Radial Stiffening Research Articles

Strain stiffening elastomers with swelling inclusions.

Inhomogeneously swollen elastomers are an emergent class of materials, comprising elastic matrices with inclusion phases in the form of microgel particles or osmolytes. Inclusion phases can undergo osmotically driven swelling and deswelling over orders of magnitude. In the swollen state, the inclusions typically have negligible Young's modulus, and the matrix is strongly deformed. In that regime, the effective mechanical properties of the composite are governed by the matrix. Laying the groundwork for a generic analysis of inhomogeneously swollen elastomers, we develop a model based on incremental mean-field homogenization of a hyperelastic matrix. The framework allows for the computation of the macroscopic effective stiffness for arbitrary hyperelastic matrix materials. For an in-depth quantification of the local effective stiffness, we extend the concept of elastic stiffness maps to incompressible materials. For strain-stiffening materials, stiffness maps in the swollen state highlight pronounced radial stiffening with a non-monotonic change in stiffness in the hoop direction. Stiffening characteristics are sensitive to the form of constitutive models, which may be exploited in the design of hydrated actuators, soft composites and metamaterials. For validation, we apply this framework to a Yeoh material, and compare to recently published data. Model predictions agree well with experimental data on elastomers with highly swollen embedded microgel particles. We identify three distinct regimes related to an increasing degree of particle swelling: first, an initial decrease in composite stiffness is attributed to particle softening upon liquid intake. Second, dilute particle swelling leads to matrix stiffening dominating over particle softening, resulting in an increase in composite stiffness. Third, for swelling degrees beyond the dilute limit, particle interactions dominate further matrix stiffening.

INDUSTRIAL TOWER LIFE CYCLE EXTENSION ACCORDING TO SIKA TECHNOLOGIES

Some aspects of the life cycle extension of RC tower which is a chemical enterprise was described. This technological tower of ammonium seliters granulation has a height of +71,30 m. From this height to the Mark +46,10 mthe tower is made in a metal frame with diameter at the axes of the column22,56 m. The facade of this part is made of mounted keramzytoconcrete panels and in line constructional glazing. Between the marks 0,00 ÷ +46,10 mthe building has a monolithic RC trunk, which has a cylindrical outline in the form of a shell with an outer diameter of12,88 mand a thickness of0,3 mwalls. During 46 years of operation in chemical influences, the surface layers of the tower’s concrete trunk significantly lost its design strength. According to the results of almost regular surveys, the category of RC trunk technical condition was consistently classified as unsuitable for normal maintenance. A significant deterioration of the technical condition came in 2017, after which the building was withdrawn from the technological process, which gave impulse to the searching process of technical solution for the strengthening and chemical protection of the tower to prolong the life cycle of the entire facility. As a result of the survey the construction of the tower shall strengthening by a system of radial and vertical stiffening ribs was developed. It required a substantial unloading of the entire tower. Swiss concern Sika, one of the world leaders in the field of development and implementation of innovative technologies and materials for construction and industry, successfully implements its developments in Ukraine. For the above-described construction the firm Sika offered repair and chemical protection systems against aggressive influences for the internal and external surfaces of the tower shell, which will allow to significantly protect it and prolong the life cycle of structure.

Nanomechanical mapping of single collagen fibrils under tension.

At the most fundamental level, collagen fibrils are rope-like structures assembled from triple-helical collagen molecules. One key structural characteristic of the fibril is the 67 nm D-band pattern arising from the quarter-stagger packing of the molecules. Our current understanding of the structural changes induced by tensile loading of collagen fibrils comes mostly from atomistic molecular dynamics simulations and tissue level experiments. Tensile testing of individual fibrils is an upcoming field of investigation, and thus far structural analysis has always taken place after the fibrils have been ruptured or strained and subsequently dried. There is therefore a gap in understanding how the structure of collagen fibrils transforms under tension, and how this reorganization affects the functionality of collagen fibrils within tissues. In this study, atomic force microscopy based nanomechanical mapping is introduced to image hydrated collagen fibrils absorbed to an elastic substrate. Upon stretching the substrate between 5 and 30%, we observe a radial stiffening consistent with the fibrils being under tension. This is associated with an increase in D-band length. In addition the indentation modulus contrast associated with the D-band pattern increases linearly with D-band strain. These results provide direct confirmation of, and new information on the axially inhomogeneous structural response of collagen fibrils to applied tension as previously proposed on the basis of X-ray scattering experiments on stretched tissues. Furthermore our approach opens the road for studying the structural impacts of tension on cell-matrix interactions at the molecular level.

Stomatal Opening Involves Polar, Not Radial, Stiffening Of Guard Cells

SummaryIt has long been accepted that differential radial thickening of guard cells plays an important role in the turgor-driven shape changes required for stomatal pore opening to occur [1, 2, 3, 4]. This textbook description derives from an original interpretation of structure rather than measurement of mechanical properties. Here we show, using atomic force microscopy, that although mature guard cells display a radial gradient of stiffness, this is not present in immature guard cells, yet young stomata show a normal opening response. Finite element modeling supports the experimental observation that radial stiffening plays a very limited role in stomatal opening. In addition, our analysis reveals an unexpected stiffening of the polar regions of the stomata complexes, both in Arabidopsis and other plants, suggesting a widespread occurrence. Combined experimental data (analysis of guard cell wall epitopes and treatment of tissue with cell wall digesting enzymes, coupled with bioassay of guard cell function) plus modeling lead us to propose that polar stiffening reflects a mechanical, pectin-based pinning down of the guard cell ends, which restricts increase of stomatal complex length during opening. This is predicted to lead to an improved response sensitivity of stomatal aperture movement with respect to change of turgor pressure. Our results provide new insight into the mechanics of stomatal function, both negating an established view of the importance of radial thickening and providing evidence for a significant role for polar stiffening. Improved stomatal performance via altered cell-wall-mediated mechanics is likely to be of evolutionary and agronomic significance.

Mechanical behaviors of the Assembled Hub (AH) joints subjected to bending moment

To satisfy the demand for assembled construction of single-layer reticulated domes, a novel Assembled Hub (AH) joint with good mechanical performance and economic benefit is introduced in this paper. Two available connection types are developed to satisfy different engineering requirements. The theoretical solutions of the elastic stiffness and the bearing capacity of the new joint system are proposed based on the component method. A series of bending tests were conducted to investigate the failure mechanism of AH joints, and the FE analysis was carried out to simulate and verify the mechanical behaviors of AH joints. Finally, the strengthening effects of two kinds of stiffeners are carefully compared and discussed. The results indicate that the AH joints type I show excellent ductility in the loading process. The failure of joints is caused by the plastic instability of the hub or the excessive plastic deformation of the closure plate. The plastic moment resistance of joint is determined by the thickness, height, outer diameter and material of the hub, as well as the bolts pitch. By contract, the AH joints type II display lower ductility but higher bearing capacities in the loading process. The failure mode is the connection failure. The ring stiffeners have a better strengthening effect than the radial stiffeners. A comparison between the computations and the experiments highlights the validity of the suggested bearing capacity formulas, which can be further used to guide the joint design.

Thermal-hydraulic design of a DCLL breeding blanket for the EU DEMO

The thermal-hydraulic design of the breeding blanket, as the main thermal source for power conversion, reveals itself as a key issue to counteract the influence of the foreseen low overall plant availability on the cost of electricity. In the case of the Dual Coolant Lithium-Lead (DCLL), the decreased contribution of helium (non-breeding coolant) as thermal source in comparison with lithium-lead (breeding coolant) presents clear advantages, like less dependence on the long-term availability of He and lower recirculating power (recompression). The short operational range of temperature (300–550°C) imposed by the use of RAFM steel is handled by adopting the Multi-Module Segment concept. This allows lower PbLi velocities by arranging in parallel the circuits of different modules. In consequence, the magnetohydrodynamic pressure drop and corrosion rates may be diminished. On the other hand, the high Péclet numbers validate the use of simpler computational codes to couple thermally both coolants, taking advantage of assuming that the heat transfer between the structure and the fluids is one-dimensional. A thermal-hydraulic one-dimensional code (PLATOON) has been developed for sensitivity analyses. The paper also addresses an assessment of the cooling of the radial stiffening plates and a preliminary study of the effects of the high heat generation gradient in the front poloidal PbLi channels.

Structural design optimization of roof slab of a pool type sodium cooled fast reactor

The roof slab of the nuclear reactor supports all the components of the reactor. Roof slab is essentially a box structure with top and bottom plates interconnected by vertical shells and radial stiffeners welded to them. The gap between the top and bottom plates is filled with concrete that provides biological and thermal shielding in the top axial direction of the reactor. The 500MWe Prototype Fast Breeder Reactor (PFBR) is designed based on the Operating Basis Earthquake (OBE) and Safe Shutdown Earthquake (SSE) which are categorized under level A and level D loadings respectively. The primary objective of this work is to optimize the design of the roof slab and to predict and ascertain the structural integrity of the optimized roof slab under static, harmonic and seismic loading conditions. Regression models for critical design parameters are developed and are used in the optimization algorithm.

A Numerical Investigation of a Novel Hood Design for Pedestrian Protection

Currently the use of new materials is becoming even more prevalent in vehicle industry for the lightweight design purpose. The design of engine hood is very important for pedestrian’s safety during a vehicle-pedestrian accident. In order to improve the pedestrian protection performance of the new material engine hood, the radial stiffening rib structure and trapezium sandwich structure engine hoods were proposed in this paper. And an energy-absorbing structure has been designed on the strengthening hinge plate to reduce the pedestrian head injury further more. The simulation results indicate that with new structures, the new material engine hoods have more uniform rigidity and better energy absorbing ability, which would effectively reduce the engine hood intrusion and pedestrian head injuries.

Shear lag analysis of a novel short fuzzy fiber-reinforced composite

A novel short fuzzy fiber-reinforced composite (SFFRC) in which the aligned short carbon fiber reinforcements are coated with radially aligned carbon nanotubes (CNTs) is considered in this study. A three-phase shear lag model considering radial and axial deformations of the different constituent phases of the SFFRC has been developed to analyze the stress transfer mechanisms of the SFFRC. Traditionally, the shear lag models have been developed with an application of the axial load only on the representative volume element (RVE) of the composite in an attempt for analyzing the stress transfer between the fiber and the matrix. The three-phase shear lag model derived in this study analyzes the stress transfer to the short carbon fiber considering the application of the axial as well as the radial loads on the RVE of the SFFRC. It is found that if the carbon fiber is coated with radially aligned CNTs, then the axial load transferred to the fiber is significantly reduced due to the radial stiffening of the polymer matrix by CNTs. When compared with the results without CNTs, it is found that almost ~20 and ~29 % reductions in the maximum axial stress in the carbon fiber and the interfacial shear stress along its length occur, respectively, if the value of the applied radial load is twice of the applied axial load and the value of the CNT volume fraction is 0.0236 in the SFFRC. Effects of the variation of the carbon fiber aspect ratio, the carbon fiber volume fraction, and the application of the radial load on the load transfer characteristics of the SFFRC are also investigated.

Thermal analysis of NAC-LWT cask under normal and fire accident conditions

AbstractTwo- and three-dimensional thermal models of a Nuclear Assurance Corporation Legal Weight Truck (NAC-LWT) cask were constructed using the PATRAN commercial finite element package. The two-dimensional model included the effect of radial stiffeners in the package’s external neutron shield but the three-dimensional model did not. A normal conditions of transport (NCT) simulation using both models predicted the peak cladding temperature was roughly 210°C. The NCT package temperatures were used as initial conditions for transient fire/post-fire simulations. Different assumptions were used to determine when the neutron shield liquid drained from the tank and was replaced by air. When the liquid was assumed to remain within the tank during and after the fire, the peak cladding temperature was predicted to exhibit a temporal maximum of roughly 300°C, ∼6 h after the end of the fire. If the liquid drained from the tank during the fire, the cladding temperature did not exhibit a temporal peak. Rather, it eve...

Openwork shell projector

A honeycomb-like shell is provided for an acoustic projector used in sonar applications to increase the bandwidth of the projector, reduce its weight, and to provide increased power density and reduced shell costs. The shell has outer and inner layers, with the honeycomb structure therebetween. The honeycomb shells have application in slotted cylindrical projectors, flextensional projectors, inverse flex tensional projectors, and oval-shaped projectors in which the honeycomb structure replaces the solid shells, with the honeycomb providing the relatively high specific stiffness required for the acoustic properties of the projector. The honeycomb shell achieves the same bending stiffness of the solid shells with less weight through the utilization of radial stiffeners between the inner and outer layers. The use of the honeycomb structure increases bandwidth by over 30%, and reduces total weight by 22%, shell weight by 65% and shell cost by 50%, making the honeycomb shell ideal for low frequency sonar applications.

Estimation of machining errors using the concept of cyclic symmetry

Keeping the form error within tolerable limits is an important consideration in the machining of cylindrical workpieces. One main reason for form error in machining thin cylinders is the static and dynamic deflection of the workpiece under the action of the cutting force. One way of reducing the form error during machining is to introduce radial stiffeners. In this paper, static and dynamic analysis of the workpiece has been carried out using the finite element method to analyze the effect of such radial strengthening ribs on the form error. The concept of cyclic symmetry has been used to analyze the problem and to improve the efficiency of the program.

Structural evaluation of the NET/ITER outboard blanket box

This paper presents the results from a 3-D thermomechanical analysis of the the ET/ITERreference design of the outboard blanket box and integral first wall. The influence of the global box behaviour under the thermal and electromagnetic loadings on the detailed first-wall stresses has been determined. The thermal part of this study investigated the influence of the back-plate temperature of the box and the inclusion of radial stiffening ribs on first-wall stresses. Radial stiffening ribs introduced to withstand disruption forces also help to redistribute forces arising from differential expansion between the back plate and first wall; the peak temporal Tresca stress range in the first wall with ribs is 269 MPa and without ribs is 316 MPa. The back-plate temperature does not strongly influence the magnitude of the stresses in the first wall. The ribs reduce the first-wall stresses produced by the electromagnetic loads but not to a level which is acceptable when combined with the thermal loads. Comparison between this 3-D analysis and 2-D finite-element calculations highlights the conservatisms present in the previous 2-D analysis used to design the first wall.

Free Vibration of Radially Stiffened Annular Plate

The free vibration of radially stiffened annular plates is studied by the Ritz method using a spline function as an admissible function for the deflection of the plates. The transverse deflection of the plate is written in a series of the products of the deflection function of a sectorial beam with small angle and the trigonometric function of angular coordinate. The frequency equation of the plate is derived from the conditions that the Lagrangian takes a stationary value. The deflection function of the sectorial beam is approximately expressed by a quintic spline polynomial, which satisfies the equation of flexural vibration of the beam at all points dividing the beam into smell elements and also the boundary conditions at both ends. The present method is applied to annular plates with radial stiffeners located at equal angular intervals on both surfaces of the plates. The natural frequencies and the mode shapes of the plates are calculated numerically, and the effects of the stiffeners on them are studied.

A Finite Element Shell Analysis of Guard Cell Deformations

ABSTRACT IN this paper the width of the stomatal aperture, as postulated by von Mohl in 1856, is shown to be a function of the hydrostatic (turgor) pressure in the guard cells, Pg, and the pressure, Ps, of the immediately surrounding epidermal cells, which will be referred to as the subsidiary cells in this paper. The aperture does not depend solely upon the pressure difference (Pg-Ps) as believed by Ursprung and Blum (1924) and StSlfelt (1966). Instead, aperture width is shown to be a simple multi-linear relationship (i.e., a linear com-bination) of Pg and Ps. The recent re-search by Glinka (1971) and Edwards, Meidner and Sheriff (1976), showing the relative contributions of the oppos-ing pressures Pg and Ps, is, thus, given a simple and lucid interpreta-tion. The analysis of a guard cell as an elliptical torus shows that a stomate could function without either of the two conditions classically believed to be essential (Meyer et al. 1960, p. 84, Meidner and Mansfield 1968, pp. 14-17, Bidwell 1974, p. 298). The thick-ened wall (ventral wall) of the guard cell facing the aperture need not neces-sarily be stiffer than the dorsal wall common to the adjacent epidermal cell for the proper functioning of a stomate. The radially oriented cellu-lose microfibrils in the guard cell wall are not vital but are important for quite different reasons than claimed by Aylor et al. (1973). Consideration of the radial stiffening by means of the in-troduction of a mechanically equiva-lent orthogonally anisotropic (i.e., or-thotropic) material causes the aperture width to be more sensitive to a unit increment in Ps than to a unit incre-ment in Pg (for parameters of physi-cal interest3). The guard cell volume, however, is smaller than the adja-cent cell volume and Pg is believed to be larger than Ps, in general. We conjecture that this increased sensi-tivity for the subsidiary cell (i.e., clos-ing) pressure is important for the functioning of the feedback control loops regulating the aperture width. We define an antagonism ratio to characterize this property. The pore length in the model is shown to be surprisingly constant during opening, as is reported for many species (Meidner and Mansfield 1968, p. 12). The guard cell is generally believed to bulge into the neighboring epider-mal cell upon opening (Meidner and Mansfield 1968, p. 15). However, the shell model suggests that the outer-most portion of the guard cell at the widest point (and not visible in an in vivo situation) actually moves away from the neighboring cell. The ap-proximate point at which the exposed surface of the epidermal cell joins the guard cell exhibits only limited mo-tion. Note that there are especially thin regions here in the epidermal cell thought to behave as hinges (Hautgelenke). Even when the ex-treme, unphysiological case of a fixed aperture length is imposed, the outermost perimeter moves away from the adjacent cell. If the epidermis is opaque, the view from outside the leaf suggests that the guard cell bulges into the neighboring cell, as claimed in the classical hypothesis, provided the stiffening effect of the micellae is sufficiently prominent and provided the guard cell pressure is significantly larger than the epidermal cell pres-sure. The opposing influence of the turgor pressure in the guard cells and in the adjacent epidermal cells is shown to be an inherent part of the stomatal mechanism (von Mohl 1856). Pressure influence coefficients for the guard cell are defined and related to parameter changes, e. g., material and thickness. The multilinear relationship of aperture width to the opposing turgor pressures was found and revealed that pore width does not depend solely on the pressure difference between the guard cell and the adjacent epidermal cell. Finally, the theory developed is shown to embrace and to clarify the experimental results of Glinka's plas-molytic study (1971) and the direct method of Edwards et al. (1976).

Effect of Boundary Conditions of Flexural Vibrations of Thin Orthogonally Stiffened Cylindrical Shells

The flexural vibrations of thin orthogonally stiffened cylindrical shells are discussed considering the effect of different boundary conditions. The orthotropic shell theory of W. H. Hoppmann, II, was usect to derive the orthotropic stress-strain law, and the equations of motion were formulated for the shell element in three partial differential equations. The equations were reduced to a single eighth-order ordinary differential equation. This equation yielded a fourth-order frequency equation by considering a relatively long cylinder. The following three boundary conditions were applied: clamped-clamped, clamped-simply supported, and both edges simply supported. The author's theory was compared with Hoppmann's theory and test results for the case of simple supports. The errors are about the same for both theories. The author's theory shows that the clamped-clamped and clamped-simply supported boundary conditions can affect the frequencies seriously in the case of longitudinal stiffeners; however, the effect is smaller with radial stiffeners. For the isotropic case, the theory simplifies to the solution of Yi Yuan Yu.