scholarly journals Interaction of void spacing and material size effect on inter-void flow localisation

2020 ◽  
pp. 1-13
Author(s):  
Ingrid Holte ◽  
Ankit Srivastava ◽  
Emilio Martínez-Pañeda ◽  
Christian F. Niordson ◽  
Kim L. Nielsen
Keyword(s):  
Size Effect ◽  
Strain Gradient ◽  
Three Dimensional ◽  
Stress Triaxiality ◽  
Void Coalescence ◽  
Porous Metals ◽  
Dimensional Finite Element ◽  
Stress States ◽  
Three Dimensional Finite Element ◽  
Ligament Size

Abstract The ductile fracture process in porous metals due to growth and coalescence of micron scale voids is not only affected by the imposed stress state but also by the distribution of the voids and the material size effect. The objective of this work is to understand the interaction of the inter-void spacing (or ligaments) and the resultant gradient induced material size effect on void coalescence for a range of imposed stress states. To this end, three dimensional finite element calculations of unit cell models with a discrete void embedded in a strain gradient enhanced material matrix are performed. The calculations are carried out for a range of initial inter-void ligament sizes and imposed stress states characterised by fixed values of the stress triaxiality and the Lode parameter. Our results show that in the absence of strain gradient effects on the material response, decreasing the inter-void ligament size results in an increase in the propensity for void coalescence. However, in a strain gradient enhanced material matrix, the strain gradients harden the material in the inter-void ligament and decrease the effect of inter-void ligament size on the propensity for void coalescence.

Size Effect on the Thermal Conductivity of Thin Metallic Films Investigated by Scanning Joule Expansion Microscopy

2008 ◽  
Vol 130 (8) ◽  
Author(s):  
Siva P. Gurrum ◽  
William P. King ◽  
Yogendra K. Joshi ◽  
Koneru Ramakrishna
Keyword(s):  
Thermal Conductivity ◽  
Size Effect ◽  
Three Dimensional ◽  
Mean Free Path ◽  
Local Temperature ◽  
Metallic Films ◽  
Dielectric Interface ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element ◽  
Electron Mean Free Path

A technique to extract in-plane thermal conductivity of thin metallic films whose thickness is comparable to electron mean free path is described. Microscale constrictions were fabricated into gold films of thicknesses 43nm and 131nm. A sinusoidal voltage excitation across the constriction results in a local temperature rise. An existing technique known as scanning joule expansion microscopy, measures the corresponding periodic thermomechanical expansion with a 10nm resolution and determines the local temperature gradient near the constriction. A three-dimensional finite-element simulation of the frequency-domain heat transfer fits the in-plane thermal conductivity to the measured data, finding thermal conductivities of 82±7.7W∕mK for the 43nm film and 162±16.7W∕mK for the 131nm film, at a heating frequencies of 100kHz and 90kHz, respectively. These values are significantly smaller than the bulk thermal conductivity value of 318W∕mK for gold, showing the electron size effect due to the metal-dielectric interface and grain boundary scattering. The obtained values are close to the thermal conductivity values, which are derived from electrical conductivity measurements after using the Wiedemann–Franz law. Because the technique does not require suspended metal bridges, it captures true metal-dielectric interface scattering characteristics. The technique can be extended to other films that can carry current and result in Joule heating, such as doped single crystal or polycrystalline semiconductors.

Fracture Initiation in Pressure Tube Specimens of Hydrided Irradiated Zr-2.5Nb Materials With Split Circumferential Hydrides

2017 ◽  
Author(s):  
Shin-Jang Sung ◽  
Jwo Pan ◽  
Poh-Sang Lam ◽  
Douglas A. Scarth
Keyword(s):  
Crack Initiation ◽  
Crack Front ◽  
Room Temperature ◽  
Three Dimensional ◽  
Stress Triaxiality ◽  
Fracture Initiation ◽  
Pressure Tube ◽  
Computational Results ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

Fracture initiation for axial cracks in pressure tube (PT) specimens of hydrided irradiated Zr-2.5Nb materials with split circumferential hydrides at room temperature is examined by conducting three-dimensional finite element analyses. With a strain-based fracture criterion with consideration of stress triaxiality, the location for the earliest crack initiation is determined near the middle of the axial crack front. For PT specimens with split circumferential hydrides, three types of strain concentration are observed in the ligaments ahead of the crack front. The computational results suggest that the internal pressure for crack initiation of hydrided irradiated PT specimens with many randomly distributed split circumferential hydrides needs only 55% to 70% of that for unhydrided irradiated PT specimens. The computational results can be used to explain the near 40% reduction of the fracture toughness at room temperature obtained from hydrided irradiated PT specimens when compared with that from unhydrided irradiated ones.

Fracture Initiation in Compact Tension Specimens of Hydrided Irradiated Zr-2.5Nb Materials With Split Circumferential Hydrides

2017 ◽  
Author(s):  
Shin-Jang Sung ◽  
Jwo Pan ◽  
Poh-Sang Lam ◽  
Douglas A. Scarth
Keyword(s):  
Room Temperature ◽  
Three Dimensional ◽  
Stress Triaxiality ◽  
Fracture Initiation ◽  
Tensile Tests ◽  
Compact Tension ◽  
Transverse Tensile ◽  
Stress Strain Relation ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

Fracture initiation in compact tension (CT) specimens of hydrided irradiated Zr-2.5Nb materials with split circumferential hydrides is examined by conducting three-dimensional finite element analyses with submodeling. The stress-strain relation for the irradiated Zr-2.5Nb materials is based on the experimental results of transverse tensile tests. For CT specimens with split circumferential hydrides, plastic strain concentration is observed in the middle of the ligaments ahead of the crack front. With a strain-based failure criterion with consideration of stress triaxiality, the necessary fraction of the load for crack initiation is about 0.55 to 0.70 to fracture the ligaments when compared to that for a CT specimen without split circumferential hydrides. The computational results can be used to explain the near 40% reduction of the fracture toughness at room temperature obtained from hydrided irradiated curved compact tension specimens (CCTSs) when compared with that from unhydrided irradiated ones.

Process-Induced Residual Thermal Stresses in Advanced Fiber-Reinforced Composite Laminates

1984 ◽  
Vol 106 (1) ◽  
pp. 48-54 ◽  
Author(s):  
R. J. Stango ◽  
S. S. Wang
Keyword(s):  
Composite Laminates ◽  
Thermal Stresses ◽  
Three Dimensional ◽  
Fiber Reinforced ◽  
Deformation And Failure ◽  
Fiber Reinforced Composite ◽  
Reinforced Composite ◽  
Dimensional Finite Element ◽  
Stress States ◽  
Three Dimensional Finite Element

A study of process-induced stresses in advanced fiber-reinforced composite laminates is presented. An analysis of the residual thermal stresses is conducted on the basis of laminate thermoelasticity theory in conjunction with a quasi-three-dimensional finite element method. Formulation of the numerical method is briefly outlined in the paper. To illustrate the fundamental nature of the problem, numerical examples for a quasi-isotropic [0 deg/90 deg/ ± 45 deg]s graphite-epoxy composite system are presented. Complex three-dimensional stress states of significant magnitude are reported. Emphasis is placed on the interlaminar stress distributions along ply interfaces. Effects of laminate stacking sequence on the residual thermal stresses are examined in detail. Implications of the results on deformation and failure of composite laminates are discussed.

3-D FEM Stress Analysis and Mechanical Characteristics in Bolted Joints Under External Tensile Loadings

2015 ◽  
Author(s):  
Shunichiro Sawa ◽  
Mitsutoshi Ishimura ◽  
Yasuhisa Sekiguchi ◽  
Toshiyuki Sawa
Keyword(s):  
Maximum Stress ◽  
Three Dimensional ◽  
Bolted Joints ◽  
Nominal Diameter ◽  
Bolt Preload ◽  
Dimensional Finite Element ◽  
M 12 ◽  
Stress States ◽  
Three Dimensional Finite Element ◽  
Screw Threads

In practical design for bolted joints, the stress concentration factor (SCF) of the first root in screw threads is important. In the present paper, the SCF in screw threads taking account of spiral in the screw threads is analyzed using three-dimensional Finite Element Method (FEM). In addition, the stress states of screw threads under repeated and static loadings are analyzed in elasto-plastic deformation range. The effect of bolt nominal diameter (M12, M24 and M33) on SCF is also examined. In addition, the experiment to measure the strains at the roots of screw threads was carried out newly. It is found that the FEM result is fairly coincided with the measured results. It is also found that the SCF increases as the bolt nominal diameter increases and the maximum stress is found to occur at the half pith from the engaged screw threads. The value of SCF is smaller in the coarse screw threads of M12 than that in the fine screw threads of M 12. Finally, the bolt ruptures for several nominal diameters are shown to occur from screw threads in the non-engagement in bolted joints under static loadings and under the repeated loadings the bolts are ruptured from the first root of screw threads due to fatigue even if the bolt preload is the higher.

scholarly journals Characteristics of selected measures of stress triaxiality near the crack tip for 145Cr6 steel - 3D issues for stationary cracks

2020 ◽  
Vol 10 (1) ◽  
pp. 571-585
Author(s):  
Marcin Graba
Keyword(s):  
Finite Element Method ◽  
Three Dimensional ◽  
Stress Triaxiality ◽  
Crack Tip ◽  
Fem Analysis ◽  
Material Constant ◽  
Stress Fields ◽  
Material Characteristic ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

AbstractIn the paper the numerical analysis of the stress fields for 145Cr6 steel, near crack tip is presented, based on three-dimensional finite element method (FEM) analysis. The FEM analysis is focused on SEN(B) specimens with relative crack length a/W ≈ 0.30. In addition to the presentation of the normal components of the stress tensor, the paper presents selected measures of stress triaxiality parameters, measured for the value of the J-integral, corresponding to the experimentally determined fracture toughness, denoted as JIC, which is considered to be a material constant or material characteristic [1, 2]. Presented topic is a continuation of papers [3, 4],whichwere based on experimental analysis, presented in [5].

Finite Element Analysis of Nonuniformity of Tires with Imperfections5

2007 ◽  
Vol 35 (3) ◽  
pp. 226-238 ◽  
Author(s):  
K. M. Jeong ◽  
K. W. Kim ◽  
H. G. Beom ◽  
J. U. Park
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Three Dimensional ◽  
Element Model ◽  
Radial Force ◽  
Element Analysis ◽  
The Finite Element Analysis ◽  
Dimensional Finite Element ◽  
Force Variation ◽  
Three Dimensional Finite Element

Abstract The effects of variations in stiffness and geometry on the nonuniformity of tires are investigated by using the finite element analysis. In order to evaluate tire uniformity, a three-dimensional finite element model of the tire with imperfections is developed. This paper considers how imperfections, such as variations in stiffness or geometry and run-out, contribute to detrimental effects on tire nonuniformity. It is found that the radial force variation of a tire with imperfections depends strongly on the geometrical variations of the tire.

Tire Modeling by Finite Elements

1992 ◽  
Vol 20 (1) ◽  
pp. 33-56 ◽  
Author(s):  
L. O. Faria ◽  
J. T. Oden ◽  
B. Yavari ◽  
W. W. Tworzydlo ◽  
J. M. Bass ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Rolling Contact ◽  
Test Problems ◽  
State Behavior ◽  
Normal Contact ◽  
New Developments ◽  
Applied Torque ◽  
Dimensional Finite Element ◽  
Tire Modeling ◽  
Three Dimensional Finite Element

Abstract Recent advances in the development of a general three-dimensional finite element methodology for modeling large deformation steady state behavior of tire structures is presented. The new developments outlined here include the extension of the material modeling capabilities to include viscoelastic materials and a generalization of the formulation of the rolling contact problem to include special nonlinear constraints. These constraints include normal contact load, applied torque, and constant pressure-volume. Several new test problems and examples of tire analysis are presented.

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