Magnetic Shielding of an Adiabatic Demagnetization Refrigerator for TES Microcalorimeter Operation

We are developing a compact adiabatic demagnetization refrigerator (ADR) dedicated for TES X-ray microcalorimeter operation. Ferric ammonium alum (FAA) was grown in a stainless-steel container in our laboratory. This salt pill was mounted together with a superconducting magnet and a conventional mechanical heat-switch in a dedicated helium cryostat. Using this system, we achieved \({<}40\)  mK and a hold time of \({>}20\) h below 100 mK. Initially, we used a 3 mm thick silicon steel shield around the ADR magnet and a Nb/Cryoperm double shield around the detector. However, this silicon steel shield allowed a \({\sim }50\)  mT field at the detector position when a full field (3 T) was applied, and caused the Nb shield around the detector to trap a magnetic field. The observed transition curve of a TES was broad ( \({\sim }20\)  mK) compared to \({\sim }4\)  mK obtained in a dilution refrigerator. By increasing the shield thickness to 12 mm, transition width was improved to \({\sim }4\)  mK, which suggests that the shields work as expected. When we operated a TES microcalorimeter, energy resolution was \(14.5\pm 0.7\)  eV (FWHM) at 5.9 keV.     

Investigation of Magnetic Memory Signals Induced by Dynamic Bending Load in Fatigue Crack Propagation Process of Structural Steel

Metal magnetic memory effect, induced by applied stress under the excitation of the geomagnetic field, has attracted a lot of attentions due to its unique advantages of stress concentration identification and early damage detection for ferromagnetic materials. To further investigate the regularity of magnetic memory signals in the fatigue crack propagation process under the dynamic bending load, the surface magnetic field intensity \(H_{p}(y)\) of ferromagnetic structural steel was measured throughout the dynamic three-point bending fatigue tests; variation of \(H_{p}(y)\) and its maximum gradient \(K_{max}\) were studied; meanwhile the possibility of using \(K_{max}\) to predict the fatigue crack propagation was discussed. The results showed that \(H_{p}(y)\) was relatively stable at different loading cycles and its maximum value appeared at the fatigue crack area before the specimen fractured; instead the \(K_{max}\) increased exponentially with the increase of loading cycles, and an approximate linear relationship was found between \(K_{max}\) and crack length 2a. The cause for this phenomenon was also discussed.     

Effect of rolling deformation and solution treatment on microstructure and mechanical properties of a cast duplex stainless steel

The present study deals with the effect of rolling deformation and solution treatment on the microstructure and mechanical properties of a cast duplex stainless steel. Cast steel reveals acicular/Widmanst?tten morphology as well as island of austenite within the $\boldsymbol\delta $ -ferrite matrix. Hot rolled samples exhibit the presence of lower volume percent of elongated band of $\boldsymbol\delta $ -ferrite ( $\boldsymbol\sim $ 40%) and austenite phase which convert into finer and fragmented microstructural constituents after 30% cold deformation. By the solution treatment, the elongated and broken crystalline grains recrystallize which leads to the formation of finer grains (<10? $\boldsymbol\mu $ m) of austenite. X-ray diffraction analysis has corroborated well with the above-mentioned microstructural investigation. Enhancement in hardness, yield strength and tensile strength values as well as drop in percent elongation with cold deformation increases its suitability for use in thinner sections. 30% cold rolled and solution treated sample reveals attractive combination of strength and ductility (25·22?GPa%). The examination of fracture surface also substantiates the tensile results. The sub-surface micrographs provide the potential sites for initiation of microvoids.     

Characterization of Silicon Wafers with Combined Photocarrier Radiometry and Free Carrier Absorption

A combined photocarrier radiometry (PCR) and free carrier absorption (FCA) technique was employed to evaluate the electronic transport properties (carrier lifetime $\tau $ , diffusion coefficient $D$ , and the front surface recombination velocity $S_{1})$ of silicon wafers and to monitor the ion implantation and thermal annealing processes in the semiconductor manufacturing. For non-implanted silicon wafers, the experimental results showed that the accuracy of the simultaneous determination of the transport properties was greatly improved by fitting simultaneously the measured PCR and FCA signals to the theoretical models via a multi-parameter fitting procedure. For As $^+$ ion implanted and thermal annealed silicon wafers, the results showed that both PCR and FCA amplitudes increased monotonically with the increasing implantation dose ( $5\times 10^{11}$ cm $^{-2 }$ to $1\times 10^{16 }$ cm $^{-2})$ , the decreasing implantation energy (20 keV to 140 keV), and the increasing annealing temperature (500 $^{\circ }$ C to 1000 $^{\circ }$ C), respectively. To explain the dependences of the PCR signals on the implantation and annealing parameters, a multi-wavelength PCR technique was proposed to extract the electronic transport properties of the implanted and annealed wafers. The results showed that ion implantation and thermal annealing caused significant decreases of the minority carrier lifetime and diffusion coefficient of the implantation layer, as well as the recombination velocity at the front surface. All three parameters decreased with the increasing implantation dose.     

Simulation of mixed-mode I/III stable tearing crack growth events using the cohesive zone model approach

A cohesive zone model (CZM) approach is applied to simulate mixed-mode I/III stable tearing crack growth events in specimens made of 6061-T6 aluminum alloy and GM 6208 steel. The materials are treated as elastic–plastic following the \(J_{2}\) flow theory of plasticity, and the triangular cohesive law is employed to describe the traction-separation relation in the cohesive zone ahead of crack front. A hybrid numerical/experimental approach is employed in simulations using 3D finite element method. For each material, CZM parameter values are chosen by matching simulation prediction with experimental measurement (Yan et al. in Int J Fract 144:297–321, 2009), of the crack extension-time curve for the \(30^{\circ }\) mixed-mode I/III stable tearing crack growth test. With the same sets of CZM parameter values, simulations are performed for the \(60^{\circ }\) loading cases. Good agreements are reached between simulation predictions of the crack extension-time curve and experimental results. The variations of CTOD with crack extension are calculated from CZM simulations under both \(30^{\circ }\) and \(60^{\circ }\) mixed-mode I/III conditions for the aluminum alloy and steel respectively. The predictions agree well with experimental measurements (Yan et al. in Int J Fract 144:297–321, 2009). The findings of the current study demonstrate the applicability of the CZM approach in mixed-mode I/III stable tearing simulations and reaffirm the connection between CTOD and CZM based simulation approaches shown previously for mixed-mode I/II crack growth events.     

Stimulated acoustic emissions from coupled strings

We consider traveling transverse waves on two identical uniform taut strings that are elastically coupled through springs that gradually decrease their stiffness over a region of finite length. The wave system can be decomposed into two modes: an in-phase mode ( $+$ ) that is transparent to the coupling springs, and an out-of-phase mode ( $-$ ) that engages the coupling springs and can resonate at a particular location depending on the excitation frequency. The system exhibits linear mode conversion whereby an incoming ( $+$ ) wave is reflected back from the resonance location both as a propagating ( $+$ ) wave and an evanescent ( $-$ ) wave, while both types emerge as propagating forward through the resonance location. We match a local transition layer expansion to the WKB expansion to obtain estimates of the reflection and transmission coefficients. The reflected waves may be an analog for stimulated emissions from the ear.     

A second-order two-scale homogenization procedure using C^{1} macrolevel discretization

The present study deals with a second-order two-scale computational homogenization procedure for modeling deformation responses of heterogeneous materials at small strains. The macro to micro transition and the application of generalized periodic boundary conditions on the representative volume element (RVE) at the microlevel are investigated. The structure at macroscale level is discretized by the \(C^{1}\) two dimensional triangular finite elements, while the \(C^{0}\) quadrilateral finite element is used for the discretization of the RVE. The finite element formulations and the new proposed multiscale scheme have been implemented into the finite element software ABAQUS using user subroutines derived. Due to the \(C^{1}-C^{0}\) continuity transition, an additional integral condition on microlevel fluctuation field has to be imposed, as expected. The integration has been performed using various numerical integration techniques and the results obtained are compared in a few examples. It is concluded that only trapezoidal rule gives a physically based deformed shape of the RVE. Finally, the efficiency and accuracy of the proposed multiscale homogenization approach are demonstrated by the modeling of a shear layer problem, usually used as a benchmark in multiscale analyses.     

Evolution of a martensitic structure in a Cu–Al alloy during processing by high-pressure torsion

A Cu-11.8 wt% Al alloy was quenched in iced water from a high temperature (850 °C) to introduce a martensitic phase and then the alloy was processed using quasi-constrained high-pressure torsion (HPT). The micro-hardness and the microstructures of the unprocessed and severely deformed materials were investigated using a wide range of experimental techniques (X-ray diffraction, optical microscopy, scanning electron microscopy, transmission electron microscopy, and high- resolution TEM). During HPT, a stress-induced martensite–martensite transformation occurs and an $ \alpha^{\prime}_{1} $ martensite phase is formed. In the deformed material, there are nanoscale deformation bands having high densities of defects and twins in the $ \alpha^{\prime}_{1} $ martensite. It was observed that a high density of dislocations became pinned and accumulated in the vicinity of twin boundaries, thereby demonstrating a strong interaction between twin boundaries and dislocations during the HPT process.     

Study on Optical Filter Heating in Background Limited Detector Experiments

Cryogenic test setups with controlled stray light environments capable of reaching ultra-low radiative background levels are required to test far infrared (FIR) and submillimeter (sub-mm) wave radiation detectors for future space based observatories. In recent experiments (Nature Commun 5:3130, 2014), in which 1.54 THz radiation was coupled onto an antenna-coupled kinetic inductance detector (KID), we found a higher than expected optical loading. We show that this can be explained by assuming heating of the metal mesh IR filters and re-radiation onto the KID. Note that the total power from the cryogenic black body source used in the experiments (at T = \(3\) – \(25\) K) is much larger than the power inside the \(1.5\) – \(1.6\) THz band we use to calibrate our detector. The out-of-band radiation can have up to 5 orders of magnitude more power than inside the \(1.5\) – \(1.6\)  THz band of interest. A strategy to mitigate the filter heating problem is presented, and when it is implemented, the validated upper limit for stray light at the detector level is down to few aW.     

Parameter Design of Linear Frequency Modulated Excitation Waveform for Ultrasonic Nondestructive Testing of Metallic Materials

Linear frequency modulated (LFM) pulses are used as excitation sources for the ultrasonic nondestructive testing of metallic materials. The detection resolution relies on both the bandwidth of the LFM pulse and the amplitude spectrum of the transducer. A bandwidth selection method to analyze the effect of the LFM bandwidth on the inspection results was proposed, as well as to select an optimized LFM bandwidth corresponding to different transducers. Meanwhile, an ultrasonic through- transmission technique to test four different pairs of transducers excited by LFM signals with different bandwidth was used. Experimental results show that the time resolution significantly improves with an increase in the LFM bandwidth. Optimum parameter is achieved when the LFM bandwidth is close to the \(-\) 12 dB bandwidth \(B_{-12\hbox {dB}}\) of the transducer, and it then remains roughly stationary. The results were confirmed by carrying out ultrasonic LFM time-of flight diffraction (LFM-TOFD) testing for a steel plate with three buried defects employing a pair of 10 MHz transducers. The waveforms of the echoes extracted from these defects become narrower with an increase in the exciting bandwidth. In addition, the diffracted waves from the upper and lower tips of the 2 mm defect can be distinguished when the LFM bandwidth is close to the \(-\) 12 dB bandwidth of the 10 MHz transducer. The proposed bandwidth selection method can enhance the efficiency and precision of the actual ultrasonic LFM detection and is suitable for different ultrasonic testing systems, transducers and inspection requirements.     

Density dependent macro-micro behavior of granular materials in general triaxial loading for varying intermediate principal stress using DEM

This study presents the density dependent behavior of granular materials for varying intermediate principal stress $(\sigma _{{{2}}})$ ( σ 2 ) in general triaxial loading using the discrete element method (DEM). The variation of intermediate principal stress is represented by a non-dimensional parameter $b[={(\sigma _{{{2}}}-\sigma _{{{3}}})}/{(\sigma _{{{1}}} -\sigma _{{{3}}})}]$ b [ = ( σ 2 ? σ 3 ) / ( σ 1 ? σ 3 ) ] , where $\sigma _{{{1}}}$ σ 1 and $\sigma _{{{3}}}$ σ 3 are the major and minor principal stresses, respectively. Isotropically compressed dense and loose samples were prepared numerically using the periodic boundaries. The numerical dense and loose samples were subjected to shear deformation under strain controlled condition for different $b$ b values ranging from 0 to 1. The simulated macro results depict that the friction angle increases with $b$ b until it reaches a peak value and beyond the peak, the friction angle decreases with $b$ b regardless of the density of sample. A unique relationship between dilatancy index and equivalent deviatoric strain exists at small strain level for different $b$ b values when dense sample is considered. By contrast, the same relationship for loose sample does not show uniqueness. The relationships among the major, intermediate and minor principal strains depict non-linear behavior. The non-linearity is dominant for loose sample. The fluctuation in the evolution of strain increment vector direction is dominant in loose sample than dense sample. The evolution of different micro results is presented as well. It is noted that a unique relationship exists between the stress ratio and the fabric measure regardless of $b$ b and the density of sample when strong contacts are considered.     

Influence of Grain Size on the Propagation of L_\mathrm{CR} Waves in Low Carbon Steel

The acoustoelastic theory states that mechanical stress relates to the wave speed. The microstructure of the materials influences the propagation of any ultrasonic wave, which is a major drawback in employing critically refracted longitudinal waves (L \(_\mathrm{CR}\) ) in field measurements. The present study investigates the effect of mean austenitic grain size (MAGS) on propagation speed of L \(_\mathrm{CR}\) waves in ASTM A36 low carbon hot-rolled steel plates subjected to different heat treatment temperatures. The samples were heated at 900, 1000, 1050, 1100, 1200  \(^{\circ }\) C for 30 min to obtain different grain sizes. They were measured as received and after the heat treatment, employing the ultrasonic method. The MAGS were compared to the grain size obtained from optical microscopy. The results confirmed the influence of the MAGS on the L \(_\mathrm{CR}\) speed, which can be represented by a second order polynomial curve. From the experimental results, we show that it is necessary to correct the effect of the MAGS on the L \(_\mathrm{CR}\) speed; otherwise we cannot measure the stresses without previous calibration using a stress reference.     

Contact models based on experimental characterization of irregular shaped,micrometer-sized particles

The goal of this study is to investigate experimentally the mechanical contact properties of fine particles ( \(<\) 120  \(\upmu \) m) using of a novel experimental setup. On the basis of deformation curves from compression tests, particle behaviour under mechanical stress can be approximated with theoretical contact models. Models examined in this study include Walton and Braun, Tomas and Antonyuk, Zener and Thornton. Influence of climatic conditions on particle behaviour as well as hardening effects related to cyclic loading were also considered. Maltodextrin was used as a model substance for primary particles, while irregular shaped titanium dioxide granules were used to study the behaviour of agglomerates. In both cases, results are in good agreement with the established theories.     

Characterization of crack tip stress fields in test specimens using mode mixity parameters

The aim of this study is to represent the combined effect of mode mixity, specimen geometry and relative crack length on the $T$ -stress, elastic–plastic stress fields, integration constant $I_{n}$ , angle of initial crack extension, and the plastic stress intensity factor. The analytical and numerical results are obtained for the complete range of mixed modes of loading between mode I and mode II. For comparison purposes, the reference fields for plane mixed-mode problems governing the asymptotic behavior of the stresses and strains at the crack tip are developed in a power law elastic–plastic material. For the common experimental fracture mechanics specimen geometries considered, the numerical constant of the plastic stress field $I_{n}$ and the $T$ -stress distributions are obtained as a function of the dimensionless crack length and mode mixity. A method is also suggested for calculating the plastic stress intensity factor for any mixed-mode I/II loading based on the $T$ -stress and power law solutions. It is further demonstrated that in both plane stress and the plane strain, the plastic stress intensity factor can be used to characterize the crack tip stress fields for a variety of specimen geometries and different mixed-mode loading. The applicability of the plastic stress intensity factor to analysis of the in-plane and out-of-plane constraint effect is also discussed.     

Accurate loading analyses of curved cracks under mixed-mode conditions applying the J-integral

In linear elastic fracture mechanics the path-independent J-integral is a loading quantity equivalent to stress intensity factors (SIF) or the energy release rate. Concerning plane crack problems, $J_k$ J k is a 2-dimensional vector with its components $J_1$ J 1 and $J_2$ J 2 . These two parameters can be related to the mode-I and mode-II SIFs $K_{\mathrm{I}}$ K I and $K_{\mathrm{II}}$ K II . To guarantee path-independence for curved crack geometries, an integration path along the crack faces must be considered. This paper deals with problems occurring at the numerical calculation of the J-integral in connection with the FE-method. Two new methods for accurately calculating values of $J_2$ J 2 for arbitrary cracks are presented.     

DEM analysis of the influence of the intermediate stress ratio on the critical-state behaviour of granular materials

The critical-state response of granular assemblies composed of elastic spheres under generalised three-dimensional loading conditions was investigated using the discrete element method (DEM). Simulations were performed with a simplified Hertz–Mindlin contact model using a modified version of the LAMMPS code. Initially isotropic samples were subjected to three-dimensional stress paths controlled by the intermediate stress ratio, \(b=[(\sigma '_{2}-\sigma '_{3})/\) \((\sigma '_{1}-\sigma '_{3})]\) . Three types of simulation were performed: drained (with \(b\) -value specified), constant volume and constant mean effective stress. In contrast to previous DEM observations, the position of the critical state line is shown to depend on \(b\) . The data also show that, upon shearing, the dilatancy post-peak increases with increasing \(b\) , so that at a given mean effective stress, the void ratio at the critical state increases systematically with \(b\) . Four commonly-used three-dimensional failure criteria are shown to give a better match to the simulation data at the critical state than at the peak state. While the void ratio at critical state is shown to vary with \(b\) , the coordination number showed no dependency on \(b\) . The variation in critical state void ratios at the same \(p'\) value is apparently related to the directional fabric anisotropy which is clearly sensitive to \(b\) .     

Nonlinear grain–grain forces and the width of the solitary wave in granular chains: a numerical study

Any impulse results in the formation of a solitary wave of time averaged width $W$ in a granular chain. If the grain–grain interaction potential $V\sim \delta ^n$ , where $\delta $ is the distance by which the grains approach each other, then it is well established that $n\ge 2$ . Here we present dynamical simulation based results which suggest that $W-1\propto (n-2)^{-\alpha }$ where $\alpha =0.3283$ or $\approx $ 1/3. While in qualitative agreement, the result is quantitatively different from the formula for $W$ proposed earlier by Nesterenko.     

Generalized fracture mechanics of ductile steels

The generalized fracture mechanics approach is applied to two ductile steels, namely mild steel and 18/8 stainless steel in plane stress. The theory defines a fracture parameter \(\mathcal{T}\) , which is a truly plastic analogue of theJ contour integral and, for an edge crack specimen, is given by $$\mathcal{T} = k_1 ( \in _0 )cW_{0_c } $$ wherek ₁ is an explicit function,c is the crack length andε ₀, W_0c are respectively the strain and input energy density at fracture, remote from the crack. The functionk ₁(ε _o) is derived experimentally and the constancy of \(\mathcal{T}\) with respect to crack length and applied load is demonstrated. The variation of \(\mathcal{T}\) with crack extension during slow growth is investigated, as is the rate dependence of \(\mathcal{T}\) in mild steel.     

Preliminary Results of the MARE Experiment

The microcalorimeter array for a rhenium experiment (MARE) project aims at the direct and calorimetric measurement of the electron neutrino mass with sub-eV sensitivity. The design is based on large arrays of thermal detectors to study the beta decay of \(^{187}\) Re and the electron capture of \(^{163}\) Ho. One of the activities of the project, MARE 1 in Milan, has started in Milan using one array of 6  \(\times \)  6 silicon implanted thermistors equipped with AgReO \(_4\) absorbers. The purposes of MARE 1 in Milan are to achieve a sensitivity on the neutrino mass of a few eV and to investigate the systematics of \(^{187}\) Re neutrino mass measurements, focusing on those caused by the beta environmental fine structure and the beta spectrum theoretical shape. In parallel, the MARE collaboration is performing an R&D work for producing absorbers embedded with radioactive metal \(^{163}\) Ho. We report here the status of MARE using Re as beta source and the preliminary results obtained with \(^{163}\) Ho.