Necking

About: Necking is a research topic. Over the lifetime, 5280 publications have been published within this topic receiving 113945 citations.

Computational Examination of the Effect of Material Inhomogeneity on the Necking of Stent Struts Under Tensile Loading

Abstract: This study presents a computational investigation of tensile behavior and, in particular, necking due to material inhomogeniety of cardiovascular stent struts under conditions of tensile loading. Polycrystalline strut microstructures are modelled using crystal plasticity theory. Two different idealized morphologies are considered for three-dimensional models, with cylindrical grains and with rhombic-dodecahedron grains. Results are compared to two-dimensional models with hexagonal grains. For all cases, it is found that necking initiates at a significantly higher strain than that at UTS (ultimate tensile stress). Two-dimensional models are shown to exhibit an unrealistically high dependence of necking strain on randomly generated grain orientations. Three-dimensional models with cylindrical grains yield a significantly higher necking strain than models with rhombic-dodecahedron grains. It is shown that necking is characterized by a dramatic increase in stress triaxiality at the center of the neck. Finally, the ratios of UTS to necking stress computed in this study are found to compare well to values predicted by existing bifurcation models.

Application of deformation instability to microstructural control in multilayer ceramic composites

Abstract: Bimaterial interfaces are known to be unstable against perturbation, due to flow localization, during deformation. In this paper a criterion for flow localization is formulated, based on the difference in flow properties of the constituent phases. It predicts a tensile force in the harder phase and an equivalent compressive one in the softer phase, leading to necking of the harder phase. A useful practical application of this instability is demonstrated in the production of a series of oxide/oxide composites with microstructures ranging from laminar to wood-like in texture. Composites of Ce–ZrO 2 /Al 2 O 3 with strong interfaces demonstrate high strength (1.1 GPa), fracture toughness (17 MPa√ m ) and hardness (12 GPa) due to greatly increased phase transformation. Alternatively, composites of Y–ZrO 2 /porous–A1 2 O 3 and Y–ZrO 2 /YPO 4 display crack deflection and graceful failure due to the presence of weak interfaces. The potential now exists for this deformation processing technique to be applied to the production of 3-D composites with isotropic properties.

Adiabatic Heating of Austenitic Stainless Steels at Different Strain Rates

Abstract: This work focuses on the effect of strain rate on the mechanical response and adiabatic heating of two austenitic stainless steels. Tensile tests were carried out over a wide range of strain rates from quasi-static to dynamic conditions, using a hydraulic load frame and a device that allowed testing at intermediate strain rates. The full-field strains of the deforming specimens were obtained with digital image correlation, while the full field temperatures were measured with infrared thermography. The image acquisition for the strain and temperature images was synchronized to calculate the Taylor–Quinney coefficient (β). The Taylor–Quinney coefficient of both materials is below 0.9 for all the investigated strain rates. The metastable AISI 301 steel undergoes an exothermic phase transformation from austenite to α’-martensite during the deformation, which results in a higher value of β at any given strain, compared to the value obtained for the more stable AISI 316 steel at the same strain rate. For the metastable 301 steel, the value of β with respect to strain depends strongly on the strain rate. At strain rate of 85 s−1, the β factor increases from 0.69 to 0.82 throughout uniform elongation. At strain rate of 10−1 s−1, however, β increases during uniform deformation from 0.71 to a maximum of 0.95 and then decreases to 0.91 at the start of necking.