Strain Intensity Research Articles

Behaviour of stub columns with initial crack defects under axial compression

An experimental investigation was conducted to evaluate the axial compressive behaviour of circular hollow section (CHS) stub columns with initial crack defects. A total of 96 specimens – 12 stub columns with one crack, 48 stub columns with two cracks, and 36 stub columns with three cracks – were tested under axial compression loading. The failure modes, load-carrying capacities, overall deflections, and strain intensities of all the specimens were examined. The design parameters were the tube thickness, long crack length, short crack length, crack spacing, and crack number. Additionally, a finite-element analysis was performed using the verified models in combination with the experimental data to evaluate the effects of the main influential factors. The initial cracks formed in the circular thin-walled stub columns accelerated the local buckling and changed both the bearing capacity and deformation capacity. The ultimate loads of the stub columns increased with the tube thickness, decreased slightly with an increase in the long crack length, and decreased with an increase in the crack spacing. The effects of the short crack length and crack number on the bearing capacity were complex and were coupled with the tube thickness. An adjustment coefficient was introduced into the predictive formula to estimate the ultimate bearing capacity. Through this, the ultimate bearing capacity can be accurately predicted.

Análise experimental de vigas biapoiadas de concreto armado reforçadas a flexão por CRFC

Este trabalho tem como objetivo examinar a eficiência do reforço estrutural utilizando Compósitos Reforçados com Fibra de Carbono (CRFC), avaliando o aumento da resistência de vigas biapoiadas de concreto armado. Para isto, vigas de concreto armado receberam a implantação de camadas de CRFC, para que fossem verificadas as diferenças de deformações, as mudanças nos valores de carga de ruptura e os modos de falha destas vigas. Foi feita a previsão das cargas de ruptura das vigas reforçadas por meio do método de dimensionamento utilizado. As vigas foram rompidas em laboratório pelo ensaio de flexão a quatro pontos até o seu colapso. Os ensaios experimentais comprovaram a efetividade deste método de reforço estrutural. No que concerne os resultados, foi possível perceber que a utilização do reforço estrutural com CRFC foi capaz de aumentar a resistência das vigas em até 34%. Além disso, observou-se que a implantação do CRFC pode mudar significativamente a ductilidade da viga reforçada. Para mais, a utilização dos incrementos de ancoragem mostrou um aumento de até 42% na carga última e aumento na deformação de tração de até 102% em relação a viga de referência, dando origem a um maior aparecimento de fissuras.

Integrated optimisation design of a dynamic umbilical based on an approximate model

An optimised design of a dynamic umbilical requires an extreme cross-sectional stress to be maintained within an allowable limit and a fatigue life to be guaranteed to be sufficient. It should be noted that a dynamic umbilical is a typical geometric bi-scale structural system. It consists of a local cross-sectional scale and a global configuration scale, which are significantly different in terms of geometric sizes. In this study, we established an approximate model to achieve an optimised design of the dynamic umbilical by considering the parameters of local cross-sections and global configurations simultaneously. The design variables of a dynamic umbilical are independently identified and defined at both local sectional and global configuration scales in the approximate model. Furthermore, we selected the maximum tension strain and the maximum bending moment, for covering local and global properties, as the objectives to be minimised. The approximate model was observed to be effective in integrating the local and global responses into one loop so that the computational efficiency could be significantly increased. We implemented the optimisation framework on a dynamic umbilical with a lazy-wave configuration, which is considered to be a basis for a case study. Furthermore, we verified the feasibility and effectiveness of the integrated optimisation strategy by numerical simulations. Moreover, we compared the optimised dynamic umbilical properties with those without optimisation. It was observed that the fatigue life of the optimised dynamic umbilical was improved significantly, thereby indicating that the integrated optimisation methodology provides a new model and algorithm for an efficient design of the dynamic umbilical.

Wake-induced vibration of two-phase conductors connected by spacers

Considering finite element approach applied to modelling of wind-induced split-phase overhead power line conductor oscillations caused by aerodynamic wake. Model represents an aeroelastic system including twin bundled conductor with spacers. Modified Simpson’s theory is used for conductor wake coupling simulation. Assuming small oscillating conductor deflection from element ends connection line compared to element length, thus the element tension and element tensile strain can be considered as constant values. Strain, as function of transverse displacements, defines as quadratic approximation. Element absolute displacements and twisting angles, together with Ritz’s method coefficients is taken as generalized coordinates, in which conductor move equations are compiled with non-linear elastic, inertial and aerodynamic forces. Appropriate linearized small oscillation equations near the static equilibrium are derived – those can be used for defining system flutter critical wind velocity. An example with split-phase twin bundled conductor, three-sub-span system is presented.

WITHDRAWN: Strain rate effect on mechanical properties of 0.24% carbon steel using artificial neural network

The effect of strain rates on 0.24 percent C carbon steel under tensile loading has been discussed in this study. To perform the test by adjusting the strain rates, an electronic tensiometer was used. Before and after research, the microstructural orientations and stiffness around the necking area were defined by an optical microscope and a micro-hardness tester. At room temperature, the mechanical properties of carbon steel are investigated, such as ultimate tensile strength, yield strength and hardness. The lowest ultimate tensile strength (429.14 MPa) and lowest yield strength from the data were observed to have a strain rate of 1 mm/min (292.8 MPa). Strain intensity of 5.75 mm/min. The maximum ultimate strength (525.54 MPa) and highest yield strength are given (376.35 MPa). If the strain rate increases, the ultimate strength, and yield strength will rise and vice versa, the results showed. It can be observed that the hardness value improved to a reasonable level of 3.5 mm/min from 1.5 mm/min and decreased to 5.75 mm/min as the strain rate increased. The ANN model demonstrated an impressive contrast between the coefficient of correlation (R = 0.997) and the error in the mean square (MSE = 1.24 10-5) and the experimental findings. This analysis shows that the ANN model is capable of predicting the impact on Carbon steel’s mechanical properties of different rates for the strain.

GEP prediction of the cracking zones in earthfill dams

One of the important factors which control the possible cracking zone in earth dams is the geometry of valley cross section. This research uses genetic express programming (GEP) for finding the best equations for the relationship between the width and depth of possible cracking zone and geometric parameters of valley cross section, such as the invert width, dam height, and the height and width of the bench and bank slopes. The GEP method can produce precise equations without asking for the assumption of the form of the equation. Four output variables of GEP are the depth and width of tension stress zone, D0 and W0, respectively, and the depth and width of tension strain zone, ∆ and C, respectively. The necessary data are produced by simulating different conditions. The correlation coefficient (R2) of extracted equations by GEP is 0.95, 0.9033, 0.9262, and 0.9212 for D0, W0, Δ, and C, respectively. This shows the excellent capability of the GEP method. Also, according to the sensitivity and parametric analyses, the slopes of valley cross section, θ and β, are the most effective parameters on cracking of the dam.

Design of heterogeneous interior notched specimens for material mechanical characterization

Nowadays, virtual predictions are essential in the design and development of new engineering parts. A critical aspect for virtual predictions is the accuracy of the constitutive model to simulate the material behavior. A state-of-the-art constitutive model generally involves a large number of parameters, and according to classical procedures, this requires many mechanical experiments for its accurate identification. Fortunately, this large number of mechanical experiments can be reduced using heterogeneous mechanical tests, which provide richer mechanical information than classical homogeneous tests. However, the test’s richness is much dependent on the specimen's geometry and can be improved with the development of new specimens. Therefore, this work aims to design a uniaxial tensile load test that presents heterogeneous strain fields using a shape optimization methodology, by controlling the specimen's interior notch shape. The optimization problem is driven by a cost function composed by several indicators of the heterogeneity present in the specimen. Results show that the specimen's heterogeneity is increased with a non-circular interior notch. The achieved virtual mechanical test originates both uniaxial tension and shear strain states in the plastic region, being the uniaxial tension strain state predominant.

Formation of Interstitial Dislocation Loops by Irradiation in Alpha-Iron under Strain: A Molecular Dynamics Study

The present work reports the formation of an interstitial dislocation loop with a lower primary knock-on atom (PKA) energy in alpha-iron under strain conditions by the use of molecular dynamics simulation. The study was conducted using a PKA energy of 1~10 keV and hydro-static strain from −1.4 to 1.6%. The application of 1.6% hydrostatic strain results in the formation of ½<111> dislocation loop with a low PKA of 3 keV. This result was associated with a threshold displacement energy decrement when moving from compression to tension strain, which resulted in more Frenkel pairs initiated at peak time. Furthermore, many of the initiated defects were energetically favorable by 2 eV in the form of the interstitial dislocation loop rather than a mono defect.

Incorporation of Smart Concrete in Large-Scale RC Beams for Evaluating Self-Sensing and structural Properties

Only using a small number of samples in the absence of reinforcement, the concrete self-monitoring behaviour is tested, which is inaccurate for real-world structures. The behaviour of concrete is primarily tested, which can be inaccurate for structures in real time. This study examined the self-sensing ability of large-scale reinforced concrete beams that are 1500 mm long and 125 mm wide embedded with smart concrete at top and bottom surfaces for a length of 350 mm. As shear failure is catastrophic, the present study focused on evaluating RC beams' self-sensing property failing under shear, and shear reinforcement was not given for the same reason. A total of six RC beams, 3 of are 250 mm deep and 3 are 350 mm deep with variable reinforcement ratios, were tested in a four-point bending test to study the self-sensing properties such as strain and crack/damage sensing. Mechanical/structural properties of all the beams have been documented, along with self-sensing properties. The results obtained showed that partially placed smart concrete in the RC beam's pure bending region successfully sensed all strain and damage/cracks without any impact due to beam depth and reinforcement ratio. During testing, it was observed that 250-mm-deep beams failed due to flexure/concrete crushing, and 350-mm-deep beams failed due to shear. In particular, smart concrete's self-sensing property showed promising results for the beams that failed due to flexure by representing all the cracks developed in the pure bending region. Fraction change in resistance (FCR) has also been obtained for all the beams during self-sensing testing, and this FCR has been successfully co-related with concrete strain in compression and steel strain in tension. An empirical equation was also derived separately for beams that failed in shear and flexure, which provides a co-relation between FCR and concrete or steel strain.

Fatigue Crack Initiation Life Prediction of the Rubber Damper Based on Seq-N Curve of Rubber Material

Abstract In this article, the fatigue crack initiation life of the rubber damper is predicted based on the Seq−N curve of rubber material. First, the general expression of the equivalent stress Seq and the fatigue crack initiation life Nf of rubber material are derived under different stress states. Second, the fatigue crack initiation life of a dumbbell-type rubber specimen under different tension strains are measured, and the fatigue parameters of the rubber material are obtained by fitting the experimental results under the uniaxial stress condition. Thus, the equivalent stresses Seq of the dangerous node in the rubber damper are obtained under different working conditions by means of the finite element numerical model. Finally, the fatigue lives of the rubber dampers are obtained by combining the general expressions of the fatigue crack initiation life Nf of rubber material with the equivalent stress Seq of the dangerous node, which are closer to the fatigue crack initiation life experimental results of the rubber damper than the fatigue life obtained based on the εGL,max−N curve. The results indicate the effectiveness for predicting the fatigue crack initiation life of the rubber damper based on the Seq−N curve of the rubber material.

Tectonics of the Isua Supracrustal Belt 2: Microstructures Reveal Distributed Strain in the Absence of Major Fault Structures

AbstractArchean geological records are increasingly interpreted to indicate a ≤3.2 Ga initiation of plate tectonics on Earth. This hypothesis contrasts with dominant plate tectonic interpretations for the Eoarchean (ca. 4.0–3.6 Ga) Isua supracrustal belt (southwest Greenland). Alternatively, recent work shows the belt could have formed via heat‐pipe tectonics. Predicted strain distributions across the belt vary between models. Plate tectonic models predict a dominant unidirectional shear sense, corresponding to subduction vergence, and strain localization within ∼10‐m‐scale shear zones. In contrast, the proposed heat‐pipe model predicts two opposing shear senses, corresponding to opposite limbs of 0.1‐m to km‐scale a‐type folds (i.e., sheath and curtain folds), with relatively equal strain distributed across the belt. Here, we present the first microstructure study using thin‐section petrography and electron backscatter diffraction analysis on quartz of oriented samples from throughout the Isua supracrustal belt. Key findings are: (1) the Eoarchean Isua supracrustal belt was deformed at ∼500°C–650°C, with potential postdeformational recovery at similar or lower temperatures, (2) the spatial distribution of the two opposing shear senses which dominate the belt (top‐to‐southeast and top‐to‐northwest) appears to be random, and (3) the strain intensity across the belt appears to be quasiuniform as evidenced by the uniformly low (mostly <0.1) M‐indexes of quartz fabrics, such that no ≤ 100 ‐m‐scale shear zones can be detected. Our findings are only consistent with the predictions of the heat‐pipe model and do not require plate tectonics, so the geology of the belt is compatible with a ≤3.2 Ga initiation of plate tectonics.

ДИФФЕРЕНЦИАЛЬНЫЕ УРАВНЕНИЯ РАВНОВЕСИЯ ИДЕАЛЬНО УПРУГОПЛАСТИЧЕСКОЙ СПЛОШНОЙ СРЕДЫ ДЛЯ ПЛОСКОЙ ОДНОМЕРНОЙ ДЕФОРМАЦИИ ПРИ АППРОКСИМАЦИИ ЗАМЫКАЮЩИХ УРАВНЕНИЙ БИКВАДРАТ ИЧНЫМИ ФУНКЦИЯМИ

The present article considers the construction of differential equations of equilibrium of geometrically and physically nonlinear ideally elastoplastic in relation to shear deformations of continuous medium under conditions of one-dimensional plane deformation, when the diagrams of volumetric and shear deformation are approximated by biquadratic functions. The construction of physical dependencies is based on calculating the secant moduli of volumetric and shear deformation. When approximating the graphs of the volumetric and shear deformation diagrams using two segments of parabolas, the secant shear modulus in the first segment is a linear function of the intensity of shear deformations; the secant modulus of volumetric expansion-contraction is a linear function of the first invariant of the strain tensor. In the second section of the diagrams of both volumetric and shear deformation, the secant shear modulus is a fractional (rational) function of the shear strain intensity; the secant modulus of volumetric expansion-compression is a fractional (rational) function of the first invariant of the strain tensor. Based on the assumption of independence, generally speaking, from each other of the volumetric and shear deformation diagrams, five main cases of physical dependences are considered, depending on the relative position of the break points of the graphs of the diagrams volumetric and shear deformation. On the basis of received physical equations, differential equations of equilibrium in displacements for continuous medium are derived under conditions of plane one-dimensional deformation. Differential equations of equilibrium in displacements constructed in the present article can be applied in determining stress and strain state of geometrically and physically nonlinear ideally elastoplastic in relation to shear deformations of continuous medium under conditions of plane one-dimensional deformation, closing equations of physical relations for which, based on experimental data, are approximated by biquadratic functions.

DEVELOPMENT OF WOOD GRINDING 2. EFFECTS OF WOOD MOISTURE ON FIBRE PROPERTIES

"The wood grinding model recently published was based on an energy balance of the active grinding zone, i.e. the limited volumes of wood and grindstone that were heated by the grindstone generated compression and tension strains in the wood surface. Generally speaking, the data obtained in well controlled laboratory grindings complied with the derived model meaning that compression–tension power ratios presented as a function of the specific pulp production resulted in linears. However, the wood moisture contents varying from water-saturated to air-dried wood needed further elaboration for better understanding. Accordingly, the aim of this presentation was to find reasonable explanations for the grinding effects on the wood fibres by considering groundwood pulp and paper sheet properties, for example shives and fines contents, as well as tensile strength and light scattering of the paper sheet. The compression–tension power ratios provided by the model reflect simultaneously both compression and tension strain in wood, and accordingly, the resulting fibre properties would be dependent on both brittle and tough fractures. Evidently, the water contents played a role in this context, both as a stiffener of the water-saturated wood, and as a wood and fibre coolant. "

Effect of load-induced local mechanical strain on peri-implant bone cell activity related to bone resorption and formation in mice: An analysis of histology and strain distributions

The purpose of this study was to investigate the effect of load-induced local mechanical strain on bone cell activity of peri-implant bone in mice. Titanium implants were placed in the maxillae of 13-week-old male C57BL/6J mice and subjected to intermittent 0.15 N, 0.3 N, or 0.6 N loads for 30 min/day for 6 days. The animals were sacrificed 2 days after the final loading. Unloaded mice were used as controls. An animal-specific three-dimensional finite element model was constructed based on morphological data retrieved from in vivo microfocus computed tomography for each mouse to calculate the mechanical strain distribution. Strain distribution images were overlaid on corresponding histological images of the same site in the same animal. The buccal cervical region of the peri-implant bone was predetermined as the region of interest (ROI). Each ROI was divided by four strain intensity levels: 0–20 με, 20–60 με, 60–100 με, and ≥100 με, and the bone histomorphometric parameters were analyzed by the total area of each strain range for all loaded samples. The distance between the calcified front and calcein labeling as a parameter representing the mineral apposition rate was significantly greater in the areas with strain intensity ≥100 με than in the area with strain intensity <100 με, suggesting that the bone formation activity of osteoblasts was locally enhanced by a higher mechanical strain. However, the shrunken osteocytes and the empty osteocyte lacunae were significantly lower in the highest strain area, suggesting that osteoclastogenesis was more retarded in higher strain areas than in lower strain areas. The histomorphometric parameters were not affected geometrically in the unloaded animals, suggesting that the load-induced mechanical strain caused differences in the histomorphometric parameters. Our findings support the hypothesis that bone cell activity related to bone resorption and formation is local strain-dependent on implant loading.

Constitutive modeling of bond breaking and healing kinetics of physical Polyampholyte (PA) gel

A three-dimensional finite strain nonlinear viscoelastic model is developed to study the mechanical behavior of a physically cross-linked Polyampholyte (PA) gel. The time dependent behavior of this gel is due to the ionic interactions of oppositely charged monomers randomly distributed along the chain backbone. In this work, we divide the physical cross-links broadly into weak and strong bonds, depending on their survival and reformation characteristics. Our constitutive model connects the strain dependent bond breaking and reforming kinetics in the microscopic regime to the deformation of the gel at the continuum level. We compare the predictions of our model with uniaxial tension, tensile-relaxation, cyclic, and small strain torsional relaxation tests. The material parameters in our model are obtained using least squares optimization. Our theory agrees well with the experimental behavior of the gel.

A user-friendly anisotropic ductile fracture criterion for sheet metal under proportional loading

Anisotropic ductile fracture is of special importance for accurate modeling of failure in plastic forming of lightweight sheet metals. This research introduces a user-friendly approach to model loading direction effect on fracture limits of sheet metals. The approach is combined with a newly developed fracture criterion (DF2016) to illustrate anisotropic fracture in shear, uniaxial tension and plane strain tension as well as fracture under balanced biaxial tension. The anisotropic DF2016 criterion is applied to describe loading direction effect on the fracture limits of two sheet metals: 6k21 aluminum alloy and a steel sheet of DP980. The predicted loading direction effect is observed to agree with the experimental results with high accuracy. The applications demonstrate that there are three advantages of the proposed approach: high accuracy, good flexibility and being very user-friendly in the calibration of anisotropic parameters. Therefore, we recommend the proposed anisotropic DF2016 criterion for numerical failure prediction in stamping of strong anisotropic metals.

Methanol electrooxidation on core-shell Ag@Pdx catalysts

The performance of a direct methanol fuel cell (DMFC) is strongly dependent on the catalytic anode. A high-performance anode is expected to offer enhanced intrinsic activity and/or a large electrochemical surface area. Herein, a series of Ag-core/Pd-shell (Ag@Pdx, x = 1,3,5) catalysts are synthesized in which the thickness of the Pd shell is varied. Both tensional strain and electron transfer between the Ag core and the Pd shell are found to affect the intrinsic activity of these Ag@Pdx catalysts. Of these, the Ag@Pd3 catalyst exhibits the best performance for the methanol oxidation reaction (MOR), showing 4.1 times higher mass activity and 2.6 times higher specific activity than a Pd/C catalyst. Furthermore, density functional theory calculations show that this high MOR performance stems from a stronger adsorption of CH3OH and OH on the Pd active sites. This catalyst is thus a promising candidate for inclusion in a high-performance DMFC.

The effect of soil nonlinearity on high-frequency spectral decay and implications for site response analysis

This study uses recorded ground motions at soil sites over a range of shaking intensities to investigate the effects of soil nonlinearity on the high-frequency spectral decay, as quantified by the parameter [Formula: see text]. Equivalent-linear site response analyses indicate that [Formula: see text] should increase significantly with increasing shear strain and ground motion intensity due to increases in soil damping. However, using more than 2500 motions from 32 sites, this study shows that [Formula: see text] does not vary systematically with the induced shear strain but instead remains at its small-strain value. This observation indicates that high-frequency components of motion are consistent with small-strain damping, rather than the strain-compatible damping used in site response analysis. It is demonstrated that equivalent-linear site response analyses for large strains can be modified to generate surface motions with more realistic high-frequency content by scaling the predicted surface motion to fit the small-strain [Formula: see text] or by employing frequency-dependent soil properties that account for the frequency dependence of the induced strains.

Estimating aortic thoracic aneurysm rupture risk using tension-strain data in physiological pressure range: an in vitro study.

Previous studies have shown that the rupture properties of an ascending thoracic aortic aneurysm (ATAA) are strongly correlated with the pre-rupture response features. In this work, we present a two-step machine learning method to predict where the rupture is likely to occur in ATAA and what safety reserve the structure may have. The study was carried out using ATAA specimens from 15 patients who underwent surgical intervention. Through inflation test, full-field deformation data and post-rupture images were collected, from which the wall tension and surface strain distributions were computed. The tension-strain data in the pressure range of 9-18kPa were fitted to a third-order polynomial to characterize the response properties. It is hypothesized that the region where rupture is prone to initiate is associated with a high level of tension buildup. A machine learning method is devised to predict the peak risk region. The predicted regions were found to match the actual rupture sites in 13 samples out of the total 15. In the second step, another machine learning model is utilized to predict the tissue's rupture strength in the peak risk region. Results suggest that the ATAA rupture risk can be reasonably predicted using tension-strain response in the physiological range. This may open a pathway for evaluating the ATAA rupture propensity using information of in vivo response.

Features of Constructing Recrystallization Curves of the 2nd and 3rd Types for High-Alloy Alloys of Various Structural Classes VZH159 and 14Cr17Ni2

The features of methods for constructing recrystallization curves of the second and third kind and the dependence “average grain size (area) - strain intensity – temperature” are given. For alloys of various structural classes VZH159 and 14Cr17Ni2 using the above methods, a recrystallization curve and the recrystallization dependence for a temperature of 1100℃ are constructed. The advantages and disadvantages of the above methods are considered.