Effect Of Prestress Research Articles

Size-dependent and nonlinear magneto-mechanical coupling characteristics analysis for extensional vibration of composite multiferroic piezoelectric semiconductor nanoharvester with surface effect

We study the extensional vibration of composite multiferroic piezoelectric semiconductor (PS) nanoharvester driven via a time-harmonic magnetic field. A theoretical analysis about working performances of device is performed based on zero-order plate equations with surface and nonlocal effects, consisting of a nonlinear magneto-mechanical coupling constitutive model for giant magnetostrictive material Terfenol-D and a linear phenomenological theory of PS material ZnO. Numerical results indicate that the basic bahaviors (including resonant frequency, bandwidth characteristic, magneto-electric (ME) coupling effect, output power and energy conversion efficiency) of the nanoharvester, can be dramatically improved through circuit types, semiconduction, external magnetic field, pre-stress and surface effect. This work is essential and crucial for understanding the size-dependent and nonlinear mechanical behaviors of multiferroic PS nanodevices under the extremely complex magnetic field and pre-stress field environments.

Resonance and cancellation phenomena in partially clamped simply supported beam bridges under moving trains

Since the development of new railway lines of high speed, the dynamic response of bridges belonging to them constitutes a subject interest for researchers and engineers, in particular at resonance. In the present work, an analytical approach is developed to analyze the dynamic response of a single ballasted track railway bridges supported by identical rotational springs and subjected to the circulation of moving loads at constant speeds. Although the introduction of rotary springs at the ends of the deck enhances the choice of the appropriate analysis model, where most of the contributions reported in this field do not consider this effect. The central idea of the proposed model is based on analyzing the continuity effect of the ballasted track (rails and ballast) on the dynamic response of railway bridges, with taking into account an axial force that models the effect of prestressing, longitudinal ballast-bridge interface, axial displacement, force braking. The equation of motion of the system is derived by using the Hamilton’s principle, two dynamic case studies of a simply supported and simply supported partially clamped Euler-Bernoulli beam are presented. The results revealed that the compression force presents an additional stiffness which affects the critical velocity and that the continuity of the track modeled by rotational springs at the beam’s end, as it increases the dynamic response decreases. Also, a dynamic analysis for the conditions for maximum response and cancellation in free vibration are derived and interpreted particularly the effect of the geometric scheme of train axles. Equating the condition for resonance of maximum free response and cancellation, cancelled resonance are obtained.

Hydroelastic linearized vibrations taking into account prestressed effects due to internal liquid weight: Numerical vs. experimental results

This paper concerns the numerical simulation of the hydroelastic vibrations of an elastic tank containing a free surface liquid, around a geometrically nonlinear equilibrium configuration that takes into account the prestress effect due to the liquid weight. The computational methodology is the following. Firstly, the hydrostatic pressure on the fluid–structure interface is considered as a non-uniform follower force which depends on the liquid height. Therefore, the prestressed equilibrium at a given free-surface level, called current configuration in the paper, is computed as a geometrically nonlinear problem, in which the height of the liquid is considered as an evolution parameter. We start from an empty structure, defined as the reference configuration, which is progressively filled to reach the level of the chosen configuration. Therefore the calculation of hydroelastic vibrations of a tank filled with liquid as a function of a emptying rate is straightforward. The methodology is validated with experimental results extracted from literature.

Chaotic and regular dynamics of a morphing shell with a vanishing-stiffness mode

Thin elastic shells are almost inextensible but easy to bend. In the presence of prestresses, geometric frustrations can produce complex elastic energetic landscapes, which have been tailored for the design of morphing structures with multiple stable equilibria or neutrally stable manifolds. We show that the co-existence of stiff and floppy modes leads to unexploited dynamical features. We build a neutrally stable cylindrical shell that under dynamical excitation alternates a chaotic behavior with a surprisingly regular regimes with a continuous precession of the curvature axis at a constant speed. We explain the experimental findings with a minimal model, showing how the intriguing dynamics is due to the subtle coupling between the prestress, geometrical nonlinearity, material anisotropy and inertial effects. Our results shed a new light on morphing structures dynamics and can be exploited in engineering applications such as energy harvesting.

Exact strain gradient modelling of prestressed nonlocal diatomic lattice metamaterials

In this article, an exact strain gradient (SG) continuum model to capture the broadband bandgap characteristics of the prestressed diatomic lattice (PDL) with local/nonlocal interactions has been proposed. By considering the periodicity of wave motion, the wavelength-dependent Taylor expansion is established, leading to a desirable prediction when the wavelength is close to the lattice scale. For PDL, the dispersion curves of the proposed continuum model are always consistent with those of discrete model in the first Brillouin zone. The proposed SG continuum model is used to investigate the effects of structural parameters, orders of SG continua and various nonlocal interactions on bandgap properties of PDL. Highlights Continuum modelling of prestressed acoustic diatomic lattices. Perfect agreements achieved between dispersion diagrams by discrete and proposed continuum models. Effects of prestress, nonlocal interactions, mass and stiffness ratios on band gap structures analyzed. Proper strain gradient (SG) orders determined to guarantee a satisfactory accuracy.

Design of a novel integrated ultrasonic tool holder for friction stir welding

Ultrasonic vibration friction stir welding (UVFSW) has shown advantages in reducing welding defects and improving welding quality in aerospace, automobile, and power electronics. In this study, we design a novel 20-kHz integrated ultrasonic tool holder in FSW. The finite element model of FSW transducer is established, where the elastic modulus is measured by non-destructive acoustic. In the three transducer prototypes with alloy steel, the effect of prestress on resonant frequency is investigated and the ultrasonic vibration is measured. It proves that the resonant frequencies are well consistent between simulation model and the experiment by the elastic modulus testing and the prestress optimization. The ultrasonic amplitude of the pin is up to 24 μm. The experiment also indicates that the vibration is different with the steel material properties. Our findings can have a guidance to the design for a general ultrasonic actuator. The integrated FSW ultrasonic tool has potential to apply in a confined space in general machining equipment.

Stability analysis of the pile-prestressed anchor composite structure based on failure mode

Pile-prestressed anchor composite structure is widely used in retain engineering, whose stability analysis is mainly based on the slip line passing through the bottom of pile. However, the existing stability analysis is unable to comprehensively consider the actual slip line passing through pile body, pile bottom and the soil under pile. Based on multiple failure modes, a stability analysis model of composite structure considering both the effects of prestress and pile body is established, and the dynamic search algorithm for the model is proposed. We compare the proposed model with the software of LIZHENG deep foundation pit and the existing calculation model and find the effectiveness of our model. It is found that the safety coefficient of the composite structure is directly proportional to the prestress, pile length and pile diameter, but inversely proportional to the pile spacing. Meanwhile, the safety coefficient increases firstly and then decreases with the increase of slip line depth. Increasing the prestress of anchor in the middle and lower part of the slope has a more obvious effect on improving the safety coefficient. The proposed stability model and search algorithm can consider multiple failure modes and obtain the safety coefficient. In addition, it can comprehensively evaluate the stability of the pile-prestressed anchor composite structure retaining slope, which has superior application value.

Finite Element Analysis of Reinforced Concrete Beams Prestressed by Fe-Based Shape Memory Alloy Bars

Prestressing of concrete structures using Fe-based shape memory alloys has been investigated extensively by experiments in the last decade. However, detailed investigations on the stress produced by the Fe-based shape memory alloys and its influence on concrete damage during deformation of concrete structure has not been investigated yet. In this study, the prestressing effect by Fe-based shape memory alloy bars on bending behavior of reinforced concrete beam was investigated numerically. A finite element simulation model was developed to investigated the bending responses of the beams including nonlinear material properties such as concrete cracking and crushing as well as the plastic deformation of the Fe-based shape memory alloy. The model is able to capture the bending behavior of the beam prestressed with the Fe-based shape memory alloy bars. Based on the numerical and experimental results, the prestressing effect by the shape memory alloy bars was investigated in detail. Although the developed model slightly overestimated the experimentally obtained bending load-deflection curves of the concrete beams, it was shown that the developed model can be used for an optimization study to select the best possible design parameters for prestressing the concrete beam with the Fe-based shape memory alloy bars. A possible reason for the overestimation is the idealized perfect bonding assumption between Fe-SMA and concrete used in the model, while slip at the interface occurred in the experiments.

A Personalized Spring Network Representation of Emphysematous Lungs From CT Images.

Emphysema is a progressive disease characterized by irreversible tissue destruction and airspace enlargement, which manifest as low attenuation area (LAA) on CT images. Previous studies have shown that inflammation, protease imbalance, extracellular matrix remodeling and mechanical forces collectively influence the progression of emphysema. Elastic spring network models incorporating force-based mechanical failure have been applied to investigate the pathogenesis and progression of emphysema. However, these models were general without considering the patient-specific information on lung structure available in CT images. The aim of this work was to develop a novel approach that provides an optimal spring network representation of emphysematous lungs based on the apparent density in CT images, allowing the construction of personalized networks. The proposed method takes into account the size and curvature of LAA clusters on the CT images that correspond to a pre-stressed condition of the lung as opposed to a naïve method that excludes the effects of pre-stress. The main findings of this study are that networks constructed by the new method 1) better preserve LAA cluster sizes and their distribution than the naïve method; and 2) predict different course of emphysema progression compared to the naïve method. We conclude that our new method has the potential to predict patient-specific emphysema progression which needs verification using clinical data.

Experimental Study on Effects of Additional Prestressing Using Fiber Reinforced Polymers and Strands on Deterioration of PSC Bridge Structure.

Concrete bridge structures require reinforcement, as their performance deteriorates over time. In this regard, this study evaluated the effect of additional prestressing using fiber-reinforced polymers (FRPs) and strands applied to a demolished, deteriorated bridge. In particular, specimens were prepared for a bridge subjected to non-, near-surface mounted (NSM), and external prestressing (EP) strengthening to evaluate the stiffness and safety of the structure. In the 200–400 kN load range, the EP method exhibited the highest stiffness (15 kN/mm), followed by non-strengthening (8.5 kN/mm) and the NSM method (5.45 kN/mm). The EP method increased the stiffness by approximately two times; however, the NSM method decreased the stiffness by 0.6 times. In the 400–800 kN load range, the EP and NSM methods yielded stiffness values of 2.58 and 0.7 kN/mm, respectively. These results confirm that the EP method reinforces the structure. The results of this study are expected to be used as basic data to reinforce deteriorated bridges in actual operation.

Analytical model and general calculation procedure for wrinkled membrane parameters

The existing buckling theory and tension field theory for wrinkled membranes cannot systematically and conveniently acquire the parametric descriptions of wrinkles considering the prestress and deflection effects. Therefore, this paper proposes a mechanical model with the prestress and deflection based on Föppl–von Kármán equations with a modification parameter considering the contribution of membrane bending stiffness. The nonlinear buckling finite element analysis and experiments in the literature are introduced to determine the key parameters as 0.5. Besides, the results also verify the proposed mechanical model has the accurate predictive ability for stress and configuration parameters of wrinkles. Then, a general calculation procedure for wrinkle parameters of complex membranes is established based on the proposed analytical model and tension field theory. It can be divided into three steps, wrinkle discrimination, finite element model modification and wrinkle parameters calculation. Lastly, the rectangular membrane under different shear loads and the hexagonal membrane with tensile loads are investigated to clarify the proposed calculation procedure. The principles in this work can provide a more effective avenue for the accurate analysis of wrinkle behavior in the membrane structure.

Durability of GFRP bars embedded in seawater sea-sand concrete: A coupling effect of prestress and immersion in seawater

Using prestressed glass fibre-reinforced polymer (GFRP) bars for seawater sea-sand concrete (SSC) structures in offshore engineering is of particular interest for improving the utilisation of GFRP and natural resources. However, limited information is available on the effects of prestressing on the durability of GFRP. Therefore, the durability of SSC-coated GFRP bars was investigated under the coupling effect of prestressing and immersion in seawater at room temperature, 40 °C, and 60 °C, with prestress levels set at 20% and 40% of the ultimate tensile strength (%fu) of GFRP. The tensile properties, interlaminar shear strength, transverse shear strength degradation after 0 d, 30 d, 60 d and 120 d, and the prestress loss of GFRP within 70 d were studied. The results showed that SSC wrapping was not conducive to the long-term performance of GFRP bars due to the alkaline environment, and the prestress further accelerated the tensile strength degradation, with the tensile strength decreasing almost to zero for the specimens (with 40% fu prestress level) immersed in seawater after 120 days at 40 °C and 60 °C. However, the interlaminar shear strength and transverse shear strength retention were 37.1% and 52.2% for 60 °C immersion under the same conditions, respectively. These findings suggest that the shear properties degenerated more slowly than the tensile properties of the prestressed GFRP bars embedded in SCC under seawater environment, which also evidences that the glass fibres were damaged more heavily than the epoxy vinyl resin under the prestressing.

Dynamic behavior of material strength due to the effect of prestress, aeolotropy, non-homogeneity, irregularity, and porosity on the propagation of torsional waves

Dynamic behavior of material strength due to the effect of prestress, aeolotropy, non-homogeneity, irregularity, and porosity on the propagation of torsional waves

The Effect of DC Voltage Pre-Stress on the Breakdown Voltage of Air under Composite DC and LI Voltage and Test Circuit: Design and Application

The use of HVDC systems is increasing in number due to technological innovations, increasing power capacity and increasing customer demand. The characteristics of insulation systems under composite DC and LI voltage must be examined and clarified. In this study, firstly, experimental circuits were designed to generate and measure composite DC and LI high voltage using a simulation program. The coupling elements used were chosen according to simulation results. Afterward, experimental circuits were established in the laboratory according to the simulation results of the designed experimental circuit. Then, breakdown voltages under composite DC and LI voltage for less uniform and non-uniform electric fields were measured with four different electrode systems for positive and negative DC voltage pre-stresses with different amplitudes. The 50% breakdown voltage was calculated using the least-squares method. Finally, 3D models were created for the electrode systems used in the experiments using the finite element method. The efficiency factors of electrode systems calculated with the FEM results were correlated with the experimental breakdown voltage results. Thus, the breakdown behavior of air under bipolar and unipolar composite voltages (CV) was investigated. In conclusion, the experimental results showed that very fast polarity change in bipolar CV causes higher electrical stress compared to unipolar CV.

Surface tension-driven instability of a soft elastic rod revisited

Surface tension-driven morphological instability of a soft (compressible or incompressible) linearly elastic rod is studied based on the Gurtin–Murdoch (GM) theory of surface elasticity. This study is inspirited by instability of shorter wavelength observed in some experiments which are not covered by the existing linear elastic models. Here, unlike the original GM model, the present model addresses the influence of surface tension-induced bulk residual stress on the incremental bulk stress associated with instability. The relation between the dimensionless ratio σ0/(μR) (where σ0, μ and R are surface tension, shear modulus and radius of the rod) and the unstable mode’s wavelength λ is studied based on the present model and the GM model, with comparison to the known results given by the existing linear elastic models. Different than the existing linear elastic models which predict the instability only if σ0/(μR) ≥ 6 with the wavelength λ/(2R) > π, the present model and the GM model predict the instability with lower surface tension and much shorter wavelengths (e.g. λ/(2R)≈1.5), which could offer a plausible explanation for instability observed in some experiments. In addition, the effects of a bulk axial prestress and the Poisson ratio on the surface tension-induced instability of a soft linear elastic rod are examined..

Optical coherence elastography for assessing the influence of intraocular pressure on elastic wave dispersion in the cornea

The cornea is a highly specialized organ that relies on its mechanical stiffness to maintain its aspheric geometry and refractive power, and corneal diseases such as keratoconus have been linked to abnormal tissue stiffness and biomechanics. Dynamic optical coherence elastography (OCE) is a clinically promising non-contact and non-destructive imaging technique that can provide measurements of corneal tissue stiffness directly in vivo. The method relies on the concepts of elastography where shear waves are generated and imaged within a tissue to obtain mechanical properties such as tissue stiffness. The accuracy of OCE-based measurements is ultimately dependent on the mathematical theories used to model wave behavior in the tissue of interest. In the cornea, elastic waves propagate as guided wave modes which are highly dispersive and can be mathematically complex to model. While recent groups have developed detailed theories for estimating corneal tissue properties from guided wave behavior, the effects of intraocular pressure (IOP)-induced prestress have not yet been considered. It is known that prestress alone can strongly influence wave behavior, in addition to the associated non-linear changes in tissue properties. This present study shows that failure to account for the effects of prestress may result in overestimations of the corneal shear moduli, particularly at high IOPs. We first examined the potential effects of IOP and IOP-induced prestress using a combination of approximate mathematical theories describing wave behavior in thin plates with observations made from data published in the OCE literature. Through wave dispersion analysis, we deduce that IOP introduces a tensile hoop stress and may also influence an elastic foundational effect that were observable in the low-frequency components of the dispersion curves. These effects were incorporated into recently developed models of wave behavior in nearly incompressible, transversely isotropic (NITI) materials. Fitting of the modified NITI model with ex vivo porcine corneal data demonstrated that incorporation of the effects of IOP resulted in reduced estimates of corneal shear moduli. We believe this demonstrates that overestimation of corneal stiffness occurs if IOP is not taken into consideration. Our work may be helpful in separating inherent corneal stiffness properties that are independent of IOP; changes in these properties and in IOP are distinct, clinically relevant issues that affect the cornea health.

Finite element modeling of UHPC slabs with dovetail joints and steel wire mesh using an innovative interfacial treating method

The joint between concrete prefabricated components is regarded as a key for structures. However, existing interfacial treatment methods in numerical simulation cannot model and predict the behavior of joint regions under various engineering conditions, leading to inaccurate results and time-consuming processes. As a continuation of the tests conducted previously, this paper presents an interface layer element method to simulate the interfacial behavior of joints between prefabricated ultra-high performance concrete (UHPC) slabs that adopt dovetail joints and steel wire mesh (SWM) techniques in numerical simulation. The models that adopt both the interface layer and the conventional treating method are established and validated by previous experimental results. The results show that the method proposed can precisely simulate the overall behavior and failure mechanism of the prefabricated UHPC slabs, where the differences are less than 5%. A precise numerical model is acquired in the case of a reduction coefficient of 20% and a frictional coefficient of 1.0 for properties of the interface layer. Parametric analyses are conducted followed by to evaluate the effect of joint forms, prestressing and reinforcement on bearing capacities of the UHPC prefabricated slabs. It reveals that the dovetail joints can improve the ultimate load of the slabs by a range from 12.4% to 17.7% in comparison with the slabs with horizontal joints. Besides, both prestressing and reinforcement can enhance the bearing capacity of slabs to some extent. The conclusions can be referred for related studies.

Experiment and simulation analysis on dynamic response of plane cable-membrane structure under impact load

This paper presents an experimental and simulation analysis investigation into the dynamic response of plane cable-membrane structure under impact load. Firstly, the impact tensile tests of the PVDF coated fabric were carried out, and the effect of strain rate on the mechanical properties was characterized. Then the experiment of a plane cable-membrane structure under impact load is carried out. The effects of prestress, impact velocity, and bullet shape on the vibration law of membrane surface are studied. Finally, the mechanical response of the plane cable-membrane structure under impact load is simulated by ABAQUS/Explicit, and the energy dissipation mechanism is characterized. The results show that the displacement of membrane surface increases with the increase of impactor velocity, and decreases with the increase of membrane prestress. The vibration frequency of the membrane surface is the inherent property of structure, which is affected by the prestress of the membrane surface and increases with the increase of prestress. The proportion of elastic strain energy in total energy consumption increases with the increase of prestress. The finite element (FE) models provide a reasonable prediction of the dynamic response of the plane cable-membrane structure under impact load.

Active action of prestressing on direct tensile behavior of mortar reinforced with NiTi SMA crimped fibers

This study investigated the direct tensile behavior of mortar reinforced with cold-drawn crimped SMA fibers with considering recovery stress induced by heating. Additionally, the fiber diameter and fiber content also were considered. The experimental results showed that the 0.7 mm fibers contributed to improve tensile behavior of reinforced mortar with passive action of bond resistance as well as active action of prestressing effect due to recovery stress induced by heating. However, the 1.0 mm fibers did not contribute to increase tensile strength of mortar regardless of existence of recovery stress. For the 0.7 mm fibers, the prestressing due to recovery stress apparently contributed to increase the tensile strength of the fiber-reinforced mortar, while bond resistance of the fiber as passive action contributed more to increase tensile strength of mortar than the prestressing effect. Moreover, the tensile strength significantly increased with increase of SMA fiber volume fraction from 1.0% to 1.5%. The oven heating method should be used instead of the heat gun heating method because of the higher developed recovery stress. The cracking strength of reinforced mortar, however, is not influenced by volume fraction and recovery stress.

Enabling shape memory effect wires for acting like superelastic wires in terms of showing recentering capacity in mortar beams

Superelastic shape memory alloy (SMA) wires embedded in mortar beams show a recentering capacity, however, shape memory effect wires can provide a prestressing effect after inducing phase transformation. In this study our goal is to empower shape memory effect wires to show recentering capacity by designing a new wire configuration. These wires will thus be able to achieve both a prestressing effect and a recentering capacity in mortar beams. To this end, various shapes of martensitic SMA wires, including as-received, crimped, dog bone, and anchoring reinforced crimped wires, were employed to examine the potential of displaying recentering capacity while preserving the prestressing force in mortar beams. Several monotonic and cyclic three-point bending tests were also conducted to investigate the crack-closing effect, as well as the load bearing of the specimens. To evaluate the effect of temperature and heating procedure, two different methods, namely, a hot air gun and electric current heating, were used to induce phase transformation in shape memory effect wires. The results generally show that for two types of as-received and dog bone wires, the displacement recovery ratio have been reduced about 65% and 74%, respectively, however, for the crimped wire and anchoring reinforced crimped wire, this ratio is almost the same. More importantly, when the results of displacement recovery ratio of crimped wires heated by electrical heating are compared with the available experimental data for superelastic SMA bars, proves the great ability of SME wires to fulfill recentering capacity.