Anodized titanium and stainless steel in contact with CFRP: An electrochemical approach considering galvanic corrosion

Degradation of Carbon Fiber-Reinforced Polymer Composites in Salt Water and Rapid Evaluation by Electrochemical Impedance Spectroscopy

The electrochemical impedance spectroscopy and weight gain tests were performed on carbon fiber/vinyl ester and carbon fiber/bismaleimide composites in 3.5% NaCl solution to study the electrochemical and water absorption behaviors. The microstructure morphology and the flexural property of the composites in the long-term exposure process were analyzed with the scanning electron microscope and four-point bending tests. The results revealed that after long-time immersion (>200 d), the water absorption of the two composites is less than 0.5%. This has little effect on the microstructural integrity, only with slight damage on the fiber/resin interfaces, but results in a significant decrease (about 84%) in the composite flexural property. The variation of the water absorption percentage shows good consistency with that of the resin capacitance (Q_c) and is negatively related to the variation of the resin resistance (R_po) and the low-frequency impedance (|Z|_0.01Hz) of the composites. A good linear relationship exists between the variations of phase angles in the middle-frequency range (0.1-10 Hz) and the |Z|_0.01Hz. The phase angle at 10 Hz (θ_10Hz) may be suggested as a suitable parameter to rapidly evaluate the performance of carbon fiber-reinforced polymer composites, just like for evaluating the protective performance of polymer-coated metals in the literature.

Effect of Fiber Wrapping on Bending Behavior of Reinforced Concrete Filled Pultruded GFRP Composite Hybrid Beams

The application of pultruded fiber reinforced polymer (FRP) composites in civil engineering is increasing as a high-performance structural element or reinforcing material for rehabilitation purposes. The advantageous aspects of the pultrusion production technique and the weaknesses arising from the 0° fiber orientation in the drawing direction should be considered. In this direction, it is thought that the structural performance of the profiles produced by the pultrusion technique can be increased with 90° windings by using different fiber types. This paper presents experimental studies on the effect of FRP composite wrapping on the flexure performance of reinforced concrete (RC) filled pultruded glass-FRP (GFRP) profile hybrid beams with damage analysis. The hybrid beams are wrapped fully and partially with Glass fiber reinforced polymer (GFRP) and carbon fiber reinforced polymer (CFRP) composites. Hybrid beam specimens with 0° to 90° fiber orientations were tested under three- and four-point bending loads. Based on the experimental load–displacement relationship results, initial stiffness, ductility, and energy dissipation capacity were compared. The experimental findings revealed that the maximum load-carrying capacities of beams produced with pultrude profiles increased by 24% with glass wrapping and 64.4% with carbon wrapping due to the change in the damages. A detailed damage analysis is provided. Similarly, significant increases were observed in structural performance ratios such as initial stiffness and ductility ratio.

Experimental Study on the Flexural Creep Behaviors of Pultruded Unidirectional Carbon/Glass Fiber-Reinforced Hybrid Bars

Unidirectional pultruded glass/carbon hybrid fiber-reinforced polymer (HFRP) bars with a diameter of 19 mm have recently been developed for various structural applications. In this study, the creep behavior of HFRP bars caused by bending was experimentally evaluated under different conditions. Our creep study included freeze–thaw preconditioned and unconditioned HFRP bars. The rate of strain and deflection were monitored continuously for a duration of 5000 h. The bars were further tested for creep under the combined effects of mechanical loading and induced thermal cycles, while continuously monitoring the strain rate. Stress levels of 50% to 70% were selected for our creep study. The creep behavior of the bars was analyzed utilizing Findley’s power-law model. On the basis of the linear approximation of Findley’s power law, modulus reductions of approximately 21%, 19%, and 10.75% were calculated for combined freeze–thaw/creep-loaded, freeze–thaw pretreated, and unconditioned HFRP bars, respectively, over a service period of 50 y. The time-dependent deflection of HFRP bars was analyzed by coupling Findley’s power-law model with Euler Bernoulli’s beam theory. The creep deflection intensified by 26.6% and 11.1% for preconditioned and untreated bars, respectively, after a service period of 50 y. The microstructures of HFRP bars was also examined utilizing scanning electron microscopy.

Right ventricle outflow tract prestenting: In vitro testing of rigidity and corrosion properties

BACKGROUND

The aim of this study was to assess the resistance to compression (stiffness) of frequently used stents for right ventricular outflow tract prestenting. In addition, to assess the corrosion potential when different types of stent alloys come into contact with each other.

METHOD

Different stents were tested in vitro in various combinations at specialized metallurgic laboratories. A bench compression test was used to assess resistance to compression of singular and joined combinations of stents. Corrosion was evaluated by standardized electrochemical galvanic tests in physiological solutions at 37°C. Single stents and combinations of stents were evaluated over a period of 4-12 weeks.

RESULTS

Relative stiffness of the stents Optimus/Andrastent XXL/Intrastent LD Max/8zig Cheatham-Platinum, expressed as load per length to deform the stent for 1 mm at 22 mm was 100/104/161/190. Adding additional stents to a single stent significantly strengthened the joined couples (P < 0.001). The lowest galvanic corrosion rates (about 0.000001 mm/year) were observed for the joined CP-Andrastent, Andra-Sapien, and Andra-SapienXT. The corrosion rate for coupled CP-Sapien and CP-SapienXT was somewhat higher (about 0.000003 mm/year). The materials with the highest corrosion rates resulted in material losses of, respectively, 17 and 24 µg/year, which is negligible over a lifetime.

CONCLUSION

Adding stents to a single stent significantly increases stiffness which will reduce the risk of metal fatigue failure. Corrosion of individual stents or stent combinations occurs, but is negligible over a human lifetime with low risk of biological effects. No mechanical integrity problems are thus expected as there is only 0.3% of the initial diameter of the struts of a stent that will be lost as a consequence of corrosion after 100 years.

Comparative study of the corrosion behavior of peripheral stents in an accelerated corrosion model: experimental in vitro study of 28 metallic vascular endoprostheses

PURPOSE

Clinical cases of stent-fractures show that corrosion behavior might play a role in these fractures. Implanted in vivo, especially in combination with other implanted foreign materials, these metallic products are exposed to special conditions, which can cause a process of corrosion. Here, we aimed to test the corrosion potential of stents made of different materials in an in vitro setting.

METHODS

A total of 28 peripheral stents of different materials (nitinol, cobalt-chromium-nickel, tantalum, V4A) and surface treatments (electropolish, mechanical polish, no polish) were tested in vitro. Corrosion was accelerated by applying a constant voltage of 3.5 V and amperage of 1.16 mA in 0.9% NaCl.

RESULTS

Nitinol stents showed the lowest susceptibility to corrosion and the longest period without damage. The Memotherm II® (BARD Angiomed®) was the only stent that showed neither macroscopic nor microscopic damages. The worst performing material was cobalt-chromium-nickel, which showed corrosion damages about ten times earlier compared to nitinol. Considering the reasons for termination of the test, nitinol stents primarily showed length deficits, while V4A and tantalum stents showed fractures. Cobalt-chromium-nickel stents had multiple fractures or a complete lysis in equal proportions. When placed in direct contact, nitinol stents showed best corrosion resistance, regardless of what material they were combined with. In terms of polishing treatments, electropolished stents performed the best, mechanical-polished stents and those without polishing treatment followed.

CONCLUSION

The analysis of corrosion behavior may be useful to select the right stent fulfilling the individual needs of the patient within a large number of different stents.

An Overview of Internal Fixation Implant Metallurgy and Galvanic Corrosion Effects

Orthopedic and hand surgery implants for internal fixation of fractures have evolved substantially over the past 50 years. Newer metal compositions have been used, and new standards have been applied to older alloys, resulting in modern implants with unique physical properties and better clinical performances. Conventional wisdom has long dictated that implanting different metals should be avoided, but few guidelines exist regarding the safety of using in proximity implant systems of dissimilar metals. To better characterize the landscape of internal fixation implant metallurgy, we have compiled the recommendations and conclusions of the currently available and pertinent literature.

A testing platform for durability studies of polymers and fiber-reinforced polymer composites under concurrent hygrothermo-mechanical stimuli

The durability of polymers and fiber-reinforced polymer composites under service condition is a critical aspect to be addressed for their robust designs and condition-based maintenance. These materials are adopted in a wide range of engineering applications, from aircraft and ship structures, to bridges, wind turbine blades, biomaterials and biomedical implants. Polymers are viscoelastic materials, and their response may be highly nonlinear and thus make it challenging to predict and monitor their in-service performance. The laboratory-scale testing platform presented herein assists the investigation of the influence of concurrent mechanical loadings and environmental conditions on these materials. The platform was designed to be low-cost and user-friendly. Its chemically resistant materials make the platform adaptable to studies of chemical degradation due to in-service exposure to fluids. An example of experiment was conducted at RT on closed-cell polyurethane foam samples loaded with a weight corresponding to ~50% of their ultimate static and dry load. Results show that the testing apparatus is appropriate for these studies. Results also highlight the larger vulnerability of the polymer under concurrent loading, based on the higher mid-point displacements and lower residual failure loads. Recommendations are made for additional improvements to the testing apparatus.

Mixing implants of differing metallic composition in the treatment of upper-extremity fractures

Mixing implants with differing metallic compositions has been avoided for fear of galvanic corrosion and subsequent failure of the implants and of bone healing. The purpose of this study was to evaluate upper-extremity fractures treated with open reduction and internal fixation with metallic implants that differed in metallic composition placed on the same bone. The authors studied the effects of using both stainless steel and titanium implants on fracture healing, implant failure, and other complications associated with this method of fixation. Their hypothesis was that combining these metals on the same bone would not cause clinically significant nonunions or undo clinical effects from galvanic corrosion. A retrospective review was performed of 17 patients with upper-extremity fractures fixed with metal implants of differing metallic compositions. The primary endpoint was fracture union. Eight clavicles, 2 proximal humeri, 3 distal humeri, 3 olecranons, and 1 glenoid fracture with an average follow-up 10 months were reviewed. All fractures healed. One patient experienced screw backout, which did not affect healing. This study implies that mixing implants with differing metallic compositions on the same bone for the treatment of fractures does not adversely affect bone healing. No evidence existed of corrosion or an increase in complications with this method of treatment. Contrary to prior belief, small modular hand stainless steel plates can be used to assist in reduction of smaller fracture fragments in combination with anatomic titanium plates to obtain anatomic reduction of the fracture without adversely affecting healing.