Abstract
The aim of the present paper is to provide an in-depth analysis of the fatigue-life assessment for μm-size 316L stainless steel components. Such components find typical applications in the biomedical field, e.g., in cardiovascular stents. To this purpose, the present work analyzes experimental data on 316L stainless steel from literature for smooth and notched μm-size components using a global computational approach. Several aspects are discussed: (i) the choice of an appropriate constitutive law for cyclic material behavior, (ii) fatigue criteria based on shakedown concepts for finite and infinite lifetime, in particular distinguishing between low, high and very high-cycle fatigue regimes (denoted as LCF, HCF and VHCF, respectively), and (iii) gradient effects in relation with hot-spot as well as average or mean volume approaches for the lifetime estimation. The results give a new insight into the lifetime design of μm-size components and could be directly applied for the fatigue-life assessment of small size structures as, for instance, cardiovascular 316L stainless steel stents.
Highlights
In the past fifty years, austenitic stainless steels have been widely and extensively used in several fields, ranging from nuclear or aerospace industries to chemistry or food and beverage processing [1]
Cycle for the 50-notch specimen of Fig. 1(a), subjected to a net pressure range of 360 MPa (see Fig. 2(c)). As it can be observed, plasticity is localized in a very small region of about 0:01 mm around the notch, where Wp assumes a maximum value of about 1 MPa; the remaining part of the specimen presents an elastic shakedown state and no Wp is manifested
The volumetric approach considers a process volume for fatigue mechanisms [67,68] and assumes such a volume to be a cylinder for the three-dimensional specimens and a circle for the two-dimensional specimens with the center corresponding to the root of the notch
Summary
In the past fifty years, austenitic stainless steels have been widely and extensively used in several fields, ranging from nuclear or aerospace industries to chemistry or food and beverage processing [1]. Type 316L stainless steel has been largely appreciated for its high ductility and strength under complex thermomechanical loadings, i.e., such a material can reach considerable plastic strains of 0.5–1% at millions of cycles. Materials like the 316L or 304L stainless steels present a complex material behavior characterized by primal and secondary hardening [2,3,4,5], which make the design of structures a difficult task. Type 316L stainless steel has gained a privileged position among the materials employed in biomedical devices, e.g., stents, vena cava filters, guide-wires for catheters and pacemaker leads [15,16]. The attractive properties of such a material, e.g., well adapted mechanical characteristics (great ductility, high tensile strength, and a raised elastic limit), biocompatibility, resistance to corrosion as well as fatigue performances, assure the long-term service required by biomedical
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