Increase In Elastic Stiffness Research Articles

Performance of bolted steel laminated bamboo lumber connections under axial cyclic loading

Bolted connections are well known for their simplistic design and installation, and have been used in bare frame structures of various types of materials including steel and timber. Compared with monotonic loading, cyclic loading is more dangerous. Bamboo has excellent toughness and deformation recovery ability but a quantitative description of the mechanical performance of bolted steel laminated bamboo lumber (LBL) connections under cyclic loading has not yet been determined. As a result, tension and compression tests were carried out separately under axial cyclic loading. Obtained experimental results indicated that the tensile specimens suffer brittle failure because of the premature cracking of LBL due to cyclic loading; the bolts remained almost straight after failure. On the other hand, cyclic compressive specimens showed considerable ductile behavior as the bolts underwent plastic deformation since LBL sustained considerable load prior to failure due. Key mechanical connection parameters such as elastic stiffness, yield and ultimate displacement, yield and ultimate load, ductility ratio obtained from the skeleton curves were carefully analyzed to study the influence of bolt number on various properties. The increase in elastic stiffness from two to four bolts is about 60 % for the cyclic tension specimens, whilst that was about 25 % for the cyclic compression specimens. Compared with the cyclic tensile specimens, cyclic compressive specimens have higher ductility ratio, which is mostly greater than 2. In addition, theoretical models for both loading and unloading curves have been proposed, which showed good agreement with test results.

Concurrent geometrico-topological tuning of nanoengineered auxetic lattices fabricated by material extrusion for enhancing multifunctionality: Multiscale experiments, finite element modeling and data-driven prediction

This study demonstrates the multifunctional performance of innovative 2D auxetic lattices through a combination of multiscale experiments, finite element modeling and data-driven prediction. A geometric modeling approach utilizing Voronoi partitioning and a unique branch-stem-branch (BSB) structure, patterned according to 2D wallpaper symmetries, enables precise concurrent geometric and topological tuning of lattices across a continuous parameter space. Selected architectures are physically realized via material extrusion of polylactic acid (PLA) infused with carbon black (CB). Experimental characterizations, supported by Finite Element modeling, reveal the significant influence of BSB structure's design parameters on mechanical and piezoresistive performance under tensile loading, with a remarkable Poisson’s ratio of -0.74, accompanied by a 15-fold increase in elastic stiffness and a 34-fold increase in strain sensitivity. Additionally, architecturally, and topologically tailored lattice structures exhibit tunable damage sensitivity, reflecting the rate of conductive network destruction within the lattice. This offers insights into the rapidity of cell wall failure, with a steeper slope of the piezoresistance curve in the inelastic regime indicating a faster breakdown and quicker onset of mechanical failure. Integration of Gaussian Process Regression enables accurate exploration of the design space beyond realized structures, highlighting the potential of these intelligent lattice structures for applications such as sensors and in situ health monitoring, marking a significant advancement in multifunctional materials.

Exploring the influence of size-related factors on geocell-reinforced soil response using coupled continuum-discontinuum analysis

Size-related factors, such as the dimensions and cell count of geocell, play a crucial role in determining the effectiveness of soil reinforcement. In this study, a 3D coupled framework that leverages the strengths of both continuum and discontinuum methods was developed to investigate the influence of pocket size and multi-cell configuration on geocell-reinforced soils. To unveil the impact of size-related factors on soil-geocell interactions, reinforced soils containing various geocell configurations (single large-sized cell, multiple small-sized cells), as well as geocell-free soils subjected to increasing levels of confining pressure were extensively examined. This thorough investigation aimed to establish correlations between macroscopic responses and underlying micromechanical mechanisms. Our findings revealed that the presence of the geocell not only enhances the densification of interparticle contacts and reduces the number of floating particles that contribute minimally to load support, but also facilitates the concentration of force chains within the geocell structure. This leads to an increase in elastic stiffness along the loading axis. These observations highlight that the geocell's confining mechanism enhances both the load-carrying capacity and the infill rigidity, thereby preventing lateral soil spreading. In essence, the geocell serves to increase the soil's ability to withstand load and maintain its structural integrity laterally.

Numerical Investigation of Cyclic Behavior of Angled U-shaped Yielding Damper on Steel Frames

Yielding dampers are often selected as a cost-effective solution for improving steel structures compared to other energy dissipation systems. The objective of this research study was to investigate the cyclic behavior of the angled U-shaped yielding damper (AUSYD) on a steel frame using numerical method. The numerical model was first verified using two experimental samples. Next, the influence of the number of dampers on the cyclic behavior of the steel frame was examined. The parametric model outcomes included energy dissipation, elastic stiffness, strength, and equivalent viscous damping ratio (EVDR). Additionally, an analytical equation was proposed for calculating the ultimate strength of the AUSYD, which correlated well with the experimentally obtained results. The study findings revealed that the increase in elastic stiffness and strength of the frame equipped with the AUSYD was nearly equivalent to the sum of the elastic stiffness and strength of the bare frame and its supplementary dampers. Furthermore, the results showed that models with 8 to 12 dampers had comparable energy dissipation and EVDR. Adding 8 dampers to the frame increased the energy dissipation and damping coefficient of the frame by 42% and 67%, respectively.

Study of Elastic and Structural Properties of BaFe2As2 Ultrathin Film Using Picosecond Ultrasonics.

We obtain the through-thickness elastic stiffness coefficient (C33) in nominal 9 nm and 60 nm BaFe2As2 (Ba-122) thin films by using picosecond ultrasonics. Particularly, we reveal the increase in elastic stiffness as film thickness decreases from bulk value down to 9 nm, which we attribute to the increase in intrinsic strain near the film-substrate interface. Our density functional theory (DFT) calculations reproduce the observed acoustic oscillation frequencies well. In addition, temperature dependence of longitudinal acoustic (LA) phonon mode frequency for 9 nm Ba-122 thin film is reported. The frequency change is attributed to the change in Ba-122 orthorhombicity (a-b)/(a+b). This conclusion can be corroborated by our previous ultrafast ellipticity measurements in 9 nm Ba-122 thin film, which exhibit strong temperature dependence and indicate the structural phase transition temperature Ts.

Progressive damage analysis of an adhesively bonded composite T-joint under bending, considering micro-scale effects of fiber volume fraction of adherends

In this study, a numerical study on failure assessment and stress distribution on the adhesive region in a composite T-joint under bending load case is investigated using cohesive zone method (CZM). The Finite Element Model (FEM) has been verified with experimental results. To study the load transfer capability of the T-joint, five different adhesives are considered in the adhesive region and the effect of geometrical parameters such as stringer thickness, corner radius, and adherend thickness as well as micromechanical properties of reinforced fiber composite adherends are investigated. Effective properties of two composite adherends including Carbon-Epoxy (IM7/8552) and Glass-Epoxy (E-glass/Epon 828) with various fiber volume fractions are estimated using a 3D representative volume element (RVE) and employing period boundary conditions (PBC) through Python scripts in ABAQUS. The results show that the fiber volume fraction of composite adherends has a significant effect on failure behavior. For instance, increasing fiber volume fraction of carbon/epoxy composite from 0.4 to 0.7 resulted in a 78% increase in elastic stiffness and a 41% enhancement in maximum load-bearing capacity. Among different adhesive types used in this study, FM300 resulted in the strongest structure and S7752 led to a more ductile T-joint.

A comparative study of structural and electrical properties in lead-free BCZT ceramics: Influence of the synthesis method

In the present work, various grain size phenomena were studied in promising lead-free piezoelectric ceramics (Ba0.85Ca0.15) (Zr0.10Ti0.90)O3 fabricated via chemical and conventional oxide methods. Phase composition was ascertained by the Rietveld refinement. Average grain size estimated from the microstructure was ∼1.5 μm in the sol-gel derived ceramic (SG-BCZT) which was much smaller than that obtained in coarse grained (∼27 μm) sample prepared by solid state method (SS-BCZT). Systematic investigation of various functional properties viz. dielectric, ferroelectric, piezoelectric and impedance emphasized the profound influence of grain size effects. The increase in grain boundary volume fraction enhanced diffuseness while lowered the dielectric peak in SG-BCZT. Similarly, increase in elastic stiffness and progressive hindrance to domain wall movements, resulted in a decrease of the remnant polarization and the associated piezoelectric charge coefficient values in small-grained SG-BCZT sample. Accordingly, higher Young's modulus value of 158.3 GPa was observed in SG-BCZT as compared to 117.9 GPa in SS-BCZT. Local-area piezoresponse force microscopy (PFM) images revealed lamellar domains with periodicity 250 ± 90 nm in SS-BCZT while small sized fractal-like irregular domains with an estimated domain width of 150 ± 60 nm were registered in SG-BCZT. Complex impedance spectroscopy results along with grain boundary conductivity were also guided by grain size effect. The mechanisms of grain size driven effects and their impact on the functional properties were discussed.

Effect of Curing Humidity on Stiffness of Cement Based Mortars with Recycled Fillers

Values of the dynamic Young’s modulus were monitored on cement-based samples containing recycled concrete. In particular, the study was focused on investigation of the relationship between the elastic stiffness and amount of recycled microfiller to replace Portland cement. The amount of the microfiller was ranging between 30 and 70 % per weight of the samples. The samples were cured in common laboratory conditions for 50 days, followed by their placement into a water bath for 2 days and consequent natural drying period for 6 days. The development of elastic stiffness was monitored using non-destructive impulse excitation method in order to demonstrate the influence of hydration when the specimens are stored in high humidity. The increase of elastic stiffness proves a secondary hydration of both – Portland cement and cement grains from the recycled cementitious material.

On the Mechanics of Ultralight Hollow Microlattices

AbstractThe objective of the present work is a thorough understanding of the mechanics of microlattices by finite element analysis. A thin‐shell model for a unit‐cell along with an isotropic material law of elasto‐plasticity captures for compression experiments (i) significant deformation characteristics in terms of stress‐strain curves, (ii) the interplay of inelasticity with shell geometrical features and (iii) the scaling behavior of stiffness and strength for various densities. The octet cell in comparison to the bcc cell shows an increase in elastic stiffness and strength by 1‐2 orders of magnitude, thus making a step towards ultralight and ultratight properties of structural materials. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Experimental and statistical analysis of spruce timber beams reinforced with CFRP fabric

Enhancement of timber beams with fibre reinforced materials gained momentum in the last few decades producing a wide range of materials, techniques and modelling methods. Experiments show that the potential improvement of structural behaviour is greatly affected by the type of reinforcement, wood species, etc. In this study a series of experiments were conducted on sawn Norway spruce beams reinforced with various amounts of CFRP sheets (carbon fibre reinforced plastic) followed by a statistical analysis. A moderate increase of load-bearing capacity and ductility (approx. 30%) and a small increase of elastic stiffness (approx. 16%) can be achieved. Statistical analysis of the results has shown that the performance of reinforced spruce beams is affected by the presence of knots in the material.

Elastic and magnetoelastic relaxation behaviour of multiferroic (ferromagnetic + ferroelectric + ferroelastic) Pb(Fe0.5Nb0.5)O3 perovskite

Resonant Ultrasound Spectroscopy has been used to characterize elastic and anelastic anomalies in a polycrystalline sample of multiferroic Pb(Fe0.5Nb0.5)O3 (PFN). Elastic softening begins at ~550 K, which is close to the Burns temperature marking the development of dynamical polar nanoregions. A small increase in acoustic loss at ~425 K coincides with the value of T* reported for polar nanoregions starting to acquire a static or quasi-static component. Softening of the shear modulus by ~30–35% through ~395–320 K, together with a peak in acoustic loss, is due to classical strain/order parameter coupling through the cubic → tetragonal → monoclinic transition sequence of ferroelectric/ferroelastic transitions. A plateau of high acoustic loss below ~320 K is due to the mobility under stress of a ferroelastic microstructure but, instead of the typical effects of freezing of twin wall motion at some low temperature, there is a steady decrease in loss and increase in elastic stiffness below ~85 K. This is attributed to freezing of a succession of strain-coupled defects with a range of relaxation times and is consistent with a report in the literature that PFN develops a tweed microstructure over a wide temperature interval. No overt anomaly was observed near the expected Néel point, ~145 K, consistent with weak/absent spin/lattice coupling but heat capacity measurements showed that the antiferromagnetic transition is actually smeared out or suppressed. Instead, the sample is weakly ferromagnetic up to ~560 K, though it has not been possible to exclude definitively the possibility that this could be due to some magnetic impurity. Overall, evidence from the RUS data is of a permeating influence of static and dynamic strain relaxation effects which are attributed to local strain heterogeneity on a mesoscopic length scale. These, in turn, must have a role in determining the magnetic properties and multiferroic character of PFN.

A theoretical–experimental approach to elastic and strength properties of artificially cemented sand

Evaluating the behavior parameters of soils and soil-binder mixes by means of theoretical models that are supported by laboratory tests still remains a key challenge in foundation design. In this context, the paper investigates some aspects of the mechanical behavior of artificially cemented sands (ACS) by means of experimental characterization and micromechanics-based modeling. Particular emphasis is given to the increase in elastic stiffness and strength brought by cementation. Based on the concept of a fictitious continuum medium and the homogenization theory, the effective elastic properties of ACS are evaluated using the Mori–Tanaka and self-consistent schemes. The elastic micromechanical approach is supported by bender element tests. Finally, the effective strength properties of ACS are assessed by means of micromechanics-based failure criterion formulated within the context of non-associated plasticity. Validation and calibration of the theoretical model are achieved by comparison with data from unconfined compression tests.

An elastoplastic framework for granular materials becoming cohesive through mechanical densification. Part II – the formulation of elastoplastic coupling at large strain

The two key phenomena occurring in the process of ceramic powder compaction are the progressive gain in cohesion and the increase of elastic stiffness, both related to the development of plastic deformation. The latter effect is an example of ‘elastoplastic coupling’, in which the plastic flow affects the elastic properties of the material, and has been so far considered only within the framework of small strain assumption (mainly to describe elastic degradation in rock-like materials), so that it remains completely unexplored for large strain. Therefore, a new finite strain generalization of elastoplastic coupling theory is given to describe the mechanical behaviour of materials evolving from a granular to a dense state. The correct account of elastoplastic coupling and of the specific characteristics of materials evolving from a loose to a dense state (for instance, nonlinear – or linear – dependence of the elastic part of the deformation on the forming pressure in the granular – or dense – state) makes the use of existing large strain formulations awkward, if even possible. Therefore, first, we have resorted to a very general setting allowing general transformations between work-conjugate stress and strain measures; second, we have introduced the multiplicative decomposition of the deformation gradient and, third, employing isotropy and hyperelasticity of elastic response, we have obtained a relation between the Biot stress and its ‘total’ and ‘plastic’ work-conjugate strain measure. This is a key result, since it allows an immediate achievement of the rate elastoplastic constitutive equations. Knowing the general form of these equations, all the specific laws governing the behaviour of ceramic powders are finally introduced as generalizations of the small strain counterparts given in Part I of this paper.

Biomechanical changes in the anterior lens capsule after trypan blue staining

Purpose: To examine the effect of trypan blue staining on the biomechanical behavior of the porcine anterior lens capsule. Setting: Department of Ophthalmology, Technical University of Dresden, Dresden, Germany. Methods: Fifty-five anterior lens capsules from porcine cadaver eyes were used. Two parallel 8.0 mm × 4.0 mm large capsule strips were prepared from each capsule. After trypan blue staining for various time intervals combined with exposure to white light (6000 lux) or with no light exposure, biomechanical stress-strain measurements were performed using an automated material tester. Untreated specimens and specimens treated with glutaraldehyde 0.1% were used as controls. The absorption spectrum of trypan blue 0.1% solution and the emission spectrum of the light source were measured. Results: After treatment with light and trypan blue, at 25% strain, there was a statistically significant increase in stress of up to 70.1% and in elastic stiffness of 47% and a decrease in the ultimate mechanical strain of up to 13%. There were no biomechanical changes in capsules with trypan blue staining in the absence of light or after a short illumination time of 30 seconds, indicating a light-dependent process. After 30 minutes of glutaraldehyde 0.1% treatment, there was an increase in stress of 321.6% at 25% strain and a decrease in the ultimate strain of 47.6%. The emission spectrum of the light source included the absorption peak for trypan blue at 580 nm. Conclusions: Trypan blue staining of the lens capsule combined with light irradiation for at least 1 minute led to an increase in elastic stiffness at 25% strain and a reduction in the ultimate extensibility. This effect is probably due to the photosensitizing action of trypan blue, leading to light-induced collagen crosslinking of the capsule collagen similar to age-related crosslinking. Nucleus expression might be impeded by the increased capsule stiffness. Continuous curvilinear capsulorhexis is facilitated.

Influence of indocyanine green staining on the biomechanical properties of porcine anterior lens capsule

Purpose. Indocyanine green (ICG) has recently been introduced in cataract surgery to stain the anterior lens capsule for better visualization of the capsulorhexis. The aim of the current in vitro study was to examine the effect of ICG staining on the biomechanical strength of the anterior porcine lens capsule.Methods. Two parallel, 8 × 4 mm anterior lens capsule strips were prepared from each of 65 porcine postmortem eyes. ICG staining combined with white light exposure of 0.5, 1, 3, and 30 min duration was conducted. Unstained, nonilluminated and 0.1% glutaraldehyde-treated specimens were used as controls. Biomechanical stress-strain measurements were performed using an automated material tester. The absorption spectrum of the 0.5% ICG solution and the emission spectrum of the light source were controlled.Results. After ICG staining combined with at least 3 min light exposure, a significant increase of stress (31%) at 25% strain and a significant decrease (7%) in ultimate strain was found. Without light exposure, there was no such effect, suggesting a light-dependent process. After 30 min of 0.1% glutaraldehyde treatment, there was a similar increase in stress (322%) at 25% strain and a decrease (47.6%) in ultimate strain.Conclusions. ICG staining of the lens capsule causes a significant increase in elastic stiffness and a reduction in ultimate extensibility, thereby facilitating a smooth continuous capsulorhexis. The effect is due to a photosensitizing effect of ICG, leading to collagen cross-linking.

Scaled boundary finite‐element analysis of a non‐homogeneous elastic half‐space

AbstractAs a result of stresses experienced during and after the deposition phase, a soil strata of uniform material generally exhibits an increase in elastic stiffness with depth. The immediate settlement of foundations on deep soil deposits and the resultant stress state within the soil mass may be most accurately calculated if this increase in stiffness with depth is taken into account. This paper presents an axisymmetric formulation of the scaled boundary finite‐element method and incorporates non‐homogeneous elasticity into the method. The variation of Young's modulus (E) with depth (z) is assumed to take the form E=mEzα, where mE is a constant and αis the non‐homogeneity parameter. Results are presented and compared to analytical solutions for the settlement profiles of rigid and flexible circular footings on an elastic half‐space, under pure vertical load with αvarying between zero and one, and an example demonstrating the versatility and practicality of the method is also presented. Known analytical solutions are accurately represented and new insight regarding displacement fields in a non‐homogeneous elastic half‐space is gained. Copyright © 2003 John Wiley & Sons, Ltd.

Cell contraction caused by microtubule disruption is accompanied by shape changes and an increased elasticity measured by scanning acoustic microscopy.

The state of crosslinking of microfilaments and the state of myosin-driven contraction are the main determinants of the mechanical properties of the cell cortex underneath the membrane, which is significant for the mechanism of shaping cells. Therefore, any change in the contractile state of the actomyosin network would alter the mechanical properties and finally result in shape changes. The relationship of microtubules to the mechanical properties of cells is still obscure. The main problem arises because disruption of microtubules enhances acto-myosin-driven contraction. This reaction and its impact on cell shape and elasticity have been investigated in single XTH-2 cells. Microtubule disruption was induced by colcemid, a polymerization inhibitor. The reaction was biphasic: a change in cell shape from a fried egg shape to a convex surface topography was accompanied by an increase in elastic stiffness of the cytoplasm, measured as longitudinal sound velocity revealed by scanning acoustic microscope. Elasticity increases in the cell periphery and reaches its peak after 30 min. Subsequently while the cytoplasm retracts from the periphery, longitudinal sound velocity (elasticity) decreases. Simultaneously, a two- to threefold increase of F-actin and alignment of stress fibers from the cell center to cell-cell junctions in dense cultures are induced, supposedly a consequence of the increased tension.

Observation of modification and recovery of local properties of polyethylene oxide

By applying large forces to the surface during an atomic force microscopy scanning, crystallized polyethylene oxide (PEO) films were modified and showed a new structure in which there are the formation of a nanometer-scale bundle structure and an increase of elastic stiffness. The modified part was removed by dropping benzene onto a rotating surface through a peeling process for the case of thin modified layers, while for thick layers, the local properties were recovered by absorbing benzene into the modified parts. In the course of these measurements, the thickness of the modified layers was estimated.

Diastolic stiffening induced by acute myocardial infarction is reduced by early reperfusion

Reperfusion early during myocardial infarction improves ejection fraction and this improvement may represent myocardial salvage in the injured segment. Alternatively, reperfusion of injured myocardium may cause intramyocardial hemorrhage with resultant increased stiffness causing a dyskinetic segment to become akinetic, thus improving ejection fraction without concomitant myocardial salvage. To evaluate this possibility, diastolic stiffness was assessed in a closed chest, anesthetized, normothermic dog model immediately after a 1 or 3 h occlusion of the left anterior descending coronary artery and during the 4 weeks after occlusion.Acute myocardial infarction in experimental dogs was accompanied by a fivefold increase in the chamber stiffness constant, a threefold increase in the myocardial stiffness constant and a significant increase in elastic stiffness and end-diastolic pressure. These changes occurred contemporaneously with a marked decline in ejection fraction. Early reperfusion (1 h occlusion) resulted in improvement of the ejection fraction accompanied by simultaneous resolution of the previously increased stiffness. Late reperfusion (3 h occlusion) resulted in permanent depression of ejection fraction with permanent elevation of stiffness. These results indicate that the improved systolic function observed after early reperfusion reflects a process other than increased stiffness, perhaps salvage of jeopardized myocardium.

Earthquake precursory effects due to pore fluid stabilization of a weakening fault zone

We report the analysis of two mechanisms by which pore fluids could partially stabilize the earthquake rupture process in natural rock masses. These mechanisms are based on dilatancy strengthening and on the increase of elastic stiffness for undrained as opposed to drained conditions. Both are studied in relation to an inclusion model in which a zone of strain weakening material, possibly representing a highly stressed seismic gap zone, is embedded in nominally elastic surroundings subjected to steadily increasing tectonic stress. Owing to the coupling between deformation and pore fluid diffusion, the inclusion does not exhibit an abrupt rupture instability; rather, a period of self‐driven precursory creep occurs which ultimately accelerates to dynamic instability. The precursory time scale is reported for a wide range of constitutive parameters, including fluid diffusivity, ratio of undrained to drained stiffness, and factors expressive of strain softening and dilatancy. Our conclusions are that the precursory times for a spherical inclusion of 1‐km radius are of the order of 15–240 days for a range of constitutive parameters that we suggest are representative. The predicted times are shorter by a factor of approximately 10 for a flattened ellipsoidal inclusion that we analyze with an 18 : 1 aspect ratio. It is suggested that perhaps only toward the latter part of the precursory period are the effects of accelerating inclusion strain detectable in terms of surface deformation or alteration of transport or seismic properties.