Use Of Viscoelastic Materials Research Articles

Clinical Factors, Treatment Selection, and Outcomes in Postcataract Fungal Endophthalmitis from Contaminated Viscoelastics

To investigate the factors associated with treatment outcomes of postcataract surgery fungal endophthalmitis outbreaks related to contaminated viscoelastics. Retrospective analysis of clinical data from multiple institutions. This study included 228 eyes of 210 patients who were diagnosed with postcataract surgery fungal endophthalmitis related to the use of viscoelastic material (Unial, Unimed Pharmaceutical Inc); they were followed up for 6 months after the diagnosis. Clinical features and causative species were identified and treatment outcomes were analyzed in patients who underwent 6 months of follow-up. Propensity score matching was conducted to elucidate the impact of vitrectomy timing and intraocular lens (IOL) removal on treatment outcomes. Clinical factors and selection of treatment modalities associated with treatment outcomes at 6 months. Baseline visual acuity (P < 0.01), age (P= 0.05), and the presence of corneal edema (P < 0.01) were closely associated with poor best-corrected visual acuity (BCVA) at 6 months. Patients who underwent immediate vitrectomy after diagnosis showed significantly better BCVA at 6 months (mean logarithm of minimum angle of resolution 0.26 ± 0.43 vs. 0.52 ± 0.52, P= 0.03) and greater degree of visual improvement (mean-0.17 ± 0.37 improvement vs. 0.10 ± 0.57 deterioration, P= 0.03) than those who underwent deferred vitrectomy. Patients who underwent IOL removal during vitrectomy required a lower number of intravitreal antifungal agent injections (mean 8.9 ± 9.1 vs. 16.7 ± 12.2, P < 0.01) and showed a lower incidence of repeated vitrectomy (20% vs. 82%, P<0.01) than in those without IOL removal. In postcataract fungal endophthalmitis, prompt vitrectomy at the time of diagnosis resulted in better treatment outcomes, and IOL removal reduced the treatment burden. Prompt and aggressive surgicalintervention should be considered for postcataract fungal endophthalmitis. Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Comparison of the Modified Jones Tube Technique and the DMEK EndoGlide Technique With and Without Viscoelastic Material for DMEK Tissue Preparation.

The aim of this study was to compare endothelial cell loss for DMEK (Descemet membrane endothelial keratoplasty) tissue preparation techniques using the modified Jones tube and the DMEK EndoGlide with and without viscoelastic material to protect the endothelium. This ex vivo study included 10 DMEK grafts prepared using each of the 3 abovementioned techniques. After tissue preparation, transport conditions were simulated for a minimum of 45 hours before deployment of the DMEK tissue and quantification of endothelial cell loss. Comparisons between preparation technique groups were made using the Wilcoxon rank-sum test. The Jones tube group had a mean endothelial cell loss of 11.0 ± 4.8% compared with the EndoGlide group with 12.9 ± 6.7% and the EndoGlide with viscoelastic group with 25.7 ± 15.0%. The differences between the EndoGlide with viscoelastic group and the other 2 were statistically significant both before (P < 0.01 and P = 0.01) and after (P = 0.01 and P = 0.02) adjusting for baseline characteristics. The difference between the EndoGlide and Jones tube groups was not significant (P = 0.73 and P = 0.53 after adjustment). Microscopy revealed endothelial cell loss in the area of viscoelastic use for the EndoGlide with viscoelastic group. Both the Jones tube and DMEK EndoGlide resulted in similar low rates of endothelial cell loss after tissue preparation, transport, and deployment. However, use of viscoelastic material to protect the endothelium using the DMEK technique actually resulted in increased cell loss in the area of its application resulting in overall higher rates of cell loss across the DMEK tissue.

Stochastic analysis of a hybrid energy harvester with viscoelastic material

The hybrid energy conversion mechanism can improve the performance of the energy harvester compared to the single energy conversion mechanism. Meanwhile, the use of viscoelastic materials can also improve the energy harvesting efficiency, but there is not much research on hybrid energy harvesting systems with viscoelastic material. Different from existing research, this manuscript investigates the probabilistic response and stochastic bifurcation of a hybrid piezoelectric and electromagnetic energy harvester(HPEEH) with viscoelastic term under random excitation. Firstly, the viscoelastic element is approximately equivalent to the linear combination of damping term and stiffness term through variable transformation. Secondly, the accuracy of the proposed method is verified by comparing the numerical solution with the analytical solution using the stochastic averaging technique to solve the equivalent system. Furthermore, the bifurcation conditions for amplitude steady-state probability density are given according to the singularity theory and the definition of the extreme point. It is found that changes in viscoelastic parameters, damping coefficients and electromagnetic coupling coefficients can induce stochastic P-bifurcation. Finally, the effects of system parameters on mean square current, mean square voltage and mean output power are explored.

Hybrid control technique applied to an aero-servo-viscoelastic simplified wing model

Considering that flutter represents a potential catastrophic event in the context of aerospace structures, numerous studies have evaluated a number of strategies to avoid and/or control this kind of aeroelastic phenomenon. Currently, both active and passive control have been investigated to prevent instabilities induced by the interaction between aerodynamic and structural forces. It is also important to highlight the successful cases in which passive control techniques using viscoelastic materials have been useful to mitigate several types of vibration problems. However, there are still opportunities to explore the potential of control using viscoelastic material in the scope of aeroelasticity, especially when involving its combination with other control techniques. Therefore, this work presents a strategy involving a hybrid approach to aeroelastic control of a simplified unswept and untapered wing, using a combination of passive and active techniques. Passive control is achieved by the use of viscoelastic materials inserted as resilient elements in the aeroelastic model, while active control is performed by means of the deflections of a flap-like aerodynamic control surface, governed by a proportional-derivative control law. The results show that the application of the passive control alone causes an increase of up to 25.4% in critical flutter speed. In addition, the association of passive and active controls lead to higher control performance and the critical speed is increased by a further 6.8%, thus providing a broader safe flight speed range. Hence, the investigation indicates that the hybrid control approach exploring viscoelastic materials can be advantageous in practical applications.

Use of viscoelastic material and design parameter optimization for optimum reduction of vibration response of primary system

Studies on vibration responses of a beam (both ends fixed) with a cantilever as absorber have been carried out. The objective is to generate the theoretical model to optimally control the beam vibrations using viscoelastic material and find the optimum parameters for the same. Constrained and unconstrained damping treatments are considered in this model. Theoretical model using different theories have been reported. Experiments have been conducted to validate the theoretical model and the results have been compared with the theoretical result. The theoretical and experimental, results depict that the use of viscoelastic material for damping of absorber system gives optimum reduction of vibration responses of main system. It is also found that the working frequency range between two resonant frequencies in the case of constrained treated absorber system is wider than in the case of absorber without damping and unconstrained treated absorber system.

On the use of viscoelastic materials characterized by Bayesian inference in vibration control

On the use of viscoelastic materials characterized by Bayesian inference in vibration control

Dynamic Analysis of Composite Sandwich Beams with a Frequency-Dependent Viscoelastic Core under the Action of a Moving Load

A dynamic analysis of the behavior of sandwich beams with a viscoelastic core under the action of a moving load is performed considering their geometrical asymmetry. The use of viscoelastic materials integrated into structures in front of the moving load is considered as a new suggestion to enhance their stability. A high-order theory, taking into consideration longitudinal and rotational inertias was used to examine the viscoelastic damping properties composite sandwich beams with account of their geometrical asymmetry and the frequency-dependent behavior of their viscoelastic core.

Quality control of parts which were manufactured from polymeric composite materials with hybrid matrix with the application of method of infrared thermography

This article contains the description of different polymer composite materials (PCM) with different types of hybrid matrices. One of the components of PCM’s hybrid matrix is hardened as the other one stays in its viscoelastic condition. The following materials are chosen to serve as viscoelastic components of hybrid matrix: technical wax compound, anaerobic and organosilicone polymer materials. The use of viscoelastic materials allows the enhancement of PCM’s stress-strain properties. This article also contains: the destruction mechanism of polymer composite materials with different types of hybrid matrices; the quality control process of products made of polymer composite materials with different types of hybrid matrices; the localization method of hybrid matrix viscoelastic components by using infrared thermography during product molding process. The results of quality control are shown as thermograms.

The use of visco-elastic materials for the design of helmets and packaging

The design of packaging to protect delicate objects, such as a head and brain, against impact requires consideration of the duration of the impact compared to a characteristic time associated with the dynamic response of the object. Relatively short impacts cause damage as a result of an excessive change in velocity. Relatively long impacts cause damage as a result of an excessive acceleration. The design strategy of packaging must either mitigate the transmitted force (and increase the duration of the impact) through a compliant cushion, or dissipate energy. In this paper we show that both of these strategies can be implemented using visco-elastic materials. In particular, very efficient energy dissipation, with complete structural recovery, can be achieved by using a visco-elastic cushion with properties matched to the requirements of the design. Specifically, energy dissipation can be maximized by ensuring that the time-scale of the accumulation of stress within the system matches the optimal time-scale for dissipation within the cushion. A procedure is described by which an optimal design for the minimum thickness of packaging can be achieved by considering both strategies of velocity and acceleration control.

Целесообразность применения деки из вязкоупругого материала при шелушении зерна гречихи

Introduction. During buckwheat processing, up to 7.0% of the kernels turn into feed meal. This loss causes a significant decrease in profits during the production of buckwheat groats. Decorticating of buckwheat is complicated by the fact that the size uniformity of the grain mass does not exceed 40–50%. Since the grain size varies greatly, the mass is divided into fractions to optimize the&#x0D; decorticating process. Sorting of grain into size fractions with subsequent calibration increases the efficiency of decorticating. The procedure makes it possible to choose the appropriate decorticating mode while maintaining the integrity of the kernel. New methods of decorticating improve the utilization of grain and, consequently, profitability. The research objective was to assess the rationality of the use of visco-elastic material for decorticating buckwheat grain.&#x0D; Study objects and methods. The research featured buckwheat grain, which was divided into six fractions by size before decorticating. The grain was harvested in the foothill part of the Altai Territory in 2018.The effectiveness of the procedure was tested using a standard abrasive deck and a visco-elastic deck with Shore hardness = A-80-95 and elastic modulus = 2.8 MPa. &#x0D; Results and discussion. A simultaneous use of a visco-elastic deck and an abrasive deck on a Valdecede machine reduced the mass fraction of the destroyed kernels at the stage of decorticating. The production tests involved processing of 23,000 thousand tons of buckwheat grain. The resource of visco-elastic decks in different fractions ranged from 6 to 12 months. The tests proved that viscoelastic decks provided a 1.5% increase in the mass fraction of buckwheat groats due to a reduction in the resulting feed meal. A set of economic calculations showed an increase in the marginal profit by 800,000 rubles per month.&#x0D; Conclusion. The use of visco-elastic decks during decorticating of buckwheat grain of all fractions increased the profitability of buckwheat groats production by 1.8% and raised the yield by 1.5%.

Improved dynamic performance in flexure mechanisms by overconstraining using viscoelastic material

Flexure mechanisms are commonly designed to be exactly constrained to favor determinism, though at the expense of limitations on the maximum parasitic natural frequencies and support stiffness. This paper presents the use of viscoelastic material for providing additional support stiffness in a certain frequency range without the indeterminism commonly associated with overconstraining. This design principle of dynamically stiffened exact-constraint design is exemplified by a parallelogram flexure mechanism. Experiments demonstrate that a custom synthesized elastomer compound can compensate for unintended misalignments without significant internal stress buildup, while improving the dynamic performance in terms of a higher first parasitic natural frequency. An analytical investigation clarifies the relationship between misalignment, internal load, stiffness and natural frequency. Using the buckling modes of the system, the nonlinear geometric stiffness is modeled accurately up to the bifurcation. The measurements and analytical model are corroborated by a nonlinear flexible multibody analysis.

Experimental Study on a New Damper Using Combinations of Viscoelastic Material and Low-Yield-Point Steel Plates

To enhance the seismic resilience of coupled reinforced concrete shear walls, a new damper working in the replaceable coupling beam is proposed in present study. The new damper is a combination of metallic damper and viscoelastic (VE) damper. The metallic damper consists of an I-shaped steel beam with multiple low-yield-point steel plate webs paralleled to each other; the VE damper is composed of multiple layers of VE material bonded between multiple steel plates. Through the composite use of viscoelastic material and low-yield-point steel, the new damper is expected to work effectively against both the earthquake and the wind. To study the respective mechanical behavior of each component of the combined new damper, eight metallic dampers, two VE dampers, and one combined damper are tested under cyclic loading first. The variable parameters of the metallic damper are strength grade of web steel, web dimensions and end stiffener configuration. It is found that the effect of the strength grade of web steel is most significant. Compared with the metallic damper using the steel web with normal strength grade, the ductility, ultimate plastic shear rotation and cumulative plastic shear rotation of the damper using the low-yield-point steel web are much larger. The effect of web dimensions on the deformation capacity is slight. With the addition of end stiffener, plasticity concentrates thereby, which prevents the flange-to-end plate weld fracture. The VE damper exhibits extraordinary deformability. The storage modulus, shear loss modulus and loss factor of the VE material decrease with the increase of strain amplitude. The storage modulus and shear loss modulus of the VE material decrease slightly as the excitation frequency increases within the range between 0.1 to 1 Hz, and the effect of the excitation on the loss factor is not significant. At last, the combined damper, an assembly of one metallic damper component and two VE damper components, is tested, which exhibits stable hysteretic behavior and excellent deformability. The predicted yield shear strength and elastic stiffness agree well with test results.

Stochastic stability of viscoelastic systems under Gaussian and Poisson white noise excitations

As the use of viscoelastic materials becomes increasingly popular, stability of viscoelastic structures under random loads becomes increasingly important. This paper aims at studying the asymptotic stability of viscoelastic systems under Gaussian and Poisson white noise excitations with Lyapunov functions. The viscoelastic force is approximated as equivalent stiffness and damping terms. A stochastic differential equation is set up to represent randomly excited viscoelastic systems, from which a Lyapunov function is determined by intuition. The time derivative of this Lyapunov function is then obtained by stochastic averaging. Approximate conditions are derived for asymptotic Lyapunov stability with probability one of the viscoelastic system. Validity and utility of this approach are illustrated by a Duffing-type oscillator possessing viscoelastic forces, and the influence of different parameters on the stability region is delineated.

Vibration reduction using meta-structures composed of tuned dynamic absorbers employing mass impacts

The vibration damping capability of a meta-structure composed of tuned dynamic absorbers employing mass impacts was investigated. The tuned dynamic absorbers consisted of a spring and a mass. The mass induced impacts within the vibrating system. To reduce the structural vibration, metamaterials attached with the multiple tuned dynamic absorbers employing impacts were proposed. The wave propagation characteristics of the meta-structure were predicted and compared with those obtained by measurements. The reflected wave from the meta-structure was completely blocked at the resonance frequency. The impact between the beam and the tuned dynamic absorbers dissipates the vibration energy. To verify the damping of one tuned dynamic absorber employing impacts, the effective damping ratio was calculated for a vibrating system with a single degree of freedom. Due to vibration reduction during impacts between the system and the absorber, the structural damping ratio was increased significantly without the use of viscoelastic materials. The proposed structure provides an efficient methodology without the use of viscous vibration damping materials in the broadband frequency range, which is essential for applications to at high or low temperatures.

Development and analysis of a consciously designed Joint Interface Module for improvement of a machining system’s dynamic performance

Machining vibrations and dynamic instability of machine tools is an important consideration in machining systems. Common approaches for improving their dynamic performance target either the process, or intelligent, yet complex control systems with actuators. Given that machine tools’ dynamic characteristics are largely defined by the characteristics of the joints, this article proposes a novel concept, attempting to create a new paradigm for improving the dynamic behaviour of machine tools—introducing modular machine tools components (Joint Interface Modules—JIMs) with joints deliberately designed for increasing dynamic stiffness and enhancing damping with the use of viscoelastic materials. Through a systematic model-based design process, a prototype replicating a reference tool holder was constructed exploiting viscoelastic materials and the dynamic response of the machining system was improved as a result of its introduction; in machining experiments, the stability limit was increased from around 2 mm depth of cut to 4 mm depth of cut, without compromising the rigidity of the system or changing the process parameters. The article also includes the results of investigations regarding the introduction of such prototypes in a machine tool and discusses the shortcomings of the stability lobe diagrams as a method for evaluating the performance of machine tool components with viscoelastically treated joints.

A beam-to-column connection with visco-elastic and hysteretic dampers for seismic damage control

A new steel beam-to-column connection for seismic energy dissipation is presented in this paper. Dissipation of energy is provided for with the use of visco-elastic material that works in shear and of elasto-plastic steel bolts that act in bending. Through both analysis and cyclic tests, it is shown that the proposed connection produces stable hysteretic cycles superior to the conventional connections. This is while the structural members and connectors including beam, column, connection plates, welds and bolts do not experience any damage even at story drifts corresponding to large earthquakes. Installation and repair of the proposed detail are easy to implement as it consists of placing a visco-elastic damper as a lower pad on the seat angle of the connection and a series of bolts connecting the top flange to the seat angle. Effects of various parameters on the behavior of the proposed connection are studied comprehensively.

3B33 A viscoelastic adaptive tuned vibration absorber(The 12th International Conference on Motion and Vibration Control)

The tuned vibration absorber is a well-established vibration control device, which can be used to suppress a troublesome resonance or to attenuate the vibration of a structure at a particular forcing frequency. Two of the drawbacks of such a device, however, are that it can detune during operation because of changes in forcing frequency, or that there may be differences between the designed and in situ behavior. A variable stiffness element in the tuned vibration absorber can be used to maintain a tuned condition so that the natural frequency of the absorber can be adjusted with time. The mechanical properties of viscoelastic material, Young's modulus and loss factor in particular, change with temperature. Viscoelastic materials are then suitable candidates for the realization of adaptive tuned vibration absorbers, although their loss factor may be high. Viscoelastic materials have also the advantage to be cheap and common, and their manufacturing processes are well established. This paper presents an investigation on the use of viscoelastic materials as variable stiffiiess elements of tuned vibration absorbers. Both numerical and experimental investigations have been carried out. In particular, three different absorbers have been built with three different materials. The materials have been chosen so to show, at ambient temperature, glassy, transient and rubbery behavior respectively. The absorbers have been built in the shape of beams and heating pads have been attached to one side of the beam in order to control temperature. The best performing absorber showed a 27% change in the tuned frequency.

A concept to reduce vibrations in steel catenary risers by the use of viscoelastic materials

One of the most important issues in steel riser systems is the VIV phenomenon (Vortex Induced Vibration). VIV may induce high levels of structural vibrations and stresses what eventually lead to considerable fatigue damage and reduction in structural lifetime. The use of suppression devices is a feasible solution to tackle this problem. Nevertheless, their disadvantage is the increase in drag coefficient; moreover, it is very expensive. This work proposes and investigates a concept aimed at suppressing vibrations in steel catenary risers by the use of viscoelastic sandwich layers and it is based on three steps. The first one considers the calibration of a viscoelastic constitutive model based on complex shear modulus measurements in a controlled experimental environment. The second one is a model validation scheme applied on the calibrated model provided by the first step and it is based on experimental data obtained out of a 1.6m long tubular sandwich structure. The third step assesses the effectiveness of viscoelastic sandwich layers using a small scale model of a steel catenary riser installed in P18 platform which is in operation in Campos Basin, Brazil. The results are quite compelling due to the great increase of damping that was observed.

Hyaluronic Acid Viscoelastic Medium as an Aid for Microsurgical Venous Anastomoses

The thin-walled structure of veins leads them to stay collapsed during anastomoses, thereby the incidence of technical failures is more common than arterial anastomoses. In order to overcome this problem, we are introducing the use of viscoelastic material based on our experience on rats. Six rats were used in order to study the technical feasibility of the viscoelastic material during microsurgical vein anastomosis. End-to-end anastomoses were performed on rat jugular veins using 0.5-1 mL of the viscoelastic medium applied to the ends of the veins and surgical field under ×30 operating microscope magnification. Then 1.8% (n:3) and 3.0% (n:3) hyaluronic acid was used as a viscous medium in order to keep the vein lumens open during anastomosis. In conclusion, we have found that 3.0% hyaluronic acid viscoelastic medium facilitates microvenous anastomosis in rat. Studies involving human practice are needed for further evaluation of this technical refinement.

Induction of Posterior Capsule Opacification by Hyaluronic Acid in an Ex Vivo Model

Because hyaluronic acid (HA) is found in many surgical viscoelastic agents, this study aimed to determine (1) if HA receptors are present in the canine lens, (2) if the rate of lens epithelial cell (LEC) migration is altered following treatment with HA, and (3) if introduction of exogenous HA into the lens capsule promotes lenticular migration, thus contributing to posterior capsule opacification (PCO). Normal and cataractous canine LECs were evaluated for expression of the HA receptor CD44 and the receptor for HA mediated motility (RHAMM) using immunohistochemistry, immunoblotting, and real-time PCR. Canine LEC were treated with various concentrations of HA, and induction of migration was monitored over time. Commercially available surgical viscoelastics were utilized ex vivo, and rates of PCO formation were analyzed. Basal protein and mRNA expression of both CD44 and RHAMM was noted. Cataractous canine LEC demonstrated significantly (P < 0.01) higher expression of CD44 but not RHAMM. Treatment with higher concentrations of HA resulted in a significant (P < 0.01) increase in CD44 mRNA and increased LEC migration in vitro. Use of CD44-neutralizing antibodies confirmed the role of CD44 in HA-induced lenticular migration. Viscoelastic material containing higher concentrations of HA led to increased rates of ex vivo PCO. Exogenous HA can induce lenticular migration and CD44 expression. Use of surgical viscoelastics that contained HA resulted in increased rates of ex vivo PCO suggesting that judicious selection and use of viscoelastic material during cataract surgery is warranted.