The vascular stents are important medical devices introduced into a vessel to protect the lumen from unfriendly stenosis. However, Nitinol stent is easy to fail in practice. The present paper focuses on the influence of defects on its mechanical behavior by finite element analysis. The essential stent cell is used with two different type of defects, which includes the face bulge defect resulted from laser burrs or TiC inclusion arises and C‐contained particle voids. Auricchio’s super‐elastic consititutive equations are used in the finite element simulations. It is found that the stress distribution is not only related to the defect type but also to the defect position. With the increasing distance from the TiC defect to the knot’s notch, the influence of defects on stress distribution of stents becomes small. For void defects, those near both the inner fillet and the outer fillet have grand influence on the stent’s global stress distribution. In particular, the higher stress concentrations are undergone near knot’s defects. For all models, the maximum Martensite Volume Fraction is near knots. The finite element analysis shows that cracks/fractures can easily appear near knots. A stent with a TiC inclusion or void defect is likely to fail. All obtained conclusions can be useful to design against stent premature mechanical failure. 相似文献
Being in the strategic direction of next-generation absorbers, multifunctional microwave absorbing materials possess great application value in military and commercial fields. However, the stringent requirements for performance necessitate the combination of multiple functions in such type of composites, which is still a challenge. This work aims to develop a foam-type absorber composed of multi-dimensional organic and inorganic materials, in which reduced graphene oxide sheets and polyvinyl alcohol membranes serve as the framework and crosslinker to form a three-dimensional skeleton. Meanwhile, SiC nanofibers as a reinforcing component can effectively suppress the over-stacking of reduced graphene oxide and enhance the conductivity and mechanical strength of cell walls. Among the remarkable microwave absorbing properties of the obtained foam, there are the ultra-light (9.85 mg cm-3), broadband (7.04 GHz), and strong absorption (reflection loss of -61.02 dB), all combined in the ultra-thin (2.5 mm). In addition, the foam possesses superelastic and excellent heat-insulating characteristics that ensure shock resistance, heat preservation, and infrared stealth. The remarkable versatility benefits from the porous structure, as well as from the synergistic effect of multi-dimensional organic and inorganic constituents of the foam. Therefore this study lays the foundation for the design of new-generation microwave absorbers with broad application potential. 相似文献
Shape memory alloys have a high potential for passive isolation of vibrations as well as capability of being used as an active vibration isolation system for their shape memory behavior, i.e. having hysteresis along with superelastic behavior. Study of this behavior necessitates recognition of distinct specifications of this alloy and also presentation of a suitable and simple mathematical model. In this paper, a mathematical model based on Auricchio model, considering asymmetry in tension and compression and also temperature effects on hysteresis at superelastic conditions has been presented. Finally, dynamical behavior of a NiTi beam under free vibration as well as application of sinusoidal and impulse loads upon free–clamped and also simply supported conditions have been analyzed. 相似文献
This study deals with the effect of strain rate on tensile and energy absorbing properties of superelastic NiTi thin wires. It also attempts to gain an understanding of the interplay of the ductile behavior, temperature and strain rate effects, energy storage and cycling. The wires are in austenite condition at room temperature and above. The strain rates imposed during testing range from 0.2 to 180%/min (i.e., 0.06–54 mm/min) corresponding to a frequency of 2.77 × 10−4 to 0.25 Hz for strain amplitudes of 6%. The corresponding frequency for 8% strain amplitude is 2.08 × 10−4 to 0.18 Hz. It is shown that NiTi SMAs exhibit ductility at both low and high strain rates. This is also true for the cold worked and heat treated conditions both below Mf and above Af. During tensile testing the stress-induced martensite (SIM) plateau increases in length and translates upwards with increase in strain rate up to a certain value. Similarly, the onset of elastic yield stress also increases with strain rate. At high strain rates the SIM segment and elastically deformed SIM segment overlap. The SIM formation is not able to cope with the externally imposed higher strain rates. This is also the reason for the reduction of hysteresis loop at the high strain rates as observed in the cyclic tests.
The dissipated strain energy density (Ed) increases with increasing strain rate up to a certain value beyond which the Ed decreases. It is clear that the mean point of the superelastic loop shifts to the right and upwards (higher stress and higher strain region) for cyclic testing with increase in strain rates. However, it shifts to the right and downwards (lower stress/higher strain regime) for both the 6 and 8% strain amplitude cycling at constant strain rate. The stabilization of residual strain and Ed is based on the same underlying mechanism relating to SIM formation and occurs at the same numbers of cycles. 相似文献
Superelastic shape memory alloys (SMAs) have the ability to recover their original shape after experiencing large strains.
A new beam-to-column connection incorporating long shank SMA bolts is presented in this paper. By using the unique characteristics
of SMAs, the connection possesses self-centering abilities. The 3D connection model is created using the software ANSYS, and
Auricchio’s model is used to simulate the superelastic behavior of the SMA bolts. With cyclic loads applied on the beam ends,
the behavior of the connection is studied. The results show the semi-rigid and moderate energy dissipation characteristics
of the connection. Since the moment-carrying capacity of bolt cluster controlled below the elastic flexural capacity of connecting
beam, a superelastic hinge forms just at the beam-to-column interface. The inelastic interstory drift angle of the connection
reaches 0.035 rad, and 94% of the total rotations are recoverable upon unloading. 相似文献
In this paper, the detailed stress distributions of NiTi stents have been studied. The primary object of this study is to set up a cell model to reveal the cause of crack initiation for stents. Auricchio’s super‐elastic model is used to analyze the essential stent cell. Two different kinds of models are analyzed. One model is the stent without defect and the other model is a stent with defects caused by laser burrs or TiC inclusions. The structural stress distribution is not only related to a specimen without defect but also to the material of a bulge defect. The maximum stresses of the stent without defect are near the knots, while the one with defects possesses the maximum stress near the surrounding of the bulge defect. It was found that cracks/fractures can easily appear within a distance of 1/3 of the knot to knot spacing. In particular, a stent with TiC inclusion defects is likely to fail near the bulge face defect. Our simulations agree with experimental results. 相似文献