Prebending Strain Research Articles

Spinodal decomposition and martensitic transformation of the high manganese Mn‒xCu alloys fabricated by additive manufacturing

Mn‒Cu-based shape memory alloys have great potential owing to their excellent shape memory properties, high damping capacity, low production cost, and ease of fabrication. In this study, a selective laser melting (SLM) technique was used to design and manufacture a series of high-manganese Mn‒xCu (x=10–40 wt.%) alloys by blending the elemental powders. Spinodal decomposition and martensitic transformation of the alloys during SLM and heat treatment (HT) processes were investigated and correlated with the tensile, damping, and shape memory properties of the alloys. The results showed that γ‒(Mn, Cu) was the main constituent phase in all of samples subjected to SLM only (hereafter as-SLMed) and the SLMed + HTed Mn‒Cu alloys. The effect of the chemical composition and manufacturing process on the phase structural evolution of the Mn‒Cu alloys were monitored. The spinodal decomposition, martensitic transformation and α-Mn precipitation reactions occurred in the as-SLMed Mn‒xCu samples with x = 15–20 wt.%, x < 30 wt.%, and x < 15 wt.%, respectively. The tensile properties of the as-SLMed Mn‒xCu alloys followed a general downward trend with increasing Mn content, while the corresponding damping capacity and shape memory recovery strain showed the opposite trend. HT can promote spinodal decomposition and martensitic transformation to form an equiaxed γ‒(Mn, Cu) grain, parallel twin plate structure, tweed microstructure, and α-Mn precipitate in the alloys. The SLMed + HTed Mn‒30% Cu alloy displayed a better combination of tensile properties (764, 540 MPa, and 12.5%), damping capacity (tan δ = 0.072 at a strain amplitude of 900 × 10−6), and one-way and two-way (εsme = 1.6% and εtw = 0.7% under the pre-bending strain of 10%) shape memory properties. In addition, the performance of the as-SLMed Mn‒xCu (x = 15–20 wt.%) and SLMed + HTed Mn‒xCu (x = 30 wt.%) alloys is comparable with and even superior to those of multi-component and commercial Mn‒Cu-based alloys, respectively.

Two-way shape memory effect in a Ti–Zr–Nb–Ta high-temperature shape memory alloy

The two-way shape memory effect in a Ti–18.5Zr–10Nb–3.5Ta high-temperature shape memory alloy was investigated. X-ray diffraction measurement shows that the alloy is composed of orthorhombic α″-martensite. ω phase is not found in Ti–18.5Zr–10Nb–3.5Ta alloy due to the suppressing effect of Ta element. The α″-martensite laths are found in the transmission electron microscope observation; after the bending deformation, there appear a lot of dislocations. The alloy exhibits a shape memory strain of 3.8% and a high reverse martensite transformation start temperature of 464 K. The maximum two-way shape memory strain of 1.2% is obtained in the alloy with the pre-bending training strain of 10%. The mechanism can be ascribed to the effect of internal stress field caused by dislocations.

Nb-Rod-Method Cu–Nb/Nb3Sn Wires for Practical React-and-Wind Applications

Bronze-processed Nb3Sn-based wires reinforced by Nb-rod-method Cu–Nb composite (Cu-Nb/Nb3 Sn) are applicable to react-and-wind (R&W)-processed Nb3Sn coils. The Cu–Nb composite material functions as a reinforcing stabilizer during the superconducting magnet operation. Moreover, it suppresses the damage of reacted Nb3Sn filaments due to applied stress during the manufacturing process such as the prebending treatment, the insulating, and the winding. New Cu–Nb/Nb3Sn wires with high tin bronze (Cu-15.7wt%Sn-0.3wt%Ti) were investigated in the superconducting properties. The round wire of 0.8-mm diameter with prebending strain ϵ pb = ±0.5% demonstrated a non-Cu- J c of 1150 A/mm2 at 12 T and 4.14 K. The rectangular wire of 1.13 × 1.7 mm with ϵ pb = ±0.5% applied from both directions of flatwise and edgewise had a non-Cu- J c of 355 A/mm2 at 17 T. In this paper, we discuss the cross-sectional designs of Cu–Nb/Nb3Sn wires suitable for practical R&W Nb3Sn applications.

Critical Current Characterization Under Pure Bending Strains of Prebent Cu-Nb/Nb3Sn Strands for Practical React-and-Wind Process

Nb-rod-method Cu-Nb reinforced Nb3Sn (Cu-Nb/Nb3Sn) wires have been successfully developed for commercialization of the react-and-wind (R&W) processed Nb3Sn coils. Superconducting performance of the Cu-Nb/Nb3Sn wires is improved by applying the prebending treatment at room temperature, because of releasing the residual stress of Nb3Sn filaments (prebending strain effects). The purpose of this study is to confirm the efficient use of the prebending strain effects for optimizing critical current $(I_{c})$ characteristics under pure bending strain on the R&W coil design. The Cu-Nb/Nb3Sn strands of 0.8-mm diameter were heat treated at 670 °C for 96 h on stainless steel grooved cylindrical holders of different radii of 10.1–32.1 mm. After half of the reacted strands were applied repeating prebending strain of ±0.5%, each of the prebent strands and the as-reacted (without prebending) strands was transferred to a Ti-6Al-4V alloy grooved cylindrical holder of 15.6-mm radius. Then, those $I_{c}$ measurements were carried out under applied pure bending strains ranging from −0.9% to +0.84% at 11–17 T, 4.2 K. As a result, the prebent strand showed no deterioration of $I_{c}$ in the applied pure bending strain ranging from −0.5% to +0.5% and had larger $I_{c}$ than that of the as-reacted strand at no pure bending strain. In this paper, the $I_{c}$ enhancements of the prebent Cu-Nb/Nb3Sn strands under pure bending strains are analyzed by using the $I_{c}$ characteristics under axial strains.

Enhanced Fracture Resistance of Flexible ZnO:Al Thin Films in Situ Sputtered on Bent Polymer Substrates.

Improving the fracture resistance of inorganic thin films is one of the key challenges in flexible electronic devices. A nonconventional in situ sputtering method is introduced to induce residual compressive stress in ZnO:Al thin films during deposition on a bent polymer substrate. The films grown under a larger prebending strain resulted in a higher fracture resistance to applied strains by exhibiting a ∼ 70% improvement in crack-initiating critical strain compared with the reference sample grown without bending. This significant improvement is attributed to the induced residual stress, which helps to prevent the formation of cracks by counteracting the applied strain.

Prebending Effect for Mechanical and Superconducting Properties of Nb-Rod-Processed Cu–Nb Internal-Reinforced $\hbox{Nb}_{3} \hbox{Sn}$ Wires

We are planning to develop three large superconducting magnets, using CuNb-reinforced Nb3Sn Rutherford cables with the prebending treatment. CuNb-reinforced Nb3Sn wires using a new Nb-rod-processed CuNb composite were developed for the Rutherford cables. In this study, the prebending effects for the mechanical and the superconducting properties of the Nb-rod-processed CuNb/Nb3Sn wire were investigated. We found that the CuNb/Nb3Sn wire with 0.8% prebending treatment had largely enhanced critical current at 4.2 K. The reduction of the n-value was observed around 0.8% prebending strain. The mechanical properties of the prebent wires were enhanced. Young's modulus and 0.2% proof stress of the wire with prebending treatment at 4.2 K are 180 GPa and 270 MPa, respectively. The residual strain was released from 0.30% to 0.15% by 0.8% prebending treatment.

The Prebending Strain Effect on $\hbox{Nb}_{3}\hbox{Sn}$ Superconducting Cabling Conductors

The prebending strain effect is that the repeated bending load at room temperature enhances superconducting properties of practical wires. The authors are now investigating the application of the effect to practical superconducting cabling conductors for high field superconducting magnets. Large current capacity and high strength are required for superconducting cabling conductors to make large scale and high field magnets. The superconducting cabling conductor with high strength wires will be useful for making high field magnets. The prebending strain effect was applied to a cabling technique with wires. High strength wires reinforced with CuNb composite and conventional wires without reinforcement were prepared, which were heat-treated at 943 K for 345.6 ks. Both wires were bent by 10 pulleys to give 0.8% prebending strain. After the prebending treatment the wires were assembled and fabricated 3-strand cables and 7-strand cables. The cables with high strength wires showed the enhancement of critical currents even after the cabling process. The results imply that the prebending treatment is applicable to the fabrication of cabling conductors for making a high field superconducting magnet.

Development of a pre-bent react-and-windCuNb/Nb3Sn multilayer superconducting coil

A superconducting multilayer coil usingCuNb/Nb3Sn wire was fabricated by the pre-bent react-and-wind (R&W) method. The pre-bent R&Wmethod is a combination of the pre-bending treatment and the conventional R&W process. A0.8% pre-bending strain was applied by ten fixed pulleys. The coil was tested inmagnetic fields of 14, 12, 11 and 10 T at 4.2 K. The coil quench current achieved100% load ratio of the short sample critical current in the 14 T back-up field. Thequench current of the outer section coil achieved 100% of the short sample criticalcurrent in the 12 T back-up field. The coil quench currents in various magneticfields are discussed from a hoop stress and mechanical disturbance point of view.

Application of Prebending Effect to Triplet Cables Using Bronze-Route ${\rm Nb}_{3}{\rm Sn}$ Strands

An application of the prebending effect to a cabling process using Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strands was demonstrated. The prebending effect is the enhancement effect of superconducting properties due to the repeated prebending treatment for practical bronze-route Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires. CuNb/Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and Cu/Nb3Sn strands were applied prebending treatment using 10 fixed pulleys with 0.8% prebending strain. Four kinds of triplets, i.e., prebent CuNb/Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn, no-prebent CuNb/Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn, prebent Cu/Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and no-prebent Cu/Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn triplets were fabricated. Critical currents were measured for the four kinds of triplets in magnetic fields up to 11 T at 4.2 K. The obvious critical current enhancement due to the prebending effect was maintained for the prebent CuNb/Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn triplet. The results imply that the prebending treatment for high-strength Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strands is applicable to the cable conductor fabrication.

Effect of Prebending Strain on&lt;tex&gt;$rm CuNb/Nb_3rm Sn$&lt;/tex&gt;Superconducting Coils Using a React and Wind Method

We have found that superconducting properties such as a critical current for bronze route Nb3Sn superconducting wires were enhanced by prebending strain (epsivpb), which is the repeated bending strain at room temperature. In this study, four kinds of react and wind (R&W) processed CuNb reinforced bronze route Nb 3Sn coils with epsivpb=1.0, 0.8, 0.5 and 0% were prepared. We investigated the effect of prebending strain for the coils. In the electromagnetic compressive stress condition, a critical current (Ic) of the R&W processed coil was enhanced by the prebending strain. These Ic values are larger than those of a short sample wire without prebending strain. In the hoop stress condition, the Ic of four coils revealed a similar value. Therefore, it is considered that the Ic was limited by the large tensile stress for all coils in the hoop stress states. These results suggest that the Ic enhanced by the effect of prebending strain is applicable for the R&W coil design without degradation in large stress and strain states

Neutron Diffraction Study on Prebending Effects for Bronze Route&lt;tex&gt;$rm Nb_3rm Sn$&lt;/tex&gt;Wires Without Reinforcement

The critical current, upper critical field and critical temperature of bronze route Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn commercial wires are enhanced by applying a repeated bending strain at room temperature, i.e., "prebending strain". In order to investigate the prebending effects from a viewpoint of a residual strain, axial and lateral residual strains were evaluated directly by neutron diffraction at room temperature. We found that the axial residual strain changes from -0.10% to 0.02 % but the lateral one is unchanged by applying a prebending strain of 0.5% for an ordinary bronze route (Nb,Ti) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires without reinforcement. Hence, in the case of the ordinary Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires without reinforcement, the prebending treatment modifies only the axial residual strain states independently to the lateral one, although it may depend on the wire structure. The critical current properties under the axial tensile strain suggest that the axial residual strain is reduced by about 0.11% but the radial residual strain unchanged by the prebending treatment of 0.5%. This is consistent with the results of the neutron diffraction

Prebending Strain Effect on&lt;tex&gt;$rm CuNb/Nb_3rm Sn$&lt;/tex&gt;Superconducting Wire During Practical React-and-Wind Process

To demonstrate the applicability of the prebending strain effect to the R&W coil winding process, we have developed the prebent react-and-wind (R&W) process, which is the combination of the conventional R&W process and the prebending treatment. The superconducting and mechanical characteristics were investigated for CuNb/Nb3Sn superconducting wires which were picked up from the prebent R&W coil winding process. The results were compared with that of CuNb/Nb3Sn wires which were prebent manually using a prebending former. The prebending treatment using pulleys enhanced Ic more than the manual prebending treatment. This is explained qualitatively by a difference of the prebending strain distribution. The prebending strain distribution is plain symmetric and axis symmetric in cases of the manual prebending and the pulleyed prebending, respectively. The axis symmetrically distributed prebending strain reduces the residual strain more than the plain symmetrical one. The mechanical property was also enhanced. The slope of the stress-strain curve for the pulleyed prebent samples were steeper than that of as-heat-treated sample. The maximum Ic of the Ic -strain curve was enhanced and the strain value corresponding to the maximum Ic shifted to smaller strain by the pulleyed prebending treatment. Though in the large stress region over 200 MPa, the Ic-stress curves of pulleyed prebent samples and as-heat-treated sample were in good agreement, suggesting that the Ic enhancement effect by the prebending treatment was not beneficial, in the small stress region, it is quite beneficial

Relationship between architecture, filament breakage and critical current decay inNb3Sn composite wires repeatedly in-plane bent at room temperature

Six Nb3Sn composite wires with different architectures (‘central and near-the-edge reinforcement’) wererepeatedly in-plane bent at room temperature (in-plane ‘pre-bending’). Breakage behaviourwas revealed from scanning electron microscopy observations by semi-quantitativeanalysis of the filament crack formation and evolution. Cracks are formed in thetransversal and longitudinal directions. Transversal cracks show some tolerance to theapplied bending strain due to the fact that filaments are composite materials;residual Nb core can arrest development of a partial transversal crack initiated in theNb3Sn outer part of the filament. Together with the density of cracksC and the evolution of this parameter with pre-bending strain,εpb, in differentregions of the wire, R–εpb curves are important to understand breakage behaviour of the wires.R is the ratio (number of full transversal cracks)/(number of full transversalcracks + number of partial transversal cracks).Parameters C and R allow us to reveal and satisfactorily understand the wire architecture—breakage—critical current decayrelationship when pre-bending treatment is applied. As a consequence, breakage criteria necessary tominimize Ic decay were defined and the positive influence of the reinforcement in preventing breakage wasobserved. It was also found that, in this regard, more Nb in the CuNb reinforcement, for theinvestigated wires, is better, if the heat treatment for the wire synthesis is performed at670 °C for 96 h. A differentheat treatment, 650 °C for 240 h, is less efficient in preventing filament breakage. Our resultssuggest the possibility of control and improvement of the breakagesusceptibility of the filaments in the wires and, hence, of the bendingIc decay, through the wise design of the wire architecture (i.e. by correlating design with thechoice of composing materials and heat treatments).

Prebending effects in bronze routeNb3Sn wires

Control and optimization of the residual strain are one of the most important issues in the developmentof Nb3Sn superconducting magnets. We found that the repeated bending loads at room temperature change the prestrain ofNb3Sn wires and result inthe enhancement of Jc, Bc 2 and Tc. We call this repeated bending strain ‘prebending strain’. In order to understand theprebending effect, superconducting properties were measured as functions of temperature,field, axial tensile stress and strain. In addition, the three-dimensional strain state was alsoevaluated by the neutron diffraction. Those obtained results strongly suggest that theprebending process changes the radial residual strain as well as the axial oneindependently. Hence, it is considered that the prebending effect is effective for the controland optimization of the three-dimensional strain state on the react and windprocess.

Application of the prebending strain effect onCuNb/Nb3Sn superconducting coils fabricated by a react-and-wind method

We have found that prebending treatment, which is repeated bending load at room temperature,greatly enhances the critical current, upper critical field and critical temperature of practicalNb3Sn superconducting wires. In this paper, we focus on the application of the prebending straineffect to practical superconducting coils fabricated by a react-and-wind method.To demonstrate the prebending strain effect on the react-and-wind coil, we prepared two kinds ofCuNb /Nb3Sn superconducting monolayer coils. For one of the coils, the superconducting wire of 1.0 mmdiameter was repeatedly bent by using ten fixed pulleys before the winding process,resulting in a prebending strain value of 1.0%. The final winding diameter of both coils was200 mm and the number of turns was 49.In the compressive stress condition, the critical current of the coil with 1.0% prebendingstrain was 296 A at 11 T, which was larger than that of the coil with 0% prebending strain.These values were much larger than the critical current of the witness sample. Theresults indicate that the prebending treatment enhanced the coil critical current.In the case of the hoop stress condition, the coil critical currents were approximately 230 Aat 11 T for both coils. The maximum electromagnetic hoop stress was calculated to be360 MPa. The short sample tensile test results qualitatively explained the critical currentdeterioration of the coil. Furthermore, the 360 MPa hoop stress did not deteriorate thecritical current irreversibly.

ＣｕＮｂ／Ｎｂ３Ｓｎ超伝導線材の超伝導特性に与える事前曲げ歪みの効果

In order to develop a Nb3Sn coil using a react and wind method, it is important to clarify the influence of bending strain because the superconducting characteristics of Nb3Sn are very sensitive to stress and strain. We investigated the effect of prebending strain epb, which means repeated bending loads, from 0% to 1.5% for superconducting wires. We found that Ic, Tc and Bc2 were enhanced by prebending strain. When the prebending strain was 0.8%, Ic values showed maximum enhancement at a whole magnetic field for CuNb/Nb3Sn wires. For instance, Ic was approximately twice at 19 T. Bc2 increased about 1.5 T at a whole temperature when epb was 1.0%. Tc increased from 17.5 K to 17.9 K at a prebending strain of 1.2%.

Effects of repeated bending load at room temperature for composite Nb3Sn wires

In order to realize a react and wind (R&W) method for Nb3Sn wires, the influences of a bending load at room temperature are investigated. Usually, the superconducting wires undergo bending loads at room temperature repeatedly during winding and insulation processes. We define these bending loads as ‘pre-bending’ treatments. We applied the pre-bending strain of 0 and 0.5% to the highly strengthened CuNb/(Nb, Ti)3Sn wires, and measured the stress/strain properties and critical currents. The improvements of stress dependence of normalized critical current and the increase of the maximum critical current by the pre-bending treatments were found. The model based on the distribution of the local tensile strain as a bending strain describes the experimental results well without the increase of the maximum critical current. When the pre-bending strain was applied, the calculated results indicate that the mechanical properties are improved due to the local work hardening, and hence the stress dependence of Ic increases.

An experimental study on in vivo dynamic mechanical properties of the knees of cats in valgus loading

In these experiments an attempt was made to investigate in vivo dynamic mechanical properties of the knee in valgus loading. Fifteen adult cats were used. Sinusoidal bending oscillation of 0.3, 1.0, 1.6, 3.3, 5.0, 8.6 and 10.0 Hz was transmitted to the knee-leg complex under each pre-bending strain in the valgus direction, and the bending moment was measured. Dynamic mechanical properties of the knee-leg complex were given as a complex bending elastic coefficient. Bending elastic and bending damping coefficient of the knee could be calculated by the least square method. As a first approximation, the knee was represented as a non-linear Kelvin model. Both bending elastic and bending damping coefficient of the knee increased as pre-bending moment was increased, and decreased as amplitude of bending oscillation was increased. Mechanical loss tangent of the knee-leg complex decreased within the range of pre-bending moment larger than 1.0 × 10 6 dyn cm as bending moment was increased, and decreased as amplitude of bending oscillation was increased.