Necking

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

Plastic anisotropy and deformation-induced phase transformation of additive manufactured stainless steel

Abstract: Plastic anisotropy and deformation-induced phase transformation of additively manufactured (AM) stainless steels were investigated via in-situ neutron diffraction, electron backscatter diffraction, metallography, and fractography. Two types of tensile specimens were manufactured: (1) One sample was vertically fabricated with its tensile axis parallel to the z-direction (AM-V), (2) The other sample was horizontally fabricated with its tensile axis perpendicular to the z-direction (AM-H). A commercial 15-5PH stainless steel (CA) was used for comparison. AM steel revealed enhanced yield strength, tensile strength, and uniform elongation over CA, which was mainly due to grain refinement and transformation induced plasticity (TRIP). Different onsets of strain nonlinearity between AM-V and AM-H were closely related to martensitic phase transformation. Stresses estimated from lattice strains measured by neutron diffraction matched well with the applied stress-strain curves. After plastic deformation, voids were formed and congregated near the solidified line where fine grains were populated. Higher dislocation density was observed in the fine grain zone, and lower density was shown in the relatively coarse grain zone. AM steels exhibited significant anisotropic fracture behavior in terms of loading direction. In contrast to isotropic failure for CA and AM-V, AM-H revealed anisotropic failure with elliptical formation of the fracture feature. The fracture surface of AM-H possessed many secondary cracks propagating perpendicular to the building direction. The occurrence of secondary cracks in AM-H resulted in rapid load drop during tensile loading after necking.

Frictional properties of olivine at high temperature with applications to the strength and dynamics of the oceanic lithosphere

Abstract: [1] Faulting and brittle deformation of mantle rocks occurs in many tectonic settings such as oceanic transform faults, oceanic detachment faults, subduction zones, and continental rifts. However, few data exist that directly explore the frictional properties of peridotite rocks. Improved constraints on the brittle deformation of peridotite is important for a more complete understanding of the rheological properties of the lithosphere. Furthermore, our comparatively detailed understanding of plastic deformation in olivine allows us to explore the possible role of thermally activated intracrystalline deformation mechanisms in macroscopically brittle processes. It has been hypothesized, and some experimental data indicate, that plastic yielding by dislocation glide (low temperature plasticity) determines the direct effect in the rate and state frictional constitutive formulation. Plastic flow may also have important implications for the blunting or necking at asperity contacts that influences the time and/or displacement dependent friction evolution effect and frictional healing. We present results from saw cut experiments on fine grained synthetic olivine fault gouge conducted in a gas-medium deformation apparatus in the temperature range of 400–1000°C with 100 MPa confining pressure. We conducted velocity stepping tests to explore the rate and temperature dependence of sliding stability. We also conducted slide-hold-slide experiments to investigate the time and temperature dependence of fault zone restrengthening (frictional healing). The mechanical data and microstructural observations allow us to explore the role of thermally activated processes in frictional sliding. The data indicate systematic temperature dependenceof rate and state variables that can be attributed to plastic yielding at grain to grain contacts. We explore the implications of such temperature dependent behavior for controlling the base of the seismogenic zone in the oceanic lithosphere, and we seek insight into possible mechanistic models for the interactions between fracture and flow that could lead to improved constraints on the strength of the lithosphere.

Evolution of dislocation structures and deformation behavior of iron at different temperatures: Part I. strain hardening curves and cellular structure

Abstract: The deformation behavior of iron has been investigated at different temperatures by means of tension tests. There exist two temperature ranges for deformation. In the low-temperature range(T < 293 K), the flow stress σ, the work-hardening rate θ at e = 0.06, and the yield stress σy decrease with increasing temperature, but in the higher temperature range(T ≥: 293 K), σ and θ at the same strain increase while σy decreases more slowly. The change of dislocation density, with temperature, ate = 0.06 exhibits the same tendency as that of the flow stress. The strainhardening rates decrease almost linearly with increasing stress up to necking in the low-temperature range, except the initial strain range. At the higher temperature range, the hardening rates decrease linearly with stress only at the early stage of deformation, but above certain strains, the decreases become more gradual; that is, the G-cr curves deviate from the linear region. The evolution of dislocation structure has also been observed by transmission electron microscopy (TEM). The results show that a substructural transition takes place in the nonlinear range of G-cr curves. In the linear decreasing region of strain-hardening curves, the deformation is controlled by the uniformly distributed dislocations or cell multiplication prevails. However, in the nonlinear region of G-cr curves, cell multiplication seems to be balanced by cell annihilation.