by Wang, G. Z.; Wang, Y. L.

In this work, notched specimens with two notch geometries were tested in two loading modes (four-point bending (4PB) and three-point bending (3PB)) at various loading rates at a temperature of  − 110°C for a C–Mn steel. An elastic–plastic finite-element method (FEM) is used to determine the stress distributions ahead of notches. By accurately measuring the distances of the cleavage initiation sites from the notch roots, the local cleavage fracture stress σ
_f is measured. The results obtained and combining with previous studies by the authors show that the local cleavage fracture stress σ
_f is closely related to the cleavage fracture mechanism (critical events) in steels. The σ
_f values do not change with loading rate, notch geometry and loading mode, as long as the critical event of cleavage fracture does not change at various testing conditions. The σ
_f is mainly determined by the steel microstructure, and its scatter is mainly caused by the size distribution of the weakest constituent in steels (ferrite grain or pearlite colony with large sizes and large second phase particles) and the change of the critical events in cleavage process. The σ
_f can characterize the intrinsic toughness of steels and may be used in a “local approach” model for assessing integrity of flawed structures. The σ
_f values could be measured by both 4PB and 3PB tests.

DOI: 10.1007/s10704-007-9151-9
Online Date: 10/31/2007
Print publication date: 7/1/2007
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by Wang, G. Z.

In this paper, the finite element calculation of the stress–strain distribution in front of a notch tip were carried out for two materials. One is a shape memory alloy NiTi with the stress-induced martensite transformation, and another is a fully transformed martensite NiTi without the transformation. Based on the results obtained, and combining a model of the fracture process zone, effect of martensite transformation on the fracture behavior of the shape memory alloy NiTi in a notched specimen of plane stress state is comparably analyzed. The results show that the martensite transformation increases the load to produce plastic deformation in the transformed martensite at the notch tip and decreases the maximum normal stress and plastic strain near the notch tip, and tends to suspend the crack nucleation and propagation in the fully transformed martensite in front of the notch tip, and thus increases the fracture load and improves the toughness. A quantitative analysis based on the model of the fracture process zone shows that the martensite transformation in the SMA NiTi causes about 47% increase in the apparent fracture toughness.

DOI: 10.1007/s10704-007-9148-4
Online Date: 10/31/2007
Print publication date: 7/1/2007
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by Gupta, Anurag; Markenscoff, Xanthippi

A new variational principle for an anisotropic elastic formulation in stress space is constructed, the Euler–Lagrange equations of which are the equations of compatibility (in terms of stress), the equilibrium equations and the traction boundary condition. Such a principle can be used to extend recently obtained configurational balance laws in stress space to the case of anisotropy.

DOI: 10.1007/s10704-007-9146-6
Online Date: 10/30/2007
Print publication date: 9/1/2007
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by Bui, Huy Duong

The paper deals with conservation laws which are not of the pure divergence type and thus do not provide a path-independent integral for use in Fracture Mechanics. It is shown that Duality is the right tool to re-establish the symmetry between equations and to provide conservation laws of the pure divergence type. The loss of symmetry of some energetic expressions is exploited to derive a new method for solving some inverse problems. In particular, the earthquake inverse problem is solved analytically.

DOI: 10.1007/s10704-007-9145-7
Online Date: 10/30/2007
Print publication date: 9/1/2007
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by Vu, Duc Khoi; Steinmann, Paul

The formulation of the spatial and material motion problem in nonlinear electro-elastostatics is revisited in this work. A finite element discretization is realized and a numerical example is presented to demonstrate possible application of the formulation in studying the closing process of cracks.

DOI: 10.1007/s10704-007-9141-y
Online Date: 10/30/2007
Print publication date: 9/1/2007
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by Ustinov, K. B.; Goldstein, R. V.

The problem of finding effective elastic moduli of media with spheroid inclusions in case of small concentration of these inclusions is addressed. A number of particular solutions, both known and new, were obtained as limit transitions and asymptotical expansion of the general solution, based on Eshelby’s approach. A special attention was paid to determining the ranges of applicability of the obtained asymptotical solutions. It was shown that for spheroid inclusions the areas of applicability of the asymptotic solutions are determined by two parameters: the ratio of elastic moduli of the inclusion and the matrix and aspect ratio of the inclusions.

DOI: 10.1007/s10704-007-9128-8
Online Date: 10/30/2007
Print publication date: 9/1/2007
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by Bian, Lichun

The maximum energy release rate criterion, i.e., G
_max criterion, is commonly used for crack propagation analysis. However, this fracture criterion is based on the elastic macroscopic strength of materials. In the present investigation, a modification has been made to G
_max criterion to implement the consideration of the plastic strain energy. This criterion is extended to study the fatigue crack growth characteristics of mixed mode cracks in steel pipes. To predict crack propagation due to fatigue loads, a new elasto-plastic energy model is presented. This new model includes the effects of material properties like strain hardening exponent n, yield strength σ_y and fracture toughness and stress intensity factor ranges. The results obtained are compared with those obtained using the commonly employed crack growth law and the experimental data.

DOI: 10.1007/s10704-007-9127-9
Online Date: 10/30/2007
Print publication date: 7/1/2007
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by Ghisi, Aldo; Mariani, Stefano

An experimental campaign consisting of tensile and fracture tests at cryogenic and room temperatures has been conducted on a Ti–5Al–2.5Sn extra-low-interstitial (ELI) alloy. It has been assessed that, at decreasing testing temperature: Young’s modulus slightly increases; yield and failure strengths increase significantly; fracture toughness decreases. Since a ductile void growth to coalescence micromechanism always governs failure in the spanned temperature interval, crack growth is simulated by allowing for material nonlinearities in the process zone, where ductile tearing takes place. Numerical results have been obtained by modeling the response of the process zone through either a cohesive model or Gurson’s constitutive law for porous-ductile media. It is shown that the latter approach can accurately describe the failure mechanism at any test temperature and for any specimen geometry, whereas the former one is not able to account for stress triaxiality at the crack tip and therefore requires a new calibration anytime the specimen geometry is varied.

DOI: 10.1007/s10704-007-9140-z
Online Date: 10/30/2007
Print publication date: 7/1/2007
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by Zavattieri, Pablo D.; Hector, Louis G.; Bower, Allan F.

DOI: 10.1007/s10704-007-9149-3
Online Date: 10/30/2007
Print publication date: 7/1/2007
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by Bocciarelli, Massimiliano; Colombi, Pierluigi; Fava, Giulia; Poggi, Carlo

This paper presents experimental and numerical results related to double shear lap tests performed on steel specimens reinforced using CFRP plates. These tests have been simulated taking into account the elastic–plastic behavior of the steel and the delamination between steel and CFRP by means of a cohesive approach. The results obtained are discussed in terms of: (i) maximum load bearing capacity, (ii) minimum bond length in order to exploit the maximum load bearing capacity, (iii) brittle to ductile transition of the interface failure (iv) combination of interface delamination and plastic deformation of the steel. Design formulas for the definition of the minimum bond length and the load bearing capacity of the joint are validated.

DOI: 10.1007/s10704-007-9144-8
Online Date: 10/30/2007
Print publication date: 7/1/2007
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