Position Of Neutral Plane Research Articles

Numerical analysis of time-dependent negative skin friction on pile in soft soils

The generation of negative skin friction (NSF) induces the additional axial force on the pile, which exerts a detrimental load rather than a beneficial one. However, the effect of soil creep on the long-term development of NSF has remained poorly understood. The study uses numerical analysis to investigate this effect. First, an elasto-viscoplastic model with an enhanced time integration algorithm is successfully implemented into a finite element code. Next, the two-dimensional axisymmetric pile-soil interaction model is established and properly calibrated with a known field case. Finally, parametric studies are conducted to examine different degrees of creep effect on the variation in NSF and neutral plane (NP) within the primary and secondary consolidation periods. According to the findings, a high creep coefficient of the soil results in an increase in NSF and descending trend of the NP. The creep induced delay of NSF is observed attributed to the increase in excess pore pressure during the early stage of consolidation. The NP position varies drastically at the commencement of consolidation when taking creep into consideration. Lastly, the study proposes an exponential prediction model to reflect the time dependence of the location of the NP.

A reduced-scale experimental investigation of facade flame behavior ejected from a top-hung window of fire compartment

In case of a room fire, facade flame ejected from a window could lead to catastrophic consequence. Top-hung window is a common feature in modern buildings. This paper investigates, for the first time, the ejected facade flame behavior from a top-hung window. Experiments are performed by a cubic scale model compartment with a top-hung window of four opening angles and four dimensions under various heat release rates (HRR). A total of 119 test conditions are involved to quantify generally the ejected facade flame behavior and morphological characteristics, characterized by its vertical height and horizontal depth (normal to facade). It is found that the position of neutral plane between the inflow and outflow at the top-hung window increases with opening angle, while being smaller as the window width is larger or the window height is smaller. The critical HRR for flame ejection is higher as the top-hung window opening angle is larger. The facade flame depth increases, while the flame height decreases, with increasing of opening angle of the top-hung window. A new characteristic length taking into account both the top-hung window dimensions and window opening angle is deduced by the mass balance analysis of the inflow and outflow as well as ventilation factor through the top-hung window. New dimensionless models are established to describe the critical HRR for flame ejection, the height of the facade flame and flame depth as a function of the newly derived top-hung window ventilation factor as well as characteristic length, showing good fitting of experimental results. The present study provides the basic data, understanding and model of facade flame characteristics from a top-hung window of a fire compartment, which is essential in estimation of its risk and adverse impact to urban environment as a new supplementary over previous knowledge limited for freely opened windows.

Neutral Mechanical Plane Shifting in Bending Elastomer Film Revealed by Quantification of Internal Strain

Neutral mechanical plane (NMP) position of a bending elastomer film is experimentally identified by internal strain analysis utilizing reflection of a cholesteric liquid crystal elastomer sensor as described in article number 2101041 by Atsushi Shishido, Norihisa Akamatsu and co-workers. The internal strain analysis revealed NMP shifting during elastic bending. Quantification of the NMP shifting in the bending elastomer film enables us to design a flexible electronic device that exhibits high mechanical durability.

Time Dependence of Neutral Plane Position in a PHC-Supported Soft Subgrade

This case study focuses on an International Circuit project in China where unmanned automobiles are to be tested in the future. The subgrade undergoes extensive settlement because of the widely distributed lacustrine deposits with high void ratio and compressibility. Prestressed high-strength concrete (PHC) pile-supported earth platforms are used for ground improvement in this area, but their effectiveness has not yet been confirmed. Associated with this adoption, the negative skin friction (NSF) of the piles and the related neutral plane (NP) position is of importance. Although NSF has been examined in detail, the NP position has not, especially with regard to its time dependence. This paper reports the settlement of the pile-supported soft soil subgrade as obtained from long-term observations of full-scale tests. The NP position is determined according to the layered settlement of the soil and the pile settlement, both of which are obtained from long-term field observations. The results reveal that the NP position has a clear time dependence that develops in stages. The NP is initially elevated with time, and then it gradually approaches a constant value. The existing models fail to predict this time dependence of the NP position in the studied sites. A exponential model is used, the fitting parameters of which have practical implications. The adopted model works well with the studied sites, especially in terms of reflecting the time dependence of the NP position and distinguishing the different stages of its development. This paper enhances the understanding of the NP and provides a reference data set for related engineering practices.

Controlling Neutral Plane of Flexible Substrates by Asymmetric Impregnation of Glass Fabric for Protecting Brittle Films on Foldable Electronics

Neutral plane strategies have been studied to reduce the tensile strain of brittle films in foldable electronics under bending. However, those strategies depend on the dimensions of components in devices, implying that they could be limited to application to various designs of devices. Herein, the glass fabric's position in a glass fabric–reinforced siloxane hybrid substrate is shifted to control the neutral plane of the substrate. Due to the stiffness difference between the glass fabric and epoxy siloxane hybrid matrix, the neutral plane of the substrate is affected by the position of the glass fabric. Therefore, the glass fabric is asymmetrically impregnated to be located at the substrate surface so as to shift the neutral plane of the substrate toward the surface. The effectiveness of the newly developed substrate is proved by comparison with a conventional colorless polyimide substrate. The neutral plane position and maximum tensile strain of the substrates are investigated by analytical calculation, digital image correlation analysis, bending test, and finite element method simulation. The results clearly show that the newly developed substrate–based structure can reduce the maximum tensile strain under bending. Consequently, the cracking of the brittle hard coating is effectively prevented.

Investigating the Reliability of Negative Skin Friction on Composite Piles

In this study, the impact of Negative Skin Friction (NSF) on composite piles concerning different variables such as different pile sections, the amount of concrete and steel consumption, and various interaction coefficients of the pile-soil system in both solid and hollow conditions are evaluated using numerical methods. Besides, the effect of the variables considered on the negative skin friction and pile’s settlement is investigated. Numerical analyses were performed using ABAQUS and MATLAB. The results showed that the amount of frictional stress on the pile decreases if the hollow sections are used. However, the hallow pile experiences more settlements than other piles’ models. On the other hand, if the amount of consumed steel in a pile is reduced, the amount of negative skin friction induced in a pile decreases, while the pile settlement increases. After examining the Finite Element of concrete piles in fine-grained soils, the safety surface of the suggested numerical relationship was considered in the phenomenon of negative friction on the pile. For this purpose, considering the uncertainty parameters such as mean, variance and probability function for overcharge, soil parameters, dimensions and different types of the single pile, the amount of settlement, the stress created on the pile, the position of neutral plane on the pile and drag load were calculated using the proposed relationship. Finally, the safety surface of the proposed relationships or comparisons of a Finite Element results in a close approximation to the real models was computed.

Experimental study on thermal hazard and facade flame characterization induced by incontrollable combustion of indoor energy usage

Abstract Fire accidents induced by indoor energy combustion occurred frequently and caused tremendous loss. This paper investigated the evolution laws of important fire risk parameters for quantitatively assessing the thermal hazard of room with triangular windows by reduced-scale experiments. The fire hazard was characterized by the risk parameters of hot gas temperature inside the room and facade flame height. Results show that the neutral plane position is hardly affected by total heat release rate of fire source, and it mainly depends on triangular opening height rather than base width. The ratios of neutral plane height above opening bottom to opening height are about 0.25, 0.25 and 0.61 for isosceles, right and inverted right triangular openings respectively. Based on theoretical derivation, an appropriate ventilation factor for triangular opening was defined to describe air mass inflow rate during under-ventilated condition. The hot gas temperature inside the room can be predicted based on the newly defined ventilation factor. Finally, a non-dimensional correlation was proposed to characterize facade flame height as a 0.53 power function of a normalized excess heat release rate. This work is of benefits to evaluate the fire hazard of buildings and then to provide calculation basis for building fire protection design.

Pre- and post-buckling analysis of FG cylindrical nanoshells in thermal environment considering the surface stress effect

An analytical approach is developed to study the pre- and post-buckling responses of circular cylindrical nanoscale shells subjected to lateral and axial loads as well as thermal environment. The effect of surface free energy as one of the key nanoscale effects is considered in the context of Gurtin-Murdoch surface elasticity theory. The nanoshell is made of functionally graded materials (FGMs) whose properties are calculated using power-law functions. The basic formulation is derived according to the classical shell theory together with the von-Karman nonlinear relations. Moreover, the physical neutral plane position is taken into consideration. Using the Ritz energy method, an analytical approach is also proposed to solve the problem. Comprehensive numerical results are presented to investigate the behavior of nanoshell under lateral pressure and axial load in thermal environment, in pre- and post-buckling domains. The influences of various parameters including the surface stress, FGM gradient index, temperature and geometrical parameters on the non-linear critical axial stress/lateral pressure are illustrated.

Modal analysis of cracked continuous Timoshenko beam made of functionally graded material

The article addresses development of the Transfer Matrix Method (TMM) for free vibration of cracked continuous Timoshenko beam made of Functionally Graded Material (FGM). The governing equations of free vibration are established for the beam based on the power law of material grading, actual position of neutral plane and double spring model of crack. There is conducted frequency equation of the beam with intermediate rigid supports using the TMM after the transverse displacements at rigid supports have been disregarded. Therefore, the frequency equation is simplified and becomes more useful to compute natural frequencies of continuous FGM Timoshenko beam with a number of cracks. The obtained numerical results show the essential effect of cracks, material properties and also number of spans on natural frequencies of the beam.

Influence of fire position on smoke movement in an inner corridor building with multiple openings

The influence of fire position on the neutral plane height was analyzed in order to analyze the smoke movement. One inner corridor building multiple openings was constructed by computational fluid dynamics (CFD) software and the airflow velocity and the pressure distribution under different fire position. The result shows that the influence of fire position on the height of neutral plane can be divided into two phases and the base height (Hb) is put forward as the critical values for the two phases. When the he height of fire (hf) is lower than Hb, namely hf< Hb, with the hf increasing, the neutral plane height increase is not significant. However, when the hf>Hb, with the fire height increasing, the neutral plane height increase significantly. Additionaly, in the condition, the position of neutral plane will be on the same level as that of the fire soucrce.

Natural Frequencies of Multistep Functionally Graded Beam with Cracks

Free vibration of cracked multistep beam made of functionally graded material is studied on the basis of the Timoshenko beam theory and actual position of neutral plane of functionally graded beam. Crack model is adopted using a pair of translational and rotational springs of stiffness calculated from the same crack depth. An exact dynamic shape function is proposed and used to conduct a simplified transfer matrix for cracked uniform functionally graded beam element. Frequency equations of the cracked multistep beam established in the form of 3 × 3-dimensional determinant for different cases of boundary conditions are employed for analysis of natural frequencies in dependence on the crack position and depth, material properties and size of beam steps. It was shown that abrupt variation of beam thickness has significant effect on the sensitivity of natural frequencies to cracks. This is demonstrated by numerous results obtained for beam with three steps in different boundary condition cases.

Theoretical analysis and experimental study of the effect of the neutral plane of a composite piezoelectric cantilever

Piezoelectric energy harvesters have been studied extensively because they show considerable promise for use in both military and commercial applications. In this work, research was conducted into the core component of a piezoelectric energy harvester, i.e., the piezoelectric cantilever. The phenomenon where the piezoelectric cantilever has a very low output when no substrate layer is present can be explained using neutral plane theory. The relationship between the neutral plane's position and the piezoelectric cantilever’s output power can be studied in depth through analysis of this phenomenon. A mathematical model of a vibrating piezoelectric cantilever is established and the neutral plane position and open-circuit voltage of a vibrating piezoelectric cantilever are deduced based on Euler-Bernoulli beam theory. Calculations and finite element simulation results show that the neutral plane's position in the piezoelectric cantilever is dependent on the elastic moduli and thicknesses of the piezoelectric and substrate layers and that the output of the piezoelectric cantilever is also closely related to the neutral plane's position. To study how the neutral plane's position affects the output power of the piezoelectric cantilever, polyvinylidene fluoride (PVDF) piezoelectric cantilevers with different substrate layers but the same piezoelectric layer were fabricated and the output powers of these layers were measured. Experimental results show that the composite piezoelectric cantilever’s performance is enhanced in terms of its output voltage, average power and power density as the neutral plane is gradually moved further away from the mid-plane of the piezoelectric layer.

Nonlocal electrothermomechanical instability of temperature-dependent FGM nanopanels with piezoelectric facesheets

Within the framework of a novel shear deformation panel theory based on exponential shear stress distribution, the nonlocal continuum theory is utilized to establish an efficient size-dependent panel model to anticipate the nonlinear instability characteristics of nanoscaled panels subjected to combination of axial compressive load, lateral electric field and through-thickness heat conduction and corresponding to both the temperature-dependent (TD) and temperature-independent cases. The nanopanels contain a substrate made of functionally graded material (FGM) and surface-bonded piezoelectric nanolayers with temperature-dependent material properties. To eliminate the stretching-bending coupling terms, the physical neutral plane position related to the FGM substrate of nanopanels is taken into consideration. The nonlocal nonlinear governing equations are deduced to boundary layer-type ones and then solved via a perturbation-based solving process which results in explicit expressions for nonlocal temperature-dependent equilibrium curves. It is found that in the TD case, by heating the outer surface of nanopanel, the reductions in the values of buckling load and minimum postbuckling load are more considerable for nonlocal hybrid FGM nanopanel than those of local one.

A New Form of Frequency Equation for Functionally Graded Timoshenko Beams with Arbitrary Number of Open Transverse Cracks

The present paper addresses the problem of free vibration in multiple cracked beams made of functionally graded material (FGM). Governing equations of the beam vibration are established using the Timoshenko beam theory, power law of material grading along the beam thickness and rotational spring model of crack. The actual position of neutral plane differed from the mid-plane due to the material properties variation is also taken into account. The frequency equation obtained in a simple form provides an efficient tool for natural frequency analysis and may also be used for solving the inverse problems such as identification of material properties or cracks in the beams from natural frequencies. Numerical examples have been carried out to validate the proposed theory and to investigate the effect of cracks, material and geometry parameters on natural frequencies of the beams.

低変態温度溶接材料を用いた溶融金属積層造形材の変形低減法に関する基礎的検討

Current work deals with investigation of the effect of the use of low transformation temperature welding wire (LTT welding wire) on distortion reduction of parts made by wire and arc additive manufacturing technique (WAAM). LTT welding wire and SUS308L wire, which was austenitic stainless steel wire, were used for making WAAM test pieces. Distortion of base plates of test pieces were evaluated by 3D non-contact coordinate measurement system. As a result, longitudinal bending distortion of the base plates of test pieces in which LTT welding wire was partially or fully used was smaller than those of the test piece which was made only by SUS308L wire. Especially, longitudinal bending distortion of the base plates of test pieces which was made only by LTT welding wire was reduced drastically from those of the test piece which was made only by SUS308L wire. However, angular distortion of the base plates were not reduced drastically even if the test piece was made only by LTT welding wire. The difference of the reduction effect of the use of LTT welding wire was discussed by considering the position of neutral plane of each distortion mode.

Imperfection sensitivity of the size-dependent nonlinear instability of axially loaded FGM nanopanels in thermal environments

The nonlinear buckling of thin shell-type structures is sensitive to the initial geometric imperfection. In this study, the imperfection sensitivity of the nonlinear instability of cylindrical nanopanels made of functionally graded material (FGM) is addressed including surface elasticity, aiming to present a background for axial postbuckling behavior of imperfect FGM nanopanels. The material properties are supposed to be graded across the panel thickness in accordance with a simple power law function of the volume fractions of the silicon and aluminum constituents with considering the physical neutral plane position. The non-classical governing differential equations are constructed and then they are deduced to boundary layer-type ones. Afterward, a perturbation-based solution methodology is employed to extract explicit expressions for the size-dependent postbuckling equilibrium paths of FGM nanopanels with and without initial geometric imperfection and corresponding to various panel thicknesses, geometrical parameters, temperature changes and material property gradient indexes. It is displayed that through reduction of the surface elasticity effects for thicker FGM nanopanels, the influence of the initial geometric imperfection on the minimum load of the postbuckling regime increases. This pattern is more significant for FGM nanopanels with a lower value of the material gradient index.

Boundary Layer Modeling of Nonlinear Axial Buckling Behavior of Functionally Graded Cylindrical Nanoshells Based on the Surface Elasticity Theory

The main purpose of the present study is to examine the axial buckling and postbuckling response of cylindrical nanoshells made of functionally graded (FG) materials in the presence of surface free energy effects. To accomplish this purpose, an efficient size-dependent shell model is introduced through combination of the classical shell theory with the well-known Gurtin–Murdoch surface elasticity theory. The volume fraction of FG nanoshells made of the mixture of aluminum and silicon is defined using a power law function. Also, in order to eliminate the stretching–bending coupling terms, the change in the position of physical neutral plane corresponding to different volume fractions is taken into account. Based upon the principle of virtual work, the non-classical governing differential equations and boundary conditions are derived. Subsequently, the governing equations are deduced to the boundary layer-type equations incorporating simultaneously the nonlinear large deflections and size effect. Finally, a perturbation-based solving process is put to use to predict the size-dependent critical buckling loads and related postbuckling equilibrium curves for FG nanoshells with various values of material property gradient index and shell thickness. It is found that the surface free energy effect is more prominent for FG nanoshell with lower shell thickness and higher material property gradient index.

Size Dependency in the Axial Postbuckling Behavior of Nanopanels Made of Functionally Graded Material Considering Surface Elasticity

Size-dependent modeling and analysis for the nonlinear postbuckling response of functionally graded (FG) cylindrical nanopanels under axial compressive load are presented based on the surface elasticity theory. The non-classical formulations are developed on the basis of the Gurtin–Murdoch elasticity theory within the framework of the classical shell theory. In order to capture the large deflections associated with the postbuckling regime, the geometrical nonlinearity is considered in von Karman sense. The material properties are supposed to be graded across the panel thickness in accordance with a simple power law function of the volume fractions of the silicon and aluminum constituents with considering the physical neutral plane position. To satisfy the balance conditions on the free surface layers, it is assumed that the bulk normal stress along the thickness direction varies linearly between those values of surface stress components at the inner and outer layers. A boundary layer theory of shell buckling is extended to the case of size-dependent FG nanopanels, and then, a singular perturbation technique is put to use to solve the nonlinear problem. It is displayed that due to the stiffening influence of surface effects, the depth of the postbuckling regime for FG nanopanels with higher material gradient index decreases, as for the metal-rich nanopanel, the snap-through phenomenon approximately diminishes.

Modal analysis of functionally graded Timoshenko beam

Dynamic analysis of FGM Timoshenko beam is formulated in the frequency domain taking into account the actual position of neutral plane. The problem formulation enables to obtain explicit expressions for frequency equation, natural modes and frequency response of the beam subjected to external load. The representations are straightforward not only to modal analysis and modal testing of FGM Timoshenko beam with general end conditions but also to study coupling of axial and flexural vibration modes. Numerical study is carried out to investigate effect of true neutral axis position and material properties on the modal parameters.

Imperfection sensitivity of the nonlinear axial buckling behavior of FGM nanoshells in thermal environments based on surface elasticity theory

A size-dependent shell model which accounts for geometrical imperfection sensitivity of the axial postbuckling characteristics of a cylindrical nanoshell made of functionally graded material (FGM) is proposed within the framework of the surface elasticity theory. In accordance with a power law, the material properties of the FGM nanoshell are supposed to vary through the shell thickness. In order to eliminate the stretching-bending coupling terms, the change in the position of physical neutral plane corresponding to different volume fractions is taken into account. Based upon the virtual work’s principle, the non-classical governing differential equations are derived and then deduced to boundary layer-type ones. After that, a perturbation-based solution methodology is employed to predict the size dependency in the nonlinear instability of perfect and imperfect axially loaded FGM nanoshells with various values of shell thickness, material property gradient index and different uniform temperature changes. It was seen that for thicker FGM nanoshells in which the surface free energy effects diminish, the influence of the initial geometric imperfection on the critical buckling load is higher than its influence on the minimum load of the postbuckling domain. It is also found that through reduction of the surface free energy effects, the influence of material property gradient index on the critical end-shortening of FGM nanoshell decreases.