Entire Loading Range Research Articles

Numerically assisted calibration procedure of nonlinear in-plane shear properties of unidirectional composite laminae based on off-axis tensile experiments

In this paper, a novel methodology is presented to evaluate the true nonlinear shear response of continuous fiber-reinforced plastic (CFRP) unidirectional laminae. It requires simple off-axis tensile experiments to be conducted and a finite element (FE) representation of them with a material constitutive law capable of handling nonlinearity in shear. Upon successful evaluation of the normal stiffness properties, the shear stress-strain response is derived via numerical calibration of the underlying FE models. The presented approach is also demonstrated by processing the raw data of an extensive material characterization test campaign conducted on a thermoplastic matrix CFRP. The outcome is compared to the conventional methods for shear response derivation using relevant standards such as ASTM D3518 and ASTM D5379. It has been successfully demonstrated that the pseudo-hardening phenomenon obtained from standard shear experiments as a result of fibers aligning with load direction can be eliminated with off-axis specimen tension experiments, thus, the true shear stress versus deformation response can be extracted up to failure. The main purpose of current work is to demonstrate the inconsistency in the available standard methods related to mechanical testing-based derivation of nonlinear in-plane shear behavior of UD plies. In addition, a novel technique is presented to achieve a more accurate prediction of nonlinear shear stress and strain along the entire representative loading range that contributes to more accurate simulations of composite parts up to failure and thus, better strength predictions.

Toward the development of plasticity theories for application to small-scale metal structures.

Experiments are performed on micron-scale single-crystal prototypical structural elements experiencing combined torsion and bending to gather data on their load-carrying capacity in the range of size and strain relevant to micron-scale structures for which little data are available. The observed strengthening dependence on size for the structural elements is in general accord with trends inferred from prior tests such as indentation and pure torsion. In addition, the experiments systematically reveal the strengthening size-dependence of structural elements whose surface has been passivated by a very thin Cr coating, an effect shown to have substantial strengthening potential. A state-of-the-art strain gradient plasticity theory is used to analyze the structural elements over the entire range of size and loading. While the computed trends replicate the experimental trends with reasonable fidelity, the predictive exercise, which is representative of those that will be required in micron-scale structural analysis, brings to light constitutive and computational issues which will have to be addressed before micron-scale plasticity theory can serve as effectively at the micron scale as conventional plasticity does at larger scales.

Constraint loss correction: Enhancing transferability of fracture toughness of Eurofer97 compact tension specimens between specimen sizes

This paper proposes and implements a constraint loss correction as a supplement to the ASTM correction factor for the master curve method (ASTM-E1921) for Eurofer97 reduced activation steel in order to enhance the transferability of results between compact tension (CT) specimen sizes. To facilitate the acquisition and scalability of reliable fracture toughness data from one specimen size to another and to apply the Master-Curve method with confidence when using small specimens, the difference in the structure of the crack tip stress field between large and small specimens was modeled. The stress intensity factors and critical volumes/stresses of two specimen sizes (1 T and 0.18 T) were calculated with 3D finite element simulations run over a large displacement range and at a temperature range of −120 to −80 °C and the results were compared with real data from a database of toughness tests of Eurofer97 steel. The K values from a miniaturized specimen without or with ASTM correction and with the proposed combined correction with constraint loss factor (which is variable over the entire loading range) were compared with simulated CT-1 T stress intensity values. It was found that this new correction factor was accurate up to a target toughness of 200 MPa.m1/2, which represents a major improvement on the current state of the art.

Numerical Modelling of the Compressive and Tensile Behavior of Ultra-High Performance Concrete in Beams

INTRODUCTION Ultra-high performance concrete (UHPC) differs in its structural behavior from conventional concrete upon loading due to its high compressive and tensile strength, stiffness, toughness, and durability. Therefore, UHPC needs an appropriate constitutive model to simulate its mechanical properties in finite element analysis (FEA). METHOD In this study, numerical models were developed to trace the structural behavior of UHPC beams upon loading since beam behavior depends on the constituents' response to compression and tension. New numerical models were formulated to display the stress-strain relationships of UHPC in compression and tension by adopting a new methodology that depended on actual results. The compressive stress-strain relationship consisted of two portions; the ascending one for elastic and strain hardening up to compressive strength and a descending curve for the strain-softening until reaching a strain of 0.0062. RESULT A linear tensile stress-strain relation was applied for the elastic tensile behavior up to tensile strength. Then, a tri-linear relationship was applied for the stiffness degradation and crack propagation upon debonding fibers from the concrete matrix until fracture. These numerical models were used in Abaqus software to simulate the UHPC beam behavior. CONCLUSION The developed models were verified and approved for beams' behavior upon loading in flexure and shear. The results indicated that the models could predict the UHPC beams' response throughout the entire loading range from the beginning until failure. The verification included bear capacity, deflection, crack pattern, and stress distribution.

Bi-Linear Bond-Slip Modelling for 1-D Tension Stiffening Behavior of a RC Element

Cracking is an inherent characteristic of a reinforced-concrete (RC) element subjected to tension or bending. The crack width growth with loading depends on the rebar-concrete bond behavior. RC bridges are designed under strict requirements to ensure their proper long lifetime performance. Limiting the crack widths improves the performance and safety of bridges that are exposed to harsh climatic and environmental effects and enhances bridge service life-cycle expectancy. This paper presents an extended one-dimensional formulation for analyzing RC elements subjected to tensile loads and solves the one-dimensional tension stiffening problem. The extended bond-slip model analyses the entire range of loading, following cracks growth up to their maximum allowed width, employing a bi-linear bond-slip relationship. The analytical solution refers to the early loading stage where the first bond-slip segment governs the entire element and a closed form solution is obtained, followed by the higher loading stage where two different bond-slip relationships govern two complementary segments of the element. Analytical expressions for the stresses, strains, and displacements in concrete, steel, and interface are developed. Cracking is followed until rebar yielding. Validation of the model with available test results shows good agreement that is superior to the commonly used linear bond-slip model.

Key factors in the adsorption of natural organic matter to metal (hydr)oxides: Fractionation and conformational change

Adsorption of natural organic matter (NOM) to mineral surfaces is an important process determining the environmental fate and biogeochemical cycling of many elements. Natural organic matter consists of a heterogeneous mixture of soft and flexible organic molecules. Upon adsorption, size fractionation may occur, as well as changes in molecular conformation. Although very important, these phenomena have been omitted in existing adsorption models. Filling this gap, a novel framework for NOM adsorption to metal (hydr)oxides is presented. Humic acid (HA) was used as an analog for studying experimentally the NOM adsorption to goethite and its size fractionation as a function of pH, ionic strength, and surface loading. Size fractionation was evaluated for adsorption isotherms collected at pH 4 and 6, showing HA molecules of low molar mass were preferentially adsorbed. This phenomenon was incorporated into the new model. Consistent description of the HA adsorption data over the entire range of pH (3–11), ionic strength (2–100 mM), and surface loading (0.1–3 mg m−2) indicated that the spatial distribution of HA molecules adsorbed in the interface is a trade-off between maximizing the interaction of the HA ligands with the oxide surface and minimizing the electrostatic repulsion between HA particles as a result of interfacial crowding. Our advanced consistent framework is able to quantify changes in molar mass and molecular conformation, thereby significantly contributing to an improved understanding of the competitive power of HA for interacting on oxides with other adsorbed small organic acids as well as environmentally important oxyanions, such as phosphate, arsenate, and others.

Behavior of reinforced concrete tapered beams

Long span framed buildings and simply supported bridges produce high bending moment and deflection at mid-span. For these structures, using conventional prismatic beams with high depth shall be uneconomic. In such instances; using tapered beams may be considered a viable alternative to overcome this issue. There is lack of experimental and analytical studies on the behavior of reinforced concrete tapered beams (RCTBs) having mid-span depth enlargement.This research introduces experimental and finite elements method (FEM) study on the behavior of RCTBs with mid-span depth enlargement and different tapering angles and reinforcement configurations. Accordingly, six RCTBs and one prismatic beam were cast and tested up to failure. The test RCTBs were divided into two groups (three tapered beams for each group) depending on the tapering angle. Consequently, tapering angles of about 20° and 36° were adopted for beams of Group I and Group II, respectively. For each group, three different reinforcement configurations were adopted. It is observed from test results that RCTBs reinforced with bottom bent rebars have developed higher ultimate strength, stiffness and toughness compared with those beams having other reinforcement configurations. However, for RCTB with tapering angle of about 20° and reinforced with bottom bent rebars, a somewhat small reduction in ultimate strength of about 16% with gain in weight of about 27% was recorded compared to the prismatic beam. FEM using ABAQUS software was used to simulate the test beams. Good agreement was obtained between the experimental and FEM results in terms of load-deflection response and crack pattern. Moreover, the FEM study was extended to cover a reasonable range of tapering angles (17° to 45°) and bottom bent reinforcement ratios (0.0031 to 0.0086). It is observed from numerical results that decreasing of the tapering angle from 45° to 17° resulted in a significant increase in the ultimate load, initial stiffness and toughness and decreasing the mid-span deflection within entire range of loading. In addition, normalized charts were presented in this study to easily estimate the ultimate strength, initial stiffness, and toughness of a RCTB having a certain tapering angle and bottom bent reinforcement ratio.

Open water performance of B-Series marine propellers in tandem configurations

The hydrodynamic performance of 4-bladed B-series tandem propellers with different design configurations in open water is numerically investigated using a RANS-based CFD solver. The integration of the co-rotating aft propeller increases the resultant thrust and torque coefficients in the entire range of propeller loading. The open water efficiency at moderate to high propeller loadings is reduced, but the range of positive thrust output is increased.Due to the induced velocities and flow acceleration caused by the forward propeller, a higher pitch ratio should be adopted for the aft propeller to generate the blade forces. While the forward propeller behaves very similar to a conventional single propeller, the thrust and torque coefficients of the aft propeller show minimal variations with advance coefficient due to high induced velocities. At higher advance coefficients and blade sections closer to the hub there is greater deviation of forces generated by the aft propeller blade as compared to a single propeller of similar design. Parametric investigations are presented, highlighting the influence of axial spacing, relative angular position, pitch difference, and diameter ratio between the forward and aft propellers on the open water performance. From the present study, a pitch ratio difference of 0.3 may be maintained between the two propellers for optimal open water performance.

A Numerical Model for Tracing Structural Response of Ultra-High Performance Concrete Beams

This paper presents a finite element-based numerical model for tracing the behavior of ultra-high performance concrete (UHPC) beams. The model developed in ABAQUS can account for stress–strain response of UHPC and reinforcing bar in both tension and compression, bond between concrete and reinforcing steel, and strain hardening effects in bars and UHPC and can trace the detailed response of UHPC beams in the entire range of loading. This model is validated by comparing predicted response parameters including load-strain, load-deflection, and crack propagation against experimental data governed from tests on UHPC beams with different reinforcement ratios, fiber volume fractions, and loading configurations (shear and flexural loading). The validated model is applied to quantify the contribution of stirrups and concrete to shear strength of beams so as to explore the feasibility of removing shear reinforcement in UHPC beams.

Development of a Novel Gasoline Particulate Filter Loading Method Using a Burner Bench

In view of the deliberations on new Euro 7 emission standards to be introduced by 2025, original equipment manufacturers (OEMs) are already hard at work to further minimise the pollutant emissions of their vehicles. A particular challenge in this context will be compliance with new particulate number (PN) limits. It is expected that these will be tightened significantly, especially by including particulates down to 10 nm. This will lead to a substantially increased effort in the calibration of gasoline particulate filter (GPF) control systems. Therefore, it is of great interest to implement advanced methods that enable shortened and at the same time more accurate GPF calibration techniques. In this context, this study presents an innovative GPF calibration procedure that can enable a uniquely efficient development process. In doing so, some calibration work packages involving GPF soot loading and regeneration are transferred to a modern burner test bench. This approach can minimise the costly and time-consuming use of engine test benches for GPF calibration tasks. Accurate characterisation of the particulate emissions produced after a cold start by the target engine in terms of size distribution, morphology, and the following exhaust gas backpressure and burn-off rates of the soot inside the GPF provides the basis for a precise reproduction and validation process on the burner test bench. The burner test bench presented enables the generation of particulates with a geometric mean diameter (GMD) of 35 nm, exactly as they were measured in the exhaust gas of the engine. The elemental composition of the burner particulates also shows strong similarities to the particulates produced by the gasoline engine, which is further confirmed by matching burn-off rates. Furthermore, the exhaust backpressure behaviour can accurately be reproduced over the entire loading range of the GPF. By shifting GPF-related calibration tasks to the burner test bench, total filter loading times can be reduced by up to 93%.

Unloaded Organ Culturing Has a Detrimental Effect on the Axial Mechanical Properties of the Intervertebral Disc.

Healthy function of intervertebral discs (IVDs) depends on their tissue mechanical properties. Native cells embedded within IVD tissues are responsible for building, maintaining, and repairing IVD structures in response to genetic, biochemical, and mechanical signals. Organ culturing provides a method for investigating how cells respond to these stimuli in their natural architectural environment. The purpose of this study was to determine how organ culturing affects the mechanical characteristics of functional spine units (FSUs) across the entire range of axial loading, including the neutral zone (NZ), using a rat tail model. Rat tail FSUs were organ cultured at 37 °C in an unloaded state in standard culture media for either 1-day (n = 8) or 6-days (n = 12). Noncultured FSUs (n = 12) were included as fresh control specimens. Axial mechanical properties were tested by applying cyclical compression and tension. A novel mathematical approach was developed to fully characterize the relationship between load, stiffness, and deformation through the entire range of loading. Culturing FSUs for 1-day did not affect any of the axial mechanical outcome measures compared to noncultured IVDs; however, culturing for 6 days increased the size of NZ by 112% and decreased the stiffness in NZ, compressive, and tensile regions by 53%, 19%, and 15%, respectively, compared to noncultured FSUs. These results highlight the importance of considering how the mechanical integrity of IVD tissues may affect the transmission of mechanical signals to cells in unloaded organ culturing experiments.

A Simple and Safe Strategy for Improving the Fuel Economy of a Fuel Cell Vehicle

A new real-time strategy is proposed in this article to optimize the hydrogen utilization of a fuel cell vehicle, by switching the control references of fueling regulators, based on load-following. The advantages of this strategy are discussed and compared, with advanced strategies that also use the aforementioned load-following mode regulator of fueling controllers, but in the entire loading range, respectively, with a benchmark strategy utilizing the static feed-forward control of fueling controllers. Additionally, the advantages of energy-storage function in a charge-sustained mode, such as a longer service life and reduced size due to the implementation of the proposed switching strategy, are presented for the dynamic profiles across the entire load range. The optimization function was designed to improve the fuel economy by adding to the total power of the fuel utilization efficiency (in a weighted way). The proposed optimization loop will seek the reference value to control the fueling regulator in real-time, which is not regulated by a load-following approach. The best switching threshold between the high and low loading scales were obtained using a sensitivity analysis carried out for both fixed and dynamic loads. The results obtained were promising—(1) the fuel economy was two-times higher than the advanced strategies mentioned above; and (2) the total fuel consumption was 13% lower than the static feed-forward strategy. This study opens new research directions for fuel cell vehicles, such as for obtaining the best fuel economy or estimating fuel consumption up to the first refueling station on the planned road.

Analytical Model of Nonlinear Semi-rigid Frames Using Finite Element Method

Performance-based design for a constructional steel frame in nonlinear-plastic region requires an improvement in order to achieve a reliable structural analysis. The need to explicitly consider the nonlinear behaviour of structures makes the numerical modelling approach much more favourable than expensive and potentially dangerous experimental work. The parameters considered in the analysis are not limited to the linear change of geometry and material yielding, but also include the effect of large deformations, geometrical imperfections, load eccentricities, residual stresses, strain-unloading, and the nonlinear boundary conditions. Such analysis requires the use of accurate mathematical modelling and effective numerical procedures for solving equations of equilibrium. With that in mind, this paper presents the mathematical formulations and finite element procedures of nonlinear inelastic steel frame analysis with quasi-static semi-rigid connections. Verification and validation of the developed analytical procedures are conducted and good agreements are obtained. It is an approach that enables the structural behaviour of constructional steel frames to be traced throughout the entire range of loading until failure. It also provides information on the derivation of the structural analysis by using finite element method.

A Family of Soft-Switching DC–DC Converters With Two Degrees of Freedom

Switching losses including reverse recovery losses, have a significant impact on total losses of DC–DC converters especially in high voltage applications. This article introduces a new family of DC–DC converters with two degrees of freedom, which can handle the mentioned issue. The proposed family of DC–DC converters contains a bidirectional and a unidirectional cell, and provides an additional control parameter. This parameter can be adjusted so that there are soft switching conditions for all the switches of the converter within the entire range of loading. In addition, properly tuning the new parameter can decrease the circulating current and consequently decrease the conduction losses considerably. Besides, the unidirectional cell contributes to power transfer, especially under full load condition. Moreover, the filter capacitor is one fourth in comparison with the conventional dc-dc converters. The proposed converter is modeled and its operation modes are studied. Also, in order to verify the findings, a 500 W prototype with a frequency of 100 kHz is implemented, and the results are compared.

Seismic Analysis and Evaluation of Y-shaped EBF with an Innovative SSL-SSBC

During severe earthquakes, the ductility and energy dissipation capacity of shear links in Y-shaped eccentrically braced frames (EBFs) are crucial to achieve desirable seismic performance and structural safety. In this study, an innovative SSL-SSBC combining the advantages of a shear slotted bolted connection (SSBC) and a very short shear link is developed to improve the seismic performance of Y-shaped EBFs. Finite element (FE) analysis methods are first validated through comparison with existing experimental results for slotted bolted connection and very short shear links. Further, FE simulations of the SSBC, very short shear link with shear slotted bolted connection (SSL-SSBC), and Y-shaped EBF are conducted to determine their mechanical behavior systematically. The FE results demonstrate that a reasonable SSBC can effectively increase the ductility and energy dissipation capacity through friction slipping, allowing the SSBC to maintain elastic behavior throughout the entire range of seismic loading, while the very short shear link in the SSL-SSBC could undergo severe damage to dissipate seismic energy. As expected, the SSL-SSBC is capable of working as both a shear dissipation damper and a metallic ductile damper in the Y-shaped EBF. This study also clearly identifies that no yielding or damage of the very short shear links occurs during small and medium earthquakes, and the deformation and damage of the very short shear link can be minimized during severe earthquakes, allowing the seismic resilience capacity of the Y-shaped EBF to be dramatically enhanced.

The Influence of the E-Modulus of Coarse Aggregate on the Stress-Strain Diagram of the Concrete with Frame Structure

The stress-strain diagrams of concrete with frame structure made with content of coarse aggregate from 0.56 till 0.64 m3/m3, with crushed granite (E-modulus = 71 GPa) and crushed silica sandstone (E-modulus = 42 GPa) are shown. It is shown that the stress-strain diagram of the concrete with frame structure made with coarse aggregate with E-modulus 42 GPa is almost linear over the entire loading range. Stress-strain diagram of concrete made with coarse aggregate with E-modulus 71 GPa has three zones. It is concluded that the concentration of intrastructural stresses under loading in the concrete with frame structure with a decrease in the ratio of E-modulus of the coarse aggregate/E-modulus of the mortar matrix is decrease that is why bad decision is to use coarse aggregate with high level of E-modulus, such as crushed granite, in concrete with frame structure.

Shear strength model for reinforced concrete beam-column joints based on hybrid approach

Behavior of RC beam-column joint is very complex as the composite material behaves differently in elastic and inelastic range. The approaches generally used for predicting joint shear strength are either based on theoretical, strut-and-tie or empirical methods. These approaches are incapable of predicting the accurate response of the joint for entire range of loading. In the present study a new generalized RC beam-column joint shear strength model based on hybrid approach i.e. combined strutand-tie and empirical approach has been proposed. The contribution of governing parameters affecting the joint shear strength under compression has been derived from compressive strut approach whereas; the governing parameters active under tension has been extracted from empirical approach. The proposed model is applicable for various conditions such as, joints reinforced either with or without shear reinforcement, joints with wide beam or wide column, joints with transverse beams and slab, joints reinforced with X-bars, different anchorage of beam bar, and column subjected to various axial loading conditions. The joint shear strength prediction of the proposed model has been compared with 435 experimental results and with eleven popular models from literature. In comparison to other eleven models the prediction of the proposed model is found closest to the experimental results. Moreover, from statistical analysis of the results, the proposed model has the least coefficient of variation. The proposed model is simple in application and can be effectively used by designers.

Nonlinear Finite Element Modeling of Shear Behavior of Concrete Deep Beams Reinforced with Internal Glass Fiber-Reinforced Polymer Bars by ANSYS

The purpose of this paper is to numerically trace the behavior of concrete deep beams reinforced with internal Glass Fiber-Reinforced Polymer (GFRP) bars and containing no web reinforcement by using ANSYS program. For this purpose, a finite element model is used for concrete deep beams that previously examined in an experimental study and its predicted failure loads were compared with the actual failure loads. The results of the finite element model were in a good agreement with observations from the experimental study. The comparisons showed that the used model has the ability to capture the shear behavior, as well as load-deflection response and crack patterns of deep beams reinforced with internal GFRP bars in the entire range of loading. The paper is also covered a parametric study on shear span-to-depth (a/d) ratio, GFRP reinforcement ratio and concrete compressive strength which they usually have high impacts on the behavior of fiber-reinforced concrete beams. The results of the parametric study showed that the ultimate failure load of beams reinforced with GFRP bars was higher than that of steel-reinforced concrete beams. The maximum failure load was observed to decrease by decreasing the a/d ratio. The stiffness and ductility of the beams were increasing by increasing the reinforcement ratio.

Characterization of resilient mounts for marine diesel engines: Prediction of static response via nonlinear analysis and response surface methodology

The paper describes an experimental procedure to find the optimal values of the coefficients of the Yeoh hyperelastic material model for a resilient mounting element for marine diesel engines. The quasi-static implicit finite element simulation of the resilient mount deformation under an increasing load is matched with the force-displacement curve of the element acquired via laboratory tests. A response surface analysis is then performed to create a predictive model. This allows to find the best values of the Yeoh coefficients and assess their importance in the predictive equation. With a limited number of runs it is possible to obtain a finite element model that simulates accurately the static deformation of the resilient mounting element over the entire loading range.

Creation of Oil-Filled Composites of Tribotechnical Purpose Based on Aromatic Polyamide Phenylone C-2

The authors of the paper suggested a recently developed technology of creating oil-filled composites based on aromatic polyamide Phenylone C-2. The depicted approach originates in the functional modification of the matrix base with nanomodified fillers and nanodimensional additives. The paper formulated the principles of absorption modification of mineral nanofiller for creating universal inhibitors of tribosystem or oleaginous polymer, more known as «maslyanit». It was demonstrated that the efficiency of polymer filling is enhanced by the joint application of the methods of preliminary solvent cleaning and dispersion of mineral particles to the nanodispersed state. The increase of the sorption capacity of natural and synthetic minerals was carried out by acid modification of minerals. A set of comparative tribological tests on a friction machine of Amsler II 5018 type according by a «finger-roller» scheme without external lubrication was carried out to evaluate the resistance of composite materials to abrasion at a constant specific pressure. It was found that the introduction of PFPE oil led to a significant decrease of the coefficient of friction practically in the entire loading range only in composites containing Aerosil. While the introduction of PMPS oil, in contrast, strengthened the antifriction effect of the samples, containing spinel and serpentine, in the load range of 209-720 N. The study of physical and mechanical properties of composites was carried out by NanoTest 600 complex. It was established that the samples with the addition of Arimid are characterized with the highest physical and mechanical properties. Besides, it as noted that the addition of PFPE and PMPS oils when creating oil-filled composites results in 20-25% decrease the microhardness and modulus of elasticity values. The carried out researches allowed concluding that the composite with that composition is most suitable for use in non-lubricated friction units.