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2016 Vol. 37, No. 4
Published: 2016-08-28
291
The latest research progress in surface adhesion and transportation
Surface adhesion and transportation, as two typical surface behaviors of material, have been the important topics and academic frontier in the field of surface mechanics. Exploring the forming mechanism and the influence factors of the two surface effects is significantly important to the design of micro/nano-device, micro/nano- sensor, micro/nano-transportation and smart materials. The latest research progress in the fields of surface adhesion and transportation are reviewed in the present paper. The research work of the authors’ group are mainly introduced. Finally, some suggestions and future development of the surface effects are proposed.
2016 Vol. 37 (4): 291-311 [
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312
The strength and deformation behavior of metallic glass
The investigation on metallic glasses can be dated back to 60 years ago, mainly on exploring ways to realize bulk metallic glasses and understanding their physical properties. In this review paper, we summarized the mechanical properties of bulk metallic glasses under different loading conditions, including tension/compression, micropillar compression, bending, torsion-tension, fracture, and fatigue. In particular, we presented cutting-on-edge analysis on the deformation behavior associated with aforementioned loading conditions: the 2% elastic limit, the spiral fracture, the anomalous notch strengthening, and the Poisson's effect during bending tests, as well as the suitable strength criterion for metallic glasses. At the end, we showed current research on the correlation between plasticity and atomistic structures in metallic glasses. The review paper might be of interest to the solid mechanics society with a focus on the deformation and mechanical properties of advanced materials.
2016 Vol. 37 (4): 312-339 [
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340
The Hosford Yield Function for Orthorhombic Materials Included Direction of Principle Stress
Although the Hosford yield function is more suitable for describing both the yielding and the plastic deformation of orthorhombic material than the Hill quadratic yield function, it suffers from the restriction that the three principal stresses have to be coaxial with the pressing direction (RD),transversal direction (TD) and?vertical direction (ND) for metal sheet. Hence, this article derives the Hosford yield function for orthorhombic materials included direction of principle stress from the six-order plastic tensors, expanded of the introduced orientation-dependent functions in its Taylor. And when n=2, this yield function can be reduced to the Hill quadratic yield function. Finally, it shows?that q-value, R-value and the yield stress， obtained from the Hosford yield function for orthorhombic materials included direction of principle stress, agree well with the results of?experiment. And there are many merits on this yield function, such as only including 11 material parameters, simple form, generality, and so on. And this yield function will lay a theoretical foundation for analyzing mechanical properties of metal materials.
2016 Vol. 37 (4): 340-347 [
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348
Experimental study on fracture toughness and its correlation with strength characteristic of sandstone under freeze-thaw cycles and dry-wet cycles
According to the actual occurrence environment of the hydro-fluctuation belt of a typical bank slope, two test schemes of dry-wet cycles and freeze-thaw cycles are adopted to explore the mechanical properties of the sandstone specimens sampled from the hydro-fluctuation belt of a typical bank slope in the Three Gorges Reservoir Region. And the variation regularities of several mechanical parameters of the sandstone specimens immersed in different chemical solutions after they undergo different cycle times are analyzed. Experimental results show that the sandstone specimens have a significant weakening tendency under the dry-wet cycles and freeze-thaw cycles. The degradation trends of its fracture toughness, uniaxial compressive strength, splitting tensile strength are consistent basically. However, a difference exists in the deterioration degree of the mechanical parameters, i.e., the deterioration degree of the fracture toughness KIC is the greatest followed by that of the splitting tensile strength and that of the compressive strength is relatively small. The degradation degree of the mechanical parameters of the sandstone specimens during the process of the dry-wet cycles and the freeze-thaw cycles is very significant, which shows that the action of the dry-wet cycles and freeze-thaw cycles can not be ignored in the simulation of the rock mass of the hydro-fluctuation belt of a typical bank slope subjected to chemical solution. Comparing to the two test schemes，the degradation degree of the mechanical parameters of the sandstone specimens is more apparent under freeze-thaw cycles. The different chemical solutions may have a different effect on the mechanical properties of the sandstone specimens, i.e., strong acid solutions may aggravate the damage deterioration in sandstones, SO42-ions have a greater effect on deterioration in sandstones than HCO3-ions.
2016 Vol. 37 (4): 348-359 [
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Numerical studies on the elastic parameters of medium porosity rubber foams based on 3D micro-mechanical models
The macro-mechanical performances of foams are mainly determined by its micro-structure and the properties of cell material, so it is helpful for foam mechanical performance prediction by constructing a proper micro-mechanical foam model. According to the microstructure of real silicone rubber foams, three dimensional (3D) random spherical cell models are constructed by Matlab language and Abaqus software. Then large compressive deformations are simulated, and the young’s modulus, shear modulus, bulk modulus and Poisson’s ratios of rubber foams are calculated. The constitutive models of the foam elastic properties are performed by numerical fitting. Obtained results reveal that the random models behavior isotropy and the models are effective to predict the elastic performances of rubber foams.
2016 Vol. 37 (4): 360-367 [
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Discussion on the Calculation of Extrusion Effect Considering Soil Damage
Abstract：Cylindrical cavity expansion theory is a common method to analyze the soil’s stress and strain during the construction of static pressure piles and mixing piles and has reached some achievement. However, there are some deviations between experimental results and the theoretical results because soil damage, which is come from soil disturbance around the pile during pile construction, isn’t considered when cylindrical cavity expansion theory of the pile is deduced. To effectively play the cylindrical cavity expansion theory role in the guidance to the pile construction, a changing cohesion formula with soil damage parameter caused by construction is structured. Based on theory of continuum mechanics and boundary conditions, the soil damage factor in the formula can be ascertained and soil changing cohesion formula containing soil damage is obtained. These theory and formula provide the basis when squeezing effect around the pile is analyzed. Based on the cylindrical cavity expansion theory and soil damage, substitute the cohesion formula into cylindrical cavity expansion theory and the distribution of stress and radius of plastic zone around the pile during construction can be analyzed by solving differential equations of equilibrium. Computation results considering soil damage show plastic zone range around the pile is bigger and stress variation around the pile is slower than that of elastic method. The reasonability of the method in paper has been verified by comparing with the different results which is obtained by the theory in terms of non-considering soil damage and considering soil damage in this paper and the existing theory in other paper. The comparison results also show this paper method considering soil damage is a rational and effective way to deal with extrusion effect during the construction of static pressure piles and mixing piles and very suits for engineering practice. Analytical method considering soil damage this paper is helpful to research pile’s construction technology in the different soil and pile’s effect adopting fine analysis method.
2016 Vol. 37 (4): 379-386 [
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