Standard Bar Research Articles

Dynamic fracture toughness and crack propagation mechanism of a heterogeneous heterostructured material under combined strengthening mechanisms

Developing fracture-resistant high-strength steels is an attractive prospect for various structural applications. In this work, a combination of carburizing heat treatment (CHT) and shot peening (SP) was used to develop combined strengthening (CS) mechanisms and to improve the mechanical strength and dynamic fracture toughness of 18CrNiMo7-6 alloy steel. Standard tensile tests and split Hopkinson pressure bar tests were conducted to investigate the strength and dynamic fracture toughness of the 18CrNiMo7-6 alloy steel. The crack initiation and propagation of samples were studied using scanning electron microscopy and transmission electron microscopy. Microstructure characterization and molecular dynamic simulations indicated that the excellent dynamic fracture toughness of the CS samples could be attributed to the grain refinement after strengthening and the formation of numerous slip bands at the crack tips, reducing the stress concentration at the crack tips. The Cr23C6 precipitates have a positive effect on the strength improvement of 18CrNiMo7-6 alloy steel. The results showed that this research can be used to guide the design of steels with high-strength and high-dynamic fracture toughness.

On the dynamic shear failure of Ti-6Al-4V in different test specimen geometries

In this paper, the dynamic shear response and failure of Ti-6Al-4V using four different test specimen geometries, viz. Hat-Shaped Specimen (HSS), Flat Hat-Shaped Specimen (FHSS), Chip Hat-Shaped Specimen (CHSS) and Double Shear Specimen (DSS), are critically examined and compared. Through a combination of experiments (using the standard Split-Hopkinson Pressure Bar system), finite-element simulations and metallographic examinations of their fracture morphology, the dynamic shear characteristics (strain hardening, strain rate strengthening effect and failure strain) of Ti-6Al-4V obtained using the different specimen geometries are critically examined, compared and analyzed. It will be shown that differences in the stress/strain uniformity, the plastic deformation zone, and the stress state induced by the different specimen geometries lead to discrepancies in the measured shear response and failure that were observed. The shear stress–strain curve obtained using the DSS will be shown to be more precise than the other specimen geometries.

Narrow bandwidth spectral beam combining of cm bar in a short external resonator based on rhombic prism combinations

A novel narrow bandwidth spectral beam combining structure of cm bar with a short external resonator based on rhombic prism combinations is proposed and demonstrated. A pair of rhombic prism combinations are employed between the LDA and the transform lens in the external resonator, which consists of a rectangular quartz plate in the middle and two quartz rhombic prisms on either side in opposite orientations in each combination. The beam emitted from a standard cm bar is segmented and rearranged, and spectral beam combining is carried out along the slow axis. A spectral bandwidth of about 5.46 nm is obtained by employing a transform lens with a short focal length of 150 mm, which is only about 1/3 of that of the conventional spectral beam combining, and a narrow spectral bandwidth of 1.14 nm is obtained when a 5x de-magnifying telescope is employed in the above external resonator, the distance between LDA and diffraction grating is 500 mm while that between LDA and output coupler is 650 mm. This novel structure provides a compact external resonator scheme for narrow bandwidth spectral beam combining.

The Quick Determination of a Fibrous Composite’s Axial Young’s Modulus via the FEM

Knowing the mechanical properties of fiber-reinforced composite materials, which are currently widely used in various industrial branches, represents a major objective for designers. This happens when new materials are used that are not yet in production or for which the manufacturer cannot give values. Given the practical importance of this problem, several methods of determining these properties have been proposed, but most of them are laborious and require a long calculation time. And, some of the proposed calculation methods are very approximate, providing only upper and lower limits for these values. Experimental measurements are obviously the optimal solution for solving this problem, but it must be taken into account that this type of method consumes time and material resources. This paper proposes a sufficiently accurate and fast estimation method for determining Young’s modulus for a homogenized fibrous material. Thus, the FEM is used to determine the natural frequencies of a standard bar, for which there are sufficiently precise classical methods to express the engineering constants according to the mechanical properties of the component phases of the homogenized material. In this paper, Young’s modulus is determined for such a material using the relationships that provide the eigenfrequencies for the longitudinal vibrations. With the adopted model, transverse and torsional vibrations are eliminated by blocking the nodes on the surfaces of the bars. In this way, more longitudinal eigenfrequencies can be obtained, so the precision in calculating Young’s modulus is increased.

Digital fabrication material processing strategy for bespoke low clinker mass concrete components

Digital manufacturing techniques are seen to be very promising in concrete construction because of their potential for increasing productivity, as well as their potential to increase sustainability due to reduced material usage via nonstandard geometry. Concrete 3D printing via extrusion has received the most attention as a method, however the problem of implementing reinforcement remains unresolved; therefore, printed concrete typically serves as either a formwork or as unreinforced masonry. The recently developed technique of Digital Casting allows for digitally produced concrete components that implement standard reinforcement bars. The technique was developed especially for digitally produced, nonstandard formworks, and relies on controlled set acceleration of a self-compacting concrete to control formwork pressure during production.Digital fabrication techniques such as Digital Casting (and 3D Printing), however, have notoriously high cement contents due to processing requirements, and this may negate any sustainability benefit that can be realized through material savings in a bespoke concrete component. Research efforts to bring these cement contents closer to standard concretes have focused on: 1) reducing paste content through increased aggregate content and 2) reducing clinker content through substitutions, with most recent efforts focused on the latter. A recent project demonstrated, additionally, that elevated clinker contents negatively impact the casting of mass concrete elements due to high heat generation, which limits the applicability of digital fabrication for mass concrete applications.In this study, the use of a CEMIII (slag substituted cement) based mix design for this type of application was examined. The mix was successfully accelerated to control formwork pressure in a digital casting process of a thick (>1 m) bespoke element with overhang, and internal temperatures monitored. The reduced heat release generated temperatures of only half of those generated by a previous mix design with higher clinker content.

Neuromuscular Control during the Bench Press Exercise Performed with Free Weights and Pneumatic Loading

The main objective of the research was to determine neuromuscular control for different external loads, from 75% to 100% 1 RM (One Rep Max), during the flat bench press (BP) exercise performed with free weights and pneumatic loading. Despite extensive research on the internal structure of the BP exercise, few studies have examined the differences between muscular activity during the flat bench press movement between Free Weights and Pneumatic Loading. For this purpose, 10 male, trained subjects performed the BP exercise under two conditions with three different external loads (70%, 85%, and 100% 1RM), alternately with free weights and pneumatic loading. Pneumatic loading was performed on the Keiser Power Rack, where the pneumatic load was transferred as the resistance of the cables attached to the ground. EMG activity was recorded during the lifts for the following muscles: PM (Pectoralis Major), AD (Anterior Deltoid), Tblat, and TBlong (Triceps Brachii). The EMG signals were sampled at a rate of 1000 Hz. Signals were band-pass filtered with a cutoff frequency of 8 Hz and 450 Hz, after which the root-mean-square (RMS) was calculated. After completion of all the tests in a single day, 2–3 s evaluations of Maximal Voluntary Isometric Contraction (MVIC) of the prime movers in the bench press movement (AD, PM, and TBlong) were performed according to SENIAM procedures. The results of the present study indicate that pneumatic loading provides a significantly different muscle activation pattern compared to a standard bar during a heavy-loaded BP exercise. The pneumatic load was superior in activating the AD and TB muscles compared to the standard bar during the BP exercise.

Fabrication of single-step novel synthesis of ZnCd(S0.5Se0.5)2 thin films for photoelectrochemical (PEC) cell application

In our study, we use a new method called the arrested precipitation technique (APT) to create CdZn(SSe)2 (CZSS) thin films. We obtain samples at different deposition times, ranging from 2.5 to 4 h, and analyze the effects of deposition time on the opto-structural, morphological, compositional, and photoelectrochemical (PEC) solar cell properties. As a result, we find that the band gap energy increases from 2.366 to 2.60 eV with prolonged growth time, as shown by UV–Vis spectra. X-ray diffraction (XRD) analysis confirms that the crystal structure is hexagonal, with the crystallite size increasing from 76 to 93 nm. The dislocation density and microstrain, determined by the Scherrer formula, decrease from 1.72 to 1.14 lines m−2 and from 4.75 × 10−3 to 3.87 × 10−3 (lines m−2), respectively. These results are validated using the Williamson-Hall (WH) plot and size-strain plot. The average grain size, evaluated using the standard scale bar method in scanning electron microscopy (SEM), ranges from 80 to 150 nm across CZ1 to CZ4 samples. Transmission electron microscopy (TEM) images of CZ4 and CZ2 reveal particle sizes of 101 nm and 87 nm, respectively, while selected area electron diffraction (SAED) patterns confirm the polycrystalline nature of the material. Energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) analyses confirm the presence of Cd, Zn, S, and Se elements in their intended stoichiometry. Notably, CZSS photoelectrodes deposited over 4 h show better performance in Photoelectrochemical cells (PEC), achieving the highest photoconversion efficiency (ɳ) at 2.33 %, as evidenced by J-V measurements.

An optimized and hybrid gating scheme for the suppression of very low-frequency radios in transient electromagnetic systems

Abstract. One of the most widely used approaches for measuring the earth's subsurface resistivity is the transient electromagnetic (TEM) method. However, noise and interference from different sources, e.g., radio communication, the instrument, the atmosphere, and power lines, severely taint these types of signals. In particular, radio transmission in the very low-frequency (VLF) range between 3 and 30 kHz is one of the most prominent sources of noise. Transient electromagnetic signals are normally gated to increase the signal-to-noise ratio. A precise selection of gate shapes is required to suppress undesired noise while allowing the TEM signal to pass unaltered. We employ the multi-objective particle swarm optimization technique to choose optimal gate shapes and placements by minimizing an objective function composed of standard error bars, the covariance between gates, and the distortion of the gated signal. The proposed method is applied to both fully sampled synthetic TEM data and to boxcar-gated field data. The best output from the search space of gate shapes was found to be a hybrid combination of boxcar and Hamming gates. The effectiveness of hybrid gating over traditional boxcar and semi-tapered gating is confirmed by an analysis of covariance matrices and error bars. The results show that the developed method effectively suppresses VLF noise in the middle gates, which are gates with center times spanning 30 to 200 µs , and in the late gates, which are gates with center times spanning 200 to 1130 µs. The analysis shows that the average improvement in standard errors obtained for the hybrid gating scheme over boxcar gating is 1.719 and 1.717 for synthetic and field data, respectively.

Arts Premium Collection

ProQuest’s Arts Premium Collection database provides access to three cross-searchable databases across thousands of journals in specialized subject areas of the arts. The primary audience of this resource comprises academic scholars and students. Access to these resources is provided by the standardized search bar layout, which is consistent across ProQuest products. A robust Advanced Search tool allows users to construct Boolean searches, apply facets, and recombine searches to efficiently access the available resources. All search results have a Details display, which provides hyperlinked metadata to help users expand their discovery. Full text and PDFs are provided, and real-time translation is available for full-text resources. Each item also has suggested resources and citation counts/bibliography for works cited in other ProQuest collections.

The High Strain Rate Response of A Bio-Mimetic Composite Plates

Biological materials are often viewed as composites, consisting of weaker components arranged hierarchically, leading to exceptional mechanical capabilities that are challenging to replicate in synthetic materials. Natural shape and structure develop through the process of striving for improved performance. This paper will provide a summary of observations from experiments conducted on a composite material designed to closely mimic a sophisticated multifunctional biological structure. The Split Hopkinson Pressure Bar (SHPB) was utilized to test strain rates ranging from 102 s-1 to 104 s-1, providing reliable and comprehensible data for analyzing the behavior of the composite material at high strain rates. The Split Hopkinson Pressure Bar (SHPB) device is frequently utilized for evaluating metals and other materials with high strength and mechanical resistance. This study will detail the changes made to a standard Split Hopkinson Pressure Bar (SHPB) apparatus for testing low impedance materials. An aluminum sample was seen to lose its specific stiffness as impact strain rate increased, but the produced material continued to improve.

Design and Non-Linear Modeling of New Wind Girder Used for Bolted Tanks

Large-capacity bolted cylindrical tanks for liquid storage are used in many applications. The tanks are made of thin steel sheets that are connected by bolts. A common problem associated with tanks is deforming under extreme loads. Adding wind girders to the tank increases the tank’s buckling capacity, which is defined as the limit load at which the structure loses stability. The girders are usually placed in the horizontal joints of the tank wall. The girders are bent from standard or non-standard steel bars with a uniform cross-section. This type of design is difficult to produce, especially with large profiles or large curvatures, to avoid distortion of the cross-section during bending. Furthermore, the girders are customized to the given openings and curvature for various tank diameters. The resulting solution is then uneconomical and more complicated to store. This paper deals with the design and non-linear modeling of a new shape of wind girder for bolted tanks that eliminates the above-mentioned disadvantages. To analyze the new shape of the girder, a non-linear numerical model of an open-topped tank with various dimensions is designed to study its buckling capacity.

3D finite element analysis of the dental implant loss effect on the stress distribution in the mandibular implant-supported prosthesis

An implant-supported prosthesis may have as few as three supporting implants, and the loss of one of them may lead to the loss of the entire structure. The framework of the Trefoil design is a standard bar made of high-strength titanium. Cyclic loading of metals and metal structures brings about the effect reducing the strength characteristics and known as fatigue. Fatigue limit is the value of stress below which the cyclic loading can-not destroy the structure. The aim of the work is to determine the treatment tactics for a patient having lost a distal implant and justify it according to the results of a three-dimensional finite element analysis of the effect of one dental implant loss on the biome-chanics of a mandibular implant-supported prosthesis with three supports. Bridge loading modeling was carried out with the Ansys 19.3 finite element analysis package and thus the stress-strain condition of the prosthesis and its components, im-plants and the frame itself, namely the bar, were determined. The stress values obtained allowed to draw the conclusion about the condition of metal structures under cyclic load-ing. The geometric model represents the mandible, including the compact and spongy bone layers, a bridge structure with two implants screwed into the spongy layer, and arti-ficial teeth attached to the implant structure. The model was created with the use of a real patient’s computerized cone-beam tomogram (CBCT) findings. The finite element model consists of 383507 second-order tetrahedral elements and 619339 nodes. The compo-nents are interconnected by contact elements of the "bonded" type, imitating a rigid con-nection without slipping. With 220 MPa being the fatigue limit for the loaded titanium implant construction, it was concluded that extended prosthesis construction can withstand an unlimited number of loading cycles at 100 N loading with the maximum stress of 154 MPa occurring in the left part of the jaw. The clinician’s tactics was determined for the potential loss of function or removal of one of the three Trefoil supporting implants: the prosthesis must not be removed until reimplantation.

Experimental investigation of mixing railway ballast grains with different form using large-scale direct shear box apparatus

This paper investigates the effect of grain form on the mechanical behaviour of a railway ballast aggregate using large-scale shear box tests. The speciality of the research is that – contrarily to most of the experimental studies, where the shape content of the assemblies are not manipulated – here, the grains were carefully sorted and the ballast samples were assembled with the desired size and form content. A new sorting method was developed for laboratory-scale samples to separate compact and non-compact (flat, elongated or bladed) grains. This method utilises the combination of standard bar sieves and shape index calliper. The geometries of the grains in the resultant assemblies were thoroughly investigated using modern 3D imaging-based shape characterisation methods. With the adequate parameter thresholds, good correspondence was found between the standard industrial and the modern imaging-based methods, which allows the virtual reproduction of the introduced laboratory sorting technique. Three types of andesite railway ballast assemblies were tested experimentally: a fully compact, a fully non-compact and a mixed one. The mixed assembly had the highest internal friction angle which proves that it can be beneficial to mix grains with different types form. The amount of broken mass and the failure modes of the grains were also recorded, and it was found that the non-compact assembly had the highest rate of breakage. The results of the study also serve as a good basis for the calibration of numerical models.

Formability prediction of interstitial-free steel via miniaturized tensile specimen for Rapid Alloy Prototyping

This study aims to investigate the feasibility of using non-standard miniaturized tensile specimens (MTS) to characterize the formability features of interstitial-free (IF) steel, specifically DX57 steel. The motivation behind this research is to gain insight into the accuracy of predicted values for the steel's formability using the designed non-standard MTS, which could potentially be used to test materials obtained from rapid alloy prototyping (RAP) routines. Tensile tests were conducted using both standard bars and non-standard MTS with different angles to the rolling directions (0o, 45o, and 90o) and the experiment results were used to determine the material properties for the following numerical simulations, which were based on the cross-die deep drawing concept. The results show that the non-standard MTS over-predicted the strain hardening exponent compared to the values obtained from the standard tensile bars. For the same punch stroke, the non-standard miniatured tensile specimen under-predicted the punch force. However, for the deformed blank, the thickness variation along different paths was compared, and the maximum thickness value difference was found to be less than 5%. In terms of the forming limit diagram (FLD), the MTS's prediction is very close to the standard test-piece's prediction; the overall major-minor strain status of the deformed blank is similar. The results of this research provide confidence in the ability to evaluate formability from small-scale tensile tests for heterogeneous alloys such as synthetic IF steels developed during RAP.

A MACHINE LEARNING ALGORITHM FOR OPTIMIZATION OF REINFORCED CONCRETE STRUCTURES SUBJECTED TO BLAST

The analysis and design of a 4-story reinforced concrete (RC) frame that is subjected to blast loadings derived from an internal explosion experiment was presented as an optimization problem. An innovative algorithm combining multi-criterion decision-making (DM) and Particle Swarm Optimization (PSO) and Machine learning (ML), called DMPSO-ML, was used for expediting convergence toward the optimum solution. The main objective function in the study included minimizing the cost or mass of the four-story RC frame subjected to blast loadings while simultaneously satisfying all requirements established by building design principles. A blast load emanating from an internal explosion experiment was considered. The modular sizes of members, standard steel bar diameters, steel bar spacing rules, architectural provisions and additional constructability requirements were obtained directly from the output of DMPSO-ML yielding automatic final designs. The results from this study established the validity of the presented DMPSO-ML algorithm for obtaining optimum results in structural optimization problems involving blast effects.

Flumazenil Pretreatment Reduces Mefenamic Acid-Induced Central Nervous System Toxicity in Mice.

Mefenamic acid (MFA), a common analgesic, causes central nervous system (CNS) toxicity at high doses with a proposed activity on the Gamma-aminobutyric acid (GABA) system. However, it remains unknown whether flumazenil (FMZ), a GABA type A receptor (GABAAR) antagonist, can reverse MFA toxicity. The behavioral and neurophysiological effects of MFA were investigated in mice with and without FMZ pre-treatment. The elevated zero maze (EZM) and marble burying tests were used to assess anxiety-like behaviors and burying activities, respectively. The standard bar test was used to evaluate catalepsy, while the actophotometer test was used to measure locomotor activity. Seizure intensity was scored, and fatalities were counted. Without FMZ pre-treatment, MFA induced behavioral and neurophysiological effects in a dose-dependent manner as follows: At a dose of 20 mg/kg, i.p, MFA-treated mice exhibited anxiety-like behaviors, which was determined by a significant increase in the time spent in the closed areas and a significant decrease in the number of entries to the open areas of the EZM apparatus. These mice also showed a significant decrease in the burying activity, manifested as a significant decrease in the number of buried marbles. At 40 mg/kg, i.p., MFA-treated mice showed catalepsy that was associated with a significant decrease in locomotor activity. At a dose of 80 mg/kg, i.p., mice developed fatal tonic-clonic seizures (seizure score = 4). Pre-treatment with FMZ (5 mg/kg, i.p.) significantly reversed the anxiety-like behaviors and restored marble-burying activity. Additionally, FMZ prevented catalepsy, significantly restored locomotor activity, reduced seizure intensity (seizure score = 0.3) and significantly reduced mortalities. The present study's findings indicate that activation of the GABAAR is involved in the CNS toxicity of MFA, and FMZ reverses MFA toxicity by interfering with this receptor.

Calibration Method and Measurement Uncertainty for the Sphere Center Distance of Standard Multi-ball Bar

Calibration Method and Measurement Uncertainty for the Sphere Center Distance of Standard Multi-ball Bar

Projection of structure and compositions of resistance to burning polymer composite materials with flame retardants based on magnesium hydroxide

Objectives. To identify general principles for the design of dispersed-filled polymer composite materials (DFPCMs) with different generalized and reduced parameters, as well as types of disperse structure with high fire resistance; to develop an algorithm for the creation of non-combustible polymer composites with flame-retardant fillers.Methods. Scanning electron microscopy and laser diffraction were used to assess the shape, size, and particle size distribution of flame retardants. According to the presented classification of DFPCMs by structural principle, standard bar samples were obtained to determine the oxygen index (OI) and the fire resistance category.Results. For the MFS-2 (medium filled system) and HFS (high filled system) structure types, the maximum resistance to burning (category V-0) is achieved with a generalized parameter of ® ≤ 0.40 volume fractions; the OI value increases in 2 times (up to ~40%) in relation to the polymer matrix.Conclusions. In order to obtain a flame retardant DFPCMs (OI = 40%, category V-0) based on ethylene vinyl acetate with OI = 20% and magnesium hydroxide (brucite), the amount of water vapor released during the decomposition of the flame-retardant filler should be at least ~250 mL/g with a coke residue ~32%. A developed algorithm for calculating compositions and generalized parameters for the creation of DFPCMs having a predetermined type of disperse structure and high resistance to burning is presented.

Trends in Maxillomandibular Fixation Technique at a Single Academic Institution.

Retrospective chart review. Restoration of premorbid occlusion is a key goal in the treatment of mandibular fractures. Placement of the patient in maxillomandibular fixation (MMF) is performed during mandibular fracture repair to help establish occlusion. A number of techniques are available to achieve MMF. We sought to examine trends in MMF technique at our institution. A retrospective chart review was conducted to evaluate patients who underwent surgical treatment of mandibular fractures between January 1, 2011 and March 31, 2021. Data including fracture characteristics, mechanism of injury, patient demographics, complication rates, and MMF technique utilized were collected. One hundred sixty-three patients underwent MMF (132 males). The most common etiology of fracture was assault (34%). There was an increasing preference for rapid MMF techniques over time, as opposed to standard Erich arch bars. No significant difference in obtaining adequate fracture reduction as determined by postoperative imaging or complications were noted between those who underwent MMF with newer rapid techniques vs traditional MMF techniques. Our institution has demonstrated changing trends in the technique utilized for establishing occlusion intraoperatively, more recently favoring rapid MMF techniques, with similar rates of complications and ability to adequately reduce fractures.

Anisotropic fatigue performance of directed energy deposited Ti-6Al-4V: Effects of build orientation

Directed energy deposition (DED), an important branch of additive manufacturing technology, has unique processes that attribute to the fatigue performance anisotropy associated with the build orientation of DED materials. However, the mechanism of fatigue performance anisotropy still remains unclear due to multiple factors of the defect and microstructure, which has limited further application of DED materials. This paper investigates the effects of build orientation on the anisotropic fatigue performance of DED Ti-6Al-4V treated with stress relief annealing, specifically the impact of defects and microstructures on fatigue performance anisotropy. The defects in the fully dense DED Ti-6Al-4V are non-directional porosity defects with smooth morphology and high sphericity; the microstructures are mainly characterized by prior-β columnar grains, α colonies and basketweave structures. To represent fatigue performance anisotropy of the material, standard round bar specimens were sampled from three build orientations, i.e., X, Y and Z directions, where Z-direction represents the build direction. These specimens were subsequently subjected to constant amplitude high cycle fatigue tests at the same loading condition and room temperature. The fatigue test results showed that the logarithmic mean fatigue lives of the X- and Y-direction specimens were close to each other, but significantly longer than those of the Z-direction specimens. Fractography and EBSD tests were conducted to explain the causes of fatigue performance anisotropy, suggesting that microstructures are more likely to explain the anisotropy caused by the build orientation than the porosity defects, with crystallographic orientation and α colony being two critical factors.