Necking

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

Deformation Behavior of NiTi/Polymer Shape Memory Alloy Composites – Experimental Verifications

Abstract: Composites containing NiTi shape memory alloy (SMA) long-fiber, short-fibers or Ti long-fiber in a Polycarbonate (PC) matrix have been fabricated by the injection molding technique. Also, prestrained SMA long-fiber/Epoxy matrix composites have been fabricated. The fracture behavior and thermo-mechanical deformation behavior are examined; (1) Fracture behavior – uniaxial tensile tests up to fracture for SMA long-fiber and short-fiber composite (SMAC). (2) Thermomechanical deformation behavior – tensile loading–unloading tests for Pseudoelastic (PE) long-fiber/PC matrix composites. Several thermo-mechanical loading tests for Shape Memory Effect (SME) long-fiber/PC matrix and SME long-fiber/Epoxy matrix composites were used.The obtained results are as follows: (1) The stress–strain relation up to the final fracture of the Shape Memory Alloy Composites (SMACs) showed the repeated up-and-down of the stress which corresponds to the necking of the specimen, fiber fracture, and matrix fracture. The strain for the...

Theoretical analysis of strain- and stress-based forming limit diagrams

Abstract: Forming limit diagram is extensively used in the analysis of sheet metal forming to define the limit of deformation of materials without necking or fracture. This article contributes in constructio...

Centimeter-Sized Bulk GaN Single Crystals Grown by the Na-Flux Method with a Necking Technique

Abstract: Centimeter-sized bulk GaN single crystals with large dislocation-free areas were fabricated by the Na-flux method with a necking technique. This necking, which is the key technique in Czochralski growth of dislocation-free Si ingots, was realized using a newly developed GaN point seed. Structural properties of grown crystals were investigated using panchromatic cathodoluminescence (CL) measurements and X-ray diffraction. Prism-shape and well-faceted bulk GaN crystals with dimensions as large as 0.85 cm (width) and 1 cm (length) were grown by this technique. The GaN single crystal grown for 400 h have full-width at half-maximum values for c// and c⊥ as narrow as 42.8 and 32.5 arcsec, respectively, indicating an extremely high quality. Panchromatic CL images of (0001) GaN wafers sliced from grown crystals revealed that large areas of the wafers were dislocation free. We concluded that the necking technique in Na flux GaN growth may be a major breakthrough for fabricating large dislocation-free GaN ingots.

Strain instability and fracture at the surface of upset cylinders

Abstract: A refined method has been developed for measurement of the localized surface strains during axial compression of cylinders. The method has been applied to 1045 steel cylinders in various conditions to study fracture under combined stress states. Because the refined measurement method is used, perturbations are observed in the strain path which would otherwise not be apparent. These perturbations precede surface fracture in every case. It is shown that geometric similarities exist between the strain perturbations in upsetting and those in trough formation preceding fracture in stretch forming of sheet material. In addition, metallographic examination of transverse sections of the upset cylinders reveals the presence of subsurface void formations prior to fracture. It is concluded that the surface fractures in upset cylinders involve localized necking of material between inhomogeneities, and it is suggested that an accurate model of this behavior may give some understanding of the influence of material parameters on fracture.