Advances in Fracture and Failure Prevention

Volumes 261-263

doi: 10.4028/www.scientific.net/KEM.261-263

Paper Title Page

Authors: W. Yang, Gang Feng Guo
Abstract: The issues of intersonic and supersonic fracture become the frontier of dynamic fracture mechanics. We describe in this paper the recent progresses in obtaining the analytical continuum solution for the initial-boundary valued problem of intersonic fracture under mode II loading, and construct an plausible analytical solution for mode III supersonic fracture.
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Authors: Pin Tong, Fan Yang, David C.C. Lam, Jun Wang
Abstract: Conventional strain-based mechanics theory does not account for contributions from strain gradients. Failure to include the strain gradient contributions can lead to underestimates of stresses and size-dependent behaviors in small-scaled structure [1]. This paper focus on the structural size effects on torsion of cylinders. The torsional stiffness of cylinders can be higher than conventional expectation when the cylinder size is in the nanometer - or micron-scale. Following the Saint-Venant theory of torsion, we established the equation of torsion in terms of the warping function on the basis of the nano-mechanical theory of elasticity. The torsional equations contain two higher order material length scale parameters and two conventional Lame constants. The equilibrium equation is a fourth order partial differential equation which can be reduced to two second order equations. Two formulations in terms of pseudo warping function and stress function are presented. Closed-form solutions for circular and thin wall section and series solutions for rectangular microbars have been obtained. The total torque depends only on the stresses conjugated to the strain and is only implicitly dependent on the higher order stress metrics. The solution reveals that the torsional rigidity is dependent on the higher order length scale parameters and strain gradients and increases asymptotically upward when the cylinder size is reduced to the size of the higher order length scale material parameters. The increase is most marked for thin walled cylinders, stiffening to more then 10 times the conventional value when the cylinder size is near that of the higher order length scaled parameters.
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Authors: Y.Y. Earmme, S.T. Choi, H. Shin
Abstract: The equivalence between anisotropic and isotropic elasticity is investigated in this study for two-dimensional deformation under certain conditions. That is, the isotropic elasticity can be reconstructed in the same framework of the anisotropic elasticity, when the interface between dissimilar media lies along a straight line. Therefore, many known solutions for an anisotropic bimaterial can be regarded as valid even for a bimaterial, in which one or both of the constituent materials are isotropic. The usefulness of the equivalence is that the solutions for singularities and cracks in an anisotropic/isotropic bimaterial can easily be obtained without solving the boundary value problems directly. Conservation integrals also have the similar analogy between anisotropic and isotropic elasticity so that J integral and J-based mutual integral M are expressed in the same complex forms for anisotropic and isotropic materials, when both end points of the integration paths are on the straight interface. The method of analytic continuation and Schwarz-Neumann's alternating technique are applied to singularity problems in an anisotropic or isotropic 'trimaterial', which denotes an infinite body composed of three dissimilar materials bonded along two parallel interfaces. The method of analytic continuation is alternatively applied across the two parallel interfaces in order to derive the trimaterial solution in a series form from the corresponding homogeneous solution. The trimaterial solution studied here can be applied to a variety of problems, e.g. a bimaterial (including a half-plane problem), a finite thin film on semi-infinite substrate, and a finite strip of thin film, etc. Some examples are presented to verify the usefulness of the obtained solutions.
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Authors: Heng An Wu, Ai Kah Soh, Xiu Xi Wang, Z.H. Sun
Abstract: Numerical simulations have been carried out to determine the mechanical property of single crystal copper nanowire subjected to tension using the molecular dynamics method. The mechanism of deformation, strength and fracture are elucidated based on these numerical simulations. No strengthening is found after yielding of the single crystal nanowire. The simulation results show that the strength of copper nanowire is far greater than that of realistic polycrystalline bulk copper. By decreasing the size of the nanowire's cross-section, which leads to an increase of the ratio of surface atoms, the yield stress is increased. The strain rate has an influence on strength, and mechanism of deformation and fracture. When the strain rate is comparatively low, plastic deformation arises from dislocation slips and twins. However, when the strain rate is sufficiently high, amorphization is a dominant factor of plastic deformation and super-plasticity is found. The fracture process is demonstrated using the atomic images.
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Authors: T.F. Wong, R.H.C. Wong, Ming Ruo Jiao, K.T. Chau, Chun An Tang
Abstract: A major challenge in rock mechanics has been the realistic modeling that can reveal the progressive accumulation of damage and shear localization in a brittle rock under compression. The Rock Failure Process Analysis code (RFPA2D) is an efficient tool and realistic model to simulate such complexities. A key assumption of the code is that the heterogeneity of elastic moduli and failure strength are characterized by the Weibull distribution with two parameters (m and σ0 ). However, these two parameters do automatically not relate to the microstructural parameters, such as grain size and microcrack statistics. Therefore, the purpose of this paper is to elucidate the micromechanical basis of these Weibull parameters, specifically how they depend on microstructural attributes such as grain size and crack statistics. Secondly, a methodology was developed to quantitatively determine the relevant micromechanical parameters for input into the RFPA2D code. Finally, the methodology was implemented by quantifying the microcrack geometry and statistics of real rock and simulating its uniaxial compression and progressive failure behavior. The simulated result agrees well with the experimental study.
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Authors: T. Li, Qing Yuan Wang, X.M. Yuan
Abstract: In the present paper, axisymmetric smooth and notched specimens of aluminium alloy LY12CZ were monotonic tension tested to study the ductile fracture behavior and evaluate the suitability for the critical void growth ratio, VGC of the material, from the micro and macro points of view. It's found that the material would change fracture morphology from tensile to shear failure in the various stress states; the ductile fracture parameter VGC is sensitive to the fracture morphology which is applicable for the case of tensile failure while not suitable for the case of the shear failure, i.e. the case of smooth tensile specimens.
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Authors: Amar N. Kumar
Abstract: Research activities on deformation and fracture characteristics of the Ti-Al intermetallics have assumed considerable significance in view of many potential applications as high temperature structural materials. These aspects are discussed in respect of two Ti-Al intermetallics with duplex and lamellar structures. The fracture toughness, crack growth resistance and fracture mechanisms are evaluated at room temperature. The differences in the behaviour of the alloys are explained in the light of microstructures as observed for the alloys.
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Authors: Shui Cheng Yang, Li Song, Hong Jian Liao
Abstract: The authors present a procedure for the analysis of the stability and propagation of cracks in arch dams based on linear elastic fracture mechanics. A finite element method was used to calculate the stress intensity factors(KⅠ, KⅡ and KⅢ) of crack in the concrete arch dam, and fracture analysis for arch dams was carried out, which based on the criterion of three-dimensional mixed mode fracture of concrete from the experiment. The analysis method can be applied to evaluate the safety of the arch dam and improve the design for arch dam.
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Authors: F. Shang, Meinhard Kuna, Takayuki Kitamura
Abstract: An elliptical crack subjected to uniform temperature gradient in an infinite thermopiezoelectric solid is investigated in this work. Theoretical attempt has been made to find the temperature and piezoelectric fields at first by using a potential function formulation. The field intensity factors due to the thermal disturbance are obtained, as well as the local fields of the stresses and electric displacements near the crack front.
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Authors: Saeid Hadidi-Moud, A. Mirzaee-Sisan, Christopher E. Truman, David John Smith
Abstract: Potentially both global and local approaches may be used to predicting the effect of loading history on cleavage fracture toughness distribution of ferritic steels. In this paper the dramatic increase in the apparent lower shelf fracture toughness of A533B steel following warm pre-stressing (WPS) has been predicted using these approaches. Extensive experimental evidence suggesting significant enhancement in fracture toughness of ferritic steels within the lower shelf temperatures following WPS are used to verify and compare the applicability and the extent of validity of the models. The global approach is based on the distribution of toughness data described by Wallin statistical model in conjunction with the Chell model for WPS effect. The local approach on the other hand is a Beremin type model that uses the Weibull stress to predict the WPS effect. Weibull stresses would essentially reflect the WPS effect on redistribution of stress-state around the crack tip. Predictions for apparent toughness using the two approaches are discussed in the light of the suggestion that residual stresses are the main cause of the enhancement, at least for the material and geometry used in this study.
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