, the introduced corrections are not always sufficient to retrieve the true reaction rate, therefore a different approach is mandatory. This work explores the possibility to quantify the counting losses using detector emulation devices and exponential fits in waiting time distributions. The methodology is benchmarked in the test case of the standard 238U(n,f) cross-section with reference to 235U(n,f) for bandwidths up to 1.9 MHz and counting losses that exceed 60%. [ABSTRACT FROM AUTHOR]