Variation Of Elastic Modulus Research Articles

Frost-resistance mechanism of multi-scale PFRC based on NMR

In order to explore the frost-resistance mechanism of multi-scale polypropylene-fibre-reinforced concrete (PFRC), the mass loss rate and relative dynamic elastic modulus variation curves of concretes made with different sizes of polypropylene (PP) fibre were analysed based on the fast freeze–thaw cycle test. Nuclear magnetic resonance testing and scanning electron microscopy were carried out to study the micropore structure of the PFRCs. The results showed that the multi-scale PFRC had excellent frost resistance. Compared with plain concrete, the concretes mixed with coarse and fine PP fibres showed a 0·242–0·427% improvement in porosity, with 75·68–84·00% of pores of radius less than 100 nm. When the total PP fibre content was held constant, but the amount of fine fibre was larger and the fibre diameter was smaller, the improvements in concrete micropore structure and spalling resistance were more obvious. For the multi-scale PFRCs studied, it was found that three sizes of fibres formed a better holistic network system as the fibres supported and complemented each other. The micropore structure and frost resistance of the concrete were improved significantly, while the cracking resistance and toughness of the specimens were adequate.

Effects of Template and Molecular Nanostructure on the Performance of Organic–Inorganic Photomechanical Actuator Membranes

AbstractPorous anodic aluminum oxide (AAO) membranes template the growth of photochromic crystalline nanowires. The resulting organic–inorganic composite can function as a photomechanical bending actuator. In order to investigate how the nanostructural properties of both the organic and inorganic components affect the photomechanical response, the composite mechanical properties are characterized using a variety of methods. There is a significant variation in both morphology and elastic modulus for two commercially available AAO templates with nominally identical pore diameters of 200 nm. After these templates are filled with diarylethene molecules that undergo a ring‐open to ring‐closed photoisomerization, the light‐generated curvature and mechanical work are evaluated using two different methods. The templates with a lower average elastic modulus (16 GPa vs 68 GPa) generate almost an order of magnitude more photomechanical work. The dependence of the photomechanical response on the chemical structure of the photochrome is assessed by comparing the performance of a diarylethene that undergoes a crystal expansion to that of one that undergoes a contraction, which leads to a decrease in curvature. Both the inorganic template and the organic active component play important roles in the overall photomechanical response, with substantial room to improve the performance.

Effects of environmental and operational actions on the modal frequency variations of a sea-crossing bridge: A periodicity perspective

Abstract The modal frequency variations of bridges associated with environmental and operational actions are among the primary research topics in structural health monitoring (SHM). Based on the periodic variations of the monitoring data obtained over 6 years for the Donghai Bridge (DHB), we investigated the effects of environmental and operational factors on the modal frequency variations and identified the main periods and influencing factors of the DHB frequency changes. Partial correlation coefficients and cyclic averaging were applied to compare the contributions of various actions to the frequency changes, and the underlying mechanisms of the frequency changes were preliminarily studied. The modal frequencies of the DHB were found to vary with periods such as 1 year, 1 week, 1 day, and 12.42 h in a manner corresponding to inherent variation cycles of structural temperature, traffic loading, wind loading, and sea level. Structural temperature and traffic loading were the primary factors influencing the DHB frequency changes, and their relative degrees of impact on the frequency changes were different for different cycles. All modal frequencies of the DHB decreased with increasing temperature due to variation in the temperature-dependent elastic moduli of the structural materials. However, as traffic loading increased, the fundamental frequencies of the vertical bending, lateral bending, and torsional modes of the girder decreased, while some higher-order frequencies increased. The influence of traffic on the modal frequencies could be qualitatively explained by employing an equivalent spring–mass model of the traffic flow on the bridge. The results of this study will deepen the understanding of the frequency changes occurring in bridges during operation and can serve as a reference for vibration-based SHM.

An analytical model for rapid prediction and compensation of springback for chain-die forming of an AHSS U-channel

Chain-die forming is an emerging technique for manufacturing AHSS component as an alternative to roll forming. The pronounced springback of AHSS due to their high strength is a key factor in chain-die blocks design. In this paper, a modified Chaboche hardening model that assumes a Hollomon–Voce combined equation and incorporates variation of elastic modulus is established to better describe hardening behaviors of AHSS. An analytical method for rapid prediction of springback of a U-channel is developed and then combined with an optimization algorithm to minimize springback. The springback compensation is validated by a chain-die forming experiment of a QP1180 U-channel by using the optimal die blocks. The proposed analytical modeling method provides a fast and effective tool for die block design of U-channel chain-die forming.

Experimental study on the fundamental frequency of prestressed concrete bridge beams with parabolic unbonded tendons

In this study, a laboratory experiment–based testing program was conducted on a large-scale high-strength Prestressed Concrete I (PCI) beam with a parabolic unbonded tendon, capable of simulating a typical prestressed bridge member. Specifically, the simply supported PCI beam was subjected to free transverse vibrations with different prestress forces to demonstrate that its fundamental frequency was unaffected by such force. A reference model, describing the behavior of the PCI beam as a combination of two substructures interconnected, i.e., a compressed concrete Euler–Bernoulli beam and a tensioned parabolic cable, predicts no change in fundamental frequency with increasing prestress force when variation of the concrete's initial elastic modulus over time is taken into account. The large-scale experimental results confirmed that fundamental frequency is not an appropriate parameter for prestress loss prediction in concrete bridge beams with parabolic unbonded tendons. Accordingly, subsequent studies will be conducted for improving a static nondestructive testing method for such detection in concrete bridges.

An Empirical Approach for the Determination of Skin Elasticity: Finger pad Friction against Textured Surfaces

Surface topography significantly influences tactile friction and perception. While friction forces can be reduced by surface texturing, selection of pattern dimensions is challenging due to the highly variable elastic modulus of the skin. This work proposes an empirical approach for the evaluation of the skin elasticity through surface transition from asperity to full contact state. To highlight the contact transition, two textures with evenly distributed identical micro asperities, but varying density, were moulded with several grades of silicone rubber. Dynamic friction coefficient measurements were performed during finger pad sliding against the textured samples with a range of normal loads up to 5 N. A combination of analytical and numerical contact models is used to explain the observed friction behaviour, estimate the development of contact area and calculate the effective elastic modulus of the skin at the micro-scale. Low density textures clearly indicate the transition to the full contact state, which is reflected in friction coefficient development, while high density textures remain in an asperity contact state, with significantly lower friction values. The effective Young's modulus is hereby estimated in the range of 0.2–0.5 MPa. Observed frictional behaviour is explained by the change in the apparent and real contact areas. The presented approach allows to study the influence of individual surface parameters on effective skin elastic modulus, which is essential for the development of functional surfaces with improved tactile perception.

Polymer composite Belleville springs for an automotive application

This paper investigates mathematical modelling and manufacturing of polymer composite Belleville springs, and their potential application. The original expression for load carrying capacity developed for metal springs is refined by considering the variation of elastic modulus and Poisson’s ratio of laminates in polar coordinates. A novel series spring stacking arrangement is proposed to achieve complex stiffness variation by progressive action. The experimental results show consistent effect of number of plies on the spring rate and compare well with the theoretical predictions. Although handmade, the variations in load carrying capacity is very small (∼10%) confirming manufacturing viability. It is shown that a smooth, variable spring rate curve can be produced by reducing slip-stick frictional forces with the use of spacers within the spring stacks. In one application, the composite springs are shown to offer significant vehicle dynamic performance improvement through reduction of the tyre contact patch force variation and vehicle body acceleration.

An efficient model transfer approach to suppress biological variation in elastic modulus and firmness regression models using hyperspectral data

The goal of the current work is to reduce biological variation of agricultural produce through an efficient model transfer approach with low labeling cost. The core step of the proposed algorithm is to use a selection strategy for choosing informative samples into the calibration set, and subsequently eliminating uninformative/weakly informative/interference samples out of the calibration set. Results on blueberry hyperspectral data validate that the proposed move-in/move-out model transfer approach can effectively diminish biological variability. The performance of the transferred model for elastic modulus prediction (Bluecrop → M2) tends to be stable with Rp and RMSEp (RPD) of 0.742 and 0.177 g/mm2/% (0.860) after the 64 samples are replaced. The transferred model of firmness (Bluecrop → M2) can predict the independent M2 samples with Rp and RMSEp (RPD) of 0.712 and 72.0 g (1.017) at the 15th cycle. For these two mechanical properties, the model transfer approach can lessen heavy annotation work when transferring the initial Bluecrop model to M2. The second model transfer does not perform well. Similar results are found in other model transfer orders such as M2 → Duke → Bluecrop. Good stability is shown during the first model transfer by results on stability analysis. Moreover, results of the comparison experiment indicate that this approach can give a better transfer result than the move-in approach. This algorithm can be extended to large scale applications that cost less to reduce biological variability. (Source codes are freely available to non-commercial users at: https://figshare.com/articles/Move-in_move-out_model_transfer_algorithm-Matlab_toolbox/6989090).

Study on the Influence of the Grind Percentage Over the Surface Hardness and Modulus of Elasticity of Parts Made of ABS, P6.6 and POM through Nanoindentation

This paper analyzes the indentation hardness and the indentation elastic modulus variation depending on the variation of the grind percentage of polymer, when the other factors that can influence the injection molding remain unchanged. The analyzed polymers were: acrylonitrile butadiene styrene ABS MAGNUM 3453, polyamide PA 6.6 TECHNYL AR218V30 Blak and polyoxymethylene POM EUROTAL C9 NAT. The samples that were studied had different compositions in new and grinding material. The G-Series Basic Hardness Modulus at a Depth method was used. The increase of the grind percentage of ABS (from 0 to 100 %) leads to insignificant changes in the indentation hardness, indentation modulus, and maximum force applied to samples of tested material. The maximum hardness (0.137 GPa) of PA 6.6 is recorded in the case of the sample with 80% grind content, and the maximum hardness of POM is recorded as well in the case of the sample with 80% grind content, as being 0.215 GPa. The variation of the grind content in the analyzed samples determines changes in the evaluated parameters, depending on the type of polymer. Combining the new material with grind in proportions experimentally established for each techno polymer leads to changes in their mechanical properties.

Various elastic moduli of AA6016 and their application on accurate prediction of springback

ABSTRACTFirst of all, the elastic modulus variation of 6016-T4 aluminum alloy has been investigated by uniaxial tensile experiments. Secondly, a new model to describe the change of elastic modulus has been proposed based on our experimental data. Then Finite Element (FE) simulations with various elastic moduli have been conducted to predict the springback of V bending. The results are shown as follows: the elastic modulus decreases, obviously, with increase of equivalent plastic strain; the proposed model is more suitable to explain our experimental data than the other models considered; and the springback prediction of V bending with various elastic moduli is more precise than with constant modulus.

Experimental Study on Corrosion and Mechanical Behavior of Main Cable Wires Considering the Effect of Strain.

To study the corrosion degradation of cable wires in a bridge’s life, this research work created an accelerated corrosion test device, which sought to identify an optimal constant strain level. An accelerated corrosion test was carried out and the corroded specimens were scanned using super depth 3D microscopy technology. Mass loss and minimum cross-sectional diameter was measured to understand the degradation characteristics of cable wires at variable strains and corrosion time. The variation of elastic modulus, yield load, and ultimate load of corroded wires, subjected to a tensile test, were analyzed. The experimental results illustrate that the average mass loss ratio of the corroded cable wires increases nonlinearly as corrosion time increases. The higher the stress level, the more serious the corrosion level. The minimum cross-sectional diameter has good correlation with corrosion time and stress level. The elastic modulus of wires does not change significantly with the increase of corrosion time. Yield load and ultimate load decreases with the increase of strain level, and the rates of decline under different strains are nonlinear.

Rate-Type Age-Dependent Constitutive Formulation of Concrete Loaded at an Early Age.

A general formulation framework for an age-dependent constitutive equation of concrete is presented to account for the development of the elastic modulus at an early age. This is achieved by expanding the total stress vs. strain relation with respect to the time-varying elastic modulus. Two types of constitutive formulation frameworks are derived depending on whether (or not) the time-varying effect of the elastic modulus was taken into account in the linearized series expansion. The causes for the age-dependent deformations under sustained loads are defined in the formulation based on the two internal mechanisms of delayed elasticity and the ageing phenomenon. The ageing phenomenon is incorporated in a conventional delayed strain concept in terms of the variable elastic modulus with time. Four cases of age-dependent constitutive equations are formulated within the presented formulation framework by employing different types of creep models. The mechanical characteristics of the terms that comprise the various constitutive equations are examined and compared. Numerical application of the time-dependent test results of cylindrical specimens indicate that the creep formulation that considered the elastic modulus development showed a good agreement with the experimental result while the formulation that did not consider the elastic modulus development underestimated the result by 15%.

Probability Study on the Thermal Stress Distribution in Thick HK40 Stainless Steel Pipe Using Finite Element Method

The present work deals with the development of a finite element methodology for obtaining the stress distributions in thick cylindrical HK40 stainless steel pipe that carries high-temperature fluids. The material properties and loading were assumed to be random variables. Thermal stresses that are generated along radial, axial, and tangential directions are generally computed using very complex analytical expressions. To circumvent such an issue, probability theory and mathematical statistics have been applied to many engineering problems, which allows determination of the safety both quantitatively and objectively based on the concepts of reliability. Monte Carlo simulation methodology is used to study the probabilistic characteristics of thermal stresses, and was implemented to estimate the probabilistic distributions of stresses against the variations arising due to material properties and load. A 2-D probabilistic finite element code was developed in MATLAB, and the deterministic solution was compared with ABAQUS solutions. The values of stresses obtained from the variation of elastic modulus were found to be low compared to the case where the load alone was varying. The probability of failure of the pipe structure was predicted against the variations in internal pressure and thermal gradient. These finite element framework developments are useful for the life estimation of piping structures in high-temperature applications and for the subsequent quantification of the uncertainties in loading and material properties.

Characterization of Cassava Fiber of Different Genotypes as a Potential Reinforcement Biomaterial for Possible Tissue Engineering Composite Scaffold Application

Cassava bagasse contains considerable amount of natural single elementary cellulose fibers and white thick root fiber (thick-core fiber) that has seen frequent application in the packaging industry as reinforcement for plastic composite development. However, a review of the literature was unable to find any study that characterized the material properties (such as tensile properties) of both the single elementary and white thick-core cassava cellulose fibers), and their application as potential reinforced filler in tissue engineering scaffold development. In this study, the tensile properties, morphology, crystallinity and thermal degradation profile of non-chemically treated single elementary cellulose fibers and thick-core fibers of different cassava genotypes were investigated. Fibers were tested according to ASTM C1557 under direct tension in a standard mechanical testing system and the cross-sectional area of the fractured regions of the fibers were determined using a 3D optical microscopy method. Cassava fibers of different genotypes did not show any significant difference in tensile properties, with average tensile strength ranging from (5.1–7.3 MPa), Young’s modulus (258–333 MPa) and failure strain (3.4–4.2 %). Tensile test conducted for several gage lengths did not influence the tensile strength and Young’s modulus of the fibers, however, strain-at-break depended on gage length. Single elementary and thick-core fibers showed similar surface morphology, degree of crystallinity (ranging from 21–40 %) and tensile properties with some variation in elastic modulus. Cassava fibers are thermally stable around 100–200 oC, where processing could be performed. Preliminary results showed an improvement in the mechanical properties of a gelatin scaffold when cassava cellulose microfibers were used as reinforcing fillers. The current findings show that cassava fiber has a reasonable mechanical strength, stiffness and thermal stability, and could be considered as a reinforced biomaterial to improve the mechanical integrity of tissue engineering scaffolds.

Experimental Study of the Fatigue Stiffness Degradation for the Carbon Fiber Reinforced Plastic at Variable Temperature

The paper represents the results of the experimental study on variation of the longitudinal elastic modulus and Poisson’s ratio for the carbon fiber specimens under fatigue loading at variable temperature. The approximating relations reflecting the test data are proposed.

Computation of mixed-mode stress intensity factors in functionally graded materials by natural element method

This paper is concerned with the numerical calculation of mixed-mode stress intensity factors (SIFs) of 2-D isotropic functionally graded materials (FGMs) by the natural element method (more exactly, Petrov-Galerkin NEM). The spatial variation of elastic modulus in non-homogeneous FGMs is reflected into the modified interaction integral M(1,2). The local NEM grid near the crack tip is refined, and the directly approximated strain and stress fields by PG-NEM are enhanced and smoothened by the patch recovery technique. Two numerical examples with the exponentially varying elastic modulus are taken to illustrate the proposed method. The mixed-mode SIFs are parametrically computed with respect to the exponent index in the elastic modulus and external loading and the crack angle and compared with the other reported results. It has been justified from the numerical results that the present method successfully and accurately calculates the mixed-mode stress intensity factors of 2-D non-homogeneous functionally graded materials.

Evaluation of stress intensity factors in functionally graded materials by natural element method

This paper is concerned with the numerical evaluation of the stress intensity factors (SIFs) of 2-D isotropic functionally graded materials (FGMs) by the natural element method (more exactly, Petrov-Galerkin NEM). The spatial variation of elastic modulus in inhomogeneous FGMs is reflected into the modified interaction integral $${\tilde M^{(1,2)}}$$ . The local NEM grid near the crack tip is refined, and the strain and stress fields that were directly approximated by PG-NEM were enhanced and smoothened by the patch recovery technique. Numerical examples with the exponentially varying elastic modulus are taken to illustrate the proposed method. The stress intensity factors are parametrically evaluated with respect to the exponent index in the elastic modulus and the crack length, and those were compared with the other reported results. It has been justified from the numerical results that the present method successfully and accurately evaluates the stress intensity factors of 2-D inhomogeneous functionally graded materials.

Regularities of stress state of unsupported working occurring in a layered massif

The paper defines the regularities of stress state of unsupported working occurring in a layered massif. The relevance of the performed research is substantiated by the importance of determining the stresses of the contour of unsupported working when the elastic modulus of the matrix and the layer is varied. Since the application of analytic methods for this case is complex, we used a numerical finite element method, implemented in the SCAD. We developed a finite-element model of the above working, where the elastic moduli of the matrix and the layer varied greatly, while its position was unchanged (the layer laying in the middle of the working). The results of the numerical analysis allowed us to build the regularities of three stress components. In order to normalize cases of elastic modulus variation, a dimensionless χ -parameter is introduced which characterizes the relation between the elastic modulus of the matrix and the layer. The obtained regularities of the stress state of the χ-parameter have a functional character and allow to determine the stresses on the contour of the unsupportedworking, depending on the relation between the elastic moduli of the matrix and the layer for all possible spectrum of these parameters.

Stationary response of stochastic viscoelastic system with the right unilateral nonzero offset barrier impacts**Project supported by the National Natural Science Foundation of China (Grant Nos. 11872305 and 11872307) and the Excellent Doctorate Cultivating Foundation of Northwestern Polytechnical University, China.

The stationary response of viscoelastic dynamical system with the right unilateral nonzero offset barrier impacts subjected to stochastic excitations is investigated. First, the viscoelastic force is approximately treated as equivalent terms associated with effects. Then, the free vibro-impact (VI) system is absorbed to describe the periodic motion without impacts and quasi-periodic motion with impacts based upon the level of system energy. The stochastic averaging of energy envelope (SAEE) is adopted to seek the stationary probability density functions (PDFs). The detailed theoretical results for Van der Pol viscoelastic VI system with the right unilateral nonzero offset barrier are solved to demonstrate the important effects of the viscoelastic damping and nonzero rigid barrier impacts condition. Monte Carlo (MC) simulation is also performed to verify the reliability of the suggested approach. The stochastic P-bifurcation caused by certain system parameters is further explored. The variation of elastic modulus from negative to zero and then to positive witnesses the evolution process of stochastic P-bifurcation. From the vicinity of the common value to a wider range, the relaxation time induces the stochastic P-bifurcation in the two interval schemes.

Stress analysis in rolling contact problem of a finite thickness FGM layer

The rolling contact problem of a non-homogeneous layer is considered here. The graded layer possesses a variable elastic modulus with an exponential distribution. The Poisons ratio is assumed to be constant. A rigid cylindrical indenter is rolling over the surface of the graded layer with a constant velocity. First, the Navier equations of equilibrium are solved in the Fourier domain. Later, the boundary and the continuity conditions are satisfied in order to extract the governing singular integral equations. The numerical solution of the integral equations is provided by means of the Gauss–Chebyshev integration method. Finally, the sensitivity of the solution is analyzed for the effective parameters namely: the stiffness ratio, the layer thickness and the coefficient of friction. The results indicate that a minimum value of the coating thickness is required to alleviate the severe stress gradients in the critical locations. If the coating thickness decreases by a 50% then the Von Mises stress will increases about 20%. Also, a softening graded layer can result in a lower stress level over the interface which may enhance the bonding strength.