Increment Of Stiffness Research Articles

Numerical and Experimental Study on Optimization of Coil Springs used in Vehicles’ Suspension System

In general, the suspension systems are used to absorb vibrations, bump, rolls, dip from shock loads due to road surface irregularities. It performs its major role without affecting the vehicles’ stability and overall handling during operation. Coil springs are used as suspension element in light vehicles to attenuate unwanted vibrations. A spring is an elastic object used to store mechanical energy and it can be twisted, pulled or extended by some force and can return to its initial position when the force is released. In this study, mild steel material was taken into consideration in designing and fabricating coil springs. Theoretical and experimental investigations were conducted to calculate springs’ stiffness and to make validation between them. Three model of springs having coils 10, 11, 14 respectively are designed which have slight stiffness difference both theoretically and experimentally. The models were analyzed to determine mechanical behaviors for randomly chosen loading conditions ranging from 29.4 N to 176.4 N which are better suited with spring size. It is noted from both numerical and experimental investigations that deflection is high when the stiffness is less and vice-versa. In addition, shear stress formation increases with the increment of stiffness and applied load. Hence, springs having high stiffness are used in suspension system to reduce vibration and other disturbances. This study shows springs of having high stiffness are comparatively compact in size and cost economic as well.

A Positive Pressure Jamming Based Variable Stiffness Structure and its Application on Wearable Robots

Variable stiffness mechanisms establish a bridge between rigid, precise robots and soft, compliant robots. In certain applications it is necessary to exert high forces while having compliance, such as in wearable robots, high payload soft grippers, and manipulators. Negative pressure based jamming approaches have been widely used to tune variable stiffness. However, this variation of stiffness and strength is limited to negative one atmospheric pressure. To enable a wider pressure range which potentially enable wider stiffness range, we proposed a Positive Pressure Jamming (PPJ) approach. The PPJ is fabricated by embedding a pneumatic actuator inside a cylindrical non-stretchable fabric sleeve which contains granules. Pressurizing air into the pneumatic actuator will jam the granules, thus stiffening the soft body. To add degrees of freedom for the PPJ, we place a pair of friction pads in parallel between two PPJ units which act as a self-locking revolute joint. Both the PPJs and self-locking joint can be stiffened at the same time thus enabling the structure to be jammed in multiple configurations. Experiments showed that approximately six-fold stiffness increment (0.69N/mm to 4.02N/mm) could be achieved by our PPJ when input pressure is changed from 68 kPa to 172 kPa with exerted force ranges from 4N to 23N. Furthermore, we apply the proposed PPJ method into limb support devices, demonstrating a promising potential that PPJ has in wearable robot field.

Enhanced electrical and photocatalytic activities in Na0.5Bi0.5TiO3 through structural modulation by using anatase and rutile phases of TiO2

This paper deals with an in-depth analysis on the role of the microstructure phase of titanium dioxide (TiO2) precursor in sodium bismuth titanate (Na0.5Bi0.5TiO3, hereafter represented as NBT) ceramics prepared through the hydrothermal method. The comparison of the grain size, microstructure, crystal structure, and electrical properties of the NBT ceramics is carried out using anatase and rutile TiO2. NBT ceramics with anatase TiO2 (denoted by NBTA) displayed superior dielectric and ferro/piezoelectric properties along with the additional functionality in terms of photocatalysis. Systematic studies of functional properties such as piezoelectric, ferroelectric, and dielectric stressed the far-reaching influence of effects on grain size. The mechanisms and functional properties of grain quantitative effects are also discussed. Grain boundaries volume fraction increment has decreased the dielectric peak but increased the diffusiveness in the case of the NBT with rutile TiO2 precursor (denoted as NBTR). Similarly, elastic stiffness increment restricts the movement of the domain wall and led to a decrement in remnant polarization along with an increase in the values of the corresponding piezoelectric coefficient in fine-grain NBTR samples.

Sustainable Use of Biomass Boiler Ash as a Reinforcement Filler for Polyamide 6 Composite

The use of biomass combustion ash as a reinforcing filler has taken the attention in recent years to reduce the overall production cost and increase the mechanical properties of plastics. This study evaluates the effect of biomass boilers ash (BBA) as a reinforcing filler on polyamide 6 composites (PA6). The chemical composition and thermal stability of BBA were analyzed by X-ray fluorescence (XRF), Thermogravimetric analysis (TGA), and Differential thermal analysis (DTA) thermographs. Test samples were prepared by varying the ash content (2.5%, 5%, 7.5%, and 10%), and also samples were prepared without adding ash as a control. Moreover, surface modification was carried out by using N-2 (Aminoethyl) 3-aminopropyl triethoxy diamino-silane as a possible coupling agent for BBA and it was tested by varying the coupling agent concentration (0.5%, 1%, and 2%) by dry process and the samples were prepared by extrusion and injection molding processes. Comparative analysis of the degree of crystallinity, mechanical properties including tensile, flexural, and thermal properties were tested. The highest degree of crystallinity was obtained with 7.5% BBA-filled composites. The addition of 2% surface-modified BBA (SBBA) filled composites (PA6 / 10% Ash 2% CA) showed an increase of tensile strength and elongation at break than the 10% unmodified BBA (UBBA) (PA6/ 10% Ash) filled composites. Stress at peak and bending modulus values in the flexural test data were increased up to 10%. But it was significantly reduced with the increasing of modifying agent concentration due to the increment of stiffness of the composite.

Experimental in-vitro investigation on Epi-Off-Crosslinking on porcine corneas.

AimTo evaluate quantitatively the effects of the Epi-Off-CXL irradiance dose on the stromal stiffening of pig corneas.SettingLaboratory of Biological structures (LaBS), Politecnico di Milano, Milano, Italy.MethodsInflation tests have been carried on 90 excised and de-epithelized pig corneas, monitoring the change of configuration of the corneal dome at specific pressures. Test have been carried out twice on each cornea, once before and once after Epi-Off-CXL performed at a constant irradiance of 9 mW/cm2 and variable UV-A exposure times. Corneas were grouped according to the exposure time (2.5, 5, 10, 15 and 20 min), proportional to the irradiation dose (1.35, 2.7, 5.4, 8.1, and 10.8 J/cm2). A theoretical model based on linearized shell theory has been used to estimate the increment of the corneal stiffness.ResultsThe linearized shell theory allowed to establish a quantitative relation between the increment of the stiffness parameters and the irradiation dose. Relative to the pre-treatment values, in all experiments the post-treatment corneal stiffness revealed a pronounced increase. In general, the stiffness gain increased with the exposure time. No significant differences in stiffening was observed between tests conducted at 2.5, 5, and 10 min exposure.ConclusionsQualitatively, the effectiveness of accelerated CXL treatments observed in pig corneas complies very well with in-vivo clinical results in humans, suggesting that experimental data in pigs can be very useful for the design of the procedure in humans. A larger irradiation dose provides a larger increment of the corneal stiffness. Due to the biological variability of the tissues, however, it is difficult to distinguish quantitatively the level of the reinforcement induced by accelerated protocols (low doses with < = 10 min exposure), less prone to induce damage in the corneal tissue. Therefore, the definition of personalized treatments must be related to the actual biomechanics of the cornea.

A new effective nonlinear strategy for lateral stability increment of an articulated vehicle rigid cargo

In this paper, the effects of the most important parameters on directional dynamics of a tractor-semitrailer vehicle are examined. Initially, a three DOF dynamic model of a tractor-semitrailer vehicle is proposed. Then, the developed model is validated by means of TruckSim software during a standard maneuver. In order to analyze the system stability, the Lyapunov method has been used and the stability conditions have been extracted based on Routh criterion. The most important parameters are selected based on the articulation angle gain. Among the studied parameters, the semitrailer mass, the distance of the tractor unit center of mass and its front axle, and the tires cornering stiffness exhibited more effective behavior on the vehicle’s stability. The simulation results show that as the tractor center of mass moves toward its rear axle, the probability of the jackknifing increases. Moreover, an increment in the semitrailer mass leads to a turn of the semitrailer with respect to the tractor. Also, the understeer specification of the vehicle strengthens due to the tire cornering stiffness increment. Moreover, in order to increase the maneuverability of the articulated vehicle a new active steering controller is proposed using two different control methods. The controller is developed using the simplified dynamic model and the basis of feedback linearization method using dynamic sliding mode control method. In this system, the yaw rate and the lateral velocity of the tractor unit as well as articulation angle are studied as state variables which are targeted to track their desired references. Then, the vehicle dynamic performance is investigated during standard maneuvers. A more investigation shows that the track of the desired values of the vehicle state variables leads to eliminate off-tracking path.

New Metallic Damper with Multiphase Behavior for Seismic Protection of Structures

This paper proposes a new metallic damper based on the plastic deformation of mild steel. It is intended to function as an energy dissipation device in structures subjected to severe or extreme earthquakes. The damper possesses a gap mechanism that prevents high-cycle fatigue damage under wind loads. Furthermore, subjected to large deformations, the damper presents a reserve of strength and energy dissipation capacity that can be mobilized in the event of extreme ground motions. An extensive experimental investigation was conducted, including static cyclic tests of the damper isolated from the structure, and dynamic shake-table tests of the dampers installed in a reinforced concrete structure. Four phases are distinguished in the response. Based on the results of the tests, a hysteretic model for predicting the force-displacement curve of the damper under arbitrary cyclic loadings is presented. The model accurately captures the increment of stiffness and strength under very large deformations. The ultimate energy dissipation capacity of the damper is found to differ depending on the phase in which it fails, and new equations are proposed for its prediction. It is concluded that the damper has a stable hysteretic response, and that the cyclic behavior, the ultimate energy dissipation capacity and failure are highly predictable with a relatively simple numerical model.

Magnetic Nanocomposite Hydrogel with Tunable Stiffness for Probing Cellular Responses to Matrix Stiffening

As cells have the capacity to respond to their mechanical environment, cellular morphology and function can be regulated by the stiffness of extracellular matrix. Moreover, biological processes are accompanied by dynamic changes in matrix stiffness. Herein, we developed a novel stiffening cell culture platform based on magnetic nanocomposite hydrogels with tunable stiffness under the application of magnetic field. This platform provided a wide tunable range of stiffness (~0.3-20 kPa), which covered most of human tissue elasticity (such as brain, fat, and muscle), and a maximum increase of stiffness and rate of stiffness increment of over 17 kPa and 1500%, respectively, without adversely affecting cell viability. Overall, the increased magnetic interactions between magnetic nanoparticles reduced the pore size of hydrogels and enhanced the hydrogel stiffness, thereby facilitating the adhesion and spreading of stem cells, which was attributed to the F-actin assembly and vinculin recruitment. Such stiffening platform not only provided valuable insights into the role of tunable stiffness as a morphological regulator of stem cells, but also allowed for better simulations of biomechanical environments in vivo to investigate dynamic biological processes.

Numerical investigation on epi-off crosslinking effects on porcine corneas

Experimental inflation tests, conducted on 90 pig corneas before and after corneal collagen crosslinking (CXL) treatment, are simulated with the finite element method. The experimental sample consists of five groups of corneas treated with different UV-A irradiation times (2.5, 5, 10, 15, and 20 min) at constant irradiance 9 mW/cm2. The linear elastic shell theory is used to estimate the equivalent material stiffness of the corneas, revealing that it increases with the exposure time in CXL corneas. In the view of numerical simulations, a simple mechanical model assuming piecewise constant elastic modulus across the corneal thickness is introduced, to estimate the effective increment of the material stiffness in the anterior stroma and the effective depth of the stiffness increment. The two effective quantities are used in the finite element models to simulate the post-CXL tests. Numerical models are able to describe the mechanical effects of CXL in the cornea. The increment of equivalent material stiffness has to be ascribed to a localized increment of the material stiffness in the anterior layers of the cornea, while the posterior layers preserve the original material stiffness. According to the simplified model, the increment of the material stiffness of the anterior cornea increases with the irradiation dose, while the effective reinforcement depth decreases with the irradiation dose. This trend, predicted by a simple mechanical model by imposing equilibrium and compatibility, has been verified by the numerical calculations that captured the global mechanical response of the corneas in untreated and post-CXL conditions.

Comparative deflection analysis of conical compression spring with standard constant rate helical spring

Springs, indisputably find vast applications in different types of mechanical systems. Springs are utilized everywhere, right from simple playing toys to automobiles and dies. Stiffness is one of the most prominent factors for a spring. While the constant rate helical springs exhibit a linear behaviour, the conical springs display non-linear characteristics. The reason considered behind an increment in stiffness with an increase in deflection in case of conical springs is that the resistance offered by the small-diameter portion is more and hence, it deflects later compared to the larger diameter portion. In this paper, conical springs are studied experimentally under variable test conditions and an effort is made in the direction of further inducing the variable stiffness to a higher extent in the conical spring as compared to presently used constant rate springs for various special-purpose applications.

Morphological and biomechanical adaptations of skeletal muscle in the recovery phase after immobilization in a rat

BackgroundRange of motion restriction following immobilization is spontaneously recovered at least in part by remobilization. However, the mechanisms underlying how muscles change with range of motion recovery are poorly understood. This study aimed to reveal morphological and biomechanical changes in the knee flexor semitendinosus muscle that contribute to knee joint contracture following the relief of immobilization. MethodsTo induce flexion contracture, we immobilized rat right knees by an external fixator at a flexed position for three weeks. After removal of the fixator, the joints were allowed to move freely (remobilization) for up to 14 days. We obtained muscle length and passive stiffness of the isolated semitendinosus muscles after measuring passive knee extension range of motion. FindingsThree weeks of immobilization induced range of motion reduction, as well as changes in morphological and biomechanical properties of the semitendinosus muscle, such as reduced muscle length and increment of passive stiffness leading to myogenic contracture. Joint immobilization-induced reduction of range of motion, representing flexion contracture, was partially reduced by 14 days of remobilization. Concomitantly, both muscle length and muscle stiffness returned to levels not significantly different from those in the contralateral side during this period. InterpretationThese results suggest that improvement of myogenic contracture during the early phase of remobilization occurs via both morphological and biomechanical adaptations.

The Mechanical Properties, Secondary Structure, and Osteogenic Activity of Photopolymerized Fibroin.

Previously, we have described the preparation of a novel fibroin methacrylamide (FbMA), a polymer network with improved functionality, capable of photocrosslinking into Fb hydrogels with elevated stiffness. However, it was unclear how this new functionality affects the structure of the material and its beta-sheet-associated crystallinity. Here, we show that the proposed method of Fb methacrylation does not disturb the protein’s ability to self-aggregate into the stable beta-sheet-based crystalline domains. Fourier transform infrared spectroscopy (FTIR) shows that, although the precursor ethanol-untreated Fb films exhibited a slightly higher degree of beta-sheet content than the FbMA films (46.9% for Fb-F-aq and 41.5% for FbMA-F-aq), both materials could equally achieve the highest possible beta-sheet content after ethanol treatment (49.8% for Fb-F-et and 49.0% for FbMA-F-et). The elasticity modulus for the FbMA-F-et films was twofold higher than that of the Fb-F-et as measured by the uniaxial tension (130 ± 1 MPa vs. 64 ± 6 MPa), and 1.4 times higher (51 ± 11 MPa vs. 36 ± 4 MPa) as measured by atomic force microscopy. The culturing of human MG63 osteoblast-like cells on Fb-F-et, FbMA-F-et-w/oUV, and FbMA-F-et substrates revealed that the photocrosslinking-induced increment of stiffness increases the area covered by the cells, rearrangement of actin cytoskeleton, and vinculin distribution in focal contacts, altogether enhancing the osteoinductive activity of the substrate.

Study on the evolution of dynamic performance of high-speed EMU after long-term service

In order to find the influence of wheel and rail wear about dynamic performance of the high-speed railway vehicle in the actual operation process, a high dimensional strong nonlinear dynamic model of the high-speed vehicle is established, and measured wheel profile is used to characterize contact geometry between wheel and rail, and relationship between stiffness of steering rubber joint and dynamic performance of railway vehicle is studied in different wheel/rail wear state. Results show, With the increment of wheel and rail wear and equivalent conicity, that stability of hunting motion of vehicle decreases, stability and safety of the vehicle all deteriorate. Moreover, with the increment of longitudinal steering joint stiffness, critical speed, lateral stability and safety of vehicles increases gradually. When it goes above 17.5MN/m, with the increments of critical speed, lateral stability and safety tend to be stable. With the increment of lateral steering joint stiffness, critical speed of vehicle tends to increase first and then decrease, and finally tends to be stable around 5MN/m, which reaches the maximum when the stiffness is 2.5MN/m. Lateral stiffness of steering joint has little influence on lateral stability of the vehicle; At low equivalent conicity, vehicle running safety decreases slightly with the increment of lateral stiffness of steering joint, while equivalent conicity increases, the vehicle running safety deteriorates sharply with the increase of lateral stiffness of steering joint. In conclusion, in order to adapt to different equivalent conicity, the optional range of longitudinal stiffness of steering joint is suggested to concentrated in 5∼17.5MN/m, while its lateral stiffness is suggested to be within 2∼5MN/m.

Backstay Effect of Diaphragm in Tall Building

Seismic analysis of structural systems with floor diaphragms has been a requisite in the recent past. The duty of a structural engineer is to be prudent about the behavior of every structural system adopted. Amongst the structural systems that are adopted world over, diaphragm with rigid and semi-rigid floor plate are adopted widely in the analysis. This research focuses on the backstay effect i.e. podium structural interaction with the tower area and consideration of retaining wall as increment of lateral stiffness as specified in latest tall building code IS6700:2016 for low and high rise structures. In the current study models were prepared with low to high rise storeys with rigid and flexible diaphragms considering backstay diaphragm placing tower at center and corner. The models were subjected to seismic forces; response spectrum along with the combination of the gravity loads. The structural responses like natural periods, base shear, displacement and inter storey drift were also studied.

Reinforcement of maritime pine cross-laminated timber panels by means of natural flax fibers

The present paper shows the first results of an ongoing research aimed at studying the potentiality of the combination of laminated timber and natural fibers to obtain high-performance structural elements. The experimentation conducted has involved a set of Cross Laminated Timber (CLT) panels made of maritime pine grown in Sardinia (Italy) and externally reinforced with natural flax fibers fabrics. A bending test program has been carried out on two CLT layouts, three-layers and five-layers panels, for a total of 34 specimens. Three-layers panels have been tested with single and double strip of flax fibers aiming to evaluate any difference in the rupture mechanism, capacity and stiffness. The proposed technique allows a straightforward application on the intrados of the panel, aimed at increasing its capacity and stiffness. Results show that in case of three-layers panels a significant increment of load-carrying capacity and stiffness has been achieved, whilst for five-layers panels the effectiveness of the reinforcement is negligible. Variations in the failure mechanisms of reinforced panels have been discussed.

The Effect of Irregularity of Lateral Stiffness in Estimating the Separation Gap of Adjacent Frames

Structural pounding can lead to local or total damage to the stories at the collision level or to the overall collapse of the building. On the other hand, lateral stiffness irregularity is common in the form of soft or very soft stories, which is due to the alternation in the type of function of the first story of the building. This paper estimates the demand for the normalized separation gap (NSG) at adjacent buildings highest collision level that were a combination of regular and irregular frames. For this purpose, the steel moment resisting frames (MRF), compounds with a total of 700 adjacent states and their NSG, is calculated by the dynamic time history analysis. In addition, irregularity increment in lateral stiffness for the first story could lead to an increase in the NSG of 84% of the adjacent combinations. In this study, a new relationship is proposed to estimate the demand for the NSG with the consideration of the effects of irregularity of lateral stiffness in the lowest story.

The Thermal Response of Multi-Storeies Concrete Frame Building in the Arabic Area

In this paper, there will be an analysis study to figure out the impact of the environment thermal loads, shrinkage and creep at multi-storeies reinforced concrete frame buildings in the Arabic area. Etabs models will be prepared based on NTDP and TDP of ordinary concrete, considering two columns heights as 3m and 6m, and two supports conditions as fixed and hinged to define the major aspects affect the thermal response of multi-storey concrete frame buildings concentrating at the thermal deformations and the columns reactions, then it will be compared with the thermal response of existing concrete building considering both methodologies of TDP as per CEBFIP99 and NTDP as per ACI Committee to define the optimum methodology to be recommended and followed The generated Etabs models confirmed that the time dependent properties method is the optimum with a clear conversion between time dependent properties model and the existing parking thermal deformations. increasing the thermal reaction forces at column supports reduces the correlated thermal displacements due to stiffness increment of the entire building, The first-level displacements of multi-storey buildings are slightly smaller than those of upper levels and single-storey buildings, but the displacements of the second level are slightly larger than those of the other levels. Meanwhile, the displacements of levels above the second storey are close to the displacements of single-storey models. Overall, there are small differences between multi- and single-storey models,. finally, the importance of analyzing thermal loads fluctuation at columns reactions for multi storeies buildings whereas the reactions of multi storeies cannot be predicted from single storey analysis.

A direct assessment for the stiffness development of artificially cemented clay

This study investigates the stiffness development by bender element tests on specimens of artificially cemented clay, considering the effects of cement content, total water content and curing period. Experimental results indicate that the small-strain shear modulus of cemented clay can be well determined by cement content and total water content. A high cement content or a low total water content results in a stiffness increment of cemented clay. The cementation effect of these two factors is taken into account in this study. However, stiffness of cemented clay increases with curing period; this effect can be well characterised by a hyperbolic function. The function is able to capture both short-term and long-term curing effects. Finally, the effects of mix ratio and curing time are combined, and a predictive model for the stiffness development of cemented clay is devised. The model is validated by experimental results on specimens of cemented clay from various sources.

Behavior and strength of headed stud shear connectors in ultra-high performance concrete of composite bridges

This study presents an experimental and numerical investigation on the static behavior of headed stud shear connectors in ultra-high performance concrete (UHPC) of composite bridges. Four push-out specimens were tested. It was found that no cracking, crushing or splitting was observed on the concrete slab, indicating that UHPC slab exhibited good performance and could resist the high force transferred from the headed studs. The numerical and experimental results indicated that the shear capacity is supposed to be composed of two parts stud shank shear contribution and concrete wedge block shear contribution. The stiffness increment of a stud in UHPC was at least 60% higher than that in normal strength concrete. Even if the stud height was reduced from 6d to 2d, there was no reduction in the shear strength of a stud. Short stud shear connectors with an aspect ratio as small as 2 could develop full strength in UHPC slabs. An empirical load-slip equation taking into account stud diameter was proposed to predict the load-slip response of a stud. The reliability and accuracy of the proposed load-slip equation was verified by the experimental and numerical load-slip curves.

Integrated ternary bionanocomposites with superior mechanical performance via the synergistic role of graphene and plasma treated carbon nanotubes

Herein, we prepared an integrated ternary bionanocomposite based on polylactic acid (PLA) as a host polymer and two different forms of carbon fillers, i.e. graphene nanoplatelets (GNPs) and carbon nanotubes (CNTs), used simultaneously at extremely low concentrations, relying on the synergistic effect of CNT and graphene nanoreinforcement and a novel, multi-step procedure to achieve a high level dispersion. The results indicated that this multi-step approach allows stiffness increments up to +66%, with simultaneous enhancement of tensile strength (up to +44%), and elongation at break (up to +36%) with respect to neat PLA, by adding an extremely low content (0.5 wt%) of a hybrid combination of CNTs and GNPs. The development of a multistep strategy to achieve molecular level dispersion of multifunctional nanoparticles integrated in a fully renewable polymer matrix allows the premise of industrial-scale production of advanced bionanocomposites with outstanding properties at extremely low loadings.