Gauge Section Research Articles

РАЗВИТИЕ МЕТОДОВ ГИДРОМЕТРИЧЕСКОГО УЧЕТА И УВЯЗКИ СТОКА

The paper provides an overview of the methods for hydrometric streamflow computation in the regime and real-time variants developed at the State Hydrological Institute and intended for inclusion in the technologies for automated processing and generalization of hydrological observations, which were included in the Roshydromet regulatory documents put into effect in 2017-2022. The results of further development of the methodological basis for water discharge calculations in the conditions of variable backwater are given on the example of the reach of the Ob River from Barnaul to Kamen-on-Ob. To control the reliability of streamflow computation at gauging sections, it is proposed to use the computation and analysis of dynamic (short-term) channel water balances as the most effective tool. The effectiveness of using the improved methods for streamflow computation and coordination is shown through examples.

Comparison study on cold formed steel of coupled channel section based on abaqus and cufsm by simple-simple end condition

Cold formed steel (CFS) channel sections are the sections which are widely using from last few decades and are designated as light gauge sections. Such sections are being widely utilized in industrial, commercial and residential purposes as a secondary bearing member. Further developments of thin walled members made it possible to use the CFS Sections as preliminary load carrying structural members. The reason is hot-rolled steel sections posses’ very low strength to weight ratio on CFS sections, and the production process of these sections is cost-effective and simple. This paper is about comparing the analysis results from CUFSM and ABAQUS of different channel sections. The loads will be applied at the edges of the members axially i.e., as a compression member with different boundary conditions.

Assessment of nutrient load on the Cheboksary Reservoir using the results of modeling runoff and removal of biogenic elements from the pilot catchments

The paper presents the results of an approximate assessment of the nutrient load on the Cheboksary reservoir of the Volga Cascade from the right-bank and left-bank parts of the catchment basin. The main solution tools are the recognition of the underlying surfaces in the catchment and mathematical modeling. The catchment basins of the Kudma (right-bank tributary) and Linda (left-bank tributary) rivers have been identified as pilot sites. The catchment basins of the Kudma (right-bank tributary) and Linda (left-bank tributary) rivers have been identified as pilot sites. The representativeness of the selected pilot sites for the catchment basins of the Cheboksary reservoir is demonstrated. The mathematical basis of the research was the “precipitation-runoff-removal” model describing the formation of runoff and removal of biogenic elements from the catchment basin. To calibrate the mathematical model, the materials of observations of water discharges and the content of chemical agents in the gauging sections of the pilot catchment basins were used. The modeling data provides an approximate estimate of the total nutrient load on the Cheboksary reservoir, as well as the contribution of natural nitrogen and phosphorus removal to the load from the catchment basin.

Characteristics of Quasi-static and Dynamic Failure of Inconel 625 Superalloy under Simple Shear

The shear flow and failure of a superalloy Inconel 625, conceived for jet engine applications, are investigated by using a modified flat gauge shear specimen with the assistance of Digital Image Correlation (DIC). The constant strain rate shear tests were successfully performed by using a screw driven Zwick machine and a bespoke spilt Hopkinson tension bar (SHTB). Nearly all gauge section is in a uniform strain state at dynamic force equilibrium condition. The constitutive relationships and the crystallographic texture show strain rate dependence. Different from the void growth induced failure at quasi-isothermal condition, the Inconel 625 fails by adiabatic shear at high strain rates. The present shear testing provides an opportunity to study the shear flow and failure of superalloy of small structural components in turbine engine.

Through‐thickness tensile characterization and analysis of fiber‐reinforced polymer composites using digital image correlation and finite element modeling

AbstractDigital image correlation (DIC) and finite element analysis (FEA) are used to assess the cylindrical spool‐shaped ASTM D7291 and I‐beam‐shaped specimens for through‐thickness (TT) mechanical characterization of thick (~25 mm) fiber reinforced polymer matrix composites. The composites are made of E‐glass woven fabrics reinforcing a vinyl ester matrix. DIC full‐field measurements and FEA showed a rather uniform strain distribution within the gage section of the ASTM D7291 specimen. However, strain concentrations are revealed at the bondlines between the end‐tabs and the test specimen, in addition to strain gradients at the curved section of the specimen. DIC‐measured and FEA‐predicted strain fields of the I‐beam specimens exhibited a region of uniform strain distribution within the gage section larger than that of the ASTM D7291 specimen. Nevertheless, high stress concentrations at the fillet (curved flange‐to‐web transition) regions and some amount of web bending occur in the I‐beam specimen. Beyond providing the TT mechanical properties of the E‐glass woven/vinyl ester composites, the current work discusses advantages and caveats of both promising specimens, providing quantifications of stress concentration factors and length of zones were strains and stresses may be considered uniform.Highlights Stress/strain distributions of through‐thickness tensile specimens are evaluated. The main drawback of the spool‐shaped specimen is adhesive failure. The modified I‐beam specimen shows acceptable stress concentration factors. The modified I‐beam is adequate for strength and Poisson ratio characterization. I‐beam specimens are easier to manufacture and do not require adhesive joints.

The influences of international standards on structural performance and fracture behaviour of 3D printed long fiber composite structures

The material properties of the additive manufactured composite structures are usually done following international standards, that show some difference dimensionally. This study focuses on the impact-induced on the tensile properties of the 3D printed continuous carbon fiber reinforced composite part due to the standards applied for sample preparation. The specimens were fabricated by Markforged® Mark two 3D printing machine using carbon fiber as reinforcement and Onyx® as matrix material based on ASTM D638 and ASTM D3039-D3039M standards. The experimental results revealed that the specimens fabricated based on ASTM D638 showed a premature failure at the location where the straight gauge section of the specimen ends, and the curved transition regions begin due to stress concentration. The tests based on ASTM D3039-3039M standard showed better tensile strength and less stress concentration compared to ASTM D638. Fracture test with SEM reveals fiber breakage, debonding, and fiber pullout, which created cavities and voids between layers as the reasons for the tensile failure.

Limit load of notched Ti-6Al-4V specimens under axial fatigue

Ti-6Al-4V is used to manufacture aircraft components, that are subjected to fatigue loads during their service life. These components exhibit flaws and are susceptible to impact damage. Therefore, it is important to study the fatigue behaviour of Ti-6Al-4V in the presence of defects to accurately evaluate the fatigue life of components. This paper reports the limit load of notched Ti-6Al-4V specimens not subjected to solution treatment and over-aging under axial fatigue. The tests are carried out in inert environments using a step loading procedure, with a load ratio R = 0. The limit loads of the specimens with a notch depth / width of the specimens’ gauge section ratio d / D = 0.0439 and d / D = 0.0877 are similar and higher than the limit load of the specimen with d / D = 0.1754 since the net area at the minimum cross section of the third specimen is much smaller than the areas of the other two specimens. The nominal stress at failure referred to the net area is similar for the fatigued specimens.

Pore-induced fatigue failure: Critical pore criterion for Ti-6Al-4V alloy manufactured by laser-directed energy deposition

Pores are the major factor inducing fatigue failure in laser-directed energy deposition (L-DED) Ti-6Al-4V alloy, posing obstacle to the application of the alloy in primary load-carrying components. Hence, it is essential to formulate criteria to identify critical pores that induce failure, an important step in evaluating the fatigue performance and predicting the fatigue life of L-DED Ti-6Al-4V alloy. In this paper, computed tomography was performed on tangentially blending fillets specimens to examine the distribution characteristics of pore geometric parameters, and location in the gauge section of the specimens. Then, fatigue experiments and fracture analysis were conducted. The results show that the location relative to the surface, size, and shape of the pores are the primary factors affecting fatigue failure. A stress state sensitive parameter was formulated by using location factors, projected area along the load direction, circularity of pores, and peak stress to establish a criterion for recognizing critical pores, the number of which can be reduced to two. The critical pore criterion based on stress state sensitive parameter was compared with those obtained via the other methods, proving its good applicability and effectiveness on identifying critical pores.

Dynamic tensile deformation behavior of AISI 316L stainless steel fabricated by laser-beam directed energy deposition

The dynamic deformation behavior of metallic materials is the key to crash-safe design in many applications, e.g., in the automotive sector. However, in the field of additive manufacturing, dynamic deformation properties have only been scarcely studied. Based on the intrinsic interrelationships of process parameters, post-process heat treatments and the resulting microstructure, the present study seeks to provide a holistic overview of the dynamic tensile deformation properties of AISI 316L stainless steel, fabricated by laser-beam directed energy deposition. Utilizing in situ digital image correlation, the local deformation behavior at varying strain rates from 100 s−1 to 1000 s−1 was unveiled. In combination with pre- and post-mortem microstructure analysis using electron backscatter diffraction and scanning transmission electron microscopy, the microstructural effects on the active deformation mechanisms were studied. The results show that twinning contributes to the overall deformation in the heat-treated condition owing to the weaker crystallographic texture. On the contrary, twinning is less prominent in the non-heat-treated condition due to its pronounced <001> texture. As a result of the differences in terms of active deformation mechanisms, superior fracture elongations are observed in heat-treated condition, which are rationalized by delayed necking due to a more homogeneous strain distribution along the gauge section. Independently from the sample condition, fractography analysis revealed a ductile mode of failure being characterized by equiaxed dimples on the fracture surfaces. Consequently, it can be concluded that AISI 316L stainless steel is excellently suited for dynamic tensile loading, although heat-treatment-depended differences have to be taken into account.

Diffusion Welding of Surface Treated Alloy 800H

Diffusion welding of heat-resistant alloys has attracted interest in the manufacturing of components with complex configurations. Controlling secondary precipitates along the interface is necessary to enhance the quality of the diffusion welding. Surface treatment to increase the solubility product (Ksp) of Ti-rich carbide is proposed to accomplish such an enhancement. The reduction of secondary precipitates along the interface induced grain boundary migration across the interface. The chemical compositions at/near the interface satisfied the material specifications. The mechanical properties of the diffusion weldment were similar to those of Alloy 800H that underwent the same thermo-mechanical processes in the range of 25–700 °C. At 25 °C, the tensile strength was 553 MPa, which satisfied the minimum specified tensile strength described in ASTM B: 409-22. The location of failure was random in the gauge section, and dimples, the evidence of the macroscopic plastic deformation, were observed on the fracture surface.

Effect of build height on structural integrity of Ti-6Al-4V fabricated via laser powder bed fusion

The additive manufacturing process involves layer-by-layer fabrication of parts, where each layer potentially experiences unique thermal histories, including cooling rates and thermal gradients. These variations can impact the microstructure and, subsequently, mechanical properties of the final product, especially as the height of the build increases. This research aims to investigate the influence of build height on the structural integrity of Ti-6Al-4V specimens fabricated via laser powder bed fusion (LPBF). The microstructural features, microhardness values, and defect characteristics, such as size, location, and distribution of defects, were analyzed along the build direction. Tensile and fatigue tests were conducted to determine the potential height-dependency of fatigue and tensile failures. The findings of this study indicated influence of build height on the structural integrity of parts subjected to cyclic loading, as the majority of the fatigue specimens failed in the upper half of the gage section (with respect to the build direction). Microstructure characterizations and microhardness testing revealed consistent grain morphology along the build direction, with uniform hardness distribution throughout the build height. However, more process-induced defects were detected within the top half of the gage section, compared to the bottom half. The results suggest that as the build height increases, there is a higher likelihood of process-induced defect formation, ultimately leading to a reduction in the structural integrity at greater build heights.

A MICROSCOPY INVESTIGATION OF RUBBER COMPOUND CRACK PRECURSORS AND TENSILE FRACTURE SURFACES

ABSTRACT Tensile stress–strain testing is used to investigate the fracture behavior of carbon black–reinforced styrene–butadiene rubber, using 50 replicate specimens. Four vulcanized rubber compounds are studied: a CB-filled SBR with standard mixing conditions (control), the same formulation with intentional poor mixing of the CB, and materials identical to the control material but formed by adding minor amounts of 0.5-mm-diameter glass microspheres (beads)—serving as large model defects/inclusions—using a two-roll mill at two levels, corresponding to average values of 0.78 and 6.24 beads per gauge section region of the tensile test specimen. Microscopy analysis of the resulting fracture surfaces was conducted to complement our recent publication on Weibull failure statistics for distributions of tensile strength and crack precursor size. All 200 fractured specimens from tensile testing at 23°C were imaged with light microscopy and exhibited fracture surfaces characterized by relatively smooth planes perpendicular to the uniaxial loading direction. Most tensile failures originated from the edges of the dumbbell specimens, in line with expectations from fracture mechanics. Light microscopy revealed concentric fracture ring features of high specular reflectance emanating from crack precursors, which are a universal feature of the failure process for these compounds and independent of precursor type, size, or location. Noncontact interferometric microscopy confirmed that the rings resulted from variations in surface micro-roughness, proceeding outward from the precursor as rough–smooth–rough to the edge of the fracture surface. Fracture rings were also observed for tensile tests performed at 80°C. The variation in surface roughness of the fracture surface has parallels to the stick–slip tearing behavior seen for rubbers torn at medium to high rates. To the best of the authors’ knowledge, this is the first time that such striking features have been reported.

Numerical modeling and experimental validation of lamina fracture and progressive delamination in composite dovetail specimens under tensile loading

In this work, a numerical simulation was conducted to investigate the lamina fracture and progressive interlaminar failure behavior of a dovetail specimen of composite fan blades. Through-thickness compression (TTC) will strengthen the interphase properties as the applied pressure increases and degrade the tensile strength combined with the in-plane shear stress, which greatly affects the overall tensile behavior on the composite dovetail specimen. This was realized with the aid of ABAQUS user subroutines VUSDFLD and VUMAT, along with an experimental validation. To demonstrate the performance of the proposed approach, two sets of tensile tests were conducted on specimens with different stacking sequences with a digital image correlation (DIC) device to investigate the deformation configurations, as well as the load–displacement curves of the gauge section. The obtained results exhibited a remarkable agreement with the simulation results, particularly in terms of the first delamination load and lamina fracture load. To further validate these observations, a sensitivity analysis was carried out. This analysis took into consideration the uncertainties associated with parameters such as the longitudinal Young’s modulus, interphase properties, friction coefficient, and the position of the contact pad.

Experimental and simulation study on compressive failure evolution of multidirectional laminates with different dimensions

The composite strength refers to the ultimate local value rather than the average value of local strength, thus the effect of size effect needs to be considered. In this study, experimental and numerical approaches are used to evaluate the influence of size effect on the compressive characteristics and failure process of multidirectional carbon fiber reinforced composites. The representative failure modes of specimens with different thicknesses are described. The reasons for the difference in failure modes are analyzed by microstructure analysis, and the crack propagation process of specimens with different gauge lengths is identified. The simulation results and microscopic mechanism analysis reveal that with the increase of specimen thickness, the final failure mode develops from longitudinal cracking to multidirectional delamination, and finally evolves into shear failure through the thickness. Influenced by the free edge effect, the specimen thickness significantly affects the final failure mechanism by influencing the location of the initial cracking, and the size of the gauge section affects the site of matrix compression failure leading to a change in the final failure mode. These findings provide some helpful guidance for the design and fabrication of thick composite structures.

Biaxial tensile behavior of Ti-6Al-4V under proportional loadings at high strain rates

To study the mechanical performance of materials under dynamic and proportional biaxial tensile loadings, the electromagnetic Hopkinson bar system was employed. Dynamic biaxial tensile experiments were conducted by this novel system. Dynamic uniaxial tensile and compressive tests were also performed. The digital image correlation (DIC) technique combined with the high-speed camera was utilized to analyze the deformation in the gauge section of the improved cruciform specimens. The cruciform specimen design was improved by finite element method (FEM) method to adapt to dynamic biaxial loadings. An inverse analysis (IA) method was adapted to deduce the true stresses in cruciform specimens. Based on the Yoon criterion, a strain rate and stress state dependent yield criterion and a related constitutive model were developed to account for the asymmetric yielding and strengthening behaviors under high strain rates. The new constitutive model was implemented in the FEM analysis and the numerical results agreed well with the experiments.

Effect of a build pause on the fatigue behavior of laser powder bed fusion 316L stainless steel with as-built surfaces

Buildpauses can occur during metal additive manufacturing (AM) with laser power bed fusion (PBF-LB) for a variety of reasons such as power outage, insufficient gas flow, or sensor failure. It is economically desirable to continue a build after the issue is resolved. However, the effect on part quality, such as microstructure, surface roughness and geometric features is not well understood. This study considers parts fabricated with a 2-hourbuildpause in the center of the gauge section. Quantitative comparisons of the dimensions, as-built surface features, microstructure, and fatigue performance are determined. Geometric deviation from part shift during thebuildpauselocation is significant, however other anomalies inherent to AM can still dominate failure. Understanding the effect of material changes from abuildpausecan help reduce scrap from unintendedbuild interruptions.

A multi-length-scale investigation of the applicability of ductility laws for annealed and work-hardened copper

Small-scale mechanical testing provides unique advantages over conventional testing in investigating the mechanical response of nuclear materials. While small-scale testing enables accelerated materials research, it raises the question of comparability to large-scale properties for engineering design considerations. Among different mechanical properties for structural design considerations such as yield and ultimate tensile stress, ductility is of critical importance with respect to structural component health. The effectiveness of using small-scale mechanical testing for probing these mechanical properties is dictated by understanding how the mechanical responses translate from the microscale to the engineering scale. Therefore, a better understanding of size scaling effects via gathering and analysis of experimental data is required to bridge length-scales. This work builds upon previous reports to provide statistical data on how mechanical response changes as the size of the specimens are reduced from conventional sizes. One hundred twenty mesoscale tensile coupons of oxygen-free high thermal conductivity (OFHC) copper in work-hardened and annealed state have been manufactured using micro-wire electrical discharge machining (EDM) and tested under uniaxial tension. The mesoscale specimens have dimensions dictated by pre-selected geometric ratios (i.e., gauge section length over the square root of the cross-section area) with gauge length dimensions of 3 mm (or less) and sub-millimeter gauge widths and thicknesses. The mesoscale responses were compared to bulkscale properties to reveal the effect of specimen size on the mechanical response as a function of grain size and material state for a single phase face-centered cubic metal.

Effect of loading rate on the compressive behaviour of twill woven carbon/polyamide laminate

This paper presents the experimental investigation on the strain rate effect on the longitudinal compressive behaviour of 2×2 twill woven carbon fibre reinforced polyamide 66. An original easy-to-use specific testing fixture was developed to perform material characterization using an electromechanical machine and a Split Hopkinson Pressure Bar (SHPB) system. The set-up was completed with a high speed camera used to monitor the deformation and failure process and to allow the strain field visualization via Digital Image Correlation (DIC). A particular attention was paid to the validity of the experiments: failure in the test specimen gauge section, stress equilibrium and strain homogeneity. The same testing fixture and specimen geometry were implemented from 1.5×10−5s−1 to 700 s−1. The results comparison shows a positive strain rate effect with a 60% increase in the longitudinal compressive failure stress.

On the use of the Combined Loading Compression fixture to estimate the intralaminar compressive fracture toughness of composites

This study reassesses the constraint effect provided by a Combined Loading Compression (CLC) fixture on notched specimens used to measure the compressive intralaminar fracture toughness of composite materials. An experimental campaign is carried out to determine whether a variation in the specimen gauge section length would result in a significant change in the nominal strength of Double Edge Notch CLC specimens. Following the testing of six sets of different specimen geometries for both a uni-directional thermoplastic and a bi-directional woven thermoset composite, the effect of the gauge length is analysed using the size-effect method. Results show that nominal notched strength variation is minimal, suggesting that the CLC clamp does not effectively constrain the gripped sections against in-plane deformations. This assessment proves that the correction factor used in the determination of the R-curve needs to be computed considering the entire specimen geometry, including the gripped regions. Furthermore, the results reveal that previous characterisation campaigns conducted using end-loaded Double Edge Notch Compression specimens could have led to a significant underestimation of the steady-state fracture toughness.

X-ray computed μ-tomography analysis to evaluate the crack growth in an additive manufactured Ti-6Al-4V alloy sample stressed with in-phase axial and torsional loading

Selective laser melting (SLM) is one of the most promising additive manufacturing technologies for obtaining end-use components with excellent mechanical properties. However, the presence of manufacturing defects harms mechanical properties and fatigue performance. This work investigated the crack behaviour within an SLM Ti-6Al-4V alloy sample stressed with in-phase axial and torsional loading by X-ray computed μ-tomography (μ-CT). A sub-volume of material that contains the most significant defects was detected and analysed. The critical defect was identified by evaluating the effective strain intensity factor (SIF) using two different proposed models, that consider the effective area of a detected defect according to Murakami’s method. The first model is based on the modified Smith Watson and Topper (MSWT) criterion. The second is based on Liu’s virtual strain energy (VSE) method. The trend of the crack growth rate was obtained by measuring the effective area for a different number of cycles. The μ-CT data was also exploited to build a finite element model (FEM) of part of the gauge section containing surface defects. Finite element analysis (FEA) results have provided information on the stress state leading to high-stress concentrations at the crack tip influencing the propagation.