Polyurethane Cylinders Research Articles

Experimental investigation and seismic analysis of a novel self-centering piston-based bracing archetype with polyurethane cores

This paper introduces a novel self-centering Piston-based Bracing with Polyurethane Cores (PBPC) as a passive seismic control device. Frames fitted with such bracing elements will be able to mitigate the loss of life, post-earthquake repair costs, and downtime recovery after a major seismic event. The proposed earthquake-resistant archetype integrates a steel shaft, steel tubes, and hollow and solid polyurethane (PU) cylindrical cores. The PU cylinders are activated using a bracing shaft and dissipate seismic energy with a self-centering response. A set of unidirectional cyclic tests were conducted on a scaled PBPC specimen to quantify the effects of pre-compression force level, loading rate, and past loading history. The pre-compressed force curtailed the undesirable viscoelastic deformation and the energy dissipation capacity of PU cores. The non– and pre-compressed PBPC elements exhibited large deformability and adequate energy dissipation; nonetheless, they recovered their initial conditions with stable flag-shaped hysteresis loops following successive compression cycles. Additionally, a new material model was developed in OpenSees software for PBPC and a comparative seismic analysis was conducted. The simulation outcomes supported by experimental data proved the efficiency of the frame fitted with PBPCs in mitigating damage compared with a buckling-restrained braced frame.

Can Synbone® cylinders and deer femurs reproduce ballistic fracture patterns observed in human long bones?

Whereas gunshot injuries in human craniums have been well studied, reliable data on fracture patterns in ballistic long bone trauma remains scarce. Further information useful for forensic trauma interpretation and reconstruction may be retrieved from experimentally produced gunshot fractures. In order to avoid the use of human specimens for experimental research, it is of great interest to determine whether alternative models can reproduce the ballistic fracture patterns of human long bones. To address this question, we shot seven healthy adult human femurs and humeri each, ten samples each of two different polyurethane cylinders from Synbone® and four femurs from female red deer. The specimens were embedded in ballistic gelatin and perpendicularly shot from a distance of 2 m, using a 9-mm full metal jacket projectile at an impact velocity of 360 m/s. The macroscopical appearance of the detailed fracture pattern considering entry, exit and general cortical traits as well as the bullet’s energy lost upon impact were compared between the models. Despite some general similarities, neither of the two alternative models entirely reproduced the fracture patterns of human long bones. Comparing the two alternative models, the surrogate model revealed more significant differences to the human fracture than the animal model. This leads to the conclusion that the polyurethane material provides a different failure mechanism than real bone, underpinning the challenge in deploying an accurate analog.

Proizvodnja i ispitivanje elektormagnetnih generatora milimetarske skale za udarne kretnje visokih amplituda

Environment vibrations are an important source of energy, often occurring at very low frequencies, but with large amplitude. The possibility to use the large amplitude of the motions is important to enhance the energy harvester's output power. In this paper, an electromagnetic energy harvester is designed and fabricated to produce electricity from low- frequency high amplitude impact motions using an elastic polyurethane cylinder. This millimeter-scale electromagnetic generator (MS-EMG) includes a movable magnet attached to a free sliding mass, a fixed coil, and a polyurethane holding chamber. Polyurethane is a very stable elastic polymer that provides continuous large-amplitude movement for the magnet and plays an effective role in impact capability. Therefore, the effect of impact excitation and the polyurethane foam was investigated simultaneously. The performance of the device was studied, experimentally, for the environment vibrations in the range of 1 to 10 Hz. The impact motions were applied using a simulator that was fabricated for this work. The fabricated MS-EMG with a volume of 1.07 cm3 and a mass of 8.74 g show the capability of producing a voltage of 44.41 mV and power of 10.48 µW over a 100 Oresistive load, using a 6 Hz frequency impact motion. Finally, an analytical model is used to simulate the device performance which showed a good agreement with the experimental results.

Influence of Lateral Constraints on Wave Propagation in Finite Granular Crystals

Abstract In the presented work, wave dynamics of 2D finite granular crystals of polyurethane cylinders under low-velocity impact loading was investigated to gain better understanding of the influence of lateral constraints. The deformation of the individual grains in the granular crystals during the impact loading was recorded by a high-speed camera and digital image correlation (DIC) was used to calculate high fidelity kinematic and strain fields in each grain. These grain-scale kinematic and strain fields were utilized for the computation of the intergranular forces at each contact using a granular element method (GEM) based mathematical framework. Since the polyurethane were viscoelastic in nature, the viscoelasticity constitutive law was implemented in the GEM framework and it was shown that linear elasticity using the strain rate-dependent coefficient of elasticity is sufficient to use instead of a viscoelastic framework. These particle-scale kinematic and strain field measurements in conjunction with the interparticle forces also provided some interesting insight into the directional dependence of the wave scattering and attenuation in finite granular crystals. The directional nature of the wave propagation resulted in strong wave reflection from the walls. It was also noteworthy that the two reflected waves from the two opposite sidewalls result in destructive interference. These lateral constraints at different depths leads to significant differences in wave attenuation characteristics and the finite granular crystals can be divided into two regions: upper region, with exponential wave decay rate, and lower region, with higher decay rate.

Torque Maintenance Capacity, Vertical Misfit, Load to Failure, and Stress Concentration of Zirconia Restorations Cemented or Notched to Titanium Bases

Different titanium bases for implant-supported prostheses can present different mechanical behavior. The goal of this study was to evaluate the torque before and after fatigue, the load to failure, and stress concentration of zirconia restorations cemented or notched to a titanium base. Forty implants were included in polyurethane cylinders and divided into two groups: zirconia restoration cemented on a titanium base and zirconia restoration notched on a titanium base. The specimens had their torque loosening and vertical misfit evaluated before and after cyclic fatigue (200 N/2 Hz/2 × 106 cycles/37°C). Load to failure was evaluated in a universal testing machine (1 mm/min, 1,000 kgf). Failures were evaluated by scanning electron microscopy. Three-dimensional models were created, and the stress concentration was calculated using the finite element method. Data from the in vitro tests were submitted to two-way analysis of variance and Tukey test (α = .5). The cemented restorations presented less torque loosening (19.79 to 15.95 Ncm), lower vertical misfit (3.7 to 10.5 μm), lower stress concentration in the restoration (88.2 to 99.8 MPa), and higher fracture load (451.3 to 390.8 N) than notched restorations. The presence of a cement layer between the restoration and titanium base reduced the susceptibility to abutment screw loosening, improved the resistance to compressive load, and reduced the stress concentration in the restoration.

Fiber optic birefringence enhanced accelerometer based on polarized modal interferometer

An inline fiber optic birefringence enhanced accelerometer (FOBEA) which applies one polarizer and a ten-meter high birefringence fiber wrapped on a transducer cylinder is proposed. Birefringence of polarized modes in panda polarization maintaining fiber (PMF) is enhanced by fiber coating and cylinders of different parameters. Accelerometers with copper cylinder (FOBEA-1) and polyurethane cylinder (FOBEA-2) are fabricated, the tested average sensitivities are 1.06rad/g (20-3800 Hz) and 16.97 rad/g (20-2000 Hz). The experimental results show the birefringence gain of FOBEA-1 is in good consistent with theoretical calculation of 1.07 and an additional birefringence gain of FOBEA-2 is 5.52 because the polyurethane cylinder works as fiber coating with the thickness of 1.21 mm. Temperature crosstalk is also investigated.

Capacity to Maintain Placement Torque at Removal, Single Load-to-Failure, and Stress Concentration of Straight and Angled Abutments.

Because the main complication of implant-supported prostheses is torque loosening and/or fixation screw fracture, the goal of this study was to evaluate the torque before and after fatigue (screw placement and removal, respectively), single load-to-failure (compression test), and stress concentration of straight and angled abutments. Eighty implants were included in polyurethane cylinders. Half of the implants received straight abutments (group S, n = 40) and the other half received angled abutments (group A, n = 40). The abutments for cemented prostheses were installed with a torque of 20 Ncm. Eighty titanium structures were machined and cemented on the abutments with zinc-phosphate cement. After storage for 24 hours, half of the specimens had their torque loosening evaluated and were then immediately submitted to a compressive test in a universal testing machine (1 mm/minute, 1,000 kgf), while the other half were subjected to cyclic fatigue (200 N at 2 Hz for 2 × 106 cycles at 37°C) as an aging protocol (n = 20 from each group). The aged samples then had their torque loosening measured and were also submitted to the compression test. Representative samples were evaluated by scanning electron microscopy. Two bidimensional models similar to the in vitro specimens were created and analyzed using the finite element method to evaluate the stress concentration. Data from the in vitro tests were submitted to two-way analysis of variance and Tukey test, both with significance at P = .5. The results show that angled abutments are less capable of maintaining the installation torque and are less resistant during the single load-to-failure test. The von Mises stress concentration was higher for group A in the cervical region. The straight abutments have better prognosis than angled abutments and less susceptibility to mechanical failures.

Influence of Restoration Height and Masticatory Load Orientation on Ceramic Endocrowns

Endocrown restorations are an alternative to restore end-odontically treated teeth. Due to the fact that in the literature it is recommended a remnant of 1.5 mm, different heights of endocrown were elaborated and analyzed, obtaining possible faults and their location. This study aimed to evaluate the mechanism of stress distribution in the tooth/restoration set, varying two factors: "restoration height"-three levels, and load application-two levels (oblique or axial), totaling six groups. For finite element analysis (FEA), a maxillary premolar was modeled with an endodontic treatment. Then, this template was triplicated and each copy received an endocrown restoration of different heights: G6 (4.5 mm), G7 (5.5 mm), and G8 (6.5 mm). The models were exported in STEP format to analysis software (ANSYS 17.2, ANSYS Inc.). During preprocessing, the solids were considered isotropic, linearly elastic, and homogeneous. Initially, a load (300 N) was axially applied in the central fossa region. For a second evaluation, an oblique load (300 N) was applied on the grinding slope of functional cusp. System fixation occurred at the base of poly-urethane cylinder. Results were evaluated through maximum principal stress (MPS). For axial load, lower stress values were generated in all groups. For oblique load, G8 showed a higher stress concentration in the cement layer and root dentin. When an endocrown restoration is performed, there is a tendency of failure in the cement line and in the root directly proportional to its size. However, regardless of the size of the element to be reconstituted, the axial direction of the masticatory loads tends to decrease stress concentration. When performing an endocrown restoration, care must be taken with its high regardless the tooth remnant high, altering even the anatomical angulations of the occlusal face, when necessary, to avoid stress concentration in thick areas.

Determination of polychlorinated biphenyl compounds in indoor air samples

A simple procedure for the determination of six non-coplanar polychlorinated biphenyls (PCBs) in medium volumes of indoor air is described. Samples are forced at 6 m 3/h through a device consisting of a quartz filter connected to the end of a conventional solid-phase extraction cartridge containing 60 mg of functionalized styrene–divinylbenzene. PCBs retained on the sorbent are directly eluted with 2 ml of hexane. Those associated to airborne particulate matter are microwave extracted in 10 min using 15 ml hexane–acetone (1:1). The proposed procedure is favorably compared to the use of polyurethane cylinders for the concentration of PCBs in terms of solvent consumption and rapidity of the desorption step. Furthermore, the functionalized sorbent showed higher breakthrough volumes than Amberlite XAD-2 for PCBs in gas phase. Quantification limits between 2 and 40 pg/m 3 were obtained for six PCBs (from di- to heptachlorobiphenyls) using GC–electron-capture detection.

Circulatory support with a direct cardiac compression device: A less invasive approach with the AbioBooster device

TX R efractory cardiogenic shock is an important cause of death in patients after acute myocardial infarction (AMI), therapeutic percutaneous cardiac catheterization, and cardiac surgery. Of the 1.1 million AMI cases annually, 7% to 10% have cardiogenic shock, which has a 50% to 60% in-hospital mortality.1 The value of short-term circulatory support with currently available assist devices is drastically reduced by thromboembolic, hemorrhagic, and infectious devicerelated complications.2 The concept of direct cardiac compression (DCC), first introduced in 1965,3 is simple and elegant, with several advantages over intravascular ventricular assist devices (VAD) in current use. Use of non-blood contacting DCC systems would avoid cardiopulmonary bypass and bleeding complications and would be technically simpler to institute, allowing more widespread use. We evaluated a pneumatic DCC device, the AbioBooster, designed and fabricated by ABIOMED, Inc (Danvers, Mass). This device consists of inflatable polyurethane cylinders wrapped within a silicone-coated polytetrafluoroethylene fabric. Air pumped into and out of the wrap causes contraction and dilatation of its circumference (Figure 1). Twelve sheep studies were performed in nine short-term and three 4-week survival experiments. The effects of the wrap after induced cardiogenic shock (esmolol β-blockade with norepinephrine) and ventricular fibrillation were characterized. To create a reproducible model of heart failure, we used a continuous infusion of a short-acting β-blocker, esmolol. An esmolol drip was started at 10 mg/min and titrated to maintain a descending aortic blood flow at 1.0 L/min or less. We evaluated the impact of the device on underlying coronary artery bypass grafts (CABGs) by performing bypasses from the left internal thoracic artery to the left anterior descending artery (n = 1) or first diagonal artery (n = 2) and from the innominate artery to the first obtuse marginal artery (n = 3) using a reversed saphenous vein graft before device application.

Quantification of Resistance to Flow at the Esophagogastric Junction in Man

Changes in resistance to flow at the esophagogastric junction contribute to the regulation of esophageal emptying and gastroesophageal reflux. To quantify esophagogastric resistance in man we have adapted our pneumatic resistometer, previously validated in the dog. The system is based on the measurement of nitrogen flow through a 5‐cm‐long polyurethane cylinder placed within the gut lumen and maintained electronically at a constant pressure gradient. In vitro experiments showed that the amplitude, length, and diameter of the constricted segment each contribute to resistance as measured by our instrument. In vivo studies performed on eight healthy volunteers showed that the esophagogastric junction was the place of maximal resistance in the gastroesophageal region. Intragastric resistance was also comparatively high whereas esophageal body resistance was negligible. Esophagogastric junction resistance was similar for antegrade and retrograde flow. During swallowing, it decreased to 10% of resting values. In three patients with achalasia, it was markedly increased and did not vary significantly during swallowing. We conclude that pneumatic resistometry accurately quantitates segmental resistance to flow in the esophagogastric region. Under normal conditions esophagogastric junction resistance exceeds gastric resistance and, hence, provides a gradient against gastroesophageal reflux. However, this resistance gradient between the junction and the stomach is much narrower than previously thought on the basis of manometric measurements.

Production of thin tubes and tapered cups by the spinning of sintered powder preforms

As an attempt to facilitate the small-batch production of axisymmetric parts such as thin tubes and tapered cups, a powder metallurgy technique has been employed in combination with a shearspinning process. Electrolytic copper powder is used as the starting material of a tube or a sheet and the powder is compacted within a simple device using a polyurethane cylinder as the pressure medium. The green compact is sintered in vacuum and then the sintered preform is spun to decrease its porosity and to improve its dimensional accuracy. The product obtained is annealed to diminish the brittleness arising from work-hardening in the multi-pass spinning. Finally, as an additional process to remove feed marks generated on the surface, the product is polished with sandpaper or a wiper roller. The relative density achieved by this process is about 0.98 and the dimensional accuracy, ductility and surface finish are also adequate for practical use.

Clinical experience with mentor inflatable penile prosthesis in 206 patients

The Mentor inflatable penile prosthesis (IPP) has been implanted in 206 patients with organic (95.2 %) or psychologic (4.8 %) impotency. The patients have been followed up for an average of 18.1 (4–42) months. A satisfactory result has been achieved in 98 per cent of these patients. A life analysis of the series shows that 88 per cent of all devices implanted will survive forty-two months without mechanical failure. One hundred sixty-four of these patients had not had previous penile surgery while 42 had had one or more penile prostheses implanted previously. The projected forty-two-month survival for the Mentor prosthesis in these subgroups is 94 per cent and 74 per cent, respectively. The improved life expectancy of the Mentor IPP, compared with the Scott IPP, is due to the superior durability of Mentor's polyurethane cylinders and to the increased reliability of the Mentor snap-on connector system. In this respect, there have been only one cylinder failure and 3 connector failures in the Mentor series. The connector failures occurred early in the series before the development of connector pliers; there have been no connector failures in the last 202 consecutive implantations. Wear-induced tubing leaks, the most common cause of device failure, occurred in 2.9 per cent of all implantations. Tubing failures were more common in patients who have had previous surgery, occurring in 9 per cent of salvage procedures and 1.3 per cent of primary implantations. The reason for the difference in tubing survival in virgin and salvage procedures is unknown; possibly the subcutaneous scar tissue present in secondary surgical procedures increases the chance of tubing segments touching and abrading each other. Laboratory studies suggest that the nylon-reinforced tubing used in the manufacture of devices implanted since 1985 is more durable than is the standard silicone tubing used in the construction of devices implanted previously.

Fabrication of nonorthotropic axially stiffened polyurethane mandrels for use in fiber optic hydrophones

Ideally, extended hydrophones consisting of optical fibers wound on a compliant cylinder have high radial compliance to maximize sensitivity per unit length and high axial stiffness to minimize effects of longitudinal dynamics to assure uniform frequency response. Bendability is also desirable in certain applications. A set of nonorthotropic mandrels consisting of polyurethane cylinders with embedded axial steel wires have been fabricated. These include two levels of stiffening and polyurethanes of four degrees of hardness. Several aspects of the molding technique used, including process selection, mold design, air bubble requirements, and adhesion of the elements are described.