scholarly journals An independent derivation and verification of the voids nucleation failure mechanism: significance for materials failure

2019 ◽  
Vol 475 (2222) ◽  
pp. 20180755 ◽  
Author(s):  
Richard Christensen ◽  
Zhi Li ◽  
Huajian Gao
Keyword(s):  
Stress State ◽  
Failure Mechanism ◽  
Density Functional ◽  
Failure Modes ◽  
Shear Bands ◽  
Failure Criteria ◽  
Atomic Scale ◽  
Ideal Strength ◽  
Failure Theory ◽  
The Ideal

Independent derivations are given for the failure criteria of the purely dilatational stress state involving voids nucleation failure as well as for the purely distortional stress state involving shear bands failure. The results are consistent with those from a recently derived failure theory and they further substantiate the failure theory. The voids nucleation mechanism is compared with the ideal theoretical strength of isotropic materials as derived by density functional theory and two other atomic-scale methods. It is found that a cross-over occurs from the voids nucleation failure mechanism to the ideal strength limitation as the tensile to compressive strengths ratio, T / C , increases toward a value of unity. All the results are consistent with the failure modes transition results from the general failure theory.

scholarly journals An evaluation of the failure modes transition and the Christensen ductile/brittle failure theory using molecular dynamics

2018 ◽  
Vol 474 (2219) ◽  
pp. 20180361 ◽  
Author(s):  
Richard Christensen ◽  
Zhi Li ◽  
Huajian Gao
Keyword(s):  
Molecular Dynamics ◽  
Brittle Failure ◽  
Failure Modes ◽  
Shear Bands ◽  
Failure Criteria ◽  
Test Material ◽  
Full Density ◽  
Modes Of Failure ◽  
Failure Theory ◽  
Voids Growth

The Christensen ductile/brittle failure theory can be interpreted in terms of the associated failure modes, those of shear bands and voids nucleation. Their conjunction is then termed as the failure modes transition and it is studied here using molecular dynamics. The test material is taken as a particular metallic glass, CuZr. First the theoretical failure criteria are evaluated and then the theoretical failure modes transition is evaluated. Both are found to perform extremely well. The overall failure theory contains three modes of failure, the two already mentioned plus a fracture criterion. A general conclusion from the work is that the voids nucleation criterion is of unusually broad relevance. Voids nucleation leads to voids growth and then further deteriorating mechanisms and ultimately failure. But the voids nucleation is the precipitating event of all that subsequently occurs in this process. Access to these capabilities is gained through the failure theory for all homogeneous, full density, isotropic materials. Only two standard testing measurements are needed to calibrate the entire failure theory, including the transitions.

Failure Criteria for Unidirectional Fiber Composites

1980 ◽  
Vol 47 (2) ◽  
pp. 329-334 ◽  
Author(s):  
Z. Hashin
Keyword(s):  
Stress State ◽  
Failure Modes ◽  
Three Dimensional ◽  
Transversely Isotropic ◽  
Failure Surface ◽  
Failure Criteria ◽  
Fiber Composites ◽  
Piecewise Smooth ◽  
Average Stress ◽  
Unidirectional Fiber

Three-dimensional failure criteria of unidirectional fiber composites are established in terms of quadratic stress polynomials which are expressed in terms of the transversely isotropic invariants of the applied average stress state. Four distinct failure modes—tensile and compressive fiber and matrix modes—are modeled separately, resulting in a piecewise smooth failure surface.

What is the Limit of Nanoparticle Strengthening?

MRS Bulletin ◽  
2009 ◽  
Vol 34 (3) ◽  
pp. 173-177 ◽  
Author(s):  
D.C. Chrzan ◽  
J.W. Morris ◽  
Y.N. Osetsky ◽  
R.E. Stoller ◽  
S.J. Zinkle
Keyword(s):  
Nuclear Reactor ◽  
Matrix Material ◽  
Dislocation Motion ◽  
Perfect Crystal ◽  
Atomic Scale ◽  
Ideal Strength ◽  
Deformation Processes ◽  
Precipitate Strengthening ◽  
Transportation Applications ◽  
The Ideal

AbstractThe stress required to deform a perfect crystal to its elastic limit while maintaining perfect periodicity, the so-called ideal strength, sets the gold standard for the strength of a given material. Materials this strong would be of obvious engineering importance, potentially enabling more efficient turbines for energy production, lighter materials for transportation applications, and more reliable materials for nuclear reactor applications. In practice, the strength of engineering materials is often more than two orders of magnitude less than the ideal strength due to easily activated deformation processes involving dislocations. For many materials, precipitate strengthening is a promising approach to impede dislocation motion and thereby improves strength and creep resistance. This observation begs the question: What are the limits of nanoparticle strengthening? Can the ideal strength of a matrix material be reached? To answer these questions, we need a detailed, atomic scale understanding of the interactions between dislocations and obstacles. Fortunately, simulations are beginning to explore this interaction.

Ab Initio DFT Study of Ideal Strength of Crystal and Surfaces in Covalent Systems

2008 ◽  
Vol 1086 ◽  
Author(s):  
Yoshitaka Umeno
Keyword(s):  
Tensile Strength ◽  
Ab Initio ◽  
Normal Stress ◽  
Density Functional ◽  
Level Structure ◽  
High Strength ◽  
Nucleation Site ◽  
Dislocation Nucleation ◽  
Ideal Strength ◽  
The Ideal

AbstractAb initio density functional theory (DFT) calculations were performed to examine various factors which may influence the ideal strength, namely multiaxial loading condition and structure with low symmetry. First, the effect of normal stress on the ideal shear strength (ISS) in covalent crystals, Si, C, Ge and SiC, was evaluated. It was found that the response of ISS to normal stress differs depending on the material, while in metals the trend is unchanged. Obtained ISS as a function of normal stress is useful to understand criteria of dislocation nucleation in a pristine crystal because local lattices at the nucleation site undergo superimposed stress components in experiment. Secondly the ideal tensile strength of silicon surface was evaluated to examine how atomistic-level structure affects the mechanical property. The theoretical tensile strength of Si nanofilms with (100) surface, which is flat with dimer-row structures, shows only 20-30% reduction even though the thickness is down to 1 nm, meaning that the flat surface possesses high strength.

Study on the Failure Mechanism of Flexible Pipes Under Large Torsion Considering the Layer Interaction

2018 ◽  
Author(s):  
Shanghua Wu ◽  
Zhixun Yang ◽  
Jinlong Chen ◽  
Qingzhen Lu ◽  
Qianjin Yue ◽  
...  
Keyword(s):  
Failure Mechanism ◽  
Failure Modes ◽  
Layer Structure ◽  
Twist Angle ◽  
Water Environment ◽  
Interaction Mechanism ◽  
Failure Criteria ◽  
Flexible Pipe ◽  
Strength Failure ◽  
Flexible Pipes

Flexible pipe is the typical multi-layer structure which is designed to resist different loads when it is utilized under the severe deep-water environment. However, there is not any structural layer to withstand the torsion specially. Tension armors are only arranged to bear the tension with consideration of the torque balance. Especially, when flexible pipe is loaded out from the cargo vessel to the installation vessel, twist angle could be accumulated at high level so that all of layers need to resist the torsion. So, the failure mechanism is very complicated due to the interaction effect between different layers. Firstly, the interaction mechanism between layers of flexible pipes is analyzed under large torsion and some potential failure modes are identified, namely the strength failure and buckling failure of tensile armor, collapse failure of the inner layers. The theoretical descriptions of involved failure behaviors are investigated and the governing physical effects of failure modes are discussed. In addition, some failure criteria for predicting the pipe capacity are introduced. Finally, the methodology can be used to predict the flexible pipe torsional capacity and to prevent the torsional failure in engineering.

Ab-Initio Study of Mechanical Properties of Transition-Metal Aluminides: A Case Study for Al3(V,Ti)

2005 ◽  
Vol 482 ◽  
pp. 139-142
Author(s):  
M. Jahnátek ◽  
M. Krajčí ◽  
J. Hafner
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Tensile Deformation ◽  
Uniaxial Tensile ◽  
Ideal Strength ◽  
Maximal Stress ◽  
Metal Aluminides ◽  
Interatomic Bonding ◽  
The Ideal

On the basis of ab-initio density-functional calculations we have analyzed the character of interatomic bonding in the intermetallic compounds Al3(V,Ti) with the D022 and L12 structures. In all structures we found an enhanced charge density along the Al-(V,Ti) bonds, a characteristic feature of covalent bonding. The bond strength is quantitatively examined by tensile deformations. The ideal strength of Al3V and Al3Ti under uniaxial tensile deformation was found to be significantly higher than that of both fcc Al and bcc V. We investigated also the changes of the interatomic bonding in Al3V during tensile deformations. We found that the covalent interplanar Al- V bonds disappear before reaching the maximal stress. The weakening of the bonding between the atomic planes during the deformation is accompanied by a strengthening of in-plane bonding and an enhanced covalent character of the intraplanar bonds. Interplanar bonding becomes more metallic under tensile deformation.

An ab initio study of the ideal tensile and shear strength of single-crystal β–Si3N4

2003 ◽  
Vol 18 (5) ◽  
pp. 1168-1172 ◽  
Author(s):  
Shigenobu Ogata ◽  
Naoto Hirosaki ◽  
Cenk Kocer ◽  
Yoji Shibutani
Keyword(s):  
Shear Strength ◽  
Single Crystal ◽  
Ab Initio ◽  
Density Functional ◽  
Strain Curve ◽  
High Strength ◽  
Indentation Hardness ◽  
Ideal Strength ◽  
Vickers Indentation ◽  
The Ideal

In this study, the ideal tensile and shear strength of single-crystal β–Si3N4 was calculated using an ab initio density functional technique. The stress-strain curve of the silicon nitride polymorph was calculated from simulations of uniaxial strain deformation. In particular, the ideal strength calculated for an applied ∈11 tensile strain was estimated to be approximately 57 GPa. Recently, a good correlation was reported between the shear modulus of high-strength materials and the experimentally determined Vickers indentation hardness value. Using the reported correlation an estimate was made of the Vickers indentation hardness of single-crystal β–Si3N4: approximately 20.4 GPa.

scholarly journals Flexural bearing capacity and failure mechanism of CFRP-aluminum laminate beam with double-channel cross-section

2021 ◽  
Vol 28 (1) ◽  
pp. 139-152
Author(s):  
Teng Huang ◽  
Dongdong Zhang ◽  
Yaxin Huang ◽  
Chengfei Fan ◽  
Yuan Lin ◽  
...  
Keyword(s):  
Carbon Fiber ◽  
Bearing Capacity ◽  
Failure Mechanism ◽  
Cross Section ◽  
Failure Criterion ◽  
Failure Modes ◽  
Channel Cross Section ◽  
Fiber Layer ◽  
Flexural Bearing Capacity ◽  
Double Channel

Abstract In this study, the flexural bearing capacity and failure mechanism of carbon fiber-reinforced aluminum laminate (CARALL) beams with a double-channel cross-section and a 3/2 laminated configuration were experimentally and numerically studied. Two types of specimens using different carbon fiber layup configurations ([0°/90°/0°]3 and [45°/0°/−45°]3) were fabricated using the pressure molding thermal curing forming process. The double-channel CARALL beams were subjected to static three-point bending tests to determine their failure behaviors in terms of ultimate bearing capacity and failure modes. Owing to the shortcomings of the two-dimensional Hashin failure criterion, the user-defined FORTRAN subroutine VUMAT suitable for the ABAQUS/Explicit solver and an analysis algorithm were established to obtain a progressive damage prediction of the CFRP layer using the three-dimensional Hashin failure criterion. Various failure behaviors and mechanisms of the CARALL beams were numerically analyzed. The results indicated that the numerical simulation was consistent with the experimental results for the ultimate bearing capacity and final failure modes, and the failure process of the double-channel CARALL beams could be revealed. The ultimate failure modes of both types of double-channel CARALL beams were local buckling deformation at the intersection of the upper flange and web near the concentrated loading position, which was mainly caused by the delamination failure among different unidirectional plates, tension and compression failure of the matrix, and shear failure of the fiber layers. The ability of each fiber layer to resist damage decreased in the order of 90° fiber layer > 0° fiber layer > 45° fiber layer. Thus, it is suggested that 90°, 0°, and 45° fiber layers should be stacked for double-channel CARALL beams.

scholarly journals Tuning Bandgaps of Mixed Halide and Oxide Perovskites CsSnX3 (X=Cl, I), and SrBO3 (B=Rh, Ti)

2021 ◽  
Vol 11 (15) ◽  
pp. 6862
Author(s):  
Hongzhe Wen ◽  
Xuan Luo
Keyword(s):  
Solar Energy ◽  
Electronic Properties ◽  
Density Functional ◽  
Photovoltaic Cell ◽  
Photovoltaic Properties ◽  
Functional Theory ◽  
New Approach ◽  
Energy Applications ◽  
Valence Bands ◽  
The Ideal

Perovskites have recently attracted interest in the field of solar energy due to their excellent photovoltaic properties. We herein present a new approach to the composition of lead free perovskites via mixing of halide and oxide perovskites that share the cubic ABX3 structure. Using first-principles calculations through Density Functional Theory, we systematically investigated the atomic and electronic structures of mixed perovskite compounds composed of four cubic ABX3 perovskites. Our result shows that the B and X atoms play important roles in their band structure. On the other hand, their valence bands contributed by O-2p, Rh-4p, and Ti-3p orbitals, and their electronic properties were determined by Rh-O and Ti-O bonds. With new understandings of the electronic properties of cubic halide or oxide perovskites, we lastly combined the cubic perovskites in various configurations to improve stability and tune the bandgap to values desirable for photovoltaic cell applications. Our investigations suggest that the mixed perovskite compound Cs2Sn2Cl3I3Sr2TiRhO6 produced a bandgap of 1.2 eV, which falls into the ideal range of 1.0 to 1.7 eV, indicating high photo-conversion efficiency and showing promise towards solar energy applications.

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