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2018 Vol. 39, No. 4
Published: 2018-08-28
333
Microstructure model, toughening and fatigue of metallic glasses: A review
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.021
Metallic glasses (MGs), fabricated by a melt-quench method, possess many unique properties compared with conventional crystalline metals and alloys, including high fracture strength up to 6 GPa, the highest fracture toughness of 200 MPa?m1/2, large elastic limit (2%, the theoretical elastic limit), good corrosion and wear resistance. These superior properties of MGs have attracted tremendous attention scientifically and industrially. However, the following three key problems hinder the applications of MGs: (1) the relationship between the atomic-scale structures and physical properties of MGs; (2) enhancements in the ductility of MGs; (3) the fatigue mechanisms and improvement of the fatigue limit of MGs. In this review, we introduce the history, the formation process, major properties and applications, challenges, structural characterizations, and atomic-scale structural models of MGs. Then, the deformation and fracture mechanisms of MGs and some strategies used to improve the ductility of MGs are also described in detail. Last but not least, we review the fatigue behaviors of MGs and provide proposals for future work in the field of MGs.
2018 Vol. 39 (4): 333-374 [
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535
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375
Interface damage model with configurational forces as internal variables
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.013
It is indicated that composite material failures are always associated with the development of material interface damage which results from the creation, growth and coalescence of the microdefects. The analysis of interface damage behavior of material is a subject with high interest which has been studied over the last few decades. Although the theories of the interface damage mechanics are proposed and developed, the damage mechanism is still not fully understood. In this study, a novel model of damage mechanics is proposed by introducing the concept of material configurational force in the framework of thermodynamics with damage internal variables, which provides a new idea for studying interface damage. Both theoretical and numerical analyses are considered. First, the of the configurational force is presented based on the energy analysis of a two-phase elastic body. Then following the pioneering work by Mueller (2002), the numerical calculation of discrete configurational force is obtained via numerical integration based on the finite element method (FEM). Second, the damage evolution law of interface damage is modeled by considering the configurational force as damage internal variables, which is described by strength and the rigidity degradation. The damage may be developed by assuming the damage evolution to be a function of configurational force. Finally, numerical simulation of interface damage of composite materials (with crack or without crack) is carried out. The evolution of interface damage is analyzed in each analysis step. And the rationality and superiority of the proposed damage model are discussed. The proposed interface damage model via the configurational force may provide a new method for studying the interface damage failure of composite materials. This method is developed from the perspective of energy gradient which may both assure the precise mathematical form and bring definite physical meaning.
2018 Vol. 39 (4): 375-385 [
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221
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386
Statistic Analysis of the Mechanical Properties of the Specific Adhesion via Small Molecular Bond Clusters
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.015
For the adhesion problem between deformable mediums through molecular bond clusters which is mediated by the specific molecules interaction, many existing studies have investigated such specific adhesion behavior mainly based on Monte Carlo Simulation. However, for few molecular bonds in adhesion system, the thermal fluctuation significantly affects the adhesion behavior. As a resutl of such strong fluctuation, the conventional statistical approach can’t accurately capture the behavior of adhesion system. Therefore, in this article, we developed a new statistical method of integral evaluation based on thermal dymanics. Based on our model, statistical results of this method agree very well with numercial solutions of master equation both for steady and dymanic states. Especially, in the case that strong thermal fluctuation donimates the adhesion system with few molecular bonds, the statistical method of integral evaluation still is valid in describing the specific adheison behavior.
2018 Vol. 39 (4): 386-393 [
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196
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394
MECHANICAL BEHAVIOR OF SEVERAL LATTICE WITH NON-UNIFORM LONGITUDINAL CROSS-SECTION UNDER OUT-OF-PLANE COMPRESSION LOAD
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.022
It is possible to design lattice with non-uniform cross-section in longitudinal direction using additive-manufacturing, which makes it crucial to studying the corresponding mechanical behaviors, including stiffness, strength and buckling. The longitudinal cross-section of truss is assumed to be hyperbolic or elliptic form, which effect on stiffness is calculated analytically by axial integration and that on buckling eigenvalue is deduced explicitly through introducing parameter variation in equilibrium equation. The truss with elliptic cross-section is applied in the practical pyramid lattice, and the analytical solutions are validated by eigenvalue buckling method. Moreover, the riks method is applied in calculated the post-buckling behaviors for pyramid lattice with geometric imperfection. Both analytical solution and numerical results show that the elliptic cross-section in longitudinal direction of truss can obviously improve equivalent compressive strength in condition that the stiffness is decreased slightly for pyramid lattice with low relative density. The research results provide theoretical basis to design of lattice material with higher performance.
2018 Vol. 39 (4): 394-402 [
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302
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403
Damage imaging and testing in CFRP laminates based on Lamb wave sparse array
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.020
A minimum redundancy sparse array is adopted to realize high resolution and accurate damage imaging and testing in CFRP laminates, by taking into account both energy skew effect and dispersion compensation. Due to complex material characteristics of composite laminates, directions of phase velocity and group velocity are in general different. The Lamb wave wavenumber curve of single mode with its geometric relationship is used to calculate the skew angle, resulting in correct direction of the damage. In order to avoid the dispersive phenomenon, the damage imaging algorithm is presented in frequency domain by applying phase delay to each frequency component, leading to right position of the damage. Besides, a minimum redundancy linear array is introduced to design a cross shaped sparse array for cutting down the cost on the base of ensuring the imaging quality. Method proposed in this paper is validated through simulation images, which can help with the experiment well. All images in the damage inspection experiment show that, with skew angle and dispersion consideration, using the sparse array can not only achieve accurate location of the damage, but can also improve the spatial resolution of the damage with a limited number of array. It can be concluded that this method has great potent in damage detection in the composite structure field.
2018 Vol. 39 (4): 403-411 [
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259
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412
Study on Crack Propagation Behavior of Graphene
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.007
The fracture parameters of graphene are very important to graphene devices. But the relative research is still in the primary stage. In this paper, the tensile fracture process of pre-cracked armchair graphene is simulated by molecular dynamics software - LAMMPS. Firstly, the energy release rate and the stress intensity factor of graphene are calculated by continuum theory and molecular dynamics calculation. It is found that the energy release rate of graphene GIC is 10.11 J/m2 and the stress intensity factor KIC is 3.33MPam^1/2. Further more，a new model based on continuum theory and molecular dynamics is proposed to accurately compute the crack speed in graphene. The factors, including initial crack length and strain loading rate, that affect the crack speed of graphene are discussed. The results show that the crack initiation length and strain loading rate affect the crack speed to a certain degree. Before reaching the limit crack speed, the shorter the initial crack length is, the higher the crack speed is. But with the increasing of the initial crack length, the crack speed is insensitivity to the initial crack length. On the other hand, the higher the strain loading rate, the higher the crack speed is. Besides, the influence relationship on crack speed between initial crack length and strain loading rate is preliminarily discussed. The results show that the influence of initial crack length and strain loading rate on crack speed is related to some extent. With the increasing of strain loading rate, the sensitivity of crack speed to the initial crack length decreases. Based on the previous findings and discussion, this study finally comes to an objective analysis of the limit crack speed. The limit crack speed is 8350 m/s. The conclusions are expected to provide some reference for the practical design and application of graphene devices.
2018 Vol. 39 (4): 412-418 [
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384
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419
Generalized finite difference method for solving Kirchhoff plate and Winkler plate bending problems
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.005
This paper presents the generalized finite difference method (GFDM) for solving Kirchhoff and Winkler plate bending problems. The GFDM is a domain-type meshless method based on the moving-least-squares theory. In comparison with the traditional mesh-based discretization methods, the GFDM is free of mesh generation and numerical integration. The numerical results show that the proposed GFDM can efficiently simulate Kirchhoff and Winkler plate bending problems under different types of transverse loading.
2018 Vol. 39 (4): 419-428 [
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348
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429
Cyclic ratcheting constitutive model considering plastic strain memory recovery
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.003
Ratcheting, a cyclic accumulation of inelastic deformation occurred in the engineering materials subjected to asymmetrical stress-controlled cyclic loading, can make the deformation of the structures exceed the designed limitation or shorten the fatigue life of engineering components. Based on the framework of unified visco-plasticity, a new cyclic constitutive model is proposed to describe the ratcheting behavior of cyclic hardening materials on the basis of Ohno-Abdel-Karim model. As we know, the level of cyclic hardening increases with the increase of plastic strain amplitude in the cyclic deformation tests for cyclic hardening materials. Then, the memory surface for maximum plastic strain amplitude effect is introduced to reflect the effect and the dynamic recovery coefficient is added to the plastic strain memory term to reflect the effect of maximum plastic strain on isotropic deformation resistance. The definition of the Tanaka’s non-proportionality is adopted to describe the multiaxial ratcheting deformation with different multiaxial loading paths. Then, the proposed model is adopted to describe the stress-strain responses of 316L stainless steel (which is a kind of cyclic hardening material ) under uniaxial tension, strain-controlled cyclic loading and stress-controlled cyclic loading cases. Comparing with the corresponding experimental results, it can be found that, the uniaxial and multiaxial ratcheting of 316L stainless steel can be reasonably described by the proposed model. Furthermore, the model can also reflect the various degrees of non-proportional addition hardening with different proportional and non-proportional loading paths properly. To sum up, the capability of the proposed model to predict the uniaxial and multiaxial ratcheting behavior of cyclic hardening material is well improved by introducing the effect of plastic strain memory recovery. It is believed that the proposed model is useful for the design and fatigue life prediction of engineering components.
2018 Vol. 39 (4): 429-438 [
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288
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