Superelastic Nickel-titanium Alloy Research Articles

Mechanical analysis of the improved superelastic Ni-Ti alloy wire using the orthodontic simulator with high-precision sensors

PurposeThe authors have been using improved superelastic Nickel-Titanium alloy wire (ISW) to close and align extraction spaces simultaneously, instead of separately using rigid wires for closing extraction spaces and Ni–Ti alloy wires for leveling and aligning. ISW has a low stiffness, which makes it challenging to generate sufficient moments. This study aimed to demonstrate the forces and moments exerted on adjacent brackets using an orthodontic simulator (OSIM) attached to a high-precision 6-axis sensor. Materials and methodsIn experiment 1, a 0.016 × 0.022-inch ISW, stainless steel (SS) wire, and β-titanium wires were ligatured into the two brackets. The 0.018 × 0.025-inch slot self-ligating brackets were bonded to two simulated teeth at the same height, and the experiment was conducted using the high-precision OSIM. The distance between the brackets was 10 mm, the V-bend angles of the installed wires were 10°, 20°, 30°, and 40°, and the apex position was set at the center of the bracket. In experiment 2, 6.0- and 9.0-mm long elastomeric chains were placed on the same brackets as in Experiment 1 to measure forces and moments. The distance between the brackets was increased by 1.0 mm from 6.0 to 15.0 mm. Both experiments were conducted in a 37 °C thermostatic chamber similar to the oral environment. Results and discussionIn experiment 1, we measured moments on both sides for all the wires. As the V-bend angle increased, the absolute values of the moments also increased. With a V-bend angle of 10°, there was a significant (p < 0.05) difference in the moment generated in the left and right brackets among the three wire types. In the ISW, −1.67 ± 0.38 N・mm was generated in the left bracket, while 0.38 ± 0.26 N・mm was generated in the right bracket at 10°. At 20°, −1.77 ± 0.69 N・mm was generated in the left bracket, while 2.37 ± 0.94 N・mm was generated in the right bracket. At 30°, −2.98 ± 0.49 N・mm was generated in the left bracket, while 3.25 ± 0.32 N・mm was generated in the right bracket. Moreover, at 40°, −3.96 ± 0.58 N・mm was generated in the left bracket, while 3.55 ± 0.53 N・mm was generated in the right bracket. Furthermore, in experiment 2, the moments increased in proportion to the increase in distance between the centers of the two brackets. Absolute values of the moments were approximately equal for the left and right brackets. The 6.0-mm elastomeric chain generated a minimum force of −0.09 ± 0.05 N in the left direction when the distance between brackets was 6.0 mm, while a maximum of 1.24 ± 0.3 N when the distance between brackets was 12 mm in the right bracket. In the left bracket, minimum and maximum forces of −0.09 ± 0.07 and 1.3 ± 0.4 N were generated in the right direction, respectively. The 9.0-mm elastomeric chain generated a minimum force of 0.03 ± 0.07 N in the left direction when the distance between brackets was 9.0 mm, while a maximum of 1.3 ± 0.1 N when the distance between brackets was 15 mm in the right bracket. In the left bracket, minimum and maximum forces of 0.05 ± 0.06 and 0.98 ± 0.2 N were generated in the right direction, respectively. ConclusionMechanical data of the ISW have been collected in the study, which was previously difficult to perform owing to the low stiffness of the wire. It is suggested that the ISW can provide sufficient moments with the addition of V-bends to close the space by bodily movement.

Experimental investigation of rotary friction welding on the mechanical properties of NiTinol alloy

In this research work, super elastic nickel-titanium alloy (NiTinol) rods were joined using a fully automated direct-driven rotary friction welding technique at various rotational speeds, namely 1800, 1900 and 2000 rpm. Mechanical properties such as tensile strength, flexural strength, impact strength and microhardness were determined for as-welded, heat-treated and cryogenic-treated welded samples. Research findings revealed that maximum tensile strength of 1112 MPa is observed which is more by an amount 27.94%, 37.15% and 36.83% at 1800, 1900 and 2000 rpm for heat-treated samples. A significant increase in flexural strength of 3.29 kN/mm2 was achieved which is 31.58%, 26.32% and 27.78% higher, and a high impact strength of 0.8 N-m/mm2 which is 57.15%, 55.55% and 54.55% higher, respectively, for heat-treated samples. The highest microhardness of 347 HV was recorded for cryogenically treated samples at 1900 rpm which is 7% and 4% more compared to heat-treated and as-welded samples.

Investigating the effect of operating temperature on the tribo-mechanical behavior of cold rolled superelastic nickel titanium alloy

NiTi alloys are the most important practical shape memory alloys (SMA) with excellent mechanical properties. Austenitic NiTi alloys with superelastic behavior are currently being investigated for load-bearing applications due to their ability to accommodate large elastic strains and better mechanical properties than martensitic SMAs. We conducted dry reciprocating tests against AISI 52100 steel balls to evaluate the tribomechanical behavior of cold-rolled austenitic Ti – 55.7 wt% Ni alloys at various temperatures, including room temperature, 50 °C, 100 °C, and 200 °C. We observed an 18.3% lower friction coefficient with an 86% reduction in wear volume at 200 °C compared to room temperature during reciprocating tests. Material transfer was captured from the steel ball to the NiTi flat at elevated temperatures and from the NiTi flat to the steel ball at lower temperatures. The primary wear mechanisms on NiTi shifted from abrasive to adhesive with increased operating temperature, and the counter balls shifted from adhesive to abrasive. Indentation testing on austenitic NiTi revealed a 12% increase in hardness with a 50% decrease in Young's modulus at 200 °C, resulting in an increased Modell ratio (Hardness/Young's modulus) with increasing temperature. This phenomenon can be attributed to the austenitic NiTi alloy's increased wear resistance with an increase in operating temperature.

Treatment of Class II malocclusion with the improved superelastic nickel-titanium alloy wire and long hooks for mandibular molar protraction

• Two patients were treated with extraction of the mandibular second premolars. • We used superelastic nickel-titanium alloy wires as working wires. • The use of nickel-titanium wires and long hooks worked to mesialize the molar bodily. The mandibular first molar must be carefully moved to prevent mesial tipping and extrusion in case extraction of the mandibular second premolar is required to achieve the desired goals. The nickel-titanium alloy has unique mechanical properties, including superelasticity and shape memory, leading to the generation of continuous light forces that may be more biologically compatible than intermittent strong forces. However, it provides poor root control because of its low stiffness. We herein have experienced the patients with Angle Class II malocclusion that uses the improved superelastic nickel-titanium wire (ISW) and long hooks to achieve bodily movement of the mandibular first molar. The 0.022 × 0.028-in slot preadjusted edgewise appliances and 0.020 × 0.025-in ISWs as the working archwire were used. We pinched the crimpable long hooks on the rectangular ISW and applied 100-150 g of contractile force between the fixed long hooks and bracket hooks of the mandibular first molars to activate the system with ligature wire lacing. The mandibular molars were uprighted and mesially moved; panoramic radiographs did not indicate severe root resorption. These experiences suggest that this method involving the combined use of the ISW and long hooks may be one of the useful methods for closing spaces by facilitating the uprighting and mesial movement of the molars in treating Class II malocclusion.

Selective and efficient solid-phase microextraction of polycyclic aromatic hydrocarbons in water by robust two-dimensional zinc oxide nanosheets grown on a superelastic nickel-titanium alloy fiber prior to determination by HPLC-UV.

Oriented zinc oxide nanosheets (ZnONSs) were directly grown on pretreated nickel-titanium alloy (NiTi) fiber substrates without a traditional seeding layer of ZnO by electrochemical deposition for the first time. The fiber coatings were characterized by scanning electron microscopy and energy dispersive X-ray spectrometry. Direct growth of ZnONSs on the NiTi fiber substrate was dependent on the type of zinc salt. The adsorption performance of the ZnONSs coatings was evaluated using representative aromatic compounds as model analytes together with high performance liquid chromatography with ultraviolet detection. The as-prepared fiber shows higher extraction capability for the selected polycyclic aromatic hydrocarbons (PAHs) than for ultraviolet filters in water samples, and better extraction selectivity for PAHs. For this purpose, the important experimental parameters were optimized for the extraction of PAHs. Under the optimized conditions, the calibration curves are linear in the range of 0.03-200 μg L-1 with correlation coefficients greater than 0.999. Limits of detection ranged from 0.011 μg L-1 to 0.082 μg L-1. Intra-day and inter-day relative standard deviations (RSDs) of the developed method with a single fiber ranged from 2.69% to 4.18% and from 4.44% to 5.40%, respectively. RSDs for the fiber-to-fiber reproducibility varied between 5.57% and 7.66%. The developed method was successfully applied for selective preconcentration and determination of trace PAHs in five real water samples. Relative recoveries varied from 84.5% to 104% with RSDs between 1.65% and 8.30%. Furthermore, the as-prepared fiber is highly stable.

A new strategy for enhanced fabrication of flake-like zinc–aluminum layered double hydroxide on nickel–titanium alloy fiber for highly efficient solid-phase microextraction of ultraviolet filters

A new flake-like zinc–aluminum layered double hydroxide (ZnAl-LDH) coating was firmly fabricated on a superelastic nickel–titanium alloy (NiTi) wire. Herein, the NiTi wire was hydrothermally treated for the in-situ growth of nickel and titanium oxide nanoflakes (NiTiONFs) and used as a fiber support for subsequent growth of ZnAl-LDH nanoflakes. The resulting coating was able to selectively extract the studied ultraviolet filters (UVFs) more effectively and quickly in comparison with the commercial polyacrylate and polydimethylsiloxane fibers. This fiber shows long recycling lifetime due to the ZnAl-LDH coating embedded into the active NiTiONFs support with high mechanical stability. For this purpose, main experimental parameters including temperature, stirring rate, extraction and desorption time, and ionic strength were investigated and optimized in detail. Under the optimized conditions, good linearity was obtained for the developed SPME–HPLC–UV method with the NiTi@NiTiONFs@ZnAl-LDH fiber. Limits of detection were between 0.009 μg L−1 and 0.052 μg L−1 for five UVFs. Intra-day and inter-day relative standard deviations (RSDs) for single fiber repeatability were less than 6.4% and 6.6% for five replicate extractions of UVFs at the spiking level of 50 μg L−1. RSDs for fiber-to-fiber reproducibility varied from 6.3% to 6.9%. The developed method was successfully used for the determination of UVFs in snow water, river water and wastewater samples. The relative recoveries of 80.1%–109% were achieved. Thus the developed method could be potentially applied to selective enrichment and determination of UVFs in different environmental water samples.

Effectiveness of low binding frictional materials: Evaluation of the binding frictional resistance of improved superelastic nickel-titanium alloy wires with different bracket combinations

Introduction: This study aimed to evaluate the binding frictional resistance of improved superelastic nickel- titanium alloy wires (ISW) with different bracket combinations and to verify the effectiveness of low binding frictional materials by applying them in orthodontic treatment. Materials and Methods: Straight stainless steel wire (SSW; 0.016 × 0.022-inch) and straight ISW (0.016 × 0.022- inch) were set to each displaced bracket, and the tensile resistance load was measured. The maximum tensile resistance load was statistically compared using the Tukey test. For exemplification, we treated a typical extraction case of Angle Class I crowding malocclusion with lip protrusion using lower binding frictional materials, which were selected based on tensile test results. Results: The SSW and metal bracket combination had the largest maximum tensile resistance load, and the ISW and metal slot-equipped plastic bracket combination had the smallest load (P &lt; 0.01). In a patient treated using lower binding frictional materials, the active treatment period was 9 months. Satisfactory patient results were obtained without using reinforced anchorage. Conclusions: Binding frictional resistance varies, depending on the archwire and bracket combination. In a multibracket appliance, selecting materials with as low a binding frictional resistance as possible may make a more effective treatment.

Comparison of the microbial flora from different orthodontic archwires using a cultivation method and PCR: A prospective study.

The aim of this study was to evaluate the effects of superelastic nickel-titanium (SE NiTi), copper-nickel-titanium (CuNiTi) and titanium-molybdenum alloy (TMA) archwires with different surface properties on dental plaque retention and microbial colonization. Totally 25 individuals, consisting of 16 girls and nine boys with mean age of 15.69±1.70, were included in this study. The effects of the SE NiTi, CuNiTi and TMA archwires with different surface properties on the amount of Streptoccocus sp and Lactobacillus sp were investigated with three different parameters including clinical periodontal indexes, microbial swab and archwire samples. Phenotypic isolation was performed from microbial swab and archwire samples using culture method; genotypic isolations were performed by the polymerase chain reaction method. There was no statistically significant difference between SE NiTi, CuNiTi and TMA archwires in terms of periodontal parameters (P>.05). When microbial swabs and archwires samples from different archwire groups were evaluated by culture method, no statistically significant difference was found between the groups (P>.05). A statistically significant difference was found between the amount of Lactobacillus sp in the swab samples of the CuNiTi archwire after the purification period (P=.023). Smutans were found to be more quantity than other bacterial types in all archwires. The amount of microbial involvement was found to be lower in CuNiTi archwires than in the post-purification period. This may be due to the antimicrobial effect of copper.

Anterior open bite due to temporomandibular joint osteoarthrosis with muscle dysfunction treated with temporary anchorage devices

Skeletal Class II high-angle open bite is often accompanied by osteoarthrosis of the temporomandibular joint (TMJ-OA). This type of malocclusion is challenging to correct, and it has been reported that patients with TMJ-OA treated with orthognathic surgery often experience skeletal relapse and a poor prognosis. This case report describes the treatment of a 25-year-old woman with retrognathia and TMJ-OA, whose masseter and temporal muscle activities were weak. Temporary anchorage devices were placed in the maxilla and the mandible, and the first molars were intruded. We used improved superelastic nickel-titanium alloy wires with tip-back bends for both arches, and intermaxillary elastics were used to upright the molars. After treatment, intrusion of the maxillary and mandibular first molars, counterclockwise rotation of the mandible, and improvement of occlusion and profile had been achieved. The patient's condyles were repositioned into ideal positions, and masticatory muscle activity was augmented and balanced. After 2years of retention, the mandibular and condylar positions were stable, and acceptable occlusion was maintained without recurrence of TMJ symptoms; harmonious activity of the masticatory muscles was retained. The findings of this case report suggest that molar intrusion using temporary anchorage devices for a patient with severe anterior open bite and TMJ-OA may be useful for improving stomatognathic function, occlusion, and facial esthetics.

Oriented ZnO nanoflakes on nickel-titanium alloy fibers for solid-phase microextraction of polychlorinated biphenyls and polycyclic aromatic hydrocarbons.

ZnO nanoflakes (ZnONFs) were electrochemically grown on a nickel-titanium alloy (NiTi) wire for use in solid-phase microextraction. Prior to the growth of ZnONFs, the NiTi wire was hydrothermally treated for in-situ growth of TiO2/NiO nanoflakes as a seeding base. The applied potential was used to control the dimensions of vertically oriented hexagonal ZnONFs. After annealing at 600°C, the resulting fiber display fairly selective affinity for polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons. The fibers were applied to the preconcentration of PCBs which then were quantified by HPLC with UV detection. Compared to commercial polydimethylsiloxane coatings, the new coating displays high extraction capability, rapid extraction kinetics and superior cycling stability. This is assumed to be due to its high surface-to-volume ratio, double-sided open access structure, and enhanced structural stability. The assay excels by (a) a wide analytical range (0.10 to 200μgL-1 of PCBs), (b) low limits of detection (20-17ngL-1), and (c) low standard deviations for the single fiber repeatability (<9.8%) and for the fiber-to-fiber reproducibility (<7.5%). Satisfactory accuracy and precision were achieved when PCBs were determined by this method in spiked rain water, river water and wastewater samples. Graphical abstract ZnO nanoflakes were fabricated on a superelastic nickel-titanium alloy wire in desired orientation with enhanced extraction capability and good extraction selectivity. The fabricated fiber was suitable for the determination of PCBs in environmental water samples.

An effective strategy for controlled fabrication and self-assembled modification of template-supported silica nanosheets on a superelastic nickel-titanium alloy fiber for highly efficient solid-phase microextraction

Silica nanosheets (SiO2NSs) were successfully fabricated on the superelastic nickel-titanium alloy (NiTi) wire as a novel fiber for solid-phase microextraction (SPME). Before sol-gel coating, the NiTi wire was hydrothermally treated in alkaline solution for the in situ growth of NiO/TiO2 nanosheets (NiO/TiO2NSs). The sol-gel coating of SiO2 on the surface of NiO/TiO2NSs template was investigated and a thin shell of SiO2 was found to cover NiO/TiO2NSs, which can enlarge the effective surface area of the SiO2 coating. This SiO2 capped NiO/TiO2NSs coated NiTi (NiTi@NiO/TiO2@SiO2NSs) fiber shows good extraction selectivity for polycyclic aromatic hydrocarbons (PAHs) and enhanced mechanical stability. After the self-assembled modification of SiO2NSs by phenyltrichlorosilane, the NiTi@NiO/TiO2@SiO2NSs@Ph fiber shows higher extraction capability for non-polar PAHs. Thus, the conditions for the extraction of PAHs were investigated and optimized coupled to HPLC with UV detection. Under the optimized conditions, the analytical parameters of the SPME-HPLC methods with the NiTi@NiO/TiO2@SiO2NSs and the NiTi@NiO/TiO2@SiO2NSs@Ph fibers were determined and compared. The SPME-HPLC method with the NiTi@NiO/TiO2@SiO2NSs@Ph fiber was developed for the concentration and the determination of PAHs in environment water samples. The relative recovery of PAHs in real water samples spiked at 5 μg L−1, 10 μg L−1 and 30 μg L−1 ranged from 88.1% to 109%. Furthermore, this fiber is stable due to the chemical bonding between different coatings and NiTi substrates. The fabrication of the NiO/TiO2@SiO2NSs@Ph coating on the NiTi fiber substrate is precisely controllable.

Avaliação da instrumentação endodôntica de dentes de cães com limas rotatórias ProTaper®

Industry data for pet products has revealed that most Brazilian families have pets in their homes and that that humans give a large amount of attention to their pets. Oral diseases are among the most quickly perceived and treated of pet pathologies; and the most common of these is periodontal disease, which can affect the pulp and requires endodontic treatment. Recently, the evelopment of superelastic nickel-titanium alloys has revolutionized endodontic therapy, as the alloys have been used to develop novel rotary instruments. The goal of this study was to evaluate the efficiency of such rotary instruments in the ex vivo shaping of canine dental root canal therapy. The sample consisted of 40 canine incisors that had been extracted due to periodontal disease. The endodontic access procedure was performed, and the root canal was prepared using ProTaper® rotary instruments. Before and after shaping the canals, teeth were examined radiographically. The cervical, middle, and apical thirds were analyzed using the Image Lab® program. Results showed that the ProTaper® rotary instruments removed significant amounts of dentine (cervical third: T=-13.225, p<0.0001; middle third: W=410, p<0.000 1; apical third: W=410, p<0.0001). Regarding shaping of the canal, the apical third had expanded significantly, and there was a positive correlation between measurements in all analyzed thirds (cervical third: r=0.924; middle third: r=0.980; apical third: r=0.993.) This demonstrates an increase in the surface area of the channels in all three thirds. In this study, we conclude that the rotary instruments used were efficient in shaping root canals. Keywords: Endodontics, rotary instruments, root canal

Facile in situ fabrication of oriented titania submicrorods embedded into a superelastic nickel–titanium alloy fiber substrate and their application in solid-phase microextraction

A novel NiTi@TiO2SR fiber was fabricated on a NiTi fiber substrate after annealing for the determination of PAHs in water.

A patient with mandibular deviation and 3 mandibular incisors treated with asymmetrically bent improved superelastic nickel-titanium alloy wires

Skeletal and dental discrepancies cause asymmetric malocclusions in orthodontic patients. It is difficult to achieve adequate functional occlusion and guidance in patients with congenital absence of a mandibular incisor due to the tooth-size discrepancy. Here, we describe the orthodontic treatment of a 22-year-old woman with an asymmetric Angle Class II malocclusion, mandibular deviation to the left, and 3 mandibular incisors. The anterior teeth and maxillary canines were crowded. We used an improved superelastic nickel-titanium alloy wire (Tomy International, Tokyo, Japan) to compensate for the asymmetric mandibular arch and an asymmetrically bent archwire to move the maxillary molars distally. A skeletal anchorage system provided traction for intermaxillary elastics, and extractions were not needed. We alleviated the crowding and created an ideal occlusion with proper overjet, overbite, and anterior guidance with Class I canine and molar relationships. This method of treatment with an asymmetrically bent nickel-titanium alloy wire provided proper Class I occlusion and anterior guidance despite the mandibular deviation to the left and 3 mandibular incisors, without the need for extractions.

Numeric Comparison of the Static Mechanical Behavior between ProFile GT and ProFile GT Series X Rotary Nickel-Titanium Files

Introduction This article aims to evaluate how different superelastic nickel-titanium (NiTi) alloys determine the static mechanical performance of endodontic files during bending and torsion. Methods Two NiTi rotary instruments with similar geometries and equal cross sections, ProFile GT (GT) and a GT Series X (GTX), were selected. The latter file is made from M-Wire, a NiTi alloy that, according to its manufacturer, has been thermomechanically processed to have larger flexibility at body temperature. The mechanical response was studied for a series of static bending and torsional loads by using finite element (FE) models. The materials were characterized according to previously published stress-strain curves. Results For the same load and boundary conditions, the GTX material significantly increased the instrument’s performance. For instance, the deflection for a 1N force at the tip of the file was found to be 28.5% larger for the GTX file, whereas the maximum stress decreased 13.2%. Conclusions Although not fully reflective of the instrument’s behavior in a dynamic rotation intracanal system, the static results showed that the GTX file is more flexible and capable of stress relief at the most critical sections than the GT file, suggesting that it has a lower risk of fracture inside the root canals during its clinical use.

An Evaluation of a NiTiCo Alloy and its Suitability for Medical Device Applications

Development of a superelastic material with higher stiffness and plateau stresses than binary nitinol is of interest to the medical device industry because it may allow for lower profile, less intrusive devices without compromising the material’s characteristics. This project studied the effect of cobalt (Co) alloying additions on the stiffness and plateau stresses of a superelastic nickel-titanium alloy. In addition, the general physical, mechanical, corrosion, and biocompatibility properties of the alloy were compared to binary nitinol. The results of this study showed Co to be an interesting alloying addition that should be considered for future medical devices in applications, where stiffness is of concern.

Deployable Trusses Based on Large Rotation Flexure Hinges

Formulations for the strength, stiffness, mass efficiency, and packaging of deployable trusses using flexure hinges are developed and comparedwith the experimentwithin. The equations are based on classical buckling theory, Euler buckling with engineering approximations, and finite element-based models to predict the column and bending strengths of solid rod and tubular trusses with slender flexure hinges. Flexure hinge material performance metrics are derived and used to show that, while bothmass efficient trusses of solid rods and trusses of tubes are feasible with existing materials, trusses of solid rods are significantly more strain limited. A representative high compaction ratio deployable truss with pultruded carbon fiber reinforced plastic rods and super elastic nickel-titanium alloy flexure hinges was fabricated and tested. The compressive strength of the truss was 48% less than predicted and the compressive stiffness of the truss was 12% less than predicted.

Treatment of severe Class II Division 1 deep overbite malocclusion without extractions in an adult

This case report describes the orthodontic treatment and retention of an adult with severe Class II Division 1 deep overbite malocclusion; treatment was completed without premolar extractions. We used improved superelastic nickel-titanium alloy wire (L&H Titan, Tomy, Tokyo, Japan) with J-hook headgear for the combined intrusion of the anterior segment and the distalization of the maxillary posterior segments. The overbite was corrected from 6.0 to 2.0 mm by intrusion of the maxillary and mandibular incisors; the overjet was corrected from 13.0 to 2.0 mm. Although no premolars were extracted, good occlusion and facial esthetics were achieved. Follow-up records 2 years after active treatment show that the results were maintained.

In vitro fatigue–crack growth and fracture toughness behavior of thin-walled superelastic Nitinol tube for endovascular stents: A basis for defining the effect of crack-like defects

Endovascular stents made of the superelastic nickel-titanium alloy Nitinol are subjected in service to tens of millions of loading cycles and even “single-event” overloads, both of which can potentially result in fracture and/or complete failure of the device. A fracture-mechanics-based methodology can provide a means to quantify relevant material parameters critical to the design against such failures. However, there is a dearth of relevant experimental data in the literature on such fracture-mechanics-based approaches to fatigue in Nitinol; furthermore, that which does exist invariably pertains to product forms that are not appropriate for stent manufacture, e.g., bulk Nitinol bar and strip. Consequently, the current work is focused on characterizing in vitro both subcritical and critical crack growth (fatigue–crack growth and R-curve fracture toughness) behavior in thin-walled (∼400 μm thick) Nitinol tubing similar to that used for medical device manufacture (following shape-setting procedures to flatten the material), with a resultant austenite finish temperature of A f∼25–30 °C, identical to self-expanding Nitinol stents. Fatigue–crack growth behavior, measured in Hanks’ Balanced Saline Solution over a wide spectrum of growth rates (down to 10 −10 m/cycle) and at a range of positive load ratios ( R = 0.1 – 0.7 ), revealed significantly higher fatigue thresholds than had been previously reported for bulk Nitinol material. In addition, we examine the critical effect of test frequency, as most fatigue experiments on Nitinol have been performed at 30 Hz or above, despite the fact that this is far in excess of the frequency of physiological loading. Finally, the fracture toughness properties are characterized in thin-section Nitinol and show marked crack-resistance ( R-curve) behavior with a dependence on crack-growth angle (with respect to the tube drawing axis); additionally, measured toughnesses are found to be lower than has been previously reported for bulk Nitinol.

Erratum: “Anomalous relationship between hardness and wear properties of a superelastic nickel–titanium alloy” [Appl. Phys. Lett. 84, 1076 (2004)

Erratum: “Anomalous relationship between hardness and wear properties of a superelastic nickel–titanium alloy” [Appl. Phys. Lett. 84, 1076 (2004)