Search

The main objective of this article is to mechanize the procedure of tracking and describing the various phases of deformation of a biological circular cell during micromanipulation. The devised vision-based methodology provides a real-time strategy to track and describe the cell deformation by extracting a geometric feature called dimple angle. An algorithm based on Snake was established to acquire the boundary of the indenting cell and measure the aforementioned feature. Micromanipulation experiments were conducted for zebrafish embryos. Experimental results were used to characterize the deformation of the manipulating embryo by the devised geometric parameter. The results demonstrated the high capability of the methodology. The proposed method is applicable to the micromanipulation of other circular biological embryos such as injection of the mouse oocyte/embryo. Supplemental materials are available for this article. Go to the publisher's online edition of theInternational Journal of Optomechatronicsto view the supplemental files. [ABSTRACT FROM AUTHOR]

Abstract: Metallic foams are a new class of functional materials. They have found their applications as sandwich cores in lightweight structures and as implant materials in bioengineering. To characterize the mechanical properties of these materials becomes an interesting and relevant research topic. In the mean time, indentation method has been well accepted as a simple and effective way to measure the mechanical properties of solid materials. We believe that it is possible to study the averaged mechanical properties of a metallic foam from a spherical indentation test. In this paper, theoretical investigation to understand the spherical indentation responses of metallic foams is presented. Based on the dimensional analysis, several scaling relationships in the indentation of metallic foams with a spherical indenter are obtained. Numerical results from the finite element simulations are used to examine the dependence of the indentation response on the basic material parameters, such as the porosity, the work hardening exponent and the shape factor, which characterizes the plastic deformation of metallic foams due to hydrostatic loading. Our numerical results show that the maximum indentation force has a linear relationship with the indentation depth for different shape factor values. It is therefore proposed to calibrate the shape factor value from the slope of the maximum indentation force versus the indentation depth from a spherical indentation test, instead of a complicated hydrostatic loading test. We also find that the spherical indentation hardness varies about 11% within the examined indentation depths. The range of the ratio of the hardness to the yield strength of metallic foams is from 2.17 to 2.95, which is different from that of solid materials. Our study provides the basis for applying a simple spherical indentation test to investigate the mechanical properties of metallic foams. [Copyright &y& Elsevier]

Mode II delamination toughness of z-pin reinforced composite laminates is investigated using finite element (FE) method. The z-pin pullout process is simulated by the deformation and breakage of non-linear springs. A critical shear stress criterion based on linear elastic fracture mechanics is used to simulate crack growth in an end-notched-flexure (ENF) beam made of z-pinned laminates. The mode II toughness is quantified by the potential energy release rate calculated using the contour integral method. This FE model is verified for an unpinned ENF composite beam. Numerical results obtained indicate that z-pins can significantly increase the mode II delamination toughness of composite laminate. The effects of design variables on the toughness enhancement of z-pinned laminates are also studied, which provides an important technological base and useful data to optimize and improve the z-pinning technique. [Copyright &y& Elsevier]

Abstract: The contact conditions at the die radius are of primary importance to the wear response for many sheet metal forming processes. In particular, a detailed understanding of the contact pressure at the wearing interface is essential for the application of representative wear tests, the use of wear resistant materials and coatings, the development of suitable wear models, and for the ultimate goal of predicting tool life. However, there is a lack of information concerning the time-dependant nature of the contact pressure response in sheet metal stamping. This work provides a qualitative description of the evolution and distribution of contact pressure at the die radius for a typical channel forming process. Through an analysis of the deformation conditions, contact phenomena and underlying mechanics, it was identified that three distinct phases exist. Significantly, the initial and intermediate stages resulted in severe and localised contact conditions, with contact pressures significantly greater than the blank material yield strength. The final phase corresponds to a larger contact area, with steady and smaller contact pressures. The proposed contact pressure behaviour was compared to other results available in the literature and also discussed with respect to tool wear. [Copyright &y& Elsevier]

A 3D intralaminar continuum damage mechanics based material model, combining damage mode interaction and material nonlinearity, was developed to predict the damage response of composite structures undergoing crush loading. This model captures the structural response without the need for calibration of experimentally determined material parameters. When used in the design of energy absorbing composite structures, it can reduce the dependence on physical testing. This paper validates this model against experimental data obtained from the literature and in-house testing. Results show that the model can predict the force response of the crushed composite structures with good accuracy. The simulated energy absorption in each test case was within 12% of the experimental value. Post-crush deformation and the damage morphologies, such as ply splitting, splaying and breakage, were also accurately reproduced. This study establishes the capability of this damage model for predicting the responses of composite structures under crushing loads. [ABSTRACT FROM AUTHOR]

Based on the strain-controlled cyclic tension-unloading tests at various strain rates (3.3 × 10 −4 –3.3 × 10 −2 /s), the effect of strain rate on the uniaxial cyclic deformation of a super-elastic NiTi shape memory alloy (SMA) was investigated. It is concluded that apparent degeneration of super-elasticity occurs during the cyclic loading, i.e., the residual strain and transformation hardening increase, but the start stress of forward transformation and the maximum responding stress decrease with the increasing number of cycles and strain rate, and finally reach to their saturated states after certain cycles. Although the dissipation energy per cycle decreases progressively during the cyclic loading and is saturated after certain cycles, it does not change monotonically with the increasing strain rate. Moreover, the temperature oscillation is observed due to the internal heat production from the inelastic dissipation and transformation latent heat, and the extent of temperature variation increases monotonically with the increasing strain rate, which is the physical nature of rate-dependent cyclic deformation of the NiTi SMA. [ABSTRACT FROM AUTHOR]

Abstract: Vickers indentation was conducted on an as-cast Zr41Ti14Cu12.5Ni10Be22.5 bulk metal glass (BMG) to study shear band formation using a bonded interface technique. The results indicate that the plastic deformation in the BMG is accommodated by the semi-circular (primary) and radial (secondary) shear bands. The inter-band spacing of the semi-circular shear bands is found to be independent of the applied load. The measured size of the deformation zone is in good agreement with the prediction of the theoretical model proposed by Zhang et al. [Copyright &y& Elsevier]