Home   |   About Journal   |   Editorial Board   |   Instruction   |   Subscriptions   |   Contacts Us   |   中文
  Office Online  
    Submission Online
    Peer Review
    Editor Work
    Editor-in-chief
    Office Work
  Journal Online
    Accepted
    Current Issue
    Advanced Search
    Archive
    Read Articles
    Download Articles
    Email Alert
    
Quick Search  
  Adv Search
2017 Vol. 38, No. 1
Published: 2017-02-28
 
1 Working Mechanism for the Mechanical Behavior of Shape Memory Polymer
 

As one of the most promising stimulus-responsive and smart polymer materials, shape memory polymer (SMP) has attracted great attention in the research field. There are three major research topics on the physics and mechanics of SMP, summarized as: exchange between the SMP and the surrounding (e.g. heat, energy, etc.), control of shape change (e.g. actuation approach, constructive modeling, etc.) and its soft matter (e.g. thermodynamics, composite, etc.). The shape memory effect (SME) in SMPs results from the thermodynamic behavior of intrinsic molecular structures, is induced (or triggered) by external stimuli, obeys the Arrhenius rule, and is the macroscopic appearance of segmental relaxation behavior. In this review, the physical and mechanical mechanisms of SMPs are presented and discussed, including thermodynamics, entropy effect, mechanical behavior and stimulus-responsive shape recovery behavior, transition temperature, temperature memory effect, multi-field effect and multi-shape memory effect. Finally, the future work of SMP mechanics is forecasted and discussed.

2017 Vol. 38 (1): 1-12 [Abstract] ( 667 ) HTML (1 KB)  PDF   (0 KB)  ( 351 )
13 Progress in Study of Mechanical Properties of Hard Ceramic Thin Film Coatings
Rapid development in manufacturing and processing technologies is bringing forward tougher and tougher requirements for tool and mould materials, such as super-hardness, high heat-resistance, excellent anti-wear capability, high strength and toughness, and long life. Hard ceramic thin film coatings (HCTFCs), as a kind of promising materials that may satisfy the above requirements, have been receiving increasing attention. Experiment, simulation and theoretical analysis are the main means to study the mechanical properties of HCTFCs, which can reveal the mechanical properties, hardening mechanism and dominant influencing factors. In this article, the progresses in the study of mechanical properties of HCTFCs are reviewed, including the preparation of various HCTFCs, experimental and theoretical analyses of the mechanical properties of HCTFCs as well as the possible influencing factors, potential hardening mechanisms of super-hard ceramic thin film coatings, theoretical models and analytical methods, etc.
2017 Vol. 38 (1): 13-38 [Abstract] ( 318 ) HTML (1 KB)  PDF   (0 KB)  ( 387 )
39 The Evolution of Intergranular Microcracks due to Surface Diffusion Induced by Electromigration
With the rapid development of microelectronics technology, more attention has been paid to the major failure mode of Copper interconnects. Based on the classical theory of surface diffusion and evaporation-condensation and its weak statement, a finite-element method is developed for simulating the shape instability of intergranular microcracks in Copper caused by the electromigration-induced surface diffusion. A detailed discussion has been given about the impacts of the electric field , the aspect ratio , and the ratio of grain boundary energy to surface energy on the shape instability of intergranular microcracks. The results show that the evolution of the intergranular microcracks has two trends when they migrate along the electric field direction and the grain boundary: being a cylinder or splitting into two small intergranular microcracks (one is relatively larger than the other). There exist critical values of the aspect ratio and the electric field . When or , the intergranular microcrack will split into two smaller intergranular microcracks. The splitting time of the intergranular microcrack decreases with an increase in the electric field or the aspect ratio, indicating that the increase of electric field or aspect ratio accelerates microcrack splitting. The critical electric field decreases as the aspect ratio increases, and the critical aspect ratio decreases as the electric field increases. In other words, the increase of the electric field or the aspect ratio is beneficial to microcrack splitting. In addition, the splitting time of the intergranular microcracks is less than that of the intragranular microcracks. The existence of grain boundary accelerates microcrack splitting.
2017 Vol. 38 (1): 39-46 [Abstract] ( 311 ) HTML (1 KB)  PDF   (0 KB)  ( 350 )
47 Nonlocal Viscoelastic Elements Based on Riesz Potential Space-fractional Operator
The fractional acoustic wave models that describe the ultrasound propagation in biological tissues can be constructed from the perspectives of time-fractional derivative or space-fractional integral viscoelastic constitutive relations. These two modeling perspectives treat the biological tissues as non-local viscoelastic material, respectively. The first perspective has been proposed in literature whereas the second one is rarely reported. The paper mainly concerns the second modeling perspective. A new stress-strain constitutive relation in the form of Riesz potential is derived after replacing the exponential kernel function in the conventional Eringen nonlocal model by the power kernel function. Using the new relation, the conventional viscoelastic elements, i.e., spring and dashpot, are extended to their nonlocal counterparts. Through the series and parallel connections of such elements, the Kelvin and the Maxwell non-local constitutive models in arbitrary spatial dimensions are obtained, and the creep compliance and the relaxation modulus of one-dimensional models are also given. The Riesz potential order and the material internal characteristic length are two primary parameters of the nonlocal models, and the retardation time of both the Kelvin and the Maxwell non-local constitutive models gets larger as the internal characteristic length increases. Data fitting of the experiment data of a kind of soft soil implies that the nonlocal models could give better descriptions of the viscoelastic behaviors of complex media, say, creep of soft soil, ultrasound in biological tissues, and vibration of nano-composites. The non-local constitutive models of different series and parallel connections of nonlocal spring and dashpot, complemented with the momentum conservation and the displacement-strain relations, lead to a family of space-fractional wave equations, which describe the power-law frequency-dependent wave dissipation and dispersion in biological tissues. This is a potential application of the non-local constitutive models.
2017 Vol. 38 (1): 47-54 [Abstract] ( 305 ) HTML (1 KB)  PDF   (0 KB)  ( 390 )
55 Experimental and Theoretical Study of Lateral Compression on Aluminium Foam-filled Thin-walled Metal Tubes
The mechanical response of aluminum foam-filled thin-walled metal tubes under lateral quasi-static loading was investigated experimentally and theoretically. Based on the energy method, some theoretical relations were derived to estimate the instantaneous and mean lateral forces, as well as the energy absorption of aluminum foam-filled tubes during the flattening process. Some lateral compression tests under quasi-static condition were carried out on the empty and foam-filled tubes using the universal testing machine. A good agreement was observed when comparing the theoretical results with the experimental ones. Additionally, the influences of geometrical dimension of tube and density of aluminum foam on the instantaneous and mean lateral forces, as well as energy absorption and specific energy absorption (SEA) were discussed based on the theoretical model. The study shows that the energy absorption of aluminum foam-filled tubes is higher than that of the corresponding thin-walled metal tubes. The total energy absorption and lateral force increase with the increases of tube length, thickness and diameter. When the density of aluminum increases, the total energy absorption and lateral force of foam-filled tubes increase accordingly.
2017 Vol. 38 (1): 55-64 [Abstract] ( 349 ) HTML (1 KB)  PDF   (0 KB)  ( 425 )
65 The Coupling Mechanism Between Highly Nonlinear Solitary Waves with Large Plate
The stress waves can form and propagate stably when the one-dimensional granular chain is impacted by a particle with an initial velocity. These stress waves, called highly nonlinear solitary waves, have constant wavelength, speed, and amplitude, and do not reflect until encountering the boundary. Solitary wave is a superior carrier and is widely used in the nondestructive evaluation of plate. Based on the properties of solitary wave, we investigate the coupling mechanism between highly nonlinear solitary waves and large elastic plate. Basing on the Hertz’s law and Intrinsic Inelasticity of large plate, we can obtain the complete coupling differential equation system between the highly nonlinear solitary wave and the large elastic plate. By solving the equations with the fourth-order Runge-Kutta method, we attain the curves of displacement and velocity of each particle in the crystal chain. By analyzing the time when the reflected wave peak appears, the energy carried by the reflected wave, and the effects of gravity, Young’s modulus and thickness of the large plate on the solitary wave, we find that the primary and second reflected solitary waves are sensitive especially to Young’s modulus and thickness of the large plate. Besides, compared to the horizontal granular chains, the vertical granular chains have influence on the whole interaction process. These findings provide theoretical bases for the detection of highly nonlinear solitary wave on the structure; and this assessment method can be applied to the fast inspection of structure and the study of controllability.
2017 Vol. 38 (1): 65-73 [Abstract] ( 378 ) HTML (1 KB)  PDF   (0 KB)  ( 417 )
74 Bending and Vibration of Sandwich Plates with High-Order Deformation Theory
Sandwich structures, due to their outstanding properties, such as high stiffness and relatively low weight, have found wide applications in aircraft, aerospace, naval/marine, construction, transportation, and wind energy systems. There are a good number of outstanding works studies devoted to the modeling and analysis of sandwich structures. Most of these works studies are based on the First-order Shear Deformation Theory (FSDT), in which the transverse shear stresses are assumed to be uniformly distributed across the thickness of sandwich plate. The FSDT is simple and accurate for thin sandwich plates, but needs a shear correction factor in order to satisfy the zero transverse shear stress boundary conditions at the top and bottom surfaces of the plate. Besides, the errors in deflection and stresses predicted by FSDT are not negligible when the plates are not sufficiently thin enough. Therefore, the Higher-order Shear Deformation Theory (HSDT) was proposed by several researchers to overcome the shortcomings of FSDT. In this paper, a special HSDT model is developed to investigate the bending and vibration behaviors of sandwich plates. In the HSDT model, the in-plane stiffness, bending stiffness, and transverse stiffness are considered in for both the surfaces and the core; the rotational displacement function associated with transverse shear effect is given based on the transverse strain distribution; the governing equations of the sandwich plates are derived by using Hamilton’s variational principle. Parameter studies are conducted to demonstrate the influences of the core elastic modulus and the surface thickness of surfaces on the bending and vibration behaviors of simply supported sandwich plates. The results calculated by using the present model are compared with those given by Reissner, Hoff and Deng. The comparison shows that the present model has a better accuracy and a wider application scope. Also, the modal solutions obtained by from the present model are compared with those obtained by using Nastran software to show the suitable application scope of each model in dealing with the vibration behavior of sandwich plates.
2017 Vol. 38 (1): 74-84 [Abstract] ( 406 ) HTML (1 KB)  PDF   (0 KB)  ( 352 )
84   Mechanical Properties of Closed-cell Metal Foam with Negative Density Gradient under Impact Loading
Metal foams are widely used as advanced lightweight construction or kinetic energy absorbers in many industrial fields. Graded metal foam is becoming a research hotspot due to its outstanding designability. The dynamic compressive mechanical behavior of closed-cell aluminum foam with continuous negative density gradient under different impact velocities was investigated using the finite element software ABAQUS. First, the random 3-D Voronoi technique was employed to construct graded closed-cell foam models. Then different impact velocities were applied at the impact end of foam along the negative density gradient direction. Like the uniform foam, three deformation modes, i.e. quasi-static mode, transitional mode and shock mode were observed with the increase of impact velocity. The densification factor was introduced to define the critical velocities of mode transition. A new method was proposed to define the local densification strain by contrasting the nominal stress-strain curves with deformation modes. This method took the effects of relative density and density gradient into account. Deformation maps of impact velocity versus relative density and density gradient were respectively presented for the graded foam. Finally, the effect of density gradient on energy absorption ability was discussed. The finite element simulation results indicated that the first critical velocity was insensitive to the relative density, while the second critical velocity increased with the increase of relative density. The critical velocity decreased with the increase of density gradient. It was found that the smaller the absolute value of density gradient was, the more energy the foam would absorb at the initial stage of deformation under low impact velocity; and the larger the absolute value of density gradient was, the stronger energy absorption ability of the foam material at the initial stage of deformation under high impact velocity would be. These research results could be applied to the design of optimal energy adsorption structure with graded metal foam.
2017 Vol. 38 (1): 84-92 [Abstract] ( 300 ) HTML (1 KB)  PDF   (0 KB)  ( 431 )
  News
  Download
Download
Download
  Links
22 Links
Copyright © Editorial Board of
Supported by: Beijing Magtech