•Tensile strength, shear strength, hardness and preload level of grade 10.9 stainless steel high-strength bolts were obtained and compared with requirements of the conventional grade 10.9 ...high-strength bolts.•Tightening tests on stainless steel bolts with lubricant were carried out.•The friction-reducing lubrication effect is related to lubricant type as well as the curing time of the lubricant.•The torque coefficient can be reduced to 0.080, with recommended lubricant and curing time, meeting the torque coefficient limit for high-strength bolts.
The lack of product specification of stainless steel high-strength bolts has restricted the application of high-strength bolts in stainless steel structures. Existing studies have found that stainless steel bolts experience thread galling during the tightening procedure, making it impossible to apply preload. Different studies have obtained different torque coefficient values. In this paper, a series of tests were carried out on two types of grade 10.9 stainless steel high-strength bolts and two types of ordinary stainless steel bolts, and the tensile strength, shear strength, hardness and preload level were obtained. The results show that the yield strength, tensile strength and elongation after break of the new stainless steel high-strength bolts can reach 1122 MPa, 1147 MPa and 16.3% respectively, proving that the grade 10.9 stainless steel high-strength bolts meet the requirements of the conventional grade 10.9 high-strength bolts. Tightening tests on stainless steel bolts with lubricant were carried out and it was found that the friction-reducing lubrication effect was related to the curing time of the lubricant. The lubricant Molykote D-321R Spray was found to be more effective in reducing friction and preventing thread galling in stainless steel bolts. With the optimum curing time at room temperature of 12 h, the lubricant can reduce the torque coefficient to about 0.080, meeting the torque coefficient limit for high-strength bolts. In the end, the preload level, torque coefficient and torque level for construction for stainless steel high-strength bolts are recommended for engineering applications.
Ce:Li6Lu1-xYx(BO3)3 (x = 0.08, 0.2, 0.4, 0.6, 0.8) mixed crystals were grown by Czochralski method to optimize the scintillation properties of lithium rare earth borate crystals for thermal neutron ...detection. The crystal structure of the mixed compounds belonged to the monoclinic system with space group P21/c. Their density decreased with the increasing yttrium content from 3.44 to 2.77 g/cm3. Their degree of supercooling ranges from 135.3 to 119.2°. The X-ray induced luminescence spectra present a double peaked emission bands with a maximum at 380 and 410 nm corresponding to 5d1 to 2F5/2 and 2F7/2 transitions of Ce3+ ions. The photoluminescence decay times are below 36 ns. Ce:Li6Lu0.8Y0.2(BO3)3 had the best light output under the excitation of α particles and γ rays, and from that point of view is the most promising lithium rare earth borate fast scintillator for thermal neutron detection.
•Ce:Li6Lu1-xYx(BO3)3 mixed crystals were grown by Czochralski method.•Ce:Li6Lu0.8Y0.2(BO3)3 crystal had the best transmittance.•The mixed crystals had a fast decay time of below 36 ns.•Ce:Li6Lu0.8Y0.2(BO3)3 crystal had the best light output.
Polymethyl methacrylate (PMMA) is increasingly used in building structures nowadays. PMMA materials utilized in structures have different fracture property compared with those used in aircrafts or ...biomedical equipment. Single-edge-notch bending (SENB) tests were firstly carried out at various temperatures (−40°C, −20°C, 0°C, 20°C, and 40°C) to determine the
K
IC
values of base PMMA materials and connected areas. The crack-resisting capacity of PMMA plate is subsequently studied. The fracture property of the PMMA joint for the Jiangmen Underground Neutrino Observatory (JUNO) central detector is investigated. The results show that base PMMA material has higher
K
IC
values than connected area. The
K
IC
of base PMMA material is lowest at 20°C and highest at −20°C, while that of connected area is lowest at 40°C and highest at −40°C. For the PMMA joint of the JUNO detector, the cracks perpendicular to the X axis are more disadvantageous than those perpendicular to the Z axis. The stress intensity factors (SIFs) at the crack front of the embedded crack decrease with the increase of embedded depth. Due to the presence of two parallel surface or embedded cracks, the SIFs at the crack front decrease.
Abstract
The Jiangmen Underground Neutrino Observation (JUNO) will build a polymethyl methacrylate (PMMA) spherical vessel of a diameter of 35.4 meters. The constitutive model of PMMA is a key ...parameter for the design of PMMA structure. The bulk polymerization bonding area is often the weak point of the PMMA structure, so it is useful to understand the constitutive model of bonding areas for FEA. However, the traditional contact strain measurement methods, such as the strain extensometer and resistance strain gauge, will have an impact on the strain of PMMA, as the lossy measurement. Traditional measuring methods also can’t measure the small-sized bonding areas as 3 mm in most structures. The non-contact strain measurement method based on the CCD camera is studied. The tensile test result shows that the influence of environment on the strain value is less than 0.01%. The two strain measurement methods, the CCD camera and strain extensometer, are compared. The strain curves obtained by the two methods are highly consistent, and the maximum strain difference is 8.53 e-4. The fracture strain of the PMMA tensile specimen is 4.32% and slight plastic deformation has occurred. The Zhu-Wang-Tang (ZWT) nonlinear viscoelastic constitutive model of PMMA is obtained by fitting the stress-strain data. The tensile test result of PMMA specimen with bulk polymerization bonding area shows that the constitutive equations are different when the length ratio of the bonding area is different. By analyzing the relationship between the length ratio and the coefficients of constitutive equation, the constitutive equation of the bonding area is finally obtained. The results show that the coefficient
E
0
of the constitutive equation of the bonding area is smaller than that of the mother material. The fracture strain of PMMA specimen with bonding area is 2.60%, lower than that of mother material, which makes the coefficient
β
of the bonding area constitutive equation opposite to the sign of the mother material. The tensile strength of specimen with bonding area is about 85.68% of that of the mother material. The lower tensile strength makes the bonding area become one of the weak points of the structure.
Pure aluminum oxide (Al
2
O
3
) and zinc aluminum oxide (Zn
x
Al
1-
x
O) thin films were deposited by atomic layer deposition (ALD). The microstructure and optical band gaps (
E
g
) of the Zn
x
Al
1-
...x
O (0.2 ≤
x
≤ 1) films were studied by X-ray diffractometer and Tauc method. The band offsets and alignment of atomic-layer-deposited Al
2
O
3
/Zn
0.8
Al
0.2
O heterojunction were investigated in detail using charge-corrected X-ray photoelectron spectroscopy. In this work, different methodologies were adopted to recover the actual position of the core levels in insulator materials which were easily affected by differential charging phenomena. Valence band offset (Δ
E
V
) and conduction band offset (Δ
E
C
) for the interface of the Al
2
O
3
/Zn
0.8
Al
0.2
O heterojunction have been constructed. An accurate value of Δ
E
V
= 0.82 ± 0.12 eV was obtained from various combinations of core levels of heterojunction with varied Al
2
O
3
thickness. Given the experimental
E
g
of 6.8 eV for Al
2
O
3
and 5.29 eV for Zn
0.8
Al
0.2
O, a type-I heterojunction with a Δ
E
C
of 0.69 ± 0.12 eV was found. The precise determination of the band alignment of Al
2
O
3
/Zn
0.8
Al
0.2
O heterojunction is of particular importance for gaining insight to the design of various electronic devices based on such heterointerface.
Abstract
Acrylic is a kind of polymer material and is gradually applied to load-bearing components. The working stress and ultimate bearing capacity of the acrylic structure are the main design ...indexes. Aiming at the world’s largest acrylic spherical vessel, the structural design, finite element analysis and full-size prototype tensile test of a new acrylic connection node were carried out in this paper. This acrylic node will bear 90 kN tension force for 20 years. According to the viscoelastic characteristics of the material and the working environment, the stress of acrylic should be controlled below 3.5 MPa for long term used. At the time, the ultimate bearing capacity should be greater than 6 times the working load. According to the stress-strain curve of acrylic, its tensile strength is about 75 MPa. There is no obvious plastic deformation after fracture, showing the material characteristics of brittle fracture. According to the failure analysis of previous acrylic node structures and the characteristics of acrylic, the new acrylic node structure is proposed in this paper. Its performance is improved by reducing the cutting amount of acrylic nodes, optimizing the structure of embedded part and avoiding sharp corners. A 1/4 symmetrical acrylic node model is established FEA software, and the nonlinear problems such as material nonlinearity and friction contact are solved by finite element method. The FEA results show that the maximum principal stress of the node is about 2.92 MPa. The relative error between the FEA results and the experimental results is 7.24%, indicating that the FEA results are credible. The ultimate tensile load of the node can reach 1000 kN, which is about 11 times the working load. The failure of the node occurs at a sharp corner of the groove, instead of the maximum stress point. Therefore, stress concentration caused by sharp corners should be avoided in the design of acrylic structure.
After the success of the Daya Bay experiment, the Jiangmen Underground Neutrino Observatory (JUNO) was launched to measure neutrino-mass hierarchy and oscillation parameters and to study other ...neutrino physics. Its central detector is set for antineutrinos from reactors, the Earth, the atmosphere, and the Sun. The main requirements of the central detector are containment of 20 kt of liquid scintillator, as the target mass, and 3% energy resolution. It is about a ball-shape detector of 38.5 m with ∼75% coverage of PMT on its inner surface. The design of such a huge detector is a big challenge because it must meet the requirements for several different types of physics measurement and possess the feasibility and reliability in its structure and engineering, all at reasonable time and cost. One option for the JUNO central detector is a hyper-scale acrylic ball submerged in the water to shield the background. This paper proposes a structural scheme for such an acrylic ball that is supported by a stainless-steel truss, inspired by point-supported glass-curtain walls in civil engineering. The preliminary design of the scheme is completed and verified by finite element (FE) method using ABAQUS. FE analysis shows that the scheme can control the stress level of the acrylic ball within the limit of 5 to 10 MPa, in accordance with the demand of the design objective of the central detector. The scheme is of outstanding global stability and allows various choices on local connections. We prove that the scheme is of good feasibility and should be a reasonable option for the central detector.
Li6Y(BO3)3:Ce crystal is a promising type of scintillator for neutron detection. In this study, the properties of Li6Y(BO3)3:3at%Ce are studied, including its γ sensitivity, neutron efficiency, α/γ ...ratio, relative light yield, neutron pulse-height spectrum and decay time. Geant4 simulations indicate that its capture efficiency for thermal neutrons is as high as 78% for the natural abundances of the boron and lithium elements. The α/γ ratio of Li6Y(BO3)3:Ce is measured to be 0.03, which is 10 times lower than that of lithium glass. If the per-MeV light yield of lithium glass is defined to be 100, then the light yields generated by Li6Y(BO3)3:Ce for γ rays and α particles are 253.3 and 24.8, respectively. Under γ-ray irradiation, the light yield of Li6Y(BO3)3:Ce is approximately 6 times lower than that of NaI:Tl. In neutron detection, the neutron signal can be clearly distinguished from the backgrounds caused by the 252Cf source itself. Li6Y(BO3)3:Ce is also a fast scintillator, with decay times of 48.6 ± 14.4ns, 24.6 ± 13.3ns and 37.8 ± 17.8ns under irradiation with γ rays, α particles and thermal neutrons, respectively. This study offers a systematic study of useful parameters of Li6Y(BO3)3:3at%Ce crystal for application in and the improvement of neutron detection.
•Responses to γ rays of Li6Y(BO3)3:Ce are studied by simulation and experiments.•Neutron capture efficiency of Li6Y(BO3)3:Ce is higher than lithium glass.•The light yields are studied by α and γ sources and the α/γ ratio is about 0.03.•Its decay time is around 24–48 ns under different kind sources irradiation.•The crystal can detect thermal neutrons by pulse height spectrum measurements.
The problems of the growth of Ce:Li6Lu(BO3)3 (LLBO) crystal using Czochralski technique have been discussed. The supercooling, cleavage crack and inversion of solid–liquid interface were the main ...problems to grow high quality LLBO single crystals with fully transparent ingot. The thermal expansion coefficients of LLBO crystal were obtained from HTXRD data: αa=23.9×10−6/°C, αb=27.8×10−6/°C and αc=9.3×10−6/°C. The LLBO crystal with thickness of 1mm grown from natural raw materials was sensitive to thermal neutrons and insensitive to high energy gamma rays (137Cs). The decay time was statistically recorded to be about 38ns by the digital oscilloscope. Therefore, LLBO crystal will be a promising fast scintillator for neutron detection.
•The problems during the crystal growth process of Ce:Li6Lu(BO3)3 crystal have been discussed.•The thermal expansion coefficients of Ce:Li6Lu(BO3)3 crystal are obtained from HTXRD data.•Very thin Ce:Li6Lu(BO3)3 crystal is sensitive to thermal neutrons and not sensitive to 137Cs gamma rays.•The decay time of Ce:Li6Lu(BO3)3 crystal is only about 40ns and it׳s a very fast scintillation crystal for neutron detection.
The central detector at the Jiangmen Underground Neutrino Observatory (JUNO) is a hybrid structure system consisting of an inner acrylic sphere and an outer stainless steel reticulated shell. The ...stress distributions of the acrylic joints must be accurately simulated to avoid “crazing”. To balance the accuracy and efficiency of the stress analysis, a multi-scale modeling method using mixed-dimensional coupling is proposed. A framework and a generalized procedure are developed to instruct the modeling and analysis. A multi-scale model consisting of a single refined acrylic joint and equipped with simplified joints is proposed and discussed. A comparison of the results using the multi-scale model with a cluster of 3 × 3 refined joints reveals that the difference is less than 5%, while the ratio of the computation resource cost and the time consumption is approximately only 1/7 and 1/5, respectively. The stress distributions of the acrylic joints in the central detector are obtained using the proposed multi-scale model.
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