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Rocks such as Kota sandstone are an excellent construction material. An experimental and numerical study was performed to test Kota sandstone in a large-diameter (76-mm) split Hopkinson pressure bar (SHPB) in a strain rate range of 101–300/s. The primary goal of the current study was to optimize pulse shaper dimensions for dynamic testing of rocks. Pulse shapers of diameters 10, 12, 15, 20, 25, and 30 mm and thicknesses 0.1, 0.5, 1.5, 2.5, 5, and 10 mm were used. It was found that the incident rise time increases and the maximum stress drops as the diameter or thickness increases. For a large-diameter SHPB, it is recommended to use a pulse shaper of diameter 15–20 mm and thickness 2.5 mm. These pulse shaper dimensions produce a ramp-like incident pulse that facilitates dynamic force equilibrium and constant strain rate loading in the rock specimens. Also, the inertia-induced stresses in the rock specimens are negligible. A thicker pulse shaper is suggested if higher strain rates are targeted. The inertia-induced stresses in the pulse shaper increase as its diameter increases and decrease as its thickness increases. Especially when the pulse shaper diameter is increased from 20 mm to 25 or 30 mm, the inertia-induced stresses become large enough to cause oscillations in the incident waves. [ABSTRACT FROM AUTHOR]

The photoinjector laser system of Shenzhen Superconducting Soft X-Ray Free Electron Laser (S3FEL) is reported in this paper. This laser system operates at up to 1 MHz and produces more than 50 μJ infrared (IR) laser pulses. With a customized fourth harmonic generation (FHG) module, more than 2 μJ ultraviolet (UV) laser pulses were obtained. The power standard deviations of the IR laser and the UV laser are 0.093% and 0.395% respectively. While the pulse energy standard deviations are 1.087% and 1.746% correspondingly. We implemented the pulse stacking scheme to generate flat-top pulses. With four birefringent uniaxial crystals, the Gaussian pulses were converted to flat-top shape, featuring 10 ps pulse width and 0.5 ps rising and falling edges. A cut-Gaussian transverse profile with very sharp rising and falling edges can be produced after the spatial pulse shaper.

In typical split-Hopkinson pressure bar experiments (SHPB), the striker bar impacts the incident bar via discs made from soft materials such as copper. These discs, also called pulse shapers, are used (i) to eliminate the high frequency components of the incident pulse, (ii) to obtain a finite rise time of the incident pulse and (iii) to obtain a constant strain rate. Although these pulse shapers have been used for over decades in SHPB experiments, no analytical solutions or simple models are available that can predict the incident pulse as a function of the striker velocity, pulse shaper geometry and material parameters. Assuming that the pulse shaper is a rigid-linearly hardening material, we derive the analytical solution for the incident pulse when the rise time of the incident pulse is less than twice the time taken for a longitudinal wave to travel along the length of the striker. For larger rise times, we additionally assume that the striker is rigid to obtain a simple numerical model to predict the incident pulse in the presence of a pulse shaper. Both these models are validated against numerical simulations and experiments to demonstrate their accuracy. • Simple models are used to predict the incident pulse in SHPB experiments. • The pulse shaper is modelled as rigid perfectly plastic material. • Experiments are conducted to validate the models. [ABSTRACT FROM AUTHOR]

The dynamic compression deformation of an in‐house cast concrete (average aggregate size of 2–2.5 mm) was modelled using the finite element (FE), element‐free Galerkin (EFG) and smooth particle Galerkin (SPG) methods to determine their capabilities of capturing the dynamic deformation. The numerical results were validated with those of the experimental split Hopkinson pressure bar tests. Both EFG and FE methods overestimated the failure stress and strain values, while the SPG method underestimated the peak stress. SPG showed similar load capacity profile with the experiment. At initial stages of the loading, all methods present similar behaviour. Nonetheless, as the loading continues, the SPG method predicts closer agreement of deformation profile and force histories. The increase in strength at high strain rate was due to both the rate sensitivity and lateral inertia caused by the confinement effect. The inertia effect of the material especially is effective at lower strain values and the strain rate sensitivity of the concrete becomes significant at higher strain values. [ABSTRACT FROM AUTHOR]

The constant strain rate loading and dynamic stress equilibrium are prerequisites for ensuring the experimental data of the Split Hopkinson Pressure Bar (SHPB). In order to achieve this requirement, a proper pulse shaper dimensions were used in the experiment. For this purpose, the pulse shaper diameter, thickness and strength and the strike bar length and its velocity on the incident pulse are studied by Ø80mm SHPB apparatus. Then, the parameters affecting the two key inflection points and three loading areas of the incident pulse are discussed. In addition, the improved methods for two typical non-constant strain rate waveforms for the concrete experiments are obtained based on the regular pulse shaping. Moreover, SHPB experiments are conducted for concrete by employing different pulse shaper dimensions. The results show that more valid data can be obtained by employing the pulse shaper with large thickness when the strain rate is non-constant during the experiment. The conclusions and method provide guidance for selecting pulse shaper for concrete SHPB experiments. [ABSTRACT FROM AUTHOR]

Intense ultrashort laser pulses at 1.55 μm are generated by a home-built light source and compressed to 20 fs by multiple plate continuum (MPC) and Fourier pulse shaping. The entire system consists of three building blocks, responsible for seed generation, optical parametric chirped pulse amplification (OPCPA), and nonlinear compression. A commercial Yb:KGW amplifier pumps a difference frequency generator and an optical parametric amplifier (OPA) to generate 1 kHz, 44 fs, 10 μJ, carrier-envelope phase stable seed pulses at 1.55 μm. A grating–lens pair stretches the seed pulses to 50 ps by introducing a great amount of normal group delay dispersion (GDD). After that, the chirped pulse energy is boosted to 5 mJ by two OPA stages pumped by a commercial Nd:YAG amplifier (30 mJ, 85 ps). To compress the amplified pulses, a grating pair compressor providing an adequate amount of anomalous GDD is employed. The OPCPA system eventually delivers 3 mJ and 80 fs pulses, limited by the phase-matching bandwidth of nonlinear crystals. To further compress the pulse duration, pulses are sent to an MPC stage, which consisted of nine pieces of 200-μm-thick quartz plates. The OPCPA output spectrum is broadened by four times and compressed to 20 fs (3.6 carrier cycles) by a femtosecond Fourier-transform pulse shaper. The pulses are characterized by polarization gating cross-correlation frequency-resolved optical gating. Due to the high pondermotive force, an intense and long-wavelength laser system like this is useful in seeding a MeV-level electron accelerator and generating coherent soft X-ray high-harmonic generation. [ABSTRACT FROM AUTHOR]

A commercial silicon p-i-n (Si-PIN) photodetector is proposed for electronic personal dosimeters (EPDs) for the sake of the detection of low-energy X-rays and/or $\gamma $ -rays. Since the EPD is a portable device supplied with a battery, front-end electronics with small size and low power dissipation are required. This paper presents a fully-customized low-power front-end readout application-specific integrated circuit (ASIC) as a solution for this application. The ASIC includes four-channel analog front-ends with a digital interface. Each channel mainly includes a charge sensitive amplifier (CSA), a CR–RC4 pulse shaper, an output buffer, a discriminator, and a digital-to-analog converter (DAC). An $I^{2}C$ interface and shift registers are designed to control the analog blocks. The modeling of equivalent noise charge (ENC) is discussed to optimize the circuit design. A prototype ASIC is designed in 0.35- $\mu \text{m}$ CMOS mixed-signal 3.3 V process. The die size is 2.4 mm $\times2.4$ mm. The preliminary test results are obtained. The input charge is 0.2–15 fC. The ENC is 119 e−+15.9 e−/pF under the power dissipation of about 1.25 mW/channel. The proposed ASIC can well meet the requirements of the EPD and other radiation detector systems. [ABSTRACT FROM AUTHOR]

The radiation intensity of observed auroras in the far-ultraviolet (FUV) band varies dramatically with location for aerospace applications, requiring a photon counting imaging apparatus with a wide dynamic range. However, combining high spatial resolution imaging with high event rates is technically challenging. We developed an FUV photon counting imaging system for aurora observation. Our system mainly consists of a microchannel plate (MCP) stack readout using a wedge strip anode (WSA) with charge induction and high-speed electronics, such as a charge sensitive amplifier (CSA) and pulse shaper. Moreover, we constructed an anode readout model and a time response model for readout circuits to investigate the counting error in high counting rate applications. This system supports global rates of 500 kilo counts, 0.610 dark counts s−1 cm−2 at an ambient temperature of 300 K and 111 µm spatial resolution at 400 kilo counts s−1 (kcps). We demonstrate an obvious photon count loss at incident intensities close to the counting capacity of the system. To preserve image quality, the response time should be improved and some noise performance may be sacrificed. Finally, we also describe the correlation between counting rate and imaging resolution, which further guides the design of space observation instruments.

A comprehensive experimental investigation was performed to study the dynamic compressive constitutive response of novel auxetic Kevlar®/epoxy laminated composites. Strain rate response was investigated using the split Hopkinson pressure bar (SHPB) test setup. Laminated composites were fabricated using the vacuum infusion process. Short Nylon fibers were flocked between the laminates with different flock densities and flock length. For obtaining dynamic force equilibrium in SHPB experiments, a copper pulse shaper was used to increase the rising time of incident pulse. To have a comparison, woven Kevlar®/epoxy composites were also characterized at similar strain rates. In addition, quasi-static tests were also performed on both woven and auxetic laminated composites for completeness of the study. For quasi-static loading conditions, auxetic composites showed higher peak strain and lower peak stress compared to woven composites. For non-flocked composites, both auxetic and woven composites showed rate dependency. Woven composites provided 353% increase in peak stress when the strain rate increased from 1200 s −1 (low) to 3300 s −1 (high). However, in the same conditions, auxetic composites showed only 155% increase in peak stress. For different flocking conditions, woven composites showed rate dependency for all strain rates, but auxetic composites demonstrated rate dependency only from low to medium strain rates. Both auxetic and woven composites experienced shear failure under quasi-static compression, where auxetic composites failed at higher shear angle of 37°, but woven composites had a failure angle of 30°. For impact loads, under no flocking condition, woven composites did undergo severe edge failure at all strain rates, but auxetic composites showed a sign of edge failure only at high strain rates. With the flocking condition, auxetic composites had through thickness shear failure and woven composites experienced splitting and fibrillation of Kevlar® fibers. [ABSTRACT FROM AUTHOR]

In this paper, we report the recent development of a low-noise front-end readout application-specified integrated circuit (ASIC) for cadmium–zinc–telluride (CZT) and Si-p-i-n detectors. The readout chain consists of a charge sensitive amplifier, a CR–RC pulse shaper followed by a Sallen–Key low-pass filter, readout buffers, and a discriminator. The layout using deep n-well (DNW) is adopted to optimize the noise performance. A prototype ASIC is implemented in TSMC CMOS 0.18- \mu \textm , 1.8 V/3.3 V mixed-signal technology. The die size of the prototype chip is 2.1 mm $\times$ 2.5 mm. At room temperature, the equivalent noise charge of the front-end readout channel using DNW implementation is 112 e− (rms) + 17 e− pF at the power consumption of less than 2 mW/channel. The linearity error is less than 3%. By connecting the readout ASIC to a CZT detector, we obtained that the energy resolutions of a $\gamma$ -ray spectrum are 3.9% and 5.5% (full-width at half-maximum), respectively, at the 59.5-keV line of 241Am source. The ASIC is a good solution of front-end electronics for personal dosimeters. [ABSTRACT FROM PUBLISHER]

This research investigates the effect of pulse shaper, lateral inertia and friction on the strain-rate sensitivity of ultra-high-performance fiber-reinforced concrete (UHP-FRC) using a split Hopkinson pressure bar (SHPB) by finite-element analysis. Assigned material parameters of UHP-FRC are provided by calibrating concrete material characteristics given in commercially available software. Following the material model calibration, a parametric study on the design of pulse shaper is carried out to satisfy the requirements of SHPB testing. Material confinement effects, including inertia effect and friction effect, are isolated from the strain-rate sensitivity of UHP-FRC under compressive impact loading. Numerical simulation results show that (1) the calibrated KCC model can well-predict the experimentally behavior of UHP-FRC; (2) an aluminum 6061-T6 disc with 1.8-mm thickness and 8-mm diameter is an ideal pulse shaper for SHPB testing of UHP-FRC at 20 m=s impact velocity; (3) at an impact velocity of 20 m=s, the dynamic impact factor (DIF) due to lateral inertia confinement reaches 1.06, and the DIF due to combined lateral inertia and friction increases from 1.06 to 1.18 with the friction coefficient increasing from 0 to 0.2. [ABSTRACT FROM AUTHOR]

Dynamic behavior of concrete specimens is investigated experimentally and numerically by split Hopkinson pressure bar (SHPB) tests. In order to accurately determine dynamic properties of brittle materials such as concrete, specimens should be subjected to particular pulse loading that can be generated by using pulse shapers. Choosing proper pulse shaper dimensions helps to obtain dynamic stress equilibrium, achieve constant strain rate and minimize pulse oscillation in the concrete specimens. To this end, SHPB tests are performed for concrete specimens and effective parameters on shaping pulses such as striker bar velocity, diameter and thickness of the pulse shaper are studied experimentally and numerically. In this regard, dynamic compressive strength, modulus of elasticity, toughness and damage behavior of the concrete specimens are calculated incorrectly if improper pulse shaper is used. Numerical results validated by the experimental data are used to provide general guidelines to properly choose dimensions of the pulse shapers for the concrete specimens in the SHPB test. Results show that use of a relatively small diameter and thick pulse shaper is suggested as a proper one for testing concrete specimens. Based on the findings of this research, if a proper pulse shaper is available for testing the concrete specimen in a specified strain rate, for other strain rates the cross sectional area as well as thickness of the pulse shaper should be changed proportional to the striker bar velocity that is related to the strain rate in the specimen. [ABSTRACT FROM AUTHOR]

The dynamic compressive behavior of ice is investigated using a large-sized (37 mm in diameter) modified aluminum split Hopkinson pressure bar (SHPB) with pulse shaper at the strain rate from 500 s-1 to 1200 s-1. A series of relatively stable experimental results of dynamic compressive strength versus strain rate and a linear fitting curve have been obtained by controlling data scatter within 25%. The composition of incident wave has been discussed. The effects of pulse shaper diameter and velocity of striker bar have been tested. The properties and principles of incident wave in different stage has been elaborated when using pulse shaper. A theoretical analysis of pulse shaper and bar size effects on the rising time of incident wave has been conducted. Results show the thickness of pulse shaper is proportional to the rising time. Enlarging the diameter and reducing the velocity of the striker bar could increase the rising time and suppress the dispersion. The diameter and wave impedance of bars also contribute to the rising time. [ABSTRACT FROM AUTHOR]

We present a combined experimental and numerical study on the strain rate effect of closed-cell Al-Si-Ti foams having different relative densities fabricated using the powder metallurgy foaming technique. The high strain rate tests were conducted with split Hopkinson pressure bar technique at 800 to 2500 s−1. Two-dimensional mesoscale finite element models were created from tomographic images of the homologous foam. The rate sensitivity of the foam originates mainly from that of its parent material, increasing with increasing relative density. Stress elevation due to other effects, such as micro-inertia, shock wave, and gas pressure in individual cells, is negligible. [ABSTRACT FROM PUBLISHER]

We describe a pulse shaper based on a combination of a 4f-line and a digital light processor (DLP) system composed by independently addressable micro-mirrors. The DLP system allows to control the spectrum of a femtosecond laser with a high resolution up to 30 GHz. Experimental results are in excellent agreement with the theory describing the spectral characteristics of the pulse shaper and they are recently used to cool the vibration and the rotation of cesium molecules. [ABSTRACT FROM AUTHOR]

Pulse shapers are commonly used in SHPB (Split Hopkinson Pressure Bar) to extend the initial rise time and the duration of the incident pulse to achieve an early uniformity of the internal stress and a constant strain rate loading within the specimen. In this study, a method for optimal design of a pulse shaper for polymeric SHPB system in testing soft materials is proposed based on wave propagation analysis. Firstly, an inverse parametric identification technology is used to obtain the constitutive parameters of PMMA and the RTV630 silicone rubber to be tested, respectively. Then, the optimal incident waveform for testing viscoelastic specimen is determined. Finally, taking the WSXJ-208 silicone rubber under impact using polymeric SHPB as an example, by comparing the incident wave gotten from the numerical simulation and the optimal incident waveform considering the dispersion and attenuation effects of wave propagating in polymeric bars, an optimal shaper geometry is obtained, and showing an obvious modification in the waveform so as to get more accurate and reliable results. [ABSTRACT FROM AUTHOR]

Generally, optimum dimensions of a pulse shaper (PS) in SHPB tests on brittle materials like rock are chosen by performing numerous experiments with different sizes of PS. The dimensions that give the best force equilibrium and constant strain rate loading in the specimen are selected. Experimental efforts can be saved if the constitutive behavior of the PS can be simulated numerically. In the current work, the behavior of pure copper is investigated at various strain rates (up to ∼4000 /s) and temperatures (till 250 °C) in as-received and annealed conditions. The mechanical behavior of copper is assessed in terms of strain hardening rate, strain rate sensitivity, and temperature sensitivity. It is found that the strain hardening rate in annealed samples is almost twice that of as-received ones. A strain rate increase strengthens copper while a temperature rise weakens it. Fractographs of quasi-static samples tested at various temperatures indicate that all samples undergo ductile failure. The experimental data is used to derive constitutive parameters of the Johnson-Cook (JC) model using a multi-objective optimization method. It is concluded that the modified JC model fits better than the original form, as substantiated by higher R 2 and lower AARE (average absolute relative error) values. The derived parameters are successfully applied to model the dynamic behavior of the copper PS in SHPB tests on Kota sandstone samples. It is observed that the experimental and numerical incident pulses are qualitatively similar, and the Russell comprehensive error is well within 0.15 for all the cases. It is concluded that investigating copper behavior till ∼4000 /s yields sufficiently accurate results to predict PS behavior during SHPB tests, although the actual strain rates experienced by the pulse shapers are higher. A sensitivity and probabilistic analysis are carried out to understand the effect of parameters variations on the incident rise time. [Display omitted] • Experimental efforts put for optimizing pulse shaper dimensions to test brittle materials like rock in SHPB are reduced. • Pure copper in as-received and annealed state characterized at different strain rates and elevated temperatures. • Constitutive parameters of copper derived for the original and modified Johnson-Cook model forms. • Model parameters successfully applied to predict dynamic behavior of copper pulse shaper in SHPB tests on Kota sandstone. [ABSTRACT FROM AUTHOR]

The goal of this study is to design a novel annular pulse shaping technique for large-diameter Kolsky bars for investigating the dynamic compressive response of concretes. The purpose of implementing an annular pulse shaper design is to alleviate inertia-induced stresses in the pulse shaper material that would otherwise superpose unwanted oscillations on the incident wave. This newly developed pulse shaping technique led to well-controlled testing conditions enabling dynamic stress equilibrium, uniform deformation, and constant strain-rate in the testing of a chosen concrete material. The observed dynamic deformation rate of the concrete is highly consistent (8 % variation) with the stress in the specimen well equilibrated confirming the validity of this new technique. Experimental results at both quasi-static (10 s) and dynamic (100 s, 240 s) strain rates showed that the failure strength of this concrete is rate-sensitive. [ABSTRACT FROM AUTHOR]

An erbium fiber oscillator with dominating gain fiber length and an intracavity pulse shaper is experimentally demonstrated. The Kerr nonlinear phase shift induced in the fibers is suppressed by the pulse shaper, enabling high-energy (8.9 nJ) high-compression efficiency (93%) pulses of less than 270 fs duration (after linear dechirping) at modest (320 mW) pump power. A stably mode-locked spectrum corresponding to 19 nJ, 83 fs transform-limited pulse is achieved at 720 mW pump power. Wave-breaking-free pulse energy can be further enhanced by introducing stronger spectral phase modulation via the pulse shaper if more pump budget is available. We also demonstrate manipulation of the central wavelength and bandwidth of the output pulse by intracavity spectral amplitude modulation via the pulse shaper. [ABSTRACT FROM PUBLISHER]

A low-power analog front-end circuit for silicon (Si) detectors has been fabricated in 0.35- μm CMOS technology. It has been designed to readout signals from large-capacitance Si detectors for incident electron energy ranging from 50 to 725 keV. In order to quantify electron energy, the front-end integrates a charge preamplifier, a pulse shaper, a peak detector, and an event-driven analog-to-digital converter (ADC). The complete front end, including the ADC dissipates 2.5 mW for a maximum electron detecting rate of 650 kHz. The charge-to-voltage gain is 60 mV/fC for a charge range of 0.6 to 32 fF. The measured equivalent noise charge is 3119 e- for a 40-pF detector parasitic capacitance. [ABSTRACT FROM PUBLISHER]